I totally agree with Stephen about the GPS vs. Compass, and use a GPS constantly on my M15 -- the only thing I'd like to say is this: I know that there ARE certain weather conditions when a GPS does not work -- and they happen typically to be exactly the conditions when you may not be able to navigate by sight. So don't throw the compass away unless you only go out for short trips in clear weather. O ~~~~~~~~~_/~~~~~~~~~~~~~~~~ Steve McClellan M15 #152 Chicago, IL
MessageGPS affected by weather? LORAN, for sure, but GPS? I use GPS in Carpe Ventum (M-17 # 604) , and also in my Formula One racer, and have been fortunate enough not to have had weather affect it. Maybe it's because I only fly when the sun is shining;), ----- Original Message ----- From: Steve McClellan To: 'For and about Montgomery Sailboats' Sent: Sunday, September 07, 2003 1:01 PM Subject: RE: M_Boats: Do we need a compass anymore? I totally agree with Stephen about the GPS vs. Compass, and use a GPS constantly on my M15 -- the only thing I'd like to say is this: I know that there ARE certain weather conditions when a GPS does not work -- and they happen typically to be exactly the conditions when you may not be able to navigate by sight. So don't throw the compass away unless you only go out for short trips in clear weather. O ~~~~~~~~~_/~~~~~~~~~~~~~~~~ Steve McClellan M15 #152 Chicago, IL ------------------------------------------------------------------------------ _______________________________________________ http://mailman.xmission.com/cgi-bin/mailman/listinfo/montgomery_boats
Steve: Good point! I use my GPS on my M15 all the time, have it mounted just inside the cabin so I can see it from the cockpit, and have it plugged in to my 12 volt system most of the time (though it interferes with the the FM radio sometimes). I have a Magellan Blazer 12, which cost about $100 the last time it was available. I have a nice combination mount and hand-bearing compass too, but I rarely use it. --Gary Hyde M15 #235 'Vanilla' On Sunday, September 7, 2003, at 06:00 AM, Stephen Martin wrote:
I suppose this will be considered nautical heresy, but here goes:
When my wife and I first started cruising about 5 years ago we were careful to calibrate (swing) the compas and make a deviation chart, etc. Mounted next to the compass was our GPS unit. After all that we had read about the importance of the compass it suprised us that in 4 years of cruising I don't think we ever looked at the compass once. We eventually quit taking the cover off. On the other hand, the GPS was used constantly.
Instead of heading, the GPS gives you your track, which is what you really want to know. Of course, some of the other benefits are that it gives you true speed (no need for a knot meter, which only gives you relative speed), position, tells you if you're on course, and tells you if your anchor is dragging.
I suppose one could argue that the compass is low tech, doesn't require batteries, and is more reliable. But I remember making the same argument for holding onto my slide rule. I still keep it stowed away somewhere in case the batteries die on my calculator.
On our new M15, insead of a compass, I'm considering either just carrying a handheld GPS or possibly mounting one on the bulkhead. Of course, I will still keep a small handheld compass stowed away for the day when the batteries die or the satellites fail. Maybe I will keep it with my slide rule.
Steve Martin, M15 "Cadenza"
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Stephen, I'm going to give it the old college try, to convince you why not only should you keep your compass, but that you should consider it to be one of your most valuable instruments and use it, in spite of the ready availability of GPS. I have a M-17, and living in LA, I've prepped it for coastal cruising. That means I've also prepped myself in how to coastal cruise, which involves navigation to strange waters. And granted, I'm a traditionalist, so my arguments are colored in that direction. But I believe the arguments are correct in principle, it's just the relative emphasis is controlled by your sailing objectives. Also, I'm a pilot, so even though I'm a new sailor with very few cruising miles, pilots and sailors have very similar tasks and desires when it comes to navigation. 1. First, you are right, GPS gives you track and speed over ground. However, your track is the result of a number of factors: leeway, tidal currents, boat balance, wind direction and speed. Your speed over ground is also based on these factors. The question is, what ** heading ** should you steer to achieve a desired track? A sailor who is unaware of the tidal currents and the boat's performance is less likely to arrive on time to the intended destination, and has a higher risk of sailing into trouble. A sailor who uses the compass for navigation is more aware of the effect of wind and tides, and is in better touch with the boat's performance, by constantly comparing the difference between the heading to steer, and the performance relative to the desired track. 2. Last month, I sailed to Catalina Island, 30 nm away. In all the last minute hubbub, I left behind the 12 volt connector to my GPS and the spare batteries (4 AA's for each 6 hours of operation). The GPS unit was showing that the batteries were about 40% of full. Not only that, but there was something weird going on with my house battery, and I was very concerned that the battery was also in deep discharge. When did I discover all this? Twenty minutes after I left port. And I was committed to making this trip that day. But, I have a bulkhead compass, and I know how to use it, and I've practiced steering to compass headings and staying on track. Through all the haze I couldn't even see my destination until I got within 5 nm. So what did I do? I steered compass headings, and every half hour or so, I turned on the GPS, checked to see whether I was still on track, and adjusted my heading, then turned off the GPS. Using basically compass, I was never more that 0.5 km off-track, and I arrived at Catalina with plenty of battery power to spare. And that was my first and longest cruise. The moral: GPS only works as long as the electrons flow. And there's a zillion ways, especially in the corrosive saltwater environment, for the power to stop flowing. And when that day comes, if you don't know what compass heading to steer ... 3. GPS gives you speed over ground, but speed over water and apparent wind speed are more important to the sailor. I set my reefs and sail changes based on boat and wind speed and sea state. Speed over ground can be confused by tidal currents. Admittedly, in SoCal this is not important, but up in Puget Sound or SF Bay if you are not aware of the effect of these sizable currents, you could either be over-canvassed, or not getting best effort out of your boat. Either way, you have increased your risk of meeting with trouble before reaching your destination safely. Especially for a small boat like a Montgomery, where there is less than one knot difference between a happy boat (4.5 knots) and an over-stressed boat and crew (5.5 knots). Why? because with using only GPS, you are unaware of what the sea is doing to you. 4. Go into any plane, from the littlest Cessna putt-putt, to the biggest commercial jet, and you will find a magnetic compass prominently mounted for use by the pilots. Why, with all the fancy and expensive and ultra-reliable electronics, do they still have a compass? Because it is one of the few, if the only, instruments that, with proper installation and a modicum of maintenance, is ** totally ** reliable. The compass is used, on a regular basis (i.e. every flight, and several times per flight) to make sure that all those fancy electronics are working and telling truth. The compass is not an anachronistic carbuncle of a bygone era of flight, but is and will remain an essential instrument of flight. A compass is a flight-safety critical piece of equipment. Without it, you don't fly. Remember that pilots and sailors have much the same problem: what heading to steer to achieve the desired track, and why is there a difference? -- For reasons like these, I'm convinced that boats should be steered primarily using the compass, the heading to steer should be calculated by the sailor, and GPS should be used as one of several means of navigation (DR, triangulation, LORAN, GPS, celestial), each of which is used to back up and cross-check the others. A sailor should be prepared and comfortable with all types of navigation methods, and the only way to be so is to do so, using each as available. So when you're sailing, make the effort to run a DR log, or do compass triangulation, and figure out what compass heading to steer to compensate for wind, tides, and currents. You asked for it, you got my $0.02. Hope it helps. John Fleming M-17: "Star Cross'd" Stephen Martin wrote:
I suppose this will be considered nautical heresy, but here goes:
When my wife and I first started cruising about 5 years ago we were careful to calibrate (swing) the compas and make a deviation chart, etc. Mounted next to the compass was our GPS unit. After all that we had read about the importance of the compass it suprised us that in 4 years of cruising I don't think we ever looked at the compass once. We eventually quit taking the cover off. On the other hand, the GPS was used constantly.
Instead of heading, the GPS gives you your track, which is what you really want to know. Of course, some of the other benefits are that it gives you true speed (no need for a knot meter, which only gives you relative speed), position, tells you if you're on course, and tells you if your anchor is dragging.
I suppose one could argue that the compass is low tech, doesn't require batteries, and is more reliable. But I remember making the same argument for holding onto my slide rule. I still keep it stowed away somewhere in case the batteries die on my calculator.
Steve Martin, M15 "Cadenza"
Hear! Hear! I would double underscore the **totally relaible** comment. Given a discrepancy between the GPS and the compass, I would go with the compass if I had no other indicators such as seeing the sun, north star, some known land point of reference... Dan John Fleming wrote:
Stephen,
I'm going to give it the old college try, to convince you why not only should you keep your compass, but that you should consider it to be one of your most valuable instruments and use it, in spite of the ready availability of GPS.
I have a M-17, and living in LA, I've prepped it for coastal cruising. That means I've also prepped myself in how to coastal cruise, which involves navigation to strange waters. And granted, I'm a traditionalist, so my arguments are colored in that direction. But I believe the arguments are correct in principle, it's just the relative emphasis is controlled by your sailing objectives. Also, I'm a pilot, so even though I'm a new sailor with very few cruising miles, pilots and sailors have very similar tasks and desires when it comes to navigation.
1. First, you are right, GPS gives you track and speed over ground. However, your track is the result of a number of factors: leeway, tidal currents, boat balance, wind direction and speed. Your speed over ground is also based on these factors. The question is, what ** heading ** should you steer to achieve a desired track? A sailor who is unaware of the tidal currents and the boat's performance is less likely to arrive on time to the intended destination, and has a higher risk of sailing into trouble.
A sailor who uses the compass for navigation is more aware of the effect of wind and tides, and is in better touch with the boat's performance, by constantly comparing the difference between the heading to steer, and the performance relative to the desired track.
2. Last month, I sailed to Catalina Island, 30 nm away. In all the last minute hubbub, I left behind the 12 volt connector to my GPS and the spare batteries (4 AA's for each 6 hours of operation). The GPS unit was showing that the batteries were about 40% of full. Not only that, but there was something weird going on with my house battery, and I was very concerned that the battery was also in deep discharge. When did I discover all this? Twenty minutes after I left port. And I was committed to making this trip that day. But, I have a bulkhead compass, and I know how to use it, and I've practiced steering to compass headings and staying on track. Through all the haze I couldn't even see my destination until I got within 5 nm. So what did I do? I steered compass headings, and every half hour or so, I turned on the GPS, checked to see whether I was still on track, and adjusted my heading, then turned off the GPS. Using basically compass, I was never more that 0.5 km off-track, and I arrived at Catalina with plenty of battery power to spare. And that was my first and longest cruise.
The moral: GPS only works as long as the electrons flow. And there's a zillion ways, especially in the corrosive saltwater environment, for the power to stop flowing. And when that day comes, if you don't know what compass heading to steer ...
3. GPS gives you speed over ground, but speed over water and apparent wind speed are more important to the sailor. I set my reefs and sail changes based on boat and wind speed and sea state. Speed over ground can be confused by tidal currents. Admittedly, in SoCal this is not important, but up in Puget Sound or SF Bay if you are not aware of the effect of these sizable currents, you could either be over-canvassed, or not getting best effort out of your boat. Either way, you have increased your risk of meeting with trouble before reaching your destination safely. Especially for a small boat like a Montgomery, where there is less than one knot difference between a happy boat (4.5 knots) and an over-stressed boat and crew (5.5 knots). Why? because with using only GPS, you are unaware of what the sea is doing to you.
4. Go into any plane, from the littlest Cessna putt-putt, to the biggest commercial jet, and you will find a magnetic compass prominently mounted for use by the pilots. Why, with all the fancy and expensive and ultra-reliable electronics, do they still have a compass? Because it is one of the few, if the only, instruments that, with proper installation and a modicum of maintenance, is ** totally ** reliable. The compass is used, on a regular basis (i.e. every flight, and several times per flight) to make sure that all those fancy electronics are working and telling truth. The compass is not an anachronistic carbuncle of a bygone era of flight, but is and will remain an essential instrument of flight. A compass is a flight-safety critical piece of equipment. Without it, you don't fly.
Remember that pilots and sailors have much the same problem: what heading to steer to achieve the desired track, and why is there a difference?
--
For reasons like these, I'm convinced that boats should be steered primarily using the compass, the heading to steer should be calculated by the sailor, and GPS should be used as one of several means of navigation (DR, triangulation, LORAN, GPS, celestial), each of which is used to back up and cross-check the others. A sailor should be prepared and comfortable with all types of navigation methods, and the only way to be so is to do so, using each as available. So when you're sailing, make the effort to run a DR log, or do compass triangulation, and figure out what compass heading to steer to compensate for wind, tides, and currents.
You asked for it, you got my $0.02. Hope it helps.
John Fleming M-17: "Star Cross'd"
Stephen Martin wrote:
I suppose this will be considered nautical heresy, but here goes:
When my wife and I first started cruising about 5 years ago we were careful to calibrate (swing) the compas and make a deviation chart, etc. Mounted next to the compass was our GPS unit. After all that we had read about the importance of the compass it suprised us that in 4 years of cruising I don't think we ever looked at the compass once. We eventually quit taking the cover off. On the other hand, the GPS was used constantly.
Instead of heading, the GPS gives you your track, which is what you really want to know. Of course, some of the other benefits are that it gives you true speed (no need for a knot meter, which only gives you relative speed), position, tells you if you're on course, and tells you if your anchor is dragging.
I suppose one could argue that the compass is low tech, doesn't require batteries, and is more reliable. But I remember making the same argument for holding onto my slide rule. I still keep it stowed away somewhere in case the batteries die on my calculator.
Steve Martin, M15 "Cadenza"
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I recently bought a book titled "Metal Corrosion in Boats", by Nigel Warren. Really a fascinating book, with all sorts of hints and discussion about how to best arrange all your metal components on a boat and how to manage the effects of corrosion above and below the water. Anyway, there's a section in the Chapter "Underwater Problem Areas", that should be of interest to all Montgomery owners, especially those with metal centerboards. I have typed this section in for you. There are other sections that deal with topics near and dear to Montgomery owners, but I'll start with this one. John Fleming M-17: "Star Cross'd ---- Centreboards (Nigel's a Brit) Most centreboards are of mild steel, sometimes galvanized sometimes not. That in itself does not produce special problems but the pivot bolt and the hoisting gear often enhance corrosion. The bearing areas in way of both the pivot bolt and the lifting tackle are especially prone to a vigorous corrosion. The actual surfaces in contact rub together and are immersed in salt water. Any galvanizing or other protective coating soon rubs off exposing the bare steel edge. The hole in the centreplate then enlarges quickly. The lifting tackle pin is necessarily close to the edge of the plate and eventually after a few seasons can pull through the edge releasing the centreplate. This process will happen even with compatible metals - in most cases a galvanized shackle pin in a steel centreboard - but if a stainless or bronze shackle is used the rate of corrosion of the hole is many times faster because of galvanic effects. With a mild steel centreboard there is no long-lasting solution to this problem except to use compatible materials, i.e. a galvanized shackle on the end of the lifting wire and a galvanized pivot bolt, and then to accept that steady wear will take place. Each year the items should be inspected and replaced when necessary. In the case of the lifting tackle at least the wear of the plate itself can easily be avoided by fitting a pair of mild steel straps and having a replaceable pin. With more difficulty, the hole for the pivot bolt can be fitted with a removable steel bush[ing]. Then at least all the wearing parts are easily replaced. Obviously the thicker the bolt and the pin the longer their life; many boats with centreboards are fitted with pathetically thin pivot bolts which while being quite strong enough when new can tolerate very little corrosion. [How true is this for Montgomery's? I wonder.] The lifting wire itself is a problem. Constantly wetted, neither galvanized nor stainless wire is likely to last long. Stainless wire will give a short life underwater because of pitting, and if a coppersleeved Talurit splice is fitted this will corrode preferentially. Polyester (Terylene or Dacron) rope is one solution, though with a chafe problem, but galvanized chain is better. The lowest link will take the wear but if an overlong piece of chain is fitted in the first place it can be cut off in due course and the next link up used instead. The galvanizing will last only a few years so replacement of the chain must be considered as a matter of course. [My Montgomery has a little wire rope pigtail attached to the board, and then a polyester line going to the cockpit. I guess he's saying I'll have to check it every so often.] A complete long-lasting solution to the wear problem at the pivot and lifting pin on a steel centreplate is elusive. Obviously a longer life would ensue if the wearing areas were of a hard and corrosion resistant metal: this suggests stainless steel. The pitting problem would be reduced by the cathodic protection given by the steel plate. So, at the pivot, one would end up with a stainless bush fixed to the plate and with a stainless steel bolt, making sure that Type 316 stainless steel was used. The bush could be rivetted, bolted or even welded in place. Similarly the lifting point could be bushed, or stainless steel tangs could be fitted. From there a stainless shackle would lead to a polyester lifting rope. [I believe that the Montgomery's more or less follow this advice, except for the stainless bushing at the centerboard pivot. He seems to say that the pivot bolt must be pulled and inspected on a regular basis, and if any significant pitting has occurred, it must be replaced. Also, it implies that even though the centerboard is painted to control rust, there must be metal-to metal contact between the cenboard and the pivot pin.] Of course a centreboard of zinc-free copper alloy would solve all the problems because the attachments could then be of the same corrosion-free alloys. Suitable metals that come to mind are copper, gunmetal [a bronze (88% copper plus tin)] and copper-nickel. Copper alloys are much the same density or a little heavier than steel. A bonus would be that no antifouling would be necessary. The lifting wire could be of Monel (which is available, though at a price). Stainless steel for the centreplate could also be considered (again Type 316) with sacrificial anodes. [The new M23 Bob Eeg is making has a centerboard of silicon bronze, though he doesn't say here whether the pivot bolt is still allowed to be stainless.] Usually cost rules out such materials and mild steel is the only practical choice; but to avoid disaster it is wise to consider carefully the pivot and lifting arrangements. ----------------
Is there any mention in that book whether or not you should ground the A/C line ( the green, when using white and black) from shore power to the same ground as the DC commonly using the (black wire as the ground and red as the positive) as the boat power like when you have a charger and using a night light. I hear some folks are now using a yellow wire instead. .................. ----- Original Message ----- From: "John Fleming" <jfleming1231@earthlink.net> To: "For and about Montgomery Sailboats" <montgomery_boats@mailman.xmission.com> Sent: Thursday, September 11, 2003 12:54 AM Subject: M_Boats: Centerboard Corrosion Discussion
I recently bought a book titled "Metal Corrosion in Boats", by Nigel Warren. Really a fascinating book, with all sorts of hints and discussion about how to best arrange all your metal components on a boat and how to manage the effects of corrosion above and below the water.
Anyway, there's a section in the Chapter "Underwater Problem Areas", that should be of interest to all Montgomery owners, especially those with metal centerboards. I have typed this section in for you. There are other sections that deal with topics near and dear to Montgomery owners, but I'll start with this one.
John Fleming M-17: "Star Cross'd
----
Centreboards (Nigel's a Brit) Most centreboards are of mild steel, sometimes galvanized sometimes not. That in itself does not produce special problems but the pivot bolt and the hoisting gear often enhance corrosion. The bearing areas in way of both the pivot bolt and the lifting tackle are especially prone to a vigorous corrosion. The actual surfaces in contact rub together and are immersed in salt water. Any galvanizing or other protective coating soon rubs off exposing the bare steel edge. The hole in the centreplate then enlarges quickly. The lifting tackle pin is necessarily close to the edge of the plate and eventually after a few seasons can pull through the edge releasing the centreplate. This process will happen even with compatible metals - in most cases a galvanized shackle pin in a steel centreboard - but if a stainless or bronze shackle is used the rate of corrosion of the hole is many times faster because of galvanic effects.
With a mild steel centreboard there is no long-lasting solution to this problem except to use compatible materials, i.e. a galvanized shackle on the end of the lifting wire and a galvanized pivot bolt, and then to accept that steady wear will take place. Each year the items should be inspected and replaced when necessary.
In the case of the lifting tackle at least the wear of the plate itself can easily be avoided by fitting a pair of mild steel straps and having a replaceable pin. With more difficulty, the hole for the pivot bolt can be fitted with a removable steel bush[ing]. Then at least all the wearing parts are easily replaced.
Obviously the thicker the bolt and the pin the longer their life; many boats with centreboards are fitted with pathetically thin pivot bolts which while being quite strong enough when new can tolerate very little corrosion. [How true is this for Montgomery's? I wonder.]
The lifting wire itself is a problem. Constantly wetted, neither galvanized nor stainless wire is likely to last long. Stainless wire will give a short life underwater because of pitting, and if a coppersleeved Talurit splice is fitted this will corrode preferentially. Polyester (Terylene or Dacron) rope is one solution, though with a chafe problem, but galvanized chain is better. The lowest link will take the wear but if an overlong piece of chain is fitted in the first place it can be cut off in due course and the next link up used instead. The galvanizing will last only a few years so replacement of the chain must be considered as a matter of course.
[My Montgomery has a little wire rope pigtail attached to the board, and then a polyester line going to the cockpit. I guess he's saying I'll have to check it every so often.]
A complete long-lasting solution to the wear problem at the pivot and lifting pin on a steel centreplate is elusive. Obviously a longer life would ensue if the wearing areas were of a hard and corrosion resistant metal: this suggests stainless steel. The pitting problem would be reduced by the cathodic protection given by the steel plate. So, at the pivot, one would end up with a stainless bush fixed to the plate and with a stainless steel bolt, making sure that Type 316 stainless steel was used. The bush could be rivetted, bolted or even welded in place. Similarly the lifting point could be bushed, or stainless steel tangs could be fitted. From there a stainless shackle would lead to a polyester lifting rope.
[I believe that the Montgomery's more or less follow this advice, except for the stainless bushing at the centerboard pivot. He seems to say that the pivot bolt must be pulled and inspected on a regular basis, and if any significant pitting has occurred, it must be replaced. Also, it implies that even though the centerboard is painted to control rust, there must be metal-to metal contact between the cenboard and the pivot pin.]
Of course a centreboard of zinc-free copper alloy would solve all the problems because the attachments could then be of the same corrosion-free alloys. Suitable metals that come to mind are copper, gunmetal [a bronze (88% copper plus tin)] and copper-nickel. Copper alloys are much the same density or a little heavier than steel. A bonus would be that no antifouling would be necessary. The lifting wire could be of Monel (which is available, though at a price). Stainless steel for the centreplate could also be considered (again Type 316) with sacrificial anodes.
[The new M23 Bob Eeg is making has a centerboard of silicon bronze, though he doesn't say here whether the pivot bolt is still allowed to be stainless.]
Usually cost rules out such materials and mild steel is the only practical choice; but to avoid disaster it is wise to consider carefully the pivot and lifting arrangements.
----------------
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MC Carpenter wrote:
Is there any mention in that book whether or not you should ground the A/C line ( the green, when using white and black) from shore power to the same ground as the DC commonly using the (black wire as the ground and red as the positive) as the boat power like when you have a charger and using a night light.
I hear some folks are now using a yellow wire instead.
Oh, that's a separate topic that this Nigel dude never really gets on about. However, there's another Nigel, Nigel Calder, who has written a complete book about maintaining a boat's electrical system. A very complex and complete discussion, full of terms like galvanic isolators and isolation transformers. The ABYC standards are complex and are not standing still on this topic. I bought the book, but unfortunately it's in a box somewhere in the garage, I think. Here are some references. Boatowners' Illustrated Handbook of Wiring, Charlie Wing International Marine, Camden, Maine The 12 Volt Doctor's Practical Handbook, Edgar J. Beyn C. Plath, Annapolis, Maryland The 12 Volt Bible for Boats, Miner Brotherton International Marine, Camden, Maine Boatowner's Mechanical and Electrical Manual, Nigel Calder International Marine, Camden, Maine Metal Corrosion in Boats, Nigel Warren International Marine, Camden, Maine One other note. It seems that the real trouble comes when you have an inboard motor, which creates an electrical path from your electrical system to the seawater. For a Montgomery, it would seem that all you need is to have an isolation transformer somewhere if you convert AC to DC. Regards, John Fleming M-17: "Star Cross'd"
When I removed the centerboard a few years ago, I discovered a set of nylon bushings had been installed for the pivot pin. I later found out that when Thomas Howe owned the boat, he had also removed it, and found an oblong wear pattern as you describe below....so he had drilled out the pivot pit hole to 1 inch (you would have to be careful to mark the center of the hole to the exact length...so the tang would continue to hit the stop pin in the same place). The nylon bushings (2 of them) are 1 inch OD, and 3/8" thick, with a 3/8" hole in the middle. You can buy them at local hardware stores, Lowes, Home Depot, etc for less than $1. They snuggly fit the hole, and separate the stainless pivot pin from the cast iron board. Presumably, this would stop the corrosion and provide an easily replaced sacrificial wear surface. A small stainless shackle is fitted to the lift end, and it has a 5/8" piece of Stay Set or some such line for the pendant. No wear was evident there. I do worry about the line being wet and rotting. The most severe wear comes at the point where the tang hits the stop pin. I think they should be two flat edges...one on the board that rests on another....perhaps a bushing made of rectangular nylon stock...with hole drilled out for the stop pin...fitted into the trunk...with the stop pin passing through it. The weight of the heavy board hitting the 3/8" stop pin is a concern. When I let the CB down....ever so slowly....there is still an audible "Clunk" when it bottoms out. If the pendant were to break and the board dropped hard....it would do some damage. A rectangular bushing, fitted inside the trunk....would give it more load bearing strength than just the stop pin spanning the inch or so of trunk space. For those new to the list who might be lurking out there, pictures and diagrams of all this are available on the MSOG: http://www.msog.org/models/m17/m-17-cb.cfm Howard M17, #278 Audasea On 9/10/03 11:54 PM, "John Fleming" <jfleming1231@earthlink.net> wrote:
I recently bought a book titled "Metal Corrosion in Boats", by Nigel Warren. Really a fascinating book, with all sorts of hints and discussion about how to best arrange all your metal components on a boat and how to manage the effects of corrosion above and below the water.
Anyway, there's a section in the Chapter "Underwater Problem Areas", that should be of interest to all Montgomery owners, especially those with metal centerboards. I have typed this section in for you. There are other sections that deal with topics near and dear to Montgomery owners, but I'll start with this one.
John Fleming M-17: "Star Cross'd
----
Centreboards (Nigel's a Brit) Most centreboards are of mild steel, sometimes galvanized sometimes not. That in itself does not produce special problems but the pivot bolt and the hoisting gear often enhance corrosion. The bearing areas in way of both the pivot bolt and the lifting tackle are especially prone to a vigorous corrosion. The actual surfaces in contact rub together and are immersed in salt water. Any galvanizing or other protective coating soon rubs off exposing the bare steel edge. The hole in the centreplate then enlarges quickly. The lifting tackle pin is necessarily close to the edge of the plate and eventually after a few seasons can pull through the edge releasing the centreplate. This process will happen even with compatible metals - in most cases a galvanized shackle pin in a steel centreboard - but if a stainless or bronze shackle is used the rate of corrosion of the hole is many times faster because of galvanic effects.
With a mild steel centreboard there is no long-lasting solution to this problem except to use compatible materials, i.e. a galvanized shackle on the end of the lifting wire and a galvanized pivot bolt, and then to accept that steady wear will take place. Each year the items should be inspected and replaced when necessary.
In the case of the lifting tackle at least the wear of the plate itself can easily be avoided by fitting a pair of mild steel straps and having a replaceable pin. With more difficulty, the hole for the pivot bolt can be fitted with a removable steel bush[ing]. Then at least all the wearing parts are easily replaced.
Obviously the thicker the bolt and the pin the longer their life; many boats with centreboards are fitted with pathetically thin pivot bolts which while being quite strong enough when new can tolerate very little corrosion. [How true is this for Montgomery's? I wonder.]
The lifting wire itself is a problem. Constantly wetted, neither galvanized nor stainless wire is likely to last long. Stainless wire will give a short life underwater because of pitting, and if a coppersleeved Talurit splice is fitted this will corrode preferentially. Polyester (Terylene or Dacron) rope is one solution, though with a chafe problem, but galvanized chain is better. The lowest link will take the wear but if an overlong piece of chain is fitted in the first place it can be cut off in due course and the next link up used instead. The galvanizing will last only a few years so replacement of the chain must be considered as a matter of course.
[My Montgomery has a little wire rope pigtail attached to the board, and then a polyester line going to the cockpit. I guess he's saying I'll have to check it every so often.]
A complete long-lasting solution to the wear problem at the pivot and lifting pin on a steel centreplate is elusive. Obviously a longer life would ensue if the wearing areas were of a hard and corrosion resistant metal: this suggests stainless steel. The pitting problem would be reduced by the cathodic protection given by the steel plate. So, at the pivot, one would end up with a stainless bush fixed to the plate and with a stainless steel bolt, making sure that Type 316 stainless steel was used. The bush could be rivetted, bolted or even welded in place. Similarly the lifting point could be bushed, or stainless steel tangs could be fitted. From there a stainless shackle would lead to a polyester lifting rope.
[I believe that the Montgomery's more or less follow this advice, except for the stainless bushing at the centerboard pivot. He seems to say that the pivot bolt must be pulled and inspected on a regular basis, and if any significant pitting has occurred, it must be replaced. Also, it implies that even though the centerboard is painted to control rust, there must be metal-to metal contact between the cenboard and the pivot pin.]
Of course a centreboard of zinc-free copper alloy would solve all the problems because the attachments could then be of the same corrosion-free alloys. Suitable metals that come to mind are copper, gunmetal [a bronze (88% copper plus tin)] and copper-nickel. Copper alloys are much the same density or a little heavier than steel. A bonus would be that no antifouling would be necessary. The lifting wire could be of Monel (which is available, though at a price). Stainless steel for the centreplate could also be considered (again Type 316) with sacrificial anodes.
[The new M23 Bob Eeg is making has a centerboard of silicon bronze, though he doesn't say here whether the pivot bolt is still allowed to be stainless.]
Usually cost rules out such materials and mild steel is the only practical choice; but to avoid disaster it is wise to consider carefully the pivot and lifting arrangements.
----------------
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Note that the M-17 centerboards were of cast iron- not steel, which is much more corrosion resistant. Does Mr. Warren talk about this? Also note that the stainless wire pennant is aftermarket; we used dacron. Jerry ----- Original Message ----- From: "John Fleming" <jfleming1231@earthlink.net> To: "For and about Montgomery Sailboats" <montgomery_boats@mailman.xmission.com> Sent: Wednesday, September 10, 2003 9:54 PM Subject: M_Boats: Centerboard Corrosion Discussion
I recently bought a book titled "Metal Corrosion in Boats", by Nigel Warren. Really a fascinating book, with all sorts of hints and discussion about how to best arrange all your metal components on a boat and how to manage the effects of corrosion above and below the water.
Anyway, there's a section in the Chapter "Underwater Problem Areas", that should be of interest to all Montgomery owners, especially those with metal centerboards. I have typed this section in for you. There are other sections that deal with topics near and dear to Montgomery owners, but I'll start with this one.
John Fleming M-17: "Star Cross'd
----
Centreboards (Nigel's a Brit) Most centreboards are of mild steel, sometimes galvanized sometimes not. That in itself does not produce special problems but the pivot bolt and the hoisting gear often enhance corrosion. The bearing areas in way of both the pivot bolt and the lifting tackle are especially prone to a vigorous corrosion. The actual surfaces in contact rub together and are immersed in salt water. Any galvanizing or other protective coating soon rubs off exposing the bare steel edge. The hole in the centreplate then enlarges quickly. The lifting tackle pin is necessarily close to the edge of the plate and eventually after a few seasons can pull through the edge releasing the centreplate. This process will happen even with compatible metals - in most cases a galvanized shackle pin in a steel centreboard - but if a stainless or bronze shackle is used the rate of corrosion of the hole is many times faster because of galvanic effects.
With a mild steel centreboard there is no long-lasting solution to this problem except to use compatible materials, i.e. a galvanized shackle on the end of the lifting wire and a galvanized pivot bolt, and then to accept that steady wear will take place. Each year the items should be inspected and replaced when necessary.
In the case of the lifting tackle at least the wear of the plate itself can easily be avoided by fitting a pair of mild steel straps and having a replaceable pin. With more difficulty, the hole for the pivot bolt can be fitted with a removable steel bush[ing]. Then at least all the wearing parts are easily replaced.
Obviously the thicker the bolt and the pin the longer their life; many boats with centreboards are fitted with pathetically thin pivot bolts which while being quite strong enough when new can tolerate very little corrosion. [How true is this for Montgomery's? I wonder.]
The lifting wire itself is a problem. Constantly wetted, neither galvanized nor stainless wire is likely to last long. Stainless wire will give a short life underwater because of pitting, and if a coppersleeved Talurit splice is fitted this will corrode preferentially. Polyester (Terylene or Dacron) rope is one solution, though with a chafe problem, but galvanized chain is better. The lowest link will take the wear but if an overlong piece of chain is fitted in the first place it can be cut off in due course and the next link up used instead. The galvanizing will last only a few years so replacement of the chain must be considered as a matter of course.
[My Montgomery has a little wire rope pigtail attached to the board, and then a polyester line going to the cockpit. I guess he's saying I'll have to check it every so often.]
A complete long-lasting solution to the wear problem at the pivot and lifting pin on a steel centreplate is elusive. Obviously a longer life would ensue if the wearing areas were of a hard and corrosion resistant metal: this suggests stainless steel. The pitting problem would be reduced by the cathodic protection given by the steel plate. So, at the pivot, one would end up with a stainless bush fixed to the plate and with a stainless steel bolt, making sure that Type 316 stainless steel was used. The bush could be rivetted, bolted or even welded in place. Similarly the lifting point could be bushed, or stainless steel tangs could be fitted. From there a stainless shackle would lead to a polyester lifting rope.
[I believe that the Montgomery's more or less follow this advice, except for the stainless bushing at the centerboard pivot. He seems to say that the pivot bolt must be pulled and inspected on a regular basis, and if any significant pitting has occurred, it must be replaced. Also, it implies that even though the centerboard is painted to control rust, there must be metal-to metal contact between the cenboard and the pivot pin.]
Of course a centreboard of zinc-free copper alloy would solve all the problems because the attachments could then be of the same corrosion-free alloys. Suitable metals that come to mind are copper, gunmetal [a bronze (88% copper plus tin)] and copper-nickel. Copper alloys are much the same density or a little heavier than steel. A bonus would be that no antifouling would be necessary. The lifting wire could be of Monel (which is available, though at a price). Stainless steel for the centreplate could also be considered (again Type 316) with sacrificial anodes.
[The new M23 Bob Eeg is making has a centerboard of silicon bronze, though he doesn't say here whether the pivot bolt is still allowed to be stainless.]
Usually cost rules out such materials and mild steel is the only practical choice; but to avoid disaster it is wise to consider carefully the pivot and lifting arrangements.
----------------
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Jerry Montgomery wrote:
Note that the M-17 centerboards were of cast iron- not steel, which is much more corrosion resistant. Does Mr. Warren talk about this? Also note that the stainless wire pennant is aftermarket; we used dacron.
Jerry
Hi Jerry, That's interesting, dacron rope. Is it stable when immersed in seawater? How often should it be checked and or replaced? Would I just tie a knot? Yes, Nigel Warren discusses cast iron, the complete discussion is below. To summarize, he says that iron and mild steel corrode at the same rate, but have different corrosion behavior. Cast irons with significant amounts of nickel, silicon, or chromium rust much more slowly than ordinary cast iron. Obviously, stainless corrodes more slowly, but it has problems with crevice corrosion, especially in areas of high flow or no flow. I'll scan that discussion in some other time. Regards, John Fleming M-17: "Star Cross'd" ---- While wrought iron is not much used today, cast iron is still popular. The various grades of cast iron are produced by varying the composition (and here carbon is important) and by varying the crystalline structure as seen under a microscope. The latter is done by various furnace procedures. Hence one sees names such as 'grey iron' and 'white iron', so called because of the appearance of a fracture. Grey iron is basic cast iron and under BS 1452 there are various grades with tensile strengths ranging from 10 T/sq. in. (150 N/mm^2) to 27 T/sq. in. (400 N/mm^2). Then there is nodular cast iron with greater strength (BS 2789), 'nodular' meaning that the carbon in the iron is held in compact graphite nodules rather than flakes as in cast grey iron. Nodular cast iron is also called SG iron, the SG standing for spheroidal graphite. Other names for it are ductile iron, nodular graphite iron, and spherultic iron. Nodular cast iron is a steel-like metal easily machined and giving a smooth finish. It is the most modern development of cast iron; previously the only reasonably ductile cast iron available was 'malleable iron'. Malleable iron is a white iron which has been heat-treated to reduce brittleness. There are three groups, whiteheart, blackheart and pearlite (BS 309, 3 10 and 333 respectively). These terms refer to the process by which they are made and their resulting crystal structure. More sophisticated irons include the nickel cast irons and the high-alloy cast irons, both having enhanced strength and ductility. The corrosion rate of iron in seawater is much the same as that of mild steel, but the form of corrosion is very different. Whereas mild steel gradually wastes away and becomes physically smaller, iron tends to retain its shape and outward size but rots away from inside. Superficially it may look sound, but a sharp prod can reveal massive corrosion underneath. This form of attack is called graphitization because a graphite residue is all that is left. The ordinary cast irons have a poor resistance to shock and fracture fairly easily; they are also readily attacked by sulphate-reducing bacteria. Ductile iron is the modern equivalent of cast iron. It does not fracture as easily but its corrosion resistance is much the same. Nickel cast iron with 1-3% of nickel is a finer-grained iron but again the corrosion resistance is barely enhanced. There are families of high-alloy cast iron: irons with large amounts of chromium, or nickel or silicon. The austenitic nickel cast irons have a low uniform rate of corrosion in seawater and do not suffer from graphitization; they rust but slowly on deck. These cast irons are often called Ni-Resist, but this name is actually a trademark. The high-silicon cast irons (about 14% Si) also have a much enhanced resistance to corrosion, as do the high-chromium irons (12-35% Cr). (See Tables 8 and 9.) Unless a high-alloy cast iron is used, with much increased cost, the various 'cheap and cheerful' cast irons corrode at much the same rate as carbon and low-alloy steels. To Conclude Common mild steel and cast iron are excellent materials in many ways; they are strong and economical - but they rust. But at least the rusting is obvious and gradual and the metal is unlikely to fail suddenly as can happen to stainless steel or high strength metals. Some low-alloy steels like Cor-Ten are 'slow rusting' in a marine atmosphere but rust much like mild steel when immersed in seawater. All steels should have the mill scale removed before painting. Hot-dip zinc galvanizing is generally far superior and more 'cost effective' than zinc or cadmium electroplating. To get the best galvanizing ask for the work to be done to a standard, e.g. BS 729. If the galvanized item is to be immersed it is essential to paint it, preferably by using a self-etch primer for the first coat. Galvanizing gives a tough self-healing coating and one which is quite inexpensive. Electroplating is a waste of time unless a standard is specified, e.g. BS 1706 Class A. Zinc electric plating is preferable to cadmium because the coating thickness is greater. Nevertheless hot-dip galvanizing will give a much longer life and yet its cost is only very slightly more than electroplating. Galvanized or plated steel makes a good base for paint which in turn gives a long life to the paint and the metal coating providing the paint is 'keyed' to the coat.
Dacron (polyester) is very long lasting. I used to fasten it with a double half hitch because the knot needs to be up tightly to the shackle. Most of the problems came on newer boats, which naturally have more sharp edges. If I were to buy an old 17, I would hoist it up and take the board out and check it out, replacing the pins, then probably do it once a year after that, especially if it was left in salt water. I'd check it out every time I did the bottom. Jerry ----- Original Message ----- From: "John Fleming" <jfleming1231@earthlink.net> To: "For and about Montgomery Sailboats" <montgomery_boats@mailman.xmission.com> Sent: Friday, September 12, 2003 12:57 AM Subject: Re: M_Boats: Centerboard Corrosion Discussion
Jerry Montgomery wrote:
Note that the M-17 centerboards were of cast iron- not steel, which is much more corrosion resistant. Does Mr. Warren talk about this? Also note that the stainless wire pennant is aftermarket; we used dacron.
Jerry
Hi Jerry,
That's interesting, dacron rope. Is it stable when immersed in seawater? How often should it be checked and or replaced? Would I just tie a knot?
Yes, Nigel Warren discusses cast iron, the complete discussion is below. To summarize, he says that iron and mild steel corrode at the same rate, but have different corrosion behavior. Cast irons with significant amounts of nickel, silicon, or chromium rust much more slowly than ordinary cast iron.
Obviously, stainless corrodes more slowly, but it has problems with crevice corrosion, especially in areas of high flow or no flow. I'll scan that discussion in some other time.
Regards, John Fleming M-17: "Star Cross'd"
----
While wrought iron is not much used today, cast iron is still popular. The various grades of cast iron are produced by varying the composition (and here carbon is important) and by varying the crystalline structure as seen under a microscope. The latter is done by various furnace procedures. Hence one sees names such as 'grey iron' and 'white iron', so called because of the appearance of a fracture. Grey iron is basic cast iron and under BS 1452 there are various grades with tensile strengths ranging from 10 T/sq. in. (150 N/mm^2) to 27 T/sq. in. (400 N/mm^2). Then there is nodular cast iron with greater strength (BS 2789), 'nodular' meaning that the carbon in the iron is held in compact graphite nodules rather than flakes as in cast grey iron. Nodular cast iron is also called SG iron, the SG standing for spheroidal graphite. Other names for it are ductile iron, nodular graphite iron, and spherultic iron. Nodular cast iron is a steel-like metal easily machined and giving a smooth finish. It is the most modern development of cast iron; previously the only reasonably ductile cast iron available was 'malleable iron'.
Malleable iron is a white iron which has been heat-treated to reduce brittleness. There are three groups, whiteheart, blackheart and pearlite (BS 309, 3 10 and 333 respectively). These terms refer to the process by which they are made and their resulting crystal structure.
More sophisticated irons include the nickel cast irons and the high-alloy cast irons, both having enhanced strength and ductility.
The corrosion rate of iron in seawater is much the same as that of mild steel, but the form of corrosion is very different. Whereas mild steel gradually wastes away and becomes physically smaller, iron tends to retain its shape and outward size but rots away from inside. Superficially it may look sound, but a sharp prod can reveal massive corrosion underneath. This form of attack is called graphitization because a graphite residue is all that is left.
The ordinary cast irons have a poor resistance to shock and fracture fairly easily; they are also readily attacked by sulphate-reducing bacteria.
Ductile iron is the modern equivalent of cast iron. It does not fracture as easily but its corrosion resistance is much the same. Nickel cast iron with 1-3% of nickel is a finer-grained iron but again the corrosion resistance is barely enhanced.
There are families of high-alloy cast iron: irons with large amounts of chromium, or nickel or silicon. The austenitic nickel cast irons have a low uniform rate of corrosion in seawater and do not suffer from graphitization; they rust but slowly on deck. These cast irons are often called Ni-Resist, but this name is actually a trademark. The high-silicon cast irons (about 14% Si) also have a much enhanced resistance to corrosion, as do the high-chromium irons (12-35% Cr). (See Tables 8 and 9.)
Unless a high-alloy cast iron is used, with much increased cost, the various 'cheap and cheerful' cast irons corrode at much the same rate as carbon and low-alloy steels.
To Conclude
Common mild steel and cast iron are excellent materials in many ways; they are strong and economical - but they rust. But at least the rusting is obvious and gradual and the metal is unlikely to fail suddenly as can happen to stainless steel or high strength metals. Some low-alloy steels like Cor-Ten are 'slow rusting' in a marine atmosphere but rust much like mild steel when immersed in seawater.
All steels should have the mill scale removed before painting.
Hot-dip zinc galvanizing is generally far superior and more 'cost effective' than zinc or cadmium electroplating. To get the best galvanizing ask for the work to be done to a standard, e.g. BS 729. If the galvanized item is to be immersed it is essential to paint it, preferably by using a self-etch primer for the first coat. Galvanizing gives a tough self-healing coating and one which is quite inexpensive.
Electroplating is a waste of time unless a standard is specified, e.g. BS 1706 Class A. Zinc electric plating is preferable to cadmium because the coating thickness is greater. Nevertheless hot-dip galvanizing will give a much longer life and yet its cost is only very slightly more than electroplating.
Galvanized or plated steel makes a good base for paint which in turn gives a long life to the paint and the metal coating providing the paint is 'keyed' to the coat.
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participants (9)
-
Dan White -
Gary M. Hyde -
Howard Audsley -
Jerry Montgomery -
John Fleming -
MC Carpenter -
n9ca -
Stephen Martin -
Steve McClellan