Well I just finished cutting the keel out of my Mac/Ven 17. Water has got in under the fiberglass covering the steel core of the keel, it got rusty and swelled up so the keel was really stuck!!! Major keel repairs are now underway. This keel is just over 5ft long and has a lead bulb on the bottom end to give it a total weight of approx 325 lbs. I am thinking of building a stainless keel this winter but my question is this...how important is it to have the lead weight at the bottom of the keel if i can get close to the same weight by building the whole keel out of steel and forgetting about the fiberglass-over-steel construction of this original keel? I know we have some engineering types on this site who will have the answer for me.
rusted swollen keel
- Thread starter gord17531
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Higgs is right
Higgs is basically right, there will be consequenses from not matching both the mass and the center of mass of the original keel. The moment [righting moment] produced by the keel is especially important. Otherwise you negatively affect either the boat's stability, or the stress on the rig. While there are changes that you can get away with - sometimes shallower and heavier for example - it requires thought and some engineering calculations. You have a number of options - easiest is to match the original weight and center of mass. Plywood/epoxy/glass with lead in strategic locations? Steel with partial lead fill? There are probably several ways to build a keel if you want to do that - or perhaps the folks at MacG sell a replacement that you can just bolt in? OC
Higgs is basically right, there will be consequenses from not matching both the mass and the center of mass of the original keel. The moment [righting moment] produced by the keel is especially important. Otherwise you negatively affect either the boat's stability, or the stress on the rig. While there are changes that you can get away with - sometimes shallower and heavier for example - it requires thought and some engineering calculations. You have a number of options - easiest is to match the original weight and center of mass. Plywood/epoxy/glass with lead in strategic locations? Steel with partial lead fill? There are probably several ways to build a keel if you want to do that - or perhaps the folks at MacG sell a replacement that you can just bolt in? OC
Higgs and oldCat are right just duplicate the
existing system. You may use SS or galvanized plate. Don't skimp on the thickness. Ckeck with your steel supplier concerning some of the more corrosion resistant alloys like core-10. Some of the modern paints are very good at keeping corrosion under control. In this case I would be reluctant to cover the steel with glass because it is likely to lead to the same problem in the future.
existing system. You may use SS or galvanized plate. Don't skimp on the thickness. Ckeck with your steel supplier concerning some of the more corrosion resistant alloys like core-10. Some of the modern paints are very good at keeping corrosion under control. In this case I would be reluctant to cover the steel with glass because it is likely to lead to the same problem in the future.
Weight a moment!
A little pun on words for your question. The weight at the end of the keel -vs- weight thru-out the keel makes a difference of the righting power of the keel. Immagine a see-saw and there is a 200 pound person on the right end of the see-saw and the left end is a 200 pound steel mass the whole length of the left side of the see-saw. The 200 pound man will have much more force because the force is a function of weight and distance from the fulcrum or moment arm. By distributing the weight of the keel throughout the keel, you have changed the "moment" of force. Bottom line - your keel will not have the same force(righting power) and heeling will be more. Your boat dynamics will be changed - no question.
A little pun on words for your question. The weight at the end of the keel -vs- weight thru-out the keel makes a difference of the righting power of the keel. Immagine a see-saw and there is a 200 pound person on the right end of the see-saw and the left end is a 200 pound steel mass the whole length of the left side of the see-saw. The 200 pound man will have much more force because the force is a function of weight and distance from the fulcrum or moment arm. By distributing the weight of the keel throughout the keel, you have changed the "moment" of force. Bottom line - your keel will not have the same force(righting power) and heeling will be more. Your boat dynamics will be changed - no question.
Not familiar with your boat, but have you
considered contacting someone like Mars Metals to see if they can cast you a new one in lead ? They might do steel too if necessary, with any luck they may have done one for your boat before.
considered contacting someone like Mars Metals to see if they can cast you a new one in lead ? They might do steel too if necessary, with any luck they may have done one for your boat before.
Thanks guys
my son the whiz kid engineer told me all about righting moments and stuff so now i know not to change the design of the keel when i rebuild it. i have contacted a local foundry about casting a new keel and they are pricing out the job right now. sounds like it will be expensive so welding a new one up from threee thicknesses of 1/4" plate might be my best bet. i am thinking with 3 layers i will be able to do some grinding to get some sort of shape other than a slab and casting a lead bulb at the bottom end can't be to tough since i have cast aluminum before. Anyway I've done some grinding and filling and patching and this should get me thru the rest of the season, guess I have my winter project all lined up already!!! ps: i will not be glassing over the new keel just real good epoxy paint.
my son the whiz kid engineer told me all about righting moments and stuff so now i know not to change the design of the keel when i rebuild it. i have contacted a local foundry about casting a new keel and they are pricing out the job right now. sounds like it will be expensive so welding a new one up from threee thicknesses of 1/4" plate might be my best bet. i am thinking with 3 layers i will be able to do some grinding to get some sort of shape other than a slab and casting a lead bulb at the bottom end can't be to tough since i have cast aluminum before. Anyway I've done some grinding and filling and patching and this should get me thru the rest of the season, guess I have my winter project all lined up already!!! ps: i will not be glassing over the new keel just real good epoxy paint.
Zinc Primers
For the steel, I would recommend a zinc enriched epoxy primer. They are supposed to go on very very thin or the primer will crack. I dont think you can brush or roll it on that thin (1-3 mils)you will probably have to spray. Then apply your other epoxy coatings on top. I'm accustomed to industrial paints so I dont know how available zinc primers are to the general public. FWIW Tony B
For the steel, I would recommend a zinc enriched epoxy primer. They are supposed to go on very very thin or the primer will crack. I dont think you can brush or roll it on that thin (1-3 mils)you will probably have to spray. Then apply your other epoxy coatings on top. I'm accustomed to industrial paints so I dont know how available zinc primers are to the general public. FWIW Tony B
Consider to pour your own lead .....
or as another poster listed consider a new lead keel 'insert' from Mars Metals. If and only if the outter 'shell' of the fiberglass encapsulation (roving) is intact it is possible to lay in lead pieces and fix them in place with fine grade waterproof (Portland) concrete .... this was a sub-par process used by many 'cheaper' boats constructed in the 60s & 70s. If you could do this with lead salvaged from auto tire store, etc. it may be a very economical way to restore the correct 'moments' needed to restore precise righting moment, etc. +/-5% mass isnt going to make that much difference. Usually, when an encapsulated (with iron internals) keel is penetrated by water, the formation of rust (red ferric oxide) generates extreme pressure because the ferric oxide is less dense than the original metal. Such pressure usually destroys the structural integrity of the encapsulation structure. In most boats a penetrated encapsulated keel usually means that the boat is 'destroyed'. I strongly urge you to carefully examine the structural and watertight integrity of the 'cavity' before you go through all the work and ultimately find that over time this restoration work becomes a costly failure. The 'membrane' on the top of the ballast which seals the ballast from the bilge is VERY important with respect to water ingress .... and is very hard to make 'water tight'. Without total water-tight integrity (even with stainless steel ballast) the restoration will probably only be 'temporary'. In any case, I personally would avoid any 'ferrous' metal (including 'stainless') to prevent rusting and its subsequent 'pressure'. IF the present ballast is iron your probable best choice would be lead (at TWICE the density of iron; hence, you only need half as much), even lead 'punchings' held in place with concrete, etc. and then totally sealed with proper encapsulation including a new 'top membrane'. If you have access to a local foundry they could do the lead casting for you, using old/used tire balance weights that you supply, etc. 325 lbs of lead would only be approx 1/2 cubic foot: ( lead density @ 11.34gm per cu. cm) X 62.4lb. per cu. ft. = 708 lb. per cu. ft. ...... or simply pour in 325lb. of old tire balance weights, fix them in place with waterproof concrete and lay on a perfect/thick FRG 'top membrane' to be sure that everything is 'watertight'. Hope this helps.
or as another poster listed consider a new lead keel 'insert' from Mars Metals. If and only if the outter 'shell' of the fiberglass encapsulation (roving) is intact it is possible to lay in lead pieces and fix them in place with fine grade waterproof (Portland) concrete .... this was a sub-par process used by many 'cheaper' boats constructed in the 60s & 70s. If you could do this with lead salvaged from auto tire store, etc. it may be a very economical way to restore the correct 'moments' needed to restore precise righting moment, etc. +/-5% mass isnt going to make that much difference. Usually, when an encapsulated (with iron internals) keel is penetrated by water, the formation of rust (red ferric oxide) generates extreme pressure because the ferric oxide is less dense than the original metal. Such pressure usually destroys the structural integrity of the encapsulation structure. In most boats a penetrated encapsulated keel usually means that the boat is 'destroyed'. I strongly urge you to carefully examine the structural and watertight integrity of the 'cavity' before you go through all the work and ultimately find that over time this restoration work becomes a costly failure. The 'membrane' on the top of the ballast which seals the ballast from the bilge is VERY important with respect to water ingress .... and is very hard to make 'water tight'. Without total water-tight integrity (even with stainless steel ballast) the restoration will probably only be 'temporary'. In any case, I personally would avoid any 'ferrous' metal (including 'stainless') to prevent rusting and its subsequent 'pressure'. IF the present ballast is iron your probable best choice would be lead (at TWICE the density of iron; hence, you only need half as much), even lead 'punchings' held in place with concrete, etc. and then totally sealed with proper encapsulation including a new 'top membrane'. If you have access to a local foundry they could do the lead casting for you, using old/used tire balance weights that you supply, etc. 325 lbs of lead would only be approx 1/2 cubic foot: ( lead density @ 11.34gm per cu. cm) X 62.4lb. per cu. ft. = 708 lb. per cu. ft. ...... or simply pour in 325lb. of old tire balance weights, fix them in place with waterproof concrete and lay on a perfect/thick FRG 'top membrane' to be sure that everything is 'watertight'. Hope this helps.
back in the water!!!!
well my keel is all patched up and worked fine yesterday. no leaks anywhere and the keel goes up and down like it should. only another 5 or 6 weeks of sailing here then i will be able to do a complete rebuild on the keel over the winter. i like my 17!!!
well my keel is all patched up and worked fine yesterday. no leaks anywhere and the keel goes up and down like it should. only another 5 or 6 weeks of sailing here then i will be able to do a complete rebuild on the keel over the winter. i like my 17!!!
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