Do you know your keel bolt details

[silver-fox]

I bought a Moody 346 a few month ago. I have previously been a long, encapsulated keel type yacht owner. I was surprised that there is virtually no information on the keel bolts on this yacht from either the designer or the MOA.

Asking around the marinas here I was amazed that I couldn't find one person with a bolt on keel who knew the dimensions of his keel bolts.

Is this information not important? Don't skippers care if there keels are held on with tooth-picks?

How many on this forum know the dimension and nymber of their keel bolts and whether they are adequate for the job. How much wastage is OK for instance.

I am seriously considering getting rid of this bolt on keel boat and returning to encapsulated for my next boat.

I am surprised your surveyor didn't recommend drawing a keel bolt or two as part of your pre-purchase survey.

I am amazed you didn't do this given the importance to you of this subject - after all its cheaper than reselling your recently acquired boat. .

 

[seabonds]

thanks, just wanted to know the size and thread type. I too pulled a stud when i purchased the boat 8 years age. Stud was pristine, nut was ugly. Plan to replace one nut and backing plate (in the sump) at my next haul out, likely the stud too since it will come out with the nut. Not too worried about the rest of them for now.
Regards,
Bill

 

[contessaman]

im not a moody owner but I have been reading this thread with interest. If the top of the bolts are rusting due to water in the bilge (inevitable?) then why arent they glassed over like they are in my beneteau? I say glassed over -it looks more like a pile of gelcoat on each one so that it could be easily chipped off to access/withdraw the bolt without damaging the surrounding hull. I have never inspected my bolts my surveyor was content to inspect keel to hull joint for signs of movement and water ingress. obviously if your nut is flakey and rusty then this wouldnt be a good idea but if you replaced the nuts I would be sticking a toilet roll holder over the top with masking tape and pouring it full of gelcoat. my previous boat, an OOD34 had stainless bolts so these were fine sat in the bilge water, but mild steel should be protected IMHO

 

[[10753]]

I've never worried about mine - surveyor checked and said leave well alone - Boat now 43 years old - I'm not sure about Moodys but its not a topic discussed so I guess they have few problems in that area.

And yes I know my keel specs - Twin keels symmetrical hydrofoil section. Construction ¼" (6.4) steel plate. Weight 560lbs (258) per keel. Ballast lead ½ ton (508) per keel. Total weight of keels 1 ½ tons (1524). Total fuel capacity 60 gallons (270). Keel fastening ½" (12.7) diameter stainless steel bolts through steel plates moulded into the hull. 30 bolts per keel.

 

[silver-fox]

im not a moody owner but I have been reading this thread with interest. If the top of the bolts are rusting due to water in the bilge (inevitable?) then why arent they glassed over like they are in my beneteau? I say glassed over -it looks more like a pile of gelcoat on each one so that it could be easily chipped off to access/withdraw the bolt without damaging the surrounding hull. I have never inspected my bolts my surveyor was content to inspect keel to hull joint for signs of movement and water ingress. obviously if your nut is flakey and rusty then this wouldnt be a good idea but if you replaced the nuts I would be sticking a toilet roll holder over the top with masking tape and pouring it full of gelcoat. my previous boat, an OOD34 had stainless bolts so these were fine sat in the bilge water, but mild steel should be protected IMHO

It is a common misapprehension that stainless steel is a better material for keel bolts than mild steel but it isn't, because once deprived of oxygen stainless steel suffers from something called crevice corrosion in such conditions and that makes it more prone to failure.

 

[seabonds]

they were/are encapsulated, but water eventually gets under there and the nut rusts, expands and cracks the coating. looks really ugly until you clean them up and see the nut more or less in tact. Studs are usually fine. I have one nut which is a bit more wasted than one would like. Thus the question, what size are they exactly? Just got a message from a surveyor fellow in England who says they are imperial size, one inch. Guess I will buy both sizes and figure it out when I pull it.
Thanks,
Bill

 

[vyv_cox]

It is a common misapprehension that stainless steel is a better material for keel bolts than mild steel but it isn't, because once deprived of oxygen stainless steel suffers from something called crevice corrosion in such conditions and that makes it more prone to failure.

Sorry, your metallurgy is very rusty LNG plants are built entirely from stainless steel due to its low temperature properties. The internals never see oxygen but they most definitely do not fail from crevice corrosion.

The vast majority of modern boats have stainless steel keel bolts and suffer no problems at all. Corrosion requires water, keep it out and no bolts will rust.

 

[timmygobang]

If you were really worried, I saw a guy in the boat yard last week applying kevlar matting to a pretty rusty keel with the view to sealing the whole thing in, effectively making it a encapsulated keel of some sorts. Can't say I'll be doing the same to mine, but I'm reading this thread with interest as I wasn't able to inspect all my keel bolts when I purchased my boat last year as the fuel tank and water tank was in the way.

 

[ghostlymoron]

I posted this photo of mine a couple of weeks ago. All the studs were in fine condition when the keel was dropped.

I don't like the idea of glassing them in but flowcoating might prevent corrosion although - how would you know if you couldn't see the nuts?

 

[Tranona]

I am surprised your surveyor didn't recommend drawing a keel bolt or two as part of your pre-purchase survey.

Not sure why that would be necessary unless there had been severe damage to the keel/hull interface so allowing water to get in. As others here have said, although the mild steel nuts may look a bit of a mess (usually because of leaks from above) the bolt itself is fine.

The idea of drawing keel bolts is a relic from the old days when bolts went right through the wooden floors, keels and ballast keels, all of which might be subject to movement and water getting in the joints. particularly bad with oak keels as oak and steel are not good friends. None of these conditions is relevant to modern GRP construction and both mild steel and stainless bolts are used successfully.

Arguably stainless is better as it does not corrode in the bilge. An alternative some use is glassing over the nuts in the bilge, but that has its downsides as often it is just a flowcoat and if it does crack it can create conditions that lead to corrosion under the GRP.

 

[GrahamM376]

Thus the question, what size are they exactly? Just got a message from a surveyor fellow in England who says they are imperial size, one inch. Guess I will buy both sizes and figure it out when I pull it.
Thanks,Bill

Are you in the MOA? If so, do a search of threads on Info Exchange. This came up - They are metric, M24 nuts/thread - same as mine were.

 

[Cappen Boidseye]

Sorry, your metallurgy is very rusty LNG plants are built entirely from stainless steel due to its low temperature properties. The internals never see oxygen but they most definitely do not fail from crevice corrosion.

The vast majority of modern boats have stainless steel keel bolts and suffer no problems at all. Corrosion requires water, keep it out and no bolts will rust.

Sorry, the shiny surface of stainless steel is produced by oxidation of the chromium in the alloy, if that coating is damaged in any way fresh oxidation occurs and the surface 'heals', but only when oxygen is available. If the stainless surface is in contact with something else (as in crevices or where two stainless surfaces contact each other, or the stainless is in contact with something else, e.g. a big lump of cast iron or lead) then oxygen is not present and the chromium oxide protective layer cannot form, this can form "brownstaining" and can go on to lead to rust or even pitting of the stainless steel. This does happen, it is a fact. In certain steam plant I am acquanted with much money is spent removing cladding from pipework to check for and treat any brownstaining which is starting. For a domestic example I have left a stainless chefs knife wet and in contact with more cutlery in a dishwasher, it now has a brown corrosion spot on it (Oops!), keep oxygen from stainless steel and it will happily start to rust.
The chromium needs to oxidise, that nice shiny surface then protects the iron in the steel from oxidising, i.e. rust. I could dig deep into my notes at work, but just Google for brownstaining stainless steel to find out more about the process.
I don't have a table of electrovalency for different steels handy to see how mild steel and stainless steel compare for electrolytic corrosion when in contact with cast iron or lead lumps.

 

[vyv_cox]

Sorry, the shiny surface of stainless steel is produced by oxidation of the chromium in the alloy, if that coating is damaged in any way fresh oxidation occurs and the surface 'heals', but only when oxygen is available. If the stainless surface is in contact with something else (as in crevices or where two stainless surfaces contact each other, or the stainless is in contact with something else, e.g. a big lump of cast iron or lead) then oxygen is not present and the chromium oxide protective layer cannot form, this can form "brownstaining" and can go on to lead to rust or even pitting of the stainless steel. This does happen, it is a fact. In certain steam plant I am acquanted with much money is spent removing cladding from pipework to check for and treat any brownstaining which is starting. For a domestic example I have left a stainless chefs knife wet and in contact with more cutlery in a dishwasher, it now has a brown corrosion spot on it (Oops!), keep oxygen from stainless steel and it will happily start to rust.
The chromium needs to oxidise, that nice shiny surface then protects the iron in the steel from oxidising, i.e. rust. I could dig deep into my notes at work, but just Google for brownstaining stainless steel to find out more about the process.
I don't have a table of electrovalency for different steels handy to see how mild steel and stainless steel compare for electrolytic corrosion when in contact with cast iron or lead lumps.

I don't disagree. You might like to look at my website for a better description of crevice corrosion and its causes. The main point, as I said before, is exclude the water and none of the recognised eleven forms of corrosion will take place.

 

[contessaman]

but flowcoating might prevent corrosion although - how would you know if you couldn't see the nuts?

I would have expected the brittle flowcoat / gelcoat to crack because of the expansion if the bolt heads or nuts were rusting beneath? flow coating has another advantage, again due to its brittleness - if there is any movement whatsoever of the keel and bolts, it will crack. so, nice little mounds of gelcoat on the inside and no sign of movement on the outside or rusty water stains from the gap when the yachts ashore = all is bon. so I think you should clean the rusty heads up, treat the rust with jenolite and encapsulate them. then monitor them, if it cracks you either have movement or water ingress from around the bolt which will merit further attention in either case. (all IMHO).

 

[ghostlymoron]

Good point Contessa. Maybe do as you suggest the stick on a blob of Sika (other sealants are available)

 

[silver-fox]

Sorry, your metallurgy is very rusty LNG plants are built entirely from stainless steel due to its low temperature properties. The internals never see oxygen but they most definitely do not fail from crevice corrosion.

The vast majority of modern boats have stainless steel keel bolts and suffer no problems at all. Corrosion requires water, keep it out and no bolts will rust.

Vyv

I can claim little knowledge of metallurgy at all and most of what I have picked up has been from you!

I was pretty confident that in the past you have made the following comments (but now doubting my memory!)

- A galvanised chain/galvanised anchor was stronger than a stainless equivalent of the same dimensions
- That even 316 wasn't suitable for use below water level or where crevice corrosion was probable

Based on the above I have been of the opinion that SS keelbolts were a) weaker and b) more prone to failure

To have my prejudices so shaken had me reaching first for the drinks cupboard and secondly for Google. Blinking back the tears, I found that Wikipedia has an item on crevice corrosion which describes it better than I can complete with supporting pictures. In addition to this Wiki item there appears to be a considerable body of opinion suggesting crevice corrosion is a problem - although I do readily accept that : -

- opinion, even expressed loudly, is not fact
- there are always more fools in majority

http://en.wikipedia.org/wiki/Crevice_corrosion.

I believed the process of crevice corrosion was as follows.......

(This is cut and paste from an American boat manufacturer's site because they describe it better than I can but they in turn appear to have sourced the information from AZOM)
CONCENTRATED CELL OR CREVICE CORROSION
This corrosion is common between nut and bolt surfaces. Salt water applications are a severe problem because of the salt water’s
low PH and its high chloride content. Here is the mechanism:
• Chlorides pit the passivated stainless steel surface.
• The low PH salt water attacks the active layer that is exposed.
The absence of oxygen inhibits the re-forming of the passive layer.
These three factors work together in a vicious cycle, repeatedly attacking the same small area. If the metal is under tensile stress- like from an over torqued keel bolt nut, the pit formed can transform itself into a crack. When a crack forms the process repeats and accelerates as
the surface area of the ‘active’ layer is now much larger.

I would welcome your comment on the above and then I will then sober up and settle down on a new position of certainty

(often wrong but always certain as the saying goes)

 

[Dipper]

I would have expected the brittle flowcoat / gelcoat to crack because of the expansion if the bolt heads or nuts were rusting beneath? flow coating has another advantage, again due to its brittleness - if there is any movement whatsoever of the keel and bolts, it will crack. so, nice little mounds of gelcoat on the inside and no sign of movement on the outside or rusty water stains from the gap when the yachts ashore = all is bon. so I think you should clean the rusty heads up, treat the rust with jenolite and encapsulate them. then monitor them, if it cracks you either have movement or water ingress from around the bolt which will merit further attention in either case. (all IMHO).

My original keel bolts were encapsulated but water got in and corroded the nuts. When I replaced them some 15 years ago, I painted about 10 coats of the very cheap rubberised car body underseal over the nuts and immediate surrounds. There are no signs of rust today. I chose car body underseal because it is flexible and I read that it 'self heals' if there are any minor breeches.

 

[contessaman]

My original keel bolts were encapsulated but water got in and corroded the nuts. When I replaced them some 15 years ago, I painted about 10 coats of the very cheap rubberised car body underseal over the nuts and immediate surrounds. There are no signs of rust today. I chose car body underseal because it is flexible and I read that it 'self heals' if there are any minor breeches.

based on my own experiences I would avoid anything flexible!

my OOD34 had struck a reef at max chat with the kite up. unsurprisingly I had awful trouble with the keel for a while. it was an unusual arrangment in that the keel was GRP with encapsulated lead in the bottom. the grp keel then had a flange which was bedded in whatever the equivalent of sikaflex was in the 70s and bolted to the hull with stainless bolts. I had the internal matrix repaired and then bolted the keel back on (keep with me theres a point to all this) again bed in sealant. I wasted a whole season and a bucket load of cash with the boat in and out of the water with leaks. eventually an old salt in the boatyard came to chat with me. he had worked in the 80s building one off racers. he asked why I kept bedding the keel in flexible sealant - I replied 'so that it wont leak when it flexes?' he said ' if theres one thing I have learned about keels, if you dont want them to move, then dont make them flexible!!'. we dropped the keel together one last time, bed it down in epoxy and CSM. when it started to go off we tightened those big bolts with a breaker bar until our muscles burned and then some more. no more movement, no more problems. many years of hard sailing and racing. keel stepped mast and hydraulic rigging pumped up rock hard.

I dont know about wooden boats. but with a plastic one, movement is bad. any thing that moves can 'work'. choose no movement.

again all IMHO and only based on my experiences.

 

[Tranona]

Based on the above I have been of the opinion that SS keelbolts were a) weaker and b) more prone to failure

Guess Vyv has already answered your question in part. Your description of crevice corrosion is correct. The issue with keel bolts (or studs) is that the conditions where crevice corrosion occurs does not normally exist. They are not in oxygen starved wet conditions unless the seal between the keel and the hull has failed - for example poor sealing or a severe grounding.

Literally 10's of thousands of boats are fitted with stainless keel bolts, and equally many , particularly older boats use mild steel and neither generally suffer from corrosion, never mind failure. Both material s are approved by all the major Classification Societies for this application and the sizes used are such that strength is not an issue.

This does not mean that there are not problems with stainless used under water and it is not difficult to find examples of severe crevice corrosion on items such as fastenings for rudder hangings (particularly if going through wood, or on prop shafts in the threads for nuts or even in the area running in a tight stern tube bearing. These are the conditions where crevice corrosion is a problem, but not in keel bolts because water is excluded from the material faces.

There are several examples on this thread alone of keel bolts being removed after 30 years or more and still in as new condition.

In my garage I have some perfect examples of corroded keel bolts out of my wooden boat - waisted where the oak keel meets the iron ballast because water got past the poor sealing between the two. Both heads (top and bottom) where the sealing rings were intact are perfect. Now replaced with stainless - but the bolt holes filled with Sikaflex. Still there after nearly 20 years and likely to outlast me.

 

[Dipper]

based on my own experiences I would avoid anything flexible!

my OOD34 had struck a reef at max chat with the kite up. unsurprisingly I had awful trouble with the keel for a while. it was an unusual arrangment in that the keel was GRP with encapsulated lead in the bottom. the grp keel then had a flange which was bedded in whatever the equivalent of sikaflex was in the 70s and bolted to the hull with stainless bolts. I had the internal matrix repaired and then bolted the keel back on (keep with me theres a point to all this) again bed in sealant. I wasted a whole season and a bucket load of cash with the boat in and out of the water with leaks. eventually an old salt in the boatyard came to chat with me. he had worked in the 80s building one off racers. he asked why I kept bedding the keel in flexible sealant - I replied 'so that it wont leak when it flexes?' he said ' if theres one thing I have learned about keels, if you dont want them to move, then dont make them flexible!!'. we dropped the keel together one last time, bed it down in epoxy and CSM. when it started to go off we tightened those big bolts with a breaker bar until our muscles burned and then some more. no more movement, no more problems. many years of hard sailing and racing. keel stepped mast and hydraulic rigging pumped up rock hard.

I dont know about wooden boats. but with a plastic one, movement is bad. any thing that moves can 'work'. choose no movement.

again all IMHO and only based on my experiences.

Perhaps I didn't explain it very well. I've only coated the exposed nuts in the bilges to stop them from rusting. The keel itself is presumably bedded in flexible mastic but I've never removed it.