Oceanis 430 (1988) keel bolt details

[Tetepare]

Well they have to pass through some thickness of fiberglass.

[boatpoker]

Originally Posted by Tetepare

Well they have to pass through some thickness of fiberglass.

Yup ! and thats normally the thickest part of the boat plus the backing washer/plate. 3 1/2" sound a bit short to me.

[Jim Cate]

Originally Posted by boatpoker

Yup ! and thats normally the thickest part of the boat plus the backing washer/plate. 3 1/2" sound a bit short to me.

Or... the hull sounds a bit thin to me!

Jim

[boatpoker]

Originally Posted by Jim Cate

Or... the hull sounds a bit thin to me!

Jim

That could be too. I once found a Lagoon hull that was 3mm (not a misprint) thick in one area.

Other photo is a Beneteau keel bolt with a 1/4" backing plate ... doesn't leave much room for thread engagement.

[Laureat]

Yes the Beneteau keel is iron, and the bolt treads are 3 1/2 inches, plus the head but you cannot insert a plate it is just a round washer.

[Laureat]

The hull thin! I bet the newer sailboat have a thinner hull than my Beneteau 1987 which is 3/4 thick, I am wondering if you ever did remove the keel bolt of your sailboat ever.

[boatpoker]

Originally Posted by Laureat

Yes the Beneteau keel is iron, and the bolt treads are 3 1/2 inches, plus the head but you cannot insert a plate it is just a round washer.

How many more photos of square 1/4" Beneteau backing plates would you like me to post (and one where the backing plate was forgetten )

[Tetepare]

Originally Posted by Laureat

The hull thin! I bet the newer sailboat have a thinner hull than my Beneteau 1987 which is 3/4 thick, I am wondering if you ever did remove the keel bolt of your sailboat ever.

I have never. I’m in fresh water.

This is all intriguing, the b430 is not a chinsy boat, I’d think there’s a good amount of fiberglass there. I looked at a bunch of b430s, as I love the design, but don’t remember if the bolts had washers or plates. I still think 3.5” is short. Prove me wrong, it’s bugging me.

[sandy stone]

I don't know if I can prove you wrong, but maybe convince you?

The people who manufacture threaded fasteners have gone to some trouble to determine what is needed for a secure, long-lived joint. Their intent is that a bolt will fail in tension before the threads strip out. After some decades of testing and experience, they determined that with steel, a thread engagement depth of 1 to 1-1/2 times the diameter of the bolt is sufficient. Whether or not that seems right to you, scientific testing proves it. Note that the depth of a nut is no more than about the same as the diameter of a bolt.

Now, Laureat above said her husband used a 27mm socket to remove his keelbolts. I believe that indicates an M18 thread, so 1 inch of thread engagement would be plenty. Let's say the keelbolts pass through the hull plus the flange of a structural grid, and a washer. Surely that cannot add up to more than 2 inches? Note also that the yield strength of a single m18 grade 8.8 bolt is over 25000 lbs, so there is quite a safety margin there.

This thread seems to illustrate that what many of us think about suitable fastener dimensions does not agree with a detailed engineering analysis, the kind that naval architects perform. Again, think about the way the keel is bolted on in, say, a Swan. The J-bolts are cast into the keel since lead is too soft for threaded connections, so we can consider them to be essentially an intrinsic part of the keel. The actual fastening load falls on the keel nuts, which are nowhere near the several inches of thread engagement that other posters have dismissed as inadequate. The inconsistency is obvious.

[goboatingnow]

The actual fastening load falls on the keel nuts, which are nowhere near the several inches of thread engagement that other posters have dismissed as inadequate. The inconsistency is obvious

Don’t start bringing facts into a CF thread on keelboats. We need to maintain the illusion that these keels are failing all over the world and only a long keel made by a long bust builder who handcrafted three boats knows what he’s doing

The armchair sailors know best after all , they have sailed the world from that comfortable perspective

[GordMay]

Originally Posted by sandy stone

I don't know if I can prove you wrong, but maybe convince you?
... The inconsistency is obvious.

Against my intuitive, gut feeling, you convinced me, with a logical, fact-based explanation.
Thanks.

[Fore and Aft]

Sandy Stone thanks for that information, I never realised how small a keel bolt you could get away with. I didn't even think about the load being on the nuts either. I take it there are some lateral load calculations when the yacht is heeled?
I love how science trumps what most people would consider inadequate sized bolts. I must admit if Beneteau sent me a shoebox full of keel bolts I would be double checking that it was right.
Cheers

[Jim Cate]

Being serious for a moment... my recollection of keel failures on Bennies et al have been failures of the hull structure rather than bolt failure. Is that a correct memory? If so, seems that worrying about the bolts is unnecessary.

Anyone with data?

Jim

[Fore and Aft]

Jim, I think you are right. I have certainly seen a Benny or a Jenny (I forget which) that had the keel torn right off and the bolts were still attached to the keel. Another thing that took me a long time to get used to when looking in the bilge of a production yacht is the keel bolts being in the bilge and the keel floors are next to the bolts.
I always remembered the keel bolts used to go through the keel floors on the custom boats we built. To me that just makes sense as it helps spread the load. Where are your keel bolts Jim? I can't remember ton the last Sayer I surveyed.
Cheers

[Jim Cate]

Where are your keel bolts Jim? I can't remember ton the last Sayer I surveyed.

There is a massive timber structure, roughly 300wide by 300 deep, a double vertical H if you wish, with the vertical members about 200 apart, epoxied and glassed. This member runs from aft of the (centrally located) engine forward past the mast step, and the keel bolts run up through the center and through large washers to nuts on the top. I'm not sure how this member is mated with the hull, but rest assured that it is solid!

The keel which is a hollow steel structure with ~4 tonnes of lead in the bottom has an inward turning flange at its top and the bolts originate there. Not sure how they are fastened... never thought to ask Gary how that was accomplished. The whole thing is bedded in epoxy bog and has never leaked a drop.

The above is obviously a labour intensive construction, but after 140,000 miles and their attendant groundings, slippings and general wear and tear, no "smile", no leaks and no worries about it falling off.

Jim