Pete,
Your ultimate goal is to tighted the nuts enough to get the studs into the
safe stretch zone without causing permanent deformation of the studs, but as
stated previously, this can often cause excessive compression of the
sandwich. In your case the keel load bearing assembly appears more than
adequate. The idea is to spread the bolt load over the largest area of low
density material as possible with a high density plate (stainless). The only
way to know if the plate is adequate is to use antiseize on the threads,
place a dial indicator to monitor the compression of the sandwich and apply
torque with a torque wrench. There will be some compression, it is
unavoidable. You want to see a linear increase in torque relative to the
rotation of the nut all the way to the stretch zone. If the torque increase
curve starts to flatten with nut rotation and you still observe increasing
compression on the sandwich, your stainless load spreading plate is too
small. Do not over compress the sandwich. Build a larger load bearing plate
and try again. Please remember that it is NOT OK to leave the studs under
tightened, because the keel will work, causing even more looseness, leaks
and potential catastrophic failure. You really need to get this right.
Steve

Pete wrote in message ...
On Thu, 15 Jan 2009 07:30:19 +0100, "Steve Lusardi"
wrote:

Be very careful here because you have not stated the material under bolt
compression. Depending on whether the material is wood, fiberglass, steel
or
aluminum and the washer diameter or cap size used to distribute the
compression load, the answer could be quite different. The torque values
or
stretch limits stated by others reflect the maximum elongation force
aacceptable by the bolt material without permanent bolt deformation and do
not consider potential crush limitations of the compression sandwich,
which
could be much less.
Steve




Thanks Steve,
the hulll at that point is 22mm mahogany strip planking with two
heavy layers of fibreglass epoxied on each side;, bonded to that
are 100mm oak beams to take the keel bolts, also fibregalssed in with
epoxy. Over most , but not all, of these beams is a 60mm thick oak
plate spreading the load from the mast over the first five floorbeams.
Under the hull is an oak packer varying in thickness from about 20mm
to about 40mm to take up the curve of the hull. So for most of the
bolts, they are all going through around 200mm of oak and mahogany
plus around 10mm of fibreglass and epoxy. Between the nuts and the oak
are 8mm thick stainless plates about 60mm x 150mm wide, linking each
pair of studs.

I know that the oak I chose for this job is the hardest I had and
therefore I don't think it will compress much. (Potentially famous
last words here)


Hope that helps, and thanks for all the replies, I'm pleased to get so
much advice.

Pete
wrote in message
. ..
Hi,
can anyone advise me on the roughly correct torque setting for
tightening the nuts on my keelbolts?
The studs are 20mm (thats about 13/16") in 316L plus one at
12mm(about 1/2")

The keel is 2 tonnes of lead if that makes any difference.

I'd hate at this stage (five long and bloody years) to over or
undertighten the bolts.

Thanks
Pete