Keel bolt torque on the hard or in the water....a classic on Stu's
List. I’ll jump in….
Torquing keel bolts in the water is equivalent to tightening the head
bolts on an engine while it's running, probably not a good idea. Bolted
joints are intended to be initially preloaded by tightening the nut and
bolt before the load is applied.
What has to be considered for keel bolts first is that the design
condition for the hull/keel joint is when the boat is on her beam ends,
that’s the maximum load that can be applied, and in this condition the
purpose of the keel bolts is to keep the hull/keel interface in
compression. If the compression goes to zero – let’s say just to
illustrate, a gap opens between hull and keel – the bolts would now be
trying to support the keel under bending load, and they’d snap in a
heartbeat. ( A quick calculation for my 35-1 keel with 6 one-inch bolts
shows about 200,000 psi stress in that condition). So the point of
torquing the bolts is to create enough pre-compression in the joint, and
if you torque while under load, i.e., in the water, you are giving up
some of that margin. Will it cause the keel to fall off? No, but we’re
lessening the safety factor, and it’s all about having some margin.
Thus the best way to tighten keel bolts is on the hard to get the most
preload.
Having said that, in Chris’s case which started this discussion, my
recommendation was to tighten the bolts in the water if his keel’s
loose, as I said above the last thing you want is to lose compression,
but to go to a little lower torque than in the specs. Then torque to
full specs when on the jackstands later.
Neil Gallagher
Weatherly 35-1
Glen Cove, NY
On 4/24/2020 1:23 PM, Russ & Melody via CnC-List wrote:
Hi Chris & Josh,
I am not in agreement that keel bolts can only be tightened while the
boat is ashore.
While that is a convenient activity during the annual haulout period
that Eastern boats get, it is not entirely practical for us on the
West Coast or the lads down south. We might only haul every two or
three years.
The technical sheet in the link shows the theoretical load on a 1"
bolt (torque to 350 ft-lbs spec) is ~12,000 lbs. This is more than the
weight of the keel such that it does not matter whether the keel is
supported on the ground or hanging in the water, the joint is held
firmly together by one keelbolt. The rest are not required to do
anything at this time.
https://www.hobson.com.au/files/technical/utd-gd-torque-tension.pdf
I suggest that the proper procedure for tightening keelboats be
observed whether the boat is in water or in the yard.
For a 1" keelboat to 350 ft-lbs torque:
start with centre nut and take it to 250 ft-lbs, repeat for other
nuts alternating for and aft sequence
remove centre nut and lubricate, retorque to 300 ft-lbs, repeat as
for other nuts as above
retorque centre nut to 350 ft-lbs, repeat as for other nuts as above
Then you can a have a beer Chris and reflect on how fortunate you are
to be sailing B.C South Coast. Anything 100 miles to the east of you
is beyond Hope.
:) <VBG>
Cheers, Russ
East side o' Vancouver Island
At 08:15 AM 4/24/2020, you wrote:
Chris,
The prevailing wisdom of this list suggests that the keel bolts only
be torqued while the boat is resting on its keel, generally about 60%
of it's weight depending on the design. In this way you are not
turning the nuts against the weight of the keel or even trying to
compress the bedding material. IMO, it is likely that you will find
more movement in the nuts when you retorque on dry land.
I am not familiar with the design of your particular boat but some
boats have keel bolts which are entirely inaccessible with the mast
in place. Make sure there isn't one (or two) hiding somewhere.
Josh MuckleyÂ
S/V Sea HawkÂ
1989 C&C 37+
Solomons, MD
On Thu, Apr 23, 2020, 20:59 Chris Bennett via CnC-List
<cnc-list@cnc-list.com <mailto:cnc-list@cnc-list.com>> wrote:
Status update: I ended up torquing the keel bolts. They were not
incredibly loose but all of them needed tightening, two by a turn
or more and the other two by less than a turn. I will know if
this removed the keel movement when the boat is next hauled out,
although I am also thinking of diving on her to see if I can
detect any wiggle that way (I live in BC and the water is pretty
cold but manageable for a few minutes with a wet suit - I hope!).
I believe that a very small looseness in a narrow keel root would
result in a fairly noticeable movement at the tip of a 3 foot
keel - even 1/8 inch of movement over 2 inches width would
translate into a couple of inches at the tip, if I have that
right. So hopefully this was the issue!
I took Drifter for a sail today after rebuilding the mast step
and did not notice any flexing or movement in the floors or hull
(made pencil marks on the floors and adjacent hull skin and
checked on different tacks). I also checked the tabbing under
the settees on one side and found it intact, so suspect that the
surveyor may have jumped to conclusions when he said the hull had
been compromised and that was what was causing the keel movement.
Â
 Thanks again to everyone for their suggestions.
ChrisÂ
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