Hi Neil,
Thanks for keeping the discussion alive. It is
good to look at these from various perspectives.
I am glad you recognize that the primary function
of the keelboat set is to keep the keel/hull
joint intact. Many people just look at the keel
weight in water vs on jackstands as the metric
for decided the re-tighten methodology. If the
row of bolts were there to hold onto the lead
keel while the vessel is on beam ends we would
not tolerate them being on centreline now, would we.
So, you have all bolts tightened up to total a
200,000 load holding the keel/hull joint together.
Good.
Floating at the marina you have 6000 lbs of lead
trying to separate that joint. In the boatyard
you have about 4000 lbs hull trying to compress
the joint (6000 - 2000 for jackstand support).
The difference is 10,000 lbs or ~5% of that
200,000 lb loading. You may recall the sheet I
linked to, where it indicates the +/- for
reaching desired torque is >20%... well within
the tolerance of the theoretical benefits between these two positions.
So I will restate that I am not in agreement that
keelboats can only be tightened while ashore.
As a moot point I believe the highest loading on
the keeljoint is not with the boat on her beam
ends, a relatively static position with the keel
well separated from flow. I believe the highest
loading to be ~30 degree heel and pounding to
weather in severe conditions where you have the
dynamic forces of leeway (lateral resistance),
leverage and shock momentum (abrupt elevation
changes due to wave height) all added to joint strain.
I do miss my old (1972) 35 mk-1. Sold her a year
& a half ago to make room in my heart for the
cruising boat project sitting in my yard. The one
bright light of this COVID thing for me is the
amount of epoxy resin & sanding I get to do now. :)
Cheers, Russ
At 02:46 PM 4/25/2020, you wrote:
Keel bolt torque on the hard or in the
water....a classic on Stu's List. Ill 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,
thats 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
lets 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 theyd 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 were lessening the safety factor,
and its 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 Chriss case which started
this discussion, my recommendation was to
tighten the bolts in the water if his keels
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.
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