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Go Back   SailNet Community > On Board > Gear & Maintenance > Keel bolt torque values ????
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Thread: Keel bolt torque values ???? Reply to Thread
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Topic Review (Newest First)
10-11-2012 09:12 PM
anerussis
Re: Keel bolt torque values ????

Quote:
Originally Posted by SloopJonB View Post
Yes. Torque specs are merely a best effort substitute for the ideal method of tightening a bolt/nut, which is to measure the stretch of the bolt. Since measuring bolt stretch is difficult to impossible in many cases, torque values which equate closely are used instead.
Yes I am aware of this having been involved in studies on the elongation of rebar and bolts used in the containment areas of nuclear power stations. However we are talking about sailboat keels of say 2000 - 2500 lbs the weight of which is distributed over several bolts. The torque values most likely should be calculated per application and consider other factors such as crushing of fiberglass and other materials used. I am not questioning the tables showing the max torque values of bolts but would like to know the torque numbers the actual boat designers and builders suggest.
10-11-2012 08:57 PM
anerussis
Re: Keel bolt torque values ????

Quote:
Originally Posted by midnightsailor View Post
FWIW:
KEEL BOLT TORQUE SPECS :

Bolt-Diameter.........Foot-Pounds............Nut-Size
0.5".......................80........................0 .75"
0.75"....................250.......................1.12 5"
1.0".....................350........................1. 50"
1.25"....................450.......................1.87 5"

Rick
Yes the same table can be found on the C&C do it yourself web pages. However as I stated earlier I used a 3' breaker bar and torqued as much as I could. I did go to a rental place and they showed me a MONSTER of a torque wrench that could do 350 to 500 Ft Llbs. It's handle was longer then 4' and it was also quite bulky and heavy.There was no way that I could get enough clearance to work this thing in my 26' C&C. Was advised that if I used a 3' breaker bar it would be near impossible to get close to 350 ft lbs and therefore no worry on damaging the bolts. Has anyone actually torqued their 1" keel bolts to 350 ft lbs ? What difference would it make if the bolts were torqued less to between 150 & 200 ft lb??? .I am still concerned that a high torque (350 ft lbs) on an older boat may result in damage such as crushing the fiberglass and worse.
10-11-2012 07:28 PM
SloopJonB
Re: Keel bolt torque values ????

Quote:
Originally Posted by anerussis View Post
Well I did just that - bought a 1 1/2" socket and a 3' breaker bar - was told that no way would I be able to torque past and most likely not even to the 350 ft. lbs spec. of a 1" bolt. My keel has three (3)1" bolts with 1 1/2" nuts - was able to turn each one an additional 1/2 to 3/4 turns. The keel also has two (2) bolts with 1/2" nuts the specs suggest 90 ft. lbs of torque - I have a cheapy torque wrench and to my surprise the nuts of these bolts turned several times before reaching 90 ft. lbs. NOW I'm a bit concerned because just because the specs for these bolts state that they may be torqued to specified values doesn't necessarily mean that for keel applications they should be maxed out - or does it?
Yes. Torque specs are merely a best effort substitute for the ideal method of tightening a bolt/nut, which is to measure the stretch of the bolt. Since measuring bolt stretch is difficult to impossible in many cases, torque values which equate closely are used instead.
10-11-2012 07:22 PM
midnightsailor
Re: Keel bolt torque values ????

FWIW: I just came across the following keel bolt torque specifications on another Sailboat Forum. This was taken it said from DIY magazine 2004-3 :
KEEL BOLT TORQUE SPECS :

Bolt-Diameter.........Foot-Pounds............Nut-Size
0.5".......................80........................0 .75"
0.75"....................250.......................1.12 5"
1.0".....................350........................1. 50"
1.25"....................450.......................1.87 5"

Rick
10-11-2012 05:58 PM
anerussis
Re: Keel bolt torque values ????

Quote:
Originally Posted by Sabreman View Post
One of the routine maintenance chores that I do in spring is to tighten keel bolts. I use a 3/4" socket wrench with a 1 1/2" socket and a pipe extender. Then I torque as much as I can. It's a keel. They're big honkin' bolts. As much torque as I can apply is what I want.

With that said, Sabre recommends 90 ft lbs torque.
Well I did just that - bought a 1 1/2" socket and a 3' breaker bar - was told that no way would I be able to torque past and most likely not even to the 350 ft. lbs spec. of a 1" bolt. My keel has three (3)1" bolts with 1 1/2" nuts - was able to turn each one an additional 1/2 to 3/4 turns. The keel also has two (2) bolts with 1/2" nuts the specs suggest 90 ft. lbs of torque - I have a cheapy torque wrench and to my surprise the nuts of these bolts turned several times before reaching 90 ft. lbs. NOW I'm a bit concerned because just because the specs for these bolts state that they may be torqued to specified values doesn't necessarily mean that for keel applications they should be maxed out - or does it?
10-06-2012 03:41 PM
msmith10
Re: Keel bolt torque values ????

On a 35 year-old boat, everything must be considered suspect.
10-06-2012 03:00 PM
Sabreman
Re: Keel bolt torque values ????

Quote:
I remove the nuts and washers, one at a time, clean out any bad stuff, recaulk, make sure the washer or backing plate is in good shape, then replace the nut and tighten, but not to full torque setting. After doing this with all the nuts, I go back and retorque part way on each nut at a time, like you're doing a cylinder head, until all nuts are at desired torque.
You should only have to do this every several years.
I've not done this on either of my keel boats. I'll have to think about it. I've only ever tightened the bolts using the logic that if the keel joint isn't separating and if it isn't leaking, why open a can of worms? On the other hand, my logic is flawed on several levels because when I've opened seemingly solid covers, dry walls, tiling, etc, etc, I've found stuff in desperate need of repair. Thanks for raising an important consideration.
10-06-2012 01:44 PM
msmith10
Re: Keel bolt torque values ????

If you have 1-1/2" keel nuts, you should have 1" keel bolts. In that case the torque setting is 350 ft lb. You can also get a tool called a torque multiplier to attach to your torque wrench since most torque wrenches won't go up that high. I bought one years ago for only this job. You'll probably also need a deep-well socket. You'll need 3/4" drive to get this kind of torque.
I'd also recommend watching your keel-hull joint. The C&C smile (separation of that joint) is common as the keel nuts loosen up with time, and the fix most guys do is just to fill the joint with caulking or epoxy, neither of which will last long.
If you have some separation, or it's been filled, I'd recommend cleaning out the joint before you tighten the nuts, then torque the nuts, then fill the seam if there's any left. Also be sure to caulk around the bolts before tightening the nuts-- I remove the nuts and washers, one at a time, clean out any bad stuff, recaulk, make sure the washer or backing plate is in good shape, then replace the nut and tighten, but not to full torque setting. After doing this with all the nuts, I go back and retorque part way on each nut at a time, like you're doing a cylinder head, until all nuts are at desired torque.
You should only have to do this every several years.
10-06-2012 12:57 PM
jgeissinger
Re: Keel bolt torque values ????

I am glad SloopJonB made his response. Re-torqueing keel bolts (actually you are torqueing the nuts, not bolts) is a subject that comes up periodically, and almost always with bad advice. He is absolutely correct in that it is not that hard to break perfectly good bolts by over tightening. It should also be noted that torque values are given for clean and lubricated fasteners, which keel bolts and nuts usually are not. Just my two cents.
10-06-2012 11:02 AM
Sabreman
Keel bolt torque values ????

SloopJon- you are correct and I don't do that any longer, just tightening by hand with a regular socket wrench. I should have been more clear in my explanation. Thanks for pointing that out. I should buy a torque wrench, and this may be my impetus.
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