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Old 20-01-2010, 19:13   #16
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Not enough torque is just as bad as too much. You want no movement there at all so that means the bolt must be tensioned (and dimensioned) just right. If you pull the stud out of the keel when torquing the bolt you should be happy it happens now and not under way. Using less torque because the studs aren't right is not a good strategy.

About bedding compound: a liquid one will just be pressed out from between the washer plate and the fiberglass. But you use a liquid one around the threads where the stud comes out of the fiberglass. The neoprene gasket goes on top of that, followed by the washer plate and, ideally nylock nuts. If you don't use nylock nuts, you should use a thread-locker or put a 2nd nut on top of the first, tightening the 2nd one while holding the 1st one with a wrench.
You must use a lubricant because the stainless nut will gall on the stainless stud otherwise. I normally use Lanokote or better yet, TefGel.

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Old 20-01-2010, 21:59   #17
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Sorry Nick, but I think you missed my points.

Nobody but you said loose, I said don’t over torque. You can break almost anything with a big enough wrench. That doesn’t mean it originally had a design flaw. 175 lb/ft is not loose!
Some other points: I have never seen ¾ bolts use aircraft nuts when used as keel bolts. Can you even get them? Not needed. Not needed to double nut either. When torqued properly a lock washer is designed to do the trick. I would worry less about thread locker than I would about thread seizure, thus the waterproof grease. Don’t think I would use a locktite compound under water and most of the heads on the keel bolts are in the bottom of the bilge.

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Old 21-01-2010, 00:59   #18
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There are a lot of very smart people on this forum.
I have many years of fastener design and technology experience in a variety of materials and conditions, and all of the information is in the posts here have covered the torque vs materials interface vs lubrication vs material strength issues. Thread strength is most important for a lubricated bolt. and in most lubricated bolts, the threads will fail before the shaft. Unfortunately this is not the same when trying to remove old corroded bolts which usually fail then the shaft's torque strength is exceeded by the friction (from corrosion) between the nut and bolt. Also, thread pitch (TPI) will have a huge impact on torque.

so, i have a question

why don't we use CP titanium bolts and nuts for keel bolts? it has similar strength to 316 SS and is a lot more corrosion resistant in salt water. Granted, it's modulus is only 66% of SS but so is it's mass so a larger fastener will equalize strength without getting heavier.

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Old 21-01-2010, 07:53   #19
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Originally Posted by pitman View Post
... Why don't we use CP titanium bolts and nuts for keel bolts? it has similar strength to 316 SS and is a lot more corrosion resistant in salt water. Granted, it's modulus is only 66% of SS but so is it's mass so a larger fastener will equalize strength without getting heavier.
halyards clear
Thanks for the information, and the excellent question (which I’ll assume is rhetorical and endorse).
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Old 21-01-2010, 09:11   #20
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Never Seen

I have never seen a torque figure posted for anything other than clean and lightly lubricated. Giving a torque reading for a dirty or dry bolt would be at the very best a guessing thing, as to how dirty, how rusty, how dry. No way could you place any confidence in those numbers. My Seidelman 37 has a fairly similar keel configuration, and weight. It also has 11 3/4" stainless bolts, with stainless plates under them. Specified torque is 120 ft. lbs. I think 120 to 130 is about right for these. 250 ft. lbs would be stretching and more than likely weakening the bolts.
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Old 21-01-2010, 09:23   #21
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There is no reason to try to torque a bolt that does not have clean threads! No amount of analyzing the "pre-torque" is valid as it changes as the threads pass each other. Clean up all threads before torqueing!

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Old 21-01-2010, 10:02   #22
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I have never seen a torque figure posted for anything other than clean and lightly lubricated ...
"Lightly lubricated" with what?

It doesn’t really matter whether Torque Specifications are “usually” for wet (lubricated) or dry fastenings. What matters is what the specification, to which you are referring, assumes. If it’s a “wet” torque, it should also specify the particular lubricant (they have differing coefficients of friction).

I believe that the FAA (for instance) states, "all torque figures, unless otherwise stated, are given with threads clean and dry*."

* Dry Torque usually assumes a coefficient of friction of 0.20, and a dry, unlubricated fastener.

Dry Torque Spec’s ➭ Steel Bolt Torque Specifications Table - Engineer's Handbook
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Old 21-01-2010, 12:01   #23
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I have a 42' boat with an 8300 lb external lead keel. Factory torque specs for the 1" 316 SS keel bolts are 235 ft/lbs with the boat resting on the keel. If it matters, there are 8 keel bolts. I would expect 3/4" 316 SS bolts to be torqued to a slightly lower value.
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Old 21-01-2010, 12:16   #24
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Here’s the keel-bolt torque spec’s from C&C. Note, they don’t indicate wet or dry. I would assume dry.
Keel Bolt Torques

Here they are from Pearson.
http://www.tech258.com/jon/technical...rque.Specs.rtf

Also remember, most torque spec’s will assume steel on steel on steel, materials that don’t experience much creep.
Boat hulls may be more like electrical wire connections, which do suffer from creep & crush, and must be re-torqued after “some” time in service.
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Old 21-01-2010, 13:06   #25
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Okay, y'all made me get my tables...

Every bolt material has a different tensile strength resulting in a different advised clamping force and thus torque. Let me give some info for often used materials on keel bolts:

Silicone bronze: clamping force 70,000 lbf/in2 ; standard dry torque for 3/4" course thread: 118.0 ft-lbf

18-8 Stainless steel: clamping force 75,000 lbf/in2 ; standard dry torque for 3/4" course thread: 127.5 ft-lbf

316 Stainless steel: clamping force 75,000 lbf/in2 ; standard dry torque for 3/4" course thread: 131.8 ft-lbf

Monel (the champion material for keel bolts): clamping force 82,000 lbf/in2 ; standard dry torque for 3/4" course thread: 152.7 ft-lbf

So, all this is for 3/4" COURSE THREADED AND WITH CLEAN DRY THREADS.

Now the correction factors... for:

SAE20 motor-oil, copper-graphite anti-seize, WD40: 0.80
SAE40 motor-oil, zinc-anti-seize: 0.75
SAE30 motor-oil, molybdenum grease, graphite: 0.70
never-seize and other specialized products: 0.45 (!!!!!!!!!!)

So, the 316 stainless bolt with never-seize or tef-gel should be torqued to 131.8 x 0.45 = 60 foot-pounds. If you use SAE40 engine oil: 131.8 x 0.75 = 100 foot-pounds. Big differences.

All this info is in "Handyman in-your-pocket", ISBN 1-885071-29-9 which some hardware stores give away for free.

Aircraft nuts: I don't know what they are, but if you mean Nylok with the nylon inserts then yes of course they are (in stainless steel anyway) available in every size we have aboard, incl. 1.25" diameter. The reason for not using lock-washers is that they should not be combined with other washers.
To compensate for nylok you have to add the required torque to the torque needed to turn it just before it goes tight against the washer. This is much easier than it sounds when using just the torque wrench to find that start value.

I would not use a regular thread locker either because I have very bad access to my keel bolts. I have Nylok nuts. But there are numerous ways to lock the nut, ask any mechanic.

When tight and re-torqued after a couple of days, I would spray it with that heavy duty corrosion block at least 5 times, waiting 10 minutes for drying each time.

ciao!
Nick.
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Old 21-01-2010, 14:32   #26
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Nick: Does you magic little book account for the hanging weight of the keel? As to not using conventional lock washers in combination with any other washer; please tell me more as this is new to me!

Anyway, I'm glad you see the point of not not twisting bolts off to check their suitability. I'll still stand by my 170 lb/ft torque on clean threads, no nylon insert nuts(aircraft nuts to me and a few million other people).

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Old 21-01-2010, 15:06   #27
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The weight of the keel is used as one parameter (draft and weight distribution and hull displacements are others) for determining the number of keel bolts, the bolt pattern and their required tensile strength. As bronze, stainless steel or monel can be chosen, the tensile strength is dependent on that choice and thus the diameter. The torque is not a factor because bolts must always be torqued to that percentage of minimum tensile strength, where 70% is a regular choice. You do NOT weaken a bolt by tensioning it; you weaken it by allowing movement (fatigue). When you don't tension it enough and the bolt comes into compression, it looses it's clamping force. The numbers in those tables are chosen so that in compression load, there still is enough clamping force to hold the clamped parts in place. Just like you do not want your leeward shrouds go slack during sailing, you do not want the leeward keel bolts to go slack either. Only pre-tensioning them to the right value helps. For the windward bolts: because they are tensioned, they won't stretch extra which limits the movement of the keel which limits the load on the leeward bolts. If they would stretch too much, the leeward bolts might even get bend and fatigue failure is quick and sudden.

The weight of the keel is not very important because that static load is insignificant compared to loads during sailing. They even take hitting the bottom with the keel into consideration. Dashew wrote that for sailing alone, he could have used just 5200 to stick the keel under the Sundeers.

These tables are the result of very smart people doing many calculations followed up by a hundred years of experience so it's very wise to use that data instead of what sailors dream up. Easy decision I would think.

cheers,
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Old 21-01-2010, 15:32   #28
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Lock washer: Imagine a bolt head (or nut, doesn't matter) that fastens a flange. The lock washer is between the bolt head and the flange. It prevents loosening.

Now imagine a normal washer under the lock washer. The lock washer prevents the bolt turning relative to the normal washer, but nothing prevents the bolt loosening with both lock washer and regular washer turning with it.

In the case of the keel bolts, you can use lock washers if you can be 100% sure that the washer plates will not turn. For most boats (incl. Jedi) they already turned a bit while torquing the bolts... and it is just as easy for them to turn back the other way with the lock washer. This is why another mechanism for preventing the nut from loosening must be used. Many mechanics will use a hammer and center punch to punch a dimple in the thread just above the nut. If you have good access for a Dremel tool to grind it away when needed it's probably the best way.

But... I don't understand why you don't want to use Nylok nuts?

Why would anyone want to twist bolts off to test their suitability? I think the nautical architects can calculate well enough to believe they are okay. If my keel would come off for maintenance, I would cut some lead away around the stud where it exits the lead to do a visual check of the bolt there. Mix the lead-flakes with epoxy and colloidal silica and put it back in.

ciao!
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Old 21-01-2010, 22:08   #29
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Nick,
Impressive data at best! You have been doing your reading have you not? I have little to disagree with much of what you wrote but will take issue on a few points: I learned this long ago when I was but a wee student: For any application there is a minimum clamping force required to prevent joint failure.

That said there is no need to torque every joint to 70% of the maximum bolt tension. In the case of keel bolts we have a couple of additional considerations; the other end of the bolt is held by lead, one of the softest of metals and the material we are compressing in the middle of this mess is plastic so the size of the flat washer is part of the design criteria.

The weight of the keel is a factor, a big factor, though this part has been designed into the boat and all we can do is work around the design considerations. I am using figures from the top of my head but looking at this from a practical point rather that a theoretical one, let’s first see what we are holding up with the boat. I guess an external lead keel on a 49 footer might easily weigh 10,000 lbs. Thirteen bolts spread the weight to about 770 lbs. of keel hanging off of each bolt. Absolutely insignificant to a ¾ bolt of any material.

At an angle of heel approaching 45 degrees things change a lot. Now the leveraged weight can not be calculated because we don’t know the shape of the keel in any dimension, including the most important which is the distance between the two rows of bolts. I’m not going to do the math here but if we simply factor X10 which I think is way outside we then get a pull on the upper set of bolts of 7700 lbs. each and a similar compressional force on the plastic sandwiched between the lower set of bolts and the lead keel. This number must be in balance with the strength of the bolt and the compressional stability of the plastic.

Now a ¾ 18-8 bolt torqued (wet threads and all that) to 180 lb/ft gives a bolt tension of around 14000-psi, far higher than the 7700 lbs by a factor of 2 and therefore I think pretty close. If you want to do some research look up this: T = .2df (t=torque, f=bolt tension and d=bolt diameter in inches.)

Your little book is wrong I think, when it comes to torque. Again, off the top of my head, but the nominal torque on a ½ grade 8 bolt is about 100-lbs/ft wet. For a ¾ bolt with a thread area of 225% of the half incher, I think the torque for the ¾ bolt is around 200 lb/ft.

We have reversed roles here to a certain extent. If you paid attention, I initially said that to over-torque was bad and not under torque. There are a couple of reasons for this logic: the bolts have been pre-stretched and we do not know the methodology for the anchor in the lead. Now using your handy little book you would under-torque.
I like using books (can actually read some of the more complex ones) but I like a good infusion of common sense to keep everything in line. Torque is one of the best examples of this. Some people have a good enough feel for torque that they can get most stuff just right without issue and other people will either twist a bolt off or leave it too loose.

I have used a big rattle wrench enough to know when it is torqueing a bolt about right, but that comes from practice. If you don’t have a feel then you use the measuring stick. Actually rotational angle is a far better method for torqueing bolts but that is outside of the purview of this forum discussion.

A simple way to test my theory or any tightening spec would be to attempt to re-torque the bolts on the compressed side of the keel when at a good angle of heel. Not at all unlike your testing of shrouds. If the torque on the compressed bolts remains constant then adequate torque is applied.

This has been fun but I don’t wish to go digging around in the old engineering texts to prove my point. I think our fellow sailor should be well on his way to getting things right.

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Old 22-01-2010, 08:19   #30
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Interesting thread.

Quote:
Originally Posted by um saudade View Post
A couple of things could occur if you over torque the bolts: You could start to pull the bolt out of the keel and you ain’t ever getting it back in. If you fatigue the bolts they will break when stressed, such as a grounding. If you over torque you can stress fracture the plastic and it will fail over time.

Be gentle. If it doesn’t leak but snags down nicely, leave it at that. I like the idea of something with a little crush under the washer but if it compresses it will need periodic re-torqueing until it is stable.
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I tend to agree with the above, breaking or pulling a bolt would be counterproductive. It can be said that so fare the 13 bolts have been adequate for the job. What is unknown is the torque used originally to tighten the bolts. Un tightening a bolt with a torque wrench is a way of finding out what may have been the original torque.

In the original post it is assumed that the “bolted connection” between the hull and the keel is done using bolts but the bolt grade is not specified and I suppose is unknown. If the boat as been build in Oz then I would assume that the bolts may heave been manufactured out of SS round bar and accordingly an OZ stainless steel grade chart should be used. The bolts may also have been made out of threaded rod.
In any case the bolts should not be overloaded when the boat is hard pressed at any angle of heel. It is possible to calculate the forces involved in this “bolted connection”. For a start “Steel Designers’ Handbook, 5th edition B.Gorenc & R.Tinyou, ISBN 0 86840 248 6” can help understand any bolted connection which can be found in a boat.

I dislike lock washer of the spring type they have a tendency to break and fall apart living a large gap also the correct use of a lock nut is to troublesome. If necessary as a keel bolt nut lock, I would use a Nylock just above the main load-bearing nut and just tight. for less important connection I just “blob” the thread above the nut with neutral cure silicon, other time for large nut, I will fit a grub screw on one of the pan of the nut. So many possibilities.
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