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  Topic Review (Newest First)
03-20-2015 01:39 PM
casey1999
Re: Keel bolt torque values ????

Here is an excellent thread about keel bolts:

http://www.sailnet.com/forums/gear-m...-nuisance.html

Here is my opinion on the subject:
Why should a keel bolt ever need to be re-torqued? The only reasons I can think of are:

1. The keel/hull joint is compressing so you need to make up for the compression by pulling the keel up (via tightening the keel bolts). Now if this joint is compressing- that to me says this is a design or build flaw with the boat. If designed and built right, the joint should not compress.

2. The keel bolts are stretching. The only reason I can think of that a keel bolt would stretch is that it is overstressed in use (meaning the boat designer/builder did not install enough keel bolts, or the diameter was too small. The other reason may be due to corrosion under the nut/washer, the diameter of the keel bolt has been reduced, thereby increasing stress (psi) and stretching the bolt.

Now in my opinion re-torqueing the bolt is not going to solve anything. It will not correct the problem.

So you constantly re-torque your auto wheel lugs? When was the last time you opened up your engine to re-torque the head bolts? When was the last time all the bolts in the empire state building were re-torqued? If a boat is designed and built right, the keel bolts should never need re-torqueing. Replacing due to corrosion from water in bilge might be a reason to replace.

Here is another thought on re-torqueing keel bolts. What if your bolts are perfectly fine, no hull to keel cracking, a dry bilge and no leaking. Say though, the stainless keel bolt to nut connection is gulled and seized. What is the point of re-torqueing? What might happen is that you strip the nut threads of what was once a perfectly good nut/bolt connection- just because the bolt/nut is gulled and seized does not mean it is not a strong connection.

How many bolts with rusted threads have you broken trying to remove? Now was not that bolt with rusty threads working perfectly fine prior to your trying to remove it? Would there be any point for me to go through my 1991 rusty LandCruiser and re-torque all the rusty threaded bolts to factory spec. I think not, I think she is good at least 200k miles more as is. Attached is pic of my old 1978 Landcruiser- never re-torqued them bolts.
03-20-2015 12:51 PM
RichH
Re: Keel bolt torque values ????

A LOT of potentially powerful misinformation is being given on this thread.

The advice of following the manufacturers and designers torque loading is a damn good one.
If that mfg. specification info isnt any longer available, then seek out a specific brand/model owners groups for what 'has historically worked', etc.
Failing all that above and if youre intentions are being precise, spend the $ and have a licensed structural engineer to calculate the stress to be applied to those bolts.

Only a damn fool will apply MAXIMUM torque to a fastener using 'cookbook' torque values.
If you set tension to the maximum, there will/may be no 'reserve' strength capacity for dynamic loading (boat heeled over onto its ear, etc.; falling off a BIG wave while heeled), you may exceed the 'dynamic' load capacity of the system including applied 'safety factors' that the designer usually has/ did incorporated into the design: 'customarily' @ SF=2 for 'coastal' design and SF=3 for 'blue water' ... and many designers go 'higher' for such a crit. stress area.

The problem is that when most of these, especially older boats, were designed no one clearly understood the effect of fatigue (endurance limit) of 300 series stainless, and certainly not the affects of 'crevice corrosion' - all potential adverse effects that can weaken the fasteners, the sub-structure and its *function* and component structural integrity.

Rx: Dont blindly 'guess' and dont 'max out' the torque .... unless you by history or spec. manual, clearly KNOW that it should be 'otherwise'.

In probably most sail boat design, how the designer views a keel vs. structural loads is to theoretically heel the boat to about 45 over, calculate the loads required to keep the keel attached and then apply those 'safety factors' on top of the calculated loads - to take care of adverse 'dynamic' and unforseen events happening to that 'joint/bolts/etc.'
The keel weight/mass adds load, the angle of heel adds 'complicated' loads (especially a keel which is a 'cantilever' - a difficult structure to analyze for dynamic service), falling off a wave while heeled ..... all adds load to the keel bolts. So if one 'strains-up' those bolts to maximum torque, you 'may' be well beyond the service stress capacity (including additive fatigue because those bolts are stressed well above their fatigue endurance limit) of those bolts during those future 'dynamic' and 'unforeseen' events.

If your boat is so old that such 'designers' torque requirements are not available, I would suggest to find that data from a 'very similar' geometrical / shape (keel shape/ weight/ depth and bolting pattern) design and apply those recommendations (from knowledgeable owners and historical performance data/info, etc.) to your boat.
As I stated if the exact mfg./design values are unavailable - then engineer/designer calcs., then owners group, etc.

Dont 'blindly' torque those bolts to their 'maximum', unless you have 'clear and unimpeachable' information that such has some historical / 'scantling' evidence that this is correct.

hope this helps.
03-20-2015 06:32 AM
albrazzi
Re: Keel bolt torque values ????

Thanks for your thoughts. My theory was the "cell" is formed by the two bolts (studs) resting in lead and tied together at the washer (backing plate) and the resistance of a loose nut or even a tight one on the contact area between the nut and the plate. I deal with anodes protecting underground pipe lines for a living so I do understand the sacrificial properties of an anode. I saw a comment somewhere in the forums from someone who didn't like tying studs together on keel bolts in this fashion somewhere on this forum but he didn't say why and I cant find it now to ask directly.
03-20-2015 02:06 AM
casey1999
Re: Keel bolt torque values ????

I don't think the galvanic corrosion would be an issue either between 304 and 316 SS or stainless and lead. Most keel bolt issues are with stress corrosion where the stainless is surrounded by salt water that has liittle or no oxygen, then the stainless corrodes. On a keel bolt this usually happens below the washer, since above the washer the sea water can still have enough dissolved oxygen to allow the stainless to form its thin protective layer that resists corrosion. So by just removing the nut and washer, you may still not see the stress corrosion that would be lurking down the next inch or so in the bolt as you head towards the keel. The only way to know for sure is to pull a keel bolt and inspect. That can be a big job, but one some folks decide to do. Also, for galvanic corrosion to happen between the lead keel a Ss keel bolts, a cell would need to form. The bilge would protect between the bolts and any exposed lead on the outside of keel, and normally the keel bolts are sealed well enough that salt water would not exist all the way from the keel bolt nut to the end of the keel bolt in the lead keel. Even if this case existed, the lead would see the loss of material (corrosion) not the Ss bolt.
03-19-2015 10:17 PM
albrazzi
Re: Keel bolt torque values ????

Quote:
Originally Posted by casey1999 View Post
I see no problem with a washer spanning two bolts- sounds like this type of washer has more surface area than a standard and therefore perform better than a standard washer- that is spreading the load of the keel bolt over the hull. 316 is more corrosion resistant than 304 so always best to use 316 in salt water environment. But seeing J boats are using 304 for the washer only, and the washer can be easily replaced- use of 304 should not be a problem.

On my 37 year old boat the keel bolts/nuts have never been touched. I do not have any keel/hull cracks and the bolts look good. When surveyed 5 years ago the surveyor tapped the keel bolts with a hammer and said they were fine based on the clear ring. I would be hesitant to start messing with the keel nuts as the nut could be seized on the keel bolt, and if I were to get the nut off, I might not be able to seal the nut as good as it is now. Now the J boats may be built less stiff and as the manufacturer recommends, maybe it is a good idea to re-torque once a year.

As far as nut/bolt torque, I never go as high as the bolt chart shows. Even when working on my car the specs call out for much higher torques on some items than I feel comfortable with. I have broken or stripped a lot of bolts when torqueing well below what a bolt torque chart indicates is acceptable. the J boat chart I provide looks reasonable- notice the torque values are well below allowable (less than 1/2 of the allowable torque value).
Sorry to ask the same question twice but I understand the benefits of a larger bearing surface for a flat washer backing plate etc.
I was thinking more along the lines of galvanic action with two SS studs in a lead keel tied together creating a potential either once loosened by service or with a salt bath and some dissimilar metals (alloy grades anyway) after some interesting corrosion on some recently replaced keel nuts.
Don't mean to hijack but the torque values question cant possibly have any more answers out there.
03-19-2015 06:03 PM
casey1999
Re: Keel bolt torque values ????

Another good article:

Located within arctile:
"Bolt suppliers sometimes have customers say that their bolts are no good because they have started breaking while being installed. Thorough investigation commonly reveals that the customer has started lubricating the bolts to make assembly easier, but maintained to same torque as was used when the were plain finished"

Proper Bolt Torque - by Zero Fasteners

What is the Proper Torque to Use on a Given Bolt
by Joe Greenslade

"What torque should I use to tighten my bolts?" is a question suppliers of bolts are frequently asked by end user customers. Many times I have been asked if a chart is published on the recommended tightening torque for various bolt grades and sizes. I do not know of any. This article provides such a chart for "Initial Target Tightening Torque. It See Figure 1. The formula for generating these values is explained below.

The widely recognized engineering formula, T= K x D x P (to be explained later in this article), was used to provide the chart's values, but it must be understood that every bolted joint is unique and the optimum tightening torque should be determined for each application by careful experimentation. A properly tightened bolt is one that is stretched such that it acts like a very ridged spring pulling mating surfaces together. The rotation of a bolt (torque) at some point causes it to stretch (tension). Several factors affect how much tension occurs when a given amount of tightening torque is applied. The first factor is the bolt's diameter. It takes more force to tighten a 3/4-10 bolt than to tighten a 318-16 bolt because it is larger in diameter. The second factor is the bolt's grade. It takes more force to stretch an SAE Grade 8 bolt than it does to stretch an SAE Grade 5 bolt because of the greater material strength. The third factor is the coefficient of friction, frequently referred to as the "nut factor." The value of this factor indicates that harder, smoother, and/or slicker bolting surfaces, such as threads and bearing surfaces, require less rotational force (torque) to stretch (tension) a bolt than do softer, rougher, and stickier surfaces. The basic formula T = K x D x P stated earlier takes these factors into account and provides users with a starting point for establishing an initial target tightening torque.

• T Target tighten torque (the result of this formula is in inch pounds, dividing by 12 yields foot pounds
• K Coefficient of friction (nut factor), always an estimation in this formula
• D Bolts nominal diameter in inches
• P Bolt's desired tensile load in pounds (generally 75% of yield strength)

The reason all applications should be evaluated to determine the optimum tightening torque is that the K factor in this formula is always an estimate. The most commonly used bolting K factors arc 0.20 for plain finished bolts, 0.22 for zinc plated bolts, and 0.10 for waxed or highly lubricated bolts.

The only way to properly determine the optimum tightening torque for a given application is to simulate the exact application. This should be done with a tension indicating device of some type on the bolt in the application. The bolt is tightened until the desired P (load) is indicated by the tension indicating device. The tightening torque required to achieve the desired tension is the actual tightening torque that should be used for that given application. It is extremely important to realize that this tightening value is valid only so long as all of the aspects of the application remain constant Bolt suppliers sometimes have customers say that their bolts are no good because they have started breaking while being installed. Thorough investigation commonly reveals that the customer has started lubricating the bolts to make assembly easier, but maintained to same torque as was used when the were plain finished

The table in this article shows that by using this formula a 1/2-13 Grade 5 plain bolt should be tightened to 82 foot pounds, but the same bolt that is waxed only requires 41 foot pounds to tighten the same tension. A perfect 1/2-13 Grade 5 waxed bolt will break if it is tightened to 81 foot pounds because the K factor is drastically lower. The bolts are fine, but the application changed. Suppliers need to understand this and be able to educate their customers to resolve this common customer complaint about breaking bolts.

The chart is provided for quick reference by fastener suppliers and users for selecting an initial target tightening torque. This chart was derived by using the formula shown earlier. An example of the calculation is as follows:

Product: 3/4-10 Grade 5 zinc plated bolt
Formula: T= K x D x P

• K= 0.22 (zinc plated)
• D= .750 (3/4-10 nominal diameter
• P= 23.046 pounds



Hopefully the chart will help suppliers with an initial answer to the customer's question, "What torque should I use to tighten my bolts?" Keep in mind this is only an estimated value. It may provide satisfactory performance, but it also may not. Every application should be evaluated on its own to determine the optimum torque value for each application. Major bolt suppliers should have tension indicating equipment necessary to help their customers determine the appropriate tightening values for their specific applications. Keep in mind that if the lubricant on a bolt and nut combination is changed, the tightening torque value must be altered to achieve the desired amount of bolt tension.

Joe Greenslade is President of Greenslade and Company, Inc. located in Rockford, Illinois. His firm specializes in providing manufacturing tooling and inspection equipment to suppliers of screws, bolts, rivets, and nuts
throughout the world.

Joe is an inventor, author, and lecturer. He holds eleven US Patents. Has written over 80 technical articles for industrial trade journals, and has spoken frequently at trade association meetings and technical conferences on issues related to industrial quality for the past ten years.
03-19-2015 05:43 PM
casey1999
Re: Keel bolt torque values ????

If you really want to get technical:
Tightening using the Bolt Head or Nut

When applied torque and the resulting tension (preload) in the bolt are measured during tightening and plotted on a graph, there is a linear relationship between the torque and the tension. The bolt tension is directly dependent, and proportional to, the applied torque. This is illustrated by the graph, which is based upon experimental results, that is shown in the diagram above. From such test results it is possible to establish the appropriate torque for a required bolt preload that may be required.

One of the disadvantages of using torque control is that there can be a significant variation in the bolt preload achieved for a given torque value. There are several reasons for this e.g. inaccuracy in applying the torque, dimensional variations of the thread and hole size variation amoungst others. However, the dominant factor is usually due to the frictional variation that is present between the contact surfaces that are being rotated.

Torque Distribution


From tests, it is known that approximately 50% of the tightening torque is dissipated in overcoming friction under the bolt head or the nut face (whichever is the face that is rotated). Typically only 10% to 15% of the overall torque is actually used to tighten the bolt, the rest is used to overcome friction in the threads and on the contact face that is being rotated (nut face or bolt head). This is illustrated in the piechart shown above. Relatively small changes in the nut face friction can have a significant effect on the bolt preload. As more torque is perhaps needed to overcome friction, less remains for the bolt extension and hence as the effect of adversely reducing the preload. If the friction under the nut face is reduced, then, for a given torque, the bolt preload will be increased.
03-19-2015 05:36 PM
casey1999
Re: Keel bolt torque values ????

Quote:
Originally Posted by SloopJonB View Post
Really, really bad "Internet" advice.

If a fastener breaks below specified torque values it was defective or failing and would have broken or failed in service.

If a factory engineering manual says "XXX foot Lbs" then that is what you should use, not something less that you "feel more comfortable with".

P.S. Spanning two or more bolts with a backing plate is BETTER than single washers, not just "O/K". Wider load distribution is always better than less or narrower.
Please quote me correctly. This is what I said:
"I see no problem with a washer spanning two bolts- sounds like this type of washer has more surface area than a standard and therefore perform better than a standard washer- that is spreading the load of the keel bolt over the hull. 316 is more corrosion resistant than 304 so always best to use 316 in salt water environment. But seeing J boats are using 304 for the washer only, and the washer can be easily replaced- use of 304 should not be a problem."

And as far as torque values, the charts give maximum. So say your stainless keel bolt has some corrosion or fatigue. Do you really want to torque it to max value a factory new bolt could handle? Do you want to torque over 2x over what the boat yard torqued who built the boat. And torque values depend on fastener thread to thread condition as well as lubrication. Torque to a max value could lead to breakage that benefits nothing. Any way my newest car is a 91 with over 200K miles- do all the work myself and they are more reliable than many new cars- so I'll stick with what works for me.
03-19-2015 05:25 PM
SloopJonB
Re: Keel bolt torque values ????

Quote:
Originally Posted by casey1999 View Post
As far as nut/bolt torque, I never go as high as the bolt chart shows. Even when working on my car the specs call out for much higher torques on some items than I feel comfortable with. I have broken or stripped a lot of bolts when torqueing well below what a bolt torque chart indicates is acceptable.
Really, really bad "Internet" advice.

If a fastener breaks below specified torque values it was defective or failing and would have broken or failed in service.

If a factory engineering manual says "XXX foot Lbs" then that is what you should use, not something less that you "feel more comfortable with".

P.S. Spanning two or more bolts with a backing plate is BETTER than single washers, not just "O/K". Wider load distribution is always better than less or narrower.
03-19-2015 01:32 PM
casey1999
Re: Keel bolt torque values ????

Quote:
Originally Posted by albrazzi View Post
Casey; how do you feel about washers spanning two bolts in a keel mounting system. Specifically my cs30 has three sets of (2) keel bolts and they each share a plate not a regular washer but a backing plate connecting the two nuts. There is a packing of some sort between the plate and the stud itself.
I know you didn't write the bulletin but I would appreciate your thoughts. The "standard" of 316/304 mentioned here got my interest. I will elaborate if necessary.

Thanks for your thoughts AL
I see no problem with a washer spanning two bolts- sounds like this type of washer has more surface area than a standard and therefore perform better than a standard washer- that is spreading the load of the keel bolt over the hull. 316 is more corrosion resistant than 304 so always best to use 316 in salt water environment. But seeing J boats are using 304 for the washer only, and the washer can be easily replaced- use of 304 should not be a problem.

On my 37 year old boat the keel bolts/nuts have never been touched. I do not have any keel/hull cracks and the bolts look good. When surveyed 5 years ago the surveyor tapped the keel bolts with a hammer and said they were fine based on the clear ring. I would be hesitant to start messing with the keel nuts as the nut could be seized on the keel bolt, and if I were to get the nut off, I might not be able to seal the nut as good as it is now. Now the J boats may be built less stiff and as the manufacturer recommends, maybe it is a good idea to re-torque once a year.

As far as nut/bolt torque, I never go as high as the bolt chart shows. Even when working on my car the specs call out for much higher torques on some items than I feel comfortable with. I have broken or stripped a lot of bolts when torqueing well below what a bolt torque chart indicates is acceptable. the J boat chart I provide looks reasonable- notice the torque values are well below allowable (less than 1/2 of the allowable torque value).
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