Bavaria 37 Cr., 2007 keel bolts retightening

[Andriy]

Hi Owners, pls advice correct procedures for the kiel bolts retightening ( in water or on kiel blocks etc )...
Also tightening torque recommended. Thanks.

[Symphony]

Enter keel bolt torque in the search function and you will find several threads on the subject including the torque settings by bolt size rather than model.

Why do you think you need to torque them, unless you have removed the keel. Normally there is no need ever to check, even if the keel has been damaged  by grounding as any such damage that resulted in nuts becoming loose would require major work such as keel removal rather than just tightening. Equally there is never any need to remove the nuts from the studs unless the hull/keel joint has failed.

[Andriy]

 Thanks  as per my info it was not tightened with torgue spanner after some repairs and they tighten all nuts while at Dock. So i need to know proper way of retightening ( in water or out of water etc )...

[Symphony]

You will find the torque settings if you do the search I suggested. Normally it would be done with the keel on the ground. Do not think there is any specific procedure for doing it in the water. If the repairer has not done the job properly it is their responsibility to make it good!

[Markus]

Generally speaking I think it's a good practice to check keel bolt torque settings of a boat from time to time, maybe once in 5 years or so. There are a number of things other than damage to the hull that might affect the tension of the bolts. First of all there's always some material creep over years and the bottom of the bilge where the keel bolts sit is also not mathematically level and always has some ridges of flowcoat, etc which might flatten over time. And for example with a lead keel and an elastic glue at the keel/hull-joint there is always some movement which over the years could flatten very slightly the highest points of the soft lead keel thus reducing the loading on the bolts. As far as I am aware, Bavaria has used extensively a very rigid Plexus glue for the keel to hull joint so the latter reason may not be so relevant for the members of this forum.

I think what ever you do before, the bolts should be checked once more when the boat is on the hard (resting on the keel) as Symphony mentioned.

[Andriy]

Found. See attached.
Only not clear with condition of the boat... in water or lay keel must lay down on hard base ?

[Markus]

Found. See attached.
Only not clear with condition of the boat... in water or lay keel must lay down on hard base ?

I am pretty sure that whoever made the manual for that did not imagine anyone to loosen the keel bolts while the boats in water so I think we can assume the boat should be on the hard.

[MagicalArmchair]

Generally speaking I think it's a good practice to check keel bolt torque settings of a boat from time to time, maybe once in 5 years or so. There are a number of things other than damage to the hull that might affect the tension of the bolts. First of all there's always some material creep over years and the bottom of the bilge where the keel bolts sit is also not mathematically level and always has some ridges of flowcoat, etc which might flatten over time. And for example with a lead keel and an elastic glue at the keel/hull-joint there is always some movement which over the years could flatten very slightly the highest points of the soft lead keel thus reducing the loading on the bolts. As far as I am aware, Bavaria has used extensively a very rigid Plexus glue for the keel to hull joint so the latter reason may not be so relevant for the members of this forum.

I think what ever you do before, the bolts should be checked once more when the boat is on the hard (resting on the keel) as Symphony mentioned.

Interesting, does anyone else do this?

[symphony2]

Found. See attached.
Only not clear with condition of the boat... in water or lay keel must lay down on hard base ?

These are the instructions provided by the factory for fitting keels that have been shipped separately from the boat. This occurs either because the boat is shipped from the factory by sea (for example to the US or Australia) because it reduces shipping cost, or because the boat is too tall with its keel on to be delivered by road. Remember that the factory is 1000 miles from the sea!

The dealer fits the keel as part of the commissioning process. The same instructions should be used for refitting the keel if it has been removed to repair damage, and any proper repair yard would do this. For obvious reasons it assumes the boat is resting on its keel.

[Yngmar]

Generally speaking I think it's a good practice to check keel bolt torque settings of a boat from time to time

Interesting, does anyone else do this?

No, and I don't believe it good nor common practice to do so. There is no indication of any benefit to this and you're much more likely to do harm than achieve anything useful. It's not as simple as just putting a torque wrench on and heaving on it until it goes click - you'll probably just end up overstretching the bolts if you do this a few times, as friction has likely increased since installation or threads may have galled (the bolts and nuts are stainless steel). I wouldn't fiddle with it without good cause.

The OP situation is different though, apparently the bolts had already been undone (why?) and need torquing up now. An interesting question is if the bolts and nuts should be re-used in this situation or have been permanently stretched.

[Markus]

Generally speaking I think it's a good practice to check keel bolt torque settings of a boat from time to time

Interesting, does anyone else do this?

No, and I don't believe it good nor common practice to do so. There is no indication of any benefit to this and you're much more likely to do harm than achieve anything useful. It's not as simple as just putting a torque wrench on and heaving on it until it goes click - you'll probably just end up overstretching the bolts if you do this a few times, as friction has likely increased since installation or threads may have galled (the bolts and nuts are stainless steel). I wouldn't fiddle with it without good cause.

The OP situation is different though, apparently the bolts had already been undone (why?) and need torquing up now. An interesting question is if the bolts and nuts should be re-used in this situation or have been permanently stretched.

The usefulness of checking the bolt tensions can be always questioned and for sure in most cases it is "useless". However, using a correct torque (to stay in the elastic area) you simply cannot "overstretch" the bolts - that is the whole point of using a torque wrench for such an operation.  Friction has for sure increased since the bolts & nuts were new, but that reduces the axial load applied to the bolt with a given torque setting as more friction between nut and washer and nut and bolt oppose the torque force, so you are even less likely to "overstretch" the bolts.

Coming back to the original post: if the keel has been taken of as your post suggests, it should be noted that different sealant/methods could now have been used by the yard. So be careful of taking information straight out of this or other forums without consulting the boat yard that did the works. To me it seems quite odd that they would not tighten the bolts properly after major works and leave it up to the boat owner...

[Salty]

“ Friction has for sure increased since the bolts & nuts were new, but that reduces the axial load applied to the bolt with a given torque setting as more friction between nut and washer and nut and bolt oppose the torque force, so you are even less likely to "overstretch" the bolts.”

With respect, surely that makes periodic checking with a torque wrench a somewhat self defeating exercise ?

[Markus]

Friction has for sure increased since the bolts & nuts were new, but that reduces the axial load applied to the bolt with a given torque setting as more friction between nut and washer and nut and bolt oppose the torque force, so you are even less likely to "overstretch" the bolts.

With respect, surely that makes periodic checking with a torque wrench a somewhat self defeating exercise ?

Yes, but only partially...  If the nuts have been stationary for a long time the axial load on the bolt needs to have reduced over time more than with new, clean threads for the nuts to move at all when one tries to tighten them. Still, you will learn at least that there is some tension left on the bolts and they are not slack.  Without a proper tension on the keel bolts, the windward bolts are in tension and the leeward ones slack. A bit similar situation than sailing with cap shrouds only hand tight.

Actually, I remember seeing a service bulletin (could not find it now quickly...) for J-boats suggesting an annual maintenance of keel bolts by taking one nut off at the time, cleaning and torquing down which would result in original correct torque. To me doing something like this every year seems "extreme"... But I think there's a good cause for at least once-in-a-decade check, especially with boats whose keel-to-hull -joint is elastic and therefore subject to more creep over time.

[Salty]

Well, I think I’m with Yngmar on this, and unless I can see something amiss I would prefer to leave well alone. I’ve had only one situation with keel bolts, and that was on a boat with bilge keels. Both keels were bolted through from the outside, through steel flanges on the outside of the hull and using countersunk stainless steel bolts. The heads of thise bolts where they passed through the external flanges were painted over, but on one of them the paint was bulging. Removing the paint released a quantity of black liquid. The head if the stainless steel bolt had almost completely corroded away, and the bolt had to be renewed. I removed the paint from the heads of the remaining bolts in order to check their condition. They were all in good order, but removing sound paint coatings probably did more harm than good.

[Markus]

Well, I think I’m with Yngmar on this, and unless I can see something amiss I would prefer to leave well alone. I’ve had only one situation with keel bolts, and that was on a boat with bilge keels.

I think there's a natural preference to "leave alone" this sort of checks, especially if one has not done it before. And especially since cases of keel bolt failures are extremely uncommon as you pointed out. So rare that one might actually argue that that in itself is a good cause not to do anything... 

However, I think the reasoning behind the recommendations to check the bolts cannot be really doubted: if the bolts are slack, the effect of fatigue is much more severe than if they are properly tightened - exactly the same phenomena which causes pre-mature rigging failure if it has been too slack. Except with a slack keel there's always also bending moment, not just tension as in rigging.

I leave here a few links to the subject just in case someone is interested in further reading on this.

Comments on the Cheeki Rafiki -case: "tightened keel bolts don't fail, loose ones do": http://www.ship-surveyor.com/images/Cheeki_Rafiki_Copy.pdf

Comments of a well known "sailing metallurgist" Vyv Cox on the keel loss of charter yacht Polbream: "It seem likely to Cox Engineering that fatigue cracks had been propagating in the keel bolts for some time, possibly due to undertightening. The gentle collision with a rock in the Scilly Isles provided sufficient force to fracture the remaining, small, area that remained intact."
http://coxeng.co.uk/metallurgy/fatigue/

This is starting to be quite off-topic, so I suppose there's no reason to argue this further - just an interesting topic. So this was my two cents on the subject... 

[Salty]

“Well, I think I’m with Yngmar on this, and unless I can see something amiss I would prefer to leave well alone.”

Any careful and conscientious yachtsman will check their boats and do whatever is necessary to maintain the boat in a seaworthy condition. The problems with both Cheeki Rafiki and Polbream were that both boats had suffered keel collisions with rocks. In both cases that would be reason enough for their owners to have considered the possibility that there just might be “something amiss,” and not just in the navigators ability to navigate !! 

In the case of Cheeki Rafiki, The report following the loss of the vessel, and of the loss of life of each of the crew onboard, commented that the vessel had suffered more than just one such collision, but that there was no record of any follow up examination to check that serious damage had not occurred. This however would not have been a matter of routine checking which this thread has been about, but was a serious emergency, and one where the keel attachment to the boat needed to be very seriously looked at and checked out. To that extent the boat should have been lifted out at the very first oppotunity, and before it was allowed to go back to sea. That examination I believe should have had the keel removed as Symphony2 has suggested, to allow a thorough inspection of the hull in that area to ensure there had been no damage done to it, and would in my opinion, have also required a new set of keel bolts to be fitted once any hull repairs had been completed.

As for doing nothing, I don’t  think that has been suggested by any of the other replies to this thread, and certainly not by me. But my examination of the keel attachment to my boat did depend on what I saw as to how far that examination would go. So if there was no evidence of loosening of the keel bolts they would be left alone. If keel bolt loosening had been evident then I would want to know why they had become loose, I wouldn’t just simply tighten them up without getting that question answered satisfactorily.

[symphony2]

Agree with this. On keel attachment systems such as the Bavaria type and the vast majority of modern designs there is no reason why nuts should loosen (if they were properly torqued in the first place) unless there is damage to the hull structure such as in the examples given. Like many of the cod surveyor type mantras the "check keel bolts and nuts for tightness" comes from the days when boats were built of materials that were not stable. Examples from the early GRP years are British built boats such as Moodys which used mild steel studs, nuts and washers for keel attachments. Boats also leaked (traditional stern glands, leaky windows, poor sealing of deck fittings and chain plates, so bilges were always wet. After a few years the nuts and washers were balls of rust and eventually washers rusted away so loosening the nut. However even in the worst cases the stud itself would be perfect and the keel still firmly attached!

Going back further when ballast keels were attached through wooden keels, hogs and floors, just being out of the water for the winter would be enough for the wood keel to shrink, nuts need retightening and gaps appear in the keel/ballast joint. On a wooden boat I owned for 40 years, I removed the keel twice to replace keel bolts and reseal and replaced the bolts without removing the keel on another occasion. This was a long keel boat with a fairly shallow wood keel of relatively stable oak, but it was out of the water, resting on its keel for the last 8 years, and every single keel nut needed tightening before it went back in the water, and even then one of them leaked.

Going back to the original question. The OP is right to be concerned if he is not confident that the repairer correctly torqued the nuts when the keel was re-attached. However, unless they were dramatically loose, for example turning with just a normal spanner on them, I doubt there is any danger of the keel coming loose or the seal failing. The margins of safety are so great as explained in the Cheeki Raffiki report. Suggest that the OP torques the nuts to the recommended level with the boat in the water then checks again when it is out and resting on its keel. Personally doubt there will be any difference.

[Markus]

Any careful and conscientious yachtsman will check their boats and do whatever is necessary to maintain the boat in a seaworthy condition. The problems with both Cheeki Rafiki and Polbream were that both boats had suffered keel collisions with rocks. In both cases that would be reason enough for their owners to have considered the possibility that there just might be “something amiss,” and not just in the navigators ability to navigate !!
 

I did not at all intend to imply that the keel bolt fatigue was the only reason for neither of these cases. I was simply trying to make a point that having keel bolts loose will induce fatigue and it's a known issue worthy of some consideration. Due to the typical oversizing of the bolts, fatigue crack propagation might well go unnoticed throughout the service life of the boat until a relatively modest grounding. This in itself is enough for me to suggest a check.

But my examination of the keel attachment to my boat did depend on what I saw as to how far that examination would go. So if there was no evidence of loosening of the keel bolts they would be left alone. If keel bolt loosening had been evident then I would want to know why they had become loose, I wouldn’t just simply tighten them up without getting that question answered satisfactorily.
 

I think you are referring to checking the keel to hull joint with boat in the slings - this is a sound check and I think very useful with rigid sealant joints. However, if the joint is of elastic compound, the elongation before break of these compounds is typically several times the original thickness. Therefore if one sees a gap in keel to hull joint sealed with elastic compound, it is indeed extremely loose or the sealant has failed for other reasons.

On keel attachment systems such as the Bavaria type and the vast majority of modern designs there is no reason why nuts should loosen (if they were properly torqued in the first place) unless there is damage to the hull structure such as in the examples given.

As I already mentioned in the beginning of this thread, as far as I am aware (and that's not far in case of Bavarias...) the majority of Bavarias use essentially non-compressible sealing compound between keel and the hull so there is less flexible material compared to keel to hull joint sealed with semi-elastic adhesives/sealants. Therefore the amount of tightening needed with this type of rigid glue should be indeed very small. With the "traditional method" of elastic sealant/adhesive, you can be assured that it does have some creep under tens of years of compression making it more important to check the bolt torques. I am not sure which method is more used with modern boats but I have no doubt the latter is the prevalent method with boats before year 2000 or so.

[Salty]

Markus, I am going to leave this conversation on the basis that I do not believe that some of the arguments you have put forward actually stack up. These include but are not limited to the use of flexible sealants between the keel and hull when you know that Bavaria do not use them, you talk of an imperfect mating surface between the hull and the keel when there is no good reason to assume that the keel moulding has not been made so that it fits perfectly against the hull it is intended to fit. You have mentioned the possibility of gel coat shape imperfections in the keel area, but considering that the exterior of the hull is laid up inside of a perfectly formed mould, and with the very high tech methods of application that Bavaria use, means that the irregularity you have referred to which might prevent a good fit with the keel, are highly unlikely to occur., and if they did, neither you nor I know what process Bavaria would follow to correct or reject such imperfection. But I do not for one moment think they would ignore it if it ever happened.
In regard to the repair I carried out on a bilge keeled non Bavaria boat, I made no suggestion of it being “in the slings” when being worked on, that was your assumption.
I am firmly of the opinion that unless there is something that I know of to be amiss, that apart from annual visual inspections of the area, I will leave the keel bolts alone.
That doesn't mean to say that if you feel you must put a spanner to your keel bolt nuts, that you shouldn't do so, most of us live in a free world. But it does mean that I don’t buy the arguments that so far you have put forward.

[Markus]

Hi Salty, I hope you are not taking offence on this debate which is starting to be a bit lengthy... To me it looks like you have misread some of my comments, or perhaps there's some details lost in translation from my broken English to proper English. Please find still below some short comments to clarify:

I am going to leave this conversation on the basis that I do not believe that some of the arguments you have put forward actually stack up. These include but are not limited to the use of flexible sealants between the keel and hull when you know that Bavaria do not use them

As I have mentioned in several comments, I have been speaking in general level and not all of the points necessarily apply to Bavarias.

You have mentioned the possibility of gel coat shape imperfections in the keel area, but considering that the exterior of the hull is laid up inside of a perfectly formed mould, and with the very high tech methods of application that Bavaria use, means that the irregularity you have referred to which might prevent a good fit with the keel, are highly unlikely to occur., and if they did, neither you nor I know what process Bavaria would follow to correct or reject such imperfection. But I do not for one moment think they would ignore it if it ever happened.

I have said nothing regarding gelcoat but was talking about interior flow coat. My original comments was: "there's always some material creep over years and the bottom of the bilge where the keel bolts sit is also not mathematically level and always has some ridges of flowcoat, etc which might flatten over time."

In regard to the repair I carried out on a bilge keeled non Bavaria boat, I made no suggestion of it being “in the slings” when being worked on, that was your assumption.

I assumed you checked the keels with boat in the slings, I assumed nothing of works being carried out in the slings - not that it matters for this discussion.

I am firmly of the opinion that unless there is something that I know of to be amiss, that apart from annual visual inspections of the area, I will leave the keel bolts alone.
That doesn't mean to say that if you feel you must put a spanner to your keel bolt nuts, that you shouldn't do so, most of us live in a free world. But it does mean that I don’t buy the arguments that so far you have put forward.

I suppose to put it shortly, my chain of arguments is more or less as follows:

• Fatigue of keel bolts should be avoided as it shortens the service life and/or reduces the safety margin of the design.
• Not having keel bolts under proper tension increases fatigue.
• There are a number of phenomena that can cause reduction of original tension of the bolts during the service life of a boat, even without grounding damage. (Please consider all the load bearing interfaces and materials between keel casting and the load bearing nut. I have listed before some possible issues but make no claim that all of them apply to all boats.)
• Reduction of tension of the bolts cannot be always noticed only by a visual inspection of the area. (Please note that the difference between slack and properly torqued keel bolt is very rougly 0.1% in length so we are talking of <0.1 mm) 
• Based on the above, it's good to also do a check with a torque wrench at a certain interval which one has to decide based on the boat, materials, usage, etc.   

[Andriy]

So remain one question... retightening check of the keel bolts must be done at which condition ?

1. Boat in water
2. Boat in slings
3. Boat at hard base

[Markus]

So remain one question... retightening check of the keel bolts must be done at which condition ?

1. Boat in water
2. Boat in slings
3. Boat at hard base

I believe #3 would be the best. With #1 & #2 you will have the weight of the keel resisting your torquing efforts and therefore less final tension in the bolts compared to #3. But if your boat is in the water, I would do first #1 and then #3 when it's possible next time. I would guess the difference between the methods to be fairly small as the keel weight distributed over ~10 (?) bolts is not that much compared to the clamping force. I would do several rounds starting with a smaller torque setting ending up with the final torque value (do two rounds with the final value to be sure there's no movement any more). Starting always from the middle bolts and working towards both ends of the keel, similar to how cylinder head gaskets are tightened (google for some illustrations if unclear).

All of the above comments are with a huge disclaimer of myself not understanding at all how it has come to pass that the boat is in the water without keel bolts not tightened and what other factors related to possible repairs may be affecting this...

[Andriy]

Thank you. Agree with you. Many cases many boats. I know even that once per 10 years- keel out, full check of the bolts and retightening with new fresh sealant recommended by manufacturer of course. My case is that we do not have torque wrench that time ( believe we do not overstretch studs ) and just come time to check tightening torque. You will be surprise but I saw many new boats where keel was connected without any torque wrench and painted over factory gel coat without any preparation with antifouling ) but this is another story... Thanks.

[Rampage]

The only thing I’ll say on this is that once upon a time the torque of wheel nuts were checked on Stalwart High Mobility Load Carriers at each timed service, irrespective of mileage.  When the age of the fleet approached 30 years, it was noticed that there were a significant number of stud failures. Metallurgical testing of the failed studs revealed that the nuts had been over tightened over time: what was happening was that because of low mileages being run by an ageing fleet, nuts were not being subjected to vibration loosening.  The act of checking the torque of the nuts using a wrench was gradually leading to over tightening which in turn led to stud failures.
So the servicing instructions were changed to so that rather than a time basis for torque checks it became a mileage based check or a check after the wheel had been removed.
This leads me to consider that routine checking of the torque of keel bolts without some real reason (such as a keel strike or repair work) is unnecessary and might even be detrimental.
I’ve also never heard of any requirement or suggestion to remove and refit the keel every 10 years.  Where does that come from?

[Andriy]

Same as the rigging- 10 years and replacement. I do not remember the source but the reason of the keel refitting every 10 years is that factory sealant ( glue ) is shrink or life time expire etc ...