Keel Bolts - a bad idea

[panthablue]

My wife and I we were watching 'Seaside Rescue' on TV late last night. It featured a large yacht which had lost its keel during sea trials. The boat had turned over with no time for the 14 man crew to launch the lifeboat. The boat was too large, and the sea too rough for any of them to dive down to try and retrieve anything, so they were stuck - perched precariously on top of the upturned hull.

Fortunately they were all safely rescued.

I have heard of several incidents where keels have broken off. Seeing the whole event played out on TV reminded me of this, and re-kindled my anger at how little anything seems to be done about it.

The problem is simply that keels are held on with keel bolts. A design concept that suited sailing boats of the 1920's, but is whoefully inadequate for todays 'extreme' design of racing boats.

With longer slimmer keels, and larger sails, keel bolts are totally inadequate to take the huge bending forces which keels are subjected to.

When will designers wake up to the fact that the top end of the keel should be fitted into a recess inside the hull so that all the bending forces are exerted directly on the hull itself.

This is the only sensible and safe way to attach the keel to the hull.

Using keel bolts is potentially dangerous.

We should outlaw keel bolts for any boat which has an 'extreme' keel design, and not just for new boats; existing boats should be retro-fitted too.


RRrrrrrrrrrrrrrrrgh

 

[sailorman]

My wife and I we were watching 'Seaside Rescue' on TV late last night. It featured a large yacht which had lost its keel during sea trials. The boat had turned over with no time for the 14 man crew to launch the lifeboat. The boat was too large, and the sea too rough for any of them to dive down to try and retrieve anything, so they were stuck - perched precariously on top of the upturned hull.

Fortunately they were all safely rescued.

I have heard of several incidents where keels have broken off. Seeing the whole event played out on TV reminded me of this, and re-kindled my anger at how little anything seems to be done about it.

The problem is simply that keels are held on with keel bolts. A design concept that suited sailing boats of the 1920's, but is whoefully inadequate for todays 'extreme' design of racing boats.

With longer slimmer keels, and larger sails, keel bolts are totally inadequate to take the huge bending forces which keels are subjected to.

When will designers wake up to the fact that the top end of the keel should be fitted into a recess inside the hull so that all the bending forces are exerted directly on the hull itself.

This is the only sensible and safe way to attach the keel to the hull.

Using keel bolts is potentially dangerous.

We should outlaw keel bolts for any boat which has an 'extreme' keel design, and not just for new boats; existing boats should be retro-fitted too.


RRrrrrrrrrrrrrrrrgh

thank you for the concern Mine are adequate the 3 tons of lead is still attached

 

[Ubergeekian]

With longer slimmer keels, and larger sails, keel bolts are totally inadequate to take the huge bending forces which keels are subjected to.

When will designers wake up to the fact that the top end of the keel should be fitted into a recess inside the hull so that all the bending forces are exerted directly on the hull itself.

Could you explain a little more what you mean here? I can't see much structural difference between a keel bolted flat against the bottom of the hull or one that goes into a recess. Are you saying that keels should have flanges on the top?

 

[TQA]

You might want to stop flying then as wings are held on with wing bolts.

OK usually in a different axis but the principle is the same. Get the engineering right and a wing or a keel will stay put.

 

[sailorman]

You might want to stop flying then as wings are held on with wing bolts.

OK usually in a different axis but the principle is the same. Get the engineering right and a wing or a keel will stay put.

not "Wing Nuts " then

 

[30boat]

It depends on the keel design of course.My two ton moderate fin keel is held by 11 25mm bolts and the whole thing is over engineered but more modern ones with very high aspect ratio profiles are bordering on the irresponsible if not actually being so(the design I mean).Andrew Simpson glued his lead keel to the hull and to the best of my knowledge it's still attached.He moulded an outer fiberglass skin for the lead keel that was glued to a female stub with a special epoxy glue.The stub itself was laminated on to the bottom of the strip planked hull.Very elegant and completely trouble free.

 

[trapezeartist]

"When will designers wake up to the fact that the top end of the keel should be fitted into a recess inside the hull so that all the bending forces are exerted directly on the hull itself."

Huh? This sounds like a lounge bar engineer slightly overstretching his understanding of the subject. Bending forces!

 

[misterg]

My wife and I we were watching 'Seaside Rescue' on TV late last night. It featured a large yacht which had lost its keel during sea trials. The boat had turned over with no time for the 14 man crew to launch the lifeboat. The boat was too large, and the sea too rough for any of them to dive down to try and retrieve anything, so they were stuck - perched precariously on top of the upturned hull.

Fortunately they were all safely rescued.

I have heard of several incidents where keels have broken off. Seeing the whole event played out on TV reminded me of this, and re-kindled my anger at how little anything seems to be done about it.

The problem is simply that keels are held on with keel bolts. A design concept that suited sailing boats of the 1920's, but is whoefully inadequate for todays 'extreme' design of racing boats.

With longer slimmer keels, and larger sails, keel bolts are totally inadequate to take the huge bending forces which keels are subjected to.

When will designers wake up to the fact that the top end of the keel should be fitted into a recess inside the hull so that all the bending forces are exerted directly on the hull itself.

This is the only sensible and safe way to attach the keel to the hull.

Using keel bolts is potentially dangerous.

We should outlaw keel bolts for any boat which has an 'extreme' keel design, and not just for new boats; existing boats should be retro-fitted too.


RRrrrrrrrrrrrrrrrgh

Sadly that isn't the answer. Hooligan V had the type of keel attachment that I think you're alluding to.

http://www.yachtingworld.com/archive/extra/400828/hooligan-maib-report

There is a new ISO standard for keels in the later stages of drafting which will hopefully improve matters. That it includes considerations on metal fatigue and applies also to 'racing' yachts is down to the dogged, un-paid work of a very modest poster on these forums (who I won't embarrass by naming). I'm sure his determination will one day save lives.

Cheers J.

Andy

 

[snowleopard]

When Team Philips lost her bows an armchair engineer on here said 'any fool could see that a long unsupported structure couldn't be strong enough'. Presumably he only flew on biplanes.

 

[vyv_cox]

In the highly publicised failures that have occurred over the past 20 years or so, I struggle to recall any that failed due to keel bolt fracture or looseness. Most were due to inadequate fatigue resistance of the portion of the keel adjacent to the bolting flange, for a whole variety of reasons. A high-profile investigation last year found that the builder did not understand the instructions of the designer and modified the design to aid construction.

 

[snowleopard]

Personally I don't hold with keel bolts either. Mine are stuck on with strips of glass & resin.

 

[Spyro]

My wife and I we were watching 'Seaside Rescue' on TV late last night. It featured a large yacht which had lost its keel during sea trials. The boat had turned over with no time for the 14 man crew to launch the lifeboat. The boat was too large, and the sea too rough for any of them to dive down to try and retrieve anything, so they were stuck - perched precariously on top of the upturned hull.

Fortunately they were all safely rescued.

I have heard of several incidents where keels have broken off. Seeing the whole event played out on TV reminded me of this, and re-kindled my anger at how little anything seems to be done about it.

The problem is simply that keels are held on with keel bolts. A design concept that suited sailing boats of the 1920's, but is whoefully inadequate for todays 'extreme' design of racing boats.



With longer slimmer keels, and larger sails, keel bolts are totally inadequate to take the huge bending forces which keels are subjected to.

When will designers wake up to the fact that the top end of the keel should be fitted into a recess inside the hull so that all the bending forces are exerted directly on the hull itself.

This is the only sensible and safe way to attach the keel to the hull.

Using keel bolts is potentially dangerous.

We should outlaw keel bolts for any boat which has an 'extreme' keel design, and not just for new boats; existing boats should be retro-fitted too.


RRrrrrrrrrrrrrrrrgh

On the off chance this is not a Troll, here's my thoughts

The keel bolts go through the hull and nuts are screwed on top of backing plates. I might be missing something but wouldn't that mean any forces ARE exerted on the hull?
Not sure how many keels have "fallen off" out of the thousands of boats that are around. Any I've seen usually have a big hole left where the keel was, not a complete hull with bits of bolts left sticking out.
What I'm suggesting is it's the hulls which have failed not the bolts.

Can I also suggest that maybe you and your wife shouldn't watch any more Seaside Rescue or you might never go near a boat again.

 

[snowleopard]

On traditional bolts it was standard practice to pull keel bolts and replace as necessary as they rusted. Today of course, the bolts are stainless but because the conditions are anerobic down there, corrosion is still possible. The problem is that the bit that's visible at the top is still nice and shiny so it's easy to assume everything is fine.

Do people still draw keel bolts and inspect them every few years?

 

[oldharry]

I have heard of several incidents where keels have broken off. Seeing the whole event played out on TV reminded me of this, and re-kindled my anger at how little anything seems to be done about it.

The problem is simply that keels are held on with keel bolts. A design concept that suited sailing boats of the 1920's, but is whoefully inadequate for todays 'extreme' design of racing boats.

With longer slimmer keels, and larger sails, keel bolts are totally inadequate to take the huge bending forces which keels are subjected to.

When will designers wake up to the fact that the top end of the keel should be fitted into a recess inside the hull so that all the bending forces are exerted directly on the hull itself.

This is the only sensible and safe way to attach the keel to the hull.

Using keel bolts is potentially dangerous.

We should outlaw keel bolts for any boat which has an 'extreme' keel design, and not just for new boats; existing boats should be retro-fitted too.


RRrrrrrrrrrrrrrrrgh

I really do not understand where you are coming from on this. The vast majority of sailing boats have their keels bolted on, and failures are extremely rare. From an engineering point of view, the top face of the keel pulled securely against the hull moulding is a well proven standard engineering practice, so that lateral stress is transmitted directly to the hull structure. Designers are well aware of the loadings involved, the calculations for which are not rocket science, and well able to design a wide safety margin for load stresses.

The very rare occasions on which it does go wrong are usually found to be because something else has affected the assembly - such as the keel bolts loosening off or corroding so allowing shock loads to change the stress patterns, or where builders have misunderstood the design and made what proved to be a dangerous modification to make the build easier, or to reduce weight.

The incidence of keel bolt failure on properly maintained production boats is virtually non-existent. In fact I can not recall it ever happening - though I am sure the forum will produce someone who does!

Cutting edge racing designs are just that: they are by nature experimental and therefore the possibility of an unforseeable factor causing some sort of rig or hull failure is just that much greater. Racing enthusiasts know this, and accept it as a part of the 'go faster' risk element in the sport.

So whats all the fuss about? Design improvements are introduced in the racing sector, and are tested and proved or disproved long before they reach the mass production boat market. By the time it all filters down to production boats, the engineering is well understood, and the necessary structural safety margins are well recognised.

 

[PeterGibbs]

Using keel bolts is potentially dangerous.

We should outlaw keel bolts for any boat which has an 'extreme' keel design, and not just for new boats; existing boats should be retro-fitted too.


RRrrrrrrrrrrrrrrrgh[/QUOTE]

Fortunately, matters today are not quite so dire below the waterline. What you fear is true of construction techniques a generation ago. Not today.

Westerley for example soon discovered as they built larger vessels in the 70's that the keel required more than just firm attachment. It needed a subframe. This is a large rigid metal structure under the floorboards into which the keel is bolted. The subframe spreads the loadings across a wide area where the hull is composed of solid GRP. And it works.

Recent cases of keel loss, and how few they are, seem attributable to poor manufacture, not design in almost every case.

Relax!

PWG

 

[PeterR]

This thread reminded me of a recent article in Maritime CHIRPs concerning the failure of a lifeboat lifting bracket:

"I have been reading your CHIRP MARITIME FEEDBACK issue no. 22 and my attention was caught by the report on the Rescue Boat Accident. The photograph of the fractured bolts (photo 3) reminded me of three failures which came to my attention when I was a Lecturer at a University.
The failures all related to high tensile stainless steel (HTSS) either in the form of chain or nuts, bolts and washers. In each case the HTSS had been used in conjunction with galvanized components and exposed to sea water or at least a marine environment. The chain had been used with ordinary galvanized shackles, the bolts to secure a galvanized backing plate and in one case the bolts themselves had been galvanized. All failures occurred suddenly, without warning, with fractures which showed no accompanying stretching or deformation. I was able to reproduce these failures in the laboratory by loading a tensile test piece overnight. The test piece was in contact with a scrap of zinc held in place by a gauze bandage soaked in sea water. When the test piece was subsequently stretched a network of cracks was revealed and the ultimate fracture resembled those of the failed components. If I omitted either the zinc or the sea water bandage, the material behaved normally stretching and necking down to a normal fracture.
To return to the failures you illustrate you do not give the material of the eye-plate but from the position of the fractures the problem would appear to lie under the decking of the rescue boat and one wonders whether the bolts had been married with either galvanized washers or nuts or perhaps a galvanized backing plate. You report that other bolts and eye-plates have been inspected and found to be satisfactory. I would warn that the type of cracking which I observed is difficult to detect non-destructively. I was able to observe it by metallographic examination but the cracks are very fine and could easily escape detection.
From time to time I hear of similar failures and it is clear that the dangers of marrying HTSS with galvanized components in a marine environment is not fully appreciated and requires greater publicity. I suspect that designers who appreciate the benefits of ordinary 18/8 stainless steel are mesmerized by the words "high tensile" and do not appreciate that the two materials differ significantly."

Most keel bolts I have seen have galvanised mild steel backing plates - add a bit of sea water in the bilge and you have exactly the conditions the author was trying to create in his experiment. I wonder if yacht manufacturers are aware of this research?

I've tried getting the S/S keel bolt nuts off to replace the galvanised backing plates on my boat but could not shift them. I'll just have to settle for keeping the bilge dry.

 

[saltwater_gypsy]

There were good articles in Yachting World about modern keel development. As I recall, the high aspect keels fit into a "Letterbox" arrangement which gives good support at the root and the letterbox can be engineered into the hull to properly distribute the loads...BUT.... all the materials, engineering and fabrication has to be to the highest (aircraft) standards. Several recent failures have been a result of low quality construction by sub-contractors.

 

[emnick]

Huh? This sounds like a lounge bar engineer slightly overstretching his understanding of the subject. Bending forces! [/QUOTE]

Why make comments like this?

 

[sailorman]

been a result of low quality construction by sub-contractors.

There were good articles in Yachting World about modern keel development. As I recall, the high aspect keels fit into a "Letterbox" arrangement which gives good support at the root and the letterbox can be engineered into the hull to properly distribute the loads...BUT.... all the materials, engineering and fabrication has to be to the highest (aircraft) standards. Several recent failures have been a result of low quality construction by sub-contractors.

More like poor quality QA

 

[panthablue]

Quote

'There were good articles in Yachting World about modern keel development. As I recall, the high aspect keels fit into a "Letterbox" arrangement which gives good support at the root and the letterbox can be engineered into the hull to properly distribute the loads...BUT.... all the materials, engineering and fabrication has to be to the highest (aircraft) standards. Several recent failures have been a result of low quality construction by sub-contractors.'

I don't get where your coming from? Aircraft quality materials etc??

Let me explain in more detail my problem with keel bolts. I appreciate I may be considered an armchair engineer, but I still think this is relevant

I have drawn up a sample keel, which I hope you can see.

In the left diagram the keel is held on by keel bolts, and the right hand the top of the keel is housed inside the hull (the retaining bolts are horizontal passing right through the both sides of the housing)

Say for example the loading at the bottom of the keel is 10kgf, the tension in the keel bolts is 1512 x 10/100 = 151.2kgf. For the right hand diagram the force on impinging on the hull is 1542 x 10/200 = 77.1kgf. Roughly half.

If you have a long keel with plenty of keel bolts - no problem. That's fine, but my son sails on a 40 footer where the length of the keel is about 750mm, the height is about 2 metres, it is very thin, and has a ballast weight at the bottom. Not untypical for a modern recing yacht. This means that the number of keel bolts is probably down to say three or four - increasing the tension in the bolts and the likelihood of failure.

If keel bolts fail, this instantly puts the lives of crews in danger. The method of attaching the keel to the hull can be improved easily, as I have described above, and I am sure there are other options. There's no excuse.