Keel Bolt Loads

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KAM

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Anyone know anything about keel bolt loads. I would be interested to know what the reserve factor is for my keel bolts and what the worst design case is. Besides grounding it is presumably falling off the top of a wave when heeled at a high angle but the Lloyds document I have seen looks very simplistic. I would also be interested to see some information on keel bolt diameters for various designs and keel weights but can't see anything on the web.
 
Modern boats generally use the ABS ( American Burerau of Shipping) standard for keel attachment. Can't find the link at the moment, but it has huge reserves built into it. Does not necessarily apply to boats built for racing and so not complying with the RCD. You will also find information on the ISAF website on keel attachment and a table of causes of failure of keels (where available). You will find, despite the hype that keel bolt failures on production boats are extremely rare, usually easily explained by the circumstances and generally due to external factors (collisions, groundings etc) rather than design failures.

Not something to lose sleep over.

If you do a search here on threads here related to the Cheeky Rafiki incident you will find the subject discussed to death - or you can wait for the upcoming MAIB report on the incident which will no doubt have an in depth analysis of the subject.
 
One would think that tension loads on a keel would be worse as said when the loads are sideways as in grounding. The loads on the bolts will then be proportional to the sideways spacing of the pairs of bolts. I would assume that the longitudinal spacing is so great as to not be concern even in a grounding. Generally I would think there is not much point in skimping on bolt sizes and numbers as they are relatively cheap and weight at that point is irelevant. good luck olewill
 
You might find ISO12215 part 9 2008 (Small craft — Hull construction and scantlings) interesting

It considers various load cases including :
Fixed keel at 90° knockdown
Canted keel steady load at 30° heel with dynamic overload factor
Keelboat vertical pounding
Keelboat longitudinal impact

I've done the calculations for my old wooden racing boat (long keel from 1960's) and found the bolts to be over engineered by a factor of 40 for a full knockdown case but that doesn't take into account dynamic factors. And an impact case would be much worse of course.

M
 
Thanks Martinaskey that's exactly what I was looking for. I though I would have to buy a copy at great expense but managed to download a copy courtesy the Bulgarian government. The EU is some use after all.

"In order to promote public education and public safety, equal
justice for all, a better informed citizenry, the rule of law,
world trade and world peace, this legal document is hereby
made available on a noncommercial basis, as it is the right of
all humans to know and speak the laws that govern them."

It looks like the same load cases as the Lloyds document but much more detail. Still a bit surprised that the 90 degree heeled case is just a static load. I'll have a go at the calcs today. I also expect a big reserve but it will be nice to know what the margins are when you are out in a big sea. The standard also has torque figures which are interesting. Mine is a lead keel. I don't have a particular problem but was thinking of checking the torque. Has anyone done this. What did you do for tools.
 
Ow my brain hurts. Using the ISO standard on my 2200kg keel I calculated 18mm bolts for cat A with all the safety factors. Mine are 33 mm so should be OK. Thanks Martin for pointing me in the right direction it was a very useful exercise. Going to have a look at the hull next should be finished by the start of the sailing season! If anyone else is doing this D 4.4.1 is slightly ambiguous.
 
KAM said:
Ow my brain hurts. Using the ISO standard on my 2200kg keel I calculated 18mm bolts for cat A with all the safety factors. Mine are 33 mm so should be OK. Thanks Martin for pointing me in the right direction it was a very useful exercise. Going to have a look at the hull next should be finished by the start of the sailing season! If anyone else is doing this D 4.4.1 is slightly ambiguous.
Click to expand...

Yes don't forget to look at the hull strength.
A long time back in the madness of Americas Cup competition Australia produce a huge challenger 90 odd feet long. It was designed for min weight and had a 12tonne keel on a 15tonne overall boat. The keel was very deep. The engineers designed the structure of the hull to take side loads of the keel and transfer them to the chainplates and mast step.
However the keel was so long that pitching motion when being towed to the course damaged the hull around the keel. A subsequent failure of a jib sheet winch in a race led them to use a running backstay winch as a jib sheet winch. The strain on the damaged hull was too much. The hull broke like a banana at the keel attachment and she was sunk in seconds. Modern technology gone one step too far.
Just remember that keel bolts are only one element in the whole keel attachment. good luck olewill
 
KAM said:
Ow my brain hurts. Using the ISO standard on my 2200kg keel I calculated 18mm bolts for cat A with all the safety factors. Mine are 33 mm so should be OK. Thanks Martin for pointing me in the right direction it was a very useful exercise. Going to have a look at the hull next should be finished by the start of the sailing season! If anyone else is doing this D 4.4.1 is slightly ambiguous.
Click to expand...

Yes don't forget to look at the hull strength.
A long time back in the madness of Americas Cup competition Australia produce a huge challenger 90 odd feet long. It was designed for min weight and had a 12tonne keel on a 15tonne overall boat. The keel was very deep. The engineers designed the structure of the hull to take side loads of the keel and transfer them to the chainplates and mast step.
However the keel was so long that pitching motion when being towed to the course damaged the hull around the keel. A subsequent failure of a jib sheet winch in a race led them to use a running backstay winch as a jib sheet winch. The strain on the damaged hull was too much. The hull broke like a banana at the keel attachment and she was sunk in seconds. Modern technology gone one step too far.
Just remember that keel bolts are only one element in the whole keel attachment. good luck olewill
 
Tranona said:
You will find, despite the hype that keel bolt failures on production boats are extremely rare, usually easily explained by the circumstances and generally due to external factors (collisions, groundings etc) rather than design failures.
Not something to lose sleep over.
Click to expand...

The uncharitable may think that it is a "design failure" not to factor obviously foreseeable "external factors (collisions, groundings, etc)" into the design. I have dim memories of the Ford Motor Company's attempts to defend such "design failures" against Ralph Nader and his lawyers.
Sleep easy!
 
awol said:
The uncharitable may think that it is a "design failure" not to factor obviously foreseeable "external factors (collisions, groundings, etc)" into the design. I have dim memories of the Ford Motor Company's attempts to defend such "design failures" against Ralph Nader and his lawyers.
Sleep easy!
Click to expand...

The question was specifically about keel bolts and sailing loads, and as the OP has found out they are way overspecified. If the question had been about what happens when boats run aground the answer may have been different.
 
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