Keels and Keels Again!

I'm curious, does the ISO structural standard have a grounding requirement for keels? I know ABS does (1.5 - 3 x the displacement applied horizontally at the bottom of the keel, and that the boat should be able to stand on the keel (1x displacement) without damaging the boat).

 

Another one... this a design I am not familiar with, described as a Vismara designed 54 production performance cruiser. After almost circumnavigating the keel fell off in sept last year, they drifted in the life raft for days.

Source was From January 2008 Yachtingworld which ran an article on keels.

Some of the magazine can be browsed here:
www.zinio.com/express2?issue=237299539

 

From Scuttlebutt:

KEEL MISSING IN ACTION
March 22 -- A very wet and weary (TP52) Strewth crew appeared out of the murk at Causeway Bay, Hong Kong, at 1500hrs today, accompanied by the faithful guard ship Cloud, the RHKYC's Kellett VI, and RIB M69. It was easy to tell which of the two yachts motoring up the harbour was Strewth - the one with the pronounced roll. Just 36 hours earlier she had lost her keel approx 170 nm south east of Hong Kong, en route to Subic Bay in the Rolex China Sea Race 2008.

Geoff Hill and skipper Ben Jonson told the tale: 'At 0300 watch-change yesterday (21 March), we were fine reaching at about 12 kts in 18 kts of breeze, and there was a loud crack. Several crew checked everything we could think of, but couldn't see anything wrong. 20 m ins later there was another loud crack, and 30 sec after that, she went. The bow went down maybe 30 deg, and the boat rolled 45 or 50 eg - just enough to get the gunwhale wet - the main trimmer dumped everything, and we came upright again with a bit of a kick on the stern from the seaway. It was all very weird, we actually started to trim up and sail again, and were hitting 8-9 kts of boat speed, but the boat was way too tender and had serious leeway, and she was very, very light on the wheel. Definitely wrong. So we rounded up, and checked the keel bolts - one of them was loose, so we thought maybe one had sheared, and the keel had swung out.

'So it was everyone on deck, harnesses on, we ran through the safety routine. Richard Grimes went over the side to see what was happening down there, and came back and said, 'Nada. There's nothing, there, it's all gone. Heck, we even sent him back for a second look just to make sure! We were really worried that the boat might roll over at any moment. If she did go, it would probably have been just like a slow roll that didn't stop, just roll, roll, roll and keep going.'

* Roger Eastham, RHKYC Boatyard Manager, contacted the boat's designer, Jim Donovan, who advised that a roll past 50 deg would push us past the point of vanishing stability - so we were proceeding very cautiously. 'A big roll and it might all be over very quickly. Also, we didn't want to let the boat slam at all - both keel bolt head were still visible inside the boat, and yes we did have appropriate-sized wooden plugs to hand, but we really didn't want the bolts to pop out. As it was we were leaking only about half a bucketful every four hours from the aft keel bolt. 'The rest of the trip home was very straightforward. We set a watch, and everyone lived on deck.'

-- Excerpts from a story posted on the Sail-World website, full story and photos:
http://www.sail-world.com/Asia/index.cfm?nid=42859&rid=2

 

It's absolutely amazing that they are still using biplane era design technology to attach these 21st century keels.

Those poor old keel bolts, vertically oriented, just aren't up to the job.

These keels need lateral bracing inside the hull.

Using shallow, fin keel style bolts on them is like end bolting a diving board to a wall. Though it could work, it is certainly not the most efficient approach. The bolts are forced to deal with two forces at once. Both tension, from the weight of the keel, and bending due to its extreme leverage.

Even canting keels don't have to do that, because the job is divided up. There is an axle, which takes the weight of the keel, then a pair of rams to counter act the leverage. If the rams, which take the greatest loads, fail, the
axle still keeps the keel on the boat.

I'm amazed that these experienced designers can't see that.

Bob

 

Many years ago while I was working at Sparkman & Stevens in NYC, we got a report of one of our boats being rammed by a whale and sheering of the keel. Rod and Olin went over every detail of the yachts design and decided that the keel attachment was not at fault.

we can design for reasonable circumstances but things will still catch us by surprise.

 

I happen to be in HK this week, and went over to look at the boat yesterday. The boat was designed by a friend of mine and I took some photos and sent them to him.

The top of the keel DOES go up into a socket in the hull, which provides the lateral bracing. This is not a traditional fin keel assembly.

That might be true, but that isn't how this keel/hull joint is constructed. This is more like cantilevering the diving board partially through the wall.

 

Maybe it needs MORE lateral bracing. I only say this because it seems that this keel attachment failed under relatively normal conditions.

This, if true, is IMHO inexcusable.

It seems to me that designers are trying their level best to keep the keel from intruding on the space inside the hull.

If I were designing one, I would have the top of the keel extend all the way up to the cabin top and have a sturdy pair of ring frames supporting it at each end.

 

You seem convinced the failure was due to a design or engineering error. I wonder what you base that opinion on?

Maybe that is why no one is asking you to design one.

 

seems to me that if a stud, or capscrew fails then the material should be very suspect
there are many poor fastenings coming out of Asia now
Grade 8 bolts(they dont grade ss, or at least not that I have seen) of the correct size would never fail that is high ten grade 8 steel Compare the sheer of grade 8 to your 316 , etc , well chalk and cheese, and I have found many fastenings are just that Cheese All of the bolted up keels I have seen lately from EU and TAIWAN have plated hex head capsrews none of which bear any grade marking
frinstANCE 304 SS TENSILE ABT 90000
22-13-5 tensile abt170000 you can see the difference
bereylliun copper 180000, some of those keel bolts may be from stuff that is 60000 how can you ever know?

 

I have long been thinking about this subject, and would like to ask/propose a solution and get your views.
At school we were tought that if you cannot make a structure 100% fail safe, you should at least try to design it so that when it fails it creates least damage.
As far as fin keels are concerned, the worst scenario is the keel ripping off the hull at hull keel joint, leaving a gaping hole, as it was the case for MOQUINI.
A better one would be a keel deliberately incorporating a weaker join someway down the fin structure, so that if there is an unforseen force large enough to threaten the entire keel, it gets either bent at this junction or gets torn off along this line.
I guess having a bent keel (which must have absorbed a lot of energy in the process) or an intactly remaining stub of a keel is better than losing it completely. At least water tightness would not be breached.
You may say this is a bit like the perforation on a toilet roll, and they shear anywhere but along the perforation! but nevertheless it might be an idea to consider.
Ideally, if it were possible to engineer it strong enough, you would have a spring loaded hinge down the keel, so that it would bend sideways and snap back into positon again.
A more likely solution would be to have the fin constructed in two pieces.
A plate of certain strength would join the two pieces. Making sure that the plate fails before the hull deck join might be one way of establishing this.
I can hear you saying, isnt it better to have the strongest structure rather than creating a deliberate weak spot.
But we see that we cannot create a fail safe structure...Hence....

 

I don't want to start a flame war ... but ...

What I get from this thread is that faster, higher performance boats are the ones dropping keels and more traditional designs don't have this problem.

It makes a good case for fast boats not having keels. It seems that the capsize rate of multihulls is going down as designers and sailors have more experience. At the same time, fast monos are getting more prone to failure. A keel-less mono is not much better off than a capsized multi.

The failures in cruising boats that use fin keels are inexcusable. Where is the need to compromise FOS on a non-racer?

 

Fair enough. I would probably refuse anyway. Unless I could make it so strong that it would be nearly the last thing on the boat to fail. I hate sitting in court.

 

Same with those pesky racing motor cars. One would think with their multi-million dollar (or Euro) R&D budgets they would get things right. Yet somehow many more people are killed and injured every year in motorsports than in racing sailboats.

By the way, there are many instances of "more traditional designs" having issues, but somehow they get glossed over more easily because they are not part of newsworthy international events.

 

Then you should not design anything for anyone. The designer cannot control many steps in the process, including, but not limited to, construction, purchased parts, and assembly.

Regardless of where the issue originates, the name of the designer is associated with the incident.

 

Hey Paul, do you really want to compare the efforts made through rules and inspections in motor racing in an effort to increase safety to the equivalent in racing sailboats? I could make a statement that the number of people that die in motor racing at under 20MPH are close to zero. I could also point out that if sailing had the equivalent of the F1 drivers union, canting keels might have never left the dock. I don't think you want to go there.

That was not the point. I just observed that there seems to be a pattern. If that perception is wrong, address that. Don't fly off the handle and avoid the question.

Pointing out that there are many instances of failure in traditional designs does not help the case for ballasted keel monos being safer than multis. What it says to me is that the standard of design and construction of sailing boats is low and has not changed much for the better.

I've gone 'round with people time and again about a need for some standards and enforcement of those standards and the idea seems to alienate most people involved with boats.

Do you agree that there is a problem? If you do, what solution do you propose?

Cheers,

Randy