Keels and Keels Again!

These were the news on Rising Farrster's tragical accident, also losing her keel in 2001:
http://www.guardian.co.uk/uk/2001/apr/03/wales?gusrc=rss&feed=fromtheguardian

From the Coroner report:

"The primary cause of the failure was inadequate hull shell thickness in way of the keel washer plates.

The 1986 revision of the ABS guide does not properly account for the shear loads at the edge of the washer plates in the case of Rising Farrster. In fact the 1986 ABS required minimum hull shell thickness of 6.8 mm is only 37% of the 18.5 mm of thickness required to produce a safety factor of 2 on shear stress in way of the washer plates.

The agreed to as built shell thickness of 5.5 mm is 1.3 mm thinner than the ABS approved laminate of 6.8 mm, or 30% of the 18.5 mm of thickness required to produce a safety factor of 2 on shear stress in way of the washer plates.

The 1996 (sic 1994?) version of the ABS guide does not properly account for the shear loads of the washer plates in the case of Rising Farrster. To comply with the later revision, the hull shell laminate in way of the washer plates would have been required to be a minimum thickness of 27 mm."

http://www.sailing.org.au/default.asp?Page=6916

Cheers.

 

Also one Schock 40 lost her canting keel : http://en.wikipedia.org/wiki/Canting_keel

 

Guillermo,

As the keel drops away, rather than jettisoning the mast by explosive (?) detonation, how about two floats emerging immediately from either side of the hull to enable the vessel to stay upright? It would then be possible to continue the voyage and possibly, in more comfort.

This rather begs the question, why not two hulls and no keel? Problem solved.

As you know, I love two hulls. BTW, nice to see the picture from Vigo.

Best wishes,

Perry

 

That system already exists. A Galician invention named "Kafloat". See: http://www.kafloat.com/

On the other hand, we'd probably do not need to blow away the mast at all (at least not all of it!), but just mounting one or more sea water ballast tanks at the bottom of the boat, usually in void condition but authomatically opening to let sea in when the keel drops away, to improve stability. Which brings the question of why do we need at all to weaken keels to break at a certain section. Just let them behave as poorly as they they do now, damaging the hull when broken, but building a watertight compartment over them which would act as a ballast tank.

Cheers.

 

And why not three (retractable) hulls...? http://www.youtube.com/watch?v=oh4q2bt61EY

Dragonfly 35, European Yacht of the Year, multihulls category, 2008.
http://www.multihullsolutions.co.uk/Dragonfly_35.html

Cheers.

 

Guillermo,

Now that trimaran is nice. There's been a thread on the forum about trailer trimarans, but the Dragonfly is just delicious. Reminds me of Porsche cars. The Herr Doktor stuck the engine in the wrong end of the first car and his company has been years trying to make the things safe. They did a great job, but the one I'd like has 4WD.

So it is with the Dragonfly, fold the wings, so it'll dock and solve the problem of paying 1.5 times the marina fees for multihulls. Excellent news.

Perry

 

I'd love that Tri for coastal cruising.


Back to keels..........

I think these extreme designs are an engineering nightmare it is very hard to make such a configuration truly robust. It is also hard to properly verify the structural integrity with non destructive testing and people delude themselves if they think a visual inspection is adequate.

However it is great to see this TP52 come in without it’s keel. Very lucky indeed that the sea conditions remained quiet , looks like the bolts fatigued and I’d like to see a picture of the fractured ends of them. Fatigue is considerably accelerated when the material is wet and normal SN curves do not apply. Bolted connections can be tricky. But only two bolts ?

Following on from previous inadequate design and or build:
I don’t know if we mentioned this one:
Was it 1995 that Coyote killed Mike Plant in the Atlantic when the bulb separated from the strut. The bulb was attached by bolting through the composite foil end into an encapsulated backing plate. The backing plate sheared the composite, unfortunately the boat was operating in heavy weather so it would have inverted very quickly as did the boat in my last post in this thread.

From a marine engineering view the solution is to design more robustly for a higher FOS or very carefully and thoroughly design and build to stringent quality control and to regularly inspect, even replace many critical components after a given operational life, after grounding and after adverse weather encounters. Most teams are too strapped for cash to do this.
If everybody would be happier with a more robust keel strut and attachment and it stopped the failures then there is good reason to regulate this, if a robust keel design is slower because of slightly higher form and WSA drag then what chance does it have at the design stage? It’s a shame that when most other aspects of ULDB racers are adequate to the task that keels continue to be a common and sometimes fatal flaw. This when the solution is so easy and simple, costing little in way of performance but requiring regulation to level the playing field.

You can expect most failures in higher stress situations, that means heavy weather. The likelihood of the vessel inverting within seconds in such circumstances is very high considering the loss of RM and the massive reduction in roll gyradius along with the stimulus of waves and wind. I think the survival of this vessel is a very rare event.

Yachting and racing fatalities would be considerably higher without the effective SOLAS services so I think it a fallacy to claim that minimal deaths means there is not a safety problem.

I was reading an article recently where the author was asking whether we consider keel loss an acceptable risk in ocean yacht racing and whether that is a good attitude. I’ll see if I can find it.

Cheers

 

From: http://www.sailing.org/22626.php

"The ISAF Offshore Committee has highlighted the safety concerns relating to the growing number of keel failures and are investigating amendments to the ISAF Offshore Special Regulations to help improve safety standards.
The spate of recent keel and hull failures has highlighted the need for yacht designers, boat builders and owners to check their yacht structure and take steps to ensure such structural problems stop.

Careful design, build and maintenance of keels and keel attachments are essential as to lose a keel can be catastrophic with loss of life.

At the 2007 ISAF Annual Conference last November, in response to recent design and build failures, the ISAF Offshore Committee appointed a working party to review the requirements for racing yacht design and build as part of the ISAF Offshore Special Regulations.

Under the existing regulations, yachts racing in Category 0, 1 and 2 should be constructed to one of the following three standards:

- the EU Recreational Craft Directive for Design Category A

- the ABS Guide for Offshore Yachts, approval for yachts under 24 metres withdrawn some years ago

- the newly approved International Standard for yacht structure - ISO 12215

The working party has now agreed that, in future, only the International Standard ISO 12215 shall be used for evaluating structure in the ISAF Offshore Special Regulations and is currently considering the implementation of a building plan review scheme to begin mid-2009 at the earliest. "



I find interesting that differentiation between the Recreational Craft Directive and ISO 12215, as the first relates to the second.
Even more interesting is to know ISAF shall use a norm yet under validation....(??)

Cheers.

P.S. Looking for more info I've found it seems ISO 12215-6 has already been ratified by the CEN in March 2, 2008. Anyone can confirm this?

 

Here's a sensible article too.

by Julian Everitt NA. Sept 2007

Keels falling off racing yachts seems to be becoming an almost acceptable ‘event' in offshore racing. Over the past two years, five yachts, and that is not including high profile, high risk Open 60s, have suffered catastrophic structural failure resulting in the loss of the keel, capsize and the death of eight people.

Back in the heyday of IOR, when design parameters were being pushed to the limit, the joint area between keel and hull got smaller and smaller. I remember at the time writing a paper for the International Technical Committee, who oversaw the development aspects of the rule, that there should be minor rating adjustments to help curb this potentially dangerous development. But in those days, tiny attachment areas were offset by the fact that the structure of the hull in the keel area was immensely strong as weight in this area was an advantage.

Now, however, with the drive to put as much weight as possible in a bulb, structure is being removed from the hull itself to a dangerous degree to allow as much weight as possible to go into the keel. This might be acceptable in a one-off, inshore boat that is built in highly controlled conditions, but is totally unacceptable for an offshore boat and for any production boat. So why are these failures happening? Enquiries have led to talk of technical failures, but actually it is a failure of common sense. Engineering has become a buzzword in yacht design. It's a good thing, of course, to calculate outcomes, but there are a couple of major random factors that influence boat safety. One is the unpredictable nature of the environment and the other is the misuse of the materials that modern yachts are built with. In production yachts it is simply not practical to build to fine tolerances. There are too many production shortcomings in the process of yacht building. The answer, throughout yacht design history, has been empirical. In regard to keel structure you have to imagine the worst scenario, design to it and then triple the answer. Saving weight in the middle of the boat may seem like a good idea to get a few more kilos into the bulb, but it might just kill you.

julianeveritt@everittdesign.co.uk

 

Guillermo
Sorry I missed your post. I haven't got ISO 12215, do you know if it addresses the keel structure well? Do you think keel designs would really be more robust under these design guidelines ?

Cheers

 

I agree - It seems so obvious - It just needs to be a strut - not necessarily the full keel structure coming through the boat.

Instead of the moments being dissipated in a hull width of a foot or so (or less - looking at some of the breakages) the moments are dissipated over the hull bottom to deck height of 6ft or more.

(I've just come back to add this bit)
That is the way aircraft do it after all - they don't attempt to carry the loads though the fuselage/wing root join

It would add some kilograms - but not a lot.

A couple of Australian boats do it that way - Inglis - monster fast boats.

With one of his bigger ones he integrates the strut with a bulkhead.

Went aboard a couple of times to do some varnishing.

Michael Storer

 

MikeJohns,

Hope this helps. One can but hope the keel is included.

http://www.ibinews.com/ibinews/ebb/tech_10.html

Pericles

 

These boats are big enough to make interior space a non issue. Thus the simplest way to ensure a keel doesn't fall off is to run it right thru to the deck to give it a two point loading instead of trying to attach it strongly enough to just the hull surface around it.

 

Mike,
I attach a couple of documents on ISO 12215-5 but I do not have here ISO 12215-6 (which has to be used jointly with ISO 12215) where keels' structures details are ruled. Be careful as the attached document on the norm is an old draft and not the final thing.

I have not been using ISO 12215 for scantling work for the time being, but some Class Societies' Rules instead, waiting for the final ISO thing as some concerns had arised on its adequacy while in the validating process. So I do not have experience with it.

Now I have to get the harmonized norm whenever it becomes available (it seems to have been ratified already, but it is not yet published as harmonized) and begin to use it, cross checking it with our habitual methods.

Cheers.

 

Thanks Guillermo, Perry.
It will be interesting to see this 12215-6 later.

Brent
The problem is that racing performance drives this type of design and average course speed is linked to putting every possible ounce of the total fixed displacement in the bulb. Without rules a soundly built fast boat will tend to be a fraction slower than a design that pushes the envelope close to failure.

Racing is about winning, and racing designers are pushed into poor or very marginal design practices in order to remain competitive.

cheers