123 page accident report on keel failure

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BurnitBlue

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All my previous boats had encapsulated ballast keels. I now own an M346 and was concerned about the reports of bolted ballast keels falling off. So after the latest Vendee incident I went google mad for a week to collect the considerable amount of information that is available about bolt on keels.

I came across this 124 page scientific report commissioned by the Texas University that owned the yacht Cynthia Woods investigating the reason the keel fell off with fatal results. Cynthia Woods was a production 38 foot cruiser racer.

For those of you who like to read accident reports this one is a comprehensive investigation into the keel bolts and hull structure if this yacht and it pulls no punches. Link below hope it works.

www.tamus.edu/.../Appendix-E-Dobroth-Design-Science-Report.pdf

Edit : Oops this link does not work see post below from saraband
 
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the link has been changed BlueTwo. Any pointers pls ?


EDIT

try this ?

http://www.tamus.edu/assets/files/c...woods/Cynthia-Woods-Report-SIAD-OGC-FINAL.pdf


EDIT 2
This cannot be right !

"Using the ABS Guide standard, the hull fiberglass laminate for the S/V Cynthia
Woods should have been at least 3.11” thick." Page 2 of the report.

On a 38ft yacht ? !!!

EDIT3. OK panic over. That figure is to take account of the narrow backing plates as installed.
 
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sarabande said:
the link has been changed BlueTwo. Any pointers pls ?


EDIT

try this ?

http://www.tamus.edu/assets/files/c...woods/Cynthia-Woods-Report-SIAD-OGC-FINAL.pdf


EDIT 2
This cannot be right !

"Using the ABS Guide standard, the hull fiberglass laminate for the S/V Cynthia
Woods should have been at least 3.11” thick." Page 2 of the report.

On a 38ft yacht ? !!!
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Your link appears to be the same basically but the pdf file I downloaded I got from Google and may be more comprehensive as it was sourced direct from the Naval Architect who directed the investigation.

Regardin laminate thickness, that was not the hull laminate but the keel stub laminate where the keel bolts pass through. Cynthia Woods was only half an inch thick. The sister ships have been grounded because of this.

Edit I cannot copy the google link netter to google yourself asking for "keel bolt dimensions" Sorry
 
The report certainly exonerates the students of Texas A&M Uni who carried out repairs, normalises hitting the putty, and lays the blame on the build - but then it was commissioned by the university who may just have been fearful of law suits. (When did I become so cynical?)

Would a British surveyor have condemned the design? I would hope so but ......
I guess the owners of soapdish and fin boats will be taking a look under their floorboards.
 
Looking under the floorboards won't do much good in relation to the laminate thickness, but would tell you something about the backing plates.

The RCD requires hulls to be built to the ABS guidelines as well. In the case of the boat in this report it was not built to the guidelines, so difficult to translate that experience to other boats that are.

Does demonstrate however, that badly built boats that do not comply with accepted standards run the risk of failure - but whats new?
 
My keel has a step in the top edge to allow a better fixing & provide fore & aft resistance + a bilge sump

Scan0003-2.jpg
 
By the way. My google searches have accessed many keel bolt reports.

After feeding my M346 specs into some design reports I am now OK on the engineering of my boat as (according to the Don Casey report) my boat has bolts able to support 420,000 pounds ballast which actually is only 4,500 pounds weight. Don Casey says that to account for dynamic forces due to wave action a safety factor of 40:1 should be made to straight tensile strength. This is 60,000 pounds for mild steel or 80,000 pounds for stainless steel for every square inch of total keel bolt cross section area.

Don't know the keel stub laminate thickness yet but I will find out in Spring when I intend to draw one bolt.
 
BlueTwo said:
By the way. My google searches have accessed many keel bolt reports.

After feeding my M346 specs into some design reports I am now OK on the engineering of my boat as (according to the Don Casey report) my boat has bolts able to support 420,000 pounds ballast which actually is only 4,500 pounds weight. Don Casey says that to account for dynamic forces due to wave action a safety factor of 40:1 should be made to straight tensile strength. This is 60,000 pounds for mild steel or 80,000 pounds for stainless steel for every square inch of total keel bolt cross section area.

Don't know the keel stub laminate thickness yet but I will find out in Spring when I intend to draw one bolt.
Click to expand...

The keel bolts are almost always over sized for the application which could be a bad thing as some folk look up the torque for the oversized bolts in engineering data books and then use this figure to tighten keel joints.

This does not take into account the lower compressive strength of laminate and so can result in crushing damage. I have seen keel stud nuts on a boat driven half way through the laminate on a 35 ft boat by overtorquing. The backing washers were standard sized washers for the nuts used.

Some boats may suffer a small narrow keel joint footprint or thin laminate at the joint or insufficient structure to carry the keel loads out into the surrounding hull or in fact all three as in this case.

Your mind will probably be put at rest when you sight the laminate thickness however do not expect 3" as I doubt if your keel is as heavy and as long as that on the boat in question so even ABS rules would call for much less.
 
Bilgediver said:
This does not take into account the lower compressive strength of laminate and so can result in crushing damage. I have seen keel stud nuts on a boat driven half way through the laminate on a 35 ft boat by overtorquing. The backing washers were standard sized washers for the nuts used.

Some boats may suffer a small narrow keel joint footprint or thin laminate at the joint or insufficient structure to carry the keel loads out into the surrounding hull or in fact all three as in this case.

Your mind will probably be put at rest when you sight the laminate thickness however do not expect 3" as I doubt if your keel is as heavy and as long as that on the boat in question so even ABS rules would call for much less.
Click to expand...


Thanks for that :mad: I was going to enjoy the first good nights sleep since I bought the boat.

Now I have to wait until spring because the boat in the report had almost the same ballast keel weight. However, the dynamic forces on that boat must have been higher because the keel is deeper with a bulb right at the bottom while the footprint looks less.
 
BlueTwo said:
Thanks for that :mad: I was going to enjoy the first good nights sleep since I bought the boat.
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Don't lose a moments sleep over this. Your boat is way overbuilt. As you will have discovered almost all the keel problems are on boats built for racing or where limits have been pushed. Heavy grounding is the potential problem for cruising boats and usually shows in deformation of the hull aft or forward of the keel area rather than the keel becoming detached.

Encapsulated keels are not necessarily trouble free. Was looking recently at a product from a very well known Swedish yard where the bottom of the encapsulated keel had been damaged through either grounding or being dropped, letting water into the ballast. To add to the owner's woes the design had a moulded in diesel tank above the ballast which had also ruptured, needing major repairs and reinforcement. So all owners of encapsulated ballast keel boats should crawl underneath to check that it is sound!
 
This is an exceptionally important report and may help engineers keep up with the huge number of keels which fall off every season.:rolleyes:
 
Thanks for the report.I couldn't believe how narrow those washer plates were.Good old common sense would have dictated much wider ones.The keel had been out for repairs prior to the accident and the laminate thickness would have been evident then.I would have immediatly beefed up the laminate had it been my boat.The connection of the bottom laminate to the floors also appears to be very thin.I'm amazed they didn't rectify the problem especially in such a high strung design. The faults are so glaring that there's no need for complicated mathematical analizes to conclude that the boat was dangerously under built.
 
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BlueTwo said:
By the way. My google searches have accessed many keel bolt reports.

After feeding my M346 specs into some design reports I am now OK on the engineering of my boat as (according to the Don Casey report) my boat has bolts able to support 420,000 pounds ballast which actually is only 4,500 pounds weight. Don Casey says that to account for dynamic forces due to wave action a safety factor of 40:1 should be made to straight tensile strength. This is 60,000 pounds for mild steel or 80,000 pounds for stainless steel for every square inch of total keel bolt cross section area.

Don't know the keel stub laminate thickness yet but I will find out in Spring when I intend to draw one bolt.
Click to expand...

When you broach, the keel may be almost horizontal.
The upper keel bolts will be in tension many times the weight of the keel, as they only have a very short lever arm compared with the CofG of the keel being a metre or more 'down' the keel. If your keel is say 6 inches thick, the load on the upper bolts could be more than 10 times the keel weight.
Only half the keel bolts are doing anything much in that circumstance.
You cannot be sure the load will be shared equally.
So I reckon your safety factor is a lot less than 40:1

The loads on this part of the hull are a bit scary, but that's why we have mech eng's with computers I suppose.
 
galadriel said:
This is an exceptionally important report and may help engineers keep up with the huge number of keels which fall off every season.:rolleyes:
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Agreed, just like every report that helps engineers keep up with the huge numbers of wings that fall off aeroplanes every month <mutters engineer, about to have a Victor Meldrew moment> and we never read.
 
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Camelia said:
Agreed, just like every report that helps engineers keep up with the huge numbers of wings that fall off aeroplanes every month. Mutters engineer.
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I think the issue is that aeroplane wings bash into the ground a lot less often than yacht keels? And aeroplanes are built under very strict quality control, so what is built is actually what was intended.
 
galadriel said:
This is an exceptionally important report and may help engineers keep up with the huge number of keels which fall off every season.:rolleyes:
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Was that a tongue-in-cheek remark? Obviously huge numbers of keels do not fall off annually.

The Uni of Texas report is a face saving exercise written by in-house lawyers and generic HQ admin types. It is an attempt to exonerate the institution by countering the independent US CG report that concluded bodged cut-price in-house repairs to a grounding the previous year contributed to the keel failure.

The UNI's response plan detailed in the conclusion of the report is laughable, more staff posts created to enforce new processes, none of which would have prevented the disaster.

All that was needed was one knowledgeable person to look at the keel mounting in the bilges and exclaim "my god we have purchased a turkey" and then recommend a $5000 reinforcement upgrade. They had already blown $20,000 on a tickbox post purchase upgrade programme.
 
awol said:
normalises hitting the putty
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They cracked multiple transverse floor beams in the grounding, hardly a routine putty event. If you read around the saga you will find that the inaugural voyage on the yacht with some VIP included a grounding and resulting disapproval of the yacht ownership group within the university. As a result they were motivated after the second more serious grounding to hush the event up and pursue a cheap in-house fix to avoid a formal insurance claim with associated survey.
 
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