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Author Topic:   Twin Engine Statistical Analysis
chopbuster posted 08-30-2004 11:11 PM ET (US)   Profile for chopbuster   Send Email to chopbuster  
This is for all the Engineer/pocket protector types out there :)

What are the statistical probabilities of any given new single engine system (failure vs reliability) and any new twin engine system.

Plotman posted 08-31-2004 09:03 AM ET (US)     Profile for Plotman  Send Email to Plotman     
Well, if you assume that with any new engine, there is a 1% chance of non-fuel related failure (eg, water in the fuel, which will get you either way) on any given outing, then with a single engine you have a 1% (1 in 100) chance of having to be towed in.

With twins, using these same odds of failure, you have twice the liklihood (a 2% chance) of having a problem with ONE or the other of your engines, but obviously you still have the other engine to get you home. Your chance of having BOTH engines go out during the same trip, leaving you dead in the water, is 0.01%, or 1 in 10,000.


P.S. I happen to be wearing Shorts, Tevas and a T shirt to work today - no pocket for the pocket protector :)

Louie Kokinis posted 08-31-2004 05:52 PM ET (US)     Profile for Louie Kokinis    

Shouldn’t we take the odds of catastrophic failure due to hitting debris into the equation :)


Jerry Townsend posted 08-31-2004 06:09 PM ET (US)     Profile for Jerry Townsend  Send Email to Jerry Townsend     
Plotman - OK - now put ALL of the other failure probabilities together.

Chopbuster - a direct answer to your question is not possible because there are many different components on an engine that can fail and they may differ from one engine manufacturer to another. Each engine manufacturer may (though I would doubt it) do a failure analyses on their engines. The reasons are that such analyses requires a lot of calculations which costs money and time and also, should an engine fail, the result is typically not a significant impact. In fact, there are several computer programs designed for failure probability analyses. --- Jerry/Idaho

chopbuster posted 08-31-2004 08:24 PM ET (US)     Profile for chopbuster  Send Email to chopbuster     
Thanks for the feed back guys. I can only imagine what the impact would be on sales were the O/B engine Mfgs. to release such data through their marketing Depts.

" Buy our engine , theirs will statistically fail before ours"

jimh posted 09-01-2004 08:34 AM ET (US)     Profile for jimh  Send Email to jimh     
My unscientific analysis suggests that failure could also be caused by common elements outside the engines, such as fuel and batteries.

Contaminated fuel can affect both twin or single engine boats. The outboard boat that has separate fuel tanks is rare. Usually there is one tank, and perhaps redundant fuel pick ups, filters, primers, and hoses. Perhaps having separate tanks would increase reliability. Or would all the extra plumbing tend to increase risk of failure?

Battery failure will disable most modern engines Many boats already have dual batteries as a hedge against this.

holiberry posted 09-01-2004 11:09 PM ET (US)     Profile for holiberry  Send Email to holiberry     
i have been out in the gulf quite a few miles before and came in on one engine a few times. don't know the scientific probabilities but, slice it and dice it as you would, two are better than one, when you put all equations in the mix. can't put a price on one engine stalling and just adjusting the trim tabs and lifting the bad one out of the water and keep going. good feeling, for what it's worth.
daverdla posted 09-03-2004 07:47 AM ET (US)     Profile for daverdla  Send Email to daverdla     
We design a fair number of computer rooms. We worry about failures, just had a brand new UPS fail on it's shake down cruise. One big concern is the single point failure that takes down everything. Jimh hit the nail on the head. It's the external components that will probably cause problems and those problems may shutdown both engines. A common fuel source, shared batteries, etc. If I took the trouble to have two engines, I'd make sure that batteries and fuel were independent. Oh, I'd also put one engine on the bow:) Physical separation of critical components is also a good idea!


chopbuster posted 09-03-2004 10:09 PM ET (US)     Profile for chopbuster  Send Email to chopbuster     
You did post "I'd put one engine on the bow" right?

Chuck Tribolet posted 09-03-2004 11:29 PM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
I've got a single. It's got maybe 500 days on the water.
It's brought me home every time. I can think of three field
repairs I've had to do. Two were fuel pickup problems at the
tank end, one was a broken steering cable.

If I had twins: the fuel pickup problems would have gotten
both engines if there were a single pickup, one engine if
there were dual pickups. The steering cable would have
gotten both engines.

And one time I needed a jump start at the dock as I was
leaving. The boat had been sitting for six weeks of nasty
weekend weather.


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