Single vs Twin: It's Baaaaack!

Engine failures occur at least twice as often with twins compared to single engines. Highly-exposed shafts and propellers also increase the odds of failure.

Mark wrote;
"Engine failures occur at least twice as often with twins compared to single engines. Highly-exposed shafts and propellers also increase the odds of failure." Yes but when one fails you usually have one left. One engine pushing the boat smartly along. Actually I think more than twice as often but the odds of getting home on one's own power are still FAR better.

manyboats said:

Mark wrote;
"Engine failures occur at least twice as often with twins compared to single engines. Highly-exposed shafts and propellers also increase the odds of failure." Yes but when one fails you usually have one left. One engine pushing the boat smartly along. Actually I think more than twice as often but the odds of getting home on one's own power are still FAR better.

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I don't disagree. But then, at least half the time twins come limping home on one engine, the single-engined boat didn't experience an engine failure.

markpierce said:

But then, at least half the time twins come limping home on one engine, the single-engined boat didn't experience an engine failure.

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Having twins, and no engine failure in 3 years of ownership , don`t agree with the first part. Seatow is happy, fees and no tows.
We never had an engine failure with the previous single engine boat either.

But I think what you are saying is "if you have only one engine, you really look after it".

BruceK said:

But I think what you are saying is "if you have only one engine, you really look after it".

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Always the best plan 'A' that's for sure.

BruceK said:

But I think what you are saying is "if you have only one engine, you really look after it".

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Yes.

markpierce said:

Engine failures occur at least twice as often with twins compared to single engines. Highly-exposed shafts and propellers also increase the odds of failure.

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How'd you dream up that one? If I count sailboaters, we know a lot more people with single engine boats who've had to shut an engine down--- you included and that with a brand new boat to boot--- than we know twin engine boat owners who've had to shut one down.

And in all cases where the single engine boater was going somewhere (as opposed to entering a slip or something) they drifted around until help came and then they went home on the end of a rope. The few people we know with twins who had to shut one down simply kept going on the other engine.

And engines themselves rarely fail. An engine shutdown is almost always caused by a supporting system. In our case it's been raw water cooling problems. In your case your new driveline fell apart. Had you been out in the middle of the bay it would have been a rope tow for you. Other causes are clogged filters, air leaks in fuel lines, transmission failures, and so on.

So while the statistical chances of an engine shutdown on a twin are twice as high as on a single, I suspect this is not born out in reality. In reality I bet the numbers of shutdowns are about the same on both sides.

And if you want to talk about who continues on to their destination under power and who drifts around until someone shows up with a towline in the event of an engine shutdown, the odds are all in the twin's favor. Personally, I'll take a theoretically higher risk of having to shut one down but reduce or eliminate the risk of drifting onto the rocks over the near certainty of hoping that a tow rope arrives before I get carried into something that isn't water.

Despite this, you fly in a single-engined airplane, even though one can't anchor in the air.

With two engines, the likelihood of any one engine to fail is twice as likely as any single engine to fail. Try to contradict that.

Anyway/meanwhile, my guardian angel has been very attentive, making sure my propeller shaft fell apart while in the berth.

Oh, did I not mention this boat has sails?

markpierce said:

With two engines, the likelihood of any one engine to fail is twice as likely as any single engine to fail.

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Sorry but that's wrong. An engine is an engine and the likelihood of an FL120 in a single engine boat failing is exactly the same as the likelihood of an FL120 in a ten engine boat failing. An engine doesn't "know" it's in a single or a twin or a ten engine boat.

Because there are two engines in a twin, each with exactly the same odds of failing, the chances of experiencing an engine shutdown with that boat are doubled.

But your notion that an engine in a twin is more likely to fail simply because it's in a twin engine boat is statistically baseless.

And while statistically the chances of an engine failure in a twin are doubled because there are two engines, the chances of BOTH engines in a twin failing are so low as to be almost irrelevant (unless you're talking about the Bounty). So the reality is that the chances of having one engine fail in a twin is exactly the same as the chances of having one engine fail in a single.

The difference is that when that one engine fails in the single, you're done for the day unless you can get it going again. But when that one engine fails in the twin, you still have another engine and so can continue on your merry way.

Most here are w single engine boats and also most say they prefer singles. But the popularity of the get home talk suggests that there are a lot of skippers here that don't trust their single engine boats and would probably be better off w a twin. I'm in that category but would be hard to change. And to have a single, claiming singles are best and to talk about all the single engined ships and airplanes and also talk a great deal about getting to safety when the single engine quits or can't deliver probably is a bit hypocritical don't you think?

markpierce said:

Engine failures occur at least twice as often with twins compared to single engines. Highly-exposed shafts and propellers also increase the odds of failure.

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I'd like to see your proof of this statement. I can not find any insurance claims data that supports your statement- and I see all the claims that come into our office.

IMO there is no statistical evidence to support this statement.

I have twins in my sportfish and they are brand new, yet I have limped in twice; once because a transmission seal blew and the other was a water hose burst, niether one was the engines fault. I fly jets for a living and have had 3 engine failures in my career, no big deal. Redundancy; as in ETOPS (extended twin ops) allows jets to go on much longer routes like over an ocean without any concern. I wouldn't fly in a single engine airplane for any reason. I did however buy a single screw trawler because; fuel economy for the long loop type cruising we want to do, running gear protected by the keel, more room in the engine compartment, less maintenance costs, and quieter, to name a few reasons. I did buy an ESI fuel filtering and polishing system and it was almost as much as the diesel! But, I want to provide the cleanest freshest fuel possible to eliminate a common problem. I must admit, I have looked at wing engines and hydraulic PTO's that run off the genny to run a Wesmar shaft system to "get home". These systems are VERY expensive; you could pay a lot of Sea Tows for one of these systems.
This argument will never be settled, but I do think about it often...and I enjoy listening to it.

Pau Hana said:

I'd like to see your proof of this statement. I can not find any insurance claims data that supports your statement- and I see all the claims that come into our office.

IMO there is no statistical evidence to support this statement.

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That's because no one tracks the number of engine failures accurately...because there's no requirement to report them for recreational craft (on the commercial side, theoretically there is).

The assistance towing companies may be able to take a stab at it but it could still be wildly inaccurate. Insurance companies would only know if a claim arose which would be a tiny number of the incidents.

Lol um errr whut??!

Blue Heron said:

Lol um errr whut??!

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referencing my post?

psneeld said:

That's because no one tracks the number of engine failures accurately...because there's no requirement to report them for recreational craft (on the commercial side, theoretically there is).

The assistance towing companies may be able to take a stab at it but it could still be wildly inaccurate. Insurance companies would only know if a claim arose which would be a tiny number of the incidents.

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There is no requirement to report engine failures, whether it be commercial craft or recreational craft. However, machinery claims are the ones most often reported, as its no small chunk of change to repair a marine engine- be I gas or diesel. Based on those claims, especially from commercial operators, is where I get my info. Singles, twins, or triples- engines fail, and there is no more likelihood of a multi-engine vessel failing than a single engine vessel.

The above sounds more like conspiracy theory with no basis in reality.

Pau Hana said:

Singles, twins, or triples- engines fail, and there is no more likelihood of a multi-engine vessel failing than a single engine vessel.

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Nobody has said that! I said that two engines have twice the possibility of any one engine to fail as a single engine to fail.

No the OP

Blue Heron said:

No the OP

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Never mentioned all engines failing. Some people just like to bring up red herrings for the sake of argument, even after I clarified the OP.

markpierce said:

Nobody has said that! I said that two engines have twice the possibility of any one engine to fail as a single engine to fail.

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That's still an irrelevant statistic because when the one engine fails in a single you're through boating for the rest of the day other than as a barge on the end of a line. And while the odds of the one engine in your boat failing are exactly the same as the odds of either of the two engines in a twin failing, the odds of you being left adrift and hoping that a tow arrives in time are almost infinitely greater than the odds of a fellow with a twin engine boat who experiences a failure of one of his engines being left adrift and hoping that a tow arrives.

So the real question is, do you want to be left adrift when an engine has to be shut down or do you want to keep going when an engine has to be shut down? That's the only question worth asking as far as I'm concerned.

Got it, Marin. Didn't I say that many posts ago?

While I have no statistical evidence to back it up, from decades around sport fishing charter and private boats, it seams that those in general with twins seem to be less diligent about engine maintenance because they know that there is always a second engine to get them home. Those of us with singles tend to be more preventative maintenance oriented for the obvious reason. Put another way, the guy with twins can wait till he looses an engine before rebuilding; the guy with a single plans a rebuild in the off season. While this doesn't address whether to have a single or twins, I believe a boat with twins on average will have far more than twice as many failures as one with a single engine.

Ted

Agreed. Borne out with experience as well.

OCD says;
" I believe a boat with twins on average will have far more than twice as many failures as one with a single engine."

Probably not "far less" but agreed ... less.

But in order to be unable to make significant headway he'll need to have a 2nd engine failure on the same day ....... highly unlikely.

Why are we talking about this? It's because single engined skippers are afraid of having their engine quit and being dead in the water. No other explanation for it.

O C Diver said:

While I have no statistical evidence to back it up, from decades around sport fishing charter and private boats, it seams that those in general with twins seem to be less diligent about engine maintenance because they know that there is always a second engine to get them home.

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I don't agree with this at all. Everyone I know personally with a twin engine boat is just as diligent--- and sometimes even more so--- about engine maintenance as the people we know with singles. A person who's sloppy about engine maintenance is going to be that way no matter how many engines his boat has.

markpierce said:

Got it, Marin. Didn't I say that many posts ago?

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Um.... no.

Mark, you starting this post was just plain obtuse. You just did it to yank chains, and because you got bored - maybe because we don't have a good anchor stousch going on at present. You got exactly the replies you expected to get, didn't you...?

markpierce said:

Engine failures occur at least twice as often with twins compared to single engines. Highly-exposed shafts and propellers also increase the odds of failure.

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Actually... they happen at exactly the same rate statistically. After all... it's just two singles right?

BUT... the odds of having the same failure, with the same disabling effect as by orders of magnitude less likely on twins.

Same goes for airplanes. Lose one on a twin... execute emergency procedure and head for an alternate destination. Lose one on a single engined plane... execute ditching / emergency landing.

Plus... on a boat, there's the idea that you have spares for every part of the critical engine (from the disabled engine).

I love this debate, but the answer is simple.

Anybody thats ever experienced an engine failure was either glad they had twins, or wished they had twins.

As to twins being twice as likely to experience failure, well thats true I suppose.

As to twins ever experiencing a total loss of propulsion power, well thats extremely unlikely and we all know it.

Yep. Operating with 5 9's of reliability is pretty common these days.

The key is thinking of twins more as a pair of singles. Either motor will experience 99% of it's failures independent of the other... same goes for boats.

Unless you're talking fuel for the most part... there is very little that'll take both plants offline simultaneously. Even those things that will, they affect a single engine configuration with just as dire consequences.