Single vs Twin: It's Baaaaack!

The friendliest place on the web for anyone who enjoys boating.
If you have answers, please help by responding to the unanswered posts.
See posts with no answers
bfloyd4445 said:
lets see, what are the pluses for twins? with luck if one breaks down the other will get you home????? any others???...oh yes, the broken down engine can be used for parts for the one running. That is assuming since it is the same age that the same part dosent crap out on it as well.
Click to expand...


So you can hang with the 'don't get a thruster crowd'?
 
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. Fortunately those who are lucky enough to have a reliable and well looked after twin setup can motor along to their destination while those with singles and without a get home setup are dead in the water - unless of course psneeld is nearby with his onboard warehouse to provide parts or will be gracious enough to tow you in.
Click to expand...

See, all this needed was two posts, how the heck did we get to 500+?
 
Am I wrong?
I'm beginning to think I have a better chance of dying in my single than the drive to the boat....?
 
Tom, Mark,
My post #2 this thread.
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.
__________________
Eric

We really are chasing our tails a bit here.
 
manyboats said:
Yes but when one fails you usually have one left.
Click to expand...

You will always have one left... unless you're talking about a single point of failure common to twins or singles (mutually probable). Therefore, you would leave those out of any statistical comparison (wouldn't matter if you had 10 engines)

That being said... lose AN engine on a single and you are in harms way... lose AN engine in a twin and you have have safe steerage, power and propulsion to get you to anchor, safe harbor or home.

The odds of coming home on the bitter end of a tow line are exponentially less with twins over a single. It's a mathematical certainty.

It's an exercise in risk analysis. Give me the failure rates of any group single point failures (single events) and I can show you the odds of any two happening at once (or one during another). No matter how many they would be astronomical.

Engine shut-down - Oil related - 1:10000 hours
Engine shut-down - Fuel system related - 1:1000 hours
Engine shut-down - Over temp - 1:10000 hours
Tranny failure - linkage - 1:10000 hours
Tranny failure - Catastrophic - 1:100000 hours

... etc

You'll soon see that there are VERY FEW things that would take both plants offline simultaneously. The more independent failures you can think up, the more distant the chance of them occurring mutually.

ie: The odds of losing your 2nd engine decrease to near zero when you lost your first to an independent event. (statistically speaking)

That should fuel the fire for another 10 posts...
 
SomeSailor said:
You will always have one left... unless you're talking about a single point of failure common to twins or singles (mutually probable). Therefore, you would leave those out of any statistical comparison (wouldn't matter if you had 10 engines)

That being said... lose AN engine on a single and you are in harms way... lose AN engine in a twin and you have have safe steerage, power and propulsion to get you to anchor, safe harbor or home.

The odds of coming home on the bitter end of a tow line are exponentially less with twins over a single. It's a mathematical certainty.

It's an exercise in risk analysis. Give me the failure rates of any group single point failures (single events) and I can show you the odds of any two happening at once (or one during another). No matter how many they would be astronomical.

Engine shut-down - Oil related - 1:10000 hours
Engine shut-down - Fuel system related - 1:1000 hours
Engine shut-down - Over temp - 1:10000 hours
Tranny failure - linkage - 1:10000 hours
Tranny failure - Catastrophic - 1:100000 hours

... etc

You'll soon see that there are VERY FEW things that would take both plants offline simultaneously. The more independent failures you can think up, the more distant the chance of them occurring mutually.

ie: The odds of losing your 2nd engine decrease to near zero when you lost your first to an independent event. (statistically speaking)

That should fuel the fire for another 10 posts...
Click to expand...

Only a tiny percentage of the time are you in harms way if you loose an engine and even then most problems with single engines don't shut you down immediately (unless you're too oblivious to see the warning signs...many here have posted they have boated a lifetime and never had a complete failure of an engine while underway...me included...

So ....now what????
 
OK... so then we're talking about an infinitely smaller set of statistical probabilities. That being said... if you're talking about reliability, the numbers CAN be described. BoatUS makes it's living towing boats in. List the things that got them in that situation, the probability of that happening, and you have a model that can be built.

For example: One common one; "Ran the boat out of fuel"

It happens (not to many skilled skippers... but it happens). Call it a 1 in 100,000 hours of operation occurrence and roll those dice 100,000 times. The odds are describable and predictable. Now... roll a new set of dice on a problem that occurs equally infrequently (but still mutually exclusive), say:

For example: "Fouled a prop"

The odds of running out of fuel... and then fouling the OTHER prop... are exponentially improbable. This only expands the model when you add another independent power system.

The business model of BoatUS speaks for itself. It's a very profitable business. Stuff happens out there.
 
SomeSailor said:
That being said... lose AN engine on a single and you are in harms way... lose AN engine in a twin and you have have safe steerage, power and propulsion to get you to anchor, safe harbor or home.
Click to expand...

Oh I don't know about that. There are a lot of boats here with 9.9 high thrust outboards mounted on the swim step to use for trolling salmon. "We came home on the kicker" is a phrase I've heard a few times.
 
psneeld said:
...most problems with single engines don't shut you down immediately....
Click to expand...

Well, from our own experience and from what I have heard on the VHF the single most common thing causing an engine shutdown outside of simply running out of fuel is a cooling problem. This can be raw water system problems--- intake blockage, impeller failure, exhaust hose failure, etc.--- or engine coolant problem-- coolant pump gasket failure, seal failure, bearing failure, etc.

And when these occur, the engine is more often than not done for the day. Yes, a raw water pump can be replaced, an impeller replaced, a coolant pump replaced. But this takes time, tools, and the part, and depending on the conditions may not be something the boater wants to do at that particular moment. A rope tow may be the more viable alternative unless he has a second engine to finish the trip with.

Broken belts, split hoses, and so on are relatively easy to fix (unless one has an FL120 without a spare belt pre-threaded through the cooling hose).

But while I know it happens, we don't know anyone who's had a belt break or a hose split open. But we do know a surprising number of people with singles and twins who have had to shut an engine down to a cooling problem, and it stayed shut down until they got home and had the problem repaired.

In all these cases the ones with one engine finished their run on a rope, the ones with two engines simply kept going.
 
SomeSailor said:
OK... so then we're talking about an infinitely smaller set of statistical probabilities. That being said... if you're talking about reliability, the numbers CAN be described. BoatUS makes it's living towing boats in. List the things that got them in that situation, the probability of that happening, and you have a model that can be built.

For example: One common one; "Ran the boat out of fuel"

It happens (not to many skilled skippers... but it happens). Call it a 1 in 100,000 hours of operation occurrence and roll those dice 100,000 times. The odds are describable and predictable. Now... roll a new set of dice on a problem that occurs equally infrequently (but still mutually exclusive), say:

For example: "Fouled a prop"

The odds of running out of fuel... and then fouling the OTHER prop... are exponentially improbable. This only expands the model when you add another independent power system.

The business model of BoatUS speaks for itself. It's a very profitable business. Stuff happens out there.
Click to expand...

I know their business model as well as their competition...Sea Tow...etc...

Very profitable????...show me the numbers as I'm friends with several franchise owners with several of the different towing businesses. That said, I could probably prove you incorrect in a heartbeat.

It's the side stuff that's profitable....

After 10 seasons of towing...I'm pretty familiar with the different scenarios of why people get towed...(plus 20+ years operational USCG monitoring thousands upon thousands of rescue cases.)

If you can get significant stats out of corporate...would love to see them too....but comparing the general boating population compared to many experienced cruisers would be an insult in my eyes....

And someone alluded to me carrying a boatload of repair gear/spares which isn't correct at all.....emergency repairs to keep going is sometimes ingenuity...not hardware...just like survival situations in general...what's in the mind is more valuable than what's in the pocket.
 
Marin said:
Well, from our own experience and from what I have heard on the VHF the single most common thing causing an engine shutdown outside of simply running out of fuel is a cooling problem. This can be raw water system problems--- intake blockage, impeller failure, exhaust hose failure, etc.--- or engine coolant problem-- coolant pump gasket failure, seal failure, bearing failure, etc.

And when these occur, the engine is more often than not done for the day. Yes, a raw water pump can be replaced, an impeller replaced, a coolant pump replaced. But this takes time, tools, and the part, and depending on the conditions may not be something the boater wants to do at that particular moment. A rope tow may be the more viable alternative unless he has a second engine to finish the trip with.

Broken belts, split hoses, and so on are relatively easy to fix (unless one has an FL120 without a spare belt pre-threaded through the cooling hose).

But while I know it happens, we don't know anyone who's had a belt break or a hose split open. But we do know a surprising number of people with singles and twins who have had to shut an engine down to a cooling problem, and it stayed shut down until they got home and had the problem repaired.

In all these cases the ones with one engine finished their run on a rope, the ones with two engines simply kept going.
Click to expand...

Highlighted is what the issue really is...done for the day would be twin engine mentality...

For a single guy it's about a 15 minute impeller change...a 1 minute use your salt water washdown system to get you someplace safer...pumps rarely fail outright/leak but give many hours warning of failure (and I've run a towboat with a 1/2inch by 1/4 inch hole in the pump for a week till it was fixed)...hoses can be wrapped in seconds...intakes cleared in minutes...

So cooling issues are only "issues" that are a problem if you allow them to be...otherwise a single guy keeps going till it can be fixed properly. But neither the day nor the trip is in jeopardy.
 
I don't disagree with your statement at all, but in all the cases I know of, "done for the day" was the attitude of the single engine boater who had to shut the engine down.

While my sampling is indeed very small, in the 14 years we've been doing this kind of boating I cannot recall a single instance of a single-engine boater we know or know of--- power or sail--- who experienced a problem like a pump failure, raw water blockage, etc. that resulted in the engine having to be shut down who did not opt for a tow to the nearest place where repairs could be made.

So while you are certainly correct in what you say, I am very much inclined to believe that the average recreational boater, when the engine quits or has to be shut down, is on the radio for a tow if they don't have a second engine on board. My belief is certainly reinforced by what we hear on Seattle, Victoria, and Vancouver radio.

Now an experienced Vessel Assist guy like yourself may be able to get them going again when he arrives. But I think the typical boater is like the typical driver--- when everything is working they're fine. But when it stops working, particularly in the case of engines, I suspect the vast majority of them are looking for help, be it a mechanic or a rope home.

This, in fact, may be a big reason why so many boats are twin engine. The majority of boat buyers/owners are probably not interested in becoming backyard mechanics able to jury rig a fix in the event of a propulsion problem. They simply want to shut the bad engine down if it hasn't shut itself down and carry on.

While it not the over-riding reason I prefer multi-engine boats, I admit that if we experience an engine shutdown, I don't want to screw with it. I'll tie off the shaft since we have to and our boat is set up so that it's very easy.

But beyond that, I have no interest at all in figuring out the problem on the spot, coming up with a workaround if there is one, and then effecting the solution. Not in a cramped engine room with the boat bouncing all over hell as it's likely to be, Murphy's law being what it is.

When I let one of our engines get a big gulp of air during a fuel transfer a few years ago and quit I knew exactly what I had done and I knew exactly how to get the engine going again. I've bled our engines plenty of times after filter changes.

But I simply didn't want to do it. The water was rough-ish, we had several friends on board who needed to be home by such-and-such a time, and I simply didn't want to grub around in the engine room bleeding the filters and injection pump. So it was a three minute job to tie off the shaft and home we went.

And from what I hear in talking to boaters we know, that seems to be the prevalent attitude. This forum represents but an infinitesimally tiny fraction of the boaters out there. Most of them, I suspect, don't care why or how their engines run as long as they do. When they don't, they get someone else to deal with it, first by towing the boat home if it only has one engine and second by hiring Acme Marine Diesel, Inc to fix it.
 
Marin said:
I don't disagree with your statement at all, but in all the cases I know of, "done for the day" was the attitude of the single engine boater who had to shut the engine down.

While my sampling is indeed very small, in the 14 years we've been doing this kind of boating I cannot recall a single instance of a single-engine boater we know or know of--- power or sail--- who experienced a problem like a pump failure, raw water blockage, etc. that resulted in the engine having to be shut down who did not opt for a tow to the nearest place where repairs could be made.

So while you are certainly correct in what you say, I am very much inclined to believe that the average recreational boater, when the engine quits or has to be shut down, is on the radio for a tow if they don't have a second engine on board. My belief is certainly reinforced by what we hear on Seattle, Victoria, and Vancouver radio.

Now an experienced Vessel Assist guy like yourself may be able to get them going again when he arrives. But I think the typical boater is like the typical driver--- when everything is working they're fine. But when it stops working, particularly in the case of engines, I suspect the vast majority of them are looking for help, be it a mechanic or a rope home.

This, in fact, may be a big reason why so many boats are twin engine. The majority of boat buyers/owners are probably not interested in becoming backyard mechanics able to jury rig a fix in the event of a propulsion problem. They simply want to shut the bad engine down if it hasn't shut itself down and carry on.

While it not the over-riding reason I prefer multi-engine boats, I admit that if we experience an engine shutdown, I don't want to screw with it. I'll tie off the shaft since we have to and our boat is set up so that it's very easy.

But beyond that, I have no interest at all in figuring out the problem on the spot, coming up with a workaround if there is one, and then effecting the solution. Not in a cramped engine room with the boat bouncing all over hell as it's likely to be, Murphy's law being what it is.

When I let one of our engines get a big gulp of air during a fuel transfer a few years ago and quit I knew exactly what I had done and I knew exactly how to get the engine going again. I've bled our engines plenty of times after filter changes.

But I simply didn't want to do it. The water was rough-ish, we had several friends on board who needed to be home by such-and-such a time, and I simply didn't want to grub around in the engine room bleeding the filters and injection pump. So it was a three minute job to tie off the shaft and home we went.

And from what I hear in talking to boaters we know, that seems to be the prevalent attitude. This forum represents but an infinitesimally tiny fraction of the boaters out there. Most of them, I suspect, don't care why or how their engines run as long as they do. When they don't, they get someone else to deal with it, first by towing the boat home if it only has one engine and second by hiring Acme Marine Diesel, Inc to fix it.
Click to expand...

And that I agree with wholeheartedly...

I would hope the serious cruisers here are a cut above mechanical ability-wise (hopefully light years beyond) the average weekend boater ... and I know the guys who steadily cruise thousands of miles a year probably are..

Believe me...I have an active towing policy and there may come the moment I'm screaming into the radio for them, the USCG, any other boater and my Mommy to come help... but so far...most things that come up are only a PIA...

No show stoppers or even remotely a dangerous situation...so I have to stan on the single for coastal cruising is neither better no worse than twins...just not as much fun when it comes to dock dancing...:D

Hey...after so much time running the single engine towboat and my trawler...I really miss messin' with twins...especially the old boss' refurbished 85' fishing vessel. It was converted to a crew boat for the offshore windmill programs. Would love to get into running that one several times a week...:thumb:
 
I tow / fix and pump out just as many twins a single engine vessels.

Be that from break downs , log strikes, running outa gas etc etc.

The twin / single deal from my experience dont play into most of the poor result's I see and experience.

Just sayin.

But as a guy that owns and operates single engines vessels today this thread has realy cleared things up for me.

When it comes to that choice of single verses twins. :rofl:
 
Marin said:
I don't disagree with your statement at all, but in all the cases I know of, "done for the day" was the attitude of the single engine boater who had to shut the engine down. .
Click to expand...

Well....
I have had to shut down a couple times for over temp issues. My tactic both times was to reduce speed to idle and get to a acceptable depth to drop the hook. Needless to say it's never fun to need to work in a hot engine room. Both times that I have had to shut down it was a directly related to my own haste at not burping the raw water pump after a haul out.. the last time I finally learned my lesson as the blister on my forearm was there to remind me for a few weeks.

I did have the big John Deere quit once rounding Cape Flattery in a rather large sea, a switch to the second Racor and the JD started instantly. Again the fault was my own, I incorrectly put the one Racor back together after a complete removal/cleaning of the unit. Both times within an hour I was back underway.. and on a single engine no less!. I will admit to a SERIOUS pucker moment as the engine quit rounding Tatoosh Island on a trip down the coast to Astoria.
This has had absolutely no effect on my stance that for me a single is the preferred choice.
HOLLYWOOD
 
A while back we listened to conversation between Marine Rescue and a Palm Beach ( smart single engined Oz built cruiser of exceptional design and quality) towing an Etchells sailboat from Broken Bay 20 miles south to Sydney. The single engine had failed, the tow terminated, the Etchells hoisted sails. The Palm Beach was drifting toward the coast, the operator waiting until the water shallowed enough to try setting an anchor. He was calm, with a certain tension. Marine Rescue were an hour away. Fortunately another boat intervened to get a line aboard and tow him to safety.
I`m pretty sure the PB owner would have liked a second engine right then, though it was clearly not the time to conduct the survey. It is remotely possible, but unlikely, 2 engines would have had the same issue simultaneously. Had I posed the question "single or twins?", while he was drifting coastwards, hoping to try to anchor off a lee shore, expecting a 1 hour wait for MR, I think he`d have opted for twins.
 
Last edited:
Marin said:
I cannot recall a single instance of a single-engine boater we know or know of--- power or sail--- who experienced a problem like a pump failure, raw water blockage, etc. that resulted in the engine having to be shut down who did not opt for a tow to the nearest place where repairs could be made.
Click to expand...

I CAN personally relate to the fate of my slip neighbor.

He had an over temp that he considered moderate, but not enough to warrant shutting down at about an hour into his cruise. The temps stayed lower when he kept the RPMs down. He limped into the closest marina and and changed the impeller and went on to his destination (watching the temps). He gets to his cruise destination a few hours later and they change the pump and he heads home the next day.

The boat overheats mildly all the way home if he pushed the RPM beyond 1700, but his watches it carefully. As he enters the river channel and breakwater, it overheats for real and he limps the last couple of minutes with alarms to the dock and then to his slip after things cooled down.

He is a single engine 45' Puget Trawler that had no choice (or limited choices) and it ended up costing him a $15K engine change. Had he been a twin, he could have come home on a single engine.

The mechanic said he likely had a slow head gasket leak, which slowly depleted his coolant and then cracked the block along the cylinder wall. I stood right there beside him when he said "If he had twins he would not have pushed it" but felt unsafe needed to run the overheating motor to get home.

Ironically though, that's part of why BoatUS stepped up and paid for the motor (a larger portion). Since his operation caused the catastrophic failure, his liability covered it. Had he simply called and said "My block cracked" they likely would not have.

It's easy to say "what if", but I like having the ability to make those decisions... and twins affords me that opportunity.
 
2 vs. 1

This has been a interesting topic, I ran into a article about the Hatteras 48LRC, it seems that they have done some form of testing regarding running the boat as a single ( as it came with twins ) by removing a prop for long passages,
Here is a link to the article:

http://www.hatterasowners.com/Brochures/48LRC/48LRA-0076.pdf

Loo at the fuel chart at the end of the article notice that the data goes from 1.8 NMPG to 2.7 NMPG as a twin vs. single at the same speed...
Food for thought?

HOLLYWOOD
 
Interesting find. Thanks.

Don't think I'd get in the water to pull a prop for the sake of fuel though. :)
 
Greetings,
Mr. hollywood. Am I missing something here? Is the 1.8 MPG per engine or overall when running with twins? If per engine that would mean 3.6 MPG (twin) vs. 2.7 MPG (single). SURELY it's 3.6 MPG isn't it??????? Hmmm...Maybe another 6 or 7 cups of coffee will straighten me out....
 
RT Firefly said:
Greetings,
Mr. hollywood. Am I missing something here? Is the 1.8 MPG per engine or overall when running with twins? If per engine that would mean 3.6 MPG (twin) vs. 2.7 MPG (single). SURELY it's 3.6 MPG isn't it??????? Hmmm...Maybe another 6 or 7 cups of coffee will straighten me out....
Click to expand...

NMPG @ 6.9kts twin both running = 1.8 NMPG (not GPH)
NMPG @ 6.9kts single, prop removed on second eng. = 2.7 NMPG

their numbers not mine. It is interesting in the write up they talk about removing a prop for passagemaking. There is a lot of info in the article.

Regarding changing out a prop in the water.. I used to change out ours on our sail boat between coastal cruising and ocean crossing. A small sailboat prop was still a tough job... a 30" trawler prop would be much harder, but it's probably doable.


looks like an interesting boat for a Nordhavn wannabe on a budget... with the exception of the twin thing

HOLLYWOOD
 
Looking at individual cases and how they were handled is fine but bears no matter on the decision for single or twin reliability.

Several professional towers here have posted and know that twins in the wrong hands are just as bad when it come to assistance.

I'll be the first to admit some people just WANT twins :D, some people NEED twins or better :rofl:, and some of us can enjoy perfectly safe and reliable cruising with singles...:thumb:

I'm not trying to prove one is better than the other...I just don't like it when some "advantages" are so overblown....that I...that I....??????

What were we talking about again????
 
Yes of course. It's even been here on TF that numerous skippers and captains have been running boats to Alaska for the summer season for years removing one prop and running the other engine. It shows the effects of thermal and frictional losses when running two engines to do the same work as one engine is doing otherwise.

But if you were to take out the engines of a twin and install new engines w half the power thereby equaling the power of the single the fuel burn would be very colse to the same possibly even less for the twin. Just possibly.

But running the way the article shows of course the single will burn far less fuel even coping w and suffering the losses of running w very significant asymmetrical thrust.

Is this thread about what engine configuration (twins or singles) is most efficient? If so many posts would/will be required to sort that out and there shouldn't be very much difference at all in the findings.

But if the question is "what if I run on one engine w my twin engined boat?" most of us here wouldn't need any discussion at all to answer that. But time spent on that question wouldn't do anything toward discovering if twins or singles were more efficient w the same hull and power.
 
Last edited:
manyboats said:
Tom, Mark,
My post #2 this thread.
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.
__________________
Eric

We really are chasing our tails a bit here.
Click to expand...

unless your vessel is a Santa Ana built defever with its electric get home motor. Or would these Down Eadst Defever's be considered twins if they are equipped with the get home oprion.?
 
In Actuality:

Cha gots whats cha gots, soooo B Happy! If she be single or twin care for her and she will likely bring you to port.

Seldom do I hear of twin engines being altered to single... or vise versa...

I repeat - - > Cha gots whats cha gots, soooo B Happy! :dance:
 
You must log in or register to reply here.

Similar threads

dhays
High GPH at normal rpm or low rpm at normal fuel consumption
Replies
29
Views
2K
rgano
rgano
C
Beneteau Swift Trawler 44 engine movement
Replies
3
Views
285
Comodave
Comodave
C
selene 53 twin cummins
Replies
10
Views
1K
Govino
Govino
W
Questions on power systems
Replies
6
Views
1K
rgano
rgano
Dan S
Prop Problem with 34' Mainship Pilot Twin Yanmars
Replies
10
Views
783
Dan S
Dan S

Latest posts

Back
Top Bottom