Single engine vs twin in your experience?

[psneeld]

It is what I wrote here :
"...-Smaller draught (for the same position of the engine and the same length of shaft line, same hull) of course with a hull adapted to the mono this advantage can be nil. (see the Beautiful Marie)...."

Sorry to infer you didn't.... just reminded readers in case they didn't read/translate your link.

My main point is that for most every pro or con, some designer has designed some modification to overcome the con that may or may not lead to just another con.

 

[Mako]

Oh good, a thread that isn’t controversial

 

[Sababa]

For me it was easy, I bought a boat I liked and it has twins.

This is the correct answer: however many engines the boat you like has is the right number of engines.

 

[long-cours.62]

This is the correct answer: however many engines the boat you like has is the right number of engines.

I even had one with ...3 engine + a small ketch rigging, And I like her !

 

[Mako]

A single with a get-home engine (or generator) is a twin. So that eliminates a big worry for redundancy.

 

[Taras]

On 2 separate occasions and on 2 separate boats, I had one engine go down and was SO glad I had the 2nd engine for propulsion. From my humble experience, a twin is better for safety reasons.

 

[SteveK]

On the many singl v twin threads I have posted that one summer, one engine became locked. Instead of working on it, we cruised on the other engine. That explains my sig line.

 

[dannc]

....
This is why the discussion goes on and on.... apples and oranges unless you make a close comparison to nearly or the same boat....

Exactly!

...
My main point is that for most every pro or con, some designer has designed some modification to overcome the con that may or may not lead to just another con....

As an example of the above, we are interested in a boat that can have a single or twins. The advantage of the twins vs a single engine, for our use is, and in order of importance,
1 - The boat can dry out while not listing.
2 - The smaller engine can be used as a generator when needed.
3 - Being able to run at slow speeds on one, properly loaded engine.
4 - Having a backup engine.
5 - Maneuverability

However, there is a design cost. A big one as far as I am concerned, is lack of engine room space. The engine room is a crawl in cave and there is not much space for a single engine and this is made worse with two engines. The engine room space/cave is a design choice to lower the air draft of the boat, which is very important for us.

The ER is very cramped. There are things that can be done to improve access, but it will always be tight with a single, and much more so with twins.

One of the advantages of the boat is that it has quite a bit of space for solar power. So much so, that for most of the year, even in high latitudes, the solar panel will handle most/all electrical needs. This really opens up the idea of using hybrid propulsion. Now, some hybrids run off the engine drivetrain, so having twins with hybrids really increases the cost, and in our case, makes the engine room space even more confined. This really says that this type of hybrid with twins is a no go.

However, there are other electrical propulsion options that are NOT attached to the diesel drivetrain which has it's advantages.

So, in our case and our usage, having a singe diesel with a separate hybrid propulsion system, along with a standalone generator, makes more sense than having twins. This maximizes the higher priority requirements but at the cost of being able to dry out the boat without it having a list.

Change the requirements and one would change the equipment and boat design choices, with the same exact hull. None of the choices are right or wrong, they just are.

 

[rslifkin]

On the many singl v twin threads I have posted that one summer, one engine became locked. Instead of working on it, we cruised on the other engine. That explains my sig line.

And yet many of us with twins would never even consider that. In my mind, a twin with an engine out is worse than a single, particularly in close quarters maneuvering. In my mind, moving the boat with an engine out is confined to getting to somewhere repairs can be made or if the boat has to be moved in an emergency. The idea of setting out on a cruise or continuing a long distance without figuring out a stop to fix the problem is an absolute non-starter in my mind.

 

[cafesport]

I’m sure this topic has been discussed before, but since the information is scattered across different channels, it’s difficult to gather it all in one place. I’m currently searching for my first trawler and would love to hear from those of you with firsthand experience:

1. Which configuration do you have, and why did you choose it?

2. What are the biggest pros and cons you’ve experienced?

3. Have you ever regretted your choice, or would you switch if you could?

4. Any specific advice for someone trying to decide between the two?

I’m particularly interested in how these setups perform in real-world scenarios, such as engine failure or docking in tight marinas.

Do you think the fuel efficiency of a single screw outweighs the redundancy, maintenance costs, and complexity of a twin engines? Or is the added safety and maneuverability of twins worth the trade-offs?

Thanks in advance for sharing your insights.Which configuration do you have, and why did you choose it?

1 Our particular hull requires 80-100 hp to hit hull speed depending on load and sea state. It was originally available in a single or twin engine config. Single was 340 hp and twin were 2 170’s. Twin hull was a modified leucander style with fully protected props, shafts, skegs and shoes for two large rudders.

2. What are the biggest pros and cons you’ve experienced?
Contrary to the conventional wisdom, more engine room space, lower operational costs per engine than our big single brethren (you might be surprised when you compare costs on a 340hp engine to a 170, filters injectors starters belts etc...). In addition no fear of groundings, shallow waters, inlets or large following seas.

3. Have you ever regretted your choice, or would you switch if you could?
No and no.

4. Any specific advice for someone trying to decide between the two?

A) Be careful not to confuse twin "big engine" boats with designed twin engine trawlers. All the newly designed Nordhavns (41,51,71 and 80) and the later designed dashew fpbs are and were originally designed as twin engine boats for numerous reasons.

B) We always dock stb side to using our port engine and no thrusters. As a former sailor with a full keel sailboat and no thrusters, maneuverability is kind of a moot point. That said docking in big crosswinds, previously a no go situation, is now doable.

C) A dirty bottom has proved to have a greater effect on our fuel efficiency than even a locked prop, so no.

 

[Datenight]

I think the answer is "it doesn't matter", and that's why the question will be debated for all eternity. Whichever you have, you will enjoy the pros and easily work around the cons, knowing the grass isn't greener on the other side.

Best answer yet.

Rob

 

[Bacchus]

I will only say IMO the " better efficiency" of a single is a myth or minor issue at best. Twins are smaller, single larger. It takes the same HP to push any given hull.

 

[jgloni01]

I’m sure this topic has been discussed before, but since the information is scattered across different channels, it’s difficult to gather it all in one place. I’m currently searching for my first trawler and would love to hear from those of you with firsthand experience:

1. Which configuration do you have, and why did you choose it?

2. What are the biggest pros and cons you’ve experienced?

3. Have you ever regretted your choice, or would you switch if you could?

4. Any specific advice for someone trying to decide between the two?

I’m particularly interested in how these setups perform in real-world scenarios, such as engine failure or docking in tight marinas.

Do you think the fuel efficiency of a single screw outweighs the redundancy, maintenance costs, and complexity of a twin engines? Or is the added safety and maneuverability of twins worth the trade-offs?

Thanks in advance for sharing your insights.

Bought a single w/bow thruster so no dual engine opinion. I did add a stern thruster and it made life much better

 

[SWAN]

Single is the only way to go. Much better in almost every way.

 

[darnold]

Had a single engine fail (fuel pump) in the middle of a major shipping lane late in the day. Was able to get it running before dark and with no freighter in sight. From then on my rule has been I want two sources of motive power on any boat I own and paddles don't count!

However, on my last boat we had both engines fail in the middle of the ferry channel. Were on our way to the dock on one engine after having the first engine fail, when the second failed for an entirely unrelated issue (electrical fault). Very much an oh S* moment. Fortunately the first engine failure was a cooling issue so I was able to restart it and travel the last half mile to the slip with no issues. The joys of owning antique boats!

 

[Laredo]

Two is more and better than one.

 

[Pascall]

The disadvantage of a double-propeller is that the chance of something getting into the screw is much higher than with a single-propeller.
This is purely practical experience.
A friend of mine has a shipyard he told me that 95% of the ships they lift out of the water because of propeller failure are twin propellers.
the cause is, the moment the bow of the ship hits a submerged object it almost always pushes away sideways and then ends up in one of the two propellers.
However, if the object being hit is pushed straight down and moves towards the propeller, the chance of it ending up in the propeller is still small because most single-propeller vessels are equipped with a heel that protects the propeller.

 

[rslifkin]

The disadvantage of a double-propeller is that the chance of something getting into the screw is much higher than with a single-propeller.
This is purely practical experience.
A friend of mine has a shipyard he told me that 95% of the ships they lift out of the water because of propeller failure are twin propellers.
the cause is, the moment the bow of the ship hits a submerged object it almost always pushes away sideways and then ends up in one of the two propellers.
However, if the object being hit is pushed straight down and moves towards the propeller, the chance of it ending up in the propeller is still small because most single-propeller vessels are equipped with a heel that protects the propeller.

That's definitely a concern on twins with unprotected props, although some do have skegs to protect the props and rudders.

But even with my unprotected twin, I've found that having enough keel (mine is slightly shallower than the props) is sometimes enough. I've never had a high speed debris hit but at lower speeds, I've found it's either on the surface and I can see it (or the hull pushes it aside). Or it's submerged and hits against the keel somewhere aft of the bow. When that happens the debris often gets pushed down far enough to clear the props and come up behind us. So far, the only time I've dinged a prop has been with a bit of sunken debris sticking up a couple feet from the bottom in a shallow harbor (and I was the unlucky first person to discover it was there).

 

[Don L]

On another thread I asked about engine failures. There were very few posts saying they had experienced a failure underway. So that kind of wipes about the need of "extra" engine in the 2 engine boats. So it seems to me to only be about speed. Of course that comes with lots of extra costs.

 

[Jklotz]

On another thread I asked about engine failures. There were very few posts saying they had experienced a failure underway. So that kind of wipes about the need of "extra" engine in the 2 engine boats. So it seems to me to only be about speed. Of course that comes with lots of extra costs.

Sure, there is added horsepower (depending), but you also get better maneuverability for docking.

 

[ranger58sb]

So it seems to me to only be about speed. Of course that comes with lots of extra costs.

Even then, twins don't necessarily mean a faster boat. It's common for single- and twin-engine installations to end up with the same (or as nearly similar as possible) total horsepower... all based on hull design. That in turn means a twin will not necessarily be any faster than a single, in any given hull.

-Chris

 

[rslifkin]

On another thread I asked about engine failures. There were very few posts saying they had experienced a failure underway. So that kind of wipes about the need of "extra" engine in the 2 engine boats. So it seems to me to only be about speed. Of course that comes with lots of extra costs.

It's not necessarily just about speed. As mentioned, twins have better maneuverability in close quarters. And sometimes it's just about what fits the design of the boat best (2 smaller engines vs 1 bigger one). Twins also enable shallower draft in some cases.

One example would be something like a Kadey Krogen 52. You can get it with a single 6 cyl John Deere or twin smaller 4 cyl John Deeres. Both versions do the same top speed (displacement hull) even though the twin has slightly more total power. But the twin is putting less power through each prop, so the prop diameter can be a bit smaller. And the props aren't under the deepest part of the hull (being off to the sides), so even with big protective skegs for the props and rudders, the draft of the twin version is listed as being 11" shallower (4'6" for the twin vs 5'5" for the single). I can think of a few places I'd be comfortable squeezing the twin version into where the single would be uncomfortably close to the mud.

 

[psneeld]

I am pretty sure I have seen quite a few posts through the years where some posted about engine stoppages for various reasons that were remedied quickly. They shied away from calling them engine failures because the problem was remedied without a major rebuild.

Even a belt failure that can be fixed in minutes still requires some engines to be shut down to prevent serious damage. At the wrong time it could be a pretty big problem.

Just in this thread, there is some pretty strong sentiment that twins can be important beyond just speed.

I also see the convenience of proceeding as opposed to being stopped, even if only seconds up to days because of a pretty simple repair to a single.

Look hard enough and there are a lot of scenarios that favor twins. It is only because I have been really lucky because I had the quick fix knowledge, the part, the tools, the safe time/location to fix, etc...etc...that I didn't mind my single. Mix in the times where it was more serious, but fortunately in the ACIW and my next longer distance cruising boat would have probably been a trin.

 

[Don L]

Are we applying the "people will find a way to justify anything"?

Not trying to argue just drill right down to it.

 

[CharlieO.]

I just found a boat I liked in my price range and it happened to be a single engine. I was preferring a single but wouldn’t have ruled out twin.

 

[psneeld]

Are we applying the "people will find a way to justify anything"?

Not trying to argue just drill right down to it.

Not at all but if people posting what an engine failures, shouldn't it mean the same for all?

If it were a poll, it would skew results.

And if someone makes a decision on bad info, like Ted posted.... a failure of a single versus a twin in a rare, life and death situation (very rare depending on how one cruises) means just that.

I have unfortunately been involved in more than my fair share of maritime incidents involving deaths or serious injuries from disabled vessels. Those incidents aren't being reported in these threads on the single vs twins debate. Not applying any cliche, just my opinion and experience.

 

[DWJensen]

I just found a boat I liked in my price range and it happened to be a single engine. I was preferring a single but wouldn’t have ruled out twin.

That's exactly where I am. I've always had singles and our current boat even has thrusters. Still hoping for a single (probably with a wing) but will be happy with twins.

 

[ranger58sb]

I just found a boat I liked in my price range and it happened to be a single engine. I was preferring a single but wouldn’t have ruled out twin.

Our first "big" boat happened that way. Mainship 34 Mk III, ticked all our boxes, happened to come with a single... and I was OK with that.

Twins since then, but mostly because the boats we picked -- for features and layout -- happened to come with twins... and I've been OK with that.

FWIW, the only "drawbacks" I have with twins is 1) loss of access around the engines, 2) unprotected props, and 3) extra cost of duplicate maintenance. I reckon the redundancy and slightly shallower draft balances against the extra cost; IOW, it's not like there's nothing in return for the additional $$$. I haven't considered the difference in close-quarters maneuverability a big deal... since thrusters can usually be added to a single if they're not installed already.

So with twins, I just suck it up on 1 and hope for the best on 2.

But if we were changing boats today... I'd still aim for the features and layout we'd want... take whatever propulsion the winner happens to have. Within reason.

-Chris

 

[Greg QS]

I have had both over the years. For me 2 engine set up is a must. I get all the pros and cons and agree. For me it boiled down to

1 . Close quarter combat. Docking. This thing parks like its on rails.
2, Power. On a semi displacement platform, I can go slow efficiently, But when needed I can go fast. I have the power to get out of the way of weather or other boats , power through a tough inlet, overpower river currents, and in rough conditions have the power to get a better ride.
3. redundancy