Decision: A single or two engines

I"m considering on purchasing a Mainship 350/390 and whether it should be a single or two engines. The single comes with a bow thruster. Two engines would be better for docking and may be safer, but I would loose the economy of a single. How much more would it cost to run two engines for economy? How much more to maintain two engines? What are the real trade offs? Thanks.

There are several long and thorough threads on this subject. I searched them and read them carefully when looking for my own boat.

Most engine failures are due to fuel issues, so if one goes down, both go. But there are those times when the extra brings you home. Docking with a thruster is not a problem once you know your boat.
In the middle of the Abacos a twin gives some added security. For costal cruising there is Sea Tow or boats US. I have only had singles.

The standard here, in more recent boats, is twins, often plus bowthruster, OR single plus thrusters both ends. And some twins, with thrusters both ends,sometimes with integrating Yacht Controller.

Problem is, I think, anecdotally, thrusters fail more engines,and if they do, an operator used to manouvering/docking with thrusters has to work without. I`ve seen it happen on our marina, and suspect it`s a greater problem than engine failure needing redundancy. And it`s likely to happen just when you don`t want. like if you need the thrusters for extended periods and they overheat or drain their batts. However that redundancy can be mighty helpful for manouvering.

And that`s why I prefer twins. But read up on the old threads, no lack of them.
The hairy chested Swinging Ds will tell you a single no thrusters is all you need, but I disagree, some help is no bad thing.

In that boat I would definitely go for a single due to accessibility for maintenance. The twins are very tight in the engine room.

Comodave,
The engines in a twin engined boat should be half as big as a single in the same boat. And should be almost as economical as a single.

It isn’t about economy, it is about accessibility in the 390. With twins it is really tight to work on the outboard sides of the engines. I would go with a single and a bow and stern thruster in a 390.

Greetings,
Welcome aboard.

The advice about availability of tow service where you cruise is a good one. I would add one's mechanical ability as a factor also.

Generally, two engines means one can exceed hull speed, thus a fast cruiser. A single engine can do that depending on the sufficient horsepower and hull shape, But a true trawler doesn't exceed hull speed and economically operates a knot or so below that. Twins are likely to have twice the engine failure than a single. A single usually has better access for maintenance, and a good chance having a keel protecting propeller and rudder.

Part of this decision is where you are going to boat. If you are on Lake Michigan your first concern would be docking and then engine failure that prevents you from getting back to shore.

On your boat docking with twins or a thruster is very doable. As far as engine shutdown fuel is the most frequent and that affects twins as well as singles. Many of the remaining issues such as water pump leaks, valve leaks etc. will not prevent you from getting home and in Michigan you can get parts the next day. Belts, filters, impellers, replacement hoses, solenoids, start buttons, engine oil can all be carried on board in less space than a a second engine would take and for a lot less money.

Four items clearly argue against a second engine in your boat, space for maintenance (critical), cost of the second engine, exposure of the twin props vs single if you go to the west side of Lake Michigan or north into Canada, and cost of maintaining the second engine over time.

One thing is clear that supports the purchase of a second engine. A percentage of possible buyers when you sell will not look at a single engine boat.

Some well made points...


One I like to throw in... after many miles in both singles and twins.
For me, one big advantage of twins is not all engine issues are the "rare" engine failures. Some are simple leaks, drips, sounds, bolt on part failures, etc...etc.


The luxury of a twin is you can continue to homeport or at least some place reasonable to do or get the repairs done. Not possible all the time with a single unless you carry a lot of parts, tools and know how.

Fuel problems are a maintenance problem. If you do the maintenance and keep your fuel clean and dry, you won't have fuel problems.

twins should be set up too operate independently. Fuel and electrical should not be shared.

I've had twins and singles ant would always go for twins if space permits. Dont worry about fuel as the amount of fuel to move the boat at any speed is independent, roughly, of the number of engines.

mramoo said:

Fuel problems are a maintenance problem. If you do the maintenance and keep your fuel clean and dry, you won't have fuel problems.

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How does one avoid a slug of water from a reputable fueling spot?

Sure you can sample at the beginning and ending of fueling, always only fill one tank at a time, have water monitoring in your fuel filters, and have lightning fast reactions to switch your tanks and filters before the engine sucks water, wait after refueling and drain your tank sumps if they have them.... but how many boaters fit this description?

Granted I have never had the problem... or thousands more boaters either...but I know of a few boaters and a few friends in USCG helos that are meticulous that have got a slug of fuel the went undetected.

Sure this type of issue can also affect twins...but usually not at the exact same time which is nice, but you may not have much time between engine stoppages.

We spent 4 months in Beaufort, NC at Beaufort Yacht Basin (awesome staff) watching the commercial fishermen enter the very narrow harbor to the Homer Smith fish house to unload. Several every day. Every one of them are singles with some vessels in the 50' range. They did things I still can't do well with our twins. They trust their singles to work hard every day. Never heard any of them (and we visited with many) talk about breaking down and being stranded. We were supremely impressed. Would it take some serious practice to get that good, oh yeah. But the single with it's barn door rudder is a sight to behold at the hands of a skilled captain.

Old saying is that the only times you need twin engines are when buying or selling a boat.

Mule said:

In the middle of the Abacos a twin gives some added security.

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Shoot. Man of war is a place i head in case of trouble. Somewhere like mid west side of andros might be a better bah. Example[emoji41]

Last time it was a split pinion gear on the engine starter. One eng boat.

NightCrawler said:

We spent 4 months in Beaufort, NC at Beaufort Yacht Basin (awesome staff) watching the commercial fishermen enter the very narrow harbor to the Homer Smith fish house to unload. Several every day. Every one of them are singles with some vessels in the 50' range. They did things I still can't do well with our twins. They trust their singles to work hard every day. Never heard any of them (and we visited with many) talk about breaking down and being stranded. We were supremely impressed. Would it take some serious practice to get that good, oh yeah. But the single with it's barn door rudder is a sight to behold at the hands of a skilled captain.

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Jan,
Fishermen usually go in groups .. most all friends. They take care of their own. That has a lot to do w their single engines. The run up from Seattle begining April 15 departure usually encounters some bad weather .. lots of slop and blow.

NightCrawler said:

We spent 4 months in Beaufort, NC at Beaufort Yacht Basin (awesome staff) watching the commercial fishermen enter the very narrow harbor to the Homer Smith fish house to unload. Several every day. Every one of them are singles with some vessels in the 50' range. They did things I still can't do well with our twins. They trust their singles to work hard every day. Never heard any of them (and we visited with many) talk about breaking down and being stranded. We were supremely impressed. Would it take some serious practice to get that good, oh yeah. But the single with it's barn door rudder is a sight to behold at the hands of a skilled captain.

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I'm not disagreeing with you at all. However, I would mention that most of those boats have a much bigger rudder than most of ours, and as they are work boats working out of working docks, they also aren't concerned as most of us are about putting a scratch in our shiny gelcoat.

dhays said:

I'm not disagreeing with you at all. However, I would mention that most of those boats have a much bigger rudder than most of ours, and as they are work boats working out of working docks, they also aren't concerned as most of us are about putting a scratch in our shiny gelcoat.

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That's for sure true. Working boats have working rub rails...

dhays said:

I'm not disagreeing with you at all. However, I would mention that most of those boats have a much bigger rudder than most of ours, and as they are work boats working out of working docks, they also aren't concerned as most of us are about putting a scratch in our shiny gelcoat.

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Indeed, on the surface it may appear so. One blustery day I watched a 40+ footer enter the runway with a 20K wind pushing him towards a dead end thinking, "no way!" the face dock was full and only a small opening between two boats on the pier. That captain swung it in there like butter, never hit the dock, stepped out with a mug of hot coffee in one hand, threw his lines to secure with the other and ambled off the dock. Single handed. No three point turn, just smooth as silk. That is pure skill. Love watching them.

Lots of good insight here. I think on some level it depends on your personality. For me, I would have bought my boat with a single but I slightly prefer twins.

On some boats access with twins can be more difficult and twins will always use more fuel unless you run just one at a time which I'm going to try. Of course double the maintenance but for reasonable engines we're not talking that much more. I DO like that you can have a more protected prop with a single, but on some twin boats the keel is lower than the props. (My keel is 10" lower) so there's some protection there. Of course there's the redundancy argument and I think overall twins are better in that way especially if you have separate tanks.

Ken

It will be your boat, your money, you skill level, the real need for a method of 'get home.' Remember, 2 engines = twice as much engine maintenance.
If you bought a boat with 2 engine with the hopes of pushing the hull design to a higher speed, you may discover, 2 or 3 knots with 4 or 5 time the fuel consumption. IMO, anything above hull speed should be reserved for desperate times or if you want to drain the fuel tanks for inspection or end of season refueling.

I come out of our fairway (very narrow) and never change gears. My 45 degree rudder deflection and large rudder area make for very sharp turns.

Trick trailing edge rudder modifications can even do better.

Bay Pelican said:

Part of this decision is where you are going to boat.

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What are yall's thoughts on twin v single when doing a lot of river cruising? How available is a tow service between down from Knoxville and around to Nashville (ie the Tennessee and Cumberland rivers)

I had this question about a year ago regarding the Mainship 400. I saw a thread here called Mainship shopping and learned a lot. I suggest you read it. I ended up buying a twin. Two engines are better than one when you run over a submerged mooring as I did. Limped home on one engine safe and sound.

Trick said:

trailing edge rudder modifications can even do better.

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Expand on your trailing edge rudder modifications please.


mike

I don’t have much to add, but my own personal experience. Previous two boats had twins (39 and 44 ft.) and I could take them in the tightest areas with confidence. I would be lying if I said I wasn’t a bit nervous regarding my recent transition to a single. I have a lot more to learn about single screws, but So far, knock wood, it has not been an issue and I have done some close quarter maneuvering in the crowded mooring and anchor fields.

Islanddreamer said:

Expand on your trailing edge rudder modifications please.


mike

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I think I recall a thread from a couple years back on that... It was pretty informative.


http://www.trawlerforum.com/forums/s3/rudder-modifications-24331.html