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Old 08-22-2018, 10:19 PM   #1
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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.
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Old 08-22-2018, 11:15 PM   #2
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There are several long and thorough threads on this subject. I searched them and read them carefully when looking for my own boat.
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Old 08-22-2018, 11:19 PM   #3
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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.
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Old 08-22-2018, 11:29 PM   #4
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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.
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Old 08-22-2018, 11:38 PM   #5
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In that boat I would definitely go for a single due to accessibility for maintenance. The twins are very tight in the engine room.
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Old 08-22-2018, 11:48 PM   #6
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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.
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Old 08-22-2018, 11:52 PM   #7
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It isnít 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.
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Old 08-23-2018, 12:25 AM   #8
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Greetings,
Welcome aboard.
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Old 08-23-2018, 12:38 AM   #9
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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.
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Old 08-23-2018, 01:58 AM   #10
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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.
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Old 08-23-2018, 05:19 AM   #11
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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.
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Old 08-23-2018, 06:56 AM   #12
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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.
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Old 08-23-2018, 08:59 AM   #13
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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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Old 08-23-2018, 09:05 AM   #14
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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.
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Old 08-23-2018, 09:09 AM   #15
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Quote:
Originally Posted by mramoo View Post
Fuel problems are a maintenance problem. If you do the maintenance and keep your fuel clean and dry, you won't have fuel problems.
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.
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Old 08-23-2018, 09:50 AM   #16
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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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Old 08-23-2018, 10:38 AM   #17
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Old saying is that the only times you need twin engines are when buying or selling a boat.
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Old 08-23-2018, 11:48 AM   #18
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Quote:
Originally Posted by Mule View Post
In the middle of the Abacos a twin gives some added security.


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

Last time it was a split pinion gear on the engine starter. One eng boat.
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Old 08-23-2018, 12:32 PM   #19
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Quote:
Originally Posted by NightCrawler View Post
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.
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.
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Old 08-23-2018, 12:50 PM   #20
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Quote:
Originally Posted by NightCrawler View Post
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.

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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