Twin diesels vs. single on a Mainship

[Hammer]

Dear veteran trawler owners,

I have moved to south west florida and I am seeking to buy a trawler to dock behind my canal house. For the last 30 years I have been a sailor, but now the wife and I are moving to a trawler.

I have looked at a few Mainship 350s that will meet our needs very nicely. Two vessels have my attention. One has twin yanmar 200 hp diesels (1866 hours), the other a big Caterpillar 300 hp (3116) with 3800 hours.

My father had a twin engine cabin cruiser, so I am very familiar with twin engine cabin boats. Grew up on them.

The twins are attractive to me for the extra speed you may get for those few times you really need it. As well as the obvious advantage of having a backup engine.

The single is attractive for lower fuel/maintenance cost and the fact it has the big skeg and protected rudder.

The broker claims the twins will do 18 knots WOT while the other broker says the single will do 14 knots WOT. I don't know if any of that is accurate or not.

I am requesting that some of you veteran trawler owners share your expertise as I make the leap from sail to power. In all your experiences, would you prefer the twins or the single?

 

[DavidM]

Lot's of room for opinion here.

In my view the Yanmar is the better engine irrespective of twin or not. The twins will give you more maneuverability and really don't need a bow thruster. The single does. The fuel economy difference between the two is negligible. The extra hp of the twins is a plus.

The big downside to twins on that boat is cramped access for maintenance. The beam of the 350 really isn't wide enough for easy access. Its younger sister, the 34T has a 14' beam and twins work well in that hull, but not so good in the 350.

David

 

[firehoser75]

Agree with David!
I too like the Yanmars compared to, however, access for maintenance can be a big, big problem in smaller engine rooms! Some items on the outboard side, may have to be done by "feel" alone. If you are not an experienced mechanic, you may have difficulites.
Also, with twins, your repair and maintenance costs go up. For me, I spend enough on my single, and I do 90% of the work myself. Twins also, as discussed, have a more exposed running gear and depending on where you boat, that could become an issue. Where I boat, there is a large amount of floatsum (like logging debris) in the waters as well as the usual crab/prawn traps, etc. that could create issues for you.
Advantages are: "get home engine", easier to maneuver, and the total extra HP.
Single, twins, pros and cons to each

 

[Dougcole]

I can't really speak to the 350 like David can, but I can give you perspective our boat, a Mainship 400 with twin Yanmar 4LHA-STP (240 HP).



I know many people prefer the single, and they have some vaild reasons but for us the twin is a clear winner. Here is why and perhaps some of these might apply to the 350 as well.


1. Speed when needed. This is a big, big deal for me. WOT on my boat, lightly loaded, is 19 to 20 knots. It cruises happily at 14.5 to 15.5 at 3,000 rpm. It is so nice to be able to get up and go when you want to. For instance, crossing the gulf stream to get to the Bahamas. It's also nice in a sloppy chop to be able to bang through it quickly rather than slogging along and rolling your guts out. Our boat is much more comfortable in 3 to 4 footers at 14 knots with the tabs down than it is at 8.


2. Engine access. I know this is counter intuitive, but in some ways the access on the twin is better than the single. There are three floor hatches into the engine room, a large one down the center and a smaller one on either side. These small hatches are too narrow to easily fit through. On the twin you open the main hatch and step down into a large space between the motors. Oil checks, transmission checks, coolant, strainers etc. are all accessed in this way. So is the stb side raw water pump, the port oil filter and most of the zincs. Access to the port raw water pump is tougher. A remote oil filter can be installed on the stb side to make that easy as well. On the single the engine sits right in the middle directly below the main hatch.



3. Redundancy. I've come home three times on one engine. None of these failures would have been prevented by a reasonable maintenance schedule. Two of these were in the Bahamas out of range of towing services.


4. Maneuvering. The close quarters situation is well documented, and though most of this can be offset with thrusters, I find twins easier. And thursters need to be maintained as well. I once lost steering on our old boat (Gulfstar 36) and came in steering with the motors. It wasn't easy but it worked.


5. Fuel. Twins and singles burn very close to the same amount, especially at lower speeds.


6. Parts. Clear winner for the single. Though parts for a bigger motor are generally more expensive, which offsets a little bit of it.


7. This one is kind of weird, I know, but when I'm working on one engine it is nice to have the other one to look at for reference.



Anyway, just my .02. Obviously other people's opinions are valid as well. Depends a lot on how you want to use the boat, I think.

 

[caltexflanc]

I have run both of the versions of that boat mentioned in the OP. At the time they were in a charter boat club I belonged to.

Personally I preferred the single engine version, equipped with a bow thruster. 14 knots? maybe in perfectly flat dead calm conditions, maybe.

The difference in the engine room is dramatic, and the single allows enough room to fit a small generator comfortably and serviceably, not to mention the main engine. The single was modestly quieter though the Yanmars are great very smooth running engines. The boat was very maneuverable using the thruster and prop walk. Mind you we are twin engine type folks by nature.

I like most everything about those boats, save for the loud bow slap noise in the staterooms which we found unbearable at anchor. We took to using the convertible sofa in the salon, which I enjoyed a lot. Quiet and handy to taking a quick peek outside close to the refrigerator and coffee maker.

 

[High Wire]

Both have their advantages and disadvantages that will be listed here. No wrong answer only preference. Only you can pick for you that boat that makes you happy. Enjoy the search!

 

[T210DRVR]

The debate over twins versus singles reminds me of the video of twin engine airplanes versus single,

They both have their pluses and minuses. The plus for the twin generally fall into maneuverability and redundancy. For a single it’s about operating costs.

While losing a single engine in a plane may be more critical, the loss of a single in a boat under difficult circumstances can be very serious. I lost an engine in a single engine aircraft one time and it required an off airport landing. The results were not perfect but I walked away. It convinced me to go back and fly a twin again.

Losing one crossing a difficult bar could be life threatening. I suppose the choice comes down to risk tolerance. The chance of a well maintained single failing at the worst possible is very low. Pick your poison, lower costs or slightly elevated risk.

 

[Ken E.]

Good posts on Mainship power. I have twins and that's my particular preference, but a strong case can be made for a single if you do your boating where reliable towing service is available.

 

[dave907]

Will you be cruising in the Summer? SW Florida has a lot of thunderstorms in the Summer. I really recommend having a boat fast enough to get out of the way of storms.

Lots of shallow water if you plan on cruising Charlotte Harbor and other inside cruising grounds. I wish I had fully protected running gear for this reason.

Luck!

Dave

 

[Sailor of Fortune]

The debate over twins versus singles reminds me of the video of twin engine airplanes versus single,

They both have their pluses and minuses. The plus for the twin generally fall into maneuverability and redundancy. For a single it’s about operating costs.

While losing a single engine in a plane may be more critical, the loss of a single in a boat under difficult circumstances can be very serious. I lost an engine in a single engine aircraft one time and it required an off airport landing. The results were not perfect but I walked away. It convinced me to go back and fly a twin again.

Losing one crossing a difficult bar could be life threatening. I suppose the choice comes down to risk tolerance. The chance of a well maintained single failing at the worst possible is very low. Pick your poison, lower costs or slightly elevated risk.

when was the last time your heard of a report of a single engine "losing power crossing the bar?'...love the dramatics but the reality is less entertaining ... Not trying to make a case for a single vs twin..

 

[Codger2]

Lot's of room for opinion here.

In my view the Yanmar is the better engine irrespective of twin or not. The twins will give you more maneuverability and really don't need a bow thruster. The single does. The fuel economy difference between the two is negligible. The extra hp of the twins is a plus.

The big downside to twins on that boat is cramped access for maintenance. The beam of the 350 really isn't wide enough for easy access. Its younger sister, the 34T has a 14' beam and twins work well in that hull, but not so good in the 350.

David

I agree with all of David's post but having had both a single with a bow thruster & twins I would be comfortable in either one. My experience is with Cats & Cummins but I now have Yanmars which I love. Had trouble with a set of 3116s years ago so I'm not fond of those. If you held a gun to my head I would choose the single (assuming it does not have 3116s) as a single with a thruster can take you anywhere. Your choice.

 

[Bacchus]

I've had both single and twins. I was concerned about moving from twins back to a single when buying our current MS but having had it for 7 seasons now I'm very happy.
I boat in areas where chance of being stranded and not able to get a tow are low so I'm a fan of single w thruster(s). I'd say go for the boat that you like the best and don't worry about power or speed.
Calculate how much longer it would take to get out of a bad Wx situation and I'm guessing it's not very significant unless the distance is great and in that case you need to be more aware of impending trouble plan ahead vs just waiting till it's in sight. Neither boat is a real "go fast" boat.

 

[ranger58sb]

Can't speak to the 350/390s, but we had an older 34' Mainship Mk III with single 210-hp diesel, NO bow thruster. Good boat, easy to work on the engine (which didn't need much)... and I think we could maybe flog it up to 14 kts on a calm day... maybe... but IIRC about 12 kts was what we might call our "high" cruise. Mostly it was really a 9-10 kt boat. Given more horsepower it likely would have been faster...

But we never felt like we needed twins. All the pros/cons are worth exploring, but we found the single to be just fine.

Today, if we had the same boat, we'd add a bow thruster... and I'd try to find a way to replace the ladder with maybe a circular staircase... Otherwise it was a good boat, as was, and I expect the feedback Mainship got from 34 Mk I/II/III owners heavily influenced the 350/390 design (like the wider beam, lower helm door, stairway to flybridge, etc.).

-Chris

 

[Mako]

when was the last time your heard of a report of a single engine "losing power crossing the bar?'...love the dramatics but the reality is less entertaining ...

It's called "extremism" and is the generally accepted way to respond when you're losing an argument

Seriously though, there have been so many threads on the subject that it's obvious that the answer is "depends" on your particular preference, risk tolerance and the application as well.

My big boat had twins, but I cruised at trawler speed 100% of the time. Granted the boat had Jimmies and their dependability was exceptional.

If I were to build a similar boat again, it would be a single properly sized to about 70-80% power rating with a mechanical engine.

Regarding a thruster, that would be high on the list unless the boat were destined to exclusively anchoring out, mooring fields and long distance cruising. Would save the trouble and expense - the next owner could always add one, although it might be good to have the shipyard install the tunnel (with ends closed) so a future retro would be simplified.

 

[Hammer]

Skippers:

Thanks all for some very thoughtful, and helpful replies. Very helpful.

David points out the value of the Yanmar as a smooth running marine diesel, but cautions against the cramped maintenance space. He states the fuel efficiency of single vs. twin is negligible. Extra power and speed a plus.

Firehouse points out the maintenance challenge but also the preference for the yanmar, but says the exposure of twin props and rudders is a concern where he boats. Routine maintenance costs are double. Preference for the single.

DougCole has twin yanmars on his mainship. He says the extra power to push through heavy chop is his top preference for twins. He has learned to live with and work around the cramped space on one side of each engine, and uses a remote oil filter system for the port engine. He points out part's expense will be more. He said the redundancy and tight maneuvering ability make his twins the winner.

Caltex has chartered both single and twin mainships. His preference is for the single with all the space in the engine room, makes life easy. No problem in close quarters with the bow thruster.

HIghwire says both are great, and to select whatever you prefer.

T2110 says his experience makes him say the safety of the redundancy of twins is worth the higher maintenance costs.

Ken has twins and that's his preference. He says a single is okay if you cruise where towing is available.

Dave097 says he likes the speed of twins to be able to outrun a summer squall, but wishes he had the single engine ground protection for the shallows of Charlotte Harbor.

Codger has had both twins and single. He likes both. Says a single with thruster will take you anywhere. But he is cautious about the 3116 as he has had trouble with that engine.

Bacchus has had both. He now has a single and is very happy, stating the actual times you need more speed are few.

Ranger has had a single and has never felt the need for twins.

Mako has had twins. But if he were to buy the same boat today his preference would be for a single screw with the most horsepower he can get.

Based on all this input, I am leaning toward the twins for the following reasons: 1) based on my experience with twins growing up, it will be familiar; 2) understanding my personality, the ability for some extra speed is a huge plus, a major plus; 3) the maintenance space challenge does not overly concern me as I have maintained all my boats myself (except for bottom paint, yechhh!). The boat will be in my backyard and I can take my time; 4) Although I have only had my sailboat diesels fail me once (clogged fuel strainer), I know luck can be a fleeting thing -- redundancy is a plus; 5) As a former sailboat skipper in need of six feet, I am very aware of navigating shoals and shallows, so hopefully that skill won't fail me now; 7) Yanmar seems to have an excellent reputation.

Now after saying that, as with real estate, price and location are important. If the prices and delivery distance were about the same, and the surveys were both very good, I will go with the twins. But if the single becomes the more attractive deal, I will go with that. But I believe my first offer may be on the twins.

Thanks all.

 

[caltexflanc]

the maintenance space challenge does not overly concern me as I have maintained all my boats myself (except for bottom paint, yechhh!). The boat will be in my backyard and I can take my time

I don't know how large and agile you are, but I'd take a good look and spend some time in that particular engine room with those particular engines if I were you. Just checking the oil and coolant levels were challenging for me. Oil changes, strainer cleaning, other basic PM, I just couldn't see myself being able to do it. Not to mention the non-engine-related plumbing and electrical which runs through there.

Personally, no way I'd do any longer term cruising and anchoring out with that set up. But you got to spend some quality time in there and decide for yourself .

 

[Dougcole]

I don't know how large and agile you are, but I'd take a good look and spend some time in that particular engine room with those particular engines if I were you. Just checking the oil and coolant levels were challenging for me. Oil changes, strainer cleaning, other basic PM, I just couldn't see myself being able to do it. Not to mention the non-engine-related plumbing and electrical which runs through there.

Personally, no way I'd do any longer term cruising and anchoring out with that set up. But you got to spend some quality time in there and decide for yourself .

I can't speak 100% for the 340, but if the ER hatch access on it is the same setup as it is on the 400, basic PM for oil checks (dip sticks on both sides of motors), strainer checks and cleaning, transmission and coolant checks, belt adjustments are all easier on the twin than on the single. Oil changes if you remotely mount one filter are the same twin vs. single. Impeller changes on the twin are tougher. Plumbing and electrical runs aren't really an issue either way, though access to the fuel gauge senders is really bad on both setups.



I haven't been in the ER on a 340 though, with singles or a twin, so I can't speak to that exact boat. What David says about the narrower beam of the 340 is concerning and could change my outlook on this. I work fine with the access that I have to the outside of my motors, but wouldn't want any less.


Did the 340 put the genset in the ER? That could be an issue as well.

 

[Hammer]

Hi,

Where did the 340 come from? That seems to be a very different boat that the 350/390.

 

[ranger58sb]

Ranger has had a single and has never felt the need for twins.

Hmmm...let me add some nuance to that...

In the 34 Mk III we had, I didn't feel a need for twins, and I think twins in that boat would have introduced some maintenance (access) headaches.

OTOH, we have twins in our current boat, and while occasionally I'd like the better access a single might provide... twins work well for us in this boat.

OTOOH, if I were to change boats... choice of single or twin would likely depend on the boat itself... and I likely wouldn't be unhappy with either choice... depending on all those pesky details, especially engine access.

-Chris

 

[Dougcole]

Hi,

Where did the 340 come from? That seems to be a very different boat that the 350/390.

You are right, I misread his post. I thought the OP was asking about the 340, not the 350/390. My bad.

 

[rslifkin]

From what I can find, the 350 should have a 14'2" beam. So a couple inches wider than mine. And I wouldn't say my engine access is bad at all with twins. Primary access is down a hatch into a nice space between the engines. Getting to the generator and the outboard sides of the engines requires some crawling (unless you want to open up a lot of the floor), but once you crawl to the area you need, there's enough room to get comfortable and do stuff. For big jobs, you open up some floor hatches for extra room in the tougher areas.

For an engine room that requires some crawling for access, having a second person around can make some jobs much easier. Just having someone to hand you things can save a lot of moving around.

 

[Seevee]

Well, I've had both single engine and twin engine boats and planes.... several. 40 in total. Some big, some small.


Bottom line, it all depends on what you want and what you're willing to pay for.


I believe the width of the 34 is about the same as the 40, so the engine room is probably similar.



Comments:
Engine room can be a big issue. Having never maintained a 34, it looks doable but a tad tight. My single is dirt simple.


Speed is nice, but perhaps not a necessity. When you get up on plane, the weight makes a huge difference, single or twin. If I'm really light, I can hit 15kts wide open, perhaps cruise in the 12 to 13 range, but at high fuel consumption. Perhaps there's a few times it would be nice, but I could argue, if you want speed in a boat, get a really fast one.


And outrunning a thunderstorm in ANY boat is wishful thinking as best. Perhaps one could maneuver for a better position, but if you need to out run one, get a plane.



I could argue the cost of a twin vs single in a trawler with the same hull operating at hull speed is bupkiss.... not enough difference to make a hill of beans. Typically the twin version (like the Mainship) has two smaller engines, so not really double the maintenance. However, engine maintenance in the overall picture is very small... if you use the boat.



Yes the twin is more maneuverable, but a single with bow and stern thrusters is pretty good and in some cases, better.



If one is operating in a area where a single engine failure would be devastating, there's an argument for a twin. Same with a plane. When I fly over the gulf of Mexico, at night in the weather, I'd prefer a twin. Same with operating a boat in the gulf. Intercoastal, day, VFR, short runs across inlets or even the great lakes, I'll take the single in both.



I could make a strong argument for either.


BTW, I'd sell my twin engine plane and get a single, but would cost me a lot more. Want one? Not so for boats.

 

[Mako]

I don't know how large and agile you are, but I'd take a good look and spend some time in that particular engine room with those particular engines if I were you. Just checking the oil and coolant levels were challenging for me. Oil changes, strainer cleaning, other basic PM, I just couldn't see myself being able to do it. Not to mention the non-engine-related plumbing and electrical which runs through there.

Personally, no way I'd do any longer term cruising and anchoring out with that set up. But you got to spend some quality time in there and decide for yourself .

Good words of wisdom. I just walked away from purchasing a very nice MS34 single last weekend, even though it was just to be a fun local toy not for serious cruising.

Of course there were several reasons, but one was how much I dislike those sole-buried engines. Even lifting all the sole-boards up doesn't make it much more enjoyable to work in your engine space (it is NOT an "engine room").

Definitely consider how "large and agile" you are.

 

[Ski in NC]

I have been on a few of the Mainships with twins. Access to the outboard sides of the engines was not good. You need to be able to put your hands on every part of the engines, and if not, to me it is a no-go. The singles were cake, could get to everything.

And then some gennies were buried under cockpit structure. That was a head-scratcher and will really complicate maintainance.

 

[Benthic2]

Intercoastal, day, VFR, short runs across inlets or even the great lakes, I'll take the single in both..

Aren't you totally screwed in a single engine plane if the engine quits, no matter where you are ?

 

[T210DRVR]

Aren't you totally screwed in a single engine plane if the engine quits, no matter where you are ?

If you are near an airport not at all. Off field landings are always a little dicey. You don’t get to do the landing twice. As evidence that it can work out I walked away with a bruise. The plane didn’t fare as well.

 

[Seevee]

Aren't you totally screwed in a single engine plane if the engine quits, no matter where you are ?

Jim Nance is correct... it depends and most often you will walk away and a fair amount of the time, the plane damage will be minor.



If you're over the gulf of Mexico, the plane will sink, and you will survive most likely if you have a raft. Without, not good. Over the mountains in a snow storm, not so good either.


I've had a single engine plane quit four times on my. Three were minor inconveniences and landed on an airport. One landed short of the runway and totaled the plane and got beat up a bit.



In a boat, you just drop the anchor.... but might just be a sea anchor at times.


One interesting statistic.... if you crash a plane, you are 4 times more likely to die if it's a twin. So, if you fly twins, being proficient enough to fly on one engine is a big deal.

 

[Codger2]

OTOH, we have twins in our current boat, and while occasionally I'd like the better access a single might provide... twins work well for us in this boat.

Ditto! We have 2- 6LY2A-STP Yanmars in our 42' Ocean Alex and though I wish there was more room outboard of the engines, it is manageable. There is a lot of room down the center, however.

 

[Keysdisease]

Isolators at the top of the deck support stanchions? Good practice

Ditto! We have 2- 6LY2A-STP Yanmars in our 42' Ocean Alex and though I wish there was more room outboard of the engines, it is manageable. There is a lot of room down the center, however.

 

[Keysdisease]

In 11 years, on an engine that was 25 years old when we bought her, we have been towed twice, both times for fuel issues. A well maintained diesel engine is very reliable, and unless I was planning to cruise some serious outback single would be my choice. For coastal cruising tow insurance should offset any anxiety.