Twin diesels vs. single on a Mainship

[danderer]

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.

A huge deal. I always had singles because I didn't feel I would maintain the proficiency I'd want for a twin, and therefore would be less safe in one should something happen.

 

[sunchaser]

Hammer
Internet shopping can only get you so far. Have you already been walking the docks and lifting hatches on the vessels in question? No harm in being patient and looking at many vessels. You may even find something different than the Mainship that better fits your desires.

 

[OldDan1943]

The following is just my opinion:
2 engines: twice the maintenance, faster boat, double the fuel costs, greater maneuverability in confined spaces.
1 engine: less fuel, less maintenance, practice spring lines, get a bow thruster and stern thruster if you need to be more comfortable in confined spaces. Loss of engine, call Tow Boat.

 

[rslifkin]

The following is just my opinion:
2 engines: double the fuel costs

Not even close in most cases. The twins will usually burn a little more at the same speed, but in most cases it won't be a large penalty.

 

[OldDan1943]

Not even close in most cases. The twins will usually burn a little more at the same speed, but in most cases it won't be a large penalty.

Why buy a faster boat and run it at hull speed? TEASE

 

[rslifkin]

Why buy a faster boat and run it at hull speed? TEASE

All depends on the hull and the cruising you're doing. Plus, depending on the hull design and engine efficiency curves, running the twin at 15 kts might give the same mpg as the single at 11 anyway. Especially once you consider that 15 kts might be enough to get it mostly up on plane while 11 will be plowing along.

That second point is also the big key. If the single only does 13 - 14 kts wide open, you're running at hull speed 99% of the time with the ability to go a little faster occasionally when you really need to. But the boat will never get up on plane, so it won't be ideal to run faster. With the twin that'll do 18 kts, you can get it up pretty much on plane without being at WOT, so even if you run at hull speed most of the time, it's possible to get up and go a bit when desired.

 

[OldDan1943]

That second point is also the big key. If the single only does 13 - 14 kts wide open, you're running at hull speed 99% of the time with the ability to go a little faster occasionally when you really need to. But the boat will never get up on plane, so it won't be ideal to run faster. With the twin that'll do 18 kts, you can get it up pretty much on plane without being at WOT, so even if you run at hull speed most of the time, it's possible to get up and go a bit when desired.

Hence my little bitty American Tug 34. Mathematically, the hull speed is about 7.5 knots. Yes, again in theory, it can also go 17 knots, but at a big time fuel usage increase and a significant reduction in travel distance. Nope, the boat will never plane, just create a bigger bow wake as it plows through the water.

 

[rslifkin]

Hence my little bitty American Tug 34. Mathematically, the hull speed is about 7.5 knots. Yes, again in theory, it can also go 17 knots, but at a big time fuel usage increase and a significant reduction in travel distance. Nope, the boat will never plane, just create a bigger bow wake as it plows through the water.

Yeah, I've never quite understood those kinds of design choices. If the hull is capable of some kind of reasonable planing, might as well give it the power to do so instead of just enough to get sorta-kinda on plane for a minute or 2 at WOT.

 

[OldDan1943]

Yeah, I've never quite understood those kinds of design choices. If the hull is capable of some kind of reasonable planing, might as well give it the power to do so instead of just enough to get sorta-kinda on plane for a minute or 2 at WOT.

10 knots over hull speed aint to sneeze at.
My Nordhavn46 did about 8 knots WOT so I am happy with the AT

 

[Seevee]

A huge deal. I always had singles because I didn't feel I would maintain the proficiency I'd want for a twin, and therefore would be less safe in one should something happen.

Smart man,


The cost of remaining proficient in the twin is a lot more than the single. Just finished recurrent a few months ago and will probably keep it up. My twin has relatively high time engines but running great, know plane and it's quite reliable. I'll take a hit in selling, but still fine for my needs. I have a partner to help with costs, which works great.



Just like one can do with a boat.

 

[O C Diver]

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?

If you want to operate the boat on plane, buy the twins with more HP. Trying to maintain a heavily loaded boat on plane with minimal HP can be a challenge.

If you plan to operate the boat in displacement mode and maybe put it on plane rarely, buy the single. For displacement operation in coastal regions of the USA, the single engine is easier and less expensive to maintain. In the area you plan to operate, towing assistance is a phone call away should you ever need it.

Ted

 

[T210DRVR]

Not even close in most cases. The twins will usually burn a little more at the same speed, but in most cases it won't be a large penalty.

Agreed. On a nautical mile per gallon my Twin Comanche does as well as my Cessna 182.

With respect to training there is no question that you have to remain sharp when piloting a multi-engine aircraft. I’ve had three engine out situations in a Twin and all ended well at an airport. In my opinion, a Twin is much more dangerous in the initial climb phase. An engine failure in the first thousand feet or so has to be handled quickly and correctly as loss of control is likely going to lead to a fatality. This is where comparing boats and planes are like Apples and Oranges.

Twins are likely to be flown in poor weather and at night when the inherent risk of flight is higher. Much of the increased fatal rate of Twins can be attributed to the missions they are expected to perform. I suppose there is a valid argument that some missions on the water favor a multi-engine craft. Of course, some of the largest ships in the world, container ships, run on a single.

The decision to use a single versus twin engine vessel comes down to an individual choice. If you are operating in a near coast environment with towing assets readily available then a single is an obvious choice. If you are operating in the ocean off the Pacific Coast of Baja perhaps the choice is more difficult.

 

[catalinajack]

Yes, the bow slap. We travelled on and off with a guy who bought a Mainship to do the Loop. He hated the boat because of the bow slap. Nothing worse than trying to sleep with loud boat noises all night long. And bow slap can happen in marinas also, not just at anchor. This fellow took to deploying swimming noodles on lines around the bow at the waterline. This peculiarity is seldom mentioned in discussions of the pros and cons of Mainships. Having lived aboard a DeFever 44, generally a quiet boat, for three years, I can assure that that boat noises, when they do occur, can be very maddeningly disruptive of sleep.

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.

 

[greysailor]

Yes, the bow slap. We travelled on and off with a guy who bought a Mainship to do the Loop. He hated the boat because of the bow slap. Nothing worse than trying to sleep with loud boat noises all night long. And bow slap can happen in marinas also, not just at anchor. This fellow took to deploying swimming noodles on lines around the bow at the waterline. This peculiarity is seldom mentioned in discussions of the pros and cons of Mainships. Having lived aboard a DeFever 44, generally a quiet boat, for three years, I can assure that that boat noises, when they do occur, can be very maddeningly disruptive of sleep.

X2 John.....
We have a Cabo Sport Fish in the slip next to us at home marina. Cabo has a small tunnel right at the chine, and the ripples in the marina line up with them and make a steady "plop, plop, plop" noise all night....grrrrrr![emoji35]

 

[SoWhat]

I don't think economics or reliability are the main determinants for making twin v. single decisions. Are you thin and agile and have high tolerance for pain? Go for the twins. If you consider walking from the couch to the fridge to be your quota of daily exercise, and call a plumber when your faucet drips, go for the single.

 

[T210DRVR]

I don’t care for the pain, but the Lehman’s are pretty accessible. By the time you install a single in the middle you are crawling around anyway. V-8’s are another animal. I can see where servicing them would be a PITA.

 

[stonejd]

Over 25 yrs ago I bought a Mainship Mark I from a PO who had purchased her to do The Loop, checked that box, and moved on. Shortly after purchasing the boat he noticed the wave slap caused by the step in the hull at the bow. He immediately had the step filled with microbaloons mixed with (?) polyester. Was a very slick OEM-appearing fix. Problem gone!

 

[Ski in NC]

I have a spray rail built out of my chine. The chine slap is horrible in some conditions. I've had to put a monkey line off the transom and pull it to "ass-anchor" just to get some sleep.

Since I have a planing boat, I need that spray rail. But dang is it loud.

 

[McDan]

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?

I operate a 350 w/ single 3116. I get very economical cruise at 1600-1800 RPM making about 9 knots. As weight is a primary determinant of efficient operation adding another engine makes equal performance impossible! If you want speed you’re probably looking at the wrong vessel; a sport fisher w twin diesels would make more sense, and stuffing 2 engines into the space avail On a 350 will make maintenance nightmares as well.
I’d recommend the single w bow thruster. Mine is nimble.
PS: My surveyor described Yanmars as ‘throw-away’ vs the CAT which can be overhauled.

 

[JoeApicella]

Go with the twins.

When we did the Great Loop I wanted a single engine for fuel economy, so I bought a 2004 Mainship 400T with a single Yanmar 370. In Beaufort, SC we met a couple with the same boat except for twin 240 Yanmars, and we cruised together to NYC. We refueled together every time so our mileage, conditions, speed, etc. were identical. You can imagine my surprise when I discovered I used about 10% more fuel at each fill up. The only conclusion I could come to was my friend was running at a lower rpm than I was to maintain the same speed. While the single will be less expensive to maintain, half the oil, filters. coolant, zincs, etc., and there was more space in the engine room, this was far outweighed by the much better handling at the dock than the single with a bow thruster. Interestingly, when I sold the 40 I bought a MS430PT with twin Yanmar 440's and got close to the same 2 mpg as I did on the 40.
Joe Apicella
Glory Days
2007 MS 43 Pilot
MTOA #4222
AGLCA GOLD 2012

 

[reepermeg]

Hello sir. I have a 99 Mainship 350 for sale. It has twin Yanmar 4cyl diesels with 5000 hrs. I am the second owner of the vessel. If interested I can send you pictures. She is currently located in NJ. My email is reepermeg@msn.com. Thanks, Bill .

 

[jeffnick]

I am blown away by the overwhelming need to require a 'spare' engine in a diesel powered boat. Do they really fail that often that this should be a valid concern? I would never have considered this an argument for twins.

 

[rslifkin]

It's not so much that engines fail often as Murphy's law states that a failure will only occur at a very inconvenient moment. There are also plenty of ancillary issues that can cause loss of use of an engine without a major or predictable failure. I've personally sucked a bag onto a raw water intake in a crowded channel before. With a twin, that was just "shut down engine with climbing temperature, assess and resolve when safe".

 

[caltexflanc]

I am blown away by the overwhelming need to require a 'spare' engine in a diesel powered boat. Do they really fail that often that this should be a valid concern? I would never have considered this an argument for twins.

Well what would you call a Nordhavn with a "get home engine" for instance?

 

[OldDan1943]

Well what would you call a Nordhavn with a "get home engine" for instance?

My N46 had a main and get home. I personally call it "good planing"

 

[Jackhulse]

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?

I went from single engine sail to a Leopard 38 sail cat with twin diesels. No comparison as to ease of handling and maneuvering plus redundancy. When I went to power the twin diesels were a must, not so much for speed, since my Endeavour 44 Cat Trawler cruises at around 9-10 knots, up to 14 @ 3200 rpm, but balance and complete maneuverability. Since I don’t have a sail as backup any more, two engines are comforting
Jack Hulse
New Orleans

 

[slowgoesit]

When we did the Great Loop I wanted a single engine for fuel economy, so I bought a 2004 Mainship 400T with a single Yanmar 370. In Beaufort, SC we met a couple with the same boat except for twin 240 Yanmars, and we cruised together to NYC. We refueled together every time so our mileage, conditions, speed, etc. were identical. You can imagine my surprise when I discovered I used about 10% more fuel at each fill up. The only conclusion I could come to was my friend was running at a lower rpm than I was to maintain the same speed.
Joe Apicella
Glory Days
2007 MS 43 Pilot
MTOA #4222
AGLCA GOLD 2012

Joe, prop selection can have a lot to do with fuel economy as well. Depending on the RPM your were running, assuming that you had a 3 bladed prop you might have been able to either go to a 4 bladed prop, or have your 3 blade repitched/replaced with one with greater pitch. All depends on whether you want a "speed prop" or a "cruising prop". Granted those terms more generally apply to outboards, but the theory remains the same for larger engines/props. Just something to consider. First stop would be to get with the engine manufacturer and try and get fuel burn vrs rpm charts. Figure the most economical fuel burn, compare that RPM to the RPM your run to achieve the speed you like to cruise at. If the RPM you cruise at is say 2000 RPM for, let's say 7.5kts and that is a speed you like, but the manufacturer says the engine operates most efficiently at say 1700 RPM, consider reproping. A marine engine with access to specifics for your boat should be able to give you more direction as to most efficient prop/engine/RPM combo for your desired speed.

 

[34 mainship]

Hi, I have a very clean 2005 Mainship trawler for sale here in Connecticut. She is a single Yanmar 350 HP. I like the easy access to the single engine, also the other things like the Gen set, water heater and other bilge creature are much easier to service.
I have had single diesel boats for years and a well maintained diesel is very reliable.
This boat has both bow and stern thruster so the difference between this boat and a twin engine boat in docking is a wash.
I will post a boat for sale notice on this site today

Bill at 860-798-0456

 

[sunchaser]

An oft repeated issue.

When boat shopping there are many times that one has no choice on whether a single or twin. Mainship seems the exception thus the original purpose of the thread.

If one is Nordhavn shopping under 60' you get a single with a get home. If you like a Fleming you will get twins. If you like OAs, Rivieras, DeFevers, Offshores, Outer Reef etc you get twins with but rare exception.

If you like KKs or Selenes, singles rule but not always once into the larger sizes. If you like the Vripek steel hulled vessel from another thread you get twins.

It would seem, this oft tossed around subject is less about the virtues of single vs twin but more about a dreamy wish list that is already defined by the used boat market listings. So if you're Mainship shopping, pick the best boat which is well beyond a choice of one or two engines. Either works as cited by many Mainship owners on this thread.

 

[Seanair]

"For the last 30 years I have been a sailor, but now the wife and I are moving to a trawler. "

Get the single.