Fuel efficiency

[rslifkin]

If I were building a new vessel I would build a boat with two engines but one shaft. You can run or both engines. I know a small tug that has that set up.

That covers redundancy but not maneuverability. Even more ideal I think would be diesel / electric drive. 2 shafts, electric motor driven. 2 engines each driving a big generator. So running on 1 engine you have half the power available, but no loss of maneuverability or anything.

 

[Captain Ron D]

Single versus twins, twins versus single. Been there, done that for decades.
First boat was a 26' Single Diesel. Second boat was a 34' Twin Diesel, Third boat was a 38' Sportfisher with twin V-8 Diesels, and current boat is a 41' Mainship Trawler single Yanmar Diesel. Care to guess which one I had to get towed in with???? Nope, the 38' Sportfisher with twin V-8 Diesels !!! Blew the exhaust elbow off the turbo and filled the engine room with exhaust. The starboard engine got soot into the intake and started wheezing and gasping also. I guess he didn't want to be left out of the 'action' Anyway had to be towed from Dana Point back to San Diego Bay. 11 Hour tow, thanks to the fine folks at Vessel Assist !! Worst part of it was having my boat towed in front of the SWYC Club House so everyone could see and laugh.! I have never had any major issue with any of the single engine boats in the past 40+ years of boating. As was mentioned prior, concentrate on quality, sound construction, proven record and proven engine (s). Can't go wrong with that. 'Captain Ron'

 

[moparharn]

This is how the big boys do it. Big pockets too. I think is clearly a great idea, but not likely something I could afford. Reliability would be in the redundancy.

That covers redundancy but not maneuverability. Even more ideal I think would be diesel / electric drive. 2 shafts, electric motor driven. 2 engines each driving a big generator. So running on 1 engine you have half the power available, but no loss of maneuverability or anything.

 

[Irish Rambler]

Jesus H guys why complicate life, keep it simple !
Lets get back to the beginning.
Are you guys down for the weekend and just out for a blast to impress your friends ? Then go for twins and pay the bills.

If your retired what's the freekin rush ?

Enjoy life, cruise at hull speed, just put the boat in gear, the admiral on your knee, the mind in neutral, relax and enjoy life

Maybe I've got the whole wrong idea ?
But a nice lunch, a glass of wine, a siesta with a drop of massage oil does wonders for your marriage

When the good lord made time he made a pile of it and you won't use it up however much you race about
Boats are built to be enjoyed so leave all your angst and worries on the quay

 

[Nepidae]

You've probably read most of the comments, pro & con.and from a strict efficiency standpoint single will be more efficient, BUT, from a safety standpoint dual engines are better.

Maneuvering is certainly better. Docking easier.

I had to stop an engine while transitioning the coast oh NJ and continue on 1 engine. Certainly lost efficiency but was able to get to port.

I think you should consider safety more than fuel economy.

BTW, with twin 135hp Ford Lehman engines we burn less than 4gph at 1700rpm moving 7-8mph.

 

[Slider70]

The other factor that is at play is how far apart are the shafts on any given twin installation? If far apart the negative of running on one engine is higher than if the shafts are closer together. Though wider equals easier docking without the expense of a bow thrusters, given one remembers if the bow goes one way the stern goes the other.

I track all my yearly costs. Upgrades and repairs to my 32 year old boat far out step my fuel costs even with the ridiculous price of fuel in Canada.

In my four large boats I have owned I have had mostly singles but now a twin. I love my twins except when working on them in a cramped engine room.

Life is a compromise.

 

[sunchaser]

Blew the exhaust elbow off the turbo and filled the engine room with exhaust. The starboard engine got soot into the intake and started wheezing and gasjping also. '

Sounds more like a deferred maintence issue than twins Vs single.

 

[rgano]

See my avatar? That's how my boat is seen by anybody but the folks who live in the immediate vicinity of my pier. I am retired; time's running out; I have no time to waste getting to where I am going on the boat; pick any excuse, but I am NOT into fuel efficiency. Twin engines? No room on this boat; so TowBoatUS it is. Used 'em once already since I bought this boat (burst seawater cooling hose). Werqs fer me.

 

[Tugalert]

YEP, Did you like the set up?

 

[long-cours.62]

Motor trimaran

One of my friend, who built sailing catamaran, built "for the fun" a motor trimaran with some "spare hull" who stay in is boat yard .
Just to see
he took a catamaran hull lengthened her to a very narrow bow , put 2 small side hull an out board and try ....
After some adjustment he got , for example, at 7 kts 0.12lt per nm
or 31.54 nm per us gallon !!
2 cabins, wheelhouse, kitchen, toilette

ok the design is not very nice because he use some different part from his backyard but 31.54nm per gallon !

 

[long-cours.62]

Motor trimaran

One of my friend, who built sailing catamaran, built "for the fun" a motor trimaran with some "spare hull" who stay in is boat yard .
Just to see
he took a catamaran hull lengthened her to a very narrow bow , put 2 small side hull an out board and try ....
After some adjustment he got , for example, at 7 kts 0.12lt per nm
or 31.54 nm per us gallon !!
2 cabins, wheelhouse, kitchen, toilette

ok the design is not very nice because he use some different part from his backyard but 31.54nm per gallon !

 

[Simi 60]

^^^^^^^ something like????

This one in the Philippines

boat

We contemplated getting a Banca at one stage.
Something like this , cheap cheap and already in paradise.

https://www.tradeaboat.com.au/details/134-2002-custom-banca-boat-custom

 

[JOY-SEA]

My favorite topic -
Twin 6 cylinder Volvo Penta on my 30 ft Regal cruiser
Boat is beautiful , rosewood cabinets , luxury galore , leather seating ,
cold a/c , My home away from home
Done it all too try and save fuel,
Running one engine 8 knots , two engines 8 knots , Still get the same
mpg , 1 - 11/2 per mile
They routed PS on starboard engine.
Try docking with no PS , Then the hour meters are not in sink ,

Retired spending lot of time aboard , I use multiple days of every week
Stay close too home port . Number of few day journeys that gas
gauge stays on full , then it drops like a anchor ,
Selling considering a different set up
My buddy has a 38 ft sail vessel , He too uses his boat often ,
He makes fun of me ,
Last year his fuel bill was 150 bucks and that was traveling
few weeks coastal ,

bucks.

 

[dacap06]

I may be opening myself up for some ridicule here,but looking for input as to using one engine out of two while underway in reasonable conditions.After helping a friend return to dock with only starboard engine available,and no need for wheel usage more than normal,I received a message from another friend that he did not want twins as too expensive to run the loop.This combination makes me ask thoughts about alternating engine use during travel.Thanks.

f


Answers to this question over the years are all over the place. Being an engineer, I am a firm proponent of "try it and see" over a long trip. If you have modern engine control electronics, you can just read your fuel flow for a given speed. In this case, I'd build a table of fuel flow vs SOG for each engine separately and for both engines together.

If you don't have modern electronics, finding a reasonably accurate answer is a lot more involved and and a lot more trouble. You might just want to measure it over a long trip for your typical transit speed.

 

[FF]

"Maneuvering is certainly better. Docking easier."

Perhaps 5% better for a skilled operator.

 

[Wxx3]

Sounds more like a deferred maintence issue than twins Vs single.

How do you care for your exhaust elbows?
Give them a massage every week??