Running on one engine

[Steve W]

I did a major rebuild on a Grand Banks 42 woodie after it was dropped from a crane, it was powered by twin Cummins of about 300 hp each which to me seemed ridiculous, a lot of them had more realistic 120hp Leamans. The owner also owned an old 45ft Great Lakes fish tug(converted to a pleasure boat) with a 671 Detroit, he claimed that with any kind of a sea running he could make the trip from Bayfield Wisconsin to Duluth minnesota quicker with the fish tug. Thanks CDK for the real world insight, its looking to me like a single is probably the way to go, my only thoughts on the twins was that there are always these Gulfstars for sale that often have smaller twins in what should be a realativly slippery sailboat hull, if only you could retract that extra running gear.

Steve.

 

[Submarine Tom]

You could sell the two and finance a single installation.

 

[BPL]

Could an outboard be adapted to give emergency power for a trawler this size?

 

[Submarine Tom]

Absolutely.

 

[WestVanHan]

Well as usual it depends where you are/what you're doing.

Mine's not a trawler- 52', twin 640 hp,30 knots top, 3 mpg at 8.2 knots @ 850 rpm both engines.
But what happens on one engine is I need to add more throttle to maintain the speed and the mpg is actually worse.

In my area-very remote,thousands of uncharted rocks, logs floating under the surface,whales, etc and up to 17 knot tides and currents.

If your single dies at the wrong time and place,you are on the rocks in 20 seconds,swept out to sea,or the tidal rip from an inlet can push you onto the opposing shore.

In a remote area,if you prang the prop or some other engine problem and if your comm fouls up-you could be stuck there for months.

So for me,two engines.

If I ever end up on the rocks and really screw up the drive-CPP is going in.

 

[longcours62]

Our "longcours 62" is fitted with twin engines (too bigs) but mainly we run just one engine for economical speed , no probleme at the helm or for the autopilot.
up to 8,3 kts we use just one engine for a consomption of 1,46 lt per nm
the most economical speed is 6,6 nds and 0,61lt per nm
but for economy/speed we stay at 7,4 kts and 0,92 lt per nm
http://long-cours.62.over-blog.com/article-motorisation-77692001.html

 

[michael pierzga]

Hmm...Ive never thought about fuel burn per mile.

Wind, waves and current always distort the numbers. At cruise speed Ive made only 50 miles in 24 hours .

Consumption per hour against a passage plan works for me .

 

[Bglad]

Hi Steve,

If you are looking at Gulfstars then you are by default looking at older vessels. I recently completed a survey on a Gulfstar 38 the buyers were considering over other trawler types from the same era. In a nutshell the Gulfstar had very small twin diesels, all fiberglass tanks, no teak on the decks ever and very little wood on the outside. A pretty well done boat in the company of others with warts of all kinds. These guys really wanted a single engine boat but after looking at the alternatives found twin naturally aspirated small diesels were a reasonable alternative. If you buy enough problems of other kinds the cost of an extra diesel may seem irrelevant...

Bill G

Frosty, many well designed displacement powercats do in fact run on one engine on ocean passages, alternating to keep the hours even, i used to own a sailing cat with one outboard on the stbd transom and it tracked just fine without excessive helm but of course it didnt have the drag of running gear on the other side as well as having decent sized rudders, planing powercats probably dont run on one engine and i doubt if planing monohull powerboats do either but i have absolutly zero interest in these types of boats. This purpose of this thread is to try to see if anyone here has actual experience with a twin screw displacement trawler in the mid 30ft size range who may have real opinions not based on speculation, i can speculate as well as the next guy.

Steve.

 

[FAST FRED]

I believe the main motive for 2 engines in the Gulfstar was a very better slight ability to maneuver at the dock.

A single will do 95% of what twins will do while docking , BUT it requires more practice and skill.These boats were not built f for pro mariners.

There will be a saving running on 1 engine at 6K , but it would be so small that the loss from the cost of feathering sailboat props would be larger.

The hassle of removing a prop would be too high , and the drag from a non locked prop would be very high and many transmissions will not survive.

A "prop lock" on each shaft would work , but again the savings would be hard to see in the normal 200 hours a year of yacht operation.

I would 2 engines operate at cruise , and the lower RPM of the pair would pay in QUIET for any "extra" fuel burn.

 

[longcours62]

Our number are the

Hmm...Ive never thought about fuel burn per mile.

Wind, waves and current always distort the numbers. At cruise speed Ive made only 50 miles in 24 hours .

Consumption per hour against a passage plan works for me .

average made on 10000 nm, but of course you have a difference depending the wind ,currents waves, last dry docking etc etc

But for make comparison between different boats , what method we must use ?

 

[longcours62]

You are right , a single do 95%

I believe the main motive for 2 engines in the Gulfstar was a very better slight ability to maneuver at the dock.

A single will do 95% of what twins will do while docking , BUT it requires more practice and skill.These boats were not built f for pro mariners.

There will be a saving running on 1 engine at 6K , but it would be so small that the loss from the cost of feathering sailboat props would be larger.

The hassle of removing a prop would be too high , and the drag from a non locked prop would be very high and many transmissions will not survive.

A "prop lock" on each shaft would work , but again the savings would be hard to see in the normal 200 hours a year of yacht operation.

I would 2 engines operate at cruise , and the lower RPM of the pair would pay in QUIET for any "extra" fuel burn.

But for example our boat are able to cruise the canal , and enter a lock or pass under a (very ) small bridge on a single could be very difficult (for example our beam is 5,03m and the looks around 5,10 m ... i lost my last hair in some windy situation
Mainly mono engine have bowthruster.
For example for pass under some small bridges we need to 'put' the stern few centimeter more left or right before going ahead with mono engine we can do that just on one side (depending of your propeller pitch) on another side you will go litle ahead and some time this "little" could be too much ( may be I am not clear !!:?:)
Mono engines are clearly, less expansive, lighter, better efficiency but need a bowthruster for some type of docking (we had few mono engined boat )