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Old 05-14-2020, 06:35 PM   #101
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Gb36 single vs twin is a great baseline example. Not sure though if percentage or real dollars is the right comparison. But I wouldn't be surprised if $30k - $40k, is the right uptick with all other things being equal. Of course, not all twins are the same - defevers are well protected running gear and accessible engines on outboard side. Not so many other twins.
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Old 05-14-2020, 06:48 PM   #102
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Lindbergh crossed the Atlantic with one engine.
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Old 05-14-2020, 06:54 PM   #103
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https://youtu.be/9Q7oxIbD3MY

And, for guys running twins...if you shut down one engine..How do you cool the stuffing box and transmission with the prop freewheeling?
As far as cooling the shaft seals, in my case PSS, both engines send water to both seals, so running on one engine cools the seals on both shafts.

Regarding freewheeling the dead-side prop, most Twin Disc gears are OK up to 8 hours if you monitor the temperature with a laser thermometer or similar. The TD owners' manual has the models and the freewheeling procedure. Other gears like the Allisons M-20's I had behind Detroit 871's can't be freewheeled at all, which requires that you lockdown the shaft. Not sure about ZF.
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Old 05-14-2020, 06:54 PM   #104
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Lindbergh crossed the Atlantic with one engine.
Yup---just after the guys in the three engine S35 crashed.

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Old 05-14-2020, 07:08 PM   #105
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Detroit Diesel 671's were designed to be re-sleeved. As long as you can get sleeves they will last 2 days past forever. Anyone who ran a few of them kept a set of sleeves in the shop.

But all sleeves didn't wear out at exactly the same time. There were manufacturing tolerances so one sleeve ID could have been oversize or the ID wasn't parallel so the failure mode was random. Same with exhaust valves. They were machined to tolerance, installed (probably without lapping) and run. All valves don't burn up at the same time.

But until the engine throws a rod through the crankcase, they are rebuildable (not counting volvo's) with replacement parts. I consider that normal maintenance but just as we amortize the cost of a new heating system we can also "amortize" the cost of a rebuild into the cost of the boat rather than considering it an expense item such as an impeller.
I was a Co-Op Engineering Student at General Motors Institute, sponsored by Detroit Diesel in 1968. So 6 weeks in Flint at school and 6 weeks in the factory on Outer Drive in Detroit. One of my favorite assignments was the "Engine Repair" department where engines that failed dyno testing would be disassembled and inspected and repaired. I got proficient enough to take a 6-71N completely apart and re-assemble in less than a full day. Wonderful engines. Developed a reputation for leaking oil, but otherwise built to last forever if you keep replacing the worn out parts. Sounded awesome. Turbo charging and electronic fuel injection controls kind of obsoleted them, but I seriously looked for a boat that was powered by one.

Since I intend to maintain the engine in my boat myself--having room to work was a major factor in choosing a single engine.
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Old 05-14-2020, 07:12 PM   #106
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Very few comments about range. I always thought the attraction of a "trawler" was how far it could go on a tank of fuel? Single engines win that contest don't they?
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Old 05-14-2020, 07:31 PM   #107
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Very few comments about range. I always thought the attraction of a "trawler" was how far it could go on a tank of fuel? Single engines win that contest don't they?
Got four fuel tanks. Presumably I'm able to boat to Seattle from San Francisco, although I've no such urge.
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Old 05-14-2020, 07:50 PM   #108
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Very few comments about range. I always thought the attraction of a "trawler" was how far it could go on a tank of fuel? Single engines win that contest don't they?
Range is a good/bad thing. If you don't use it, fuel goes stale.

Personally, my benchmark is 1500 nms range which will get me from Panama Canal to Florida. Or Socal to Acapulco to Panama.

To answer your question though, singles are more efficient than twins, but not by much. More about how the boat is setup and tankage..
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Old 05-14-2020, 07:53 PM   #109
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Very few comments about range. I always thought the attraction of a "trawler" was how far it could go on a tank of fuel? Single engines win that contest don't they?
Not necessarily. Range varies more with the design intent of the boat than anything.
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Old 05-14-2020, 08:08 PM   #110
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Stroutmail wrote;
“Very few comments about range. I always thought the attraction of a "trawler" was how far it could go on a tank of fuel? Single engines win that contest don't they?“

Trawlers are coastal cruisers and long range is not a big priority or even a priority at all for most. Wint our little Willard we can go to Ketchikan from Seattle. But it would require running 24-7 and no stopping or anchoring. And if we solwed to 5 1/2 knots we could go forth anchoring as usual. Plenty of range as there’s lots of places to stop and get fuel.
And in most coastal areas in the US there are many more places to get fuel than in the PNW.

Re fuel burn singles v/s twins a twin would be quite To more likely to have better range than a single if she was powered the way twind should be powered .... that is w the same total hp. But for some dumb reason twins and singles in typical trawlers of the 70’s and 80’s the twins had the same engine as the singles. So how’s a boat w twice as much engine going to be equal or better fuel burn wise as a single? If the GB 36 had 190 cu. in. 60hp engines in the twin it would almost certainly beat the single in burn rate at a given speed.
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Old 05-14-2020, 08:22 PM   #111
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As far as cooling the shaft seals, in my case PSS, both engines send water to both seals, so running on one engine cools the seals on both shafts.

Regarding freewheeling the dead-side prop, most Twin Disc gears are OK up to 8 hours if you monitor the temperature with a laser thermometer or similar. The TD owners' manual has the models and the freewheeling procedure. Other gears like the Allisons M-20's I had behind Detroit 871's can't be freewheeled at all, which requires that you lockdown the shaft. Not sure about ZF.
Our ZF45A are good to freewheel. Also, the PSS don't need water upto a certain speed (11kn I think it was?) and since on one engine we can only push to about 8kn, we haven't got the cross-over PSS water connections.
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Old 05-14-2020, 08:28 PM   #112
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Trawlers are coastal cruisers and long range is not a big priority or even a priority at all for most. Wint our little Willard we can go to Ketchikan from Seattle. But it would require running 24-7 and no stopping or anchoring. And if we solwed to 5 1/2 knots we could go forth anchoring as usual. Plenty of range as there’s lots of places to stop and get fuel.
And in most coastal areas in the US there are many more places to get fuel than in the PNW.
Good point. If I run 6.5 kts or so, even with my fuel guzzling gassers, the only place I know of in North America that might be questionable in terms of range with a good reserve is the Alaska run. And even that is probably do-able.
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Old 05-14-2020, 08:32 PM   #113
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Range is a good/bad thing. If you don't use it, fuel goes stale.

Personally, my benchmark is 1500 nms range which will get me from Panama Canal to Florida. Or Socal to Acapulco to Panama.

To answer your question though, singles are more efficient than twins, but not by much. More about how the boat is setup and tankage..
Beebe provided a definition of passage-maker of 2400nm range at 7.4kn, self sufficient for two weeks. I've amended it slightly with powercats in mind to be 2000nm at 6-8kn. Everyone has their own ...

Singles use less fuel than twins - up to a certain speed. That's not necessarily "efficiency" unless you focus only on fuel used and forget weather travelled through, time of departure and arrival, extra/less engine maintenance due to lower hours, and many other factors.

If you want to limit the discussion to only the speeds in which the boat can go on one engine, and then compare that to the fuel used with one engine vs two engines, you'd be usually right to say one engine is more efficient... unless the weather and sea conditions slowed you down to a speed that wasn't "efficient" in other ways where cranking up the second engine to go the same speed would help - like getting out of the way of a low pressure.
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Old 05-15-2020, 07:04 AM   #114
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https://youtu.be/9Q7oxIbD3MY

Always wondered if anyone ever used an outboard for a "get home" engine? A remarkably small outboard will move a 36 foot trawler at 4-5 mph in smooth water.

And, for guys running twins...if you shut down one engine..How do you cool the stuffing box and transmission with the prop freewheeling?

One issue might be that outboards are generally gasoline. And a majority of trawlers are diesel . . . so your supply of gasoline might not be enough to get you home.



On Freewheeling one prop. Check with the manufacturer of your transmissions. Some, like Velvet drives tolerate freewheeling just fine with no time limit according to the manufacturer. Others, not so much!
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