Fuel economy

[markpierce]

People acquiring two-engined boats when they only want to use one engine; perhaps because the vast majority have twins because they want to go fast, and that's all that is available (singled-engined boats are relatively rare). Seems like using one of two engines saves only a small amount of fuel. Oh! the madness.

 

[Hydraulicjump]

This whole discussion is why I tune into Trawler Forum. I just learned a ton. Thanks posters. Much appreciated.

Maybe Joseph Conrad’s Heart of Darkness (most disturbing book I have ever read) would be correct in reference to using one engine when you have two: “The horror! The horror!”

I have only one. To quote Andrew Carnegie “put all your eggs in one basket and WATCH THAT BASKET” (Twain is associated with this quote too).

Thanks you all. Great discussion.

 

[motion30]

People acquiring two-engined boats when they only want to use one engine; perhaps because the vast majority have twins because they want to go fast, and that's all that is available (singled-engined boats are relatively rare). Seems like using one of two engines saves only a small amount of fuel. Oh! the madness.

And I was shopping for my boat 10 years or so ago I was in the market for a single engine 45-footer company as you stated they are rare and I simply could not find one

 

[Nomad Willy]

Mark wrote;
“ People acquiring two-engined boats when they only want to use one. “


At least they may get their engine loading up where it should be.

 

[motion30]

Thanks guys you were giving me some insight into different thoughts. I was just thinking about going far and the best way to improve my fuel economy. I have lived at anchor for like 8 years and rarely approached stocks only to fuel. I was planning to go to Guatemala from Key West last year when the price of fuel increased close to $2 a gallon the two or $3,000 additional cost in fuel put me out of the game. Looks like fuel prices are slowly dropping and I am thinking about a trip this year either Bahamas or Mexico. Keep your thoughts coming has anybody actually removed the prop and ran their boat like this? I could not find any information on that Hawaii trip

 

[Fletcher500]

I had thought the story about the guy pulling his prop half away across to Hawaii was an old wife's tale but there are quite a few people who have referenced it over the years. It would be interesting to see the actual article if anyone has it.

 

[lwarden]

All this talk of removing props mid-ocean seems crazy. Way too risky to do out in the open water.
Why not install additional clutches (or make some sort of drive disconnect) for each prop shaft at the coupling? Then just have the idle one freewheel while the other one drives? I doubt the drag would be significant if it had a bearing to support it well. I would think such a clutch exists in the world that would do.

 

[Comodave]

I had thought the story about the guy pulling his prop half away across to Hawaii was an old wife's tale but there are quite a few people who have referenced it over the years. It would be interesting to see the actual article if anyone has it.

No, it was a real story in PMM. I would not do it but he did. I used to have all the old issues but I got rid of them when we moved to Michigan. Now the magazine is pretty useless IMO.

 

[hollywood8118]

The freewheeling prop uses more energy than the fixed one. The water the boat is moving through sees the prop as a disc, vs the water slipping through the blade if fixed.


When we sailed across the pacific we locked our fixed pitch prop in place, the boat sailed faster with the prop locked than spinning, and the ride was much quieter too!
HOLLYWOOD

 

[Lepke]

Heavy duty diesels burn fuel more efficiently at 205°F So does my diesel PU. The truck gets 1/2 to 1 mpg better with a 203° thermostat. My Detroits improve 5%+. I do other things with the Detroit 671 naturals, like fuel additives and balance the cylinders hp output. I also run a H + Oxy generator that's good for about a 2 gph improvement. The engines were burning about 12 gph @ 10 kts. They needed a overhaul bad and that was some of the improvement, but I went to 8.5 gph @ 10 kts now. No changes in the hull or props.
Running on one engine with the prop spinning on the other, I make 4 kts and it's hard to turn and it burns 5 gph.

 

[catalinajack]

Heavy duty diesels burn fuel more efficiently at 205°F So does my diesel PU. The truck gets 1/2 to 1 mpg better with a 203° thermostat. My Detroits improve 5%+. I do other things with the Detroit 671 naturals, like fuel additives and balance the cylinders hp output. I also run a H + Oxy generator that's good for about a 2 gph improvement. The engines were burning about 12 gph @ 10 kts. They needed a overhaul bad and that was some of the improvement, but I went to 8.5 gph @ 10 kts now. No changes in the hull or props.
Running on one engine with the prop spinning on the other, I make 4 kts and it's hard to turn and it burns 5 gph.

And, yet, Lehman diesels have 205-degree overtemp alarms. Might there be a good reason for that?

 

[rslifkin]

And, yet, Lehman diesels have 205-degree overtemp alarms. Might there be a good reason for that?

It may be that Lehmans are fairly temperature sensitive (some engines are more sensitive than others). Or it may just be that if they normally run 180*, they figured 205* was an appropriate point for a warning, as they shouldn't get that hot without something being wrong (even if they could go hotter without imminent damage).

 

[diver dave]

Is it true that these hotter engines also spec special oil? GM dexos comes to mind. I may submit lube life is the major consideration with temperature.

 

[rslifkin]

Is it true that these hotter engines also spec special oil? GM dexos comes to mind. I may submit lube life is the major consideration with temperature.

It'll depend on the engine and how the oil is cooled. Raising the oil temps a few degrees (it won't necessarily change as much as the coolant temp increase) won't necessarily push the oil to the point where a different oil is needed (and you can switch to synthetic to handle higher temps better). And some engines are just harder on oil than others regardless of temperature.

With my engines (seawater oil coolers, no oil thermostats) the biggest issue is that the oil runs too cold at low RPM. I don't know that I have enough heat exchanger capacity to change to coolant loop oil coolers, so I've been debating adding thermostats to the oil cooler circuits to get oil temps up a bit. Hotter coolant temps would bring the oil temps up a little as well, as more heat would be rejected into the oil.