psneeld
Guru
You could have done a simple search. Your question has been asked and answered before. Free wheeling a prop has also been addressed.
No definite answers I know of....
You could have done a simple search. Your question has been asked and answered before. Free wheeling a prop has also been addressed.
No definite answers I know of....
Surprisingly, twins cost little if any more. That has been my experience anyway when pricing out vessels (Nordhavn and KK) for new build or used that can often be made either way.
"Surprisingly, twins cost little if any more. That has been my experience anyway when pricing out vessels (Nordhavn and KK) for new build or used that can often be made either way.
So his reduced fuel consumption was based on a reduction of speed not running on one engine. My boat burns 2 GPH at 7 knots, 1.2 GPH at 6 knots, and .7 GPH at 5 knots. Savings are huge when you slow down.A friend had a trawler, now lost to Hurricane Michael, with two NA 4-cylinder Detroits and ran all the time on one engine with RPM reduced such that he made the wake of a canoe. He didn't care if he ever got anywhere. Says the fuel savings we enormous from his earlier 2-engine practice. He did not lock the off shaft.
For arguments sake let's say the OP's vessel burns 5gph at normal cruise. He cruises 200 hours per year resulting in 1,000 gallons consumed. At US prices= $2.50 the cost is $2,500.
Shutting off one engine and resultant fuel savings, if any, then is part of the debate. If all in factors amount to a 10% fuel savings then I've got $250 in my pocket.
But wait. I've run more hours, gone slower, missed 3 current changes, increased cruising hours while saving $250. Those dollars are not noticeable given our annual expenditures of 100X or more of that amount. Leaving the boat at the dock will still not materially result in big savings. So the biggest savings is to sell the boat.
I did a totally unscientific uncontrolled study of GB36.
My WAG indicated a premium of 20% or higher for twins, and there were twice as many on the market.
Had the opportunity to run on one engine to get home with rudder cranked over and free wheeling prop. No Thanks.
I have 44ft Marine Trader with twin Cummins 210hp. The other day I had a warning light for the port engine, so i turned it off and continued on with just the starboard. I was surprised that I felt no difference and didnt even need to increase rpms to maintain the same 7ish knt speed.
Does anybody here with twins ever intentionally just run on one engine for fuel economy? Are there any mechanical risks from long term use (due to the uncentered nature of forces?)
What's the deal with all the grumpy old man snark??
I asked a simple question.
And it is a fact that most trawlers are overpowered for displacement speeds. Not saying it isn't nice to have the power & the twins for certain situations...but it's not even close to NEEDED for slow speed icw cruising....your calculations will tell you that.
Now whether it's bad for the transmissions (I have borg-warner) is out of my range of knowledge. But that's why I specifically asked about any mechanical risks in the OP...
I have a gulfstar 43 mki with twin 135 Perkins. On one screw I burn 4gph at 1500 making about seven kts. On two screws at 1500 I make about 8.5 kts and burn 2.5 gph total.
With the full keel and locked prop (to prevent tranny damage) I burn almost twice the diesel on one screw as I do two.
If you could make it efficient enough to nearly match a mechanical drive, a diesel electric setup with twin screws and 2 or 3 gensets would be a very attractive option. Just bring more genset power online when you want to go faster. Might still be a little less efficient at high speeds, but at low speeds you could almost certainly do better than anything other than a setup with engines optimized for that specific slower speed (which wouldn't have the ability to go much faster).
For those talking about extra maintenance costs for shafts, props, etc. on a twin, don't forget this: a single with the same total horsepower will have much bigger shafts, props, etc. so the overall maintenance costs will be a lot closer than you'd think, just with less individual parts involved.
On arrival the transmission of the engine that I was not running was damaged - needed a rebuild. Cause? Not sure but I suspect running without lubrication?