Twin screw
- Thread starter davesail
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bfloyd4445
Guru
chuckle....the old twin vs, single thing again. I've been trying to decide which i shall buy a single or twin. I'm leaning towards a single just because of the fuel efficiency and cost savings myself. If you run on one engine you still have extra drag and the running engines prop isn't in the correct location causing a helm issue.
JohnP
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Congrats on the new Boat.. You can search some of the old threads, I think a lot has been said about running only one engine. If I had a twin I think I would run them both. I talked with a bunch of Grandbanks 36 owners at one of their get togethers and running both did not really amount to a big difference in fuel burn. The speed was the main factor, find your best cruising speed and if you push beyond that the fuel consumption goes up a lot.
Good Luck JohnP
twistedtree
Guru
There are lots of arguments on both sides. Things to consider if you decide to try it are:
1) If you have dripless shaft seals, they often, but not always, require pressurized water to cool and lubricate them. The water flow sometimes also lubricates the cutlass bearings. If you shut down an engine, the water flow stops if it's drawn off the engine's raw water system and could lead to seal and bearing problems. Be sure you understand how this works on your boat, and whether it's a problem with the engine shut down and the prop still turning.
2) Some transmissions have limits on the shaft turning when the engine is shut down. With the engine off, there can be less lubrication within the transmission. Some manufacturers limit the amount of time that you can free-wheel, and others require that you lock the shaft completely. Check out what the requirements are for your transmission, and be sure you are following them.
Note that if you let the shaft/prop free-wheel it will minimize drag. Just be sure you aren't trashing your shaft seal, cutlass, or transmission while you do it. And if you have to lock the shaft/prop, the drag will obviously reduce the gain from shutting down the engine.
Good luck and let us know the results if you do some testing.
1) If you have dripless shaft seals, they often, but not always, require pressurized water to cool and lubricate them. The water flow sometimes also lubricates the cutlass bearings. If you shut down an engine, the water flow stops if it's drawn off the engine's raw water system and could lead to seal and bearing problems. Be sure you understand how this works on your boat, and whether it's a problem with the engine shut down and the prop still turning.
2) Some transmissions have limits on the shaft turning when the engine is shut down. With the engine off, there can be less lubrication within the transmission. Some manufacturers limit the amount of time that you can free-wheel, and others require that you lock the shaft completely. Check out what the requirements are for your transmission, and be sure you are following them.
Note that if you let the shaft/prop free-wheel it will minimize drag. Just be sure you aren't trashing your shaft seal, cutlass, or transmission while you do it. And if you have to lock the shaft/prop, the drag will obviously reduce the gain from shutting down the engine.
Good luck and let us know the results if you do some testing.
Nomad Willy
Guru
davesail,
Look on BoatDesign.net. There is an extensive thread on running single w a twin.
Look on BoatDesign.net. There is an extensive thread on running single w a twin.
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BruceK
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Every so often an auto maker puts a little engine in a big car and claims it is economical. Most of the time the little engine has to be run hard to move the auto and uses a lot of fuel. You`d need to do tests, I suspect you save some fuel, but will it halve consumption? Doubt it.
You might have to maintain some helm to steer straight on one, which has a braking effect. The rudders are designed for 2 engines, not 1. Others have already pointed to transmission issues. You lose the ability to steer using engines, and lose speed unless you run the single hard.
I think: if you wanted twins, you bought twins, you run them both.
You might have to maintain some helm to steer straight on one, which has a braking effect. The rudders are designed for 2 engines, not 1. Others have already pointed to transmission issues. You lose the ability to steer using engines, and lose speed unless you run the single hard.
I think: if you wanted twins, you bought twins, you run them both.
psneeld
Guru
It really depends...I had a sportfish that I trolled on one engine a LOT.
When I saw the efficiencies in real numbers...and having made many runs up and down the ICW delivering boats seeing how often you slow down anyway...I always thought that I would keep that boat and run her to Florida and back on one engine.
I knew I would save a lot of money on fuel... but it is a trade off with having to find and possibly pay for more spots to tie up...but that's a different cruising discussion.
The reason I say it all depends is because many here will argue theory that may or may not not apply to your boat....which determines everything.
Get with a loca guy you know/trust that has their act together and take them on a few calculation runs. They can tell you whether or not your boat is a candidate to run on one.
When I saw the efficiencies in real numbers...and having made many runs up and down the ICW delivering boats seeing how often you slow down anyway...I always thought that I would keep that boat and run her to Florida and back on one engine.
I knew I would save a lot of money on fuel... but it is a trade off with having to find and possibly pay for more spots to tie up...but that's a different cruising discussion.
The reason I say it all depends is because many here will argue theory that may or may not not apply to your boat....which determines everything.
Get with a loca guy you know/trust that has their act together and take them on a few calculation runs. They can tell you whether or not your boat is a candidate to run on one.
I think Bruce summed it up very well. If you want/need/like single engine economy, lighter weight, and better engine access, buy a single engine boat.
If you want/need/like twin engine maneuverability and redundancy, or like me simply like operating multiple engines-- I love hearing the big whale watch boat in our marina fire up; it has three engingines-- then buy a twin engine boat.
But to my way of thinking, buying a twin and then trying to operate it as a single is a waste of time. Even if a prop can be freewheeled without damaging other drive components, you're not saving anywhere near enough fuel to make up for the higher purchase price, higher service, maintenance and repair costs over time, reduced engine access, and doubled weight the boat has to lug around and that the one operating engine has to push.
I believe in the overall scheme of things running a twin on one is a false economy. The few people I know who do it, after hearing their reasons why, it's obvious to me that they should have bought a single engine boat in the first place. It would have served them much better.
If you want/need/like twin engine maneuverability and redundancy, or like me simply like operating multiple engines-- I love hearing the big whale watch boat in our marina fire up; it has three engingines-- then buy a twin engine boat.
But to my way of thinking, buying a twin and then trying to operate it as a single is a waste of time. Even if a prop can be freewheeled without damaging other drive components, you're not saving anywhere near enough fuel to make up for the higher purchase price, higher service, maintenance and repair costs over time, reduced engine access, and doubled weight the boat has to lug around and that the one operating engine has to push.
I believe in the overall scheme of things running a twin on one is a false economy. The few people I know who do it, after hearing their reasons why, it's obvious to me that they should have bought a single engine boat in the first place. It would have served them much better.
Nomad Willy
Guru
Floyd your touch screen may be nice. I have the i-pad w the touch screen but the most important element of my computer is picture viewing and I've got a very bright and sharp 27" stand alone i-mac. My router is a "Time Machine" that backs up automatically at any interval I choose. No security problems that I know of but went into the Time Machine and looked around and saw all kinds of spam and really undesirable stuff. You guys can have that window stuff .... been there done that. My computer is actually user friendly. And you should see the pictures!
FF
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Cruise Speed is the key,
With twins you may be able to run in the low teens , 1mpg or 1/2 mpg and get the trip over quickly.
You can also get a better slip earlier in the day, a better seat at the bar or in the dining room.
On a single or a twin at displacement speeds the trip cost will be 1/3 - 1/5 or so and if you anchor no marina fees need be paid till south of Port Orange FL,
Really depends on the old question, is it the TRIP or the Destination that is your goal.
The difference in fuel burn at idle is very minor , the better question is how much trash is in the water , do you want to loose both props at once?
With twins you may be able to run in the low teens , 1mpg or 1/2 mpg and get the trip over quickly.
You can also get a better slip earlier in the day, a better seat at the bar or in the dining room.
On a single or a twin at displacement speeds the trip cost will be 1/3 - 1/5 or so and if you anchor no marina fees need be paid till south of Port Orange FL,
Really depends on the old question, is it the TRIP or the Destination that is your goal.
The difference in fuel burn at idle is very minor , the better question is how much trash is in the water , do you want to loose both props at once?
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Pineapple Girl
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Apple / Mac/ iwhatevers convo moved to off topic
http://www.trawlerforum.com/forums/s51/apple-mac-iwhatevers-twin-screw-thread-9085.html
http://www.trawlerforum.com/forums/s51/apple-mac-iwhatevers-twin-screw-thread-9085.html
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