Sterndrive Question

[mmullins]

Does anyone have any experience running a twin engine sterndrive on one engine with the other trimmed all the way up? I know running a twin inboard on one engine can overheat the idle transmission. I just wondered if the same would happen with an idle stern drive trimmed up. It seems like an economical way to cruise and just use the second engine when needed.

 

[DavidM]

No experience but as long as the trimmed up prop doesn’t turn, you should be fine running on one engine.

David

 

[Gdavid]

The shifting mechanisim and gear box of an outdrive is in the bottom the of the drive, just forward of the prop and cooled by the water passing over the aluminum housing. No risk of overheating from being turned off whether trimmed up or trimmed down but I would caution to determine which engine has the power steering pump, turning this engine off will result in much heavier steering. I also would not idle the engine with the drive trimmed up, just turn it all the way off as the universal joint would be spinning at an extreme angle.

 

[Ken E.]

Have you tried running the boat with one drive up? My guess is that steering would be a problem, as Gdavid mentioned. You should also do some do some fuel consumption tests to see if it's even worth doing it, with having to run the on-engine harder. The best way to save fuel that I've found is just to go slower.

 

[mmullins]

I’m operating at displacement speed. Just don’t need 2 big gas V-8’s to travel that slow

 

[Crux]

The shifting mechanisim and gear box of an outdrive is in the bottom the of the drive, just forward of the prop and cooled by the water passing over the aluminum housing. No risk of overheating from being turned off whether trimmed up or trimmed down but I would caution to determine which engine has the power steering pump, turning this engine off will result in much heavier steering. I also would not idle the engine with the drive trimmed up, just turn it all the way off as the universal joint would be spinning at an extreme angle.

The smallest Merc drive, the Alpha, is only model with shifting in lower unit.

All others are the Bravo series which have cone-clutch shifting in upper unit, cooled internally by circulating gear oil alongside water pickup passage.
No effect on either when trimmed up/engine off

If you try this 'engine off' idea and like it, to equalize hours you can easily add the power steering back to the one without it. But, that would require a valve arrangement, and an occasional engine space visit to select which engine to handle steering with the other in 'bypass'

 

[Gdavid]

The smallest Merc drive, the Alpha, is only model with shifting in lower unit.

My mistake, most of my experience is with the alphas but a big block would be a bravo.

 

[Slo-Mocean]

Being the boat is a 1978 if the same as in his signature it would be a old TRS with either a Merc trans or a B&W, still odd to have sterndrives on a trawler style vessel.

 

[mmullins]

Being the boat is a 1978 if the same as in his signature it would be a old TRS with either a Merc trans or a B&W, still odd to have sterndrives on a trawler style vessel.

Ha! Sorry for the confusion. My current trawler is a single inboard diesel. I'm looking at possible replacements for my aging crew. I've never been a fan of I/O's but the thought of raising one drive out of the water and running on one engine looked appealing. I wasn't aware of the power steering factor. Of course, I could replace the stock wheel with a big sailboat wheel:lol:

 

[Slo-Mocean]

Ha! Sorry for the confusion. My current trawler is a single inboard diesel. I'm looking at possible replacements for my aging crew. I've never been a fan of I/O's but the thought of raising one drive out of the water and running on one engine looked appealing. I wasn't aware of the power steering factor. Of course, I could replace the stock wheel with a big sailboat wheel:lol:

My brother has a 39 Sea Ray with twin 454 gas up on the Great Lakes that he cruises yearly on one engine at 8 knots. Just sets the auto pilot and plays cards.

Why a stern drive over in boards ?

 

[mmullins]

My brother has a 39 Sea Ray with twin 454 gas up on the Great Lakes that he cruises yearly on one engine at 8 knots. Just sets the auto pilot and plays cards.

Why a stern drive over in boards ?

I prefer inboards. One of the boats I was considering had sterndrives. I was going to poo-poo it outright and then it hit me that one could stow an engine, operate off one and use the other for docking, faster speeds when needed or emergencies. I would rarely operate it above displacement speeds.

 

[DrissZougari]

please keep in mind that stern drives are never completely out of the water. in your case, the prop will be forced to turn in the worst position "ie up".

 

[Jetstream]

We had a 34 foot flybridge boat with twin stern drives and I did on occasion operate it on one engine. Ours were Volvo Penta's but they are mostly similar. You will get very good efficiency on one but it's not worth tilting the inoperative leg up as the drag from the cavitation plate and prop will actually increase on most boats as the legs in our case anyway were still fully submerged at full up tilt.