Twin Drives - General Question

[mpkoontz48]

On dual motor boats (both gas and diesel), is it the case that one motor is turning opposite? Always?

Does that make one engine easy to replace while the other is a bear to replace?



Thanks,
Mark

 

[FF]

Frequently the engines rotate the same, the reverse shaft rotation is done inside the tranny.

Yes some engines can be built with reverse rotation , but it is no longer common.

 

[mpkoontz48]

Frequently the engines rotate the same, the reverse shaft rotation is done inside the tranny.

Yes some engines can be built with reverse rotation , but it is no longer common.

Hadn't thought of that -

Is it a "special" tranny, or just controls hooked up opposite?

 

[rslifkin]

It depends on the boat. Older gassers (like my boat) typically have counter-rotating engines. Diesels and newer gassers typically have both engines rotating the same. Depending on the transmissions they use, some have different versions for standard and counter rotating (such as a Velvet Drive CR2), some are designed to run the same in either direction, just hook the shifter up the other way around (like most modern ZF transmissions).

So basically, every possible way you've thought of has been done at some point.

 

[jleonard]

Some of the older diesels are counter rotating. I had such a "bastard", a single Perkins T6.354 in my old Mainship.
Some of the parts were difficult to find, such as the coolant circulation pump as the fins needed to be in opposite direction.

 

[Pete Meisinger]

Older gassers were almost always counter rotating.

A buddy once froze both of his gassers through a bad winterizing job. (he drank a bit) He put two new engines in the boat. In the wrong holes! He had to pull them out and do a switcheroo.

pete

 

[Ski in NC]

Reverse rotating engines (both gas and diesel) were common in the 60's, 70's and into the 80's. Common in Detroit two-strokes, Cummins v-blocks and some Perkins. The transmissions in that era (Allison, Capitol, Velvet drive) tended to have a dedicated fwd gear, and had a reverse gear but it was not as robust and not intended to handle full power for long periods.

Starting in the 80's, modern transmissions started becoming popular and these could handle full power in either direction and engines could both be std rotation. Pretty much anything in the 90's up the engines are all std rotation with counter rotation done in the gears.

How the rotation change was done on the engines varied a good bit. Detroits were designed from the start to be built in either rotation so nothing weird there. Some of the car based engines (gas) were never designed to be reverse rotation, and so there can be challenges there. Unique camshafts or cam drives, etc. Starters and pumps different.

Note that all modern engines used in trawler type boats are std rotation as is common in highway and industrial equipment. Rotate CW when looking at front of the engine from the front.