what's the usual method to achieve counter rotation?

[captndon]

My limited twin engine experience was with a twin gas sportfisher in the US. I always thought the most common technique for LH/RH rotation was because of the rotation of the engines. My research on this board suggests a high incidence of achieving this with the gearboxes instead. It also appears that this might be tricky because all gearboxes do not perform this way.

I'm living in SE Asia and good cheap used diesels are easier to source than marine gearboxes. For my planned project, can a diesel be modified to turn either way? When installed which rotation is stbd and which is port?

[whitepointer23]

with diesels you normally run a reduction and most modern reduction gear boxs can be set to turn either way. much easier than trying to convert an engine. i have counter rotating engines and they are a pain to do anything with. the other alternative is to turn 1 engine around and run a driveshaft off the crank pulley to the gearbox.

[captndon]

I understand - it's the "most" word that has me worried. I've read many posts here with many "yeah but" included. So my question stands - can an engine shop convert to opposite rotation. I simply want to know my options. Thanks.

Oh and the other question too - what's the optimal rotation - inward or outward? Or does it matter?

[whitepointer23]

outward, right rotation starboard, left port. surely you can do a search and find what boxs can convert, i would hate to imagine what the engine shop would charge for a one off job. another option is to use detroit diesels, you can make them run any direction. 2 strokes not the new 4 strokes.

[CDK]

Originally Posted by captndon

I'm living in SE Asia and good cheap used diesels are easier to source than marine gearboxes. For my planned project, can a diesel be modified to turn either way? When installed which rotation is stbd and which is port?

You need the gearboxes anyway if you want to power a boat, so pick ones suitable for continuous running in reverse. Way cheaper than converting a 4 stroke diesel engine.

Changing engine rotation is only feasible if camshafts, starter motors etc. are available for that purpose.

[captndon]

OK - I've got a clearer picture of the specifics now.

Thanks

[gonzo]

You can take the power from the nose of the engine instead of the flywheel too. One engine points backwards from the other. This has been done for decades.

[captndon]

Good comment - do you think I'd find details on coupling the gearbox on this website?

[gonzo]

Some engines, like Caterpillar are already set up for it. Others may need some modification. What engine are you planning on using?

[captndon]

I have not decided yet. My untested plan is for a 3 to 4 ton power cat. I'd like to cruise at 16 knots and expect calculations to point to 100 hp or so for each hull. Approx 2:1 reduction.