Engine operating angle

[KKat]

I am installing reconditioned Nissan Diesel SD33 engines into my home built 55ft power catamaran. Because of the shape of the hull I will have to tilt the engines to accommodate the props. This engine was originally used in the Nissan Patrol and C80 SUV's and later the marine version in the Bayliner 3270. My questions are; what is the maximum angle at which I can safely run the engines? and what is the maximum angle of the prop-shaft/propeller to the waterline? I have built he hulls in a small fishing village in Malaysia which has a wealth of knowledge of sampan fishing boat construction but once things get technical I can't get much help. Thanks for any help. Brendon

[speedoo]

Engine operating angle limit will have to come from Nissan. Prop shaft angle maybe from them also.

[Pauls]

Nissan will spec the max angle the engine should be mounted at. If you're somewhere where you can't get any info, it's almost certainly safe to 12 degrees, more than that you need to get accurate info from Nissan.

As for max prop shaft angle, the bigger the prop shaft angle the less efficient. You want it as shallow as possible, working with the diameter of prop you will use and the clearance between the prop tips and the hull. Make this clearance 20% of prop diameter if at all possible, don't make it less than 15% of diameter.

Regards, Paul

[delmarrey]

Some marine transmissions have an angle limit as well. You'll want to check that too.

As for the motor's, any more then 15º and one can start having lubrication problems. They require special oil pans & pick up tubes. Also, a custom dip stick needs to be placed at the lowest end of the oil pan.

[40 South]

You can get down-angle gearboxes that allow you to mount the engine flatter than the shaft angle. The gearboxes have an angle built-in between the input shaft and the output shaft.

[Irish rambler]

I'd go with 40 South and use a down angle gearbox with a flexible coupling similar to Python. The problem is if the engine angle is to great when you get in a rough sea you may find your engine sucking the oil through the vent and racing out of control and of course emptying the sump of oil which would be a disaster. Design out all potential faults now, in the building stage, the guys n gals on here will give you great advice based on experience, not a salesman looking for commision trying to flog you unnecessary gear.

[40 South]

If you must install at a high angle you could also consider modifying the sump and weld a new deeper sump/well at the lowest point and route the oil pickup to the new sump/well.

You may find high install angles require more oil in the sump so that the pickup doesn't starve in rough weather or high heel angles. You may also require more internal baffles to slow sloshing oil.

You may also like to consider a "dry sump" as used in race cars that pull high "G forces". A scavenging oil pump, external container for the oil and another oil pump to return the oil to the engine. A bit complex but it will work.

I run 2 X 410HP MAN diesels at 15 degrees with standard marine sumps and oil system with no problems.

Hope that lot helps.

[GordMay]

FWIW: Yanmar calls this the "Rake angle"; which they generally limit to 8 degrees.

I didn't notice any spec in the “SD” Service Manual ➥ Nissan Diesel Engines SD22 SD23 SD25 SD33