Down angle gearboxes

[KAM]

I am just planning a new engine installation and can not decide between a horizontal engine which is easier and neater with an 8 degree down angle gearbox or to go for a straight gearbox and tilt the engine 8 degrees. Presumably with the downangle box the engine will tend to pitch with thrust loads and cause slight drivetrain misalignment. Would appreciate comments from anyone with experience of a down angle box.

 

[Foxy]

How about an aquadrive, reducing vibration etc.... or is the angle far too big?

 

[Strathglass]

I am just planning a new engine installation and can not decide between a horizontal engine which is easier and neater with an 8 degree down angle gearbox or to go for a straight gearbox and tilt the engine 8 degrees. Presumably with the downangle box the engine will tend to pitch with thrust loads and cause slight drivetrain misalignment. Would appreciate comments from anyone with experience of a down angle box.

Your choice of tilt angle should be influenced by looking at the allowable fore and aft tilt angle for your engine.

Some engines have a wider tilerance to tilt angle than others.

Iain

 

[Neil_Y]

True, thrust forces emmediately put the shaft out of alignment with the engine if it is on soft mounts. But this also happens with a staright drive train as the mass of the engine in lumpy seas will ensure it doesn't stay straight for very long.

Add to this the use of rubber bearings which can't support the shaft rigidly in line and you have a typical bendy wobbly marine drive train.

On smaller hp you won't notice it being that bad, but it all adds to noise and vibration.

I would say that if the engine is happy to run at an angle you really won'y notice the difference.

 

[saxonpirate]

I am just planning a new engine installation and can not decide between a horizontal engine which is easier and neater with an 8 degree down angle gearbox or to go for a straight gearbox and tilt the engine 8 degrees. Presumably with the downangle box the engine will tend to pitch with thrust loads and cause slight drivetrain misalignment. Would appreciate comments from anyone with experience of a down angle box.

I agree with the above comments, but will add this. Depending on your present prop shaft angle there's still a chance that you'll have to tilt your new engine with an angled gearbox. I recently rebuilt and installed a Volvo MD 17D with an MS2 box that is angled to 7 degrees. I still had to add a little tilt to the engine though. As for thrust misalignment, as has been mentioned this will momentarily take place anyway. The critical thing is to have the correct engine feet. If there's a chance of fitting an engine with an angled box I'd go for it.

 

[scottie]

down angle boxes

down angle boxes were introduced to suit the flat bottom boats that are now the norm.
Far better to have the engine as near horizontal as pos

 

[KAM]

Seems that a down angle box may give the best installation but I was wondering why Yanmar don't do an angled box option with their new range of small engines. Do they know something I don't. When I changed the sterntube on my last boat I angled the sterntube sideways so that I could remove the shaft past the skeg without moving the engine. There was no noticable difference in performance. I was wondering whether to do this again is it common practice on other boats.