Split or helical gearbox

[juiceclark]

Some of you may have read my expressed amazement that, with everyone putting around in damned "Manatee Zones", Steyr is the first company to come out with a hybrid. Well, with economy in mind I think I'd be remiss if I didn't touch on the subject of a split gearbox to run twin screws with one big diesel.

Is anyone using a split gearbox in a sportfish or other boat with significant hp? A single 1500hp, 3412 Cat. should get much better efficiency than a pair of C18 800hps. Moreover, the engine will cost about 30% less than twins...and we're talking around $40,000. (only 10,000 gallons of diesel) All the other pluses of having a single...like a lower salon floor, bilge space, etc. would be nice gravy.

My plant manager says he's seen info about a helical gearbox from "Marco Industries" but I can't find anything about it online. As we get ready to have drawings done for different power options, I'd sure like to address this possibility if it's practical, reliable and sensible.

I guess it would be a gearbox that splits the power out like a differential then connects to the shafts with a 90 degree joint on each side. Might look like this:
http://www.gearedupsystems.com/products.html

or very simplified:

[FAST FRED]

Are you attempting to run 2 shafts from one engine?

It would be required to add a tranny to each shaft to use the twin props to dock the 5% of the time its needed.

A single prop will be more efficient at all times compared to a splitter shafts 2 trannys and stuffing boxes etc.

The opposite is easily done.
Two engines of the same or different size operating a single shaft.

OTS in thousands of military boats.

FF

[juiceclark]

Yes...two shafts like in the link above. You only use one tranny and there's a clutching mechanism that controls the power to either prop. It's a very common setup in everything from trucks to tanks but I've only seen it in a couple of drag boats with massive, 1000hp blown big blocks.

I've seen the double engine on one prop set-up in pics of tug boat layouts...pretty cool. But with a sportfish we don't need more torque like a tugboat - with a big diesel we need more economy.