Split or helical gearbox

Discussion in 'Inboards' started by juiceclark, Aug 20, 2008.

  1. juiceclark

    juiceclark Previous Member

    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:

    or very simplified:
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    FAST FRED Senior Member

    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.

  3. juiceclark

    juiceclark Previous Member

    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.
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