Gearboxes on Boats

O

ontheplane

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Hi all,

We all expect a MINIMUM of 5 forward gears on our cars these days (some merc drivers get 7...) - so why do we still only have on forward and one reverse on a boat.

With the fuel prices as they are these days, and Volvo, mercruiser etc spending a fortune on developing posh drive systems - why is no-one looking at perhaps a 3 or 4 speed system, perhaps based on the VW DSG system where there would be no decernable loss of drive. It would allow for a finer pitch prop to be fitted for acceleration, and a higher top speed from higher gearing. (Or a higher pitch prop, and get the acceleration from a lower 1st gear).

Am I mad or could this work?

I know someone did a 2 speed box that you added into a Volvo leg - works well but costs a lot because it's put in aftermarket, would be much cheaper put in from new.
 
I'm sure it could be made to work, but i suspect cost would br prohibative. The DSG system does offer continuos drive, but so does a CVT gearbox, which have been around for years.

I suspect packaging would be tough, pushing up cost and perhaps reliability. It is often something I have also pondered on - I can only assume VP or Mercruiser have probably thought of it, tried and tested it and binned it.
 
Mercruiser brought out a 2 speed box a few years ago, withdrew it after a short while due to very poor sales!

Sunseeker fit a 2 speed box to their XS2000 sportsboats.
 
Yes I agree - it would need to be based on an existing system to keep costs down.

I was pondering the other day what a 2.5lit VW Turbo diesel with DSG would be like in a small boat - it would fly AND be economical methinks
 
There is a basic and fundamental reason why multi speed gearboxes are a waste of money on marine applications(apart from a the odd specialised racing application).It involves torque and rev bands and stuff involving pushing 5 tons of mass through a high density medium and somebody did explain but have totaly forgotton now. /forums/images/graemlins/grin.gif
 
You have a fully and infinately variable automatic gearbox, it's called prop slip. Or you can fit one of those pitch changing prop thingies.
/forums/images/graemlins/smile.gif
David
 
I can only see them as being of use in two circumstances:

1.) When you're heavy and underpowered, and can barely get over the hump to get planing. Correct solution is to fit bigger engines.
2.) If you've got some sort of very high perfomance tuned petrol (racing ?) engines where the torque comes in so high up the rev range that the lower ratio helps with acceleration

dv.
 
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