has car-like gears ever been tried on a boat ?

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BOATKID

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why would it not work /forums/images/graemlins/confused.gif

dragons den here I come
/forums/images/graemlins/laugh.gif /forums/images/graemlins/laugh.gif
 
Because you are driving through water, not on tarmac. Stick to the day job!
 
Because a correctly set up boat is already in top gear.
I beleive there are some very powerful cruisers that use a special low gear for manouvering and berthing, but you will not get more speed or economy by using gears if that's what your thinking...
 
there was a two speed gear box prototype thingy at london boatshow many years ago. It caused many threads here, and a lot of press interest, but don't know what came of it.
 
Variable pitch prop is much simpler and lighter. And its a far from novel idea! Fine pitch for slow speed and acceleration, coarser for higher speed. Feathered for sailing. Reverse the pitch for astern and what's more you can do away with reverse on the gearbox making that smaller and lighter.


Aircraft props use Hydraulic pressure through the propshaft to control pitch, no reason why the same thing wouldn't work on a boat.

Why hasn't someone done this already?
 
Im on overdrive now /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif

automatic gearbox on a shaft drive /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif

anyone know an patent application website
/forums/images/graemlins/laugh.gif /forums/images/graemlins/laugh.gif

dont think I'll invite the dragons in on this one
 
"automatic gearbox on a shaft drive "

Man y moons ago a small 25 footer moored near me was in desperate need of a no money replacement powerplant to propel a worth even less boat.

The solution was apparently to install an old ex taxi donkey complete with .................................................................its automatic gearbox ............and no little effort was spared to get the thing to fit.

Its first foray out in the river terminated with loud bang 2 mins into the voyage and it was towed back by a sympathetic onlooker.
It sunk a few short months later to the not unhappy other club member .
 
had a 18ft boat years ago with a perkins with a vauxhaul manual gearbox fitted it worked a treat 3rd gear seamed to work best and no need for a clutch oil seal sometimes went in the box but just went to the scrappy for another box
 
It would work and has been done extensivley. Problem is that on many boats you can live with one gear hence variable gears is nice-to-have not necessary. Agianst that background and the fact gearboxes cost £££loads, it isn't done much. Remeber gearboxes are mainly designed around the torque thay have to handle, not the power, so the gearboxes needed for a pair of MTU1500hp diesels would be monsters, in terms of weight and cost.

The other approach is to use variable pitch props as others have said. These are v expensive and no-one is tooled up to make them for small boats due to the thin market. They are widely used on superyachts and big commercisl boats. The other factor is that in fast small boats the drag of the hub with all the pitch-varying mechanics is massive, and can burn up the savings (and more) you made from having variable pitch

The third approach is to have a prime mover whose torque can be maximised at zero rpm, so no gearbox needed. Ie an electric motor. This is widely used kit on superyachts and commercial ships, and it would be nice to think it could become a reality on 60 footers in the not too distant future. Imagine, instead of 2x800hp and a 35hp genset, you have 4 engines of 50, 150, 400, 1035hp. Turn on the 50 for pottering - 40hp to move the boat, 10hp for domestic electrics. Then turn it off and use the 150hp for fast pottering. Then the 50+150 for 10knot long cruises. Then the 400 alone for a bit faster, then you can go to 450, then 550, 600, then you turn on the biggie. Lots of combos. asnd the engiones can be located where you want them in the boat

Right now this 3rd option isn't commercially viable with kit currently avaialbe, cos the electric motors and the switchgear/control gear is big and expensive. But the technology exists and it's a shame it isn't avialable. That new Mochi gets part way there and the reason they've done it is cos they got the electrical switchgear/control gear compact
 
Well I dont know if beefed up CVTs are available off the shelf. All car CVTs wouldn't work, becuase the max torque of even a 250bhp car engine is small compared to a 250hp marine diesel, and an order of magnitude lower than the torque of an 800hp marine diesel, so the CVT box wouldn't last 5 minutes. But, like I say, I dunno if someone makes a beefed up CVT box that can handle 1000 foot pounds of torque, say. That would work.

Next question is how long would it work for. CVTs (of the automotive variety) intrinsically aren't the most reliable things ever engineered by man. It's ok if a Ford Fiesta breaks down but I wouldn't want one on a boat! I'd expect customer take up would be slow for tradtional CVTs becuae of this (maybe prejudiced, maybe correct) attitude. So I can't imagine ZF tooling up to make them and trying to flog them to MAN, CAT, MTU et all.
 
I always thought all boats already had a form of infinitely variable auto box (or rather prop) at low speeds it slips in the water under acceleration just tike a torque converter slips in the fluid and as the speed increases the slip becomes less and less. Anybody remember the DAF Marathon infinite auto. You put your foot down and the engine revved to max and the car eventually caught up with the revs.
 
Used to know a bloke with a 4 engined boat, think it worked off hydraulics, might be wrong, never saw it. Used to do trips out of Dublin, or was that Belfast. /forums/images/graemlins/confused.gif
 
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