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jet drive is a water pump, moves the craft on the principle of changing momentum of water within the pump. No transmission per say...for reverse you have a C shaped cup up that re-directs the jet in reverse.
In theory you can go wide open and slam it in reverse and stop the craft in 1 boat length. It practice you will be ejected out of your seat.
The high speed ferrys use them. At speeds > 30Knts they become slightly more efficent then a conv. prop. At slower speed, they are less efficient.
You save on appendage drag ( no prop/skeg/shaft or rudder) which can add up to several knots at high speed. Also reduces draft.
I have a lot of data form hamilton jet drive company showing all this and they use to have a nice web site but I think it has changed.
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