Quote:
Originally Posted by 8gv
I think the car/boat comparison gets off track due to the use of multi speed transmissions in cars.
Yes today's cars get great performance with less displacement. Much of that comes from improved valve train and injection technology. The delivery of that performance requires gearing. Does anyone recall cars with a two or three speed automatic? Now it's 6, 7, 8 or a CVT.
I'd like to see some torque curves on the engines in question.
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A muti-speed transmission would be a waste in boat, 2 speeds would be more than adequate (well obviously, since single speed transmissions have worked great for decades...). One thing to note, adding gears will not make the boat faster or appreciably more fuel efficient, it will only improve acceleration.
There have been a few attempts at two speed transmissions in boats. I think the luxury brand Riva still offers one. Mercruiser used the planetary gear section of a GM 2 speed powerglide transmission to make a marine 2 speed that fit behind their I/O engines about 20 years ago. If memory serves, they dropped it from their line quickly since it did not sell well.
An ideal solution would be a planetary gear set that takes the place of (and fits in the space of) the coupler on an I/O and uses an external brake to stop the ring gear (and shift into low). The shift to high would be accomplished by simply releasing the brake which would let the ring gear spin freely. With the brake released, the entire gear set would spin at engine rpm with no gear reduction and little load on the oil in the gearset. Planetary gears can handle huge amounts of torque for their size and may work great with today's smaller engines that make losts of HP but not so much torque.