Performance Boat Shop

Why dont boats have forward shifting gears?

I know the pitch of the prop makes a difference but could a boat get the same performance at 3K RPMs like they do at 6K?

Public Comments

1. That would take away the BBWWWAAAAHHHHHHH issue. Boat speeds are limited by hull design. Most motors can easily approach max stress without extra gears.
2. Typically it would be more efficient to change the pitch of the prop while gaining speed. This would effectively be the same thing as changing gears in a car. There are however some boats that do have transmissions and shift gears. I know for sure of one drag racing boat that has a two speed transmission. Also, another poster has answered that boats typically have a hull speed that limits their ability to go faster even if they had different gears, but this isn't quite true. This only applies to displacement hull boats. That means boats that stay down in the water when moving. Boats that plane, or ride on top of the water once they get going are not limited by the same principles.
3. There are marine transmissions that do have more then one forward speed, ZF makes one. This link shows the many choices from ZF. http://zf-marine.com/ZF/Transmissions/DutyIndex.cfm?Speed=2-Speed&DutyRating=Pleasure&Config=ALL
4. In cars you go on flat roads, then up hill, then down hill, meaning that the effort of moving the car changes according to conditions. On a boat...the forces involved are moving through water, so there is little to be gained by "shifting gears. Therefore, Boats are "propped" for the best performance according to it's intended use.
5. most speed racing ones do!!
6. In larger vessels it's not uncommon to find variable pitch propellers. That's the most effective because it can be adjusted for speed or load. It also allows the engine to run at it's most efficient rpm.