propellar design

[djreidt]

why couldn't a towboat of say 1800 hp use a two speed transmission. A low gear to get the barges started and a "overdrive" once you got the mass moving. would this be possible and would it improve speed and fuel economy?

[Sketch]

I've wondered the same thing. Given that the shaft would have two turning speeds for any acceptable engine RPM range you would want to have a variable pitch prop to make the system at all effective. Who makes a transmission suitable for marine use? Has it been done, or do properly designed variable pitch props already do the job without the additional weight and complexity of a transmission?

Kevin

[Lars]

MB Boats, a manufactor of wakeboarding boats, equips their boats with a two speed transmission. They write:

MB Sports’ aggressiveness towards the pursuit of the creation of the two-speed application has been a work in progress for years. The Brendel Family has been in the boat industry since 1950. They have always been one of the lead innovators in pushing the industry to the next level of technology. In the early 1970’s the Brendel family was the first to use a two-speed transmission in a race-boat, which transformed the boat racing industry. From this background and experience, the idea for a two-speed transmission in the water-ski/wakeboarding industry was developed and created.

[CDBarry]

The thrust to get a string of barges started is relatively small compared to that required to keep them moving, so a two speed transmission doesn't have much use for that application.