2 speed trans

[M Shore]

I was told there is such a thing as a two speed transmission for a boat can any one give info on this if true what would be the pro\con

[Sodar]

I was told there is such a thing as a two speed transmission for a boat can any one give info on this if true what would be the pro\con

It has been done in high performance V-drives for years. MB Sports introduced it in their B-52, but I have not heard much about it.... That is all I can offer!!

[86mcskier]

go to mb sports website, they show the pros of course.

[Harvey]

The pros are better gas mileage and the ability to load the boat with more weight and get out of the hole with better efficency. The cons: It shifts HARD!!! I hear you can actually feel it shift in the rope while boarding. I imagine that the life of the two speed trans is going to be shorter than your single speed trans as well.

[djhuff]

I think the future of this design would be a 2 speed that you shift while not moving. Kind of like changing props, but with gears, you pick either wakeboarding, or cruising and then go. Don't know if the prop could handle teh excessive speed of spinning so much faster than designed, or if the torque would directly transfer to a higher pitch.

[dmayer84]

I think the future of this design would be a 2 speed that you shift while not moving. Kind of like changing props, but with gears, you pick either wakeboarding, or cruising and then go. Don't know if the prop could handle teh excessive speed of spinning so much faster than designed, or if the torque would directly transfer to a higher pitch.

2 speed Tranny with adjustable pitch prop

[M Shore]

My thoughts are maybe a cruising gear when you want higher speed less rpm this is a very interesting concept to me. As we all know for all the hp a mastercrafts top speed is poor.

[RobertT]

There would be no point to a two speed tranny if you had an adjustable pitch prop, as far as I could tell.

You could have a much smaller more efficient engine which may be an issue if gas gets way over six or seven bucks a gallon.

The ability to keep the strain on the engine in the perfect window at all speeds would be awesome. Picture jumping out of the hole like never before, with almost no prop pitch at all. Then, as a computer keeps track of how much stress is on the driveline the prop automatially adjusts to the perfect pitch to allow the engine to work at its peak efficiency at all speeds and at all RPMs.

Top speed numbers would go way up as well.

think about it. We have a one speed tranny. One. Just like a car that you have to lock into only one gear. When you have a tranny fail you always want it to lock itself into 2nd gear. You can get it going...its hard but you can do it if you must. Not much top speed, but you have to choose sooooo.

We choose our gear by choosing the prop. Sure, you can get increadible hole shot up to 15mph if you designed a prop just for that (very little pitch), but you would over rev at 20mph.

You could put a prop on your boat and get at least another 10mph out of it (lots of pitch) but it would take a mile to get up to speed.

Thats overly simplified, but the point is that a variable pitch prop would be the single biggest advancement in boating that we have seen in my uneducated opinion. No need for 400hp. Even a loaded Xstar would be able to jump out of the hole and still have a 50+ mph top speed.

I just dont understand why its not being done. I must be missing something.

[dmayer84]

I think I remember hearing that a lot of larger ships have it. On smaller boats like ours since all of the pieces are a lot smaller it is probably a lot more expensive and harder to implement.

[dmayer84]

They do have them for yachts http://www.ab-marine.com/autoprop/in...tallation.html

[Sodar]

I have a lot of friends who have boats with Turbo 400 tansmissions in them. Here is a picture of a 20' Schiada V-drive with one....

[Hrkdrivr]

The variable pitch prop is how most turboprops (and some piston engines) work on airplanes.

In the C-130, the jet engine "core" is always running at 100% RPM (~14,000 RPM). The reduction gearbox turns the prop at about 1,000 RPM.

When you push up the power, you dump more gas on the fire and the prop changes pitch (increase) to keep everything running at 100% RPM. Vice versa when you pull power back.

The gearbox/valve housing that does all this takes about 150 shaft horsepower away, but the jet produces about 4100 shp, so it's not missed too much.

The problem is it's big and heavy and if you lose oil pressure it has a nasty tendency to explode and send the prop who knows where.

I always wondered why boats didn't have either transmissions or variable pitch props. The scientifics of making a variable pitch prop small enough and cheap enough for small boats may be too big a hurdle to get over...for now.

[milkmania]

I have a lot of friends who have boats with Turbo 400 tansmissions in them. Here is a picture of a 20' Schiada V-drive with one....

they done went and put that motor in there backwards

[rcnjson]

FWIW,
That DDG in the random pictures thread has variable pitch props. I do agree, it would be some kind of advancement. You don't need a reverse gear either, the prop can spin the same way for forward and reverse if the pitch is shifted. The engine could just spin a constant rpm and controlling the pitch would be all you need for accelerating and slowing down.
k

[Sodar]

they done went and put that motor in there backwards

Nah.... we put it in the right way!!!