X-Rated30

I have wondered this many times -- just not in relation to multiple speed trannies. I think the answer is that at a certain (steep enough) pitch, the prop would lose efficiency. Unfortunately, it also seems like at a certain (high enough) RPM, the prop would lose efficiency.

martiniboat

Lots of great viewpoints here!

Hydrocruiser

NO kidding the first time I pulled the sticks back on a 30' scarab i about sent everybody through the windshield. How about those props that were popular that may be still around that shift from low to high pitch? Kinda like a transmission. http://www.land-and-sea.com/marine/t...rque-shift.htm any experience with these ? The tragectory here looks like a potential lunar launch. This guy must be hitting 5000 RPM with a 10 pitch or something!

mopower

I tried a Torque shift on my 211 Liberator that was a slug getting on plane.
Worked great when it worked...but it didn't always work. The water where I boat had too much dirt and silt in it and it would screw up the prop. Had to disassemble and lube it once a week. I finally added mo power ( a better alternative)

Ron P

I had two speed B&M boat trannies in my old race boat. First race, one of them locked in first gear. We sent both back for a rebuild after 20 minutes of use. SAME THING happened at the second race. Out they came and Hubers went in. Never another tranny problem.

We learned that they two speed B&M tranny worked great, as long as you never shifted into first gear.

martiniboat

Are the B&M trannys based on a TH400? I remember seeing some literature on them somewhere. How long are the B&M's compared to the Hubers?

Brian

bob

Seems like with the higher hp applications the main maintenance area of the engine is valvetrain. This could perhaps be solved with overhead cams? These normally have a higher operating rpm range. How about a 3-4 speed auto, stagger set up in a v or in a cat, with a surface drive where the trans could basically be coupled with a short shaft thru transom into a c/v joint not requiring gears on transom to drop output shaft? Trans would allow high rpm range operation and possibly better valve train/engine life and engines mounted lower in hull for better heigth of c/g? 3-4 speed trans cost may also be interesting.

Reed Jensen

I'm afraid that most automotive automatics aren't designed to take high horsepower applications for long periods of time. I know a high output small block will toast even the best turbo 350 in almost no time. Even if you spent lots of dough upgrading a powerglide... I just don't think they can stand up to the marine environment for a long time.

26scarab

It seems like a gearbox would benefit a turbocharged motor. At least getting on plane an accelerating.
Forget automatics, a Lenco or Liberty pro-shifted trans would work but those would be just like a crashbox around the docks.

martiniboat

As boat combinations (hull/hp) become faster and more powerful I wonder if we'll see more two-speed trannys in boats? It sure sounds to me like the high pitched poker runners or SERIOUS offshore enthusiasts could use that low gear around the docks etc.

Ron P.- I can't imagine your frustration after being 'messed'-over on TWO races! Question- What was the 'order of operations' with that setup? Would you downshift in the corners and run top gear in the straightaways?

Brian