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Let's talk transmissions...main reasons for NOT having multiple gears in a boat.

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Old 06-11-2004, 05:19 PM
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Quote:
Originally Posted by ragtop409
...if you had a BIG motor you could get away with a overdriven gear but then why not just run a larger pitch prop? Rag's
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.
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Old 06-11-2004, 07:08 PM
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Default Re: Let's talk transmissions...main reasons for NOT having multiple gears in a boat.

Lots of great viewpoints here!
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Old 06-11-2004, 07:12 PM
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Talking Re: Let's talk transmissions...main reasons for NOT having multiple gears in a boat.

Quote:
Originally Posted by glassdave
boats resitance to motion is somewhat linear. in other words it requires continuously increasing torque as speed increases. in a car with multiple speed transmissions they can take advantage of the fact that once it is moving, friction is fairly low and higher (lower numerically) gear can be utilized. i believe there are some diesel packages that do use multiple gear trans's , they have the avaliable torque though.
.



in other words . . boats dont coast to well
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!
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Old 06-11-2004, 10:23 PM
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Default Re: Let's talk transmissions...main reasons for NOT having multiple gears in a boat.

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)
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Old 06-11-2004, 10:28 PM
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Default Re: Let's talk transmissions...main reasons for NOT having multiple gears in a boat.

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.
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Old 06-11-2004, 11:19 PM
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Default Re: Let's talk transmissions...main reasons for NOT having multiple gears in a boat.

Quote:
Originally Posted by 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.
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?

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Old 06-11-2004, 11:46 PM
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Default Re: Let's talk transmissions...main reasons for NOT having multiple gears in a boat.

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.
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Old 06-12-2004, 12:31 AM
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Default Re: Let's talk transmissions...main reasons for NOT having multiple gears in a boat.

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.
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Old 06-12-2004, 07:58 AM
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Default Re: Let's talk transmissions...main reasons for NOT having multiple gears in a boat.

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.
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Old 06-12-2004, 08:26 AM
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Default Re: Let's talk transmissions...main reasons for NOT having multiple gears in a boat.

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?

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