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

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Old 06-12-2004, 09:30 AM
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Default Re: Let's talk transmissions...main reasons for NOT having multiple gears in a boat.

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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.
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in other words . . boats dont coast to well

Exactly. I would think a smaller, lighter boat would be best off.

Look to spend 3 grand, and have to move your engine forward a MINIMUM of 12".
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Old 06-12-2004, 12:28 PM
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Default Re: Let's talk transmissions...main reasons for NOT having multiple gears in a boat.

My dad looked into the AF 2 speed for his boat. There was not enough room behind the engines. I would like a 2 speed to use more like a transfer case with hi or low gearing for around the docks or out in the ocean.
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Old 06-12-2004, 02:02 PM
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Default Re: Let's talk transmissions...main reasons for NOT having multiple gears in a boat.

There have been a couple of occasions where I wish I had a two speed transmission... when the waves were so big I couldn't get on plane without pounding the boat into pieces. It would have been nice to have a lower gearing so that I could have powered around a little better than just off idle.
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Old 06-12-2004, 06:55 PM
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Default Re: Let's talk transmissions...main reasons for NOT having multiple gears in a boat.

I've had two and three speed auto's in my ski race boats since the 70's. Yes, they were based on the turbo 400 but well beefed up. We're talking very hard starts here with a skier giving thumbs up all the way. Over the years we went from 800 hp to 1500 hp, from V-drives to dry sump #6's. The "park' position is extremely valuable for two reasons; changing props and preventing walking in neutral. A boat with an auto and no park will walk away from a dock.
I currently have a 40 foot pleasure boat w/two SC1000's and #6's with B & M two speeds, and they are mostly useful for wakeless speeds in the marina.
As far as balance goes, we'd move the motors forward anyway, and now we're even putting quick fill/dump ballast tanks in.
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Old 06-12-2004, 07:29 PM
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Default Re: Let's talk transmissions...main reasons for NOT having multiple gears in a boat.

Martini,

The idea was to use first around the docks, under low speed conditions and possibly around corners. The boat was Mr Technology so we had to have all the trick stuff.

The first race, we ran from the pits to the race course plus the parade lap in first. At the green flag I pushed the button for second and one went to second and the other froze in first. We sent them back to B&M, they charged us $1500 and said there was a strand of fiberglass inside the case that cause the problem. How would that get inside of a sealed tranny?

The next race, we ran 5 miles under slow speed conditions in first, went out the inlet to test and again one was locked up in first. The next day, we started the race by using 36" pitch props. It lasted for half a lap until both trannies let go. Next day with B&M on the phone, they wouldn't agree to do anything to help so in the garbage they went. Good riddance.
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Old 06-13-2004, 01:32 PM
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Default Re: Let's talk transmissions...main reasons for NOT having multiple gears in a boat.

BoB -that surface drive idea using the auto transmission is EXACTLY the idea I've been toying with for my next project boat. I'll continue to 'sponge' information on that idea.

burtandnancy- That's a great observation with the 'walking' in neutral. I never really thought about that before. What has your experience been with the 2-speed B&Ms and 1000hp running through them?

RonP- I suspect sabotage!

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Old 06-13-2004, 01:51 PM
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Default Re: Let's talk transmissions...main reasons for NOT having multiple gears in a boat.

Ron P

Sounds like somebody should've thrown a couple of trannys thru the front window at the B&M customer service facility...

As far as a "cruise gear" it's not gonna work on a normal boat for reasons already mentioned. You could actually DO it but you would be lugging the motors unneccessarily and you'd get precious little benefit.

A drag tranny or a low speed dock and/or bad water tranny? Sure. If they'd be reliable then they would be great.

Many many big diesels have a low speed "mode" but this is not a low GEAR. The low speed MODE simply lets the drive clutches SLIP to allow low(er) speed operation. Sounds destructive, but they are engineered to do this. They call these "trolling valves" and they reduce the clamping pressure on the clutches.

I remember some true 2 speed diesel trannys a while back but I'm not sure they are necessary. Neat though.
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Old 06-13-2004, 02:13 PM
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Default Re: Let's talk transmissions...main reasons for NOT having multiple gears in a boat.

mcollinstn- Interesting, you've got my wheels turning with the mention of a 'trolling valve'. Would the engineering involved with these particular trannys simply be a larger surface area clutch pack that could effectively disperse the extra heat associated with 'slipping' the clutch? (and perhaps a matched transmission oil cooler) Different plate material compositions? Hmmn...

As an example: Take someone with a high hp, highly pitched water rocket. Could the line pressure in the transmissions (B/W 72C's for example) be reduced to allow easier docking? Could the clutch packs take that kind of abuse (for lack of a better word) even for the time required to dock? I've never had to dock a twin engine boat with high pitched props so maybe it would be unnecessary.

Whadda ya think?

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Old 06-13-2004, 06:27 PM
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Default Re: Let's talk transmissions...main reasons for NOT having multiple gears in a boat.

Martini, my experience has been perfect (so far). No problems, but I don't abuse them either. The boat comes out of the hole just fine in high gear, I just use low for show and of course the marinas. In fact, with my big props and 800 rpm idle, I usually only put one in gear. The B & M's aren't very long(length) as compared to the old turbo 400's. I've been told two stories, that they are based on a Chrysler torque flyght or a power glide. Mine are rigged to shift from a single toggle on the dash. Finally, someone told me to never, ever down shift at speed, and I never have.
I warm the motors up with my hydrohoist only half way down, then submerge or I secure it tightly to the dock, or naturally if I'm coming off the trailer, warm her there. I love the handling putting her into the slip, slicker 'n snot.
The only dissadvantage, the back seat is moved up and the engine hatch is longer. That problem is eliminated in boats using stand-off boxes like an IMCO where the trans goes in the box. Great retro if you've got Bravo types.
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Old 06-13-2004, 10:16 PM
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Default Re: Let's talk transmissions...main reasons for NOT having multiple gears in a boat.

Hmmm;--I guess that I would listen to the "Toilet PhD" and "Bite my shiny metal ass". There was more there than just opinions. (in my opinion) --- jp
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