A few years back I was reading about a new design 2 speed trans for Mercruiser EFI B-III applications.. Some boats were fitted out and testing performed and published.. Mostly the results showed little if any top speed gain.. At low end
hole shots were much stronger and acceleration to top speed was much better..

Two identical boats were fitted out,, one had a 7.4 Big Block EFI-B-III.. The other with a Small Block 5.7 EFI B-III.. As expected the big block boat accelerated harder and outran the small block boat on top end.. Then the small block boat had the 2 speed trans installed.. Then retested and the acceleration was as good if not better then the big block boat.. I am not sure if top speed increased but the small block also had the benefit of consuming less fuel then the big block..

Anyone know what happen?? I thought this would have caught on better.. Mid to larger sized single engine cuddy's would be a good market..

Our 232 loaded with coolers and passengers must pushing 6000 pounds.. I would think a lower set of gears would help a small block engine push the boat from hole shot to planning speed.. I would think it would at least transfer some of that stress the coupler and input shaft take when coming out of the water..

I think that transmission came out of Mercury Racing and was called the Black-Trac transmission. Haven't heard any reference to it for several years.

Nothing on the Mercruiser sight . . . so it is probably a few years away.

You'll have to work with what you got . . . you probably would not switch out engines anyway . . too much $$$. End up buying a new boat.

With the smaller block engines, I would think a tranny is the best way to get good low-end power. I am wondering if they will make it part of the outdrive ??? If so, then all you would have to do is get a new outdrive . . . the engine and coupler could stay as is.

I wonder what a 7.4L WITH a tranny would feel like. Probably would need seat belts in the boat

It was in 97 or 98. They modified a chunk of a GM powerglide and fitted it behind the engine, if memory serves. Never caught on. Too bad, I'd love one in my boat.

If one had to choose between a DP or B3 drive or a 2-speed gear switching system with a single prop, the largest performance benefit would come from the dual-props I think, which explains why the system never caught on.

More weight, more complexity, more friction loss, minimal gain for all but the heavier, slower boats.

Hole shots with a two speed would be great. The way boats are geared now would be like pulling out in high gear in your car. The "gearing" is set for your highest end, leaves little at the low side.
I would definitely want a dual prop set up with a 2 speed. Otherwise, it would be like running 195/70/14 rear tires on a Z06.

I see space being a concern. You would have to shift your engine forward a bit. But if you used a planetary drive (not so soft of shifting) it wouldn't take up a ton of room and would be pretty reliable.

I agree Mutt: Would boaters be willing to spring for another couple grand ($$$$) for a shifting drive system on top of the already a couple grand DP/B3 setup.

Powerglides have planetary gear sets. The parts on them that made them long were the bell housing and the tailshaft housing. Remove those and they don't take up much space.

Heck, those shifting props had a lot of promise (and were commercially available for awhile).

As I recall, they were around $1K. I think the wisdom there was to invest the extra $1K to help defer the cost of a larger engine and you would not need a shifting prop.

But with today's concern about fuel mileage, who knows, perhaps these ideas will make a comeback.

I dunno, maybe they are still made?

I think the 2-speed idea is fantastic. However, the main problems with ANY transmission would be the space it eats, the extra weight, and the horsepower it eats.

However, there IS a very simple device that would accomplish *pretty much* the same thing in a boat as a 2-speed transmission, would add little if any weight or space, and won't eat any horsepower at all. It could be operated by the ECM or the driver.

I'm talking about replacing the coupler with a plain old locking torque converter.

There's billions in use in cars so it's not like they're expensive, it shouldn't be any problem making room for or retrofitting one, they can be set up with virtually any stall speed to replicate any 'first gear ratio', the ECM can be programmed to lock it at any time, OR the driver could lock it manually with a simple switch, and personally, I think a torque converter would make for less stress on the drive when shifting into gear.

I've brought this up many times over the years. I'm still at a loss why nobody ever tries it...?

And the two speed is back... http://www.boatingabc.com/forums/ubbthreads.php/topics/574912.html#Post574912