Propulsion effiency for all rpm.

[Art]

You don't need a torque converter to use a car auto tranny in a boat. The wet clutches are super similar to the ones in Velvet Drive. With some clever finagling you can render the torque converter into the mechanical equivalent of a brick, then modify the valve body to select the gear you want.

Harker's island boys have been running car engines and trannies in boats for as long as cars have had engines and trannies.

Auto trans, std trans, whatever they can find.

You do need a thrust bearing, though.

Dave- you drive a CVT? I think you need to turn in your Gearhead card!!!

Now, that's what I'm talken bout!!

 

[DavidM]

Dave- you drive a CVT? I think you need to turn in your Gearhead card!!!

In so far as 21st century automobiles are concerned, I turned in my gearhead card a long time ago!!! There isn't much you can do yourself with today's cars, so I just gave up.

BTW, I do think that the CVT is the wave of the future: efficient and simple- in principle at least. We even tow a 3,500 lb trailer with ours and so far no issues in 25,000 miles. It adjusts the ratio to the load seamlessly, just like you would want for a boat transmission except on the car it does it in a fraction of a second.

At least for now, my boat diesel engine is all mechanical and I use that to keep my gearhead card current.

David

 

[Ski in NC]

CVT has been tempting engineers for at least a century. Want to waste some serious time, try to do a patent search on those. More Rube Goldbergs out there than you could imagine.

The belt trick does work, either pushing or pulling. But getting into the details, it is not easy to manage wear on either the belt or the sheaves. And once worn, the smoothness is gone. I have not looked into the guts of the latest ones, but somehow they seem confident they licked the wear issue. At least enough to go to market.

Just joking about the card.

Stil crunching gears in my car and truck. Dinosaurs.

 

[Art]

I like Dinosaurs!

 

[Nomad Willy]

Don't even think of using a car Tx as reverse gear will be so low geared you'll run around slamming into floats.

 

[boatpoker]

For about $35k plus another 15k for installation you can buy a Hundested propeller.
My dock neighbour has one on his 40' Bruckmann

 

[Art]

 

[Lollipop]

I have a Land and Sea Torque Shift for an OMC V6 outboard if any one is interested. I had it on a 26' Aquasport with a 175 hp. It would start out at 9" pitch and give you one heck of a hole shot and then the RPM;s would remain the same and the pitch of the prop would change as the torque reduced. They were completely adjustable by changing the springs. I don't know why but it is still on the shelf in my shop.

 

[Underway]

Don't think there's any of these two in one out gears currently availible though.

This whole topic was discussed 5-6 years ago on TF. Another variant on the drive system comes from Ramsey Silent Chain located in one of the Carolinas, who built a combining gearbox drive system for a prototype Navy fast assault boat some ten years ago. The boat was about a 40' twin prop with four big Yanmars. Two engines per shaft driving into a conventional transmission. The chain boxes were a "stacked"/tandem arrangement (one in front of the other) bolted to the input end of the conventional transmission. Fairly thin and light, pressure lubed, with a roughly 6 inch wide chain carrying the load of each engine. Overrunning clutches to account for one engine off line. The concept allowed for many drive system variations....one small engine and one large, for example. I contacted them and spoke with a "real engineer" about building a single engine to two prop design. Turns out they had built and installed just such an animal in a 46' twin screw motoryacht.

The cases could be made to order....sprockets could be swapped around with relative ease to change ratios. I was investigating a 350 HP single in a twin shaft boat, which would have required 4 inch wide chains to carry the load in the event of a sudden failure of one chain. The transfer cases were simple and pressure lubed. No problem...just money.

 

[Nomad Willy]

Interesting skid.
Sounds like some of the gears that were available for the war stuff to multiply the power of DD that powered almost everything at the time.

A back yard twin shaft single engine arrangement could be cobbled together w toothed belts like the HTD. One would probably need to do w/o counter rotating props though.

 

[Underway]

Interesting skid.
Sounds like some of the gears that were available for the war stuff to multiply the power of DD that powered almost everything at the time.

A back yard twin shaft single engine arrangement could be cobbled together w toothed belts like the HTD. One would probably need to do w/o counter rotating props though.

Don't believe there's an issue with counter rotating as the input shafts on most transmissions are in one direction...rotation direction of the prop is handled by the gearbox....at least that how the Twin Disk in our boat work.