Joe92GT

I have a question for the experts. Lets say theres a continuously variable transmission that can hold high hp numbers (+1000) and is not overly heavy or large.

Say it also had full continuous control over a large range of speeds from under to over driven. You can tell it what ratio to be at, how fast to ramp up/down ect (obviously computer or feedback controlled).

How useful would that be in high performance boating? Good for a diesel app., variable propping?

Chris Sunkin

Multi-speed drives have been used in offshore. They're great for course racing where out-of-corner acceleration is important but of no value once you're up and going. It's VERY hard on drives.

Diesels would be the application that would see the least amount of benefit considering their exceptionally broad torque curve. They work great on engines like the Lamborghinis since they're down on bottom-end torque compared to the V-8's

Joe92GT

Yeah, but multi speed is different than continuously variable. With a CVT the jerk could be kept very minimal. I'm assuming that the shock of changing gears is whats hard on the drives.

The torque curve on diesels are great, but the rpm limit is very low, so there isn't as much range for propping for top speed and acceleration at the same time.

Up until recently I do not believe there existed a CVT capable of holding high hp at constant load that didn't weigh as much as the boat itself.

320es

I am sure the shifting would be part of the problem but even with a cvt you are multiplying the torque the engine is producing as well as raising the rpms closer to the torque peak while the boat is getting on planewhile the loads on the prop are very high. I think it would be drive killer for sure.

sleeper_dave

Developement on CVT's has all but ceased by the auto makers. They just can't be made efficient or strong enough. Then there's the issue of driver perception. What good is a CVT if you have to program it to have artificial "gears" so that the driver doesn't think his tranny is slipping. CVTs are dead in the automotive world, and you don't want to think about inflicting that kind of extra pain on yourself by trying to put one in your boat. You think bravo's fail a lot... a CVT would last about as long as an alpha beind a 1075.

CVTs are fine for snowmobiles, but making them handle the abuse a car can put out, let alone a marine engine, is a big hurdle that will likely never be overcome, simply because of the lack of percieved benefit. Someone would have to come up with a new way of making a CVT, there is only so far you can go with belts and pullies when it comes to transmitting torque.

Chris Sunkin

The shifting force isn't the issue. Even if it was, the control system on the engine can momentarily de-fuel, just like an automotive transmission does. The issue is torque multiplication. If you had a 1000 hp/1000 ft/lb engine and your transmission started with a 2:1 ratio, your drive would have to deal with 2000/2000 horsepower & torque. The drive couldn't withstand it without substantial upsizing. Outdrives are the weakest link in any marine propulsion system. There's a delicate balance between size/weight and performance/cost. You'd have to upgrade to #6 drives on a 500-to-600 horse boat with 2:1 low-range ratio transmissions and 1200 hp blower motors would need ASD-10's or shaft-drives. That weight and drag would consume top speed and negate whatever advantage you might find in the area of acceleration.

Idling around the docks would be much more pleasant though.

Diesel powerbands are so wide it's inconsequential. They've run diesels in race boats in Europe for years- quite competitvely.

Chris Sunkin

Another point- the parasitic losses are going to be higher than a geared transmission- slightly for a mechanical and significantly for a hydraulic (hydrostatic) setup.

In larger applications, what might be considered CVT drive systems have been in use for some time. Some are electrically powered and some use variable-pitch propulsion

Joe92GT

Thanks for the replys!

Sure, they are dead in the auto industry. However, while exhibiting at the power-gen show, I saw a company that designed one for high KW and even MW(~1300hp) generators. Very neat stuff, very capable of holding the power. I can not find a website, I'll look for some of the information I got.

Edit: Website http://www.cvtcorp.com/eng/index.html

The engineer I talked to said it scales very well as far as size/weight vs. power handling.

Joe92GT

The website does not show much, but it is a very new way of making a CVT.

DORaymond

Would that be 1000/2000 horsepower & torque?