Continuously Variable Transmissions

[hoytedow]

...unless they're steamed.

[wardd]

rabbits like their veggies/diesels raw

[hoytedow]

True. My bad.

Well, lets make the things clearer.
The thread was about CVT, right?
There is only one proven, cheap, and reliable system available at present: a CPP! No doubts ok?
Engine efficiency (and the marine world talks engine and Diesel in the same breath) is varying under different loads ok?
The graphs shown here by Baeckmo and me had a bandwidth from above 20% to above 60% in specific consumption between optimal and worst! Not 5 to 10% !!! At least my calculator says so when 160 to 200gHp and 210 to 340gHp are the given figures.
But what is engine efficiency? The optimal ACHIEVABLE figure right?
With a fixed prop we cannot operate a Diesel at optimal consumption points under different loads. There is ONE point and that was it. Above or below we loose efficiency in consumption.
BUT consumption is by far not all. Being ABLE to operate under certain conditions is more likely the point to adress.
Leaving the planing speeds and looking just at the displacement world, where the CPP is common, we have several sensible reasons.
A displacement yacht of say 500 tonnes and with a installed power of 2x 500 hp (to make calc.s easy), goes 13kn max. and say 11kn at 80% power setting. The max. range is thought to be 3000 miles at 9kn! Ok?
Ah, but at that max. range only 120hp is needed for propulsion.
So now you clever guys tell me what is a efficient way to achieve a long engine life, a efficient cruising speed and a minimum service bill?
1000 hp set at 12% ??? The service bill will make you laugh....







...from fear and fury

[wardd]

coming at it from a different angle

i have a john deere diesel tractor with a hydrostatic transmission, at first i was reluctant to run it at high speed only used engine speed that gave me the travel speed i wanted

after a while the diesel started running raggedly

now i run the engine at rated rpm and use the transmission for speed control

engine now runs much smoother

seems diesels like to spin

[TeddyDiver]

Originally Posted by wardd

seems diesels like to spin

Some diesels do.. not familiar with John Deere, but Toyota 2.44 is one I'm familiar with and it belongs into same category. Not good for marine engine..

[brian eiland]

Looks like some interesting discussions have occurred in this subject thread that might well be applied to this "New Age Trawler/Motorsailer; Kite-assisted PowerYacht" I brought up in this subject thread.

I've not had time to go thru this subject thread throughly yet, but to remind myself to do so, I hereby contribute this posting, and ask some of the more knowledgeable participants to suggest what form of propulsion package they might suggest would be most applicable for this vessel concept.

An excerpt from that vessel posting:

Back to those design concept drawings by Humphrey’s (attached PDF). I can fully imagine a scaled-down version of this tri-hull design, in the 65-70 foot range...

The power would be a single main engine sized to develop the vessel’s desired top speed, and it could transmit this power by conventional shaft/prop arrangement, or with a azimuthing Volvo IPS dual prop unit, or via a retractable azimuthing Rim-Drive prop unit as I included on my latest dynarig motorsailer design.
1) Volvo IPS : http://www.yachtforums.com/forums/ya...750-850-a.html
2) Rim Drive : http://www.yachtforums.com/forums/te...ropellers.html

Supplementing this single main engine would be a single DC diesel/electric power unit to provide for:
1) Ships electrical requirements
2) Slow speed operation by electric (wing) motor belted to main prop shaft
3) Maneuvering thrusters as required depending upon azimuth capabilities of main prop.

The entire ship would be powered by only two engines, basically sized to provide:
1) Full main diesel power, unimpeded by interceding diesel/electric conversion
2) Slow speed operation and ship’s systems via the smaller diesel/electric unit
3) ‘Twin power’ emergency backup as either engine can run all gear
This configuration more ideally meets the latest thinking for the new diesel/electric DC technologies onboard smaller vessels. Alternatively, two identical diesel/electric plants might be sized such that in combination they would supply the max power required of the vessel, and half power for lesser times.

...or maybe a CPP prop that would feather,
...and maybe driven by a chain belt drive leg such as THIS

[FAST FRED]

" Alternatively, two identical diesel/electric plants might be sized such that in combination they would supply the max power required of the vessel, and half power for lesser times."

While it might not give the "bragging rights" of all this complexity

anyone wanting to create an efficient cruiser will find the parts readily aviliable at a marine scrap yard.

A US Navy landing craft coupled two engines to a single shaft since WWII.

Usually 2x 6-71 , can be had for about $6000 Navy rebuilt.The light duty Cummins are more modern but shorter lived.

The 6-71 might be swopped for a 2 or a 3 on a small boat that cruises on 20 -60hp, or left in place and simply used for 150hp per engine , as needed.

The bellhousing is SAE 1 so most any engines could be used , although a 6-71 and 3-71 would allow lots of parts canabalization for the offshore cruisers.

FF

[brian eiland]

Originally Posted by FAST FRED

...A US Navy landing craft coupled two engines to a single shaft since WWII.
FF

I do realize these type of two engines on one shaft possibilities, but then where do you get your electrical power for the ship, the kite winching, the bow thruster, the dive compressers etc, etc. You would need to add another generator plant...remember I said two engines for the entire vessel. Thats why I included at least one diesel/electric unit in the combination of the two.

For the best effeciency (in a higher fuel price world), those paired engines on one shaft would require a variable pitch prop.

[FAST FRED]

For the best effeciency (in a higher fuel price world), those paired engines on one shaft would require a variable pitch prop.

Perhaps , it would really depend if the power of identical engines were needed, or if a large /small combo would suffice.

The small engine could easily provide power for most requirements .

The DD and many other more industrial engines have built in geared PTO's , most rated for 30- 45 hp cont output.

Plus the triple pully on the crank at another 40-50HP .Propulsion and or house.

A bus alt is 24V and 300A , enough for modest house loads with a Trace 4024 , 4KW , which can be ganged to 8KW.

The usual PTO will run an off the shelf Hyd pump, with or without clutch, as found on working fish boats.

FF

[mikeharwood]

Hello,

I just came upon this thread and thought that the Torotrak IVT might be suitable for use on boats. Then again I could be completely wrong

Mike

Torotrak - Infinately variable Transmission

[marshmat]

Torotrak transmission - certainly a possibility. If they can get it to work reliably in long-term use, ie. 10,000+ hours between major servicing, it would likely be an excellent alternative to a conventional geared transmission for road vehicles, and there would be cases where it would be a good alternative to a conventional gearbox in the marine world.

If the transmission losses can be made comparable to those in a conventional planetary or 2-shaft gearbox, at not too big a cost premium, an IVT could very well become a viable option for some boats. Perhaps not so much for those that always cruise at one speed, and you'll never convert die-hard CPP lovers, but for some boats- like these "fast trawlers" (wtf?) that are popping up all over the place- a fixed prop and variable transmission might be useful.

A fully integrated installation would communicate with the engine's computer; ie. the throttle lever would directly control prop RPM, and the details of what combination of IVT setting and engine throttle setting would give the most efficient operation and a properly loaded engine would be handled by the computers.

Of course, there are those more traditional types who would prefer a direct mechanical linkage between the captain's hand and the variator pistons.

Various forms of this thing have been going around for quite a while- if I recall correctly, Ford was experimenting with a similar IVT in the mid-90s. From what I understand, one of the big problems with toroidal variators is the potential for greatly accelerated wear if there is any slippage of the variator rollers. Torotrak is saying that they have a specialized "traction fluid" oil, whose viscosity is highly pressure-dependent, to resolve this issue.

[Brian@BNE]

Ok, old thread I know.

But, does anyone know if Torotrak (or similar products) referred to above are available for 20-50 HP range, and what the prices are? What is the efficiency of the Torotrak?

Proposed application is for motor-assisted sailing, where part of the effective thrust is from the sails and therefore the prop demand power is lower than would otherwise be the case for given speed. A fixed gear 2-3 speed might be OK. Just wondering if the last couple of years has changed things - car transmissions seem to have advanced quite a bit in that time, any good developments in marine tranny's?

A CPP would be a great alternative, but I don't think they exist at these low power levels. And trying to swing a 750mm Helseth designed for min 200kW (their smallest?) will probably mean some inefficiencies, not to mention a disproportionate cost.

[Brian@BNE]

This NSK device for cars, announced a couple of months ago could be ok. They claim 97% efficiency. Power range should be about right?

http://www.nsk.com/company/pressloun...ess111129.html

[TeddyDiver]

Originally Posted by mikeharwood

the Torotrak IVT might be suitable for use on boats.

I can see one basic flow in this concept and it's because fixed pitch propeller has so limited operational range due the power curve shape and cavitation issues at high revs. That is just IMHO..