Belt Drive

Actually I had read all of your posts as well as you site before posting this. haha. Do you have any details on any installations?

 

A belt drive will deliver a lot of side thrust compared to none at all from a conventional gearbox. How will you tension it, move the engine?

Although it may be done I cant think of a reason to do so.

Boats have been around a long time and an engine, gearbox and shaft is about as simple as it gets.

 

I was thinking a thrust bearing in front if the transmission, and an axial loaded bearing mounted close to the belt. If the belt could be mounted very close to the axial bearing... say 5 inches center to center, and there was a coupling to the motor placing the first motor mount at say 20 inches center to center. Sum of moments equals zero... Therefore there is 4 times the force on the bearing as there is on the motor mounts. I'm not sure what the tension for a toothed belt transmitting that kind of power would be, but I don't feel like it would be too astronomical. And the axial bearing would be taking the brunt of it. Say 50lbs of belt tension... 10 lbs on the motor 40 lbs on the bearing. 100lbs of tension 20lbs on the motor. I feel like this would not do much damage to the motor.

And again the reason would be to get inboard engines below deck on smaller boats. Twins on even a modest vee, sit up much higher on a hull than a single sits. Lower decks, more stability. Again, the fore motor would be belted to the port and run the port propeller and the aft motor would be belted to the starboard and run the starboard propeller.

For an example of deck height. This is a Penn Yan 23 with engines below deck.
This is a Bertram 25 with an engine box protruding above deck.


The idea would be to try to get the lower decks of the Bertram with the flush deck of the Penn Yan.

 

Weight: ONLY 18 KG !
The most light-weight engine for the most light-weight jet tender
easy to handle, the tender not weight-down your yacht and not heavy jib-crane is required.
Excellent power/weight ratio

 

In order to get a reasonable service life from a toothed belt ,the shafts must run exactly parallel ,and I mean exactly ,the movement of your engine mounts will prevent this .you will have to build a separate "cage " for the drums, and put a flexible coupling in the engine drive shaft. Ask anyone who owned a series 3 Tdi Land Rover Discovery. the pulleys on these were only a gnats cock out. but they shredded timing belts and had to be modified.

 

they were v belts which are quiet and multiple v belts can transmit a lot of power

 

Brian,

Do you have a link for that engine. Looks like it belongs on an aircraft?

Dino

 

sure but lots of vehicles used the simpler smooth belt and pulley's for years without a hitch, because they didn't need perfect alignment. A lot of the motorcycle companies ended up belt drive simply because of maintenance issues ( or lack thereof ) and just about every car out there these days has some funky serpentine rig under the hood. Belts are pretty tried and true and in a marine application I'd think take some of the thrust load off the engine/transmission and focus it on the end of the shaft where it belongs.

For a small boat it seems like it would be perfect cause of all the small lightweight systems out there that could be modified to make it happen.

my two cents
cheers
B

 

Totally agree with you on the low power issue Boston my V6 Chrysler Voyager proves your point. What many people don't appreciate ,is that a toothed belt is a precision component ,and must be installed as such ,if you need it to last. The shorter and wider the belt,the more important this becomes. Michael pierzga mentioned a rubber tyre friction drive earlier, that got me thinking.

 

So add another Axial bearing on the engine side of the belt and a Drivesaver and its good to go? http://www.henrysmith.com/globedrivesavers.htm How much power can be transmitted through a flat belt or a v-belt? I think stiffer engine mounts would be okay as well considering the motor is not longer taking any of the thrust loading.

 

No, what I meant to say is a flexible coupling on each end of the drive shaft which will incorporate a sliding spline ,and an axial bearing on the "cage" then it should work . I don't understand your reasoning for the stiffer engine mounts. I don't know what components are available in the US but the simplest way to do this may be to obtain some toothed pulleys with taper lock bushes and what we call plummer blocks ,although the thrust bearing may need something more sophisticated. You may be able to make a simple cage with steel plate and studding ,but this too will have to be sturdy enough to cope with the thrust and continue to ensure perfect alignment. As for loadings I would have thought these were obtainable from your local suppliers. Reverse ? well you've got me there.

 

Ok. I was just saying since the engine is not bearing the thrust the engine mounts don't need to be able to handle the trust loading anymore. So all they have to do is absorb engine vibrations. I figured the stiffer the mounts were the less the engine would move, and in turn the less movement you would have to engineer for.

What if you just went with an over-sized belt. I noticed the belt on that little 40hp looked rather large. Maybe by going with an over sized belt you could loosen the tolerances and remove the necessity of a "cage." Not that I feel producing such would be overly difficult.

 

If its belt drive the engine is now taking side thrust as is the shaft.

Wether its chain, tooth belt or V belt the engine is pulling one side of the belt towards it. The engine would need to be adjustable to tension the belt and would need to be solid. How could you have a soft mount engine tensioning the belt?

 

Look down on the page of one of the former postings:
http://www.aermarine.com/tubolari_eng.htm

 

Here's another kevlar belt drive. But I believe they are out of business considering the current state of the marine business worldwide.

http://www.yachtforums.com/forums/23397-post3.html