Synchronous Belt versus V-Drive

[makobuilders]

I'm researching an alternative to using a V-Drive for a reversed engine, which would be an industrial belt/pulley drive (eg. Gates Synchronous Belts and Sprockets). Such belts are rated into the hundreds of horsepower (remember the supercharger on your '67 blown Camaro?).

My intended application would be a small trawler of 60-80hp, long range crusing at displacement speeds.

I appreciate feedback from anyone with experience. Thank you.

[CDK]

If your only objective is to change direction, the belt drive is a perfect solution: very low losses and silent. But you still need a F/N/R gearbox.

The belt drive needs its own housing with 4 bearings and some means to provide tension, all perfectly aligned, otherwise you need a supply of expensive spare belts.

A dual or triple chain drive will be cheaper and less critical. I can post a drawing of you're interested.

[gonagin]

I'd like to see those drawings if you don't mind.

[CDK]

Please note that this drive was made for a different application than yours, you may want the shafts to be further apart. The lower shaft gets a CV joint connecting it to the prop shaft.

Numbers refer to standard bearings, chain and sprockets available in Europe.

[crowsridge]

CDK, What kind of rpms can the chain and belt drive above handle? I was looking at the same issue. One project, Id like to double the rpm and since its jet drive, I dont need FNR. Having one gear on top and half that dia on the bottom side seems pretty simple.
They put belt drives on dragtser and race car blowers. I cant come close to those stresses.

Thanks, Chris

[baeckmo]

Ooops, you can not change the direction of rotation on a jet. They are made for clockwise rotation, looking aft. In addition to that, a jet is not suitable for low speed operation, since its efficiency is more or less catastophic at speeds less than 25-30 knots.

So sorry, back to the design stage and rethink!

[CDK]

Originally Posted by crowsridge

CDK, What kind of rpms can the chain and belt drive above handle?

Manufacturer data usually is a graph with a limit of 10.000 rpm for the smallest pulley, but that doesn't mean it is an absolute limit. Usually there is a derating factor applied to the max. workload for a given transmission setup.

Belts and chains used to drive cam shafts in high performance engines come close to that speed.

[crowsridge]

Thanks Guys,


I wasnt trying to go slower. I wanted to turn the motor around, putting it over the pump intake and shaft keeping it at the transom as much as possible. I dont want to reverse the rotation. I want to increase the rpm's. So thats where i need to use the gearbox idea but with gears, instead of belt or chain. If I go with a gear on top at say 8" ccw @ 3500rpm's and a 4" on bottom would be cw @ 7000?

Is that workable?

The above chain/belt plan could work if I leave the motor in front of the pump facing forward?

Some gears are quieter than others?

Try that version.

Thanks, Chris

[baeckmo]

You have not specified what jet you are talking about. Before that's clear, the rotational speed cannot be set. For cavitation reasons, in particular if you stick to the "low speed trawler" concept, the lowest possible rpm's is the path to follow.

[crowsridge]

I'm interested in using pwc pumps. Jet jons seem to be what they're referenced most often online. I wanted to get away from the high rev 2 stroke engines normally in them. Google jet jon and even Glen L where I got my plans from features them. They have a separate forum section for just jet ski powered boats.

Chris

[CDK]

No Baeckmo, he is building a 17.5 ft Glenn-L rogue runner, not a low speed trawler!

[Chase_B]

A jet usually has a gate that swings down in front of the thrust nozzle, that's the way my Berkley was , I have Belt reduction on one of my airplanes, very smooth, very quiet but allignment is very important, if your going for a 2 to 1 increase or reduction , in the aircraft world it's not common , but rather a close equation is prefered, 1.? To 1 or 2. ? To 1, something to do with vibrational harmonics with exact divisional reduction, not sure if this is so in all applications

[crowsridge]

So, if I go to three gears, I get to the rpm increase I'm after, gets me to the proper rotation for mounting backwards over the pump, and, I'm not doing it in a 2-1 jump??? Did I get that all in there?

CDK you are right about the Rogue Runner. I am looking into making a shorter version, maybe even S&G to try a smaller lighter jet version too.

[baeckmo]

Originally Posted by makobuilders

My intended application would be a small trawler of 60-80hp, long range crusing at displacement speeds.

I appreciate feedback from anyone with experience. Thank you.

Huh...? That's the original question! Solly I'm a bit slow sometimes when a thread has been hijacked..... Now that said, I still think crowsridge should define the operating envelope better:

-Size of boat
-Total weight
-Required cruising speed

That gives the required thrust and from there you may select jet size, engine power and jet shaft speed.

[FMS]

You're being too sensitive.

makobuilders' application is a 60-80 hp displacement speed longrange trawler.

I don't believe anyone would chastise you for starting a new thread for your application in a 17.5 ft Glenn-L/hankinson rogue runner.