geared engine

[anthony_marquart]

I have been wondering what would happen if you put a two speed transmission, like in an RC car, in a boat.

You ca adjust the shift point,... you can change the gears,...

Seems like you might be able to run more pitch and still launch...

Any thoughts? it might be most applicable in a .12 size boat,... Am I crazy?

 

[lohring]

Don Maher has been running a gear up boat at the straight lines for the past two years. The problem with internal combustion engines is limited rpm and a poor power curve especially compared to electric motors. That's why cars gave transmissions. The propeller makes a good torque converter, but it has limitations. You really only need a gear box in boats when you run over a wide range of speeds. Few heat racing boats do this, but straight line boats are running out of pitch.

Lohring Miller

 

[Jerry Wyss]

My thoughts are,, (and I know you don't like'm), that if the transition could be done gradually, like

with a CTV (Continuously Variable Transmission) it might be possible. It would probably be more

difficult the smaller you go in engine displacement. The .12 to .21 engines we run have a narrow

powerband, usually up high in the rpm range. A much milder engine would probably have to be used

and the prop choice might not even come close to what you could achieve with the curret setups.

Car tires have a direct contact with the surface they run on, Boat and airplane props have no such

direct adhesion to they're running surface,, slippage will occur and possibly lots of it.

Sounds an awfull lot like what I wrote before on this subject.

 

[Nigtmare]

My thoughts are,, (and I know you don't like'm), that if the transition could be done gradually, likewith a CTV (Continuously Variable Transmission) it might be possible. It would probably be more

difficult the smaller you go in engine displacement. The .12 to .21 engines we run have a narrow

powerband, usually up high in the rpm range. A much milder engine would probably have to be used

and the prop choice might not even come close to what you could achieve with the curret setups.

Car tires have a direct contact with the surface they run on, Boat and airplane props have no such

direct adhesion to they're running surface,, slippage will occur and possibly lots of it.

Sounds an awfull lot like what I wrote before on this subject.

So Jerry. maybe a water jet drive will be the trick .

 

[Mike Broad]

A while back some FSRV boaters experimented with variable length tuned pipes. At low revs the pipe length was increased and them reduced as the engine revs rose. This solution may increase torque at low revs enabling a larger prop to be used.

Mike Broad

 

[Propjockey]

Variable pitch prop?

 

[Tim_Duggan]

Now you're talkin'.

Question is HOW to do it on props our size and keep it together at 20,000+ rpm?

 

[Ken Retallick]

Now you're talkin'.Question is HOW to do it on props our size and keep it together at 20,000+ rpm?

Ive been thinking about this one for a long time Tim!

Its not so much the Rpm, its the constant loading and unloading forces of our surface drive setups that bend and break even our solid props.

 

[Tim_Duggan]

I agree Ken,

What about something external to the prop that could induce more prop slip at lower rpm and then reduce the amount of slip as the revs increase? Potentially less mechanical than variable pitch? Question is HOW?

 

[Flyguy55]

I agree Ken,What about something external to the prop that could induce more prop slip at lower rpm and then reduce the amount of slip as the revs increase? Potentially less mechanical than variable pitch? Question is HOW?

 

[Flyguy55]

When I raced in the 70s , There was a 2.5 liter hydro that was very fast with a 2 speed transmission.

He had an air shifter . I dont remember the ratios , but he used the lower gear to get going , and through the corners.

Its been done in full size boats. It might work very well in RC boats

The Older I get , the faster I was

 

[ozzy2]

An ansew to Tims question the offshore racing cats us a system of injecting air into the props pathe to induce more ventilation to allow the prop to unload at low speed then as the speed increases the ventilation decreases and prop bites more giving an effective variable thrust. This can be done with models

 

[Tim_Duggan]

Interesting Paul, Very interesting.

Are you heading up on Sunday?

 

[ozzy2]

Yes i'll be there i need the practis for the nationals

 

[Ron Olson]

Some of the ventilating of props is done on boats withe through the prop exhaust like the Merc's. Holes were drilled along the frony of the prop and at low speed the exhaust would go out those holes until the boat got up to speed.

I believe that the variable pitched prop for boats has been done but with parts breakage problems.

 

[Ken Retallick]

Ron, theres the answer to all our probs!! pull bigger props AND keep the noise down!

I have been working on a couple of ideas for variable props, and that i will be casting props again soon (finally) i will have to try them out.

 

[Tim_Duggan]

Ken,

Tried to respond to your PM but it said your inbox was full!

On the subject of air ventilation - I wonder just how much is required and how consistent it would be on a surface drive system?

 

[Ken Retallick]

Tim, inbox has some room again!

Air ventilation could be worth a try, but i can see it being very effective on a surface drive. Many boats do have

prop slip on take off, some of my own props do, which i find a good thing, as i find them simple to launch, with no loss in speed.

Props which bite on launch can be difficuilt, as there is full load on the engine all the time.

 

[boaterbill]

If you want two or three gears,to change speeds. Why don't you guys work on getting your engines to double and triple cycle. This is very possible as you guys know.

my 2 cents worth.

Bill

 

[J Solinger]

I have been wondering what would happen if you put a two speed transmission, like in an RC car, in a boat.You ca adjust the shift point,... you can change the gears,...

Seems like you might be able to run more pitch and still launch...

Any thoughts? it might be most applicable in a .12 size boat,... Am I crazy?

I think this idea has merrit. I've chewed it on and off for a few years. I agree that a .12 engine would benifit alot from it. The idea is to be able to drive a high pitch prop that you can't launch or can't get on the pipe with. The issue that I keep running into though is motor mounts and hull space. With the driven shaft running under the engine the COG gets higher than I want and with the shaft running next to the engine I run into motor mount troubles. The whole assembly will also get a little heavy, from a .12 perspective. I don't know what the best orientation of the components is but I still like the concept.