New DIESEL outboard.

Hi LF,
so this raises more questions.
I like the technology aproach but am trying to understand how it works in practice.

The only place the curves are of value is in the pre-pulley contact and assuming the symmetry of the leg, both tension and slack sides are in contact with the curves. Synchronous belts like this are not driving quite like a chain, but require intimacy of contact to achieve the friction required to transmit the forces. That intimacy is why the high preload which also means the tension side surface contact will have friction heat generation.
Assuming ~ 90mm dia pulleys, if a smaller width belt was used, design preload could be as high as 1,100kgf. Belt speed is likely in the order of 26m/s
The standard design tools do not accommodate contact above 180 or widths beyond standard. Both attributes the OXE has.

Looks to me like the belt width is massive over sized for power transmission so how does this relate tension?

The water cooling the housing will take the heat from the curved surfaces but what about from the belt?

Also reverse bending is not a preferred condition for these belts.

So how do they do it?

 

The way I see it, the guides serve at least two functions. They increase contact with the pulley, and they guide the belt into a narrow space to allow a narrow, less draggy profile in the water.
LF

 

With the belt drive, instead of forcing it into a narrow central skeg, might it be better to have two separated skegs meeting the gearcase bore at more or less a tangent to the outside circumference, one carrying the belt on its downward travel, the opposite side the upward travel ?

 

Something like this:

 

I am shocked from Mr Efficiency or all people - a high drag bottom end with reduced belt contact angle and really hard to install the belt. Just joking. They where not satisfied with that and look what they have done.
I'll stick with OXE on this one.

OXE is very very cunning.
It achieves something the Merc and Volvo has not done. The elimination of the highly loaded pinion tooth in the bottom end.
Konrad expect 2,000hrs out their units (actual service may be considerably higher depending on use profile). But this is 4 to 5 x Merc. expectations in same service.

So now OXE is looking at 5,000 or 10,000hrs from a diesel drive. When you look at lifetime costs it starts to make serious sense to burn less fuel, run longer and harder for less money.

What do you think?

 

Good idea. If the 2 legs were streamlined foils you might have a combination of drive leg and twin rudders. Low speed steering may improve . It would have to be a split case to enable belt fitting but I think mr e is really onto something here. There should not be any more drag than an inboards skeg.

 

Yeah, fitting the belt seemingly would require a split case. I know next to nothing about belt drives, maybe this would allow more contact surface, assuming that is beneficial..

 

Chain vs Kevlar or Carbon Fiber Belt

http://www.ramseychain.com/faq.asp?id=9
9. How does Ramsey Silent Chain compare with belts?
Silent chain drives compared with belts:

Higher speed and power capacity
Detachable and therefore more easily installed
Greater efficiency
Larger drive ratios possible
No slippage
Higher drive ratios at short center distances
Less affected by temperature or humidity
Lower bearing loads
Less affected by oil or grease

 

Silent Chain

I might suggest that some read thru some articles Here:

click on the Chain Doctor

http://www.ramseychain.com/eng_fundamentals.asp

...and pay attention to 'chordal action'
Look closely at the detailed interplay of belt's tooth with their sprocket teeth,...more wear and friction possibilities than one would first assume.

...ah ha,...just located this one additional reference link I was think of
http://www.ramseychain.com/prod_sc_pt.asp

 

DVD on Belt drive Prop System on large Ferry

Just posted

http://www.boatdesign.net/forums/inboards/belt-drive-37290-5.html#post742807

 

Mudcrab. Check your math. Just noodling around, I get about 400 pounds of pretension as an estimate (800 pounds bearing preload, assuming the prop hub would be designed to shear with a peak torque of around 1000 ft pounds, which is a total guess) . But if emphasis is placed on using the belt to smooth torque pulses, is could be higher. Still, its a lot less than your estimate. I would expect some fancy fuel management and very good vibrational analysis would be needed, and using a belt to modify the vibration modes requires that the belt properties need to remain in spec for the life of the belt, not just that the belt stays in one piece.

The prop curve will help somewhat in this respect. The worst torque pulse problems usually occur at the low end of the power band, but that can be mapped out without any real problems so long as you can still get on a plane. Or just accepted for a brief transition period during full throttle acceleration.

4000 engine rpm/1.5 ratio/(60sec/min)= 44rps belt shaft

44 rps * pi * .09m = 12.6 m/sec belt speed, yes?




Does anybody have a table of actual OB prop hub shear torques? I couldn't find that info. Perhaps a clutch system would be used in the hub for military and commercial duty. That could get the belt pretension down a good bit and maybe pay for itself.

 

I'd wager they are using green sand 3D mold printers for their casting. That's some some sweet tech there.

 

Steyr 1 piece blocks have been in production for well over 20 years that I know of . Wouldn't that be before 3d printers.

 

Perhaps that company needs to be considering a few smaller HP outboards to fill out their offerings. Maybe one utilizing the engine you brought up.

 

Hi Phil,
the maths comes directly from Gates Design software set up for the estimated task as in the OXE.
The pretension values accommodate power transmission via the friction mechanism and mitigating centrifugal forces. As I understand it the the drive mechanism is not just tooth shear load - rather a combined friction grip of the pulley. This can only be achieved and maintained when you can deliver a negligible stretch belt and a load of tension.

PolyChain is a relatively new product that has outstanding performance characteristics. Might pay to visit the Gates site and do some background familiarization. There are numerous examples of it replacing steel chain then lasting phenomenally longer - not lube, no maintenance.

I don't buy the 'insignificant drag ' estimates of the twin fin leg. If you read anything from any of the manufacturers - every new model OB/SD has an 'improved efficiency' lower end through form improvement. If they think it's worth that effort then I think they might understand why they spend their money there.
Cheers