Controlable Pitch Prop

yep but KISS is not environmentally friendly so its a disappearing
who wants electronic diesels offshore?

 

The ones that are currently available are designed to work at higher loads (during holeshot) on ski boats. They are designed to be "set and forget" as they are marketed toward ski boat owners who generally just want to set it and forget it.

For those more into fine-tuning, the size of the holes in the prop can be adjusted, but I'm not sure to what extent.

Anyway, the point I was getting at, is that one could conceivably manually introduce air (or exhaust gases) into the prop stream to temporarily reduce engine load when needed. The boat would lose some propulsion/acceleration in the process, but it would allow the engine to get back into the proper operating range before applying full load on the propeller again. It really becomes a technique of manually "feathering" the prop with an air valve. Definitely not for those who want to "set it and forget it", but more for those who want ultimate control and fine-tuning.

 

Do you have a link to one of these ski boat systems

 

That's exactly what wooden propellers on home built aircraft do, they are still very popular on the smaller planes that use a converted VW engine of about 60hp.

I think there is one homebuilt called a 'Fred', and another called 'aircamper' that still used wooden props........

On take off under full power the the ends of prop flexes to fine pitch, then a cruise revs it opens out and bends to coarse pitch.

How about machining one from polythene, or some other flexible and strong type of plastic.

PS: Why not buy an old variable pitch unit off an aeroplane, and adapt it for boat?
All the bits that you need are there, and they are very slim units to avoid air drag........

 

>Perhaps a flexible prop that reduces in pitch as load increases. Wow !<

Evinrude had plastic props , up to 25 hp in the 1960 era that would do this.

On slow displacement boats , where the operating conditions at cruise change very little the saving of fuel from a CPP might be 10% at best.

At one or 2 gph , the CPP would have to be free! to justify higher install costs.

 

http://www.mercurymarine.com/propellers/advantage/technologies/pvs/

You can also google "vented propellers".

 

Fred these are toys we are playing with- ask any wife there is NO justifying the cost. . In my case as Imperial Oil once advertised about not using their products " You Pay Now Or You Pay later". The item in question of course being the 3cyl., $10,000 plus install diesel engine. Treat a modern high speed diesel poorley (carbon it up) and you can shorten it's life by 50%. Do that a couple of times over a 10 year cruising (motorsailing)period and that 3 to 4 thousand dollar CPP looks like a good investment. ( I just mistyped "cursing" for "cruising" very appropriate if one loses an engine ) . I haven't received a reply back from B.V. Mogema so I think I will re enquire. There are a couple of forum members on here from Holland possibly I can PM them to do a little research. Maybe even give me a lead on a used unit.

 

How did you connect a vented prop with cpp??
I guess you screen name is the clue
google Land and Sea torque shift props, they really did change pitch

 

Just had a thought: a CPP and a flexible prop serve very different purposes. A CPP, efficiency benefits aside, helps if the engine isn't adequately loaded for best service where a flexible prop helps prevents overloading the engine. To get comparable use in terms of engine loading I guessing you should size a flexible prop at some mid point of the throttle -- not that that's necessarily news to anyone. The same might be said of a prop with aeration I suppose.

There would still be the efficiency aspect of the CPP to consider, though, which brings me to an earlier musing: these were never inexpensive but back in the day engines were large (and often in the cabin), heavy, extraordinarily expensive and frequently weak on the top end no matter that their ponies were real stallions. CPPs simply got the most out of any of them. They fell out of fashion as power became lighter and less expensive, fuel remaining cheap. It may not have been penny-pinching on the part of mass producers after all.

It's just sad, what with low power cruising never really having gone away, that small units, besides used, aren't available.

One option I would like to throw out there, which I've been considering for a different kind of wheel, is the slush box from an automatic transmission. For load optimization one might serve the trick and also help protect a prop from damage, up to a point, from impacts. One might do good duty too with the earlier suggestion of using a used reefer diesel (which I had not thought of before) if, as I suspect, these may not be designed to have to take jolts associated with driving a vehicle. Of course for a prop the thrust bearing would have to mounted after the slush box.

 

There's still the problem of feathering the prop but never say never --somewhere there is got to be a company still producing these units. Most likely a third world up and coming country. If for nothing else than it is such a basic simple system that eliminates the heavy expensive complicated marine transmission. OR, a modern well known brand that still have their former product line blueprints and tooling sitting on the back shelf ready to go awaiting a wake up call. If B.V. Mogema is no longer manufacturing these smaller units, it is my hope they still have the tooling and a supply of left over parts that might be available at a reasonable price. There is no reason why a couple of retired/semi retired back yard machinist couldn't make a go of it with such a niche product. This is not a complicated high teck piece of propulsion eqpt. to manufacture especially with todays CNC machines. Any ears perking

 

feathering props
http://www.australpropeller.com.au/maxprop.htm

 

It would be interesting to use a CVT (continuously variable transmission) that is available on some newer cars. On the other hand, they may have so many computer controls that it might be difficult.

Or just don't treat the engine poorly. When the primary benefit is fuel economy, I suspect that the numbers don't work.

 

yep
but first we need to invent the variable diameter propeller and that will be a marriage made in heaven

 

Powerabout --Have you priced a feathering/folding prop, cost as much as a CPP unit. Plus most are poor performers and require mucho maintenance . I personally don't like feathering or folding props and take all their performance claims with a grain of salt. That still doesn't solve the problem of improper loading of the engine at low RPM. Motorsailing and CPP is a match made in the starry sky.

 

yes yes and yes
I guess the cpp market for small engines dried up as the benefit is not large enough so no market.