Controlable Pitch Prop

Good Morning All, Some good points overnight -- Great info re the two blade FF. It gives me a fall back position as I do have a new two blade 22 in. dia. bored for a 1 1/4 shaft that I could have machined. Meanwhile I am waiting for a reply from B.V.Mogema before setting out on another search for a CPP/VPP system. Regardless I'm hoping if I am successful It is within my budget.

 

Don't forget about vented propellers, although the ones that are currently available are more suited to ski boats than to your particular application. I don't know if anyone has built one specifically for a diesel motor sailor.

However, the concept may be useful. Consider using an introduced air stream just ahead of the propeller, in the rpm range(s) where an engine may be temporarily overloaded. Think of it as controlled cavitation.

 

A serious question to ponder here for a moment: if CPPs were available for smaller engines what do you think the price point would be for which they were actually attractive options and not just viable for people who are willing to throw money at anything that might make their boat "environmentally friendly" or give them bragging rights on cruising range or what have you?

Absolute aside: seems the FDA approved powdered alcohol, or palcohol, ... by mistake. That was reported on the TV as I was typing if anyone wonders where that came from. Insert joke about "what were they drinking?"

 

something seems wrong, price/availability wise.

if these were fairly common decades ago, shouldn't they now be ten cents a ton from China, or at least Taiwan?

AFAIK, they don't rely on some rare metal that got expensive or something.

Is it just that in yesteryear it was cool to have a displacement motor yacht, but now it is all about 'express cruisers' with planning hulls, designed from sales brochures that manage to evade the benefits of CPP?

 

It isn't like no one tried, here's a image of a patent for one for outboards: http://patentimages.storage.googleapis.com/pages/US3138136-0.png

 

This is wild speculation, but perhaps modern electronics and controls would simplify the design to the point where it is self contained. For example, a prop where you run for a minute and the prop measures its own load, then you shut down (to remove the load from the blades), it adjusts itself and then you proceed. Perhaps using batteries charged by prop rotation.

The idea of pumping exhaust gas down a hollow propeller shaft to allow it to sometimes achieve higher rpms (similar to cavitation) is interesting. Is it practical?

 

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

 

This is exactly what vented props do, and it does work, at least in boats with high-performance outboards. The props (I'm thinking particularly of Mercury SS props here) feature replaceable inserts whereby you can alter the diameter of the holes in the prop to fine-tune the amount of slip you need for fastest holeshot. They work for what they were intended to do, but not sure if that concept could be applied to a displacement-type situation with a diesel motor sailor.

 

Do they work (allow the motor to rev more freely) when the boat is backed-off, due to sea conditions, barely planing, which loads the engine ?

 

How about the concept of two propellers on the same shaft, or twin concentric shafts, somewhat similar to a Volvo duo-prop or Yamaha TRP? You could have the props counter-rotating for maximum thrust when needed (initial acceleration), then only a lower pitch prop turning for lower speeds / higher loads and then only a higher pitch prop turning for higher speeds / lighter loads. The main downfall would be the drag of the non-powered prop in the water, but if it could be left free-wheeling, that could be mitigated somewhat. May have to do away with the counter-rotating option to keep things simple...

 

Rurudyne --I would expect that a price in the $3000 to $3500 range would attract good sales and re introduce this great product back into the small boat industry. Only two sources of manufacturing would have the capability to offer this price. As a sideline of a large manufacturer who is presently in the CPP business or sourced from Asia.

 

the larger versions when connected to electronic high speed diesels have a computer to decide rpm versus pitch so you only have one lever

 

Wireless internet with your smart phone, women in bikinis, a crowded lake on Labor Day and trying to mix your palcohol drink ... yeah, I can see where just one lever could have safety benefits.

 

yep
they're fool proof

 

Like automobiles the more bells and whistle's you add the more the cost as the youngins will and are learning. Slowely but surely they are becomong slaves to both the banks and manufactureres. KISS is the way to go, manual operation and control is my route.