Controllable Pitch Propellers/Shafting

[JamesCaird]

Hi all-I am interested to know if there is any available Controllable Pitch Propeller System in North America. I am thinking of such for a 20Ton Auxiliary. I have seen some systems on larger vessels, European for the most part, but am wondering what is out there now. I am doing an engine(auxiliary) change and am considering new shafting, thrust bearing and all. Currently have a feathering prop, which is fine, but am thinking about going further into this. Any experience out there? Current propulsion is about 80 HP and shafting is 1.75 ". Current wheel is 24" diameter. Cheers and thanks/JC

[rbgarr]

Useful considerations raised here about CP propellor setups (Hundestadt):
http://tinyurl.com/386r8v

[paladin]

The article makes a couple of good points, not the least is the remark about his "pyrometer". The device that he speaks of is called an exhaust gas temperature gauge, and is normally installed in the exhaust port of the last cylinder in a line. That cylinder will run just a bit hotter than the other cylinders. You can increase or decrease rpms manually on your engine, and the exhaust gas temperature will take a sharp drop from a steady rise when the air/fuel ratio is the proper proportions and is visible when the engine rpms are at a point where the craft is running efficiently but the engine is not straining or overloaded.
I also concur with the remarks on the Hundestadt system. I have sailed on a couple/three boats and found his remarks to the point. By using an efficient prop on a pleasure boat, properly matched, there is little noticable net gain. Jay Benford is a big proponent of the system, and is where I first became aquainted with them 25 years ago.

[Ian McColgin]

I am a fan of CP but understanding the limitations is helpful. Understanding modern alternatives - the AutoProp - also helps.

At one time CP was installed with a reduction gear but no transmission. You started or went neutral with a dead flat pitch. This also meant that you might well have the prop turning at times when you'd perhaps be happier to have it still, like picking up a swimmer or just after you've run down a lobster bouy. But in displacement boats this was not really such a problem and the extra cost of the CP, shaft and controls was off-set by not installing a transmission.

The pitch range from efficient under load to efficient light is actually less than many folk figure because you don't really get a "low gear/high gear" effect of putting more power in the water by higher prop RPMs. Go too far past the "right" RPMs for your unity and you're just spinning water sideways off the prop. Rather, you flatten the pitch but keep you're RPM close to reduce loss due to excess pitch for a given boat speed leading to the prop blades stalling.

If you know how to scull, you already know this. The good sculler starts with the oar at a fairly flat pitch and gains speed by adding more pitch, not by adding speed to the oar waggle.

For a pricy solution, the AutoProp does it for you. The props are machined to your boat's power, displacement and desired (realistic) speed. Each prop is balanced and the pitch is self-controled, steepening as you accelerate. You need a transmission with FNR but you have a normal size shaft and hub. Each blade is independent, not geared together, so a barnicle on one blade is annoyingly noticable.

In Vietnam some patrol boats were equipped with CP. In tests with a skilled handler they could "crash stop" faster than conventional FNR and fixed props, but there were problems with boat handlers not reading the pyro. The experiments proved that CP can be engineered for highspeed heavey (armed) boats that need low speed and tow flexability, but it's still true today that CP is best in more moderate speed boats, like fishing boats, where the load demands are quite varied.

A boat like Granuaile that's really meant to be efficient under power and has room for a pretty big wheel could well profit from CP. I'm still running numbers to figure out if Marmalade wants one. One real problem for that is that Marmalade is only 6 tons (ONLY?!?! On 25'?!?!) with a smallish engine. Most CP units want more power to a bigger prop than I can fit.

Anyway, if you're a bit of a propeller head and plan on long cruising with some real motor use and especially if you anticipate great flexability in loads - like maybe you're gonna scavage floaters on a stretch of river, raft them up, and tow them to a mill for a bit of cash - then CP might be worth the extra care and expense.

[Tylerdurden]

Have you considered diesel/electric? Most efficient of all systems as the diesel is at optimum most of the time.

[JamesCaird]

Hi Guys-Thanks so far for the responses. Further to the idea-what got me thinking about CP was the idea of really isolating the Diesel on soft mounts and driving the prop through torque tube(with appropriate joints) to a thrust bearing somewhere down the line. (The boat's shaft is 22 feet long-so I have plenty of space to work with!) I am familiar with the Evolution shaft system, bearings and seals, etc, but was investigating further ideas. I am also familiar with Diesel-electric (an ex-submariner!) but don't yet have the generator nor the motor. Have also seen that installation in some large yachts which have several large gensets already for house loads. Anyway-thanks so far and keep thinking.......Cheers/JC

[Figmental]

How about diesel -hydraulic ? It is very compact, flexible, powerful, efficient, vibration proof, and what else, clean? Hydraulic motors supply rotational power for a large number of devices.
As an old heavy equiptment operator knows there was a revolution in the last century when hydrostatic drives came out for bulldozers and other track drives...Same thing is common now as auto A/C compressors, radial pistons runnuing on a swash plate.

Anybody got a Northern Hydraulics catalog. They always had deals on motors and pumps.

David

[Tylerdurden]

How about diesel -hydraulic ? It is very compact, flexible, powerful, efficient, vibration proof, and what else, clean? Hydraulic motors supply rotational power for a large number of devices.
As an old heavy equiptment operator knows there was a revolution in the last century when hydrostatic drives came out for bulldozers and other track drives...Same thing is common now as auto A/C compressors, radial pistons runnuing on a swash plate.

Anybody got a Northern Hydraulics catalog. They always had deals on motors and pumps.

David

If this a pleasure craft, the use of copious quantity's of hydraulic oil is neither Green or prudent if a mishap occurs.
I dug heavily into this option but the cost of green vegetable based oils and their requirements for change out makes the whole mess prohibitive.