servo gear pitched propellor systems

Hi Nilo,

I have no experience with the servogear system in particular, but I am familiar with CPP systems in general.
A CPP system is mainly interesting if your boat is going to operate at very differring loads and speeds. Tugs for example want to sail fast to the ships, but then need high power at slow speed when towing, but also fishing trawlers or cargo ships that have a large difference between loaded and ballast condition. The difference between light loaded and fully loaded is usually not as extreme in yachts.

At lower speeds with a yacht, you don't require the full power of the engines as you would on a trawling fishing vessel so it's ok that you don't use the maximum power your engine can deliver. With a CPP, you can reduce pitch, have higher revs and go full power even at lower speeds.

There are five reasons I can see why you would want a CPP system on a yacht:
1. the increased manoevrability. You can go from full ahead to full astern in a very short time, while the engines just keep running at the same speed. However, if you have a reversing gearbox with trolling valves, I think you'll have almost the same manoeverability (but other may object), but at a smaller cost.

2. If you plan to use a shaft generator, you want the shaft revolutions to be at a fixed rpm. A CPP systems allows you to change the speed while maintaining the rpm. It is however not recommended to let the propellers revolve in neutral for a long time (for example alongside) just to power the shaft generator. For yachts, it's rarely interesting to have a shaft generator, as they spend so much time at anchor and little time cruising. I think some of the larger expedition yachts do have them these days.

3. Your yacht is a sailing yacht: the CPP system allows you to flare your propeller blades to reduce resistance when under sail. Also when under sail, at any sailing speed you can adjust the pitch exactly so that you can deliver extra motor power (but that's cheating if you ask me).

4. On a motor yacht with a CPP system, you'll be able to accellerate faster than with a fixed pitch system.

5. Fuel economy: as you can always use an optimal propeller at every speed, you'll have a longer range at economical speed.

I have investigated CPP-use for a yacht once, but in the end we decided not to put it on, for reasons of extra cost & added complexity. But every yacht is different, and it may be worth to do the maths and see if point 5 balances up against your initial investment in a reasonable time period.


Bruno
Naval Architect
Innomare

Nilo,

You might find that http://www.yellowfin.com/VSDTechnology.asp have the type of technology you would appreciate. There are videos on the site and a number of reports on their media coverage page. http://www.yellowfin.com/pr_shipnboat.pdf is from Ship & Boat International.

They are looking to work with boat builders and offer an alternative propulsion system to Volvo's ISP.

Regards,

First Pericles

Hi Nilo,

CPP is a good, simple and reliable solution for propulsion.

Innomare already mentioned all "+" points.

Time goes on, and now these sytems are all electronically - hydraulically operated. No more separate control air system, all electronics became smaller / more reliable, hydraulic units are installed as a small package...

I have experience with different (very modern and quite old) systems:
KaMeWa (now belongs to Rolls-Royce), BERG, Wichmatic, LIPS (both last belong to Wartsila Propulsion now).

They all have the same principal, however, every manufacturer has it's own "patent" to be proud of...

Just a few i-net sites for Your consideration:

http://www.rolls-royce.com/marine/products/propulsion/propellers/controllable_pitch.jsp

http://www.bergpropulsion.com/Content.aspx?PageID=3163&PageTypeID=3

http://www.wartsila.com/Wartsila/gl...ications/brochures/product/propulsors/cpp.pdf

Hope that information will be useful for You,

Best regards,

Andrei

Hi Nilo,

have you had a chance to compare the fuel efficiency of two different ways to sail at a low cruising speed (say 14-15 knots)?

1. Both engines running low-loaded (I suppose at higher rpm than would be the case with fixed propellers?).

2. Running on one engine only and giving the other prop a maximum pitch for minimal resistance (and freewheeling if a trailing pump is installed).

It would be interesting to make these comparisons on a long crossing on a windless day. You could have four scenario's to measure (the two above, plus both the same with the propellers fixed as if they were FPP, designed for maximum speed).
I am also interested to hear if option 2 is viable or if the autopilot has to give too much rudder to compensate.

Thanks for sharing your experiences!

Bruno