servo gear pitched propellor systems

nilo · 03-11-2006, 03:11 AM

i am planning to install servogear pitched propellor systems on a boat i am building. does anyone have experience to share?

Innomare · 03-11-2006, 10:09 AM

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 · 03-11-2006, 12:40 PM

dear bruno,

thank you very much for the extensive information. in my case, points 1, 4 and 5 are valid. i have already considered that it would be a good investment, as the boat has a very large range; up to 25+ knots at half load and i am hoping to cruise quite frequently at lower speeds. so, i am particularly looking for experience with this specific application to find out if there are any particular points that i need to know.

First Pericles · 08-18-2007, 04:02 PM

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

nilo · 08-18-2007, 04:35 PM

thanks, i now have a first hand experience and they are working very efficiently. if anybody needs more information, i would be glad to share.

TSI AV · 08-19-2007, 06:31 AM

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/pr...able_pitch.jsp

http://www.bergpropulsion.com/Conten...3&PageTypeID=3

http://www.wartsila.com/Wartsila/glo...ulsors/cpp.pdf

Hope that information will be useful for You,

Best regards,

Andrei

Innomare · 08-20-2007, 06:12 AM

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

nilo · 11-13-2007, 05:13 PM

Quote:

Originally Posted by Innomare

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

Hi Bruno,

I have noted that I still owe you a reply on this. Sorry for overlooking.

Servogear is a computerized system and the pitch automatically adjust itself at different rpm levels based on the load on the engines.

Of course there is also a fixed rpm mode, where you can adjust the pitch. This mode is set at 1100 rpm on my boat and it is used basically during maneuvering. This gives a very good elasticity and smooth movements for close counter handling.

To give you some idea for consumption levels; at 1100 fixed rpm when we are cruising at maximum pitch we burn around 30 liters per engine and we cruise at 11 knots. As far as I recall, when we go to normal mode, we can cruise around 13 knots at 1400 rpm and then we burn around 50 liters per engine, of course per hour. Will check this next time I use the boat for more precise figures.

Yes, we had the chance to cruise on a single engine for long periods of time due to an electrical fault. The auto pilot was nicely compensating. Unfortunately I do not recall whether there was a major change in consumption, because we were basically involved in getting rid of the trouble, which neither us, nor Cat service were not able to figure out for some time. The symptom was indicated as low fuel pressure and not as an electrical fault. We located the fault accidentally after long suffering. We were able to activate the engine by pumping out the air (we thought we were able to work it out like that), then we found out that only a cable was partly disconnected.