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.