Boat prep and propeller tests
The big project that we have been planning over the winter is replacing the Volvo folding propellers with EWOL feathering props. I’ve been anxious to see if we could get better motoring performance, not because I plan on doing a lot of motoring, but rather because the speed under engines seemed very slow to me, 5-6 knots at 2,000 rpm, and I was worried there might be something wrong.
The new propellers were fitted during the haul out at Canet, so Stéphane was able to try them during the run back to La Grande Motte on Monday. Unfortunately it didn’t go so well. The engine rpm was limited to 2,000 and there was a lot of vibration that increased with the rpm.
The limited engine speed could be corrected by reducing the pitch of the props, but the vibration was a bigger concern. We were fortunate that Sergio from EWOL is in La Grande Motte this week for the International Multihull Boatshow, so he joined us onboard Wildling to supervise the testing. Let me say how impressed we have been with EWOL, they truly stand behind their propellers, and have been very involved in helping us find the best propeller solution for the Outremer 5X.
We had a scuba diver go under the boat to change the propeller pitch, which is a very simple procedure on the EWOLs, and then we took the boat out for some test runs at different engine revs and wind directions. The reduced pitch allowed us get the revs up to the design max range, but the vibration was still present. The consensus of the team is that the diameter of the propellers is too large, which is leaving too little space between the blade edges and the hull surface. This causes cavitation and turbulence, and that causes the vibration. A smaller diameter prop with the correct pitch “should” eliminate the vibration while still keeping the performance.
That’s the bad news. The good news is the performance is much better with the EWOL props. Instead of 5-6 knots at 2000 rpm we were getting around 8 knots, and over 11 knots at full speed. EWOL is making us some smaller props now, and we will fit them and retest in a few weeks time.
Although it would be nice to have everything perfect the first try, it usually takes some trial and error to get the right propeller match for a new boat, so this is to be expected. One of the main reasons I selected EWOL for this project was because they were willing to work with Outremer to find the right solution, and they have certainly been true to their word on that count!
Other than the propellers, Wildling is pretty much all ready for the sailing season. After her delivery back from Canet-En-Roussillion, we went over everything with Stéphane. The wind angle sensor stopped working during the trip back from Canet so we replaced it. It was a bit intermittent last July during our first voyage, but then worked fine since, so the gremlins that caused the original problem must have returned.