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.
Hello Doug! Great to hear that the EWOL props are working better!
Fun, I’ve been near Wildlings this afternoon! We Are currently in La Grande Motte for the Salon. She is a true beauty 🙂 are you going to be around these next days? Cheers
Hi Nicolas, I’m sorry I missed you at the boat. We had to leave for Aix-en-Provence because our kids start school their on Monday. I’ll be back in about 1 week though. I hope you’re enjoying the salon! Cheers
Hey, Doug, thanks for posting. I was curious if you were also testing the ‘in reverse’ power/efficiency of the EWOLs?
Hi Swanie, yes we’re definitely interested to see how they perform in reverse, although it’s a bit harder to do objective testing. EWOL states they have much more reverse thrust because they are feathering props, not folding, and it did seem to be the case when we maneuvered in the marina, but because I wasn’t driving for the last test, I can’t really say how much difference there was. I’ll have to see how they feel when I’m driving and I’ll let you know.
Congratulations on a beautiful boat and an excellent blog. I am also deciding between VP 4 or 3 blade folding props and a feathering prop. Which VP props do you have (diameter and pitch)? Which EWOL diameter did you fit? DO you know the first and second pitch of the EWOL props? Do you know how much clearance you have between the EWOL props and the hull? Regards
Hi Igor, I’m afraid I don’t have very much information on the sizes. Here’s what I can tell you. The critical dimension on the VP props is to have greater than 2cm clearance between the hull surface and the blade edges. This is what the Volvo Penta engineer told me. With the VP props there is 3cm clearance. With the EWOL props there was 2cm clearance. The standard EWOL prop angles (check their literature, I think they state them) were too great when the propellers were installed and the engines would not achieve maximum rpm. We had to reduce pitch by 3 degrees in order to get the RPM back up. Further evidence the props were too big. If you call or email Sergio at EWOL, he will be able to give you all the technical data. He is very helpful.
We believe the problems I had were all related to a mismatch between the propeller size and our boat, and have nothing to do with the design of the propellers themselves. We’re hoping the smaller propellers will work much better. BUT, one thing I found during this process, is that there were some real problems getting the EWOL propellers to feather when sailing. At times they got stuck in forward mode, and it seemed to depend on what angle they were at when the engines were stopped. We need to video this underwater to see what’s going on. EWOL swears it’s not possible, but I know what I experienced when we were sailing the boat, so the only way to know for sure is video. The VP propellers just fold. They have a very simple design, and they will always fold when you block the engines. They may not be as efficient as EWOL, but they are simple and effective. Also the EWOL blades are quite thin. They are lighter than the Volvos, and much higher performance, but it seems they would be more easily damaged by impact.
I hope that helps a bit.
Hello Doug, I am considering an EWOL for our cruising trimaran however I am concerned re your impression that the prop sometimes did not feather when sailing. Did you get around to the proving/disproving of this very important aspect, or do you know of someone who has done so?
John
Dear Doug,Thanks for the info. I am still undecided on my new props and was hoping to hear from your new EWOL test. Regarding clearance between the props and the hull, reading Dave Gerr’s Propeller Handbook and others, there seems to be a concensus to have approx 15 to 20% of diameter as minimum clearance between blade edge and hull. From your photos, you have the 20″ or larger VP folding 4 blade props (only available in 20″, 21″ and 22″ diameter), I suggest that you aim for a 20% X 20″ = 4″ = 10 cm clearance between hull and blade tips to avoid hull vibration (2 to 3 cms is definitely way too little clearance.) Please keep us posted on your EWOL tests and remember that you can easily install the new propellers underwater without the need for a haulout when they are ready. Best of luck!
hi Doug has there been any news on the smaller diameter EWOL props? have you been able to test them as yet?
Hi Ron, no update on the EWOL props. I am still of the opinion that they won’t work on a 5X because the saildrive legs do not extend low enough under the boat to give adequate clearance to avoid the turbulence. I was hoping EWOL would work with Outremer to test them, but so far they have not been willing to do a test.
Hi John,
I did not personally have enough experience with the props to know how big an issues this is. I can say for sure that it happened to us during testing several times, and it took quite a bit of fiddling with forward and reverse blocking of the shafts to get them to feather. I heard from at least one other person that they had the same problem.
The Volvo folding props may not be high performance, but they are very rugged, and they fold immediately, every time.
Regards,
Doug
Doug, thanks very much for your report. I agree re the folding Volvo. We have one on our cruising trimaran and it does not miss a beat. My research seems to indicate that the Flexofold prop may be a good choice, for very good all round performance and minimal prop walk, which can be a problem with our single engine.
Anyway, happy hunting!
John
Flexofold are nice props and they have a good reputation. The biggest headache with changing props for us was figuring out the correct pitch and diameter. There’s pretty widespread agreement that it’s a trial and error process, and most boat builders have to test 3 or 4 different prop models to find the one that best matches the characteristics of the boat. The best case is if you can find a prop manufacturer that’s willing to let you test several different size and pitch props to get the right match. We also found that hauling out to do the changes was pretty much required, despite assurances that the props could be easily changed underwater. It can quickly become a complicated and expensive process.
Cheers
Doug, you have detected what I think may be the only problem with Flexofold. I have checked with the main man and via the French distributor. Flexofold will not consider giving support if the prop they supply is wrong. I offered to meet the cost of the diver (the blades can be changed in the water) if they would supply exchange blades, but they refused. I think they should offer replacement blades of different pitch at cost to them, otherwise the exercise could be expensive and frustrating. Our boat is in Laboe, Germany for the winter and again I will attack this problem with him to see if we cannot get them to be more considerate re support of the customer.
Otherwise, like you, we will stick with the folding Volvo which may not be the best but at least it does the job. It could be that the perfect prop is like the perfect boat – unobtainable!
Cheers, J
Wow, I really don’t understand the attitude of these prop vendors. They completely discourage boat owners from buying their products. Maybe they have so much business from the boat manufacturers they don’t need people like us to buy their products.
Cheers
Doug, I’m going to have one more go at Flexofold re support via the distributor in Germany and will report on the progress or otherwise. I agree that this is an absurd situation. For our boat, Flexofold recommended an 18 x 13, the French dist recommends an 18 x 14?! Our current Volvo is an 18 x 16. Like you, if I cannot get some sort of support I don’t think I will bother.
Incidentally, your comment about your boat maybe not going fast enough; if the current prop is about the right size indicated by the fact that the engine can just, or just about, get to max revs, then a change in props will probably add 10-15% (0.5 – 1.0kt) more speed at the most.
Hope to have the latest from Flexofold within a week or so.
Doug, Here’s the latest from Flexofold –
“I think that you have misunderstood the service provided by Flexofold!
Being 25 years in the business, we of course keep a high level of customer support.
Should a problem be coursed by a defective propeller or wrong calculation from our side, we of course fix it.
Only demands for a possible return or exchange of blades are, that the propeller is max 1 week in water, without any kind of paint or other anti-fouling and that it´s returned in original packaging and original condition.”
So I will be ordering a Flexofold as they do seem to be right up there, have you seen this test?
http://www.flexofold.com/upload_dir/docs/Test_YachtingMonthly_low.pdf