Prop speed

[ohioan55]

I've decided to try prop speed on my R21ec to see how it affects speed and cavitation. I've read a good deal on this product, and it seems people either love it or hate it. the reason is I notice a lot of cavitation when going over about 2000 RPM. Not sure if this is a class characteristic, or just and issue with prop cleanliest. I have never cleaned the prop thoroughly and have noticed it is somewhat cruddy each time I pull. This is our 3rd year with this boat, and I was focused on other aspects of the boat earlier. I'll try to come back and update this as I'll be pulling the boat at least 3 times this summer (we are making a trip up the Ohio River). I'd add an image, but can't seem to get that to work currently.

 

[ohioan55]

Finally got our boat in the water today. I must say the prop speed treatment made a noticeable difference in speed and engine performance. MAX engine RPM went from 2600 to 3100 and picked up over 1.5 knots top speed. Also, minimal cavitation at 3100 RPM as compared to a lot of cavitation at 2600 RPM. As promised, I posted to let you know my observations.

 

[Chimo]

An interesting comment and perhaps timely for me. I was looking at Prop-speed today as the boat is hauled for its semi-annual anode change. You tried two things at once, cleaning the prop and applying prop-speed. Which of these, or perhaps a combination of both, caused your improved performance is hard to tell. For now I think I will polish the prop and see if I get some change. Prop-speed may be a next step depending on results.

Thanks for the feedback

 

[ohioan55]

Part of the prop speed application process is a thorough cleaning of the prop, but you are correct. Hopefully the prop speed will keep the prop clean, as advertised.

 

[Newf]

Don't know anything at all about prop speed as this was the first time I had ever heard about it but I would doubt that the product itself could possibly make that much difference to the RPM. The reason I say that is with my 2014 R21-EC I get 3100 to 3200 RPM's at WOT. No growth on my prop as I trailer it, so it's in and out of the salt chuck on every trip.

At 2500 to 2600 RPM's it will do 7 knots. At WOT with no wind or current it with do 9 to 9.5 knots depending on how it's loaded. This is on a prop that is clean visually but certainly not polished. I have not "cleaned" it, other than with a fresh water hose in 8 years.

On your 2015 boat, with I'm assuming the Volvo Penta D1-30, if you were only getting the 2600 RPM's at WOT then I would suggest that there were issues other than a dirty prop. I may be totally wrong in that assessment but it seems that a dirty prop would not result in a 500-600 RPM drop. Even if that was possibly, with a clean prop you should be getting the 3100-3200 RPM's WOT with the D1-30 without any prop speed product.

Again, assumptions are made that we have the same engine with the same prop and I'm certainly not questioning the numbers that you saw before and after prop cleaning and prop speed application. Just saying that my opinion is that there are others things at play here,,not sure what.

Newf.

 

[ohioan55]

I would be interested in your experience after cleaning your prop. My prop was dirty last year and it was thrashing a good deal, which is why I cleaned the prop. The prop speed does give the prop a slipping feel, almost like wet rubber when sitting dry on trailer. I did want to pull the prop and take it to a prop shop, but the turnaround was months.

 

[Newf]

There is no growth or anything showing on the prop. The numbers I noted above are the same RPM's and speed as it was when it was new.

I agree that with the smooth finish you now have on the prop there would be less resistance in the water. How much is hard to tell.

I would be interested to know what your RPM would be if you put it in neutral and gave it WOT for a few seconds.

I did this today on mine and it was 3500 RPM. With it in gear and WOT, I got 3200 RPM so a loss of 300 RPM to push the boat with clean prop and bottom. All things being equal if you did this, you should get more that the 3500 RPM in neutral WOT if the prop speed is beneficial. (Or am I looking at this all wrong????)

 

[FlyMeAway]

I may be totally wrong in that assessment but it seems that a dirty prop would not result in a 500-600 RPM drop. Even if that was possibly, with a clean prop you should be getting the 3100-3200 RPM's WOT with the D1-30 without any prop speed product.

I know it's a bit surprising but your assumptions would be wrong. I've seen dirty props get 500+ RPM WOT drops and easily 1-3 knots of drag on a boat that only goes 7 or 8 knots. Dirty props cause a lot more issues than most people think they will. Most sailors know this well (a dirty prop can easily cause a few knots of lost sailing performance, and just as bad when firing up the engine). Of course it depends on how dirty -- I once saw a boat in a yard where the prop was so heavily encrusted you couldn't see bronze; apparently the owner thought his engine was having serious issues and didn't think to check the prop until after spending a few boat bucks on a mechanic in the water 😀

 

[ohioan55]

I'll have another data point soon. We also did this treatment on a friend's Albin 33, which goes back in the water next weekend. I'll post observations on its performance next week.

 

[Newf]

(I know it's a bit surprising but your assumptions would be wrong.)

Ha ha. Sometimes my assumptions don't surprise me at all as I continue to learn from others.

In this case my surprise was that you would lose 500 RPM due to a "somewhat cruddy" prop. I have seen fouled props and hull bottoms from boats that sit in a marina for extended periods of time and would expect that type of reduction in RPM's. So based on this, a 500 Rpm drop from a "somewhat cruddy" prop with no mention of a dirty bottom appeared to be excessive to me but obviously your observations show otherwise.

I continue to learn. Thanks for sharing your knowledge on the topic.

Newf

 

[Chimo]

After posting previously on this one I thought I would add a comment.

I pulled the boat out of the water on Monday after it had been sitting idle in the boathouse for a little over three weeks. Because it is in a boathouse I don't get growth on the bottom. There is a chance for some on the stern where daylight comes in underneath the curtain but that is minimal because I hang a weighted tarp off the stern whenever I dock. I do, however get slime. This usually rubs off after half an hour or so running at cruising speed, about 13 kn. Just for interest I went for a quick run and max RPM were 2600 to 2700 at WOT. The rating is 3000. I had 62 US gallons of fuel on board as well as about 1/3 of a tank of fresh water and the usual junk.

When they pulled the boat I asked them to pressure wash the hull lightly [I wasn't going to be painting] and clean up bits like the tops of the trim tabs, trim tab actuators, swim platform supports etc. After the boat was waxed and splashed back in the water I took it for another run and it easily hit 3010 RPM.

I'd like to think that the gain in RPM was because I did such a fantastic job waxing the whole that the aerodynamics were so much improved but in reality the performance gain was because the slime had been washed off. Just an interesting example of how important having a nice clean smooth bottom can be. 😉

 

[ohioan55]

Just as an update: We launched our friend's Albin 33 last week and prop speed made a marked difference for this boat as well. Less cavitation and more speed. I don't know that this treatment would make much difference for boats that have higher speed props, but for boats that travel at speeds of 10 knots or less, well, it's worth considering. Without further research, it reduces cavitation and seems to make the prop more efficient. That's my observation so far.