Prop/WOT/engine height - would appreciate your thoughts.

[Sunbeam]

Thanks for the input, Chris. I think your Yamaha 75 is about as close as one could get to the F80 without actually being one, so it's especially helpful. I'm going to assume that your prop is a 3-bladed one (seems like I kind of got an oddball by going with the 4-blade, which is making it hard to compare. Maybe that was an "oops" but the reasoning of the person who suggested it sounded good at the time).

Of course I kind of wrecked my data set by changing so many variables between my first and second try. And next thing you know I (hope to) be at Powell, which is yet another variable! I don't know that I'll get out again before heading there. Maybe if I get there in time, I'll try out both of my props before the cruise. At least then I will have "equal data" and be able to really properly compare the original 13.5 x 15 (which is the size you have good luck with) with the new prop I got (13.25 x 13).

I may decide to get either a 13.5 x 13 (3-bladed) or a 13.x x 11 (4-bladed) to bring along, but I'm not sure about that yet. I'm going to try to understand the 4-bladed thing better first.

Sunbeam

PS: If you see this - do you get a sort of "sing" at certain RPM's? I noticed one between slow and about 1900 RPM (8mph) - it seemed like it was coming from the prop area. I'll have to see if it stays the same with another prop.

PPS: I'll be very interested to see Rana Verde again now that I have specific things to look for (like that special boat-lightener you carry along )

[thataway]

In the middle of the night I was thinking about the motor level at fully loaded and very light boat. The boat certainly sets a couple of inches deeper (I have never calculated the amount of weight to bring the C Dory waterline down one inch--a factor I usually figured on my cruising sail boats).

There will be some difference in the prop and water flowing off the transom, but it will not be much. In the Tom Cat it did not seem to vary as far as the visibility of the Permatrim. Recently I saw a photo of a cavitation plate or foil which was correct--I'll see if I can find that.

Sunbeam, with your intended use, I suspect that the boats waterline will remain fairly constant, so I would adjust it for your current loading. I had more data for the C Dory 25, since it did not have the foil when I first got it, and my experience was very similar to Tom's.

I have been lucky to not have hit any rocks at Powell--but I agree that a hammer and course file are always in my tool kit, as well as at least one spare prop, trust washer, at least one extra crown nut and several cotter pins. (I once had a cotter pin break in a dinghy, and both the prop and crown nut spun off a dinghy when I put it in reverse. Fortunately it was in very clear water and I found them both--put a piece of wire in there to get back to the big boat to replace the cotter pin!.

What you clarified about the spray is normal. I had thought about the visual lines for you and raising the seat also. If one has a vessel with a clear windshield and sloping bow, the visibility in the C Dory seems a bit restricted, with the pilers and fore deck, but you get used to it

[Sunbeam]

I was just putting my hammer into the "goes to storage" pile, but I hadn't thought about possible prop work (uh-oh, there's another pound in the boat ). I'll put that aboard now (already have a file in the toolbox). I think I have spares of the others because I got all new with the new prop, and then packed away the full set of previous parts, but I will double check - glad you mentioned it.

[Sunbeam]

Edit: See bottom of post.

A specific comparison question:

(I know I could probably get this info from a prop shop, but maybe it will prove helpful to others too if it's here.)

I'm looking at Solas aluminum 3-bladed props that say they will specifically fit my engine. In 13 pitch, there are two diameters, one is 13.5" and the other is 13.75" (in other words, everything else about them is the same).

Given that all else is the same, what difference(s) would the change in diameters cause?

Sunbeam

****
Edit: I got in touch with the prop shop where I bought my current prop (note that when I ordered it I basically "knew" what I wanted and just ordered it, so they didn't really help me select the one I have - so they can't be faulted for it). In talking to him he did say that going with the 4-bladed when I did wasn't totally illogical, as they can be better for a "heavy" boat. However now, he felt that going down to an 11 pitch 4-bladed would probably be "too much," and would really cost in top speed (not that that's a priority, but I don't want to totally lose it all).

Upshot is that he suggested I try the 13.75" x 13 pitch 3-bladed, and he said why didn't he ship it to me at Powell, I try it, and if it worked well I send him some money, and if not I send him the prop back. I can't exactly argue with that kind of service I think I will do that as then I will have all three props, and can try them all with the rest of the variables remaining constant.

I did also ask about the 13.5" vs. the 13.75" in 13 pitch, although I had already found that in the "real world" online, the 13.5" was pretty much impossible to find, or at least far, far less "normal" to order. He said that would be more for a smaller/lighter boat, and the 13.75" would be the logical one to try.

So, once I find someplace to receive a UPS package around Powell, I'll get it on the way, and I should be positively bristling with props (I haven't ruled out raising the engine at all, but am not sure I'm going to do that before Powell).

[thataway]

Did you use the storage facility in Big Water? They can get a UPS package for you. They did it for me.

You would have slightly less blade area, with the 13.5" diameter, and it would spin slightly faster--not quite as much water moved per revolution. Usually as you go down in prop pitch you go up in diameter (slightly). The 13.5 inch diameter Solas prop has a bit more rake to it than the 13.75" and is definitely more of a lighter boat prop, with a little less blade surface area and different cup.

[Sunbeam]

[Sunbeam]

[thataway]

No surprises here. very heavily loaded you may have been able to run an 11" pitch (your 7500 foot elevation prop--think Yellowstone or Tahoe).

I guess being an old guy I have never been concerned with sounds of a prop. Was the fully trimmed down motor and 1/3 to 1/2 trim tabs the most efficient speed? If you were running in following seas--(which you would rarely get at Powell), the running bow down might not be a good idea.

Also the Permatrim helps with getting the bow down--if necessary but you don't want it trimmed that way if the Permatrim is on, for down wave use.

[ghone]

Hi Sunbeam. Missed this before. As we're pretty heavy, I find the 13 1/4 x 15 3 blade being a good fit. I run 5800-5900 wot and trimmed well when in flat water on the coast. I don't have Permatrim or any foils on the motor. I do have Bennett tabs. For wot I had the throttle at full open and then played with tabs and engine trim until I saw the highest rpm and speeds. At Powell we ran 5400 +- in flat water. Most of the time on Powell was 6 knots however. We ran quick just to see. We are spending much of our time in displacement mode with higher speeds for getting in prior to happy hour or crossing large bodies of quickly changing waters, ie Georgia and Haro straits.
I am happy with this prop for elevations up to Powell. Higher we'll need a 13 1/4 x 11. I carry my original 13 1/2 x17 for a spare. Only good on a light boat. I would likely see about 5200 ish at sea level with this one. No hammer aboard. Just a spare prop. Both being aluminum. Wreck it and I need to find a rock to use on straitening blades! I prefer bent blades to bent drive train so use aluminum props.
As an aside on the noise issue, as I wear hearing aids and Carolyn has outstanding hearing, when it comes time for high speed runs, we pop on the Bose noise cancelling headsets. These plug into IPad or phone for in flight music and also have a jack for VHF so I can talk on the radio even at speed. I have felt the boats are fairly noisy at full song, but maybe I'm easily fatigued thru impaired hearing. Bose is worth the money. I sometimes think the battery has quit so take them off to see, now it's loud!!
Best of luck. George

[Sunbeam]

[ghone]

Hi Sunbeam. The 13 1/4x15 works fine on Powell. Runs 5300-5400 wot. I use it here on the coast also. For much higher I'd just go to 13 pitch. Leave the diameter about the same We find we don't blast around at wot much. Cheers George

[Sunbeam]

Thanks for the confirmation, George. Will be interesting to see what I get at WOT (with the boat loaded vs. super light). Maybe the 15 pitch 3-bladed prop would be fine for all situations - I'll find out when I try it. Doesn't seem like the 4-bladed one I have is going to be the best for anything (oops). Meanwhile the 3-bladed 13 pitch I have on loan has worked well on Powell (5500 WOT loaded but with some supplies used up so maybe 80% of original load).

I never cruise at WOT, but my understanding is that being able to attain an RPM in the WOT range (and preferably higher in the range) means one isn't lugging the engine at other speeds, so is desirable no matter how fast one cruises. For normal "going fast," I've been limiting my RPM to 80% of WOT. But this is all amateur knowledge/reading on my part (and don't ask me about docking, ha ha). Going slowly is nice (and quieter!).

[thataway]

My reason with for the Permatrim is to get the bow down more for really rough stuff. It does provide some lift for the stern on getting up onto plane.

It sounds as if you are running your boat a bit more bow down than I do, but without seeing it in person it is difficult to know.

Engine height will make a difference.

[Sunbeam]