Prop Issue????

Neal Haarberg

Active member
I purchased a new Solas prop about a couple months ago. The same part number as the last 2 that I have had on my boat so it is nothing new. I went fishing yesterday and before I left I noticed 2 marks on the prop. After a day on the water the 3rd blade has a mark. It's really weird, there is nothing that can be in contact with the prop where the damage is and the "scratch" marks are in direction about the axle like would be expected if it was hitting something. I added the red line to illustrate the "scratch" direction. I had recently adjusted the trim tab but I don't see how that can damage the prop. Has anybody seen this before?


View attachment Prop marks.jpgView attachment 20210628_121412 (2).jpg
 
A likely suspect is that air is in contact with the prop as it spins. Either it breaks the surface at high speed (surface piercing), or a bubble is forming in that location (cavitation).
 
SJ Fairbank said:
A likely suspect is that air is in contact with the prop as it spins. Either it breaks the surface at high speed (surface piercing), or a bubble is forming in that location (cavitation).

I agree that this looks like cavitation damage. May be one small thing causing the cavitation, or it may be a combination of factors. My best advice would be to research "cavitation", read as much as you can, from various sources. Then try to separate what part(s) of that information applies to your rig and how your "set up" needs tweaked.

I know that doesn't sound real helpful, but every rig and every set up is unique to itself.
 
Look at the relationship of the hull and prop from aft of the boat, with the motor trimmed to running position. As Dave said, cavitation is the most likely suspect. There does, however, appear to be some "shine" on the leading edge of the prop. If so (don't count on my old eyes), and the top of the prop arc isn't a couple inches below the hull at running trim the motor may need to be lowered/or the shaft is too short. As Dave suggested, online research should help diagnose the problem. Best of luck.
 
After a quick search on cavitation that is it. I never knew that cavitation could be so damaging to a prop. This year my new job has allowed me to go fishing a lot more than in the past so it has seen considerably more hours with just me in the boat. No blind, decoys, dog blah blah than it typically would. I was thinking about going to a higher pitch prop for summer anyway. now I have an excuse[;)] Then I can swap it back out for bird season and see if the problem persists. The question now becomes go up 1 pitch or 2? I wish I had a tach to see what RPM's I was getting to help choose my summer prop.
 
Neal, call prop manufacturer or stop at a prop repair shop. I had a new prop the spun once in a while. Brought them the props, they inspected them and put in new inserts, problem solved.
 
Neal Haarberg said:
After a quick search on cavitation that is it. I never knew that cavitation could be so damaging to a prop.

Here is a very good video on the dynamics of cavitation. Although the narration uses engineering terminology, the message is still easily understood by the average Joe.
cavitation explained
 
Capt Rich Geminski said:
Neal, call prop manufacturer or stop at a prop repair shop. I had a new prop the spun once in a while. Brought them the props, they inspected them and put in new inserts, problem solved.

Capt,

Are you saying the damage shown on the surface of the blades, is due to the hub slipping? Please explain.
 
Dave, the good news is I am an engineer so the video makes perfect sense.
Rich, good suggestion I am sure there is a good prop house in the Portland area. I just have to find it, plus I avoid going in to Portland like the plauge. I have contacted Solas tech support so we will see what they say.

What I think is happening has to do with my setup. I have a break away plate which sets my outboard 6 inches off of the transom. RIght now the cavitation plate rides right at the waters surface. which is what I want since as we all know duck hunters go into shallow water all the time and an inch or 2 can make a difference so I do not want to lower the motor. With the lighter load the prop is spinning faster in the hole shot and at speed. From what I understand that would create a lower pressure on the back side of the prop than my duck hunting setup which is just enough to create the cavitation. That is why my initial thought was to go up a pitch or two which would put more load on the outboard not causing the prop to spin as fast in the hole shot or at speed therefor increasing the pressure on the back of the blade . Without a tachometer I very easily could be wrong, for right now I am going to put my old backup prop on so the new one doesn't get damaged any more before duck season until I can get a new prop. I won't be getting a new prop for another week or so and there are tiger muskies that I want go chase in the next couple days! Thanks everybody for all the input, this is a new one for me. We will see what Solas has to say
 
I went ahead a purchased a tiny tach and was able to take the boat out for a spin. At WOT I was at 5450 RPM's and Evinrude says 5500-6000 for my outboard. From what I understand 1 pitch typically will change RPM's 200-300. It looks like I need to go down 1 pitch for summer and 2 pitches for Duck hunting when the boat has a blind and gear. Actually I got a tiny tach knock off on ebay for half the price. I did have to make an extension for the ground because the wire wasn't quite long enough to reach from the spark plug wire. It is so nice to have data instead of guessing. I don't know why I didn't do it sooner! My plan is to just run this prop for the rest of the summer then save it as a spare and get a more appropriate one for duck hunting before the season and then get a summer prop next year. It will be nice to have a better hole shot especially when it's nasty out on the river!
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