Cavatation? Yamaha F225 with Saltwater Series II SDS 19 x 15-1/4

[Angler1]

Got to run my brand new Saltwater Series II SDS 15-1/4 x 19 prop today for a few hours. Best speed was 44MPH at 5600 RPM on a Hurricane GS 211 Deck boat, however, trimmed up all the way to get that speed.

When pulling the boat out of the water I was disappointed to see what looks like small scratchs and nicks in the back side of the blades towards the outside ends, on each blade. Had to reverse throttle hard off of the trailer and off of a beach, so thought I might have kicked up some small rocks. But now I'm wondering if this is possbily cavatation burn. There are no burnt spots, but they are little shiny scratches/pits in the stainless steel.

Does this describe what cavatation burn would look like, and what could cause this? The old prop was a 13-3/4 x 19 black stainless and doesn't show any damage.

 

[steelespike]

Re: Cavatation? Yamaha F225 with Saltwater Series II SDS 19 x 15-1/4

Usually cavitation burn is closer to the base of the blades and tends to be kind of like a streak.
I have 3 al props right here lightly used to heavy use. The lightly used one has streaks at the base of 2 blades 3/4" X 1/8 inch
paint removed with a shadow in the paint on the third blade.The medium prop has 3 streaks about 1/2" X 2" that look like someone ran a
wirebrush on a drill over it. The heavily used prop has large irregular patches about 2" X 3" with some pitting.
The ss props would have similar evidence in any paint present but would resist better any erosion of material.
My props are all Merc.props off a Merc 50 that has been on the same 18' Crestliner utility since 1965.
Evidence of cavitation burn can be an indication a prop is working very efficiently.
Your prop doesn't appear to have cavitation burn at this point.

 

[Texasmark]

Re: Cavatation? Yamaha F225 with Saltwater Series II SDS 19 x 15-1/4

Additionally, I doubt that a few hours running could possibly etch SS even if it were cavitation. On beach debris, possibly, if the prop had a pristeen finish on it where minor abrasions would be readily apparent.

Apples and oranges on boats, engines and all, but my boat gets it's top speed with my engine trimmed all the way out too. However, that point is before the prop breaks loose and is due to the high angle of my transom. Had my transom been a few degrees shallower I would have to tuck in in a tad like I had to do on my last boat.

Mark

 

[Angler1]

Re: Cavatation? Yamaha F225 with Saltwater Series II SDS 19 x 15-1/4

Thanks gentlemen,

From your description of cavatation burn steelespike, I'm guessing this isn't the problem. However gentlemen, if the prop was breaking the water, trimmed out, is that the point where cav burn could occur? When air is introduced?

With normal trim (the normal amounts I used with the black 13-3/4 x 19 Yamaha prop) I couldn't get rpm above 5400 with this prop, and top speed was about 40-41. I kept trimming up until I got RPM to about 5600 and 44 MPH on the GPS. There was some change to the sound and expect I was breaking water. Even so, not sure if that would cause burn on the outside edges and these small pits/scratches. (The 13-3/4 x 19 black prop was giving me 6100 rpm and unfortunately didn't have a GPS on board then, but felt like low 40MPH)

At normal trim, my cav plate is about 1"-1-1/2" under water and a high trim I was just about breaking water with the back of the cav plate. This 15-1/4 prop is "tight' to the bottom of the cav plate, so I'm sure I was introducing some air trimmed out. Based on what I saw, I plan to raise the engine one hole, so I can operate with normal trim ranges. I was up there pretty good to get full speed on the top of my trim guage.

In any case, does any of this information help a case for cav burn?? Or no way? I'm in PA and fish lakes. The lake was high and dirty and perhaps I did dig up some muddy earth in reverse. But didn't see mud or feel any earth. It's a brand new prop, so just trying to get this right before I damage it more.

Thanks

 

[steelespike]

Re: Cavatation? Yamaha F225 with Saltwater Series II SDS 19 x 15-1/4

First I just want t to be sure you understand that burn occurs on the back side of blades.
As I understand it cavitation burn is caused from very low pressure causing the water to boil.
On my worse prop It is obvious that the worse burn is near the base of the blades gradually covering more and more area
all the way to the trailing edge. Never closer than about 1/2" to the leading edge.
I should note that on these 3 props there is no paint wear on the thrust side of the blades only on the actual leading edge of the blades.
I'm thinking this speaks to an excellent factory paint application on these Mercury sourced props.
These props were run in the relatively clear water of the St. Lawrence river in up state NY.
My feeling is with your props when you introduce more air you are actually reducing the boiling affect.
It just occurs to me; I wonder if there is some sort of electrolysis going on. The pits in the stainless
make me wonder.Or maybe just a defective paint job.

 

[Angler1]

Re: Cavatation? Yamaha F225 with Saltwater Series II SDS 19 x 15-1/4

Thanks steelespike, ...I do understand cav burn occurs on the back side. The pits are on the back side. However, they are following the outer lobe edge about 1-2" from outside towards the hub. The first 4-6 inches from the hub are perfect. The prop has no paint. It is polished stainless steel on a top of the line brand new Yamaha SS II SDS prop. I only ran this prop for maybe, all together, an hour at full throttle. And this was the first time the prop saw water. So this is baffling me.

Perhaps I put it in some rocky mud and did this, but I really don't think so. And the push side of the prop is perfect. If I pushed pebble laden mud, it had to be in reverse. And I question if that would even scratch it like this. (However, reverse thrust with the blades in a few inches of rocky mud, does indeed describe what this looks like....so maybe that's it.) The skeg is fine with no sign of scratches or damage.

This is way I'm trying to understand cavitation, since the only change to the boat from last season is this new prop. And thought maybe the new prop was cavitating baddly....but this damage is not what you're describing with your props. Looking at Hurricane's web site and the performance reports, they do use this prop and the earlier generation Saltwater Series props...so the actual SS II technology, cupping, rake, etc. should be okay for this rig.

I thought about electrolysis, but is it possible to see this type of damage in maybe a total of 4 hours in the water?

Strange! Oh Well. The only thing to do now I guess is run it again, and see if it gets worse. If it rots away by the end of the season, I'll have to try another one.

Thanks

 

[steelespike]

Re: Cavatation? Yamaha F225 with Saltwater Series II SDS 19 x 15-1/4

Probably not electrolysis. Run her and keep an eye on things.Probably a one time condition.

 

[Texasmark]

Re: Cavatation? Yamaha F225 with Saltwater Series II SDS 19 x 15-1/4

I ran a Merc Laser prop on my Ranger bass boat at about 50 mph, 6000 engine rpms for 7 years. My BIL is still running it. Only thing on the prop are a few scratches from running in sandy shallow water. I ran my engine out to the point that the speed would fall off, rpms would advance, and tuck it back till it settled down. I could hear the engine singing at 6k rpm and the 3 prop blades whacking the water at half that speed and just made a humming noise.

Mark