Prop Slip

[snlphillips]

First time poster, long time reader. Thank you everybody that has contributed to this great website.

I recently bought a 1998 Parker 2320 notched transom w/ '06 Yamaha F250. I went through this boat with a fine toothed comb and found a several little things that need attention but the price was right and I don't mind working on boats.

The prop slip problem. On the sea trial the boat ran 32mph (gps) at 5800rpm on flat water with minimal current. I figured 40-45mph at WOT with this set up. Prop is a stainless 17 pitch 3 blade. Owner gave me the original 19 pitch 3 blade black aluminum prop with the boat. I put the 19 pitch prop on and had similar results. It even sounds like the motor was "spinning out". Lower unit looks good, prop hub is tight. Motor is mounted one hole up from the lowest position. I read a lot about prop selection and it sounds like my set up would do well with a Rev4 17p or 19p prop. However, I doubt just the prop is going to completely solve 30-35% prop slip. The next step of troubleshooting is a lot more intrusive and I'd like some opinions. I have a Raymarine C120 with plastic thru hull transducer mounted in the flat portion of the hull right in line with my outboard, see photos. I'm thinking this is a big part of my problem. I may try to scrape the bottom paint off it and generally try to smooth things out and take it for a test run. But I'm thinking for optimum performance, buy a new 20* transducer and mount it to the side.

What do you guys think? Am I missing anything else? Is there anything else on the motor that I should check? Compression test and LU corrosion all looked really good.

https://goo.gl/photos/pZ7JrNvCQijUBwKCA
https://goo.gl/photos/htQnVLNWXGiZBNir8

 

[Brent]

This article discuss OB height and anti ventilation plate location
http://www.veradoclub.com/index.php?topic=137.0

Do you have Permatrims?
Trim tabs?


Many folks ask Ken at Prop Gods for advice

 

[snlphillips]

Good article. I'm pretty sure my outboard is at a good height. Check out the picture in my original post. I think the cavitation plate looks good. I don't have permatrim but I have oversized trim tabs. I've ran them up and down through the full range and 32mph is the best I could get. I'll talk to Ken about what prop I should use and send him a pick of my outboard placement.

I'm still worried about that thru hull transducer placement. I've read of a few people with transducers in that location. But I think they were all bracketed boats.

 

[Brent]

I agree the OB height is good and you are getting good max rpms


How are you measuring speed?

 

[Brent]

Maybe the props needs new hubs?

 

[snlphillips]

I measured the speed with the GPS and double checked that with my phone GPS. I looked at the prop hub and it doesn't look like it's slipping. Maybe I'll remove the hub tonight for a more in depth inspection. I emailed Ken with all my info and pictures. We'll see what he says.

Thanks for the input so far.

 

[Brent]

You can place a mark on the hub another one the prop then run the boat and afterwards check the marks

I am thinking the speed should be higher

 

[snlphillips]

Ken already replied. He's saying my prop is the biggest culprit. I ordered a 4 blade 17 pitch. Quicksilver Q4 was the one he put in the email but then switched to a similar one with more stern lifting characteristics when I talked to him on the phone. Prop is on order.

I'll mark the hub and prop and go for a spin this weekend to see if it's slipping, just for curiosity sake.

 

[Brent]

post an update

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[Bigboy]

I have a Formula 233 with a F250 and I run a Mercury Mirage Plus 17" pitch for heavy loads and see 46MPH at 6000rpm. I also have a Quicksilver 19" pitch for lighter loads and can get 48MPH at 5800rpm.

 

[snlphillips]

Update:
Checked the hubs in both props, neither were slipping.

19p 3blade yamaha aluminum prop hit 32mph at 6100rpm, rev limiter was easy to hit when tabs were up and motor trimmed.
17p 3blade yamaha stainless prop hit 33mph at 6100rpm, I could hit the rev limiter with the tabs and motor trimmed for max speed. 5500rpm cruise at 25mph burning 15gph

Got my new Power tech OFS4 17 pitch from Ken at prop gods. 40mph at 5800rpm More importantly my cruise is a comfortable 30mph at 4400rpm burning 12gph.

All number were collected with 2/3 fuel tank and 4 people on board.

Why was the prop slip so bad on the other two props? IDK. I blame it on that in line thru hull transducer. It's probably creating a little disturbance that the new prop is better at dealing with.

Ken said I'd be a little fast with a Rev4 but the OFS is popular on the west coast because it maintains plane at a lower speed. We're often fighting 2' wind wave on top of 5' swells on the west coast so a lower planing speed is a nice characteristic.

 

[Brent]

Thanks

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[Lucky John]

I can't wait to get my OFS4 -16 pitch and see how it does on my 300. Hopefully by next week

 

[warthog5]

I'm pretty sure my outboard is at a good height.

I disagree.... Needs to be moved up a notch.

The 4 blade gave you more lift and accomplished this.

 

[snlphillips]

I'm pretty sure my outboard is at a good height.

I disagree.... Needs to be moved up a notch.

The 4 blade gave you more lift and accomplished this.

Ok, so the cavitation plate was too low in the video? Outboard was already up on notch in that video.

I'll take a look at the cavitation plate again on my next outing and see if it looks higher with the new prop.