Effect of prop surface finish.

[tonyrr]

I am using a Comprop (moulded plastic) four blade prop on a Yamaha high thrust 50 h.p. outboard. The boat is a 25 foot lobster type (modified semi-displacement) about 5000 pounds fully loaded.

My principal interest is in efficiency (expressed as highest MPG at just below displacement speed). A typical rpm would be in the 1800 range.

The surface of the plastic prop is slightly "nubbly", i.e. a rough matt, definitely not a polished finish.

Here is the question. How much power loss might there be using such a prop Vs a highly polished one (stainless??). Is there anything measureable, or is there nothing to go for at slower speeds? I assume that at much higher speeds a polished prop would be well worth while.

Thanks for any responses.

Tony.

 

[Dhadley]

Re: Effect of prop surface finish.

On ss race props some or all of the blade surface on the high pressure side will be a satin finish rather than a super polish finish. I doubt that you'd see much if any difference especially on a plastic prop. The plastic will obviously flex a lot more than ss.

 

[tonyrr]

Re: Effect of prop surface finish.

Under my slow speed conditions, what difference to prop efficiency do you think the Comprop flexing Vs an SS prop might cause?

Tony

 

[steelespike]

Re: Effect of prop surface finish.

I don't remember the details but there was a posting here a few months ago.If I remember right he took an average condition aluminum prop removed the very minor nicks and gave it a high polish.There was a measureable improvement but again I don't remember the details.IMO you would be better off with a metal prop.Don't know if Hustler makes one for your application
but they do make aluminum props that deliver stainless performance at al. prices.It is possible that the right 4 blade prop might deliver best mileage
in your stated rpm.Any prop must allow motor to reach its max recomended rpm at wot(wide open throttle).Found post;Search "prop polishing".

 

[tonyrr]

Re: Effect of prop surface finish.

Thanks, that was a helpful reference.

Tony.

 

[cribber]

Re: Effect of prop surface finish.

Yup, that was my prop... It had seen it's fair share of the lake bottom and my GPS numbers were falling off for hole-shot and WOT speed.

It was getting to the point of replace it or see if it could be fixed. Fortunately it worked for me since it was mainly surfaces dings and a few gouges. I got a noticeable improvement and regained my 4 sec hole-shot and got 3 mph increase that settled back to just above OEM spec after a few outings. Nothing can replace SS completely...

It did look shiny for one day on the water!!!
http://i179.photobucket.com/albums/w310/Cheep_photos/PropJob.jpg

I wouldn't recommend self repairing a bent or cracked blade, leave that to the professionals.
http://i179.photobucket.com/albums/w310/Cheep_photos/boat-harris056.jpg
We met a cypress knee in about 5-6 feet of water and lost. Only destroyed the prop thankfully... the lower unit was fine and replaced it with a stock prop since these are like car tires here and carry a spare!!!