2nd run on new prop and i find a huge rock

[ONERCBOATER]

well go figure after years of being almost rock free, i pony up and get a solas SS 9.25x 10 to replace my 9.5x10 stocker on the ol 15hp johnson (1983). Overall a bad choice i guess..... top speed dropped, rpm dropped, and then....gasp.... yesterday out with Mom and my son i find a huge rock and bend the heck out of the edge.
So my response was to use a cresent wrench to sort of straighten out the edge and minimize the wrinkle. and just use low power to finish fishing out the day.... (yeah i know not so good for lower end as not balanced)

Anyhow a day later much less mad... I looked over the prop and noted that if i removed 1/4" of the leading edge and tips after hammering out the wrinkles I would have a smooth working propeller. I can ballance it well as I have prop ballancers for large scale rc plane props that are large enough to do the job and very sensitive. And i can assure that the profile and shape is the same on all 3 blades using the one good blade as the shape to copy.

the question is... while i am pretty sure that removing material will raise my rpm (likely a good thing for this engine) will losing that much blade area effect the thrust greatly? or should I just give up and buy a lower pitch aluminum solas and try to be happy, as i can't afford to spend another $125.00 on a prop with xmas so close.

Any constructive input would be appreciated.

Sean

 

[FAC]

Re: 2nd run on new prop and i find a huge rock

I say go for it you wont loose anymore on the propeller and if something doesn't seem right then stop.

 

[steelespike]

Re: 2nd run on new prop and i find a huge rock

You might price a repair;l if the prop is cupped they could remove some cup at the same time and possibly get the revs up.Do you have the before and after performance specs?

 

[ONERCBOATER]

Re: 2nd run on new prop and i find a huge rock

new the prop cost $125 including shipping, I got to run it a few times before the tach arrived by mail, on the morning I went out to run it with tach and go fishing I found the rock :redface: what I do know is that by sound the engine was running around 4000 to 4500rpm (I know that is subjective and not a good way to measure thats why i bought the tach that i didnt get a chance to use.) to be short and to the point it was acting much more like a 9.9 than a 15hp esp after I decked the john boat (adding weight)

I could well be mistaken, but the marine shops around here are either outrageous or astronomical in labor charges, should I expect to be able to get it professionally done for less than replacement cost?....called local shops, $90.00 to repitch, $120 to repair.

looks like I am going to chuck it in lathe and remove .25" or so and then retaper it and balance. I guess the 1st step will be to make a template out of thin sheet aluminum so that I can be assured that all blades are identical after this. Then after the cutting, I would guess I can use a pitch gauge and check pitch across the prop every 1/4" to make sure it is the same, then sharpen and balance.

Does that sound like the way to go? (really starting to think about using a cheap aluminum prop for the winter.)

Sean

 

[steelespike]

Re: 2nd run on new prop and i find a huge rock

I guess a home repair is your best solution.Stainless props cost more to repair.
I think we need to know more about your boat. Size weight etc.
Yoiu might check that the carb is opening all the way. The antivent plate(just above the prop should be about even with the bottom of the boat usually ends up about an inch above.This could result in a couple of mph under ideal condsitions.

 

[ONERCBOATER]

Re: 2nd run on new prop and i find a huge rock

it's a 12ft jonboat, 48-50" beam currently decked with 1/2" 5 ply and very light outdoor carpet. has two swivel seats on posts (walmart specials) and a trolling motor, a groups 27 deep cycle, 6 gal tank, depth/fish finder and me old 15hp.

I have raised the drive as far as i could before she sucked air and lost thrust, the stock OMC 9.5 x 10 ran shallower (without sucking air) than the 9.25x10 SS solas and gave me a higher top speed.... I will be winding up with a 8.75 X 10 SS when I am done turning the prop down. will see what happens with it... Thinking I may want to put some rails down the side to break the water free from the hull to loosen her up a bit (kind of a chine rail)

I know I have about as much as I can stick on/in this hull....and am beginning to look for a 14 to 16ft replacement.... but cant afford it at the moment.

If I could just get over the hump RPM wise I think I should be able to plane out nicely about 19-22mph and will be flat tickled for the mean time.

Sean

 

[steelespike]

Re: 2nd run on new prop and i find a huge rock

I bet the boat is about 32" at the chine.?Part of your planing problem is the small footprint of the 12 footer. A 1448 or 1652 I believe will plane easier a run faster with a load.And you will feel like your on a cruise ship compared to the 12.
Our 15 foot aluminum utility with a 25Gale would struggle to plane with 4 adults.
Same motor on an 18' utility planed easily with 6 adults.
The rails may give you a little lift and break the water away from the sides but be real careful with a following sea if they catch a wave they may roll you over.
Same thing happened with a flat bottom steel boat I had.

 

[ONERCBOATER]

Re: 2nd run on new prop and i find a huge rock

well the result from turning 0.500 inches from the prop was interesting, lost much less thrust than I expected, motor revved just a little more and i gained 0.5mph, not much but at least i got rid of the really damaged material, and got the prop rebalanced.

I know on big boats that have a hard time getting to plane that sometimes it helps to drill the prop and allow a small amount of exhaust gasses to free it up until you get moving, I do have through hub exhaust so this is available to me, has anyone ever tried it on a smaller outboard (15hp in this case) and what were the results. It seems this may be exactly what I need to let the engine get fully into it's power band. I figure that no real harm should come if i start out small and work up till i get the desired result or find out it doesn't work, worst comes i can plug the holes back up. What do you guys think?

oh and a side note, the jon boat will be parked for a month or so, it seems that I am the proud new owner of a 20ft sun tracker pontoon boat , long story but at $750.00 for a running pontoon with a cabin on it i couldn't pass it up. It cost me a 1911a1 pistol as i didn't have the cash. The plus side is that I have enough left over to replace the decking and carpet . Should be almost good as new in a month or so.

Sean