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  1. #1

    Default Bigger prop runs exactly the same as smaller prop

    Hey y'all I have a 1997 evinrude 115. E115eleua. This boat has been in my family all of its life. (Since 97.) we had a 13 1/4 by 21" pitch prop that always ran the boat at 48 mph top end. The motor mount has never been moved, the load on the boat has actually lightened. It's a 277 fs boat by sprint. Well a few years ago my uncle took a chunk out of 2 blades on the aluminum prop. We had the exact same brand spare prop, only it was 13 1/4 by 19" pitch. With the 19" it's hitting 41.7 mph. I finally got the 21" pitch prop repaired, and went to run it and the boat is still hitting only 41.7 mph. The guy at the shop said he had to do ALOT. Of welding to get mine looking right. I don't have the tools to measure prop pitch, but is it possible that with al the welding he bragged he had to do that the pitch isn't 21"? We ran that exact prop for years, and now it doesn't run any different then the so called smaller prop. It kinda looks the same size as the 19" pitch. Any ideas on why it would run the exact same?!

  2. #2

    Default Re: Bigger prop runs exactly the same as smaller prop

    As you increase the pitch it lowers the rpm and vice versa. It is doubtful that the pitch was altered by the welder. You would know immediately, as only 2 of the blades were welded. Since it has been a couple of years since you got 48mph it may be the engine and not the prop. It can be that you are not running on all 4 cylinders.Check that and do a compression test. The cylinders need to be within 10lbs of each other. It is more important for the cylinders to wear evenly than to be at factory specs.. If the boat stays in the water, check growth.

  3. #3

    Default Re: Bigger prop runs exactly the same as smaller prop

    Boat stays out of water.. I know I'm on all 4. We let the engine run and pulled the plug wires one by one and the engine dropped each time. Last year I put on a remanufactured powerhead from obr and got rebuilt carbs, new fuel pump, etc. compression check isn't the greatest. Cylinder 1-130, 2-105, 3-130, 4-110. Also in early March we did a leak down test. First 3 cylinders were 8% leakage, #4 was 15% leakage..

  4. #4

    Default Re: Bigger prop runs exactly the same as smaller prop

    Oh and I also noticed that my carbs plastic float bowls are warped. All of them.

  5. #5

    Default Re: Bigger prop runs exactly the same as smaller prop

    Also noticed that the cupping on two of the blades is pretty much gone. And the smaller pitch prop(same brand and diameter) has a lot more cup to it

  6. #6
    Join Date
    Dec 2015
    Location
    maplevalley WA
    Posts
    3,470

    Default Re: Bigger prop runs exactly the same as smaller prop

    MPH means absolutely nothing when sizing your prop. I find it impossible you get the same RPM between a 17 and a 21 pitch prop. It also sounds like your hull may be water logged in the doublebottom likely water soaked foam under the deck? That would be the most logical reason for the performance issues. Take the boat and trailer to a scale and estimate the weight of boat and trailer and engine. take a hammer and tap on the deck there is a distinct sound when you have dryrot then it is a matter of opening it up and removing all the bad wood and water soaked insulation. Is the boat exposed to the elements on a year round basis? Once the water gets in it needs to physically be removed it does not just evaporate.
    It takes a nickle to go first class!
    If it aint broke dont fix it!!

  7. #7

    Default Re: Bigger prop runs exactly the same as smaller prop

    The boat is not wood it's all fiberglass. Sounds like I might have to deal with it as is. I'm gonna test run a brand new, not reconditioned prop from evinrude and see if it makes any difference. If not then it tells me it's either the engine or the boat, or both. How can I tell if my transom or anywhere else on the boat is water logged? Since it's fiberglass not wood? Or is it the same exact test as you just stated? What would it sound like with a hammer?

  8. #8

    Default Re: Bigger prop runs exactly the same as smaller prop

    Kim you were halfway right! It wasn't in the hull, (at least not that I can tell) but I pulled my gas tank and WOW what a mess! The fiberglass on the bottom was pretty black and is definitely rotted. Guess I do need to get rid of the boat..

  9. #9
    Join Date
    May 2011
    Location
    slough ,berkshire uk
    Posts
    155

    Default Re: Bigger prop runs exactly the same as smaller prop

    Prop repair guy did not put back cup ? then he is an idiot and yes it would now be about 19 pitch.
    the cup gives atleast an inch on the props pitch, if omc original it about 1.5 extra as the blade also sweeps up and has tip cup,this gives it
    around 2 inch pitch on total.

  10. #10

    Default Re: Bigger prop runs exactly the same as smaller prop

    Yeah work quit using the guy(go figure) the same week I got my Prop back. Even with my boat waterlogged in the back the prop still shouldn't turn the boat about the same Rpms with the exact same gps speed as the known 19" pitch prop

  11. #11
    Join Date
    May 2011
    Location
    slough ,berkshire uk
    Posts
    155

    Default Re: Bigger prop runs exactly the same as smaller prop

    21 pitch would be faster if enough power or slow the boat down compared to the 19. I have both of those props, the 21 has more pitch and more cup on the tips.

    cant believe the guy took the cup out. obviously bluffing is way through life. 99.9 % of prop guys take great pride in their work and would make the prop like
    original unless you asked for it to be altered.

    have great admiration for good prop guys, they usually turn scrap into a piece of art.

  12. #12

    Default Re: Bigger prop runs exactly the same as smaller prop

    There's cupping, but I'm talking MINIMAL. My known 19" pitch prop has much more cup to it, very noticeable. Prob why work quit using him.. he repainted it too and with all the running issues I've had I maybe ran the boat half a mile and the paint is coming off.. I just replaced the float bowls on the carbs yesterday, hopefully we didn't miss anything or mess any of them up and the boat still runs good.

  13. #13
    Join Date
    May 2011
    Location
    slough ,berkshire uk
    Posts
    155

    Default Re: Bigger prop runs exactly the same as smaller prop

    best thing to do is have a look on fleabay for a good used 13x21 or 12 3/4 x 21 omc SST stainless prop.
    you will find one of these in good condition for less than the price of repair to alloy prop and it will improve performance all round.
    Alloy prop is rubbish compared to stainless at same sizes
    if you want a real top end performance prop go for a used omc Raker prop 13.5x 20 maybe even a 13.5 x 22 on your rig.
    a 22 will be a touch slower from zero but a lot more top end speed as it raises the front bow for more speed

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