Propellor question.....

Discussion in 'Boat Repair Help' started by Cathooker, Mar 1, 2006.

  1. Cathooker

    Cathooker New Member

    Messages:
    299
    State:
    Ga
    What is the advantages or disadvantages of a cupped prop? I am currently running a 17 pitch prop on my engine(factory installed) but am thinking of going to a 15 to up my rpm a little....will this give me a little quicker response and get me up to plane faster. I have an Evinrude 55 hp on an 18ft carolina skiff flat bottom. I can't afford to put a bigger engine on there just now so I need some other options. I know this set up will not run down the river 70 miles per hour but I don't like goin fast on water anyway. I inherited this boat from my dad. I fished for many years with him in this set up and always wanted to tweak it a little but he was subborn about "messing" with it.....lol....it takes too long to get up to plane. Any suggestions?
     
  2. jim

    jim New Member

    Messages:
    2,579
    State:
    Jacksonville NC
    Go to the mercury marine website and they have a propeller selector section that will help you out.It also explains all the things about props including pitch,rake and cupping.:)
     

  3. Bubbakat

    Bubbakat New Member

    Messages:
    4,532
    State:
    McMinnvill
    You can come off the 17 cupped to a 17straight and that will add a few r's to the tach. As for hole shot you can drill the prop and make it come out of the hole better.
    The cupped prop will give you one heck of a bite.

    Where do you live and if it ain't to costly to you I have a good 15 pitch you are more then welcome to try. I run a 17 cupped on my 85 and am going to go toa 19 cupped. Will be more then glad to help you here.

    Look and see if your cavation plate is even with the keel or no more then an inch abouve the keel.
     
  4. Cathooker

    Cathooker New Member

    Messages:
    299
    State:
    Ga
    Thank you for your help and the info Guys. Bubbakat, I live in Northwest Ga. near Rome. I appreciate the offer of the prop for testing. I may take you up on it if my other options do not work out.
     
  5. blackwaterkatz

    blackwaterkatz Active Member

    Messages:
    3,659
    State:
    Andrews, SC
    Cathooker, do you know how many rpm's you're turning now? A lot depends on the boat design, how much weight you normally carry, even how the load is balance within the boat. Those flat bottom skiffs usually carry a load pretty good without an awful lot of horsepower. At first glance, the 17" sounds a little large for that boat/motor combo, but I don't know the gear ratio, or recommended prop sizes. Your local ex-OMC dealer can probably help you determine that.
    If you haven't done so already, verify the correct rpm range for the engine vs what you are turning now. Going from 17" down to 15" will probably give you about 400 more rpm (just a guess), depending on gear ratio. You want the rpm's to be near max with a light load. If at all possible, stay with a cupped prop, raise the motor up on the transom until the cavitation plate is near level with, or just slightly below the bottom of the boat. This will usually also give a little boost in performance, but isn't as good an idea with an uncupped prop, due to cavitation.
    You didn't mention if the prop is stainless or aluminum, but the cupped stainless props can often be run a pitch size larger than aluminum.
    Good luck. The skiff is a good boat, and those 55 'rudes were tough, too.
     
  6. three_rivers

    three_rivers New Member

    Messages:
    688
    State:
    Tupelo Ar
    Does it have a whale tail on it? I've heard they will help the motor pick up the boat faster and keep you on plane at slower speeds. Just a thought....
     
  7. blackwaterkatz

    blackwaterkatz Active Member

    Messages:
    3,659
    State:
    Andrews, SC
    I've got one of those on my motor. It really makes a difference getting on plane fast when I'm fishing those shallow flats in <2' of water. I think it cost about $30.
     
  8. Cathooker

    Cathooker New Member

    Messages:
    299
    State:
    Ga
    The one that is on it now is an aluminum prop. It is not cupped. The cavatation plate is even with the bottom of the boat. I remember that this boat / motor combo did very well until Dad changed props a couple of years ago. I have seen those whale tails on boats....... can someone explain that principle to me? I have been driving boats and fishing out of various boats for many years but Dad always maintained them. He is now in a nursing home with alzheimer's disease and it is up to me now to figure all this stuff out.
     
  9. Snobal

    Snobal New Member

    Messages:
    40
    State:
    Canton, OH
    If I have it right, the whale tails work like trim tabs would but are not adjustable. The water flow pushes against it and actually raises the back of the boat slightly to help plane out. My dad had one on a Checkmate speedboat with a 115 Merc and it made an unbelievable difference. The bow of the boat was so light it never wanted to plane without the whale tail and it ran so shallow that you couldn't open the motor up all the way on any of the inland lakes around this area.
     
  10. blackwaterkatz

    blackwaterkatz Active Member

    Messages:
    3,659
    State:
    Andrews, SC
    Cathooker, here are a couple of links that should help you. For reference only:
    There are several styles of hydrofoils here: http://www.cabelas.com/cabelas/en/t...276&parentType=category&cmCat=MainCatcat21276
    You gave an important clue:
    I don't suppose you have the old prop around to verify sizes? Maybe the dealer your dad purchased the boat from can suggest the proper size prop. If it was performing ok before the prop change, he may have ended up with too large a pitch. The prop diameter can also affect performance. Cabela's has a listing for your motor prop size. http://www.cabelas.com/cabelas/en/t...parentType=index&parentId=cat21368&id=0013594
    I would say you need no larger than a 15" pitch, but the only way to know for sure is to verify your engine's rpm's.

     
  11. Cathooker

    Cathooker New Member

    Messages:
    299
    State:
    Ga
    Thank you everyone for all the help.

    Alan
     
  12. Bobpaul

    Bobpaul New Member

    Messages:
    3,039
    State:
    Supply NC
    A whale tale is like an airplane wing and the theory of flight.

    Water passing over is at a lower pressure because of the conture, and creates lift.
     
  13. Snobal

    Snobal New Member

    Messages:
    40
    State:
    Canton, OH
    Thanks bobpaul! I was close just had the operation wrong. At least I had the outcome right. That's what matters most!
     
  14. fishin`fool

    fishin`fool New Member

    Messages:
    9
    State:
    north carolina
    hi guys im new to the boc and was trying to find some bass tracker parts any body know where i can look?