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Thread: thoughts on this bottom mod?

  1. #11
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    another
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  2. #12
    Administrator Ron Hill's Avatar
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    Default Do You Have The Plans to This Boat?

    Quote Originally Posted by coupe View Post
    Its a old Hal Kelly OK 9. Any good? any bad?

    I'd love to have a set of plans for this boat.

  3. #13
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    Default If it's 12" or more it's too wide ......

    Quote Originally Posted by coupe View Post
    I did take it out, don't like the pad. I think its not enough "area" to carry the weight, and now it "porpoise" a lot. Its very flat, maybe it needs to be angle down slighty...act like a trim tab? On the plus side, it turns razor sharp now, I can go into a turn almost wide open and it'll hold the edge very nicely. It only has a merc 9.8, I GPS'ed it to 28 mph, stock 2 blade prop. I got a merc 20, but I don't have the nerve to try it on there again. It was very "wild" to drive with a tiller on that motor for some reason.
    In your photo the leading edge of that pad is very abrupt . Could the abrupt area be 'lifting hard' while the front of that pad is in the water and then you have nothing else (power or speed) to keep the nose up ? Also, having the water rushing off the pad (to the sides at the rear) and directly hitting on the hull bottom tends to 'lift the tail' at speeds . It just 'looks too wet', with no place for all the water to go except 'across the bottom and drag' . I would build the entire pad up to twice it's current height . Then go 3' forward of the transom and continue up into a 'sharp keel', blend it all in at the bow area, so it's smooth . Lastly I would add 2 big strakes about 6" out from that keel on each side, ending where the 'keel line ends' (2" deeper than the pad). At the bow, a sharp keel for the rough stuff, next a pair of big (2 1/2"-3" wide) strakes to hold the nose up all the time, and finally your 'built up pad', deep enough that it's water spray does not hit any of the boat bottom at speeds . You would then have good displacement at rest (nice freeboard) and be wet at only a few inches of keel and strakes, plus about 50% of the pad, and everything else would be 'flying' and dry .

  4. #14
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    Question, when I ran the 20 horse merc on it, it had this weird tendency to drive the back of the boat "sideways" for lack of a better word. It was really hard to drive, and seems as it got up to speed it would just drive kinda uncontrollable. Could it have been the 2 blade prop tryin to "paddle" the boat sideways? It was fine until the boat got up to speed, then it would start. I only ran it across the cove twice because it was too scary to go anyfurther. That prop has a good bit of cup on the trailing edge of the prop.

  5. #15
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    I also think this year model (1976) does not have as big of a skeg as some later models, which may give less control.

  6. #16
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    With only a flat wet surface, I could understand the uncontrollable feeling . There are not sharp, defined edges for resistance (like a sharp keel) To further that problem would be the prop having 'more bite' than the 'drag of the lower unit fin' and then you have lost your 'polar moment of drag' on the entire mass . Even if you make the fin larger, that will only help in straight lines . With no shape or definition to the hull bottom and without a 'turn fin', it will still 'wash out' in the turns .

  7. #17
    Team Member JohnsonM50's Avatar
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    What I can add might be apples to oranges but alot of race runabouts have a pad that is about 24" to 30" wide on about 36" overall. The same principle of dead flat pad on a flat main bottom, it's being too narrow is possible. As for water running off the pad onto the upper bottom, that being near the lower chine minimizes the potential for excess lift. The abrupt pad front is definitely not optimal, the transition from bottom to pad up front should be smooth even if the intent is it will be aired out. I think this because the variations of planing will from time to time dip that edge at speed.
    Props: any & all props are likely to act differently on a boat than another. Racers usually run a surface prop of less dia. at higher rpm's & will have some kind of fin, not a keel. They can be difficult to get right of course but generally work well. With a stock type motor the prop is bigger, has more torque against it & runs deeper. This can be equally difficult to tame. Sometimes a pair of squat boards will help or even a whale tail. I'd recommend you not permanently attach a pad till you like it [like it looks like you have]. It's also important to define what you want.. great handling, great acceleration, great speed or of course all three.

  8. #18
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    Im not scared of work, LOL. I think I'll cut it back off and give it another go, not really work when your having fun. Needed a winter project anyway.

  9. #19
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    What is planed next ?

  10. #20
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    Quote Originally Posted by Tuneafish View Post
    What is planed next ?
    The pad that's on it now is heavy. Im thinking about cutting it off, making a new wider, thicker one and making it "hollow" but filling it with high strength foam core so it wont be so heavy, and yes, put some strakes on it as well.

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