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Thread: 2005 Merc 40m mods for river racing

  1. #31
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    Interesting answer. I would have thought extra weight of the sightly longer boat was responsible, but that's more "logical, Captain".

    Jeff

  2. #32
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    Quote Originally Posted by Fastjeff57 View Post
    Interesting answer. I would have thought extra weight of the sightly longer boat was responsible, but that's more "logical, Captain".

    Jeff
    We have tried the same brand boat, a 1648 and a 1548, the 16 weighs about 20# more, we added 20# to the 15, still won't run the same, 16' is slower. That is why I run a 1556, I wanted the extra room but not the added length. And to me, square inches are square inches, be it width or length.
    D
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  3. #33
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    Quote Originally Posted by Cajun View Post
    We have tried the same brand boat, a 1648 and a 1548, the 16 weighs about 20# more, we added 20# to the 15, still won't run the same, 16' is slower. That is why I run a 1556, I wanted the extra room but not the added length. And to me, square inches are square inches, be it width or length.
    D

    dam 15x56?? my alweld is a 15x52 and deffinitly feels wide enough

  4. #34
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    Cajun,

    I've got a problem with my jon boat porpoising. It is a 1648 with 7 degrees V on the bottom. Motor is a 70hp Johnson with 19 pitch omc SST prop. The cavitation plate is 1.5" above the bottom of the center chine and 0.5" above the bottom of the boat.

    There are 5 chines across the bottom of the boat. I added an 1/8" hook to the two outside chines. The boat still porpoises at neutral trim. Should I add more hook to the outside chines, hook the middle pair a little, or something else?

    Thanks

  5. #35
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    Quote Originally Posted by Cubman View Post
    Cajun,

    I've got a problem with my jon boat porpoising. It is a 1648 with 7 degrees V on the bottom. Motor is a 70hp Johnson with 19 pitch omc SST prop. The cavitation plate is 1.5" above the bottom of the center chine and 0.5" above the bottom of the boat.

    There are 5 chines across the bottom of the boat. I added an 1/8" hook to the two outside chines. The boat still porpoises at neutral trim. Should I add more hook to the outside chines, hook the middle pair a little, or something else?

    Thanks
    Try to not disturb the water flow in front of the propeller. Add a little hook to the next 2 corrugations, but, stay away from the center of the hull. You could also try a propeller with less rake. Rake=bow lift.
    D
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  6. #36
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    Do you have a gas tank or batteries towards the front of your boat or do you keep all the weight in the back?

  7. #37
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    Quote Originally Posted by Cubman View Post
    Do you have a gas tank or batteries towards the front of your boat or do you keep all the weight in the back?
    First, I can't tell you how many times I have been asked at the dock "how fast will that boat run"? When I reply , "it'll run mid 40's loaded". I usually get a reply of "well, my rig runs right at 50mph". I then smile and wave as I pass their 50 mph rig in the intracoastal canal with my mid 40's boat.

    You are trying to compare two totally different design hulls, won't work. My hull won't bounce with 2 men sitting on the back seat. My motor weighs right at 250 pounds, set back 10" on a lift plate that weighs 47#.

    Load configuration depends on what I am trying to accomplish. For that all important, one time, big top end number, tank and battery in the rear, boat completely empty.
    For normal hunting and fishing loads, I distribute the load. My start battery and fuel tank in the rear, 2 large deep cycle batteries are against the front deck, my 82# thrust MotorGuide is mounted on the deck, cooler in the middle, all gear in the middle. For duck hunitg, I had 2 guys sitting against the front deck, one sitting on the back seat next to me, dog and all gear in the middle. Again, our boats are nothing similar. I have a hull that lifts itself. I can run near zero trim, that allows me to use all available horsepower to push the load forward. The faster my hull goes, the higher up on the V it runs. You have no V to climb up on.
    You have X number of horsepower in that motor, how many of those ponies you gonna use to lift the bow and how many to push it forward. The more positive trim you run, the more ponies you waste to raise the bow.
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  8. #38
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    Quote Originally Posted by Cajun View Post
    First, I can't tell you how many times I have been asked at the dock "how fast will that boat run"? When I reply , "it'll run mid 40's loaded". I usually get a reply of "well, my rig runs right at 50mph". I then smile and wave as I pass their 50 mph rig in the intracoastal canal with my mid 40's boat.
    Numbers mean nothing to me. I just want to get the best for performance out of what I have, while using it to do what I enjoy doing- fishing and hunting.
    You are trying to compare two totally different design hulls, won't work. My hull won't bounce with 2 men sitting on the back seat. My motor weighs right at 250 pounds, set back 10" on a lift plate that weighs 47#.
    From where I sit I see that we are both talking about modified V duck boats. My motor weighs 254 pounds, but I don't yet have a jackplate.

    It looks like the edge has some fancy backwards turning chines, and you've got a few more degrees v than me, but otherwise the running surface seems very similar.


    Load configuration depends on what I am trying to accomplish. For that all important, one time, big top end number, tank and battery in the rear, boat completely empty.
    For normal hunting and fishing loads, I distribute the load. My start battery and fuel tank in the rear, 2 large deep cycle batteries are against the front deck, my 82# thrust MotorGuide is mounted on the deck, cooler in the middle, all gear in the middle. For duck hunitg, I had 2 guys sitting against the front deck, one sitting on the back seat next to me, dog and all gear in the middle. Again, our boats are nothing similar. I have a hull that lifts itself. I can run near zero trim, that allows me to use all available horsepower to push the load forward. The faster my hull goes, the higher up on the V it runs. You have no V to climb up on.
    Are you saying 7 degrees V is insufficient to cause lift?

    I appreciate your advice Cajun, right now I am concerned whether I should even try to get alot of speed out of this boat or if it is futile.

  9. #39
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    Sorry, I have about 6 converstaions going at once and my simple mind can't keep them separated. I am asnwering a guy on another forum about his FLATBOTTOM boat also and get the conversations mixed up, sorry.
    7 degree V is enough to climb up on if you can get the angle right. The Edge, like most hi-perf boats, has turndown tabs at each rear corner to prevent porpoising. Same effect as hooking the hull. You need to add hook until you can run about 2 degrees positive trim. If you are running negative trim right now, once it goes positive, you should see about 500+ rpm and a bit more speed. If you really don't want to hook the bottom, adjustable trim tabs are in your future. The most I have ever hooked a hull was 3/16ths from the back seat to the transom which was 16". On this particular boat, I had to hook all but the 3 center corrugations to make it lay down.
    D
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