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  1. #1
    Join Date
    Aug 2003
    Manhattan Beach, Ca.
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    Need good boat designer help

    I have a 20 ' tunnel boat first powered by a 175 Merc that ran real well when tested in it's original form-no decking/flooring, bare bottom seats, essentially stripped! (67 mph) I took the next step and added flooring, big fuel tanks seats, live wells for beer, fish, life jackets, gun racks, batteries and added a 225 opti max for power. End of good running tunnel boat! I mounted the engine on the transom=worked fair but bow would not come up and boat started skating at around 50 mph. Moved the engine back 5 inches=performance about the same. Moved the engine back 14" and performance about the same. All this in smooth water but a really uncomfortable/dangerous ride as speedo climbed to 55mph and boat started cross tracking. Runs better in rough water. Decided to make major changes since moving engine from transom to back didnot change performance. Have a 22 inch set-back but decided that was just too much, boat is just too heavy for a tunnel. Boat runs well at 30 mph but as speed increases, boat "flattens out". Bow will simply not come up and chines start to pick up water almost all the way forward making for a really wet ride. I have too many $$$$'s invested to junk it or I would.
    Have decided to "fill" in the tunnel and convert the tunnel to a semi-vee boat with the keel line 1" deeper than the current runners at the stern and approximately 3" deeper than the runners at the dead rise. The object being to give the boat riding surface forward to help carry the bow and lift the chines out of the water. On paper, this looks pretty good. I will build a keel line into the tunnel first to get the "look" I want, then build frames and stringers to support and shape the aluminum skin. QUESTION: Would I create more bow lift if I were to stop the newly formed bottom approximately 12" short of the transom. or should I continue the newly formed bottom all of the way to the transom? Would either change the ride of the boat? Finally, will using more set-back help in lifting the bow or destroy lift.
    This probably sounds like more trouble than it is worth but I don't give up easily. I have built hydroplanes, racing run-a-bouts and Mod VP's, but now I'm old enough to thank God I'm still boating and just want a good running hunting and fishing boat. I am simply into this one too deep to start over. I am thanking any one in advance that will jump on this. I called Glenn-L for some help but they no longer have boat designers on their list and could not be any help! S&F has been very helpful on the technical thread, I'm hoping some one will be kind enough to come to my rescue here! Rod P.S. Have a number of viewers but no offers to help with my problems. May need to move my post over to technical posts. If you have any expertise in this area, please lend your thoughts!
    Last edited by capnzee; 01-08-2016 at 02:31 PM.

  2. #2
    Join Date
    Feb 2009
    Edgewater,B.C. CANADA
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    You should get a hold of James Russell at AeroMarine Research, he is a Supporting Vendor here. His TBDP would help you a great deal, much cheaper and easier to make changes on a computer than make bad changes on the boat.

    1980 Cougar 19 tunnel,90 2.4L Bridgeport EFI in middle of restoration.
    1988 BAJA Sunsport 186, 96 225 Pro Max
    79 12' Auminum, 95 Merc 9.9
    RIP Stu
    "So many idiots, so few bullets"

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