I build my own RIB, looking for keel size info?

Discussion in 'Boat Design' started by marcostdo, Sep 15, 2014.

  1. marcostdo
    Joined: Jan 2011
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    Location: dominican republic

    marcostdo Junior Member

    Hi everybody,

    I was looking to buy something similar to the Aquaquad RIB but with a sport oriented design instead fishing design. The TomKat production is ended and how any other product is available on the market, I have no more choice that to build my own model. Size is 3.35 x 1.75 with 0.45 tube. Power is 25/40 HP and empty weight must be around 90 kilos without engine. Aquaquad seller claim 65 kilos but with any layer shedule I'm affraid to do it so light. About tubing, I will use Thundercat type collar with hijacker but how the final result can be a little bit subject to capsize in violent turn by unexperimented pilot, I would like to add a keel with à planning pad like the Aquaquad directly in the master hull shape before to make the mold? That will allow me to use regular round tube too but with a best planning and best turn capacity. I need the help of somebody who can give me the size for the planning pad (A and B) like shown in the Aquaquad attached picture please. The idea is to make only one mold hull working with both kind of tube. With Hijacker tube on planning the keel is out of the water and don’t affect speed performance. I agree so much anybody who can give me this info because I will be sure that my boat will work at the first time without the need to make many test and modification. If somebody can help me, he will really make me save lot of time and work! Many thanks.
    Attached picture is TomKat, some Aquaquad +keel size needed and my model under construction.

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    Last edited: Sep 15, 2014
  2. philSweet
    Joined: May 2008
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    Location: Beaufort, SC and H'ville, NC

    philSweet Senior Member

    I think the keel and wedge is there mostly to stop the outboard leg from becoming a giant water scoop and drowning the power head. Width only needs to be about 90% of the width of the leg. I doubt it yields very much in the planing department. But you could pick a number like 60 pounds per square foot of area and see if that feels right to you. Being a long and skinny surface, it won't produce a large lift for it's area. You might be better off playing with foils on the outboard leg.
     
  3. marcostdo
    Joined: Jan 2011
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    Location: dominican republic

    marcostdo Junior Member

    Thanks a lot for your help Phil! I will forget all about best planning idea without hijacker tubes. I was totaly wrong with the function of the keel and his flat back wedge. To confirm that I understood you I attached picture of Zego and thundercat. Those boats have a vinyl splash guard because they don't have the keel and the propeller splash can flood the cockpit and the engine right?
    A last question please about the gap 'B' shown in my first post picture : I think about 5 to 8 centimeter, is it good?

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  4. philSweet
    Joined: May 2008
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    Location: Beaufort, SC and H'ville, NC

    philSweet Senior Member

    I don't know. You are going to have to play with that. The boat's speed will be quite sensitive to how much of that keel is in the water. You just want enough so the motor doesn't scoop water. You typically run a lot of tuck (motor down and under), so it's prone to scoop water. In the first photo above, look at the skirt bolted to the motor leg. It is better to not create that splash at all rather than to deflect it.
     

  5. marcostdo
    Joined: Jan 2011
    Posts: 9
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    Location: dominican republic

    marcostdo Junior Member

    Got it Phil. Now I just need to continue the job. I hope to post you soon a picture or short movie to show you how your help was helpfull. Thanks again! BTW I'm a little bit french , so sorry if I'm not fluently in english.
     
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