Weight balance. Will it ride better with weight in the rear or dead center?

Discussion in 'Boat Design' started by clctrader, Jan 22, 2008.

  1. clctrader
    Joined: May 2006
    Posts: 21
    Likes: 0, Points: 0, Legacy Rep: 3
    Location: Miami FL

    clctrader Junior Member

    I posted here because I thought you guys should know more than the average boat repair guy. I have a 26' center console. It came originally with twin Yamaha 200hp outboards. I have just installed a heavy diving platform and twin Evinrude V8 300hp 4.0's . I am finishing up the floor right now but before I install it permanently, I wanted to know if I should move the gas tank a little forward to compensate for the weight of the engines and platform in the rear ???

    Or should I leave all the weight in the rear of the boat?

    How will it ride better? Any help would be great as no one seems to give me an answer and I dont want to regret installing the floor without making adjustments.

    Thanks in advanced.
     
  2. Frosty

    Frosty Previous Member

    The only thing to do is launch the boat and take some people with you . Tell them to move forward or backwards at various speeds and see how it likes it.

    Or if you have no friends or family a few sand bags work well.

    You sure you understand thouroughly the effects of engine trim?
     
  3. Gilbert
    Joined: Aug 2004
    Posts: 525
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    Location: Cathlamet, WA

    Gilbert Senior Member

    If your boat, loaded as it will be used, balances at a point close to 1.25 times the waterline beam forward of the transom it will be pretty close to where it should be.
     
  4. Guest625101138

    Guest625101138 Previous Member

    You can make a reasonable assessment of tendency to porpoise from this site:
    http://illustrations.marin.ntnu.no/hydrodynamics/resistance/planing/index.html
    I have made some guesses at boat parameters and chosen a very pesimistic LCG. See attached. If it is as far back as 2m then it could porpoise.

    If the boat is on a trailer and you have found the ballance has changed it would give you an indication that you might have a problem.

    The heavier motors and higher power both work toward instability. Just be a bit careful the first time you do a full speed run. Try to do it in calm conditions and if you find the boat starts to surge then back off. Moving weight forward will help. Trim tabs or power trim should also help but be careful of trimming the motors too far out trying to get more speed.

    Other issue is freeboard over the stern at rest.

    Rick W.
     

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  5. Thunderhead19
    Joined: Sep 2003
    Posts: 506
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    Location: British Columbia, Canada

    Thunderhead19 Senior Member

    Holy Moly! Moving tanks around isn't really the ideal solution because the behaviour of your boat can vary drastically as you use up your fuel. Looks like you added several hundred pounds, as far aft as it will go. I don't know the beam of your boat, or the existing freeboard, how crazy you might be, or what transom angle you've got, but if I were you, I'd put a watertight deck hatch in the floor near the bow and have some room down there for a couple of 50 lb sand bags at least.
     
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