bolt metal plate to boat hull to extend LWL

Discussion in 'Powerboats' started by sdowney717, Aug 24, 2015.

  1. sdowney717
    Joined: Nov 2010
    Posts: 829
    Likes: 30, Points: 28, Legacy Rep: 274
    Location: Newport News VA

    sdowney717 Senior Member

    What affect would bolting a metal plate 2 feet long onto a hull to extend the transom outwards. For example, follow the slight deadrise of 8* I have and make it 8 feet in width. Put some reinforcing strut on top at the outer edges set at an angle from plate edge to transom.

    So a piece 2 feet by 8 feet bent to the hull contour.

    Or even creating a wood hull extension using construction grade treated wood with 3/4 plywood sheets..
    Use 1 sheets plywood 4x8 split into 2x8 and extend the hull bottom aft. Wood definitely cheaper to make and no corrosion.
    You basically extending the underwater length.

    And how would that work instead of say having trim tabs.
     
  2. rasorinc
    Joined: Nov 2007
    Posts: 1,854
    Likes: 70, Points: 48, Legacy Rep: 896
    Location: OREGON

    rasorinc Senior Member

    If this is a wood boat I think it is easier to add 2' in front of the transom.
     
  3. Barry
    Joined: Mar 2002
    Posts: 1,058
    Likes: 59, Points: 48, Legacy Rep: 158

    Barry Senior Member

    Is this for your Egg Harbor?

    The center of lift would move back for a given speed which could help get the nose down which you were having problems ie not getting over hump speed where the bow drops

    You had said that you had taken off the trim tabs and perhaps you are thinking that this extension would help and it might though it would not be adjustable.

    Many of the older squirt boats had a plate that was almost fill chine width, with manually adjustable turnbuckles which allowed for fine tuning of the attitude at cruise speed but power trim tabs are the way to go

    Might be better to consider building or buying the widest trim tabs that you can to have the adjustability. Ie high angle to get above hump speed, then trim it down for the best
    planing trim angle at cruise.
     
  4. Barry
    Joined: Mar 2002
    Posts: 1,058
    Likes: 59, Points: 48, Legacy Rep: 158

    Barry Senior Member

    If you consider building the hydraulic trim tabs, the most important variable is the length of the tabs as this increases the length of the high pressure stagnation line. ie chine/transverse length

    I would mount these about about 1 inch above the bottom of the bottom of the boat so you ventilate this one inch area, then the trim tabs will give you a better lift, better being more lift for the amount of drag that they will induce. Ie you are creating a second stagnation line that you will not get with just extending the hull

    Then the front to back width is the next important variable as you will not have to increase the tab angle down to get the same amount of lift. Which reduces drag.

    I am using the following numbers to just demonstrate the point and will probably not be accurate

    A 6 inch wide tab might need 30 degrees down to generate 500 pounds of lift but the highest drag. A 12 inch tab might need 20 degrees down to generate the same lift but less drag, a 24 inch wide tab might need 10 degrees down to generate the same lift but offer the least drag
     
  5. sdowney717
    Joined: Nov 2010
    Posts: 829
    Likes: 30, Points: 28, Legacy Rep: 274
    Location: Newport News VA

    sdowney717 Senior Member

    Yes, my Egg Harbor 37.
    The tabs I took off to repair I think are 42 by 9 inch.
    The transom has a curve to it, so the trim tab plate mounts to the bottom of the hull.

    So was thinking could just make a permanent bigger more effective extension. Or just fix the tabs.
     

  6. Easy Rider
    Joined: Oct 2009
    Posts: 920
    Likes: 46, Points: 0, Legacy Rep: 732
    Location: NW Washington State USA

    Easy Rider Senior Member

    You almost can't go wrong w the extension.

    There was a thread on extending a C Dory some time ago.
    Manufacturers often extend boats. Some hull shapes are easy to extend. Others not. I think about it more than most as I really like long narrow boats. Neither of my powerboats are though. If it was easy I'd extend my Willard 30 amidships and aft.
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.