20 Berty

Discussion in 'Boat Design' started by McFarlane, Apr 27, 2009.

  1. McFarlane
    Joined: Apr 2009
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    McFarlane Macka

    Gday all
    I have just purchased a 20ft bertram, it had lantana growing through it, bit of mess but a good project. Any thoughts on weight distribution if i put an OB on it, will it be to heavy in the bum. turning it into a CC and would like to get rid of the engine box for more space.
     
  2. Typhoon
    Joined: Mar 2009
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    Typhoon Senior Member

    I've done work on a 28 Bertram runabout that had been converted from twin V8's to outboards on pods. If anything it floated a small bit highe rat the transom after the swap. Yes, the outboard's weight is way out there, but you'll be losing I'd say a good couple of hundred kilos of sterndrive/iron engine to compensate.
    By the way, the boat performed MUCH better after the swap, faster on 2/3 the horsepower and less fuel use.

    Regards, Andrew.
     
  3. McFarlane
    Joined: Apr 2009
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    McFarlane Macka

    Thanks Typhoon for your reply
    There is an alloy fuel tank up the centre line of the boat, capacity 180L which i hope may compensate for any wieght pushed aft. Im building a centre console at the moment for it and will test it in positions before i fasten it down. How far down were the pods made to the bottom of the hull on the 28 you worked on? did it porpoise with the pods? did it have trim tabs?.
    Cheers
    Macka
     
  4. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Transom brackets, including those with air chambers must be "application specific", meaning that they are engineered for the boat. One person's bracket may not work on another persons boat. The bracket manufactures can work out the details for you and it's one of the reasons these things cost so much (the engineering).

    If you attempt to do your own bracket, it's very likely you'll have balance issues and poor ride/handling attributes. This says nothing of the load and stress transfer from the bracket to the butt of the Bertram.

    Unless you have a fair amount of engineering experience, I'd strongly recommend you have a bracket designed by one of the manufactures.
     
  5. rasorinc
    Joined: Nov 2007
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    rasorinc Senior Member

    How about putting your outboard forward of the transom and create a hole in the bottom and transom for the engine to lift and lower? You would have to build an inside transom and do some structural work, knees, bracing around the cut out area etc. You could cover the engine with a seat. Then nothing is seen and the weight is still in the same area. Look at the photos here to see a transom tunnel.http://www.glen-l.com/designs/workboat/dsn-swcd.html
     
  6. Typhoon
    Joined: Mar 2009
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    Typhoon Senior Member

    The outboards were mounted on an off the shelf fibreglass pod. We have several manufacturers of pods both fibreglass and stainless steel here in Australia, pick one you like and mount it all up so teh outboard cavitation plats is level with or just slightly higher than the keel line for single outboard. All the pods I have seen are very well engineered and have the correct mounting angle. As Par says, search up some manufacturers and have a chat to them, they'll recommend a model they sell and be able to tell you how to reinforce teh transom, if it is needed.
    The hardest part of such a conversion is the steering, hydraulic makes things easy.
    No need for trim tabs with an outboard, just trim it.
    The 28 Bertram went extremely well, no poropising at all and oodles of trim range available. By mounting outboards on pods, partuicularly on heavier boats, you get even more leverage so teh trim is even more effective. I seriously doubt rear weigth will even be a factor with your proposed setup. Bertrams are fairly beamy and have lots of deadrise, so heaps of buoyancy. Even twin V8 Berties tend to sit with teh chines just at water level or just above. A big bonus with the pod was a nice landing platform at the rear of teh boat at just above water level, made getting in and out of a dinghy a breeze.

    Regards, Andrew.
     

  7. McFarlane
    Joined: Apr 2009
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    McFarlane Macka

    I will definatley look into having one designed for the boat, or speak to some manufactures of pods, ive only got enough money for one hit at it, so it has to be correct. Thanks for the photo Rasorine , interesting design but think ill go for the pod. I started stripping the boat today and found that the bildge floor seamed to be a liner and it seams to have foam underneath, like the hull was foam sandwich, does anyone know how the bertram hulls were made? I Hope the foam isnt wet, I think I may have opened a can of worms.
    Regards
    Macka
     
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