25ft midcabin boat. From I/O to twin outboard conversion

Discussion in 'Boat Design' started by Forsmanni, Aug 31, 2020.

  1. Mr Efficiency
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    Mr Efficiency Senior Member

    the water coming from the transom is not flat, unless the boat is flat bottomed, you need a reasonable conformity to the bottom, to get engine height right, more easily, and no attachment of water to the pod. What is the boat make involved here ?
     
  2. Forsmanni
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    Forsmanni Junior Member

    Of course water is not flat, but bracket/pod will not touch water when driving on plane. The water will rise after the transom about 1" after every 10" distance. So my setback here is 27" long = Outboard AV-plate can be rised aprox 2-3" above the original bottom line. The pod is touching water just when boat is sitting still (adding flotation to stern which is good) and when you are going on plane. When you are going to plane I cant figure why would vee-bottom be better than flat. Flat bottom pod is creating more lift to stern (like trim tab) and maybe even help the boat get on plane. When the boat jumps to plane, just the outboard engine is touching water and getting clean water because the pod is now working just like normal Setback bracket.

    Edit: Also that picture is just illustrative. Not in scale. If you meant that pod back corners will touch the water. The corners will not be so low in real life.
     
  3. Mr Efficiency
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    Mr Efficiency Senior Member

    So you think all the vee-hulls makers that have veed pods are getting it wrong ? Think again, the outside edge of the pod will be close to the water when the centre is well above it, and there won't be anything to hide the outboard leg behind.
     
  4. Forsmanni
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    Forsmanni Junior Member

    Pod makers are making the veed bottom because of extra flotation. With flat bottom you can not make that much underwater volume for the pod, because you must make it narrower or install it higher. Like I said that picture is just illustrative and I understand your point here. And maybe you are right. It might be that I cant make enough under water volume to get enough flotation with this setup. I have to make some calculations still. Flat bottom pod would be just easier to make but maybe thats not worth it :).
     
  5. Mr Efficiency
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    Mr Efficiency Senior Member

    No, not for extra flotation, I don't think you need to worry about flotation in a 25' boat with one two-stroke outboard back there. Do you intend to make this pod integral with the boat, or bolted-on ?
     
  6. Forsmanni
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    Forsmanni Junior Member

    Bolted on. That I can make this boat I/O powered still in future if I want. Im doing this outboard conversion just for interest and fun. I want to know how much better the outboard will perform than that heavy old V8 in big familycruiser like this.

    Four Winns natural position in water is pretty "stern heavy" if you know what I mean. So even if I use XL- shaft 25" outboard, the swim platform is going to be very close the original waterline (If I make the swim platform attached to pod). Its true that I will remove very much weight with the old engine but the outboard engine weight is coming so much further back that I think the boats position is going to be even stern heavier than original. Thats why Im making floating bracket not just setback/swim platform. Of course I have to calculate this more specifically before I start making the pod.
     
  7. Mr Efficiency
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    Mr Efficiency Senior Member

    I wouldn't expect much trim difference, but of course it depends also on the weight of the pod, and the extra work on the transom. It would be ideal if you could find the same boat that has been converted to a podded outboard, likely in the USA, Should be the odd one around to copy, if it has proved satisfactory.
     
  8. brendan gardam
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    brendan gardam Senior Member

    The last pod I used was flat bottom that cleared the water while planing. That boat porpoised at speed and I could not stop it. Another pod I had followed the hull shape so was an extension of the hull and that showed no signs of porpoising.
     

  9. brendan gardam
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    Location: east gippsland australia

    brendan gardam Senior Member

    I have just put a deposit on a huntsman 23 with a pod and 225 merc efi on it. The owner removed a v8 volvo and fitted the outboard; he said it tops out at 40 knots. The old inboard would have struggled to get over 32 I think. The huntsman 3 is an extremely heavy hull from the 70s where if they weren't sure they gave it a few more layers of glass; it also has a 9ft 6 beam.
     
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