Re-using old catamaran hulls

Discussion in 'Boat Design' started by Phlames, Jul 23, 2018.

  1. Phlames
    Joined: May 2017
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    Phlames Junior Member

    I was intrigued with the tornado(?) hulls pictured. I have a pair of old tornado hulls that I want to use as a fishing platform. The photos show a scale (roughly made) model of what I had in mind and include a 30hp to scale and a 'person' about 1.8m tall. While I would like to centralise the weight, I think the outboard position is the best compromise and it frees up the fishing space. The pod is about 3.6m long and 2m wide and I think the all-up weight would be about 400 Kg including two adults giving about 20 knots speed. I apologise for the thread drift but I think it is obvious that many facets of your requirements and my design are similar except for the comfort of an enclosed cabin. I would be interested in comments about my design.
    IMG_1426.jpg IMG_1428.jpg
     
  2. fallguy
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    fallguy Senior Member

    I don't understand the for'd vee windscreen? abovedecks. If for strength an extra beam would be better.

    The benefit of cats is the wide usable platform.

    It seems a bit silly for a wide hull footprint and then coming to a point for'd on the deck...

    Then have you done anything regarding weight?

    The centers of mass appear a bit aft. I am only going on a look see mind you.

    The rails also look rather low

    Isn't the tornado hull a displacement hull?

    I might be inclined to at least consider smaller engines on the hulls or twins, but if it folds then no.

    Bdeck clearance? Did I miss it?
     
  3. Richard Woods
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    Richard Woods Woods Designs

  4. fallguy
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    fallguy Senior Member

    I now understand the vee. It is because the hulls may not get the cabin space out of a good wave.
     
  5. BlueBell
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    BlueBell Ahhhhh...

  6. Phlames
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    Phlames Junior Member

    Richard, I am familiar with the waterbug and I assume you meant to say the Browns' regularly commute across the water. The waterbug inspired me but I need to trail my boat and the height of the waterbug
    on a trailer would be excessive.
    fallguy, you raise some points about the model. The tornado is indeed a displacement hull with a theoretical hull speed much greater than I require. The pod has a vee'd bottom to eliminate wave slamming under the bridge deck and to allow a lower profile for trailing behind a car. The vee also allows a lower floor in the pod.
    I decided to reduce the tornado 3m beam to a 2.1m beam for trailing regulations but the maximum buoyancy is still at the sides for stability. The weight distribution is not ideal due to the need for maximum fishing operational space. Putting the engine further forward would be better for weight distribution but would interfere with fishing space and would also require rudders to be fitted. My scaled model shows that the hulls are modified at the front (more weight forward) and the scale also suggests that the rails are above knee height . The anticipated structure mass is about 85 Kg - not a lot heavier than a tornado! Remember that the rig, sails, rudders. boards and beams, etc make up a substantial proportion of the weight of a tornado and these are all removed for my fishing boat.
    Finally, another benefit of a catamaran is that long, thin hulls can be easily driven through the water at displacement comfort levels. By using the tornado I have chosen the best hulls for my boat (why would anyone go for planing hulls unless you were a chiropractor or such?).
    BlueBell, mea culpa for being a newbie to forums!
     
  7. fallguy
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    fallguy Senior Member

    I am all for it for the fishing!

    What is the transom width?
     
  8. Phlames
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    Phlames Junior Member

    The tornado cat hull has a transom width of about 285mm. The centre pod ends about 900mm forward of the tornado's transom(s) and the pod is about 2m wide at the end.
     
  9. upchurchmr
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    upchurchmr Senior Member

    fallguy likes this.
  10. fallguy
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    fallguy Senior Member

    Great post. I built a Dierking based set of outriggers years ago I use in Minnesota.

    I also like the wider cockpit for'd.

    I would also see if there were any way to put two 9.9 engines on the hulls for better steering and more cockpit. Of course then you must have a helm/wheel.
     
  11. Phlames
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    Phlames Junior Member

    The Dierking tornado based boat I think is heavier than my design and certainly wider which leads to trailing complications. I accept that my narrower beam and therefore hull spacing will lead to more drag through the water but I am not after top speeds. The water flow between the hulls will be interesting to observe since I have designed the vee of the bottom of the pod to be just above waterline at rest. I expect it will be in the water flow when under way and will provide me with better understanding of interactions between the wakes of the hulls and the effect of the vee bottom on them. The size of the vee means there are storage options underfloor in the fishing platform. The aspect of two engines was considered. I have a (self designed and built) 35' power cat at present with twin 90hp outboards and I appreciate the steering advantages but I think in this application the weight penalty is severe and transom mods will be necessary. They will also adversely affect weight distribution.
     
  12. Phlames
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    Phlames Junior Member

    upchurchmr, I have pondered your comment re the front of the tornado hulls in my design. The slim width is standard tornado and I put the 'covers' on for the
    'holy s##t' moments that may occur going into the back of a wave at speed; the extra height will adversely affect windage but may be a good insurance against
    'unexpected' nose diving. You are correct re steering in these moments but the driver will probably be thinking of other things at that point!
     
  13. upchurchmr
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    upchurchmr Senior Member

    My mistake. I certainly agree with what you intended, having sailed a Tornado during those moments.

    Many years ago I saw an article about a person who cut off his fwd decks, installed oversized horizontal sub decking, with the intention of making the bow slightly wider as it got toward the deck. He then replaced the original deck, which caused a "bulge" in the sides of the fwd shape. He reported that nose diving was so improved that he didn't feel as much concern when driving hard.
     
  14. IronPrice
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    IronPrice Senior Member

    If you want to fish from it then the sides of the platform need to be be directly above, or overhang the outside edges of the hulls. Ie platform wider than outside width of hulls.
     

  15. Phlames
    Joined: May 2017
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    Phlames Junior Member

    Iron Price, the platform sides and hull sides are almost perfectly aligned vertically although I admit to thinking about putting the hulls a little outside the pod sides to give a 'step' that might assist landing fish
    as the angler would be closer to the water surface. I may provide that sort of access through the rear quarters each side of the rear of the pod, What say you?
     
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