opinions on modifying trailerable trimaran

Discussion in 'Multihulls' started by massnspace, Apr 19, 2016.

  1. massnspace
    Joined: Jan 2015
    Posts: 5
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    Location: Seattle

    massnspace Junior Member

    I am looking for informed opinions on some ideas I have for modifying a folding trimaran for a business idea I have. By informed I mean opinions based on some type of actual experience or knowledge in this area…I will read those carefully and just skip over the other random replies I am sure I will receive.

    My goal is to get a smaller (25 to 30 foot range; the make is not decided on yet and not fully relevant) folding trimaran, loaded with several passengers, up to about 11-12 knots under power using a larger motor than the boat was designed for…I am guessing between a 25 and 40 HP is what I will need. I also would require the boat to still sail decently…of course not as fast as designed, but sail safely and also at about 11 knots when the wind is up. Again, I would need these speeds both under power and sail for my business plan to work; I am not just doing this to mess around with a boat.

    My understanding at this point is that any smaller folding tri will, when overpowered with a larger motor than designed for, tend to slog down in the back end. I have several ideas that could be used independently or in concert for how to overcome this digging in, and invite opinions on them:

    1. Move weight forward in the boat. Battery, water, etc. to the front. Of course this will affect overall trim a bit, but would it help to keep the bow down when applying the extra power?

    2. Angle the thrust of the outboard very slightly upward. In other words, angle the new engine bracket I will have to design/fabricate anyway so that the engine tends to push the stern of the boat upwards slightly and thus the bow down. Of course some efficiency is lost…but I am only talking about a few degrees and wonder if that would also help to force the bow down.

    3. Design, build and add 2 removable, tapered underwater “pods” that bolt up under the stern. These would in effect change the underwater profile of the last 4 or so feet of the boat…they would be flatter sections...adding a larger planing type of surface there. (I have experience in 3D design work, CNC fabrication and composite building. I am sure I can design and build these to integrate with the hull smoothly on the edges….but will they work?) I would be willing to hire a marine architect, if possible, to run these pods thru some type of analytical hydrodynamic software to determine the best shape to use.

    By the way, I understand I can buy a Telstar 28 folding tri at any time...and from what I understand they are designed to motor quickly (in the teens), but I also understand from quite a bit of research that these boats may not have been designed correctly...several for sale at present have major stress cracks/delamination issues near the folding mechanism on the main hull. I am not interested in those types of issues....especially when responsible for the welfare of paying customers.

    Thanks for reading….informed opinions and questions welcomed!

    David
     
  2. Richard Woods
    Joined: Jun 2006
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    Location: UK, USA and Canada

    Richard Woods Woods Designs

    I think the Telstar used a 50hp outboard. Certainly a 25 won't be enough, 40 maybe

    Speeds will depend on payload/passenger number, so that will be a major factor. If more than 4 I would suggest a trailable catamaran. My trailable 26ft Elf catamaran would sail in the mid teens and motor at 12knots with 6 on board with a 40hp outboard. So it should be possible with a trimaran if you can keep it upright and not heeled at speed. Cornering at speed should be considered

    I will be back in the PNW in late May for the summer if you want to discuss it in person

    Richard Woods of Woods Designs

    Www.sailingcatamarans.com
     
  3. bruceb
    Joined: Nov 2008
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    Location: atlanta,ga

    bruceb Senior Member

    weight

    Mass, Mr Woods IS an expert, I would suggest paying attention :)
    I do have experience with a 24'tri, and it is certainly too small to carry the load of both the passengers and required engine/s. You might come close with 27' or larger, but then you quickly get into too large to easily trailer. I have experimented some with power on my 33' tri and trying to use the engine for lift doesn't work very well either- not unexpected, but I was curious.
    Cats do seem to make more sense, but even then, you are pushing the envelope. Good luck.
    B
     
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