Fiberglass and foam sandwich construction, a few questions.

Discussion in 'Fiberglass and Composite Boat Building' started by CaptainObvious, Jun 29, 2018.

  1. CaptainObvious
    Joined: Jun 2018
    Posts: 10
    Likes: 0, Points: 1
    Location: Thailand

    CaptainObvious Junior Member

    I would think the urethane foam would help in keeping the fiberglass from bowing in, depends on the thickness of the laminate, as I said that's something I'm still not sure about, how thick, how many layers and what type of fiberglass to use.
    Perhaps I should scrap that idea and just glue foam panels (10 or 20mm thick?) to the inside of hull and leave it like that? it would be an open sandwich construction, perhaps with a light roving layer on top of the foam on the inside. This is the part where I'm not sure which way would be the best that's why I thought of asking people with practical experience.

    The foredeck, my idea is to put a compartment in there for carrying things, I'm not into sunbathing and neither is my girlfriend so no need for that. Actually I intend to make the foredeck as a third molded piece, mainly because it would allow me to make the deck in one single piece without having to cut holes in it for the front seat leg space.
    This is how it would look like with just the hull and deck, as you can see I could just put a flat foredeck over the bow.:
    Render3.jpg

    I'm not done with the modelling yet, I would like to have a better idea of the thickness of the laminate and foam before that, i.e. I may increase or decrease the gap between hull and deck on the sides; but the overall shape and arrangement is there.


    The seating would be two at the back with fold down back rests, so it's easy to get in using the steps in the transom, two benches at the front and either two benches in the middle or two back-to-back seats. I have this idea of making the back to back seats fold down flat, the seats would slide out to each side and the backrests would fold flat in the middle making a place to lay down, use as a table or just pile luggage or gear. In any case the good thing about the back-to-back seats in the middle is that it would be easier to move around the boat.
    I'm still not sure if I'd put a helm and throttle at the front or just have a hand operated outboard at the back.

    I may just as well show a render of the general arrangement, I don't think I'd put backrests on the front seats though. The panels on top would cover 8/9 square meters which theoretically would provide between 1.8/2.0 pkW/h which is much more than other solar (or solar assisted) boats of similar dimensions that I have seen. The idea being to motor over to some place using solar and battery power and while doing stuff the panels would recharge the batteries. Back of the envelope calculations show that it should be able to run all day like that.

    Render1.jpg
     
  2. BlueBell
    Joined: May 2017
    Posts: 1,134
    Likes: 193, Points: 63
    Location: Victoria BC Canada

    BlueBell Ahhhhh...

    Okay, now I like what I see here.
    Keep your battery small and make use of all that sunshine you get!
     
  3. Mr Efficiency
    Joined: Oct 2010
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    Location: Australia

    Mr Efficiency Senior Member

    If you are content with 5 knots tops, you will probably be OK, beyond that will be out of reach, with the loads you mention.
     
  4. fallguy
    Joined: Dec 2016
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    Location: usa

    fallguy Senior Member

    It is basically a harbor taxi.
     
  5. Mr Efficiency
    Joined: Oct 2010
    Posts: 8,493
    Likes: 473, Points: 83, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    It has a certain visual charm to it, well done there, but I doubt the laws of physics will allow the brisker performance the OP desires.
     

  6. fallguy
    Joined: Dec 2016
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    Location: usa

    fallguy Senior Member

    It would be nice if he understood the numbers better.

    He has basically boxed himself into the hull width by making the hulls footwells. So...20" hulls.

    Then at say 14 feet long...

    This is a very fat hull as the ratio explains.

    My cat hulls are 32' long and the hull is max of 22" on the bottom and I forgot the WL max, but iirc 26". Ratio is about double his...

    If he reduced the hull dimension WL and below to say 10"; he'd effectively double his ratio. Then he could raise the sides and watertight the narrow hull section and widen the hull above the WL for the feet. This would help I'd say, but he might not float high enough.

    Ultimately, some reconfiguration of the hull width and boat length seem needed to achieve the 10 knot goal.
     
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