Modifying a Glass-Over-Foam Hull

Discussion in 'Boat Design' started by chazb40, Oct 14, 2007.

  1. chazb40
    Joined: Oct 2007
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    chazb40 Junior Member

    First things first: I am not a sailor, nor boat builder, nor designer.

    I am a kiteboarder who wishes to use a "sit-on" board for long distance riding.

    I have two sit on boards ("Surfrunners": they are 200cm & 240cm long, respectively) but am unhappy with their performance in anything but downwind conditions. The have a slight camber and tri-hull cross section, but it's not enough to "edge" crosswind

    I have the choice of adding dramatic fins/keel or giving them an update to the hull.

    To avoid the possibility of underwater damage/breakage, I would like to add catamaran-like "egdes" to the outer hull bottom. The result being almost a twin-tunnel or cat-type of hull with rounded outer edges and sharper chined inner edges.

    I can purchase all of the requisite materials in town (I live near Lake Michigan). How do I go about "adding on" to what's already there? Do I have to just "roughen up" the current epoxy surface, or cut through to the base foam to to this properly. Or, can I just built them apart from the boat and drill through the current hull and bolt them on/through and then seal things up?

    I wish I could give you more info. I could snap a few photos, if anyone would like to look at what I am dealing with.

    There is no predecessor for such a craft, so this is quite a "learn-as-you-go" thing.

    Basically what I need is a smaller (say half) sized version of what I've seen online: a Laser Vortex sailboat/dingy. That may give some of you an idea of what I am looking at/for.

    Most people I've looked at online using SLE Kites for sailing used old, modified small sailing catamaran hulls. These are too large and heavy for my purposes.

    So, is this an effort worth the results?

    Or, am I better off just buying four 40 cm fins and fin boxes and mounting them on the sides. (And buying some spares for the inevitable submerged logs...?)

    Any help, or advice would be appreciated.

    As you can easily tell, this isn't my normal line of expertise.

    Thanks!

    Chaz
     
  2. rwatson
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    rwatson Senior Member

    Fins will give you better performance, but boats without fins can go to windward eg laser vortex , hobie cats, clipper ships etc if the design is right.
    My first take was to think about leeboards, easy to build, mount and dismount without major structural work, and they rotate up if you hit something.
    Adding a whole new edge to the board would be a lot more work, but not impossible.
     
  3. Munter
    Joined: Jul 2007
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    Munter Amateur

    Be aware that kiteboards operate very differently to normal watercraft. In their normal mode water first hits the board at the upwind rail and crosses to the toeside rail.
    Adding big appendages to limit side slip needs to be thought through so that you don't end up with a craft that trips over the leeward rail every time a gust comes through. Kiteboards can bleed off pressure because they are flat and have so little fin area. If you add big leeboards or big appendages you will need to have an alternative method for depowering or risk being flipped in the gusts.
    The other alternative is to go for a smaller kite that doesn't risk overpowering the hull quite as much but that just doesn't sound fun does it?
     
  4. chazb40
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    chazb40 Junior Member

    Thanks for your replies! I am not really looking for too much under the water. More a large strake or giant-oversized chine than anything else. Two other benefits would be gained by adding something more to the hull bottom: more flotation (I could carry gear-I am at the weight limit now with minimal CG supplies & some water) & impact safety (if the addition is a flexible foam something-or-other, submerged logs & driftwood pose less of a problem at 15kts. 20 miles from shore. My ideal goal is to take one of these two boards/boats across Lake Michigan (www.XLakeMI.com)

    My boat/board cannot angle or edge to the water nearly as well as a regular kiteboard or surfboard due to the seated riding position. I just want to be able to capture some more edging capability.

    For sailboaters reading, this is the exact opposite of what happens to you in a crosswind: while your body is leaning back into the wind, your craft will be leaning downwind as the force is sent through the mast, and you counterbalance by shifting weight.

    For a kiteboarder, the rider will use his weight and body position to have the board tipped (sometimes significantly) into the wind and use the "edging" force of the flat board pushing against the water to keep going in the same direction and keep things pointed right. Pictures attached. Note that the board vs. boat are leaning in the exact opposite direction for almost similar conditions.

    The proposed general placement and size of the modifications are in yellow on the small pictures below.

    As per my first post: anyone with any idea how to do these modifications please feel free to respond. Or, just tell me it's silly and can't be done. :rolleyes:

    Thanks for your time, folks!

    Chaz
     

    Attached Files:

    Last edited: Oct 17, 2007
  5. kapnD
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    kapnD Senior Member

    Chaz, I think all you need is hard edges on your board. The pics look like the rails are all egg shaped, and will slip easily sideways when you apply pressure, whereas a flat bottom with a sharp clean edge will provide the necessary bite. Small skegs near the edges at the back will help control too. Google surf ski, its a sit down surfboard, intended to be paddled like a kayak, but would probably work fine with a kite. Don
     
  6. rwatson
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    rwatson Senior Member

    Fins will do it.

    Rails are ok for stopping side slip, but for usefull pointing, you need fins. Everyones doing it! :) I think the comments about the 'grip' needing to be on the windward side are important.

    For grounding, they need to at least "pop out", and they will need to be easy to drop again - like windsurfers.

    I reckon it would be easiest to insert a glass sleeve on the edges to hold one or more fins. as per illustration

    I would experiment with the holes just forward of centre, then you can play with the lengths and shape.

    The suggestiion to have a skeg on the stern sounds really usefull too.
    Remember - fibreglassing is fun !!!
     

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  7. BWD
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    BWD Senior Member

    Have you kited on surfboards? It's easy.
    I would just find a really big surfboard and use that.
    Has the right hydrodynamics for kiting -ability to vary the lateral resistance from nothing to enormous by edge control. I have seen utube video of someone riding sitting down.

    Last winter I saw a picture of Laird hamilton on a 14' by 26" board. That would be a better starting point for the project IMHO.

    Throw on a kayak seat and footbraces, lash a kayak or stand-up surf paddle to the front, stand up and kitesurf if you want to go fast and it's choppy, sit down if you want. If the kite is lost, you can paddle. If the wind dies you can roll the kite up and lash it down and paddle.
    If you want to go surfing instead, you can undo a couple of screws and get rid of the seat and braces.

    I would not add those drooping sponson keels to the rails of your surfthing. No matter what rail or fin you put on, a kite will be able to overwhelm it if you don't control edging. Having normal surfboard rails makes it easier to balance forces as the kite moves around in the window.

    If you do it anyway instead of listening to my silly advice, sand down to glass where you want to modify it, then epoxy on layers of foam to rough in the shape, sand and fair to the new shape, glass over the additions, overlapping 1.5"+ around the edges, fair the new galss into old, and paint. I would just use the blue styrofoam insulation sheets, and put 3 layers of 6oz glass on them.
    Don't disturb the glass and foam already there, use it as a foundation.

    I think the reason you can't edge that thing is it's short and wide and the rails are extremely thick. Use a surfboard!!!!
     

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  8. kapnD
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    kapnD Senior Member

    I guess I'm more oriented to performance kiting in ocean conditions, but I would definately not place any kind of appendage under the forward 80% of the board. It will trip you up and spin you out, and you may wind up wearing the fin in your ***! Also, the board is no place to carry survival equipment, as you will loose it before the kite.
    No offense intended, but why sit down? SEems to me that the performance you give up by sitting could be overridden by the time gained by standing. Sitting will decrease your visibility and hamper your ability to trim the sail and board quickly. And there are definately boards already available for stand-up that will haul ***.
     
  9. chazb40
    Joined: Oct 2007
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    chazb40 Junior Member

    Thank You for All The Replies

    Everyone has a wide range of ideas, including scrapping my own, which is good.

    The more advice I get, the better my options to test out and choose from.

    I really like the modified large board with the room for "loot." :)

    I prefer the sitting down option, as my standing time is limited due to knee/back injury/arthritis. I should take up bowling, but enjoy my time on the water too much.

    If anyone else has any ideas, keep 'em coming. I have until next year to prepare. I had to stop this year after re-injuring my left knee and getting surgery #2 on it. Needed some recoup time. Now, the colder weather/water makes it much less likely.

    Sincerely,

    Chaz
     
  10. BWD
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    BWD Senior Member

    well, in a boat you are better off standing than sitting as far as your back is concerned, if your knees recover well. how long you can (or want to) kitesurf standing I don't know. Maybe if there is good wind and you keep the kite high you will be able to keep pressure on knees under control.

    Another thing to think about is the kite cat, sort of a descendant of the Legaignoux bros. wipicat: Don't know about paddling it, but it could have a trolling motor for backup, maybe a human powered prop. Seems good. info at lynnkitesailing.co.nz
     

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  11. chazb40
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    chazb40 Junior Member

    BWD:
    Thanks for the tip! This looks like the ticket!

    Really interesting website. I sent Stefan there an e-mail and will follow-up with a call tomorrow to see what it would take to try out one in the U.S. (before plunking down $4k... plus shipping...).

    Chaz
     
    Last edited: Oct 19, 2007
  12. chazb40
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    chazb40 Junior Member

    Uh, Oh...

    Well, I'm back and posting again..

    Apparently Peter Lynn's business went belly up:websites shut down and so is the phone number.

    So: again, since I am a kiteboarder, not a boat builder: O.K., guys, how would I duplicate a "kite cat?":

    [​IMG]

    (and, to all of you boat builders who have replied here (and sent me e-mails): thank you for all of your help!! :) )

    Sincerely,

    Chaz
     

  13. chazb40
    Joined: Oct 2007
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    chazb40 Junior Member

    Well, Spring is here!

    So, I'm back to mulling over what to do with this surf runner in the garage to get it to "edge" like a kiteboard or surfboard or surf kayak.

    Latest suggestion was to put chines along the bottom which are "hard edge" to windward and soft edge to leeward.

    For an example of what was sent to me by a kiteboarder, I have attached some rough drawn-on pictures.

    So: Boaters and designers out there: would this keep side slip to a minimum while not flipping over in a gust or while traversing the face of a wave at other than a 90 deg. angle?

    Thanks for your help, guys!

    Sincerely,

    Chaz

    [​IMG]


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    [​IMG]


    [​IMG]
     
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