How are beach cat hulls made?

Discussion in 'Multihulls' started by Sly, Mar 8, 2010.

  1. Sly
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    Sly Junior Member

    I've been trying to find some information online (pictures/videos/ect) but can't seem to find anything. The majority of monohulls are made in a mold these days and then the deck is placed on top. But im having trouble grasping the idea of how the hulls on a F18 (Hobie Tiger/Wildcat, NacraFusion) are made.

    I know a mold is clearly used and the gelcoat followed by glass is placed within. But how to they seal it all off? Do they use two molds and make half of the hull in one and half in the other, stick some ribs and floatation within and glue them together?

    Is there any info or a step by step guide to how they make them?
     
  2. Chris Ostlind

    Chris Ostlind Previous Member

    Two molds (tools) split vertically for one hull. If the hulls are symmetrical, then it's pretty straight forward stuff. Open tool, wet layup, while still being done, is going away in favor of vacuum bagged and infused resin molding. Exotic boats are getting built with pre-preg and wheeled into an autoclave for a specific heating cycle for full cure and post cure of the laminate.
     
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  3. jonr
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    jonr Senior Member

    I don't know, but I would guess the top/deck is a separate piece.

    http://www.hobiecat.com.au/images/sailboat/tiger/tiger_main.jpg

    I'd be interested in how they make their smaller boats with a rotomoulded foam core. I'm also interested in anyone using CNC cut foam male molds, vacuum bagging and then dissolving out the foam.
     
  4. ccolton
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    ccolton New Member

    Gougeon Brothers on Boat Construction

    I recommend that you look into this book - there is sufficient information to describe the stitch and glue method of boat building which is probably the best way for a home builder to build a beach cat. I am currently contemplating building an A-Class cat using this method.

    If you do a google search on "building a beach cat" I think you will find a lot of relevant information.
     
  5. luckystrike
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    luckystrike Power Kraut

    Another construction method for beach cats with plywood is called tortured ply or stressforming. It is also one chapter in the gougeon book. If you want to see how it's be done look here:



    The Blade is a formular 16 cat, designed for amateur builders. But the famous Tornado Cats can be built this way as some older A-cat models or the Taipan

    Grrreetings from the North Sea Coast, Michel
     
  6. luckystrike
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    luckystrike Power Kraut

  7. Fanie
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    Fanie Fanie

    Come on you guys, Chris gave a qood in a nuttshell explanation. The deck is part of the hull. There are even video's on youtube that shows how it is done. Do a search for vacuumm infusion.

    Sly, it would probably be cheaper and a lot easier to buy the cat 2nd hand than building it. Be carefull to associate self build with cheap. Or it can be just that, reall cheap !
     
  8. themanshed
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    themanshed Senior Member

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  9. Fanie
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    Fanie Fanie

    Hi Themanshed,

    Look like you're doing a nice job there !
     
  10. themanshed
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    themanshed Senior Member

  11. Ike
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    Ike Senior Member

    Jonr

    How they make roto mold hulls is the same way they make roto molded tanks. First you make a metal (usually aluminum) mold that is in two pieces that is shaped on the inside like the hull or tank. These aren't cheap to make so if you are not going for volume it isn't worth it. You make a lot of these and fit them on a wheel (similar to a ferris wheel) that allows thme to rotate in two axis. You pour polyethylelene beads into the mold and clamp them halves together. The ones I have seen actually use vice grips to clamp them. It's quicker than screw clamps. Then you move this big wheel into a huge oven and heat it until the plastic beads melt. By rotating the mold in two axis the plastic coats the entire inside of the mold. You then slowly cool it until the plastic hardens. When it's ready you release the clamps and out pops the hull or tank. If you want to foam it you cut a small hole, inject 2 part foam and fill it up.

    Look here http://commons.wikimedia.org/wiki/File:Rotational_Molding_Process.svg

    Here is a link that shows a tank mold being made. http://advancetankandsupply.com/About_Us.html

    As I said it is not a cheap process but once you have the molds and the ovens you can turn them out by the thousands. This assumes you have the market to sell them.
     
  12. Chris Ostlind

    Chris Ostlind Previous Member

    In all fairness to Sly...

    Some cat hulls are made in two parts as hulls and decks. The Hobie 16 has been made that way for many years and they are still made today.

    As for the rotomolding of plastic catamaran hulls...

    It is possible to completely eliminate the business of using expensive aluminum tools for rotomolding. Lots and lots of white water kayaks, for instance, are made from high temp epoxy tools, taken directly from the shaped plugs. They can be spun for a couple of hundred boats before they wear-out. This allows the boats to be tested as fully rotomolded designs before anybody goes to the expense of producing an aluminum tool.

    Commonly, the high temp epoxy tool is superceded by yet another fresh design and the epoxy tool previously used is trashed.

    Producing an aluminum tool runs somewhere in the USD$2000 a foot range for a hard core production tool for the output of rotomolded designs. The high temp epoxy method is in the hundreds of dollars. You can readily see the advantages of going with the latter until things shake-out in the market.
     
  13. jonr
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    jonr Senior Member


  14. Chris Ostlind

    Chris Ostlind Previous Member

    The foaming core is added before the tool is closed. It is released when the outer shell of resin has been properly distributed. There can even be a third layer of another plastic that is released within the tool to form a smooth inner layer.

    Keep in mind that these spinning/rocking tools are incredibly hot. They are mounted to an armature that can spin the tool at a prescribed rotating speed, as well as rock them fore and aft, to distribute the molten plastic resin according to a computer program for proper thickness of the material.

    The cooling cycle is also very carefully controlled, as that is the period when the plastic is thermo-set to its final shape within the tool. When the whole thing completes its operational heat/cool cycle, the tool is wheeled out of the oven and it goes through an extended cool-down period while spinning and the tool is then opened to remove the part for post production fixturing.

    A simple kayak is easy to do, but a complex, thickness controlled and multi-layer part, is much more involved.
     
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