How to Make Small Catamaran.

Discussion in 'Boat Design' started by rtbreeder, Jul 24, 2011.

  1. rtbreeder
    Joined: Jul 2011
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    rtbreeder Junior Member

    I'm 11 years old, and I've been sailing a Hobie wave for 4 years. (I'm a 3rd generation sailer) Its great, But I cant right it when I flip. (I only way 65 pounds). I have a pretty good idea on how things work on a boat, and my dad is very handy. I designed 7' catamaran, and took out a tape measure and sat down in it. I'd l plan on making it with entirley homemade materials, because i've never heard of a catamaran that small. I like the size. Idealy, I'd like to be able to right it myself. I've never built a catamaran before. Any tips would be appreciated. Thanks!!

    -rt
     
  2. Richard Woods
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    Richard Woods Woods Designs

    I think 7ft is too small, as you say the smallest beach cats have been around 10-12ft. Even if it looks good now you don't want to outgrow it before next season

    One reason why the smallest/simplest cat I have designed is the 14ft Pixie

    You might also consider the 3m (10ft) trimaran class

    Richard Woods of Woods Designs

    www.sailingcatamarans.com
     
  3. rtbreeder
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    rtbreeder Junior Member

    Thanks, But my brother is on the way.

    I understand that I will outgrow it, but my younger 8 year old brother wont for a while. The only place I'll be sailing it is our lake, which has about 3 square miles of water surface area. Waves rarely get above 1'. It's meant to be a 1 person small, 'athletic' boat. I want it to be able to go fast, and be rightable for someone my weight. I like the size, plus we have neighbors with younger kids, around 6&7. I'm probably going to stick with the 7' idea. I finished drawing out the plans, and the trampoline will be 4' wide, 3' long, and the beginning part of the trampoline will be 3 feet from the tip of the bow, and one foot from the stern. The mast will go on the front bar of the trampoline, as this should give me good balance IF I can sit to it accordingly. I plan the rudders to be shaped like the ones on the hobie wave, just 20'' long, and 7'' wide, proportionally, this should give me good control. Now for the hulls/pontoons. I plan to build part of them out of 16'' PVC pipe. I'll cut it it half, and cut of the bottom slightly, to give me the angle that all hulls have. Then, using sheet plastic, (like sheet metal) I will cut it and angle it, giving me a decent hull, and low drag. I'll take the tops of the hulls and cover them with sheet plastic, giving me room to sit on the hull, Over all, this will make the boat 7' by 5' 4''. This should be enough room, and even when I out grow it, there will be others who might be able to use it. I plan to make the mast rigging similar to an opties, or a sunfish. (Both have the same concept) I've done my best to think things through, an the dimenshins are decided, but any other tips and helpful info would be greatly appreciated. Thanks!!

    -rt
     
  4. eyschulman
    Joined: Jul 2011
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    eyschulman Senior Member

    How about a float on masthead of what you sail now that may make it right with your weight Or you can carry a soft plastic container that you can fill with five gallons of water and a shoulder strap to help with righting.
     
  5. outside the box

    outside the box Previous Member

  6. messabout
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    messabout Senior Member

    Here is one more person who will tell you that 7 feet is too small. There are a few problems with that size that you may not have fully contemplated.

    It will be difficult to make the hulls with sufficient bouyancy. Let us say for example, that you are lucky enough to build a boat that weighs only 90 pounds. The skipper at 65 pounds and a PFD, wet shoes, and a water bottle will add up to 160 pounds or more. You must assume that all that weight will be supported by only one of the hulls. After all you'll be flying a hull some of the time. The supporting hull must not be fully immersed. Surely not more than half immersed. So each hull must support a minimum of 320 pounds. That'll need five and an eighth cubic feet of flotation. That comes to about 8900 cubic inches. If the ends are plumb then we can divide by 84 inches or 7 feet. 8900/84=109.9 square inches . Round off to 110 sq. in....

    Are you still with me??? The hulls will have some shape. That is, you will have pointy ends. You must account for that. Use a pretty good wild guess of 55% for the average of the sections. Divide the 110 number by 0.55 to get 200 for a quotient. That is how many square inches the center section of your hull must have. Ok suppose the hull is 14 inches tall that means that it will be a tad more than 14 inches wide. if and only if the sections are rectangular.

    You can see by inspection of these numbers that PVC pipe will not provide enough volume to do what you need. Forget PVC, it is too heavy for the boat you hope to have. Make the boat longer so that it will not have to be so wide at the waterline. Six to one length to width ratio is not very good for a cat hull.

    I suspect that you are really more than 11 years old, or that you are a very precocious young person, or that someone else is writing for you. I like the precocius option best. If that is the case you will have no problem understanding the simple math and you will understand that . Make the boat longer! One other thing. If the cat is too short it will pitch like a bucking bronco. That is a wet, uncomfortable and even dangerous condition
     
  7. Ike
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    Ike Senior Member

    To make this simpler, a slim 7 foot catamaran hull will not support enough weight. It needs to be longer or wider and deeper. Longer is the best option. Otherwise it will sit way too low in the water.
     
  8. Poida
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    Poida Senior Member

    The other option is, you only have to right it when it tips over. I had a cat and wanted to go sailing without the hassle of continally righting it. So I cut the mast down and removed the lower part of the sail below the rib.

    Did it work?

    I never found out as there was a rubbish collection by my council shortly after and I thought it would be a great opertunity to throw away the part of the sail I cut off.

    Later when I decided to go sailing again, I found I had thrown the wrong part of the sail away.
     
  9. waikikin
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    waikikin Senior Member

    An Arafura Cadet might suit you, my neihbour years ago had its big brother the Arrow Cat- very quick back in the day.
    All the best from Jeff.................... plans are $30 Australian.......... http://arrowarafura.com/getting-involved
     
  10. rtbreeder
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    rtbreeder Junior Member

    So what would be a good material to use?

    The boat will be 9' long, with a square trampoline that is 4' by 4'. counting pontoon width, this will make the boat AT LEAST 5 feet wide.

    The hulls will probably be made out of 3mm plywood, with some epoxy finish.

    The trampoline will be 3 feet from the bow of the boat, and 2 feet from the stern.

    The sail will have 58 sq. ft of surface area, and will be made out of tyvek.

    rudders will be 20'' by 7''. This should give me good handling.

    The mast will have the same rigging concept of a sunfish & optie's. The mast will be located on the front (alumium?) beam, and will probably be made out of alumium as well.

    I don't have the depth of the hulls worked out yet.

    Thanks for all the tips that people have given me. They are greatly needed and appreciated.

    -rt
     
    Last edited: Jul 25, 2011
  11. rtbreeder
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    rtbreeder Junior Member

    I think that I might stick with 12'' PVC pipe. RebelCats have proven it effective. The site is:

    http://www.rebelcat.com/

    It has a flotation thing for PVC pipe, and my calculations say that what I'm going with should be good. Therefore, the hulls are cleared. Next comes the trampoline and rudders. any tips on anything non-hull are appreciated. Thanks!

    -rt
     
  12. Squidly-Diddly
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    Squidly-Diddly Senior Member

    how about a "ballast bag" that you could pump full of water and use to

    add to your body weight?

    Such a system could also be used by other cat sailers wanting to sail boats over their weight class.


    I guess it would either be:

    a)hanging the bag up and pumping it full

    b)filling the bag in the water, then a set of pulleys to hoist it up.

    Either would be simpler than a whole new boat.
     
  13. messabout
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    messabout Senior Member

    And the rebel cat is offered in two lengths.....15 feet and 21 feet. Thats a long way from the 7 or 9 foot one that you contemplate. A 12 inch diameter cylinder will displace 45 pounds per foot when completely submerged. Subtract the weight of the cylinder, PVCpipe in this case, from that figure. Maybe 40 pounds per foot to the good.....but you do not want the floating object to be completely immersed. Half immersion is the maximum. Now we are down to 20 pounds per foot of useful flotation. Your nine footer will be good for something like 180 pounds per float. Marginal at best.
     
  14. rtbreeder
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    rtbreeder Junior Member

    So...

    Go with a 9' boat with the 12 inch PVC pipe? Or make the hulls with 15'' pipe?
     
    Last edited: Jul 25, 2011

  15. rasorinc
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    rasorinc Senior Member

    Try to find Styreen pipe in 12" A lot lighter then pvc and has a high crush strength.
    It is used for septic systems and I've seen it in 6" but never looked for 12". use 3 in the 6" size for each sponson will give you a little extra factor and still be cheaper than pvc # 40. Look on line for it. No you will probably need 5 of them each side for an extra factor--maybe 6 but i'm to tired to do the simple math. still cheaper I bet
     
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