camping kid build for raft race

Discussion in 'Boat Design' started by Tiny Turnip, Jul 10, 2009.

  1. Tiny Turnip
    Joined: Mar 2008
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    Tiny Turnip Senior Member

    On 18th July my mate and I are heading for a small Scottish island for up to 4 weeks heavy camping, with as many boats as we can take, and 4 small boys aged 6,7,8,9. on 25th July is the islands annual raft race, and it would be churlish not to have a go. only rule seems to be must be hand built.
    We won't stand much chance of getting materials on the island, so we have to take them, as well as all the camping gear, on a 350 mile drive, and build on the campsite, with minimal hand tools. In a week. We'd like the boys to build as much as possible - they can bang a nail in, screw a screw, saw okish.
    Taking all this into account, We're looking at the catamaran design shown in the sketches. each hull from 2x 8' by 4' sheet of 1/8" ply, or hardboard, cut into 2 x 2' by 8' long ways. Joints bodged with sikaflex (PUR) and gaffer/duct tape, with either an internal stringer 1 1/2" square, to screw sides into, or sandwiched between 2x 1 1/2" x 1/2", gunnells similar. The spars hold the hulls to shape, attached with some 12mm width cable ties, and the boys sit on the spars to paddle.

    All thoughts and comments welcome, but in particular:

    I guestimate 4x boys to weigh 250-280 lbs. are we going to get enough bouyancy here? using the internal stringer keel rather than the external sandwich looks like it will give more volume, but the transition to stem and stern I'm guessing will be harder.
    Is the ply/hardboard going to be flexible enough and controllable - the best clamping arrangements will be a few G cramps and some roofrack tie down straps.

    We weren't going to do built in bouyancy - the race is only 400 yards in very benign conditions, with rescue boats, and all the kids have life jackets.

    I'll have a go at a little card model, but in the meantime, does this look like a goer? problems, improvements??

    Many thanks

    Adrian
     

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  2. joefaber
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    joefaber Junior Member

    Here is a possible starting point for what you've in mind.
    http://www.instructables.com/id/Raft-Action!/
    This one is a bit crude, but I'm sure you can streamline the design to suit your needs.

    Also, have you considered building a small boat out of corrugated cardboard?
    I know it seems a bit odd, however, it would fit you needs quite well.
    Go to the following site: http://www.cardboardboatregatta.org/ and click on the 'BUILD A BOAT' tab.
    You'll find some very straightforward information about designing and building a simple boat.
    You could even pre-waterproof the cardboard, as you're not going to be entering a cardboard regatta.
     
  3. Guest625101138

    Guest625101138 Previous Member

    TT
    A monohull will be decidedly faster. I would go for a 16ft long monohull.

    It would essentially have a bottom and two sides but I would also enclose the ends to prevent water from slopping in.

    The bottom would be about 1ft wide, sufficient to allow one knee down and one foot down in classic canoe posture. The master could sit on the aft deck to be a little more comfortable - probably the tallest so he has the reach to paddle efficiently.

    Small self tapping screws in combination with liquid nails is probably the best method of fixing ply to stringers. (Are you permitted a battery power screw driver) There would be two chine stringers and two gunwale stiffeners about the size you suggest. These play a roll in the structure as well because they will transmit torque between the ends. Also the gunwale stiffener would run on the outside in the cockpit area to provide extra splash protection.

    Some capped PVC tube can be used for outriggers just lashed to cross beams.

    The sides would be say 12" high and flare outward to something like 16" at the deckline.

    It would be something like my V14 hull only shorter and fatter with a cockpit having enough length for four boys to frenetically wield paddles without injuring each other.

    The master calls the stroke by the way.

    Maybe a little less than 16ft so you can stagger the transverse joints at the middle.

    This will be about 50% faster than your little cat and I think a simpler build as there is only one hull involved.

    Make the cockpit about 10ft long and the sides parallel for the cockpit. Start the curve at the cockpit bulkhead at either end. It will only need to have an arc about 1ft long and then run straight sides for the last 2ft to the bow and stern.

    You will need a little rocker on the floor fore and aft of the bulkheads if the side pieces are cut in parallel lengths because the sides are flared. Also the bow and stern will have a rake to match the intersection of the flared sides. Just a bit of detail to keep in mind.

    Your cardboard model will sort all this out.

    One last thing. Water does not mind going round sharp corners providing the angle is only small. There is nothing bad hydrodynamically with hard chines and parallel sides for your speed of interest.

    Rick W
     
  4. Tiny Turnip
    Joined: Mar 2008
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    Tiny Turnip Senior Member

    Joe, Rick - Many thanks for the replies. Joe - I did think quite hard about cardboard - I'm just desparately short of time before we head off, and there's nowhere local to buy it in large sheets. We might go for it next year if the timing works, and I have a bit more time to think through engineering the rigidity in. Id love to do a cardboard geodesic boat...

    Rick - many thanks. I think I will go for your design complete, Once I got happy with lapping the two side pieces to get the length (PUR and tiny screws should give plenty of moment resistance.) I can see it would be easier to build too - and like the curved bow and stern, the slight flare, and the rocker. The enclosed ends will slow down any sinking, too! Hull 12" high (might go to 14" for a little more freeboard,) 18" wide. maybe an extra bulhead in the middle. I have drain pipe for the outriggers ends stopped with squirty foam filled 2litre pop bottles - a fairly snug fit. I guestimate there will be about 4 to 6 inches between the bottom of the out riggers and the water surface. Outriggers about 3 feet out from the hull?
    Now, I wonder if using an international team of online consultants is cheating?
     
  5. Guest625101138

    Guest625101138 Previous Member

    TT
    Sounds good. I went with 12" to conserve the material. I started with 14" but I did not not do any estimates of draft. I think the extra freeboard will be better.

    The closer you get the outriggers to the water at rest the better. It will have a small amount of initial stability so if they get some experience they may be able to ballance it.

    Rick W
     
  6. joefaber
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    joefaber Junior Member

    TT,

    It's cheating only if you have someone else do the work.

    Information is why we come to this forum and adapting
    Ric's elegant V14 design should work very well.

    As to large pieces of cardboard,
    check with a local appliance store.
    Refrigerators come in large boxes. :}

    Be sure to post some photos of the boat and event.
    Hope you and your lads have a great time.
     
  7. Tiny Turnip
    Joined: Mar 2008
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    Tiny Turnip Senior Member

    The build took two dads and 4 occasionally willing small boys 2 1/2 days.
    The boys did really well. placed 2nd out Of a field of 20 mostly adult teams over 500 metresish round the bouy. And the winners got out and walked! (it was a fairly anarchic race) If the boys had had more practice time to get the steering sorted they would surely be unbeatable. In the end we set the outriggers to be an inch or so into the water to inspire confidence in the stability.
    For reference, the two competitive Dads peaked at 3.9 knots in 'Crusher' by gps.
    I'll post some photos when we return and I have access to a PC. Next projects for the holiday are tuning fangle and fitting the Optimist rig to Crusher.
    Many thanks to all , Rick especially, for the encouragement and guidance. we couldn't have had a happier, more fun few days.
    Adrian.
     
  8. Guest625101138

    Guest625101138 Previous Member

    TT
    It sounds like a lot of fun.

    Spare a thought for us on the bottom side of the globe. I am doing some testing today and I know the water will be cold. The sun is shining though.

    Looking forward to seeing the photos.

    Rick W
     
  9. Tiny Turnip
    Joined: Mar 2008
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    Tiny Turnip Senior Member

    Crusher pictures

    Some pictures of Crusher, the outrigger canoe I built with my friend Paul and our 4 small boys, aged 6 to 9, who came second in the raft race and won a terrific 6kg halibut, which served 18 of us! Well done boys!
    [​IMG][​IMG] [​IMG]
     

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  10. Tiny Turnip
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    Tiny Turnip Senior Member

    and a picture of Fangle and Crusher beached together. Aaaw!
     

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  11. hoytedow
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    hoytedow Wood Butcher

    Totally cool.
     
  12. messabout
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    messabout Senior Member

    Good work TT. Those boys are fortunate to have such great dads.

    Hoyt, dammit when you give us latin how about translating for we of little knowledge. Are you a teacher, priest, other? Please continue with the lessons. I like it and occasionally remember a word or two from high school latin class which was back in the dark ages.
     
  13. Tiny Turnip
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    Tiny Turnip Senior Member

    Thanks. we certainly had a blast last summer.
     

  14. hoytedow
    Joined: Sep 2009
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    Location: North of Cuba

    hoytedow Wood Butcher

    From the Latin under my name, loosely translated: "Fool me once and shame on you, fool me twice and shame on me."

    More literally: "Any man can make a mistake; only a fool keeps making the same one."
     
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