Fast raft design

Discussion in 'Boat Design' started by KiwiAndy, Jan 1, 2011.

  1. KiwiAndy
    Joined: Jan 2011
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    KiwiAndy Junior Member

    I would like to build a fast raft for a competition.

    Some details:
    - Raft race is in a estuary. There won't be much wind or tidal current.
    - I have access to an unlimited number of plastic 50 Gallon drums (from work). So I would like to incorporate these into the design.
    - The raft will carry two people.
    - The raft must be people powered. Instead of using oars or paddlies, I am considering attaching a bicycle and using this to power a propellor.

    I've never built a boat or raft, so any ideas or suggestions would be greatly appreciated.
     
  2. rwatson
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    rwatson Senior Member

    There are heaps of threads about designing rafts, pontoons etc etc on this site you can search out - it might save a lot of repetitive advice.
     
  3. BATAAN
    Joined: Apr 2010
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    BATAAN Senior Member

    The "Jangadas" of Brazil and the bamboo surf fishing rafts of early Formosa could bring up some good Google images to start you out on what others did.
     
  4. Mr Efficiency
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    Mr Efficiency Senior Member

    Take the tip, KiwiAndy, a catamaran configuration will win the race, they always do in these events !
     
  5. gonzo
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    gonzo Senior Member

    Is a catamaran considered a raft under the race rules?
     
  6. KiwiAndy
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    KiwiAndy Junior Member

    Catamarans are allowed. I was originally thinking of a Catamaran. But then was thinking that perhaps a single hull (2-3 50 Gallon drums connected lengthwise) would work with some PVC pipe on either side similar to an outrigger canoe.

    Also, are the drums okay by themselves? Or should I fashion a bow on the front? And since more drums equals more flotation & I have access to unlimited drums, should I err on the side of using more drums?
     
  7. gonzo
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    gonzo Senior Member

    Rafts made out of drums unless really long, say 80' or so, will not perform well without a bow and a stern fairing. That is if they are fastened end to end. Sideways they do even worse. You will find it impossible to stay on the high side of a drum. A catamaran will give you stability. Outriggers may work if they have enough floatation. However, if you are thinking of a bicycle powered propeller, a catamaran would be better. The bicycle should be sideways so the drive can be direct, lighter, less complicated and have less friction losses.
     
  8. michael pierzga
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    michael pierzga Senior Member

    The rules indicate that the racing rafts should be constructed out of refuse...garbage. Best to immediately start collecting the biggest blocks of foam you can find .

    No notation in the rules indicates that you must fight " fair". Turn these blocks of foam into an " Urban Assault Raft " .

    Choose a fast hull like this aircraft carrier ......cut this fast hulls profile into a sheet of plywood , use adhesive to bond the foam blocks to the ply profile sides then carve the hull shape into the foam. Once shaped, wrap shrink wrap plastic around the hull, hit it with a hot gun to give a smooth racing bottom.

    Going to need carve out an oarsmans station and mount some kind of athwart ship structure to handle the force generated by a powerful set of oars. A deck shaped Sheet of ply should do the trick.

    Once the rig is sea trailed, add weapons.

    Fit SOLAS orange smoke bomb launchers aft, port and starboard to break free at the start and to create confusion at mark roundings .

    Once clear, pound the competition with an Aft turret mounted 150mm , top loader, water balloon cannon . Balloons misfire...use zip lock bags.....zips are also easier to refil and load on the run ..... you can double or triple your available throw weight.

    Might be best if you built a small fleet of Assault rafts then manuvered in pack formation to achieve total river dominance.



    anchored Foam block mini subs might be handy, station them down range to defend the perimeter
     

    Attached Files:

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

    Hi Andy

    a thread covering our raft race build 18 months ago - an outrigger stablised monohull, which was very fast, four boys aged 6 to 9 coming second in a field of 20 mostly adult teams.

    http://www.boatdesign.net/forums/boat-design/camping-kid-build-raft-race-28311.html

    Perhaps you could fashion a pointy bow and stern to strap onto a long chain of barrels, sling a couple of spars over the top, to connect outriggers on either side, and then lay a bit of a deck on that...

    Of course, as Gonzo says, the outrigger mono would be better suited to paddles than pedal and prop, though pedal can be done on an outriggered mono, often slung over the side, giving a slightly asymmetric setup.

    Lots of info on pedal drives here,

    http://www.boatdesign.net/forums/boat-design/pedal-powered-boats-23345.html

    but quite a high degree of complexity in getting a fast, efficient and robust drive set up.

    Good luck and have fun!

    Adrian
     
  10. Submarine Tom

    Submarine Tom Previous Member

    "The rules indicate that the racing rafts should be constructed out of refuse...garbage."

    One mans garbage is another mans gold!

    Long catamaran is the way to go. Sit lots of paddlers on the pontoons/barrels with their feet and legs out of the water.

    Good luck!

    -Tom
     
  11. Leo Lazauskas
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    Leo Lazauskas Senior Member

    Maybe it's time to unleash a Warlike Weinblum.
    http://www.cyberiad.net/wakeweinblum.htm

    You can overtake "friends" without hitting them with your wake,
    or you can hit your "enemies" with large waves you create!

    Have fun!
    Leo.
     
  12. Village_Idiot
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    Village_Idiot Senior Member

    Go with the cat style for stability, esp. with pedal power (have paddle power for backup). Longer is better, not only for speed/efficiency/stability, but the boat is that much closer to the finish line (by length) after it leaves the starting line. Only issue with length is much slower turning if you have many corners in the competition course layout.

    Cut the end off of a barrel and fasten the open end together into a wedge shape (may require some heat). Do this with four barrels to give you pointy ends for both bow and stern for both rows of barrels. If you can't re-form the barrels, then go ghetto and fasten the end barrels vertically to reduce drag, or form some pointy ends with refuse foam/plywood/waxed cardboard.

    Yes, it does help to have pointy transoms - consider the canoe.
     
  13. KiwiAndy
    Joined: Jan 2011
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    KiwiAndy Junior Member

    Preliminary raft design

    Raft design 1.jpg

    Thanks very much to everyone who's provided their suggestions so far!!

    Please see attached pictures for my preliminary raft design.

    Any suggestions or feedback would be very much appreciated!

    The basic design is:
    - Catamaran
    - Each hull is 3x 55 Gal drums
    - Platform is 1200mm x 2400mm plywood
    - Thrust is provided by 2x APC 16x16 propellors which are driven by 2x bicycles
    - I'll attach a rudder to the handlebars of the rear bicycle via rope & pulley system
    - I'm allowing 250kg for the total weight of raft plus riders (probably closer to 200kg)

    Some key questions I have are:
    - Should I reconsider going with a monohull design? (the main reason I've gone with a catamaran is for stability)
    - At the moment, one propellor is in-front of the other propellor. They will be seperated by approx 1.5m. Is the first propellor likely to cause much interference with the performance of the second propellor?
    - Has anybody used the APC 16x16 propellor before? If yes, what gearing ratio did you use? I am a cyclist so have strong legs, but I don't want to accidentally set the gearing ratio too high. Currently I'm thinking about 5:1. I'll be cycling at about 90rpm, so the propellor would be spinning at about 450rpm. Should I be aiming for a significantly higher or lower gearing ratio?
     
  14. KiwiAndy
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    KiwiAndy Junior Member

    Preliminary raft design

    2nd design picture attached.

    Raft design 2.jpg
     

  15. KiwiAndy
    Joined: Jan 2011
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    KiwiAndy Junior Member

    One further question, should I bother trying to enclose the chain within a steel tube? Or should I just leave it bare and directly exposed to the water? The latter is far simpler to build...
     
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