boat designing help!! PLEASE!

Discussion in 'Boat Design' started by ber1023, May 29, 2008.

  1. gschuld
    Joined: Nov 2007
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    gschuld Junior Member

    so basically averaging 14 mph. I have read that a stock 5ph seagull is actually more like 3-4 hp. Not too familiar with the seagull outboards personally, but I would certainly think that LONG and fairly thin, super light weight, and as aerodynamic as possible would be sensible as long as the design can handle the roughest conditions that the race will likely see. During the "open" part of the course, how rough are the conditions generally. 2ft chop? And how much of the course is rougher compared to the protected areas?
     
  2. Seagull170
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    Seagull170 Junior Member

    Gentlemen I think your missing the big problem in the round Bermuda race, it's the conditions, depending on the wind direction, it can vary from almost flat (6 inch ripples on the north side) to a 6 foot swell on the south made unpredictable by echoes from the very rocky shore line & the large coral niggerheads the size of a house, on an average day. On a bad day with the wind blowing up the length of north shore you could be faced with a short 2 foot chop that will lift the bow of a 20 foot plus boat 30 degrees @ 15 mph, only to return with an impact that 1/4 inch marine won't last long in! Have a look on google earth. they travel anticlockwise.

    Plywood has always been the favoured construction material due to it's costs/strength, weight, ease of use advantages.

    Bermuda is a small island without many of the facilities that we consider normal living on one of the larger land masses, meaning that everything including marine grade ply has to be shipped in from the US mainland with the costs that incures.

    The time a planing hull was used with twin Seagull sports, that the young man referred to, the hull made it half way, before self destructing & almost sinking 2 minutes from a safety boat, there wasn't enough undamaged hull remaining to consider repairing it, but it did make some good pics!

    The longer hulls have all performed better with the lower powered Seagulls as demonstrated by them running in a different class when over 21 feet
     
  3. Tcubed
    Joined: Sep 2008
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    Tcubed Boat Designer

    ber1023,

    why do you not want a stabilizer?

    Being able to remove minimum stability constraints from the hull design gives you a huge advantage. And with the leverage of a stabilizer it can be made very very small and unobstrusive. An eight litre float at 1.5 M for static stability would be ample and a 0.02 M^2 hydrofoil for keeping this tiny float in the air whilst under way would add much less resistance than you would then be able to remove from the hull as it no longer needs to have any kind of righting arm.

    I could not see anything in the rule which would prevent you from doing this.

    Also are you allowed to modify the transmission?

    As you reduce hull resistance more and more you need to get a higher gear ratio somehow in order to take advantage of it.
     
  4. Seagull170
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    Seagull170 Junior Member

    Picture yourself surfing diagonally down the back of a long 2 meter swell, If your sponson is on the high side the hull will have to stay parrallel with the back of the swell, as long as nothing untoward happens & the sponson digs in , no problem, but what happens when you reach the bottom & the sponson is still on the wave, ooh your going to get wet!
    If the sponson is on the low side you could be in a worse situation in a low bouyancy hull half full of water.
    These guys often use a hull called a Flea, which is a very V bottomed 21 foot hull that is almost impossible for the unskilled to keep level, but the skilled skippers of which, plane on the chines in worst that the North Atlantic can throw at them.
    I haven't seen anything in the rules that restrict transmission modifications, but changing the prop or the pitch requires a lot less skill & expenditure!
     
  5. Boston

    Boston Previous Member

    this has been one really fun thread to read
    you guys are like a bunch of dads at the kids soap box derby contest

    ber1023
    there is a lot of high end advice here
    as as stated in the beginning
    its all up to you how you now to weed through it, and pick your design
    I for one sincerely hope you kick but

    best
    B
     
  6. Tcubed
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    Tcubed Boat Designer

    Seagull 170 ,

    I think i understand what you are trying to say but i really don't think it is an issue due to the geometry.

    The foil is at say 1.5 M from hull centreline and the hull is say 9 M long. The foil is positioned a bit aft of midships. The boat should behave as if it were a wider boat from the point of view of lateral stability but enjoy the advantages of unrestricted narrowness.

    I know that changing a prop is much easier than anything else but eventually pitch becomes so great it is no longer efficient.

    Would it be allowed to use the powerhead as an inboard and make a chain drive transmission ?

    By the way , i feel a great deal of "kindred spirit" with you ber1023 as i was in the same kind of frame of mind at your age. Also the whole concept of limited power races is very admirable and sets an example for the planet.
     
  7. Seagull170
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    Seagull170 Junior Member

    I knew somewhere I had a picture,

    Do you mean something like this

    The tri huller Is a NZ Seagull boat & the other a Bermudian wave piercer look at that background.
     

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  8. doppler491
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    doppler491 New Member

    My boat:
    [​IMG]

    I also have bottom shots if anybody is interested in seeing how we design them. With the 6hp on the back, that boat ran @ 15mph+. It is 24' long.
     
  9. Delaney
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    Delaney Junior Member

    :cool: This is a fascinating thread. Where can we find the rules online and who is the sponsor? If not online, then who can we right to for a copy and how much to enter.
     
  10. doppler491
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    doppler491 New Member

  11. daiquiri
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    Location: Italy (Garda Lake) and Croatia (Istria)

    daiquiri Engineering and Design

    Ok, you won me over! I took a note that at least once in my lifetime I want to get there and partecipate in that race. :)

    And this:

    [​IMG]

    is what I call a perfect sport attitude. Respect. :D
     
  12. Boston

    Boston Previous Member

    definitely on the things to do list for me as well
     
  13. Tcubed
    Joined: Sep 2008
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    Tcubed Boat Designer

    Ok here is a little doodle i made of what i had in mind. The proportions are not quite right but you get the idea. I don't have any time right now to refine the design.

    The engine would go right behind the strut that holds the 'ama'. There is therefore as little weight as possible in the ends. It would go into a dry well. By that i mean there's a lightweight watertight bulkhead either side of the engine, but there is no water in between them because the shaft goes through a hole which is subsequently sealed with glass/epoxy or other appropriate material. The bulkheads are for just in case the seal fails.

    It should really have a fairing to go over the fellers heads too. The hull's beam is just enough to squeeze into and no more. Not drawn in either is the little blade rudder . The stern is the end closest the viewer.
     

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  14. Mynhardt Coertz
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    Mynhardt Coertz Junior Member

    I could not wait to see what is gonna come of this ! hope it'll be a real winner
     

  15. Seagull170
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    Seagull170 Junior Member

    Pretty hull

    As this is an open water hull the crew must have access to the motor when it stops. To fix & restart

    The hull has to be strong enough to support 2 crew, the motor & the fuel when supported 10% in from either end & 1 crew member is bouncing up & down.

    The motor should have access to 600 liters of air per minute if enclosed.

    The crew must be able to paddle the hull when there is no other method of propulsion.

    How cool would this look in stealth colours?

    The crew should really have access to the prop, it's a seagull boat, if the prop hits anything you run the risk of needing to change the sheer pin or prop spring.

    Sorry to be negative but these safety matters must be addressed.
     
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