Seagull racing boat

Discussion in 'Boat Design' started by Horsley-Anarak, Nov 15, 2010.

  1. Horsley-Anarak
    Joined: Jan 2009
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    Horsley-Anarak Junior Member

    Hi

    I have just made another boat to use for Seagull racing.

    Stitch and glue, using 1/4" exterior ply and polyester resin.

    I built it to use in the Lerryn Seagull race this December in the UK.

    It is just under 12 foot, to use in the 12 foot class and weighs 27.4kg.

    There can be a bit of chop on the river so I gave the bow a bit of v, but tried not to have too much rocker.

    There must be two people on the boat so my crew will be my 7 year old daughter, as she is light.

    The rules of the race do not allow planing, so I was hoping for a semi planing hull if there is such a thing.

    Is there anything that I should have done differently to make it go quicker? it is as long as possible, beam is 3' which gives just enough stability and it is light.

    I am interested to build a 24' version and would be grateful for advice that will let me improve on this design.

    Thanks

    H-A
     

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  2. gonzo
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    gonzo Senior Member

    You need to find out what their definition of planing is. From that, you can design something that gets maximum speed without breaking the rules.
     
  3. tom28571
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    tom28571 Senior Member

    There must be more rules than that. No total weight restrictions? No beam restrictions?

    Obvious solution from what you say is a displacement multihull, which by definition, does not plane. Easily beat any displacement monohull.

    Get your daughter to recruit one of her lightweight 7 year old friends and drive the boat herself.
     
  4. Horsley-Anarak
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    Horsley-Anarak Junior Member

    The only rules are:

    Traditional twin leg Seagull engines only.

    Maximum of ten engines (same number must be running at finish as start).

    Displacement hulls only.

    Three classes A. Canoes and Catamarans, B. Boats 12' and over, C. Boats under 12'

    Crew of at least two.



    It is a good humoured race but very competitive.

    So keeping to the rules is there anyting else that I could be doing for an under 12' displacement monohull, with an elderly old underpower outboard.

    The only grey area that I can see is being able to go above hull speed with a displacement hull (semi planing).

    H-A:)
     
  5. philSweet
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    philSweet Senior Member

    I would suggest you get yourself elected to the rule committee;)
     
  6. pistnbroke
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    Location: Noosa.Australia where god kissed the earth.

    pistnbroke I try

    Well H-A I am supprised you made it in 6mm ply ...this is a one use raceing boat 3mm ply would have been fine and no need to skin the bottom ..coat of epoxy resin and thats it .
    depends how you view the rules ...it clearly is not a displacemet hull ..by design its a planeing hull....flat bottom no rear rocker and a sharp cut off at the transom...so if they let you race they clearly mean hulls must not plane...you put a 9.9 on it and it will plane.
    so how to get it as fast a possible with your 1 Hp (!!!! ) remove the fins on the motor to reduce drag ..as you are not on the plane these will still be in the water . Then trim is the critical factor ....I would pass a length of 12 mm threaded rod bent to the shape of a staring handle through the transom ...fixed nut on the other side and bearing on the motor leg ...When you have WOT bring your daugher towards the rear and crank up the motor so the boat starts to pound ..this will reduce your area of contact with the water and increase speed. You must of course have a rev counter so you can adjust the prop pitch to give you max permitted rpm at WOT ( small ammount of molybdem in the fuel helps reduce friction and 1 % xylene will help a full burn and starting )
    I f you carnt plane no point designing it with a ride pad ..
    If the bottom is shiney as in mirror finish you should abraid with a dish washing pad to just remove the shine ....
    make sure you have no cup in the bottom or it will hold it down like glue.

    keep quiet dont tell charles ...!!!
     
  7. messabout
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    messabout Senior Member

    Your pictures show a lovely little skiff. I have a weakness for that type. I have built several of them. When kept narrow they can exceed "hull speed", But not by much. The 12 foot hull is so short that it will not be going very fast anyway. The flattie skiff suffers from excess wetted srface. You can reduce the wet surface by a useful amount with a minimum of additional build labor.

    Let us imagine a bottom width of 30 inches. Let the bottom be flat in the middle, say 10 inches wide. The outer part of the bottom, call em the garbord planks if you like, will be 10 inches and taper upward to slightly above the waterline. This is not a suggested design, just an explanation. Tinker around with the math until you get a three plank bottom with the least wrap for the displacement needed. A full vee bottom is also worthy of study in terms of minimizing wetted surface but the panels will be wider and demand thicker material. Explore the trade offs. You can get a loading figure of better than 13 pounds per square foot if you fiddle with it enough. Flatties will not deliver as favorable a load rate as a contoured bottom type.

    The advantage of dividing the bottom into three elements is that you can get away with thinner material. Four millimeter okumee would be a fair choice. You should concentrate on weight reduction everywhere on the boat. Every pound of boat and occupant is a pound of water that you have to push out of the way in order to get where you wish to go.
     
  8. Horsley-Anarak
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    Horsley-Anarak Junior Member

    Glad you like it, I thought a flattie had a one piece bottom.

    This hull is made from 5 pieces including the transom.

    I did look at 4mm ply but thought it was a trade off between the additional weight of 6mm, against the amount of additional elements that I would need to add to make it rigid enough to use.

    27.4kg is I think quite light, I built it with a view to being light. The cloth that I used was 80g/msq and I tried to keep every thing to a minimum but still have a boat that will not fall apart or be too floppy.
    I did find that just one seat made it very rigid.

    In the under 12 foot class most of the boats are very slow, so all I need to do is be slightly faster.
    It would be nice to beat most of the longer boats though.:)

    I am expecting about 7-8 MPH, I did take my GPS when I tested it but the tree cover proved to be a problem.

    I have posted another picture that shows the V of the hull better.

    H-A
     

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  9. michael pierzga
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    michael pierzga Senior Member

    Good God !!..I was just thinking about the Seagull engine on my minitug 40 years ago and .. LOOK...Its another SEAGULL !!!!!!!!!!!!!! Love those babies ! Oh and nice skiff......
     
  10. keith66
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    keith66 Senior Member

    I like the rule up to 10 engines, same number must be running at finish as at start! We used to have a Seagull race at our club, long thin boats were favoured, tuning the engines is supposed to be darn near impossible but i bet it has been tried. I have seen Avgas used also acetone doped fuel, both engines blew up.
    Best mod for Seagull racing you can fit is a 30mm 90% plastic waste pipe elbow taped to the carburettor intake pointing downwards. This makes them keep going when buckets of water & water pistols are being fired at the carb intake!
     
  11. michael pierzga
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    michael pierzga Senior Member

    Super cool !!!!!!!!!!!!!!!!!!!! Imagine ten of those babies running full tilt ! The two stroke exhaust smoke plume would be visible from space !!!!!!!!!!!!!!!!!!!!!!!!!! I rarely ever see those beautiful Seagulls in person these days. The last time I saw 4 in one harbor was in a waterfront fisherman's cafe. 4 ancient seagulls standing on their lower units with steel pipes welded to the seagulls legs so they could form the 4 posts of a really cool , glass topped bar. Let me know if you need a carberator or something. I can bring a spanner with me next time I visit that cafe.
     
  12. Horsley-Anarak
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    Horsley-Anarak Junior Member

    That bar sounds great :)

    The most I have seen are in the picture below.

    They were going very slow.

    H-A
     

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  13. michael pierzga
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    michael pierzga Senior Member

    HOLY MACKERAL ! Check thoses babies out !!!!!!!!!!!!!!! Makes me want to dress in Mod Squad bellbottoms, jump on an old Vespa, speed to the regatta , then watch the action while poking my head out of an old chop top Mini. Every sailor in the world should at least once in their life experience a SEAGULL. Long live the SEAGULL !!!!!!!!!!!!!!! Gee...can you make a seagull counter rotate ? ... half your Multi Seagull Maxi racing rig clockwise rotation, half counterclowise rotation ?
     
  14. gonzo
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    gonzo Senior Member

    Unless you can define what displacement speed is under the rules, no one can give you an answer you can use.
     

  15. Horsley-Anarak
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    Horsley-Anarak Junior Member

    The rules are very vague.

    This years race in Lerryn is its 23rd year.

    In the past there were boats that were going too fast to be safe. to organise a race in the U.K. the insurance and health and safety requirements can be quite prohibitive.

    The organisers needed to reduce the speed of all boats.
    That is why they ruled out the solid leg engines and stopped the small planing hulls.

    Last year there was a Hobi cat with two engines, and props from this forum , it was doing in excess of 12mph. That is well beyond its hull speed, unless it was plaining.

    The organisers did not realise that it must be planing, so it won the trophy.

    Square root of the waterline length x ? = speed. It is all a little vague.

    My point of this post was not the rules of the only seagull race in the UK, but looking more into the semi planing hull design.

    There are loads of Seagull races in New Zealand, one of which is over 80 miles and takes two days.
    Some of the boats in this race are doing in excess of 20 mph.

    It would be nice if there were more in the UK, but levels of interest are not that high. But saying that it appears to be on the increase.

    What is a realistic Froude number for a Cat with a 12 foot 6 waterline length that does 12 mph?

    I work it out to be 2.97. That boat did not look to be planing, but it must have been planing.

    If my hull does near that I will win the under 12' class.;)

    Failing that perhaps we can have a Seagull race in Totnes, rules decided by gonzo.

    H-A
     
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