boat designing help!! PLEASE!

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

  1. powerabout
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    powerabout Senior Member

    we used stock oversize, polished the domes and made both pistons the same weight.
    You get some power for free with oversize as you increase the compression ratio, and also the crankcase compression ratio.
    you can also plug the wrist pin on any engine

    For sure these days I would be putting a friction coating on the skirt and a heat rejection coating on the dome
     
  2. Athlon64M
    Joined: Jun 2008
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    Athlon64M Naval Architect Student

    ber1023

    So Planning Hulls are not illegal?

    What is the diameter of the prop that you have?

    How much do you and your passenger weigh?

    Basically I'm getting at total Dry weight (How much it will weigh right before they start the race)

    Also any idea how many RPM's those engines crank out?
     
  3. ber1023
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    ber1023 Junior Member

    a good boat is about 135 lbs, im 125 my dad is 175 and engine is about 60 ish.. stock it should turn 4000

    props range i used a 25hp omc prop cutdown im not sure what size

    planning is legal..
     
  4. floydrob
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    floydrob Junior Member

    hi, i'm 15 too but live in scotland. the local racing league here ios the gareloch's. they are large sailing boats of wooden construction. i sailed them 4 a while and won several times but got fed up and have now decided to build a fast motorsailer.

    i have decided to start a leage of my own with some mates and hopefully other people will join in... the max engine size is 20hp, max length is 14ft and it must handle offshore conditions.

    i took the hull design from an 8ft hydroplane and enlarged it to make it 14ft. i put the cuddy on the boat today and it looks quite good. i sealed the hull wilt silicone (its plywood construction) but i'm not happy with it. i'm going to cover all the edges in fiberglass this week but i spent most of my time designing and has only taken a week so far to build

    i am giving it a sail and a removable centreboard cos i like sailing and dont have anywhere to put a yacht aswell as a speedboat. the cuddy is also for recreation but it is quite low so shouldnt slow me down too much.

    it's not the first boat i have made but the last one was totally experimental, i tried out the "one sheet skiff" by herb mcleod which is surprisingly good, i realli liked that boat. i put a 6hp seagull on it and took it to an inshore loch-loch lomond and she flied! no joke...so fast for such a small boat but the trouyble started when i put it in the clyde and follower the zap cats out to open water. it kept up with them ok, but it took alto of beating and i hit a wave dead on at about 25kts and she flew over the top and nose dived straight into the trough. that was the end of that boat. lol. i plan on making another, they dont cost much and are very fun. looking at those long boats, i have an old racing kayak sitting behind my shed, could i cut a hole through the 2 skins, join them up with some fiberglass and put an outboard bracked and an outboard on it? it would be pretty close to me sitting it the middle of the kayak so i can control the engine and also to keep the balance right. think that would be fun :D

    mu mate has a 12ft dinghy he is reinforcing with metal frames to hold a 20hp outboard, the current bopat is rated to 4hp! lol

    could sum1 advise me, should i take the engine and drive from a jetski to give me jetdrive or should i just put an outboard on it and a decent prop?

    here are sum pics of the progress
     

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  5. ber1023
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    ber1023 Junior Member

    outboard, jet drive is 30% less efficent..
     
  6. Grant Nelson
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    Grant Nelson Senior Member

    Man, wear a life jacket - your gonna need it!
     
  7. floydrob
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    floydrob Junior Member

    so do u mean a 20hp outboard would maake it go 30% faster that a 20hp jet drive? or is it just fuel economy?
    grant, i'm not stupid for a start and i have safety boat qualifications with royal yachting asociation and instructor level in sailing. so 50% of the time, i'm th eone tellin ppl to wear lifejackets, i no that its the smart arses that think they will be fine without 1 that usually end up in the water.
     
  8. longliner45
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    longliner45 Senior Member

    floydrob,,way to go ,,I like to see a young person doing it ,,and ignoring all the naysayers ,,you can do it ,,and im sure it will be done ,,good luck ,,put saftey first,longliner
     
  9. Grant Nelson
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    Grant Nelson Senior Member

    Hey, I never said don't do it.... but a boat for rough water with no real deadrise at the bow, and a very wide stern that will, on a following wave, push that bow that has very little bouyance in it onder the water, and gosh, look a floydrobs post above a bit - flipped his boat - so I was only stating the obvious, with a bit of respect, just like I have with bungy jumpers... with heck, without those risking all in the leading edge, those of us burdened with other duties to others and can not dare (or dont dare to dare) can be thankful... OK?
     
  10. longliner45
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    longliner45 Senior Member

    my bad,,you are correct to point out flaws,,it is yours and my obligation ,,moreso yours ,,I am not a desinger,constructive critism is ok,,I think it is great a 15 yr old can be so focused,look for him in 7 -8 yrs from now ,,he will be a top name somewhere in desing or building,,,,with plenty of first hand expiriance ,,not books or computer enhanced ,,books are good though,,longliner
     
  11. Grant Nelson
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    Grant Nelson Senior Member

    Cool thought...
     
  12. ber1023
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    ber1023 Junior Member

    floydrb a seagull wont do 25knts on anyboat..

    2nd

    ever thought of why a jetski needs 250hp +/- to do 60hp? when i can do that with a racing 10hp? jet dirve is less efficent so u need more to go faster most of the time
     
  13. chowdan
    Joined: Jul 2008
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    chowdan 1980 PAC41 Liveaboard

    ber1023: those are some nice looking boats!

    I'm going to start giving some thought to these boats. I do think a outrigger with a narrower main hull will speed you up a lot. Also maybe having a design so that when you are sitting inside the cockpit your head is the only thing that is popping out and your body is inside the hull. that would cut down on drag(think of formula 1 cars...the guy is totally hidden except his head)

    just an idea.
     
  14. rwatson
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    rwatson Senior Member

    Yeah - like I said early in the conversation - reduce the drag above as well as unde the water
     

  15. gschuld
    Joined: Nov 2007
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    gschuld Junior Member

    Ber1023,

    What was the average speed(MPH) of the winning boat in the stock seagull 5hp category this year? The stock Seagull class is what you are looking to design around, yes?

    George
     
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