boat designing help!! PLEASE!

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

  1. grob
    Joined: Oct 2002
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    Location: Cotswolds Waterpark, UK

    grob www.windknife.com

    software

    To answer your original question it sounds like you want to learn how to design as much as you want to win which is a great thing, also if you came 5th in opti worlds you are probably used to winning.

    If you want to do this yourself I would advise you learn to use two bits of software, both are free and are likely to give you the biggest gains,

    1) look at Michlet, http://www.cyberiad.net/michlet.htm this will help you design the best displacement hull shape for your weight
    2) look at Javaprop http://www.mh-aerotools.de/airfoils/javaprop.htm this will help you design the best prop for your optimized hull.

    There is lots of advice on this site on how to use these two programs, Like Chris Tucker I will be happy to advise but you have to do all the work.

    What Michlet cannot do is predict performance in waves so you will need to use some common sense and also look at the features of boats that have done well in the past.

    All the best

    Gareth
    www.fourhulls.com
     
  2. messabout
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    messabout Senior Member

    We have a collossal variable that has not been fully examined. That variable is the Horsepower rule. My first take on that rule is that it is made to be beaten. Here's what I'm thinking....The only way horsepower could be verified is by using a dyno to test each participating engine before the start of the race. Take the example of a 125 cc engine. A two stroke of that size could have a propeller shaft output of somewhere between4 and 25 horsepower. At the upper end that is 200 HP/Liter entirely do-able for a knowledgeable engine guy. A tin Jon boat with a hot engine could easily outrun the 20+/- MPH boats shown in the pictures.....Perhaps not, if the long skinny boats had a cheater engine too. If there is no restriction on engines we could be running blowers or nitrous to make em really fly.

    So before we hurt ourselves designing the ultimate boat let us get the power question resolved. An outfit named Land N Sea has just the dyno that would be needed to level the playing field. Absent the power measuring device the 5 or 6 HP rule is meaningless and boat design is a moot point.
     
  3. ber1023
    Joined: May 2008
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    Location: bermy

    ber1023 Junior Member

    the engines are british seagull or selva sport 6.... there are different classes depending on boat size, engine and modifiyed or not.

    NOS doesnt last long and i superchargers are hard to get very small. HP is measured at the prop so at the powerhead it might put out 7hp and 6 at the prop.

    ppl in the modifiyed class are running 24mm carb, ported, wiseco piston and high compression. thats about maxed out for a 6hp


    IM 100% gaurentted these boats are displacement and not planing, i know this.

    also thanks for the links,

    i have more pictures if you guys would like ill put them up and tiny turnip yes those are correct rules.

    one of the fast boats weights 135lbs

    there is a few boats that are basically 1 layer or 2 layers of fiberglass to cut down on weight
     
  4. ber1023
    Joined: May 2008
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    ber1023 Junior Member

    pics, and stuff

    i couldnt figure out exactly that designing software and i cant see where to down load the prop thing, but thanks


    i have pictures of other boats but they are more dinghy and slower desings, these boats are fairly fast
     

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  5. ber1023
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    ber1023 Junior Member

    to the person who is coming to bermuda for newport bermuda race.... which club are you going to? the RHADC or the RBYC?
     
  6. powerabout
    Joined: Nov 2007
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    powerabout Senior Member

    We used to race in a class in Australia called 'Bathtub'
    Class was a stock 6hp, any prop allowed.
    Boat has a fibreglass bath moulding which is what you sat in and any mono hull underneath, I think there was a minimum length but I cant remember.
    The straight part of the keel was from the transom to about the front of the bath and then the curve to the bow.
    The bath floated the boat so the hull could be very light.
    speeds where always over 30mph to about 35mph
    As in any boat racing the order from 10 down to one in importance;
    10 - boat
    9 - boat
    8 - boat
    7 - boat
    6 - boat
    5 - prop
    4 - prop
    3 - set up
    2 - reliable engine
    1 - driver
     
  7. ber1023
    Joined: May 2008
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    ber1023 Junior Member

    do you have a picture of one of these boats i can see?
    today was the round de island race, ii just got home and i won my class with a stock british seagull and avg about 12mph in a boat just like the heinken one i posted

    the fastest boats ran about 18mph with 2 adults...

    the fastest boat with twin engines must have been pushing 30 cuz on the southshore of bermuda in the open sea it was flying ridicoulsly
     
  8. ber1023
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    ber1023 Junior Member

    also what props did yo uhave?
     
  9. powerabout
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    powerabout Senior Member

  10. ber1023
    Joined: May 2008
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    ber1023 Junior Member

    where did you get the props from? what size? cleavers? do you know where i can get one for a 6hp evinrude..

    thanks

    also where can i get plans for one of them boats
     
  11. powerabout
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    powerabout Senior Member

    ber1023
    That was 20..whoops 30 yrs ago in Melbourne Australia
    I suggest you follow the link as they have several classes and one of them has no regulation on props.
    We used both cleavers and round eared bow lifing props depending on the conditions and hull we used.
    1977 evi/jono 6hp was good for about 7200 rpm with adjustable high speed jet ( was a kit available then) as crossflow engines get rich when you over rev them.
    Compression ratio was so high it was very difficult to start the engine from the boat.
    We used to practice to destruction on the engines re how lean and how low we could go with the oil mixture.
    One thing to practice is from a safe running wot then lean it out for max rpm and measure the distance before it locked up and use this on the race to the line. It was always worth a few places..a quick hone and 2 new pistons. ready for the next heat.
    ATF in the gearbox...cheating was rife..depending on the venue and the level of scrutineering..remove the reverse gear from the gearbox for a bit less drag, oversize carburettors, ported engines, a pressure pack of nitrous oxide in your jacket to be sprayed in when knowone was looking, exotic fuels, grind the gearcase down untill it was paper thin, getting towed onto the plane coz we ran the engines so high, thin the prop blades down so thin they were only safe for one race.
    We also had several boats both lightweight and heavier ones as we raced on rivers, ponds and on large bays.
    Merc didnt have a 6hp at the time so they sold a 6hp kit for their 7.5 and had it UIM /ICOMIA certified.
    We tested some and found it made **** all difference..nice, so we used Mercs in some races and not in others.
    You couldnt run a merc as high as it ran out of water so for rough races with heavy boat we ran mercs set lower on the transom and Evi's mounted way high on lightweight hulls in flat water ( High = prop shaft above the bottom of the boat)

    The world champion for several years was a local guy as well, Gary Dethridge as I remember.
    We never went overseas it was just a bit of fun for the apprentices in the workshop of the marina I worked in.

    OMC had race versions of the 15 with a low profile gearbox as there is/was a tunnel boat class in the US. This may be a lead for props.
    Peter Dean from Propco ( now in the US) I think made us some props as he was from Melbourne as well.

    ( I just wish we had carbon kevlar and epoxy in easy reach in those days)
     
  12. dcstrng
    Joined: Dec 2007
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    dcstrng Junior Member

    A hull shape possibility I’ve always meant to explore, but have only superficially, is to apply trochoidal wave theory as a predictor of hull volume distribution, hull shape… we usually use prismics, but I’ve often wondered if they weren’t really just an expedient proxy for what should be used… Anyway, using trochoidals, theory might suggest (simply) picking a wave speed (with the usual square/square-root manipulation) to correspond to the hull speed desired, then plot the curve as a volume, select the hull-length desired and beginning to measure back from the wave front… my sketches (of decades ago…) usually plotted out to a hull shape not unlike what one would expect for the speed, but with a tad more aft curve (especially for planning hulls where the stern was almost flat as one would expect, but usually with a very slight curve discernable with a straightedge – in as much as trochoidals do not produce straight lines..).

    Probably has limited application, but seems applicable for high efficiency hulls… in any case, always wondered about it…
     
  13. ber1023
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    ber1023 Junior Member

    powerabout, this is very interesting it seems these were fully blown race motors!.

    when you say kit what do you mean?
    did stock pistons and everything handle the high compression? and how much did you shave the head? and the NOS! how easy did that hook up and did it blow the engines? i have a14 pitch 2 blade race prop i might beable to fit on my 6.. is that the size you are talking about?
    i want to learn as much about these modified 6s as i can
    with the over size carbs.. did you just use 8hp carbs? or bike stuff?

    thanks
     
  14. powerabout
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    powerabout Senior Member

    ber1023

    The engines were meant to be stock, shaving the head, reboring to max, custom prop and av gas were the only items legal.
    The others were for cheating.
    The kit I mentioned was a adjustable high speed jet needle valve similar to the low speed adjustment that came out through the front of the cowl.
    I cant remember but it was probably a high altitude kit or something or some kit for a commercial 6hp.
    There wasn't an 8hp in those days we just modified a stock carb.
    When I read the rules that Canadian club has invented they have been written around what I said we did but they do allow for the mods in other classes.
    The pistons just survived as we were about to have customs ones made when the boss pulled the plug on the whole thing.
    ( we did also machine the second ring to half thickness on its face to thin it. This required making a holding fixture, we also filled/padded the crankcase to help high rpm power, This is all just standard 2 stroke stuff)

    We did have a legend in the industry helping us, Ronnie Burridge, he raced in 250 and 350 hydros that made 70hp at 18,000rpm, rotary valve, fuel injected, ajustable expansion chambers etc, engines that he made himself, ( similar to Koing's and anzarni's) although he always said he didnt make the spark plug and lead
    I imagine these days I would be looking at thermal and friction coatings that are very simple to use now but unheard of in my day.
    Oils must be much better now
    Dont forget 90% of your speed is in the boat / prop not the engine
     

  15. ber1023
    Joined: May 2008
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    ber1023 Junior Member

    wat pistons did you fit in to them once rebored?
     
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