The difference between a traditionell hull and a FasTrac hull

Discussion in 'Boat Design' started by kursinal, Oct 11, 2006.

  1. yipster
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    yipster designer

    i did read all i could find on stepped bottoms for decades, it took a long time to get the R&D right, poor stability caused again un-predictable steering
    some major power boat producers called it a marketing hype and stay'd with un-stepped hull's and some still do
     
  2. Bob S.
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    Bob S. Junior Member

    I own a Wellcraft Airslot (1971) that was one of the first stepped hulls as I understand. The goal of the designer (as explained in his successful U.S. patent) was to achieve better on-plane performance, not higher overall speeds. I can attest that this vessel comes onto plane very easily without any bow high attitude during initial acceleration. The step is shown at item "S" in the patent drawing. The theory is that as the boat begins to advance under power the waterline under the bow creeps back as the bow raises. When the waterline meets the step the bow drops back down to a comfortable attitude during the rest of the acceleration phase. It really works. I've owned many boats and this boat performs remarkably in this regard.

    This hull also had unique sponsons that provided incredible stability and a cleft lip so to speak at the bow that does a great job of knocking down spray. It appears to be a forerunner of the Whaler hulls of later years.
     

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  3. Verytricky
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    Verytricky Large Member

    I had the missfortune to drive a Honda 225 raceboat. It is at first glance exactly the same hull as the B24 - A little longer perhaps ( 26 foot? ) but the same sort of three sections, two steps. The hull looks to me to be the same, yet at 60 mph the boat is all over the place, throwing the occupants around, and scaring the <snip> out of me. Unstable as all hell!

    Yet what appears to be the same boat can easily do 80mph without issue. I am trying to take that hull to 105 mph, and the designer says I can do so. I believe him, as I have experianced three versions of stepped hulls, and his is completely stable. The other hull is a Lorne campbell designed 32 footer, same sort of step configuration - not as stable as the B24, but much more stable than the Honda race boat.

    Possibly the engines/weight/setup have something to do with it, but I can clearly see that what looks to be the same design is really very very different when you push its limits.

    For information, Occe Mannefeld designed a B28 and a B23 which were different versions of the stepped hull. All look similar. The B24 hull was the lastest, and best. The B28 can not go much over 95 without getting really edgy, despite being longer and wider. So he has learned and he has improved. I would look in his direction for answers, as it is my belief that he has 'cracked it'.
     
  4. yipster
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    yipster designer

    no doubt Occe Mannefeld designed a great boat with the B24 and almost all new speed boats nowadays have stepped hulls
    never was faster than 55 "land" miles wot myself, fast enough tho to see size does matter in chop and inland speeding getting very restricted

    did not see that Wellcraft Airslot before and still am fascinated seeing hullforms
     
  5. Verytricky
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    Verytricky Large Member

    Hi Yipster,

    My thoughts here were that not all stepped hulls are created equel, even those that appear to be similar. So an experiance of one stepped hull should not be the defining characteristic for the whole class. Even from the same designer, earlier models were not up to the same 'standard'? as later versions.

    Speed is ( for me ) the defining characteristic in a boat. But speed without control is worthless. Beauty ( for me ) is in the speed and handling in the water, and being able to handle all conditions well.

    I always thought that if I was serious about understanding why stepped hulls work well, I should go to the person who has done it right, rather than look at all the designs that exist. To be honest, I have spend a load of time underneath both of my stepped hull boats, measuring and even making moulds from the hull to bring in the lounge and try determine why one works so well, and why the other does not make the grade.

    The differences are subtle, and I fail to see why they should make so much of a difference. Obviously I am not the person who should be doing the investigation, rather someone who understands the concepts should do so. I hope to understand one day what makes one hull better than the other.

    I would love to get hold of your information on stepped hull design.

    Marc
     
  6. yipster
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    yipster designer

    Marc, understand your a speedster and in much i agree, interesting to hear your findings similar to things i heard before
    the white water, reduced resistance a planing boat gets from cavitation i could simple answer but
    there is quit a bit more on this forum and a search shows lots of good info

    most history and theory i got is throu many years of reading boatingmagazine" (see they also have a forum now )
    and other publications. get also profesional boatbuilder magazine free with articles on the subject by pro's
    by no means do i pretend to be an expert here but see you want to be the customer and the designer at the same time
    but i understand couse as i heard before, stepped hulls are verytricky
     
  7. kursinal
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    kursinal Junior Member

    Interesting conversation you have. When we talked to that guy he told us that if WATER removes the air below the "step" it will occur a great speedreduction.
    So for safety we should install safebelts on every step-bottom:ed boat.
    And it might be better because people will buy safer boats, right?
     
  8. yipster
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    yipster designer

    there are lanyards and live jackets on all fast boats, dont really know if safety belts would be good
    race pilots get catapulled out sometimes, perhaps better than uncontious beeing strapped in while upside down?
    canopy boats probably keep you in but dont know much about belts with oxigen masks :confused:
     
  9. kursinal
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    kursinal Junior Member

    True, but I was talking more like higher speeds, because it wont be fun if u go from 50 mph to 30 mph in less than a second. Some kind of safebelt wouldn't be wrong imo
     
  10. Verytricky
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    Verytricky Large Member

    I run a canopy boat. And yes, we are strapped in with a 5 point harness. We carry compressed air, much like divers do. If a crash occurs we should be safer strapped in. And the inevitable flooding of the canopy is dealt with by having air onboard.

    You can run an air system that only supplies air when it is under water, and it is over your face the whole race - But I am not happy with that, as it is uncomfortable.

    My thought was - being thrown out of my boat at 80 mph and hitting the water, or worse, staying in the boat like Victory at Cowes and hitting the water....:(

    Or being securly strapped to the boat, and crashing with the boat, waiting for the canopy to flood, then escaping.

    I have seen two crashes in my racing time. In one crash, the guys were canopied, and they got out and helped recover their own boat. In the other, the crew suffered two broken collar bones and a broken leg. Both were in hospital for over a week.

    As for the guys who go over 80mph - I think that is madness not to have a conopy. The UIM agree - they ban the P1 boats from exceeding 90mph, whilst they allow unrestricted speeds in the canopy classes.
     
  11. yipster
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    yipster designer

    kursinal;110790, "it wont be fun if u go from 50 mph to 30 mph in less than a second"
    dont know how much stepped hull drag climbs while slowing down
    do know coming of plane better be done gradually anyway :eek:

    verytricky, thanks for the canopy and IUM info

    anyone with an opinion on standing behind the wheel going fast?
     

  12. antonfourie
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    antonfourie Senior Member

    Yeah, make sure you wear the "kill switch" like on a PWC
     
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