28ft into 30ft

Discussion in 'Boat Design' started by gentleman, Oct 22, 2011.

  1. gentleman
    Joined: Oct 2011
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    gentleman Junior Member

    28ft'er into a 30ft'er, is there a special formula for this?
     
  2. philSweet
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    philSweet Senior Member

    add two feet
     
  3. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    A 28' to 30' proportional scaling is acceptable, though it'll be heavier and fatter then typical for this size 30'er. Scaling at about 7% (28 to 30 feet) is within the realm of doable. A lot depends on the design as well. It's usually much better to just change the station spacing to attain this additional length, as this treatment has a minimal affect on the wetted surfaces, stability and displacement. Proportional scaling on the other hand (all dimensions are increased) typically has huge affects on wetted surfaces, stability and displacement.

    As an example a fat 28'er can be proportionally scaled into a pig of a boat, while a narrow 28'er can be proportionally scaled into a reasonable craft. Which design are you looking to alter and more importantly why?
     
  4. gentleman
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    gentleman Junior Member

    if we can't find the plan's for a 30ft'er, were gonna have to go the the 28ft speedabout. thanks PAR, i was told to go from small to bigger you would half to widen her out also, what your sayin is to keep the width the same, just add 2ft in length? 28 to 30, is 2ft the most you can change a boat? 3 or 4ft is out of the question?
     
  5. philSweet
    Joined: May 2008
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    philSweet Senior Member

    Unless you plan to power this with original iron, there is going to be a fair amount of weight and balance issues to think about. You will probably need to contract for some help in order to preserve the things you want to preserve. I didn't realize you had posted about a boat elsewhere. I thought your question was a bit light on details. I'm mostly a sailboat guy so I'll leave you guys to it. Good luck.
     
  6. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Generally, resizing a boat should be left to professionals. If respacing a set of station molds, you could go to 32' on some hull shapes and be relatively safe. Again, it all depends on the design. Many design are previously stretched versions of slightly smaller models, so without knowing the design, it's a crap shoot.
     
  7. gentleman
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    gentleman Junior Member

    yes i will admit my details are more then abit light, sorry i should have decribed alot more then i did..first of all, we got plans for a 28ft wooden boat, we want to make into a 30 ft wooden mold to make a fiberglass haul off of it. we plan to put 750hp it, i'm not sure what the old racer had for power back then?
     
  8. gentleman
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    gentleman Junior Member

    thanks PAR, i know if we build this boat and he puts his engine in it and she doesn't go as good or as fast as his other boat, he's not gonna frig around with it to try to it going better. he still has his other, i told my brother if we build him a boat and it turns out not as good as we hoped, me and him are left standing there with a boat with nothing to do with it lol. we don't plan to put a engine in it, thats out of our league money wise and tec wise. so hopfully it's not just a crap shoot.
     

  9. gentleman
    Joined: Oct 2011
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    gentleman Junior Member

    thanks everyone for posting advise on here for us, i hope i don't offend anyone in anyway with my responces to your advice that you guy's give. were new at boating thing, we really don't know much at all about boats, we make our living on them lobstering and fishing, other then that it's all rocket science to us. thanks.
     
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