Can you resize a design without complications?

Discussion in 'Boat Design' started by MartinV, Jul 19, 2011.

  1. MartinV
    Joined: Jul 2011
    Posts: 9
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Netherlands

    MartinV Junior Member

    I was wondering; if you were to have plans for say an 36" boat, can you just half all the measurements and build an 18" boat without complications, or would the entire design have to be altered? I am talking mainly about hull shape off course.
    (in extreme: think about RC model boats)
     
  2. gonzo
    Joined: Aug 2002
    Posts: 15,816
    Likes: 1,216, Points: 123, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    It would change completely. The have length boat will have eight times less volume, with all the differences that implies. Also, the size of humans stays the same, so the proportions change.
     
  3. Ad Hoc
    Joined: Oct 2008
    Posts: 7,283
    Likes: 1,171, Points: 113, Legacy Rep: 2488
    Location: Japan

    Ad Hoc Naval Architect

    This is called a geosim.

    But depends what you mean by "..the entire design.."

    You would have to ensure that the scaled down version is scaled down in all respects, at least for the hull form. But not everything scales down in the same proportions, such the the weight for example. A bollard on a 36" still weighs the same on a 18", or hull thickness, as an example.

    So, geomising a hull is easy, how it affects the design and will it still achieve what you want....you have to investiagte that.
     
  4. j.harkin
    Joined: Jul 2011
    Posts: 3
    Likes: 0, Points: 0, Legacy Rep: 5
    Location: new zealand

    j.harkin New Member

    it can be done. i brought a rig off a yacht who's owner got some lambert 12ft skiff plans, scaled them up to a 26fter with wings and trapezes, sailed it like that for a few years then stuck a chainsaw through the middle, added 6ft and put a canting keel in it. nothing wrong with stability or bouyancy and it's a very fast, successful racing yacht
     
  5. CDK
    Joined: Aug 2007
    Posts: 3,324
    Likes: 148, Points: 63, Legacy Rep: 1819
    Location: Adriatic sea

    CDK retired engineer

    If downsizing weren't possible, the WL in Delft, Netherlands would not have existed for nearly 70 years.
    But there are a lot of practical problems like downsized materials not being available or overly expensive. And it may be difficult finding a crew of midgets.
     
  6. Ad Hoc
    Joined: Oct 2008
    Posts: 7,283
    Likes: 1,171, Points: 113, Legacy Rep: 2488
    Location: Japan

    Ad Hoc Naval Architect

    Don't they have a lot of smurfs in Holland?? :)
     
    1 person likes this.
  7. BATAAN
    Joined: Apr 2010
    Posts: 1,614
    Likes: 99, Points: 0, Legacy Rep: 1151
    Location: USA

    BATAAN Senior Member

    Scaling up is totally different than scaling down.
     
  8. BATAAN
    Joined: Apr 2010
    Posts: 1,614
    Likes: 99, Points: 0, Legacy Rep: 1151
    Location: USA

    BATAAN Senior Member

    RC model boats are much much more heavily ballasted in proportion than the real thing, as they have little form stability.
     
  9. viking north
    Joined: Dec 2010
    Posts: 1,868
    Likes: 91, Points: 48, Legacy Rep: 1146
    Location: Newfoundland & Nova Scotia

    viking north VINLAND

    Political correctness as taught in sensitivity training now guys it's "little people" :) What a great world it would be if we were all little people, smaller automobiles, smaller houses, smaller boats but man the oceans would be huge---
     
    1 person likes this.
  10. BATAAN
    Joined: Apr 2010
    Posts: 1,614
    Likes: 99, Points: 0, Legacy Rep: 1151
    Location: USA

    BATAAN Senior Member

    Less for each leaves more for all.
     
  11. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 491, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    If a 36' boat is scaled down 50% to an18' boat, the laws of mechanical similitude will apply, meaning it will be a vessel with 16 times less stability of the original (which is why smaller boats are proportionately wider then bigger ones), she will have 8 times less mass and her surface area will be decreased by a factor of 4. In short she will be unstable given this scaling proposal. If you look closely (okay you don't have to look very close really) RC models usually have an absurdly large set of appendages under a model sailing yacht. This is because of the stability loses mentioned. The same rules apply for powerboats as well.

    This said you can make an 18' version of the 36' boat, but it will incorporate "styling clues" not precisely reduced physical dimensions. In other words it'll carry more beam then the full size version, but the sheer line will be shaped similar to the full size, to bring along the styling clues. There are other factors to consider as well, so your best bet is to find an18' boat and work with it so it looks like the 36' yacht.
     
  12. MartinV
    Joined: Jul 2011
    Posts: 9
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Netherlands

    MartinV Junior Member

    So summarizing; yes it can be done, but you will lose the sailing characteristics of the original design. So preferably you would have to have it designed from scratch and create a look-a-like.
     
  13. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 491, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    A direct 50% proportional scale down of an existing design can't be done. It'll just flop over on launch day and embarrass you dearly. This radical of a reduction has to be a wholly considered design.
     
  14. frank smith
    Joined: Oct 2009
    Posts: 980
    Likes: 14, Points: 28, Legacy Rep: 185
    Location: usa

    frank smith Senior Member

    I think the Bolger Long micro design enlarged 50% would be interesting .
    the result would be 30x9 , and would be a good platform for a lug rig. Heck you could even build in a set of stairs , and make the house out of a old VW bug , to get that euro look .
    Very cool , which it is not here . As Gandhi said, its hot ma.
     

  15. boatn00b
    Joined: Aug 2011
    Posts: 4
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: EU

    boatn00b New Member

    I wonder what'd happen if you tried to scale a 30-something ft stepped (racer) hull up to about 55. And tried to put a couple of full size cabins and a flybridge on it. Obviously, planing area would go up with square of scale, and the weight would increase in 3rd power...and it'd weigh even more than that of course...Still, possible or not?
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.