Modifying shunting proa asymmetrical hull?

Discussion in 'Boat Design' started by mystrwizard, Oct 26, 2009.

  1. mystrwizard
    Joined: Oct 2009
    Posts: 16
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: SoCal

    mystrwizard Junior Member

    I have some plans for a shunting proa, actually they are the Table of offsets and stations. I wanted to scale up this boat by about 125% but also adjust the beam width and maybe adjust one of the sides a little. Scaling up seems pretty easy, just increasing all the numbers and spreading out the stations but what about modifying the hull a bit? Should I loft it on paper and do the changes? (about to learn basic lofting on my own), are there basic programs that I could plug in the info and then modify the hull?

    This is not a big boat, we are talking scaling up to 22 ft. or so and kind of a one-off. This is for personal use so do not want to invest much money on making this change, i.e. buying software if possible.
  2. gonzo
    Joined: Aug 2002
    Posts: 16,654
    Likes: 1,615, Points: 123, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    I assume you mean scaling by 25%. Displacement increases by the cube of whatever ratio you scale it up. That means all the scantlings have to be recalculated accordingly. You can use scantling rules to do that.
  3. peterAustralia
    Joined: Mar 2006
    Posts: 436
    Likes: 60, Points: 28, Legacy Rep: 233
    Location: Melbourne Australia

    peterAustralia Senior Member


    I think you are the same fellow who put the query in the yahoo group proa_file?

    I read posts there, used to be a member, though no longer. My 2 cents is as follows. Firstly it is not that hard, dont stress. Secondly there are a couple of existing designs out there already. Janusz has built a 23ft proa that he sails in Poland. He has an excel spreadsheet of the offsets, how do I know, because he emailed it to me years ago. So if you ask him nicely on the yahoo group I am sure he would be happy to forward that to you.

    Thirdly there is an existing proa out there about 20ft or so. It is in plywood and epoxy. It is deep V type with a crab claw rig. Looking at wikiproa website, I think the proa is Te Wheke by Paul Bowker Wheke Proa Hokianga New Zealand

    Janusz pjoa (23ft proa) is also on wikiproa website.

    What is wikiproa? Well google wikiproa and go to the website.

    How to build your proa, maybe you just want to extend Paul's boat by a couple of feet of so. Just put in a plug and go.

    Table of offsets and all that. Yes if you want this it can be done. To put it into a computer is pretty straight forward. I do things like this all the time. I think it is best to start with something closer to your end product. By that I mean is better to start with a 19ft proa and extend to 22ft, than to start with a 17ft proa and extend to 22ft.

    If you have a table of offsets and want them extended by 25 percent, I can do this, just ask. It would take me less than an hour.

    I would recommend ply over strip planking as I think it is faster and easier, especially for a deep Vee craft.

    last but not least, you can get away with a tacking boat if you are desperate, just an idea. Here are some examples.

    N Peter Evans

  4. Guest625101138

    Guest625101138 Previous Member

    Have you looked at the Harrigami boats Rob Denney is now building?

    Sign in and have a look through his album:
    I have attached one of his recent images. He will build these hulls at a fraction of the cost of more conventional construction methods.

    Rick W

    Attached Files:

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.