Alum sailcat

Discussion in 'Metal Boat Building' started by Reefhunter, Jan 13, 2014.

  1. Reefhunter
    Joined: Oct 2013
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    Location: St Johns, NF

    Reefhunter Junior Member

    Over the last two decades my Dad and I built steel motorsailors in the form of gulets. That trade sorta drifted off into never land. So, we built a couple of mahogany/glassed over sailing cats - the GR 50 and GR 42. The 50 I sold after my Dad's passing and I kept the 42 which I live on, when I'm not fooling around designing or delivering a boat.

    Neither of us really liked fiberglass hulls - too thick and heavy. And didn't want to spend $300k on a stiff hull. So, I thought why not aluminum - 5083/5182/5086 specifically - it can be welded easy and will take a beating. It's lighter than glass and easier to maintain. 0.25 on hulls and deck, 0.75 on the keels. Keel cooled, 10kw electric engines with LP generators. A 100# tank holds 24-gal of the LP.

    Any thoughts on aluminum vs glass hulls?
     
  2. rwatson
    Joined: Aug 2007
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    Location: Tasmania,Australia

    rwatson Senior Member

    The thing with aluminium is that you are virtually restricted to flat panels for hull shapes, which is a pain for sailing or part sailing vessels.

    Also, for production, you cant turn aluminium hulls out of moulds on a continuous basis, they all have to be welded individually.

    There is no one perfect solution unfortunately.
     
  3. Reefhunter
    Joined: Oct 2013
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    Reefhunter Junior Member

    Not using moulds - welding plates. Only want to build a one of.
     
  4. Northeaster
    Joined: Sep 2011
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    Location: Eastern Canada

    Northeaster Senior Member

    Dream of building a Mumby 48 someday. Starting out building a 25' aluminum powerboat now, just to see if the dream stays alive, or if the smaller project kicks my butt.

    Many good pics / info on the Mumby on the net, including:

    http://silvertern.blogspot.ca/

    have a look at some of teh earlier pics to see how it was put together. Some of these are built by amatuers, and some by the designer himself, as well as others in small numbers.

    I could live with the looks and performance of those "flat" panels!
     
  5. rwatson
    Joined: Aug 2007
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    Location: Tasmania,Australia

    rwatson Senior Member

    Nothing wrong with that design - I would love to have one.

    The narrow hull shapes made from the flat panels - ( and they are flat ) , a virtue. Almost two airfoil shapes.

    However, they are sacrificing loading ability, and although the wave cutting, smooth ride is enhanced with flat panels, you are going to get a wetter ride in a blow.
    Compared to
    http://www.dazcat.co.uk/Archive_D14CH.3.html
    for example


    On monohulls, having to do hard chines does reduce the sailing performance a bit, but I have seen some great aluminium monohull yachts in the cruising class.

    Its just the purists, searching for optimum performance that would specify compound curves on a hull, where 'glass is the least expensive way to go.
     
  6. Northeaster
    Joined: Sep 2011
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    Location: Eastern Canada

    Northeaster Senior Member

    Sorry, I was just being lighthearted about the flat comment - but I am always looking to learn. I am admittedly not very knowledgable about boat design.
    I am familiar though, with the fact that materials like steel or aluminum sheets cannot be bent in more than one direction, and thereofre designs that are fully developable are preferred - and hard chines on monos vs round chine/bilge, etc.

    I am confused though - I was under the impression that the Mumby has narrow hulls in an effort to produce a fast cat. I thought they chose performance over huge load carrying ability by design.
    I assumed that if the designer had wanted to make a slow ship, capable of carrying more load, he could have designed it that way, still using aluminum "flat" sheets, bent for the most part on only one axis (if that's the correct term).
     
  7. Reefhunter
    Joined: Oct 2013
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    Reefhunter Junior Member

    My kind of boat! Tho I would have not having all that plastic inside.
     
  8. rwatson
    Joined: Aug 2007
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    Location: Tasmania,Australia

    rwatson Senior Member

    You dont need to be confused. You are just repeating what I said -
    narrow = faster, wetter, wider = more load, slower , more load, less wet

    I suppose he would have done that with a hard chine if they had wanted wider.
     

  9. GhostriderIII
    Joined: Apr 2014
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    Location: Iceland

    GhostriderIII Junior Member

    FYI - As a notification: Capt Sam - my Father (reefhunter) who up until this month was planing to build a metal sail cat left this world on the 21st. He had just turned 75 and now he's joined his Dad in the sea.

    I am the 3rd generation of boat building family. As soon as I am finished with the current movement of cargo, I plan to keep up the tradition of quality woodhulls - overseas.

    If no one objects I'd like to keep his memory alive with my GhostriderIII
    __________________
     
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