Displacement Diet

Discussion in 'Sailboats' started by Boatmonster, Mar 30, 2011.

  1. Boatmonster
    Joined: Mar 2011
    Posts: 1
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    Location: San Diego

    Boatmonster New Member


    I have lurked on this site for years and now have a question I hope you folks can assist me with.

    I have the opportunity to use the tooling for a 28' sailboat which is not longer in production. Basic stats: 28 LOA, 25' LWL, 8' Beam, 8,100 lbs Displacement, 3,100 lbs. Ballast and draft of 4'.

    The boat is transportable but not really a trailer sailor. When in production she was built like a brick outhouse and capable of blue water cruising.

    This would be a perfect boat for me to travel with but at 8,100 lbs. plus the trailer, we are looking at 10,000 lbs plus. You would need one heck of a towing beast to move her around. Additionally, the spars and other rigging is also over sized for my needs and raising and lowering it without a crane would be extremely difficult.

    No physical changes to the tooling can be made. Is there a way to put the boat on a diet? A new rig design would shave some off. A smaller inboard would assist a little. The original interior is finished with half a forest of lumber. Eliminating a large amount of it would also drop some pounds.

    As mentioned, the boat is way overbuilt for my needs:

    The lamination schedule calls for a minimum of seven layers of alternating 1 1/2 oz, mat and 18 oz. roving on the sides, increasing to nine layers at the waterline, 11 layers at the garboard and 22 layers at the stem, keel, and stern. Thicknesses vary from 5/16" on the side to 3/4" at the keel. Chainplate areas are heavily reinforced.

    The deck/cabin is fiberglass and wood composite construction The cabin top is 1 1/4" thick; the decks are 1" thick; and the cabin sides are 3/4" thick.

    I am not a builder or designer but can build the boat. The owner of the tooling does not have the time or interest as well.

    So, can the lamination schedule be reduced? If so, where does one start to find an individual that can develop a new one?

    Appreciate any thoughts or information on the project.
  2. CutOnce

    CutOnce Previous Member

    Changing a designer/NA's scantlings, and changing the design intent of a boat is a serious endeavor, not to be entered into lightly.

    Given the information supplied, my personal opinion would be that there are better options:

    1) Use the money allocated to the built/repurposing of the design to buy a used boat that more closely meets your needs.

    2) Use the money allocated to hire a NA/designer to help define, source and build a boat that perfectly meets your needs.

    Since any redesign of the current hull will require participation of a NA/engineering professional to get all the basics right, you might as well just start fresh. A good NA will search through existing designs to find one that fits perfectly both function and budget, before considering a new custom design.

    Being able to use existing tooling/molds isn't a real bargain if the design is wrong for your needs - saving a little money on one part of the project to end up spending more to adapt and compromise.

    I could be wrong, and you may end up with the perfect fit at the right price, but my experience tells me not to go down this road.

  3. BYDE
    Joined: Mar 2011
    Posts: 54
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    Location: Italy-China

    BYDE Junior Member

    are you sure that the boat is trailerable? it looks a bit on the edge to me, in terms of maximum beam and weight, to be transported with a standard trailer and driving license. But I don't know precisely your local laws.

    That's already a good diet.
    If you use a deeper keel/bulb then you can also reduce a bit of ballast.

    You can use sandwich also on the sides of the hull, that will cut much weight (and costs too).
    Without having the drawings of the hull it's difficult to modify the lamination schedule, it'd be a bit risky for a small gain. Keeping an equal strength, but using a lighter material is a safer approach imo.

    I can help with the diet and to redesign some parts, but I agree with CutOnce that major modifications may be the wrong approach. Especially if you don't own the drawings of the hull, as it'd be difficult to predict precisely the performance of the boat. If you want me to throw a rough figure, I'd say that you could manage to 'safely' reduce the weight about 10-20% no more

  4. Eric Sponberg
    Joined: Dec 2001
    Posts: 2,005
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    Location: On board Corroboree

    Eric Sponberg Senior Member


    CutOnce and BYDE offer you good advice. You won't be able to take a whole lot of weight out of the boat without compromising the strength of the structure. The laminates would have to be re-engineered. Even if you did make the boat significantly lighter, it would no longer float on its lines--it would ride too high out of the water. That is just as bad as being too deep in the water. It won't have good stability unless you replace some of that lost weight as ballast to get the hull back down on her lines. If you want a lighter boat, it is best to find a design or a mold for the weight that you want rather than trying to build something that was never intended in the first place.

    I hope that helps.

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