"Small" design changes

Discussion in 'Multihulls' started by SmokeyBear, Dec 14, 2020.

  1. SmokeyBear
    Joined: May 2020
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    SmokeyBear Junior Member

    Hi all, thanks to the generosity of Buzzman I now have a set of plans for a Farrier Command 10. I have been studying them and definitely prefer this design over others that are more readily available, including the team scarab designs and several catamaran designs. However I'd like to make a couple of what I would consider "small" changes. Namely I'd like to add a scoop type transom similar to what Jim Brown had on Scrimshaw, and I'd like to remove the backstay in favor of a the masthead shrouds and forestay described in the original plans for use with a masthead genoa. I'd like to run a main with a larger roach or a square top, and was thinking it would probably work as it is similar to a modern rig design. I am sure that it would be perfectly acceptable, however it would make me feel better if I could contact a designer and have them look at my proposed changes and give me an idea as to the impact it will have on the boat. As such I was wondering if anyone knew of any designers that might be willing to take a look at my drawings and work with me on it.

    Also, while FAR more significant, I was just wondering out of curiosity about the feasibility of "rounding" out the hull below the waterline a little more by adding a second chine roughly 3/8-2/3 of the way down and widening the angles by 1/3 or less of their current value. I know chines create drag and therefore slow the boat, but I was wondering if adding the second chine would serve to "round" the bottom of the hull similarly to to more modern F36. This is a mostly academic exercise as it would require a redrawing of the bulkheads and possibly adding stations, but I consider it and interesting question nonetheless.

    If anyone has any suggestions I would definitely appreciate it.
     
  2. upchurchmr
    Joined: Feb 2011
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    upchurchmr Senior Member

    Kurt Hughes at mulihulldesign.com has been known to modify other designers boats.
    Why not just make the bottom from waterline down as a full round design. Strip plank it up to the plywood designs and it will be really sleak.
    Strip plank is not difficult, especially if you are going to paint it.
     
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  3. SmokeyBear
    Joined: May 2020
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    SmokeyBear Junior Member

    Thank you, I really appreciate the advice.

    I was thinking about strip planking the bottom today actually. I was thinking that rounding it and strip planking would certainly be much simpler than trying to get the ratios right for another chine. I know doing the same thing with the amas will increase their buoyancy, but from what I understand about modern multihull theory I think it would be an improvement.
     
  4. upchurchmr
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    upchurchmr Senior Member

    The buoyancy change might not be very big.
    You might have to create some intermediate forms (removable) to get the strips to lay smoothly.
     
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  5. Rumars
    Joined: Mar 2013
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    Rumars Senior Member

    You can build the boat to plan, glue XPS on the bottom and sand it whatever shape you want, then glass.
     
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  6. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    I was not going to post on this thread, but what are you suggesting?

    Surely not xps to stay?
     
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  7. Rumars
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    Rumars Senior Member

    Why not, it's only there for shaping.
     
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  8. upchurchmr
    Joined: Feb 2011
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    upchurchmr Senior Member

    XPS is trash.
    It is so weak, that you need to add lots of glass/epoxy to give enough strength to keep that "second" skin intact.
    This is a heavy method to get round shape.
    Sort of like putting "lipstick on a pig".
    Its also hard to get the shape smooth without a lot of filler.
    Just do a good structural job in the first place.
    IMHO.
     
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  9. DCockey
    Joined: Oct 2009
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    DCockey Senior Member

    Do the original plans show a backstay?

    With the backstay removed loads on the side shrouds may increase by a large amount. Worst case it modifications of primary structure may be needed to handle the increased loads.

    Added: Thread on another forum with short discussion of eliminating the backstay on a Command 10. Command 10 backstay - Cruisers & Sailing Forums https://www.cruisersforum.com/forums/f48/command-10-backstay-150845.html
     
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  10. SmokeyBear
    Joined: May 2020
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    SmokeyBear Junior Member

    Rumars, I appreciate the suggestion. I had initially thought of doing building to plan and then adding to the hull with a hollow chamber filled with foam to get the rounded shape. In essence it would have been similar to the torpedo blisters on a WWII battleship. However I dismissed the idea about 2 seconds later when I realized that it would add significant weight, and any leaks would go unnoticed from the inside, thereby allowing the foam to become saturated and adding literal tons to the displacement. As for XPS, I've seen it used and wasn't very impressed with it. So my plan is to change the underwater profile by rounding out the frames and doing strip planking below the waterline at least, possibly the whole hull.
    So I'm going to finish drawing up my proposed changes before asking Mr. Hughes to take a look at them. That way he can see what I'm wanting to do versus having to guess.
     
  11. SmokeyBear
    Joined: May 2020
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    SmokeyBear Junior Member

    The original plans show a running backstay that, as far as I can tell, is mostly for controlling the draft of the mast in the original fractional rig. The original plans also include additional provisions for a masthead forestay and masthead shrouds led further aft on the amas in order to accommodate a masthead rigged genoa. Once those are added it looks very similar to a modern multihull rig. However I do share your concerns and will be asking about that as well.
     
  12. SmokeyBear
    Joined: May 2020
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    SmokeyBear Junior Member

    For the temporary forms to support the strips, am I right in thinking that some styrofoam blocks wrapped in cellophane and tacked in place would be sufficient to prevent sagging?
     
  13. Rumars
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    Rumars Senior Member

    It's always better to build the outer skin in the final form to begin with. XPS will add weight, but not absorb water, even if damaged. It's not the most elegant way to do it, just cheap and quick.

    For strip planking the stations are normally MDF, ply, or solid wood, to allow for the temporary screwing or nailing of the battens. XPS will not work, it can't retain the fasteners.
     

  14. redreuben
    Joined: Jan 2009
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    redreuben redreuben

    So you have xps in your hull and your lying in your bunk on a balmy night with a bit of Pink Floyd on the stereo but all you can hear is. ..........
    Squeak squeak squeak squeak squeak squeak squeak squeak squeak squeak
     
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