1/10 Scale frigate...

Discussion in 'Wooden Boat Building and Restoration' started by volkswagen50, Apr 1, 2009.

  1. rwatson
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    Location: Tasmania,Australia

    rwatson Senior Member

  2. BATAAN
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    BATAAN Senior Member

    Here's one I built, and some others I rigged.
    If you want a sailing model, about 1/6 scale is about right. The 100 gun ship in the green screen shot is 1/12th scale, the brig whose deck I'm standing on is 1/4 scale and the BLACK PEARL the modelmaker is in front of is 1/6.
     

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  3. GAZZABO
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    GAZZABO Junior Member

    In Russell NZ there is a 1:5 scale model of Cooks Endeavour built by Ralf Sewell and it sailed! It is in the museum there and has photos and I think a film of it sailing.
     
  4. vhhjr
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    vhhjr Junior Member

    I am impressed Mr. Bataan! Did any of these models sail? What a fun job.

    This is a hypothetical question as I have never built anything like these ships. Only some models. There is a company that makes large scale sailing ship models:
    http://modelsailingships.com/ships/grasshopper.html
    Using their Brig as an example, it is 50" on deck, with an 18" beam and weighs about 72 lbs ballasted. The sails are radio controlled using 4 winch servos. If this was scaled by 5X for a 21' length and a beam of 7.5' and it's scale weight would be 9000 lbs. A 4X version would be about 17' on deck with a 6' beam and a weight of 4600 lbs. I assume the high weights are to balance the scale sail rigs. The ballast might not have to be this high as I have scaled the ballast as a cubic function and sail area scales to the 2nd power. Using this approach the gross weights would be 2700 lbs for the 4X and 4900 lbs for the 5X. This would cause the hulls to float higher in the water than scale.

    How reasonable is it to assume that the saling data from the model would be applicable to the scaled up versions?

    Would it be possible to control the sails using the same bracing system that these models use?

    VHH
     
  5. rwatson
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    rwatson Senior Member

    Sounds like you are on the right track vhhjr.

    Just bear in mind, that the wind force is also cubed (like ballast) - so scaled ballast on a model may need to be higher to cope with the "cyclonic" 10 knot breeze encountered by models on the local pond.

    That's why model yachts have to have such big lead bulbs and long keels.

    I would love to see a radio controlled square rigger - it must be possible. Getting it to look authentic would be worth it.
     
  6. vhhjr
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    vhhjr Junior Member

    Any Progress

    Have you made any progress on your square rigger?

    I did some static tests in my neighbors pool with the Mitty and found that with the addition of considerable keel ballast I got reasonable heel angles with forces that I calculated to be that of a moderate wind with full sails broadside.

    The question is; can yuou scale up a model to a manned size boat? There's seems to be lots of opinion that scaling down is fraught with danger. How about scaling a working model up 8 to 10 times?

    Vince Homer
     
  7. PAR
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    PAR Yacht Designer/Builder

    The exact physical laws apply to scale, regardless of direction (up or down). This isn't opinion, but cold, hard and unforgiving physics. Again (if you haven't followed the thread) look up mechanical similitude and the problems quickly appear.
     
  8. vhhjr
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    vhhjr Junior Member

    I know from model ships that I have made that a true scale model is not stable and requires much more ballast (or keel length) to stay upright. If one scales up a stable model does the full size boat end up with too much ballast? Is it correct to assume that the ballast to gross displacement ratio for the model is higher than for the full size boat?
     
  9. rwatson
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    rwatson Senior Member

    You got it at last.

    This is a formula from my scale model worksheet.


    =(K34/(5*5*5))


    K34 in this example is the maximum trailerable weight of the boat. (1990 Kilos)

    this formula gives the scale model weight of a 1:5 scale model.


    Substitute the 5*5*5 for a 7*7*7 for a 1:7 scale, or 10 for a 1:10 scale model etc.


    Reverse the formula to scale UP to a full size boat.

    eg =K34*(5*5*5) will give the scale weight of a full size boat of 1:5th scale
     
    Last edited: Aug 3, 2012
  10. BATAAN
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    BATAAN Senior Member

    No, none of these sailed. In a film environment, EVERYTHING is about control and these ships are moved with a 'Johnny', or mechanical controlling rig, either a pitch/roll machine or a track, in a flat-bottomed tank about 40" deep.
    You can see how one of the models was built in two parts, to fit the various Johnnys built for various shots.
    Note: Study "Jarvis Brace Winches" for how later full-sized steel square rigged ships used winches to control their sails, and consider applying them to a model.
     

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  11. ancient kayaker
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    ancient kayaker aka Terry Haines

    Here are some points that occur to me:

    Heeling force varies as the 3rd power but righting moment varies as the 4th power, that’s physics as Par noted. However in a small boat the crew can move to adjust righting moment. Hull size can probably be optimized to take advantage of this. Too small and the crew won’t fit or can’t do its job; too large and hiking is pointless. This would be a useful avenue to explore.

    Righting moment is further limited by crew shape, crew is not amenable to casting into a convenient form and insists on breathing, this impact is additional to scaling effects.

    There is no need to pursue true scale underwater unless the boat is to be displayed on land. Additional beam has already been suggested, perhaps this can be disguised by increasing tumblehome, and hull shape factors can be changed for improved stability.

    Sail area: for true scale not much can be done but there is no need to fly the equivalent of the full sail set of a full-sized boat. A heavy weather set can be modeled with as much accuracy as desired. However, real square riggers carries storm sails high to avoid wave interference, something that will not affect the scale boat, so reefed mainsails will ikely be the order of the day plus whatever is required for balance. Sail size should also take into account the reduced wind speed near the surface.

    However, if true scale is not essential then advantage can be taken of scaling; a 35% reduction of heelng moment can be obtained with a linear scaling of rig of only 13%, which will not be very noticeable.

    Note; there is no need to set the sails for maximum thrust; style is more important than substance here. There is also the matter of mechanical assistance. If that is going to be provided, my approach would be to set the sails for minimum heeling moment, counter that with crew position and use the motor to actually move around. Of course, that might be too far from the original desires expressed in the first post.

    Speaking of mechanical assistance, a diesel seems a bit over the top, a boat of this type is not going to be safe at sea, it is only suited to display in sheltered waters close to land and in any case is going to sail like a pig, even worse that the original. A small, quiet trolling motor seems more appropriate to me, with the batteries mounted as low as possible, and much more pleasant for the crew.
     
  12. vhhjr
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    vhhjr Junior Member

  13. vhhjr
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    vhhjr Junior Member

    It worked! I attached various lead strips to the keel and used some weights on the boats rail. For heel angle I built a lightweight inclinometer that was mounted on the aft deck.

    I also had templates that fit around the hull amidships that I used to mark the waterline on each side. Not quite sure what to do with these, but thought they might be useful in determining the CG or metacentric hieght.

    Initially I was assuming that weights scaled up to the 3rd power, but from the email above I see that righting moment is to the 4th power. This means that a larger version of my model will be even more stable under heeling forces than I thought.

    I have a slightly larger version (36" LWL vs 30") under construction that will hopefully be an RC model. The original was made of posterboard and didn't take too well to the water.

    Vince Homer
     
  14. vhhjr
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    vhhjr Junior Member


  15. DCockey
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    DCockey Senior Member

    ,[​IMG]
    George Washington briefly owned a 15' ship, Federalist. It was built in Baltimore in 1788, and then sailed from Baltimore down the Chesapeake and then up the Potomac to Mount Washington. It sank six weeks later during a huricanne.

    A reproduction designed, Maryland Federalist, was built and sailed in 1987. It was designed by Melbourne Smith and built by Alan Rawl. http://www.msa.md.gov/msa/mdstatehouse/html/federalist.html
     
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