mast placment

Discussion in 'Sailboats' started by Knox, Mar 15, 2008.

  1. Knox
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    Knox Junior Member

    where do you find out where to put the mast on a sailboat?
     
  2. alan white
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    alan white Senior Member

    Placing the mast is a fine art indeed. Normally, the center of effort of the entire sailplan is slightly ahead of the center of lateral resistance.
    The CLR is the point along the side of the boat where one would place a stick and push, and the boat would recede away without the bow or stern leading.
    So many factors are involved, however, that where exactly to place the center of effort (and hence the mast) varies from boat to boat by up to perhaps 15%.

    Alan
     
  3. Landlubber
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    Landlubber Senior Member

    Knox,

    A bit more on the subject. Without getting into Simpson's Rules and other calculations, the CLR of your boat is easily obtained by simply making a cutout of the underwater total area of the vessel, put it onto a ruler edge and finding the centre balance point. This position will be the CLR, as alan stated above.
    If you find the centre of effort of the sail plan (main and jib) you then drop a perpendicular line through the hull and measure the distance between the CLR and this line. This is then known as the Lead (pronounced leed). It is , again as stated above about 15% (17%) (OF THE TOTAL WATERLINE LENGTH
    The boat will balance at the helm somewhere in the ratios quoted above for a bermudan sloop rig. Moving the mast forward or back will adjust the weather helm of the vessel. It is often simply a matter of raking the mast a bit to alter the sail areas centre of effort/CLr ratio, thus tuning the feel of the helm.
     
  4. Knox
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    Knox Junior Member

    is it any different on a trimaran?
     
  5. alan white
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    alan white Senior Member

    It involves the fore/aft placement of the floats, considers much higher speed, and the fact that the trimaran doesn't heel much (CLR/CE difference is determined on monohulls based among other factors on balance when fully heeled). Otherwise, much the same factors would apply, though I'm no expert.

    Alan
     
  6. PAR
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    PAR Yacht Designer/Builder

    Knox, it would be more helpful to understand what you're attempting to do. I can think of only a few possible reasons to need this type of information, all requiring a fair amount of actual vessel specific dimensioning, which of course we haven't got.
     
  7. Knox
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    Knox Junior Member

    ok the info on the boat
    overall length 17 feet Beam 6 feet
    3 hulls in a triangle formation
    the hulls are 8 feet long and 2 feet tall and about 4 in thick
    the 2 hulls would be at the bow
     
  8. alan white
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    alan white Senior Member

    Knox, you should make some effort to speak in "boatese" by calling the dimensions and parts/pieces by their proper names.
    this is not hidden information. Every boat ad, for example, describes the boat in question using the proper terms.
    I don't usually complain about grammar or spelling too much, but I'll make an exception here, since that last comment takes the cake.
    PAR, or anyone here who would help you, deserves the effort.

    Alan
     
  9. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    After reading your previous posts about you three legged whatever you might call it, my strong recommendation is to seek an education in the several disciplines necessary to confidently sand on a skinny design limb, which you concept appears.

    Without a reasonable grasp on the fundamental principles involved, you're basically shooting blanks. I say this having just read the very basic nature of your previous inquiries.

    How do you design a car or airplane or elevator? There are plenty who think outside the box, I certainly do and have a neat foiler with tandem boards in the works. I suspect it'll do 30 knots on a good day, if I can keep it's scrawny *** upright. I'm not trying to offend, but it appears you're looking for answers to the very basics you'll learn from just one good book. There's no free rides, particularly if you want to climb out on a limb from a design or engineering point of view, more so if you'll be sailing farther from shore then you can swim back to.

    You're not going to dumb luck your way into it, there's just too many variables, any of which can spoil your day. It'll take research, education, experimentation and solid engineering. So "got milk . . . "?
     
  10. Guest625101138

    Guest625101138 Previous Member

    Knox
    Like I implied, it is an interesting concept and not without merit.

    I let Godzilla loose on the layout and I faired out the result and standardised on a hull and the relative positioning for symmetry. The optimum ship was not symmetrical. The design speed was 16 knots. Optimum hulls ended up just over 2m long.

    I figure on a reach (apparent wind) with apparent wind strength of 25 knots, sail as shown, it will do 17kts. Any stronger than this and it will bury the nose. Your weight would be at the very stern slightly to windward of centre.

    The drag is slightly more than a planing hull of the same weight at 17 knots. However this ship would have two advantages over a standard planing dingy. It has awesome sail carrying capacity for its weight and it would not be upset too much by chop - just ride smoothly through it.

    Compared with a catamaran or more conventional trimaran, you have three short hulls that could be easily stacked for transport. I tried an idea like this with a pedal boat to get something that was more compact for transport - see V8 picture.

    Now all you have to do is build it to have a total weight of 50kg. Not an impossible task with modern materials. The further out you push the centre hull, the more drive you would get but I did not look to see if this would add more drag.

    Rick W.
     

    Attached Files:

  11. Guest625101138

    Guest625101138 Previous Member

    Here is another view of Trinox from below.

    Rick W.
     

    Attached Files:

  12. Knox
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    Knox Junior Member

    thank you alot Rick Willoughby
     
  13. Knox
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    Knox Junior Member

    oh and i forgot to say i like to do the math
     
  14. Knox
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    Knox Junior Member

    i was thinking what would happen if you had the one hull at the stern insted of the bow becuse as you said at a certin speed the nose will go down in to the water
     

  15. Guest625101138

    Guest625101138 Previous Member

    I am working on the basis that your body weight is moveable ballast. You need to be able to move your weight around to counter the tipping moment generated by force on the sail that is about 3m above the drag on the hull or side resistance.

    Sailing upwind the force will have a very large side component that needs to be countered by sitting out on the windward hull toward the stern. If you have one hull at the stern then it becomes much more difficult to locate weight where you need it.

    It is easier just to push the forward hull further forward. There is a point of no return though because things have to get heavier as the moments go up.

    Also I placed the hulls in the minimum drag position for the chosen design speed and did not check what happens if they are moved about.

    Rick W.
     
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