Constant section masts?

Discussion in 'Sailboats' started by RHough, Nov 23, 2010.

  1. RHough
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    RHough Retro Dude

    Ah yes, Skene's Elements. I wonder if I brought that with me this trip ... great book!

  2. TeddyDiver
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    TeddyDiver Gollywobbler

    Like money in the bank :D
  3. Crag Cay
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    Crag Cay Senior Member

    Perhaps we're trying to be too specific about when changes happened and why. I think the evolution of masts and rigs is more convoluted and complex than a simple time line. The Thames sailing barges trading along the coast of SE England developed a rig where one man (and a dog) could handle 3500 square feet of sail about 100 years ago. About the same as a maxi multihull today.

    Again with masthead rig vrs fractional, most gaff rigged sailing vessels had a jibtop stay that went to the top of the top mast. Can't get more 'masthead' than that. Certainly by the 1930s there are plenty of both masthead and fractional rigged boats under both the CCA and RORC rules. In fact the only rule where I can't find any masthead rigs in the metre rule. I will have to have a look at the rule in detail to see why.

    By 1910, elliptical, tapered, variable wall thickness masts were usual on the big race boats. These masts were beautifully fabricated in steel. Similar spars were made for smaller boats in wood. It was the advent of extruded aluminium spars after WW2 that reduced the spar makers art to a simple taper at the top of an otherwise constant section and wall thickness. I think it was the prohibition on carbon spars in some of the earlier (1990s) Whitbread races that saw a return to fabricated rather than extruded aluminium masts. I remember hundred of parts being assembled to get the right weight, stiffness and moments at every part of each spar. They, of course, worked out much more expensive that the carbon spars that were banned.
  4. philSweet
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    philSweet Senior Member

    I want one of those dogs!
  5. Milan
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    Milan Senior Member

    Working boats rigs shapes, (as well as boats themselves), were result of multiple factors. Aside from material characteristics, limitations of available technology, local conditions, specialization for their specific trade, (low freeboard for hauling nets on some fishing boats for an example), there was one most important factor above everything else – economy - working boats were not built and sailed for fun. They had to provide daily bread. Therefore, they were always as simple and as economical to build, use and maintain as possible. Their sailors wouldn’t choose complicated solutions to achieve slight improvement in speed, (for much higher costs), if there was simpler, cheaper way, that worked almost as well.

    Yachts on the other hand were toys of the rich man. They could afford complications and experimentations.

    The most widely used rig type on the Dutch traditional sailing boats is a short gaff. It is a cheap, simple sail, with a long luff, (good for windward sailing), quite clean aerodynamically, much lighter then long gaff with a topmast.

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  6. gggGuest
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    gggGuest ...

    Mostly oval, some pearshaped on a quick scan. Mast hoops had largely gone by then: they are of course not compatible with rigs with multiple cross trees because they won't pass the spreaders [grin]. The only time I see them in the books is on a gaff rig with a single set of cross trees at throat height.
  7. RHough
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    RHough Retro Dude


    Okay. Lets revise this a bit.

    Tapered masts are not unusual at all, they seem to be common.

    Luff tracks and sliders allowed hoisting past spreaders.

    Multiple spreaders are mainly so headsails can be have smaller sheeting angles.

    We know that the RORC Rule favoured masthead rigs, we know that total area rules in development classes favour fractional rigs.

    Is it fair to conclude that there is no reason other than economy to use a constant section mast?

    Can a case be made for the masthead rig with constant section mast other than simple, cheap construction?

  8. gggGuest
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    gggGuest ...

    As cases go simple, cheap construction is a pretty damn good one. There are quite a few applications in life for which that's a winner[grin]. But of course in a lot of situations fractionals are just as cheap and just as simple.
  9. RHough
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    RHough Retro Dude

    How about stating it very general design terms.

    What are the drawbacks (if any) to using a constant section masthead rig on a production boat?

    It is pretty well agreed that reducing pitch adds speed and comfort whilst sailing. The constant section masthead rig has a high centre of mass.

    Same for roll.

    Masts heavier than they need to be require heavier hull/deck structures.

    Larger head sails require heavier, more expensive gear.

    For racing a masthead rig requires a larger sail inventory and each sail is more expensive. (function of area) For cruising a single "medium size and weight" roller furled sail ends up with the boat motoring more often in light air. (trend towards larger engines and more tankage)

    How far does the savings in structure, deck gear, sail inventory and auxiliary power go towards offsetting the added cost of a tapered mast?

    Could tapered mast fractional rig boats be built to be price competitive with the boats with the cheap and simple masthead rigs we've seen for years?

    It would seem that the relative ease of use and the (probably) kinder motion of a lighter fractional rigged boat would be just as important to the casual sailor and cruiser as it is to the racer.



  10. michael pierzga
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    michael pierzga Senior Member

    If by narrow sheeting angle you implie a narrow shroud base then this is again controlled by material limitations. Enormous compression loading. Enormous strain on the hull.

    Even now with modern materials the Mega sloops face engineering challenges. Think of Mirrabella V. 100 meter tall mast. Check out the sail technology needed to achieve this !

    Height wise think how heavy traditional sail materials were. Not possible to humanly handle one big sail so they used two small sail. The weight aloft affected righting moment. The result was low aspect rigging , many masts and many sails. Need more power add another short mast. Nothing wrong with multiple masts..other than the huge windage they present.

    As far as mast taper. Obviously less weight and windage in the high wind area aloft is the goal . A fractional can go extreme taper, a masthead rig, since it has all its gear on the masthead...halyards, stays..has to leave some real estate availble to mount it...the taper cant be so extreme...hence more widage and weight aloft for a masthead rig

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