Constant section masts?

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

  1. RHough
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    RHough Retro Dude

    The latest masthead vs fractional thread has got me thinking and googling for a few hours ...

    I still have some questions.

    When did the first masthead rigs appear?

    When did alloy extrusions come into use?

    When did the first untapered mast appear?

    My gut feelings are ...

    The area distribution of large main and small headsails comes from gaff rigs with short masts.

    A gaff rig with a topsail is very much like a leg o' mutton fractional rig.

    Sometime after the advent of rating rules and development classes the most effcient use of area was found to be a large main and small jib.

    Sometime (after WWII?) alloy masts replaced wood.

    The IOR rule (1969?) did not rate actual sail area, just the triangles. The IOR rule favours masthead rigs.

    The questions become:
    Were masthead rigs favoured or competitive before the IOR rule?
    Did constant section masts appear before or after the IOR rule?
    Is thers a reason to use a constant section mast other than ease of construction and lower cost?

    I wasn't born until 1952 to I'm not old enough to remember much before the IOR rule.

    Anyone have some insights to share? or some links I may have missed?

    Thanks!

    Randy
     
  2. Perm Stress
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    Perm Stress Senior Member

    "The IOR rule (1969?) did not rate actual sail area, just the triangles".
    Actually not.
    1) IOR Rule just assume by default a 150% genoa, and count jib area based on this.
    2) for mainsail, IOR heavily penalize any over-length in battens and limit some girths.


    "The IOR rule favours masthead rigs."

    1) In IOR, for rated area calculation, foretriangle with 150% overlap is counted with factor of 1, while mainsail is counted with factor of 0.5. So, here fractional rigs are very heavily favored.
    2) spinnaker area is limited by some proportion to fore triangle area; any surplus is penalized out of proportion. At this point, masthead rigs look favored. However, with really big foretriangle (~1.5 times the area of main triangle), maximum spinnaker is too big, requiring to have a separate, smaller spinnaker for reaching and other than light airs work.

    "Were masthead rigs favoured or competitive before the IOR rule?"

    They were for sure competitive under old RORC rule, when overlap was "free".



    "Is there a reason to use a constant section mast other than ease of construction and lower cost?"
    I cannot think of one.
     
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  3. michael pierzga
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    michael pierzga Senior Member

    I believe the first masthead...modern masthead with multi spreader geometry was developed by Herreshoff. He developed the first mainsail track sliders . You might want to google it...long time since I read his books.
     
  4. gggGuest
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    gggGuest ...

    Scanning Uffa Fox' 1930s books fractional rigs were almost universal: the only exceptions I spotted were a few cutter rigs and mizzen masts, so I think we can assume that it was primarily a post war development. Some of the fractionals are as much as 15/16ths though.
    They certainly predate the IOR and I wouldn't disagree with the poster that blames the RORC rule. OTOH when you look at the use of masthead rigged flying jibs on cutter rigs there is an obvious evolutionary process in which a cutter with a masthead flying jib and a genoa below it has the two sails replaced by one bigger one.

    This is a very good point which might use a little expansion: in those days spinnaker poles were typically limited toJ measurement (mast foot to bow) which is of course too short for efficiency and added to rule advantages of a mastplaced further aft. Northern hemisphere dinghy classes tended to retain similar proportions: look at the Flying Dutchman for instance. Southern hemisphere dinghies tended not to, and had much longer poles: the fractional revolution ofthe 70s was started by Southern hemisphere dinghy racers.
     
  5. Crag Cay
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    Crag Cay Senior Member

    Ian Protor is always credited with being a pioneer of the aluminium mast. He won the Merlin Rocket nationals in 1952 with what is said to be the first extruded spar which he had built by Alcan. It was also tapered by cut and welding. His inspiration had come from war time service in the airforce.

    By the 1960 olympics most competitors were using spars from Proctor Metal Masts. He was certainly into yacht masts by then as well and dominated the spar market here into well into the 80s. Twelve of the competitors in the 1987 Americas Cup used Proctor masts.

    Part of his obituary:

    While Proctor's name is associated with some of the best-known dinghy designs in Britain, he is even more widely known as a mast-maker. Proctor believed that the way forward lay with tapered aluminium alloy masts, extruded, or drawn out, rather than cast in a mould. This technique meant that a mast could be produced with a bend in it that would marry with the shape of new sails with curved rather than straight edges. He experimented with two masts, one for his Rocket, one for a National 12. After some setbacks, he persuaded what is now a division of British Alcan to manufacture what became known as the 'bendy' mast.

    The business that was started has supplied everyone from local dinghy sailors to round-the-world and America's Cup yachtsmen. Proctor was a director of Ian Proctor Metal Masts from 1959 to 1986 (and chairman of the company for most of that period). He remained fascinated by the design detail throughout, but latterly he largely left the running of the business to others.
     
  6. Milan
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    Milan Senior Member

    When looking at the traditional rigs, we should keep in mind materials limitations. In the time of stretchy sail material and stretchy (rope) rigging, luff of the bigger fore sails couldn’t be kept tight, so their efficiency suffered. They were also more difficult to handle without winches.
     
  7. michael pierzga
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    michael pierzga Senior Member

    Material limitations were the sole reason behind the low aspect ratio, multisail rigs of the past. They were designed to get the most out of the materials they had.
     
  8. RHough
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    RHough Retro Dude

    WOW Great information here.

    The materials limitation is one I had neglected to consider. The taper comes from material for sure, trees taper thus solid wooden masts taper. The exception is a gaff rig mast that is constant section below the throat and tapers above. (Mast hoops work better on a constant diameter.)

    Although I don't agree that they were the sole reason for low AR rigs. Material limited single sections for sure but multiple sections allowed tall (and adjustable) rigs. Square rigged ships are the obvious example.

    Gaff Cutters are another very elegant example of a variable rig. Heavy air (winter?) rigs were simple gaff rigged sloops. The Jib flying from the headstay at the stem to the masthead and the gaff brought the peak of the sail above the masthead. The light air (summer?) rig added a bowsprit and topmast. The inner forestay went to the end of the bowsprit and some boats had outer forestays running to the topmast. Now the boat could set a Gaff Topsail, and one or two flying jibs. The modern equivalent would be sailing with a reefed main and staysail for the "winter rig" and full hoist main and masthead flying jib for the "summer rig" without the advantage of reduced weight aloft and at the stem or the benefit of the much larger foretriangle the bowsprit provides.

    Michael also brings up the multiple spreader rig.

    AFAIK The main reasons for multiple spreaders are height of rig compared to shroud base and the ability to use smaller sections.

    Was increased rig height the driving reason?
    Was reducing the mast section the driving reason?
    Was sheeting angle for Genoas the driving reason?
    Combination of these?

    The change from mast hoops to slides also eliminates the need for a constant section round mast, allowing oval sections and full taper. Pretty smart guy.

    R

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  9. michael pierzga
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    michael pierzga Senior Member

    Less mass aloft, less windage, great sailshape control , ever taller masts are all tied to the development of modern materials. When I first started out as yacht captain the only way to go international on the sailing yachts was to work the international ocean racing scene. Spent 15 years on the race boats and the equipment nice cruising yachts use today is lighter and stronger than anything the grand prix yachts of the 70s and 80s could achieve. Material advanced. Simply look at modern fabric rigging ? we were using lenticular rod. we used to acid etch the mast walls of aluminium masts to remove weight. wire halyards ????? primitive.

    The old guys were smart also..they just couldn't achieve it with available materials.

    It fun to read the classic views on rigging and masts by Rod Stephens . have a read...everything makes sense.

    http://www.sparkmanstephens.com/yachtdesign/rodstephens_book/RAS_On_Sailing_Master.pdf
     
  10. michael pierzga
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    michael pierzga Senior Member

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  11. gggGuest
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    gggGuest ...

    Maybe so, but I have in front of me Uffa Fox 1936 book Sail and Power, and every wooden mast in it is hollow and built up from pieces longitudinally, some two halves, some 4 pieces some more. The wooden masts in those days - or at least the top end ones he describes - were tapered at the bottom as well as the top. That was of course before kicker/vang loads.

    In the above Uffa says that sheeting angles is the key reason for multiple spreader rigs. He has a drawing of 16 rigs from J Class through to I14s and Canoes, and they are, with one exception of a gaff cutter, all two or three crosstree rigs. Even the I14 has three crosstrees!

    Uffa also says [to predict the future] would be fatal, as a mast or anything else constructed in this world depends entirely on the materials at the builders' disposal.
     
  12. TeddyDiver
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    TeddyDiver Gollywobbler

    Disagree.. It was merely the limitations what the crew could handle safely..
     

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  13. RHough
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    RHough Retro Dude

    What was the section on the built up masts in the 30's? Round or Oval? My ever failing memory tells me that as long as mast hoops were used, the luff section of the mast was round and constant OD.

    Thanks for the info about sheeting angles. That was my memory also.

    R
     
  14. TeddyDiver
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    TeddyDiver Gollywobbler

    Skene's describes all kinds of sections.. much more than used commonly today..
    round, oval, square, triangular, octagon etc..
     

  15. RHough
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    RHough Retro Dude

    :)

    and that was a moving target!

    I seem to recall reading that one of the many reasons to change from square rigs to fore and aft rigs was that the crew per area ratio was half on a fore and aft rig. The numbers were 1 per 300 ft sq for a square rigged boat and 1 for 600 sq ft for a fore and aft rig IIRC.

    R
     
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