Skinny Class 40

Discussion in 'Boat Design' started by Paul Scott, Jan 16, 2023.

  1. Paul Scott
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    Paul Scott Senior Member

    Working at a high level with talented folks can ;) be life at it’s best.

    Your presentation does beg the question (again;)) of why windsurfers are so fast- the d/l is abysmal, and the sail area/displacement not so great. Sail area/wetted surface is good, control of the board’s interface with the water is more than any other sailing craft, and the interaction of sail to the hull’s interface (sic) has a lot of independence, as well as a balance of forces. How much does a stayed rig control hull hydrodynamics/drag? Every once in a while, in light airs, say 3-5 knots on Amati, on a tight reach, with no heel, no weather helm, with blade and jib, she’ll just take off effortlessly to 7 knots or so. It’s the closest I ever been to D2 or Serenity board feel in the same conditions. The same once sailing by the lee in 25-30k, and we sustained ~22k for 20 minutes, no weather helm, in a 3-5 chop against tide. Amati was doing the windsurfer thing, seemingly skipping from wave to wave, no nose diving. Full main only. The feeling of balance was smooth, no brutalities. Llord does point out that even a heavy planing hull will be faster in these conditions, IIRR, because of wetted surface reduction. Perhaps the scow or wider hull changes the center of lateral resistance that even to a small extent, and there is more balance between the sail and hull? And even with more wave resistance, it’s faster? Although if that’s right, Myszek’s narrow scow might have some advantages beyond wetted surface and wave penetration, giving more balance between sails & hull, especially with a flatter hull, which would mirror some slab sided windurfers. Van de Stadt designed some single mainsail keelboats that had what was in effect a freestanding mast with a kink in the bottom part of the mast so the mainsail moved to weather when going downwind- voila! A moving center of effort! Would that work within open 40 rules and shrouds? I think VdS’s open 40 was considered fast(mid to upper 20 k?), although with the experimental auto pilot, there were a lot of things going on. Here are some images IMG_1234.jpeg IMG_1214.jpeg IMG_1225.jpeg IMG_1229.jpeg IMG_1226.jpeg IMG_1222.jpeg IMG_1221.jpeg of 2 of his designs.
     
  2. Paul Scott
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    Paul Scott Senior Member

    Although Newick’s Ocean Surfer did take a stab at a canting mainsail with shrouds on Ocean Surfer- I talked to a guy who sailed on her, and he said when the main was canted, things got light- :rolleyes: The track you see in the pic was for the mastbase- apparently things could get sticky….

    IMG_1578.jpeg
     
  3. Alan Cattelliot
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    Alan Cattelliot Senior Member

    There has been several different built -proto & serie- based on the 'MAGNUM". As far as I know, the serie version are in glass, while the custom are "full" carbone.
     
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  4. myszek
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    myszek Junior Member

    It's interesting to compare windsurfers with Class 40 boats.
    Funny thing, windsurfers appear to be a 1:3.5 scaled 40's. If we scale Class 40 boat by a factor about 3.5, we obtain approximately
    • length 3.5m
    • weight 110kg
    • mast height 5m
    • sail area (basic) 9m^2
    So far, so good. But also
    • width 1.3m which is much more even than Formula Windsurfing
    • righting arm 30cm, which is at least two-fold smaller than available for windsurfers
    And the speeds scale like a square root of length, so if an original 40 is sailed at 6m/s wind, then the scaled one would sail at 3.2m/s. That's no fun for windsurfers, nobody sails in such a light air.
    On the other hand, windsurfers with a 9m^2 sail can sail at 20kt of wind. When scaled to Class 40, it would be 37kt, i.e. force 8.

    Conclusion: despite the geometrical similarity, windsurfers operate at much stronger winds and much higher speeds than 40's. They can, thanks to the mush bigger righting moment. And obviously, they operate in the full planing mode.

    ***
    I always liked single mainsail rigs, but in Class 40, rotating masts are banned, canting masts are banned, mast fairings are banned, double-skin sails are banned, fixed stays are mandatory... so it seems that the rig other than a classical main+jib+gennaker does not make any sense.

    regards

    krzys
     
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  5. skaraborgcraft
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    skaraborgcraft Senior Member

    I think its probably a good thing as it helps to keep costs down. Even racing a Mini has become an expensive proposition, without sponsorship.
    I see there are Class 40 boat in the Solo Globe currently underway.
     
  6. myszek
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    myszek Junior Member

    You are probably right. I guess this is also the reason of the upper limit for 90deg stability (it prevents using extremely lightweight masts and hull structures to increase the bulb weight).

    Anyway, my point here is, that one cannot experiment with non-standard rigs in Class 40. Even deck spreaders are banned there.

    regards

    krzys

    ps. it's however a topic for a long and interesting discussion, whether any unusual rig can be really more expensive than the standard Bermuda one
     
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  7. Paul Scott
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    Paul Scott Senior Member

    The class is messing with a lot of spreader combos, which may lead to something more interesting. Anyway, free standing rigs have a lower cg, which begs the question of how high shrouds need to go- as in how much freestanding mast above the top spreader is ok? Are aero Gunter rigs allowed?

    The question of rig tech does save $$, but if you add sails into the equation? The Open 40’s can have a LOT of sails- brute force for light airs can make up for a lot, but the resulting low aspect sails do have a lot of drag. Any class 40’s using Yankee style code zero light air jibs?
     
    Last edited: Jan 15, 2024
  8. Paul Scott
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    Paul Scott Senior Member

    I was being a bit tongue in cheek about formula boards :cool: for those of us who are light air aficionados, though, sailing any d2 or Serenity in light airs (even 1 knot!) was amazing- not much could touch them. The D2’s were definitely small scows. Serenity not so much… The first image is a modern d2 that is good in heavier stuff. IMG_1442.png IMG_1360.jpeg IMG_0936.jpeg
     
  9. Paul Scott
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    Paul Scott Senior Member

    Some light air boards here - the Serenity is the slender double ended one- tops out at 15 knots, but crazy good in the light IMG_1580.jpeg
    IMG_1579.jpeg
     
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  10. skaraborgcraft
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    skaraborgcraft Senior Member

    I think the above shot just confirms a single boat is a compromise, but able to perform to its peak performance in the winds and waters it was designed to do so.
    Much to be said for being able to choose which board and which size rig to suit the days conditions. I could never master turning them.....and staying on.
     
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  11. Paul Scott
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    Paul Scott Senior Member

    - wasn’t nicknamed ‘ log rolling ‘ for nothing!
     
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  12. Alan Cattelliot
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    Alan Cattelliot Senior Member

    Wonderfull collection. Is this yours ?

    Following this discussion, I've made some small drawings on the corner of my sketch book, comparing the righting arm of a Class40 and the one of a windsurf board. Not in terms of numbers, but in terms of mechanical design...There are opposite poles (quoting AdHoc, in a recent exchange about something else...:rolleyes:), one being a stable configuration, the other not a all. I wonder.... You've put on the table the question of the rig, which is in close relation with the question of the sail(s), and their shape.... I often have the feeling that there is quite a positive trim generated by most of the sails used on windsurf board. In fact, this very effect is so prominent that there are some combinations of sails and boards that simply do not fit together, while others will save you some crazy warming up of the quadriceps.

    In conjunction with the hull shape, could there be some "magical" aerodynamic effects, amplifying the plannnnnnning :D mode ?

    Another idea.... while the scow shape seems to bring speed to the monohull, what about the multihulls ? See here the picture of the Brest harbour, one day before the start of the Arkea Ultim Challenge. Razor blades every where.... Hulls are like the "toothpicks" used for high speed windsurfing back in the days.
    upload_2024-1-18_17-9-29.png
     
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  13. Paul Scott
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    Paul Scott Senior Member

    Unfortunately no, not my quiver, I wish I had pics of any of them!

    I did sail a borrowed speed stick (wow!- But boy did they disappear fast) in the 80’s, and come to think on it, there were some skinny PanAm boards early on. A bunch of ideas there that weren’t developed! I had a Ken Winner race board/funboard (production model of an early Pan Am board) that definitely rewarded (quadriceps included!) the right sail combo- this was when tight leaches were starting to fade- twitchy board in any chop, but fast in a bunch of conditions.

    I’ve been of the opinion that the square formula boards are little sail powered airboats- riding on a carpet of foam ball bearings. ;)

    Taking the notion of of sails that help planing for 40’ keelboats, perhaps the mainsail might be (is being?) used as the default high wind sail, set back even farther to match CE with planing CFloat/ center of hull dynamic lift / more hull out in front of the sail to have more leverage/lift down wind to limit pearling, which is what bigger tri racing designs seem to be doing, almost to the point that they look like iceboats from a distance in the big stuff? Which might make skinnier bows more usable (needles slicing waves again eh?), as long as they could be balanced with lighter headsails in the light, when sail handing is easier anyway. Anyway, moving back over the stern on a windsurfer made tripping over the bow less of a concern (a longitudinal lever arm to add to your sketches?), although slapping was part of it, which might even be worse slamming on a keelboat. Finot seemed/seems to go that way anyway (moving the mast farther aft). Are class 40’s allowed to use daggerboard style rudder cassettes to move CLR depending on SLR’s? Using heroically sized offwind headsails in big winds has always seemed a bit insane, but how far forward do the 40’s bring their apparent wind?

    This is turning into an ideational flow of the unconscious. :eek::confused::rolleyes:

    I suppose this revolves around the 40’s hull weight, how much and where the planing surface might be to lift that weight and surface area out of the water. But water ballast is allowed, so windsurfing hull dynamics might be relevant again? Water ballast in the bows plus light air headsails for the light stuff? We do that with water bottles every once in a while, and it works to get the stern up out of the water, and get the bow through chop more smoothly. Hood’s heavy designs were great in the light- Be the usual global design balancing act…
    How much can a class 40 skip over the waves? Amati has done it a few times…. Why is the font suddenly so small?

    :confused:

     
    Last edited: Jan 19, 2024
  14. Paul Scott
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    Paul Scott Senior Member

    Anyway, here’s something windsurfer related that might amuse, if anyone hasn’t seen already- !warning! Massive amount of historical pics- every board I’ve owned is in here-

    - a lot of info, in advert form-

    -you need to like looking at mainly planforms- (and wondering about stern shapes)

    -hours that you’ll never get back :cool:-

    Windsurfing brochures & ads ’80′s – early 2000′s (F2, Fanatic, Hi-Fly, Aquata, Bic, Magnum, Tornado, WindSpeed) part1 https://hitthewave.wordpress.com/2011/05/02/windsurfing-brochures-ads-80s-90s/
     
    Last edited: Jan 19, 2024
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  15. Alan Cattelliot
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    Alan Cattelliot Senior Member

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