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Flat Sails are Okay - mehitabel

  • 23 Oct 2013 18:30
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    Reply # 1419786 on 490687
    Anonymous member
    US Sailing has a handy Sail Area / Displacement calculator here
  • 23 Oct 2013 17:11
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    Reply # 1419736 on 490687
    Anonymous member

    I have had a spreadsheet with the data on probably 150 boats for many years, but it has been hacked about a bit and I haven't time to tidy it up. They're mostly boats that are local to the south coast of England, but they do include quite a few 'foreign' boats as well. It is quite interesting to compare boats, so some members may want to play with it. I'm not quite sure what would be the best way to publish it, so if anyone had any suggestions then let me hear them. There are some Bermudan/ junk comparisons in it.

    Cheers,  Slieve
  • 23 Oct 2013 04:50
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    Reply # 1419434 on 490687
    Anonymous member
    David, it's a great idea, but most of our members work empirically rather than theoretically and would go cross-eyed at working out the figures (me included!). But quite a lot of profiles include the boat's displacement and sail area.

    If anyone has the energy to set up their own database of these ratios, using information already in the profiles, it would be an immensely invaluable resource, as you imply.  Once done, a space could be made in 'Profiles', the info circulated back to each member and they might then copy and paste it into their profile, for other people to access when doing research.

    I see you have ticked the box saying that you would be prepared to contribute ... :-)
  • 23 Oct 2013 04:17
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    Reply # 1419417 on 490687
    Deleted user
    Hey Folks,

    Thanks for a great discussion! It's filling in a picture that has been seriously puzzling me for years!

    One thing I note is that most of the hard data involves Beaufort numbers and knots.

    Where possible, it might help to express our speed, rather, as a percentage of hull speed (displacement hulls, our top speed in knots is about 1.33 times the square root of the active water line length, measured in feet (I apologize for the archaic Imperial formula!)), aka speed-length ratio. By factoring out length induced speed differences, we can compare rig advantages more meaningfully.

    For example, a boat with a 36ft heeled waterline would have a hull speed of 9kts. If my flat cut sail drives us to 3kts in B2 wind, I'm doing 33% of hull speed. Now  I can compare with a cambered rig on any sized boat, which might be driving its hull at higher percentages, and weigh up the advantages.

    Another common number that is helpful is the SA/D (Sail Area to Displacement ratio, calculated as sail area in square units, divided by hull displacement in cubic units to the 2/3rds power... the units cancel out). This gives us an at-a-glance indicator as to how much sail is (potentially) driving how much boat, and helps inform our comparisons.

    For example, a boat with a higher SA/D number has an advantage over one with a lower number. This should be taken into account when comparing the relative performance of their sails.

    Each boat will have a hull speed and SA/D ratio, but it gets tedious stating them with every comment... maybe they could be calculated (optionally) once for each vessel, and included in member profiles?

    Thanks again for a great discussion!

    Dave Z
  • 13 Jan 2011 05:48
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    Reply # 494796 on 494708
    Anonymous member
    Brian Kerslake wrote:
    Several years back my wife and I left Sines, West Portugal in our Sunbird 32 schooner 'Matanie' (25 year-old flat junk sails) in company with two sailboats also from Penryn, Cornwall....

    It will be interesting to do it again with the cambered panels which Chris Scanes is making for our 1988 Freedom 39 Pilothouse Schooner, 'Paradox'. I'm sure we'll be glad of the promised better windward performance when we again experience the inevitable sloppy seas and light winds of the Algarve where we often had to use the engine more than we wished. 
    No doubt the junk rig sailors had the best time with changing conditions and sail adjustments on that trip, and as usual. I would like to be able to compare such varied experience as yours to our present boat and rig, and hope still to be satisfied... When you have enjoyed your new rig on 'Paradox' I trust you'll let us know how good.
    Thanks,
    Kurt 
  • 13 Jan 2011 01:32
    Quote
    Reply # 494708 on 490687
    Deleted user
    Several years back my wife and I left Sines, West Portugal in our Sunbird 32 schooner 'Matanie' (25 year-old flat junk sails) in company with two sailboats also from Penryn, Cornwall. We'd met them from time to time on the way south, and we all left Sines at about the same time. Soon after the 0530 start the wind came up from the N or NW force 3-4 occasionally 5, with a growing swell on the starboard quarter.

    'Matanie' sailed all of the way to Cabo St Vincent - 70 to 80 nm - and round the corner. The 37-foot ketch motor-sailed (just the main) from mid-morning, all afternoon and into the evening - more comfortable, they said later. The 30-foot steel gaffer did the same, flying her topsail until it was too much to handle, and reefing and unreefing main and jib now and then - hard work. We had one panel down in each sail in the morning, with the foresail hauled tight to the centreline to counter rolling, and two down in each, just in case, as we eased sheets to round the Cape. All the way down the Portuguese coast most bermudan-rigged boats motor-sailed, as did the very few that passed us going north.

    Our friends in the 'big' ketch got into Lagos (15 or so nm east of the Cape) in time for dinner ashore, as planned. We and the gaffer anchored in Baleeiraa, just round that very big corner, as planned. We got in first.

    Which of these three boats had the most enjoyable sail, and didn't need to reef further as it rounded Cabo St Vincent, where the wind gusted to 30-35 knots for perhaps 20 minutes? We just eased our sails, knowing we could quickly reduce sail if we needed to. And next morning, when a threatening swell came into the anchorage (while the wind still blew offshore) and quickly rose high while windsurfers circled us, we sailed out under foresail only with the engine ticking over. It felt like cheating.

    It will be interesting to do it again with the cambered panels which Chris Scanes is making for our 1988 Freedom 39 Pilothouse Schooner, 'Paradox'. I'm sure we'll be glad of the promised better windward performance when we again experience the inevitable sloppy seas and light winds of the Algarve where we often had to use the engine more than we wished. 
  • 12 Jan 2011 18:40
    Quote
    Reply # 494369 on 493646
    Anonymous member
    Slieve McGalliard wrote:

     

    ...There doesn’t seem to be the same following for the more complicated rigs of the ‘90s, with their multiple running lines and adjustments. The hinge battens do not seem to be recommended, particularly the commercial ones which have a habit of breaking.

     

    ...

    If sailing to windward and sailing at the speed of the flat sail there should be less heel.

    If sailing to windward with the same heel as the flat sail the speed should be higher.

    ...

    The camber does not only affect windward performance. There is more forward directed drive and speed on all points of sail up to the dead run when the sail is fully stalled.

     

    ...

    Possibly the most significant point would be the affect in light winds....Please remember this is referring all points of sail.

     

    ... 

    The beauty of the cambered sail is that you have the choice to sail as a flat rig or faster, and all with the same ease of handling, reliability and durability.

     

    ...

    Cheers

    Slieve


    Hi Slieve,

    I'm very pleased that another pioneering camber guru has written - and you're devilishly convincing.

    There's nothing that can't be improved. When I'm tempted to experiment, especially if it means cutting sails apart, however, I end up asking myself, 'What's wrong with what we have?'

    I let cars pass me on the highway, all the time.

    But I'm human... I will very likely continue, as I do in odd moments, sketching battens that will easily adopt a smoothly-curved camber on either tack and that won't require changes to our rig, and are tough-as, and replaceable with straight battens.

    Flat sails are okay. Curved sails are better. It's human nature to strive for that top few percent. Well, several percent...

    Regards,
    Kurt
  • 12 Jan 2011 00:04
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    Reply # 493836 on 490687
    Anonymous member

    Thanks for the quick reply Tony. Interesting. I've always felt it was an under used control. I feel they are an essential part of my rig, even if they are only tensioned with a hand tug.

    Cheers,  Slieve
  • 11 Jan 2011 22:11
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    Reply # 493758 on 490687
    Deleted user
    HI Slieve, Ron Glas is still rigged exactly as you have stated!! we have not changed vanything as yet partly because we are founder members of the flat earth [sail] society and partly because we headed off cruising as soon as we had her seaworthy. DOWNHAULS---- a lot of extra line when making sail but brilliant when reefing in rising winds . When reefing its great to be able to hoist reefed sail against a tight downhaul. also great to help haul down that big main if the wind is still in the sail. its possible [tho not fun] to haul the main down running downwind in fresh winds .on the down side they add extra friction when making sail. on balance I would not do without them. tony
  • 11 Jan 2011 21:14
    Quote
    Reply # 493689 on 490687
    Anonymous member

    Hi Sally and Tony (Ron Glas)

    According to PJR your ‘

    Grade One Listed Monument ’ is rigged-

    “Two-masted Chinese schooner rig designed by McLeod. Tapered hollow timber masts. Total sail area 810 sq ft (75 m2).

    MAINSAIL. 540 sq ft (50 m2). Aspect ratio 2.2. Yard angle 70°. Five-panel parallelogram with two-pane fanned head, total seven panels. All battens the same length. Balance 10 per cent at batten 3. Six-part single sheets with three two-point spans. Top batten not sheeted. Long batten parrels. Luff hauling parrel. Batten downhauls. Fixed gallows.

    FORESAIL. 270 sq ft (25 m2). Aspect ratio 2.2. Yard angle 70°. Five-panel parallelogram with two-panel fanned head, total seven panels. All battens the same length, Balance 10 per cent at batten 3. Six-part single sheets with three two-point spans. Top batten not sheeted, Long batten parrels. Partial standing luff parrels. Batten downhauls.”

    I would be pleased if you could comment on any changes you have tried or made on a permanent basis, and in particular would like to know if you still use the downhauls. If so, how are they rigged and how do you use them? What effect do they have? I am asking as I believe they are not generally shown the respect they deserve.

    Cheers,  Slieve.

     
       " ...there is nothing - absolutely nothing - half so much worth doing as simply messing about in junk-rigged boats" 
                                                               - the Chinese Water Rat

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