Noobie raising the main sail question.
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Posted: Oct 05, 2020 - 05:26 PM
Ok, I see your point now. But would you agree that most of the load is used to bend the mast rather than taking wrinkles out? If so, you start from a needed load being the same in all configurations, which divided by 2 or by 1.5 will give the resulting sail tension (assuming that the halyard goes down through the mast track). Therefore the standard configuration would be better for the sail than the one with purchase, for the same desired mast bend.
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Posted: Oct 05, 2020 - 05:44 PM
On the other hand, If the halyard will be in front of the mast, you want less tension there than in the sail to allow for mast bend. Therefore case 2 is worse than case 3 but better than case 1. -
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Posted: Oct 05, 2020 - 05:57 PM
on a mast with diamond wires and prebend cut into the luff- yes
agreed - that is why you use a hook and downhaul
this example was to illustrate why not to take the mast off the hook - it adds compression to your mast
I use this when i reef my main - i lower my main a few feet and reduce the sail area a bunch by furling the unused bottom panel so the 1.5:1 + less sail area = about the original amount of force on the mast/sail -
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Posted: Oct 06, 2020 - 07:01 AM
"take the wrinkles out" is the minimum cunningham tension, only appropriate for light winds. It makes your sail as deep as possible.
As the wind gets stronger, you start tensioning the cunningham further to flatten the sail. Don't be afraid of maxing it out. Do it on land - look at the sail and mast with both minimum cunningham tension ("wrinkles out") and max tension. Look at it from 20m from the boat, sideways, you'll see a straight mast vs a curved mast.
Look at it lying down on the trampoline, looking up to the top of the mast. You'll see the battens show a deep curve, vs almost straight. -
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Posted: Oct 06, 2020 - 04:40 PM
Yes, it's clear, I wasn't questioning the need to crank the cunningham. Anyway, the original question has been answered, not a good idea to get rid of the hook. With some purchase perhaps less likely to break something but not meaning it's a good idea.
Edited by Andinista on Oct 06, 2020 - 04:43 PM. -
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Posted: Oct 06, 2020 - 05:12 PM
Maybe I am wrong about this or maybe my 18-2 has been modified but it does not seem to have a Cunningham. While I have been on some boats that used one I have never owned a boat that had one. Seems to me if I crank the down haul and out haul as much as possible it sorta acts like a Cunningham in flattening the sail. On the other hand I have never really sailed the 18-2 in over ten knots; and realistically not over eight knots so I usually set the boat up with a the down haul and out haul not cranked down a lot so the sail is fuller.
So in addition to the original question about beach cats using a hook and ring to raise the main I am also asking which beach cats do, or do not, have a Cunningham. -
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Posted: Oct 06, 2020 - 06:21 PM
Cunningham and down haul are the same thing, to tension o the main straight down at the mast base -
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Posted: Oct 07, 2020 - 02:38 AM
In addition to my previous post, even my customized halyard system uses the hook. It would be dump to leave it out. But at the 5.0 the original Cunningham is relatively weak (3:1) and very poorly described in the vintage manual.
I'll build a bracket which holds three pulley, add two swivel cleats and than have an strong 8 or 10:1 translation which should work way better. -
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Posted: Oct 07, 2020 - 03:38 AM
Google says there are subtle differences, downhaul is apparently a more generic term for a system to tension the luff by pulling either the sail directly or the boom (boom vang is something else though), whereas Cunningham refers to the specific case where you tension through the tack or a secondary grommet on the sail. On beachcats I don’t think there’s any practical difference on the final effect.
Edited by Andinista on Oct 07, 2020 - 03:42 AM. -
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Posted: Oct 07, 2020 - 10:15 AM
If you add a cascading element you might save some blocks. Here for instance, there are two pulleys for a 4:1 system. Not tu suggest that same configuration but to illustrate the idea.
https://www.harken.co.uk/content.aspx?id=3898
Edited by Andinista on Oct 07, 2020 - 10:16 AM. -
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Posted: Oct 07, 2020 - 02:31 PM
A Cunningham is an old concept, and in practical use is a compromise at best.
It pulls down on the sail from a weaker location, above the tack, which is really the definition of a Cunningham.
It was replaced by the downhaul on beachcats because the designers realized the worth in having a powerful downhaul shaping the entire sail from the tack, AND they made room for attaching the blocks to the mast at the bottom (instead of the deck plate) to allow the mast to rotate.
The Cunningham was an add-on in concept and design, that was seldom challenged or changed until Hobie Alter.
The monohulls that need a Cunningham frequently have a fabric halyard holding the sail up, which stretches and needs to be tightened when the wind comes up with a winch and a crank handle, etc.
Beachcats have powerful mainsheets, and downhauls.
If I need more downhaul, my crew uses one arm and pulls, just like it was designed to work nearly four decades ago.
The word Cunningham gets batted around in the catamaran world a little more now because the America's Cup and Olympic NACRA 17s brought cat sailing a little closer to mainstream conversation, and the monohull sailors use terms that they are comfortable with. Even some catamaran manufacturers have recently used these mis-terms in their sales pitches to try to breed familiarity (internal mast "Cunningham").
This is why you get weird looks when you say Cunningham to a beachcat sailor. It is not a familiar term.
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Sheet In!
Bob
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Prindle 18-2 #244 "Wakizashi"
Prindle 16 #3690 "Pegasus" Sold (sigh)
AZ Multihull Fleet 42 member
(Way) Past Commodore of Prindle Fleet 14
Arizona, USA
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Posted: Oct 09, 2020 - 11:59 AM
Good explanation! My first sailing experiences was on a O'day 25 Cruiser, which had a cunningham. Fast forward 10 years to my first beachcat, a Hobie 18, and I'm looking at the downhaul thinking WHT is this thing for? Lol.
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Tim Young
Hobie 18' + other stuff that floats and goes.
Kentucky
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Posted: Oct 14, 2020 - 06:15 PM
Gee, I have this moment at least once a day.
Glad to hear someone else does too!
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Sheet In!
Bob
_/)_____/)_/)____/)____/)_____/)/)__________/)__
Prindle 18-2 #244 "Wakizashi"
Prindle 16 #3690 "Pegasus" Sold (sigh)
AZ Multihull Fleet 42 member
(Way) Past Commodore of Prindle Fleet 14
Arizona, USA
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