The Nacra 5.0 mainsail has a 5 hole adjustable clew plate as it is a boomless rig. Hook the mainsheet system to the front hole and you pull more on the foot than the leech reducing draft and power for higher wind conditions. Hook the mainsheet system to the back hole and you pull more on the leech than the foot increasing draft and power for light wind conditions. With the adjustable clew plate concept it is my understanding that no matter what hole you hang the mainsheet system from (even the back hole) the mainsheet system should be angled forward, bottom to top. Said another way, the back clew plate hole should between the mainsheet traveler track and the mast such that you are always pulling, at least slightly, on the foot.

I have recently encountered a sail where this is not the case. The back clew plate hole is astern (in back of) the mainsheet traveler track even with the mast straight up (no rake). This means that you would pulling no tension at all on the foot and in fact be compressing the bottom batten, when close hauled. I don't think this is correct and would like to check it.

If some of you would be so kind please check the dimensions A and B shown in the pic below and post your findings here. Please also note the loft that made your sail and it's approximate age.

A: the dimension from the clew plate middle hole to the back hole (center to center).

B: the dimension from the back of the mast luff track to the center of the middle clew plate hole, basically with your sail up hook a tape over the front edge of the batten cap and measure to the center of the middle hole.

The second pic shows my sail and the sail in question on my boat. The mainsheet system is hung in the rearmost clewplate hole on both sails.

Further I welcome any comments relative to boomless rigs on other boats and whether the clew plate location arrangement I have outlined above is correct.





Thanks in advance.



Edited by leeboweffect on Jul 23, 2017 - 03:17 PM.

--
Hobie 16 (3 formerly)
MacGregor 25 (formerly)
Chrysler Dagger 14 (formerly)
NACRA 5.0 (currently)
High Point, NC
--

i'm not a boomless sailor - but your arguments seem legit to a degree (no pun intended)

sans boom, you probably do want a little more angle to help push your sail forward, induce rotation and increase draft -

you could fix this by a. drilling a new hole in the back of the plate in question - looks like there is room or b. add a forward facing rotation inducing arm so you can control your sail better

leeboweffect

This means that you would pulling no tension at all on the foot and in fact be compressing the bottom batten, when close hauled. I don't think this is correct and would like to check it.

This could well be an intentional geometry.
In light air, the "batten compression" force would increase the draft in in the foot of your main.
Boomless, there is no other way to induce this in light air (short of bungees pulling from the mast).
So the back hole is intended specifically for light air, and you use the forward holes for other points of wind. And its up to you to determine which one gives you the correct sail shape for your situation.
Have you talked to a NACRA sailmaker about this?



Edited by klozhald on Jul 24, 2017 - 07:43 PM.

--
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
--

Thanks MN3, but,

MN3

sans boom, you probably do want a little more angle to help push your sail forward, induce rotation and increase draft -

I certainly understand your thought on the geometry, but my concern is the opposite. What if you can now not flatten the foot sufficiently in high wind conditions. I have seen 3 sails now with the clew plate in the position of sail #1 and all I'm trying to understand is why did one sail maker move it back changing the lead angle from 90 to 95 degrees. If it was intentional based on experience and issues with the more forward location great, but it could just be a measuring error.

Thanks klozhold.

klozhold

Have you talked to a NACRA sailmaker about this?

Not yet as I was hoping to get more information from this post such as to have a meaningful dialog. Please again note, I'm not saying the clew plate location on sail #2 is incorrect or wrong I just want to determine if it was done intentionally or not. Every boomless rig I have ever seen wears the geometry of sail #1.



Edited by leeboweffect on Jul 25, 2017 - 08:02 PM.

--
Hobie 16 (3 formerly)
MacGregor 25 (formerly)
Chrysler Dagger 14 (formerly)
NACRA 5.0 (currently)
High Point, NC
--

The clew plate itself is a very universal part and is not specific to the application. The sail maker has a window of room to install the plate. Its easy to consider that the plate itself has a larger range than would prove useful on your sail. I would not get hung too much on which specific holes relation to another sail.

--
Greenville SC

Offering sails and other go fast parts for A-class catamarans
--

Thanks bacho. Here's what the geometry looks like with the mainsheet system in the front clew plate hole for both sails.



--
Hobie 16 (3 formerly)
MacGregor 25 (formerly)
Chrysler Dagger 14 (formerly)
NACRA 5.0 (currently)
High Point, NC
--

leeboweffect,
i have owned 3 nacra 5.8's which were boomless sails. i had 3 fixed plate sails and one with an adjustable traveler. my memory was that when i hooked that back hole, the sail had 'major' draft in it, so i'm not sure all holes were 90d or forward of the rear beam. i obtained my top speed ever when using that back hole and 2 guys out on the wire in winds that were close to 14 knots.

Quote

Said another way, the back clew plate hole should between the mainsheet traveler track and the mast such that you are always pulling, at least slightly, on the foot.

also, you're just considering the angle when the sail is straight back, mid-tramp with the traveler centered. when the main is traveled out or 'eased', the angle would not be backwards 95d as your picture shows. so you would be pulling slightly rearward on the foot at any other position than 'midships'.

in 'super-light' to almost no wind, a flat sail works best because there isn't even enough breeze to create any shape (draft) in the main.

here is a side view of one of my 5.8's. imagine the traveler at the leech position and it's 'backwards' too.


are you sure that main came from a 5.0?
j

--
Aquacat 12 (sold)...'87 Nacra 5.8 (sold)...'03 Nacra Inter18 (sold)
Venture 15 (sold)....'89 Nacra 5.8 (sold)...'91 Nacra 5.8NA (sold)
'99 Nacra Inter20 (sold)
--

Great input and photo arch. Yes, I get it that when off center and sail filled the angle would be less than 90 deg.. Just asking a simple logical (to me) question as folks generally don't change things without reason. All I'm looking for is the reason when 3 other sails I've seen have the clew plate located like sail #1.

I was hoping that someone would offer up a technical piece on boomless sail design theory. I checked what I have on my shelf to no avail.

The Art and Science of Sails - Whidden

Sail Performance : Techniques to Maximize Sail - Marchaj

Your photo is great and provides an example that the over 90 deg. geometry has been done and that's an older pure Skip Elliott (older as in no Pattinson pure green griffin) sail (assuming the adjustable track wasn't added Xworks).

arch

are you sure that main came from a 5.0?

100%

--
Hobie 16 (3 formerly)
MacGregor 25 (formerly)
Chrysler Dagger 14 (formerly)
NACRA 5.0 (currently)
High Point, NC
--

This adjustment is also useful for downwind vs up wind sailing, for downwind the sail is more open so as said above the logic is different. With an adjustable system it makes more sense but for a long downwind distance and if you have a hook to change position quickly, it may make sense too

I have been following this thread because I sail a Nacra 450 which is boom less and I am never 100% sure I am using the right spot on my clew plate for the prevailing wind conditions. Anyone have a good rule of thumb??

--
Pete
2001 NACRA 450 SOLD
2000 NACRA 500 TOTAL LOSS
2004 NACRA INTER 20 SOLD
2016 NACRA 500 Sport
DeLand, FL
--

Well for me,I put it in the middle and forget it. There are many more areas of improvement in my sailing to worry about than this one. After I get myself 99% dialed in in all conditions and situations, and get everything else dialed in perfect on the boat I'll maybe think about some adjustments. Over on the Supercat site the Factory gurus seem to think it doesn't make too much difference.

--
Tim
Collierville (Memphis), TN
Supercat 15--sold :(
Hobie monocat--given
Vanguard 15--traded for...
Nacra 4.5--sold
Nacra 5.7
Hobie 14–sold to make room for...
Supercat 17–sold
--

That's pretty much me. Because of the uncertainty of it I put it in the middle almost every time and roll on. I did put it in the back once in a lighter air regatta but felt like I couldn't point as high. Any thoughts on that?

--
Pete
2001 NACRA 450 SOLD
2000 NACRA 500 TOTAL LOSS
2004 NACRA INTER 20 SOLD
2016 NACRA 500 Sport
DeLand, FL
--

saltlife77

That's pretty much me. Because of the uncertainty of it I put it in the middle almost every time and roll on. I did put it in the back once in a lighter air regatta but felt like I couldn't point as high. Any thoughts on that?

I would defiantly experiment a lot more
every time i sail on my buddies gcat he adjusts it (like a typical outhaul)

"center" hole n med air (not necessarily the center hole, but whatever he considers his center)

upwind - hooked further forward in med to med/high air - traveled centered - even more forward in heavy air (to flatten sail)

downwind - hooked back a hole in light to med air - to add draft and traveled out more

caveat: we are forever dealing with sea breeze / wind shifts / island hoping and the occasional change of destination so it's impossible to adjust all the time - its only when there is an island stop or going into heave-to to make an on the fly change

Quote

. I did put it in the back once in a lighter air regatta but felt like I couldn't point as high. Any thoughts on that?

so many variables: in some sail plans being super flat in super light (upwind) air works - old sails, different rigs, different wind.... to many variables - I would try again (keeping every other variable the same as much as possible: rig tension, crew weight, wind and tide conditions, etc)



Edited by MN3 on Jul 27, 2017 - 11:37 AM.

OK thanks for the insight. I am going to start to play around with it more often.

--
Pete
2001 NACRA 450 SOLD
2000 NACRA 500 TOTAL LOSS
2004 NACRA INTER 20 SOLD
2016 NACRA 500 Sport
DeLand, FL
--

saltlife77

OK thanks for the insight. I am going to start to play around with it more often.

cool - and arch's comments above seem to be right on and he has lots more boom-less experience than i

saltlife77

I have been following this thread because I sail a Nacra 450 which is boom less and I am never 100% sure I am using the right spot on my clew plate for the prevailing wind conditions. Anyone have a good rule of thumb??

For upwind and particularly upwind in high wind hang your mainsheet more forward (towards the mast). For downwind and particularly downwind in light wind hang you mainsheet more to the rear (away from the mast). As it seems we are learning here the optimal settings to use are very boat and geometry dependent, front hole your boat may not be front hole on another 450 if the sailmaker moved the clew plate.

Note that this adjustment is a finesse thing and if all your doing is day sailing put it in the middle and forget it.

--
Hobie 16 (3 formerly)
MacGregor 25 (formerly)
Chrysler Dagger 14 (formerly)
NACRA 5.0 (currently)
High Point, NC
--

Quote

particularly upwind in high wind hang your mainsheet more forward (towards the mast).

i whole-heartedly agree with this statement. i can attest that the sail is 'flatter' and spills a lot of excess wind when it's blowing hard. the difference of staying in control or white-knuckle 'losing it'.

FYI, i've begun keeping the main sail sheeted in and more centered downwind instead of far out to the side. it keeps the sail away from chafing on the shrouds and honestly, i don't really notice that much of a speed difference, plus it allows some wind to reach the jib too. it's all very dependent on the angle i'm sailing too.

at the expense of being too blabby, i'll relate another reason why i don't ease the main out really far on the downwind leg. years ago, in heavy wind, i gybed and when my sail went from far starboard to far port, i watched it hit the shroud and break 5 of the battens. so now when i gybe, i gradually sheet the main toward the center so it only swings slightly across, and under control.
j(a control freak)



Edited by arch on Jul 27, 2017 - 11:32 PM.

--
Aquacat 12 (sold)...'87 Nacra 5.8 (sold)...'03 Nacra Inter18 (sold)
Venture 15 (sold)....'89 Nacra 5.8 (sold)...'91 Nacra 5.8NA (sold)
'99 Nacra Inter20 (sold)
--

Quote

Note that this adjustment is a finesse thing and if all your doing is day sailing put it in the middle and forget it.

That's been my motto...even in the few regatta's I have entered. Seems to difficult to adjust on the fly so I set it in the middle on the beach and go with it. Thanks.

--
Pete
2001 NACRA 450 SOLD
2000 NACRA 500 TOTAL LOSS
2004 NACRA INTER 20 SOLD
2016 NACRA 500 Sport
DeLand, FL
--