retrofit mast rotation and boom Nacra 5.0/500
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Posted: Aug 24, 2020 - 10:45 AM
The easiest way to get rig tension when you are by yourself through the headstay. Have a shackle or a ring at the apex of the bridle and a bow shackle at the end of the headstay. Simply tie a length of 3/16 to either place and loop it around a few times to get purchase and finish with some half hitches.
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Bill Townsend
G-Cat 5.0
Sarasota
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Posted: Aug 24, 2020 - 12:10 PM
this is the Portuguese turnbuckle method (my preferred method on both my cats). lashing a line.
When i owned an h18, i rigged with a loose sidestay, hopped in my harness and adjusted my sidestay adjuster, OR i learned another method was (main up) to point bows into the wind (in the sand)- travel all the way out and sheet my main
once sheeted hard, you will have a loose sidestay: you can tighten your side stay adjuster.
caveat is to stay alert of ANY wind shifts and be prepared to uncleat the main if the wind picks up and things get silly
You can always be on the wire at the same time as an added safety measure.
Can be done in the water too - but it helps to have someone hold the bows or put them on the beach if the wind is accommodating. -
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Posted: Aug 24, 2020 - 04:19 PM
You guys are over thinking all this. Remember the old adage "if it works, don't fix it". I owned a Nacra 500 for ten years, bought new, and it did not come with any positive mast rotation device. Nacra marketed the 500 and the 570 as their "recreational boats". They are all recreational, I guess they should've touted them as their more user friendly boats and that they are with no boom, no boards, no mast rotation inducer and jib blocks mounted on the main beam. What you give up in performance you make up for in ease of rigging and handling. The boat was designed for the mast to rotate just from the pressure of the luff with diamond wires limiting the mast bend. Any additional performance obtained by increased mast rotation won't be worth having to reset the rotation device during every tack. Adding a boom will only help if the boom is long enough so when the mainsheet is attached to the rear of the boom it actually pulls forward inducing mast rotation and that would make it possible to put a much simpler rotation limiter on it. One more thing I'm not sure of is the mast bases on boomless and booms might be different. The socket where the ball fits in might be further aft or forward depending. That location would certainly have some affect. If you're real fuss an easy thing to do that will help a boomless rig in lighter airs is a camber control along the foot of the main. Basically this is a small line attached at the clew and the tack of the main with a two way fiddle block with cleat somewhere along it's length. Use this when it becomes apparent that the lower part of the main is too flat because on a boomless rig the mainsheet is pulling aft. As for me, I'd keep the 500\5.0 stock and have fun!
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Bill Townsend
G-Cat 5.0
Sarasota
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Posted: Aug 25, 2020 - 08:59 AM
all due respect: that is for the owner to decide
this is the only reason i would ever agree with adding rotation control to this boat
this is the exact reason my friend on the g-cat uses it - and it is one more step during tacking, but he is one of the fastest people to ever sail a g-cat (we sailed with the designer for over a decade) -
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Posted: Aug 26, 2020 - 11:16 AM
And how is it done, by forcing or limiting rotation? The former supposedly would reduce sail draft because the mast angle would be better aligned with a flatter sail shape, but the latter helps increasing mast bend which flattens the sail.
Assumptions:
- mast type = classic, no wing mast
- upwind sailing
Edited by Andinista on Aug 26, 2020 - 11:18 AM. -
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Posted: Aug 27, 2020 - 09:06 AM
There's been a lot of opinions on this one, only his time I have a question instead. I recently downsized from a G-cat 5.7 to a 5.0. It was a good move because I sail alone most of the time, only 150 lbs and 70 years old. The 5.0 has a boom and a mast rotation limiter. I do use mast bend to help flatten the sail. I would be inclined to use a lot more mast bend but the 5.0 lacks diamond wires. Is there any danger in breaking the mast if I let it rotate almost 90 degrees and sheet down really hard?
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Bill Townsend
G-Cat 5.0
Sarasota
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Posted: Aug 27, 2020 - 09:25 AM
Hard to tell.. I've read that mast prebend is more relevant on modern wing masts and not so effective with older ones, not quite sure though. Have you considered more purchase on the downhaul? The 5.0 comes with what, 3:1? a lot more is commonly used on many other boats. Also, the 5.0 doesn't have a boom, yours is either modified or a 5.2? -
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Posted: Aug 27, 2020 - 09:25 AM
Oh.. you are not talking about a Nacra but a Gcat 5.0 I think...sorry -
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Posted: Aug 27, 2020 - 09:47 AM
IMHO: lots of factors here make it boat specific
mast stiffness
spreaders/not (prebend)
boom/not
rotator/not
sailcut (cut for prebend or not)
Here is some data i found on this site that seems to give some insight here:
"Loose diamonds and use mast rotation to allow bend along minor axis (sideways). When mast is rotated near 90 degrees, it will easily bend sideways and flatten the sail. Reducing mast rotation aligns major mast axis with the sail and keeps it full. Downside to this is the bottom of the mast can bend into the slot between the jib and main.
Pre-bend is the other method. Set spreader rake about 2-3 inches and tighten diamond wires extremely tight. Get a loose gauge to measure it. Then use downhaul to bend the mast back along its major axis. The tight diamonds keep the mast from bending into the slot. It also allows the top to twist off during a gust."
I hope someone with better theory knowledge will pipe in but it is my understanding inducing heavy rotation will flatten the entire sail and allow the mast to bend
as cunningham (downhaul) will bend the mast to match prebend cut into the luff and will flatten the sail mostly at the top and allow more twist -
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Posted: Aug 27, 2020 - 01:15 PM
Could you post some fotos of your rigged boat? Would be great so see how its made.
The bend thing: when sailing in double trapeze conditions I increase the spreader rake. This hasn't that much impact on the visible sail shape but huge impact of what I can handle. More prebend takes huge loads of power and allow to sheet in very hard. This also is extremely necesarry because the mainsheet is the most powerful method to get the sail flat.
Anyway I will make some changes to the boat over the offseason and I'll share it with you guys.
Edited by hannes-neo on Aug 27, 2020 - 05:25 PM. -
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Posted: Aug 27, 2020 - 10:51 PM
Message deleted... wrong thread..
Edited by Andinista on Aug 28, 2020 - 07:07 AM.
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