New bridle on Nacra 5.5 :: Catamaran Sailboats at TheBeachcats.com

New bridle on Nacra 5.5

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revintage

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Posted: May 22, 2018 - 04:44 AM

Removing the bridle foil in order to make a F16/Tornado style bridle set up on my slightly widened 5.5(9.7ft). Will use a self tacking jib with its tack at the spin pole/bridle strut junction and a F18 spinnaker.

Trying the wire angle from the 5.5 foil, the bridle/forestay crossing point is rather high at 3.5ft.

Wonder if the 5.5 hulls can take the beating from a lower bridle crossing point and if so, how low can you go?

See pics from some trial-and-error in my workshop, where the simulated forestay should lean a little more to the rear.

Edited by revintage on May 22, 2018 - 05:07 AM.

--
Brgds
Lars

Frankentri 5.8/5.5/Inter20
Aerow trimaran foiler

https://www.facebook.com/groups/1192604934176635
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Andinista

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Posted: May 22, 2018 - 03:02 PM

If we look at the plane formed by the bridles and a= the angle between one bridle and the horizontal, here is what happens.
Bridle tension may be decomposed in two forces
a) one in line with the forestay, = T/2 = half the tension of the forestay
b) one horizontal, from hull to hull = F

F = T / (2 • tan a)

If a=45, F= 0.5•T (half the forestay tension)
If a=30, F= 0.87•T
If a=15, F= 1.87•T

With the bridle foil on you apply the same formula (the a angle is bigger compared to no foil and same jib base height). So you can measure the angle with foil and without foil at the desired position and calculate the factor by which the tension will be increased.

Edited by Andinista on May 22, 2018 - 03:05 PM.
revintage

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Posted: May 23, 2018 - 07:08 AM

Hi Andinista,

Nice to hear from you again. All you say is correct, I also made calculations, but looked at tension in line with the bridle wire BT, where forestay tension is FT.

This is the ballpark figures I get with 2500mm hull distance at the chainplates:

a=41 BT=FT*.75 for each wire H=1071mm, equivalent to 5.5 foil

a=34 BT=FT*.9 for each wire, H=838mm, Tornado

a=30 BT=FT*1 for each wire, H=722mm

If we look at the Tornado rules, triangle height in line with the forestay is min. 838mm and I guess width between hulls is about the same as my widened 5.5, 2500mm.

Think I´ll go for the 838mm triangle height of Tornado. This will give a BT increase of ca 1.2x. Sailing only inlake with flat water and never over 18-20knots, makes me think this will work.

Still the question is how strong the hulls are in the bows and how well the chainplates are anchored inside the hulls? I rely on the Nacra boys built them with some kind of safety factor.

Static tension is easy to measure, wonder how much forestay tension is with full sheeting upwind?

Could you please double check my calculated 1.2x load increase when going down to Tornado bridle height?

Edited by revintage on May 23, 2018 - 09:45 AM.

--
Brgds
Lars

Frankentri 5.8/5.5/Inter20
Aerow trimaran foiler

https://www.facebook.com/groups/1192604934176635
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Andinista

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Posted: May 23, 2018 - 12:03 PM

QuoteCould you please double check my calculated 1.2x load increase when going down to Tornado bridle height?

It seems right:
From a= 41 to a=34 BT increase = 17%

I would look more at the horizontal component where the hulls are weaker. Mine have some scary wrinkles near the front beam showing that lateral effect..

Increase on the horizontal component = 29%

But more importantly, the biggest impact might not come from the bridle modification but from adding a spi. My gut feeling (I'm just an electronic engineer...) is that the combination of both things mean a real risk of breaking those hulls.

So how much do you like risk?
Edchris177

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Posted: May 23, 2018 - 02:16 PM

QuoteSee pics from some trial-and-error in my workshop

That’s a workshop?
How do you ever get anything done in such a clean organized place

Edited by Edchris177 on May 23, 2018 - 03:01 PM.
Andinista

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Posted: May 23, 2018 - 03:17 PM

As I see here, F20s have the bridles/forestay connection higher than the spin pole but the jib start from the jib pole. That might be safer.
https://www.youtube.com/watch?v=rZqPSBJcJvc

Edited by Andinista on May 23, 2018 - 03:20 PM.
revintage

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Posted: May 23, 2018 - 06:16 PM

Edchriss177,

What about contributing to the actual subject of this thread. What´s your idea of bridle angles and height, got anything to come up with?

--
Brgds
Lars

Frankentri 5.8/5.5/Inter20
Aerow trimaran foiler

https://www.facebook.com/groups/1192604934176635
--
revintage

Rank: Mate

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Posts: 282
Posted: May 23, 2018 - 06:23 PM

Hey Andinista,

The F20 system is actually what I am aiming for, this is also how Tornado and Nacra 17 did it. My concern was, that the bridle height when going by the 5.5 angles where very high and I wanted to have a shorter compression strut for the jib to be Velcroed around.

Tornado bridle heigth is ca 800mm, but jib is at ca 300mm.

Will anyway wait with shortening the bridle until the rest of the rig is up and the Infusion jib is hoisted. Either way I will get rid of the bulky bridle foil.

Edited by revintage on May 24, 2018 - 05:51 AM.

--
Brgds
Lars

Frankentri 5.8/5.5/Inter20
Aerow trimaran foiler

https://www.facebook.com/groups/1192604934176635
--
Edchris177

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Posted: May 23, 2018 - 10:48 PM

Hey Lars,
It was merely a tongue in cheek comment on the beauty of your shop. Most, including myselt, would love to have such a clean organized workspace. Perhaps the intended meaning gets lost?
Sheesh, lighten up a bit...we’re all on your side.

--
Hobie 18 Magnum
Dart 15
Mystere 6.0XL Sold Was a handful solo
Nacra 5.7
Nacra 5.0
Bombardier Invitation (Now officially DEAD)
Various other Dock cluttering WaterCrap
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revintage

Rank: Mate

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Posted: May 24, 2018 - 05:01 AM

Hi Edchris177,
Really sorry for my "Grumpy Old Man" over reacting comment. Must admit I actually thought you where bullying me, as I consider the workshop being a total mess at the moment, when I´m trying to force things, to get this cat out on the water. Outside Frankencat2 is waiting to come in and inside Frankenboat4 is waiting for rebuild.

Note snow outside the window!

Edited by revintage on May 24, 2018 - 03:25 PM.

--
Brgds
Lars

Frankentri 5.8/5.5/Inter20
Aerow trimaran foiler

https://www.facebook.com/groups/1192604934176635
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randii

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Posted: May 24, 2018 - 01:52 PM

I would love to have that kind of open space... most of my boat work gets done outside, as the shop is full of motorcycles, 4x4s, and like projects.

Please keep sharing your franken-efforts!

Randii
Andinista

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Posted: May 24, 2018 - 07:02 PM

Maybe you could add a second stay for the jib.. not ideal but safer. It shouldn't take the load though
Edchris177

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Posted: May 24, 2018 - 10:27 PM

Apology accepted. I enjoy following your projects. In much the same vein as Carolina Catamarans idea a while ago of trying to re-invent Beachwheels, one has to admire a guy who gets n idea, & tries to make it work.
I'm jealous, most times a cow couldn't find her calf in my workshop.

--
Hobie 18 Magnum
Dart 15
Mystere 6.0XL Sold Was a handful solo
Nacra 5.7
Nacra 5.0
Bombardier Invitation (Now officially DEAD)
Various other Dock cluttering WaterCrap
--
revintage

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Posted: Jun 10, 2018 - 05:00 PM

Hey Andinista,

Did some more thinking about how to lower the bridle. By adding a third bridle part to the rear, with a pelican striker passing the striker rod going to the rear beam this should be possible. With a 460mm high bridle angle=20 and BT goes from 1,5 to 2,9, ie if we still want each bridle wire take FT/2=0.75 there will a substantial tension to the pelican striker that has a=22. As the spi pole acts as a compression rod, more tension can be added to the pelican striker than the bridle wires.

Not sure I got it right, what do you think?

--
Brgds
Lars

Frankentri 5.8/5.5/Inter20
Aerow trimaran foiler

https://www.facebook.com/groups/1192604934176635
--
Andinista

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Posted: Jun 10, 2018 - 05:59 PM

Hi Lars, that’s very creative. And your boat looks very nice, congratulations!
I think it would be hard to adjust load sharing between the central wire and the bridles. If the central wire is lose it just doesn’t get any load. Maybe with a turnbuckle.
Andinista

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Posted: Jun 10, 2018 - 06:08 PM

What about adding a bow foil like H21? (I think). Or a third beam in front
Andinista

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Posted: Jun 10, 2018 - 06:21 PM

Wait a minute, I forgot you have the real bridles further up. Those are the ones taking the main part of the load. If you tension the central wire it may contribute but is it really worth it?
revintage

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Posted: Jun 10, 2018 - 08:02 PM

Yep, the bridle is at 107cm now, but it will be lowered to 46cm. A turnbuckle was my idea too, to get the tension right in the central wire. As I have a Spinlock Rig-Sense, keeping track of the wire tension can be done quite easily.

The reason for the lowered bridle is, that I want it below the jib tack. To much work to make the jib luff pocket pass the highly placed bridle as I first planned.

If my guesstimate of 1,3x is correct, this means there will be a compression of the spin pole of 0,3x, so no problem for the 40x2mm alu pole.

Have ordered 5mm Hampidjan Dynice Dux(spliced breaking load 4300kg!) for the new forestay. Will also use it for the pelican striker.

Must try this !

Edited by revintage on Jun 10, 2018 - 08:03 PM.

--
Brgds
Lars

Frankentri 5.8/5.5/Inter20
Aerow trimaran foiler

https://www.facebook.com/groups/1192604934176635
--
Andinista

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Last visit: Dec 13, 2023

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Posted: Jun 11, 2018 - 05:43 AM

Good luck then!
Just in case: Years ago I had a Laser II, it’s jib had a wire inside the luff (permanently) and wasn’t rigged through the forestay. That would work I think, with a good halyard
Andinista

Rank: Mate

Registered: Aug 18, 2003

Last visit: Dec 13, 2023

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Posted: Jun 11, 2018 - 05:51 AM

Quotekeeping track of the wire tension can be done quite easily

The real tension is only applied when sailing though. I think there might
Be some flexibility on the central wire/pole that may make it hard to hold enough tension compared to the bridles. Just my impression, no maths..

Edited by Andinista on Jun 11, 2018 - 06:19 AM.