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PostPosted: Thu Mar 01, 2018 3:32 am 
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Site Rank - Deck Hand

Joined: Fri Aug 01, 2014 7:13 pm
Posts: 6
I have a modified wave jib , I want to add a furler and remove the forstay (will add a wire to the jib like a 14 turbo) to do this I will have to make the bridle very short (nearly horizontal) this will put a lot of preasure on the eyes so I might need a better solution, I cam thinking of fixing a plate under the eye and connecting the bridle to this via a shackle.



Can anyone see any issues with this?


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PostPosted: Thu Mar 01, 2018 6:25 am 
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Joined: Wed Aug 08, 2007 10:20 pm
Posts: 132
Location: South Boardman, Mi
Horizontal forces can be calculated as follows:
F1*(tan(θ1)/tan(θ2)=F2

F1 is the original horizontal force on the bridal wire tang.
F2 is the horizontal force with the new bridal wire angle.
θ1 is the factory bridal wire angle, measured to a line running between the bridal wire tangs on the hulls.
θ1 is the new bridal wire angle

The Upward force component will not change.

If you go from 30 deg to 5 deg (nearly horizontal) you will see your horizontal forces increase by a factor of 6.7.

If you go from 30 deg to 2.5 deg, horizontal forces will increase by a factor of 13.2


To sum up, you will likely rip out the tangs from the hulls. or break something else. I would not recommend doing this...


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PostPosted: Thu Mar 01, 2018 7:53 am 
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Joined: Mon May 09, 2005 10:25 am
Posts: 3559
Location: Jersey Shore
You would need to install a bow spreader (compression tube) to resist the higher inboard load from the shortened bridle wires. Some boats (NACRAs for example) do away with the bridle wires altogether and run an inverted dolphin striker on the bow spreader to allow the forestay to attach directly to the spreader itself. This allows the lowest possible attachment.

Bottom line, as the bridle wires shorten and get closer to horizontal, the inboard load increases exponentially and you definitely need to allow for this or you will certainly break something.

sm


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PostPosted: Thu Mar 01, 2018 9:52 am 
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Joined: Tue May 27, 2003 12:44 pm
Posts: 12533
Location: Oceanside, California
Correct... do NOT shorten the bridles. Add a spreader bar.

_________________
Matt Miller
Director of Parts and Accessory Sales
Warranty and Technical Support
Hobie Cat USA


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PostPosted: Thu Mar 01, 2018 6:01 pm 
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Site Rank - Deck Hand

Joined: Fri Aug 01, 2014 7:13 pm
Posts: 6
Thanks for the reply.

I already have the spreader bar. I was hoping the inward pressure would just be taken up by the bar, I was more worried about the eye.

You can't apply any upward pressure to the bar because it's too weak.


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PostPosted: Thu Mar 01, 2018 6:07 pm 
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Site Rank - Deck Hand

Joined: Fri Aug 01, 2014 7:13 pm
Posts: 6
Thanks for the that very helpful!

I have a spreader bar at the moment, the eyes are screwed over the spreader tangs which attach to the bar. I had assumed the bar would take all the inbound force as a compression load and the fulls would not be effected.
I was more worried about the eyes.

I did watch this video https://www.youtube.com/watch?v=tUK8d4igCL0 and he attached the jib bridle to the hulls directly by drilling holes in the bow, not keen on this idea.



speed633 wrote:
Horizontal forces can be calculated as follows:
F1*(tan(θ1)/tan(θ2)=F2

F1 is the original horizontal force on the bridal wire tang.
F2 is the horizontal force with the new bridal wire angle.
θ1 is the factory bridal wire angle, measured to a line running between the bridal wire tangs on the hulls.
θ1 is the new bridal wire angle

The Upward force component will not change.

If you go from 30 deg to 5 deg (nearly horizontal) you will see your horizontal forces increase by a factor of 6.7.

If you go from 30 deg to 2.5 deg, horizontal forces will increase by a factor of 13.2


To sum up, you will likely rip out the tangs from the hulls. or break something else. I would not recommend doing this...


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PostPosted: Thu Mar 01, 2018 6:14 pm 
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Site Rank - Deck Hand

Joined: Fri Aug 01, 2014 7:13 pm
Posts: 6
The getaway joins the Bridles to the spreader bar to keep the distance down, but I don't think this would work on the waves bar.

srm wrote:
You would need to install a bow spreader (compression tube) to resist the higher inboard load from the shortened bridle wires. Some boats (NACRAs for example) do away with the bridle wires altogether and run an inverted dolphin striker on the bow spreader to allow the forestay to attach directly to the spreader itself. This allows the lowest possible attachment.

Bottom line, as the bridle wires shorten and get closer to horizontal, the inboard load increases exponentially and you definitely need to allow for this or you will certainly break something.

sm


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