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Old 13-10-2016, 04:04   #1
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Backstay to Bimini frame frame concern.

Hi folks, after considerable net surfing I must either conclude, there is no simple answer to my quest or.......I simply haven't asked the right people yet, so here I am again!
I am installing a substantial Bimini frame of 30mm SS and would like to attach the split backstays to it to avoid penetration points in the canvas.
What kind of loads does the backstay have to cope with other than those created by my hauling the tensioner tackle? Apart from back plating the Bimini attachment points, is there anything else to consider? Or is it just a dumb idea?
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Old 13-10-2016, 04:17   #2
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Re: Backstay to Bimini frame frame concern.

Look at the diameter of the backstay as compared to your other stays & shrouds. Note that it's as big as the headstay & your cap shrouds. Therein is your anchor as to the loads on it. Which is why trying to do what you're proposing is highly impractical at best. AKA choose another, easier, system to reinvent.
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Old 13-10-2016, 04:23   #3
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Re: Backstay to Bimini frame frame concern.

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Originally Posted by UNCIVILIZED View Post
Look at the diameter of the backstay as compared to your other stays & shrouds. Note that it's as big as the headstay & your cap shrouds. Therein is your anchor as to the loads on it. Which is why trying to do what you're proposing is highly impractical at best. AKA choose another, more practical, system to reinvent.


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Old 13-10-2016, 04:32   #4
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Re: Backstay to Bimini frame frame concern.

Loads aside, a split backstay moves. The two legs move closer and further apart depending on the adjusted tension. The ability to ease and harden the backstab also results in small motions in various directions.
As others have stated this is a bad idea. Better to have the aft bow aft of the backstay and have "boots" sewn around the legs of the backstay.


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Old 13-10-2016, 10:07   #5
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Re: Backstay to Bimini frame frame concern.

We have a split back stay and a Bimini with boots. It has leather trim to deal with the chafing and is tied tightly around the stay so rain does not penetrate.
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Old 13-10-2016, 12:25   #6
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Re: Backstay to Bimini frame frame concern.

Quote:
Originally Posted by MollyJo View Post
Hi folks, after considerable net surfing I must either conclude, there is no simple answer to my quest or.......I simply haven't asked the right people yet, so here I am again!
I am installing a substantial Bimini frame of 30mm SS and would like to attach the split backstays to it to avoid penetration points in the canvas.
What kind of loads does the backstay have to cope with other than those created by my hauling the tensioner tackle? Apart from back plating the Bimini attachment points, is there anything else to consider? Or is it just a dumb idea?
C'mon guys, anything is doable.

Method 1: Beef up the deck and the hull/deck join at/near bimini attachment points, and use very large backing plates.

Method 2: Install chainplates in the hull for bimini attachment.

In either case, the goal would be to transmit the load in-line with the back stay, rather than introduce any lever arm, which would amplify the force on attachment points tremendously, and convert it from a purely tensile force to rotating moment.

But before investing any effort, ask yourself, "Is the benefit worth the cost?"

Method 3: Run the back stays through the bimini cover, and use boots to seal out (at least most) water.
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Old 13-10-2016, 13:32   #7
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pirate Re: Backstay to Bimini frame frame concern.

Quote:
Originally Posted by MollyJo View Post
Hi folks, after considerable net surfing I must either conclude, there is no simple answer to my quest or.......I simply haven't asked the right people yet, so here I am again!
I am installing a substantial Bimini frame of 30mm SS and would like to attach the split backstays to it to avoid penetration points in the canvas.
What kind of loads does the backstay have to cope with other than those created by my hauling the tensioner tackle? Apart from back plating the Bimini attachment points, is there anything else to consider? Or is it just a dumb idea?
Let me inform you that all the Moorings/Sunsail boats in around the world utilize exactly this system of attachment, so in order to understand how it is done check a Beneteau or Jeaneau out of Charter and they will have the Bimini attachment, which my boat also has Beneteau 52 Cyclades and after five years of up and down in the very windy Carrib, still going strong
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Old 13-10-2016, 13:44   #8
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Re: Backstay to Bimini frame frame concern.

^^^^

I do not believe any of those boats have a split backstay.


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Old 13-10-2016, 14:43   #9
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Re: Backstay to Bimini frame frame concern.

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^^^^

I do not believe any of those boats have a split backstay.


Sent from my iPhone- please forgive autocorrect errors.
Last time I checked they all did
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Old 13-10-2016, 15:54   #10
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Re: Backstay to Bimini frame frame concern.

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Last time I checked they all did
Doesn't matter either way, the cost of such a retrofit would run well into the 4-digit range, if not higher. As it's not just the bimini frame & it's attachments which need strengthening, but also the hull. And it would need extra reinforcing along a couple of axis. As this modification is akin to attempting to mount a mainsail traveler on a bimini or panel arch which wasn't specifically designed for such a task. And designed for it from before it's birth.
Is it doable, yep, does it make sense. Not really.

If drips through skin penetration in the bimini are such a big issue, buy a dry top for each crewman. It'll be much cheaper.
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Old 13-10-2016, 16:50   #11
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Re: Backstay to Bimini frame frame concern.

Years ago I thought it was smart to attach additional stays from the top of my mizzen mast to the top, both sides, of my new 1 1/2" ss davits. It did not take long before the mast pumping destroyed the davits.
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Old 14-10-2016, 19:59   #12
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Re: Backstay to Bimini frame frame concern.

Thanks for the insights. I guess my concerns are confirmed although I have seen boats with this arrangement it is likely they were designed that way. It wasn't so much about water ingress for us here in West Australia (we need shade), but more about not poking holes in a brand new cover if avoidable. Not a big deal to add boots but probably won't. We'll just hem the holes.
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Old 14-10-2016, 20:59   #13
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Re: Backstay to Bimini frame frame concern.

Quote:
Originally Posted by MollyJo View Post
...is it just a dumb idea?
...This.
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Old 15-10-2016, 12:14   #14
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Re: Backstay to Bimini frame frame concern.

The only way I can see this working is if you treated the Bimini frame like a spreader with discontinuous rigging and welded a solid tie rod between the upper shroud and lower shroud, then brought the loads down to the deck via the lower shroud. The biminiehere would need to be floating, with its height above deck set by the shroud tension...

But I am not sure what this really gets you.

To engineer a biminie strong enough to handle shroud loads is possible, but would need to be massive.
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Old 15-10-2016, 17:38   #15
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Re: Backstay to Bimini frame frame concern.

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The only way I can see this working is if you treated the Bimini frame like a spreader with discontinuous rigging and welded a solid tie rod between the upper shroud and lower shroud, then brought the loads down to the deck via the lower shroud. The biminiehere would need to be floating, with its height above deck set by the shroud tension...

But I am not sure what this really gets you.

To engineer a biminie strong enough to handle shroud loads is possible, but would need to be massive.
Why? 1" thick wall SS tube will support way more tensile strength than the backstay. Split the back back stay and attach to each side of a 1" Bimini bow that is in line with the back stay and all you have to worry about is the strength of the attachment points. Not a big deal at all.
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