T&T: Paravane Rigging

[Jon Boy aka:TrawlerGuy]

Hey John, By my way of thinking, it seems that the most pertinent info would be what your paravane structure/rigging can withstand, since that is what you don't want to fail. Then you can do your load limit work backwards to achieve a link that will fail before that load is encountered. 

Our "weak link" is supposedly the 3/4" rope link with S/S thimbles--
<http://groups.msn.com/TrawlerMV/mariahgwynnsisland62.msnw?Page=4> 
--that attaches the 5/16" S/S cable from the bird to the top of the outrigger boom. However, our system is very heavily built and even when we did pick up and drag several hundred feet of fishing net one night, (see previous TT post) it did not break anything or part the 3/4" rode. 

I don't think that building to a generic load factor, such as 10 lbs/sq in, is a good idea since the absolute last thing you want is to loose a bird, so long as your structure is not in danger as I said above. I say this not because loss of the bird is such a catastrophic loss but because when it will be stressed the most, far past normal conditions, is when you will be in a worst case situation/conditions and, I can tell you from experience, that is when you'll be praying that it does not fail. Both from the prospective of being with out it and from the prospective of what it's going to do to the operation of the vessel at "that" time. Not good... 

So, my logic, and our experience from when we were in a situation were we very much NEEDED the paravanes to keep working, says that I don't want the "weak link" to fail unless the "system" is in eminent danger of failure.

Hope you understand why I say this and I'm suggesting that, instead of working only from the scenario of simply fouling the bird on an immovable object, you will work from the prospective that your paravane system is there to control excessive roll and then work from a scenario of a situation where you will need it to be there working for you in the most extreme conditions, even though you don't intended to be in it, and the last thing you want is for it to fail prematurely.

Cheers, Jon


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>>>>>>ORIGINAl Message: 12
Date: Mon, 3 Sep 2007 11:18:09 -0700 (PDT)
From: John & Liz <outtahere100 at yahoo.com>
Subject: T&T: Paravane Rigging
To: T&T <trawlers-and-trawlering at lists.samurai.com>
Message-ID: <774581.57870.qm at web52705.mail.re2.yahoo.com>
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Hello All,
I have finally started rigging my paravanes and am having trouble deciding on what breaking strength to use for the line to the fish. In the event that I snag a fish on a large object, I want it to break away before damage occurs to the paravane boom, superstructure, etc. My problem is that I have been unable to find information as too much force is generated by the fish. Does anyone know of a strain gauge that I could insert in line with the fish to measure the force being generated?    
Thanks, John