Paravane stabilisers actual loads.

[Airstream345]

Turns out I recorded a short video of their setup last year (with permission). You can view it below.

https://youtu.be/TO2vElSMI8w

I'll note that when the poles are out the cables are horizontal - which also tells me there isn't any downforce on the rig, but the is compresion force on the poles (they are mounted low near the rubrail) and horizontal force on the topping lift and chainplates.

This was the boat/rig that gave me the "aha!" moment about how paravane forces work. The fish pull down and back. The pole multiplies that force (in this case horizontally) and the boat rotates back to equilibirium between the two fish. Given this rig has no actual "rig" it finally made a ton of sense.

It's a lot like a sailboat mast.

 

[Airstream345]

A few more detail photos. Note: 3/8" 7x19 Type 316 Stainless Steel Wire has a breaking strength of 11,000 lbs

 

[Jeff F]

Yes, dragging it though the water would be like flat plate drag, Cd around 1.1. If it generates lift instead, it can be a little bit higher, but you are unlikely to exceed a Cl of around 1.3 with the crude shape of a fish. A properly shaped asymmetric airfoil can get up to maybe 1.6, a lot higher with a bunch of high lift devices - but fish are usually just a flat plate of steel or aluminum.

Thanks. That actually made sense to me .

Edit to add: actually I'm still slightly confused, but it helps. Off to educate myself...

 

[Simi 60]

Yes but bulkheads would be needed for vertical support. But I would think the the roof can handle the horizontal forces involved here.

I would think it could as well
But I don't want to risk it based on essentially, a guess or gut feel.

I could move it back about the same distance aft of the blu centre line
Whilst it doesn't have bulkheads there as such there is a 1/4 bulkhead on a deck beam where bathroom on one side and stairs on the other have supporting structure.
And still no solar panels to contend with.

I used an on-line calculator for columns under buckling forces which showed that the diameter has a much greater impact than thickness on the compression forces that a tube can handle

That being the case maybe I should look at 100 x 3
Like foam sandwich or any sandwich, the further apart the skins the stiffer the panel.

 

[Jeff F]

Don't know if it's relevant Simi, but when I went down this imaginary trail a couple of years ago my solution was a bridge made of aluminum, with four legs going to the deck. Entirely self supporting and able to take all loads from the PV.

Edit to add that you need to deal with tension as well as compression loads on deck.

 

[Jeff F]

That was my favourite arrangement of all I've seen. Radar, anchor and search light, antennae and so forth on top. Passengers and solar underneath if need be.

 

[Jeff F]

You can also conceivably play with fore and aft positioning. It's entirely self contained.

 

[Jeff F]

With adequate spacing you have a triangular outrigger hinging down from the bottom of each leg. All loads transferred to the bridge.

 

[Jeff F]

Probably about midships, almost all west coast of North America fishing boats have the stabilizer poles set well forward. Which reminds me about another load on the system; with poles forward the fish will damp out a bit of the pitching motion as well.

Rereading the thread. It's got me interested again [emoji16]

IIRC Beebe suggested 2/3 back. Or maybe it was someone else.

Most of the systems I've looked at were on east coast fishing boats, and they've run the gamut.

It's worth considering. I think I'd want them aft in a following sea and forward in a head sea.

I guess it's your job to figure out such things! Thanks for chiming in.

 

[Jeff F]

Hey Simi, build the poles far enough apart and you can play with fore/aft adjustments easily.

You can taper fore and aft as you go up. The separation is only needed for the first metre or so.

 

[Simi 60]

Don't know if it's relevant Simi, but when I went down this imaginary trail a couple of years ago my solution was a bridge made of aluminum, with four legs going to the deck. Entirely self supporting and able to take all loads from the PV.

Edit to add that you need to deal with tension as well as compression loads on deck.

Not realistically possible due to solar shading and cost

 

[Simi 60]

Hey Simi, build the poles far enough apart and you can play with fore/aft adjustments easily.

You can taper fore and aft as you go up. The separation is only needed for the first metre or so.

I don't know what any of this means.

 

[dannc]

...
IIRC Beebe suggested 2/3 back. Or maybe it was someone else. ...

Pretty sure Beebe was 2/3 back or 1/3 forward of the stern and Buehler's Diesel Ducks have the paravane poles at about that position.

Later,
Dan

 

[Simi 60]

Work boats pulling big loads from well forward
Loads far bigger than paravanes/fish will exert.
Plenty of this sort of thing all over the interwebs

 

[dannc]

I did not see anything about loads on Kasten's website but I might have missed it. He does talk about sizing of the fish for different size boats, Roll Attenuation and Bilge Keels

Wayne on Mobius, https://mobius.world/, has published information on paravanes but I could not find anything on load or the size of the paravanes though I could have sworn I read the specifications on the tubes. There is information on the size, building and weight of the fish. Mobius just crossed the Atlantic and used the paravanes quite a bit. The paravanes worked as expected and matched what others have said about paravane effectiveness.

Later,
Dan

 

[Simi 60]

Should link to this post as it's an update to this one

Long story short, we have ran our smaller paravanes in short but fwd braced flopper stopper arms at 7.5 knots and in up to 25 knots of wind and associated slop.
Just did a full days run with them in.

I built in a 2mm VB cord fuse that is good for around 150kg/330lb and as yet, that fuse has not blown.

https://www.trawlerforum.com/forums/s31/teaching-fish-swim-stabilisers-68993.html