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Old 01-21-2023, 03:12 PM   #81
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Compressive strength perpendicular to grain for Douglas Fir is 870 psi, strength in tension is about half this and strength in sheer and bending is quite a bit higher than this.....so the 10 psi load will not be an issue unless the fish are awkwardly wide......

When I was a lot younger and stronger, hand lifting plywood paravanes of perhaps 400 sq. inches with 30 lb lead weights on them was barely possible. This was with the boat stopped and drifting. Part of that was the slippery 3/8" towing wire. When the boat rolled the wrong way (away from the fish), it was all I could do to hang on, and if it was a big roll I'd give away wire.....
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Old 01-21-2023, 09:55 PM   #82
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Cool boat. The poles look to be about mid waterline?
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Old 01-22-2023, 12:52 PM   #83
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Cool boat. The poles look to be about mid waterline?
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.
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Old 01-24-2023, 03:37 PM   #84
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Spoke to the owner of this vessel online

Says it has 500 X 400 (19.6 X 15.7) plywood fish made from one inch ply.

Upright arms appear to be tied into flybridge side with the 2 stays visible
Forward load to pole end is attached to hardwood rail with 3 X 2 inch screws
Boat construction is white cedar and I assume, epoxy/glass.

Says she came to Australia from the US on her own bottom with that setup, but not him doing it.
But he has used them here in Oz.

He agrees, loads can't be that big as that rig would have torn itself apart if they were.
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Old 01-24-2023, 04:12 PM   #85
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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.
IF.... we go ahead the best place structurally for our is on the wheelhouse bulkhead.
Unfortunately, that is slightly fwd of centre as measured by the waterline

Further aft has less supported spans plus removal of solar panels to contend with.

We do have a barn door sized rudder and the vessel tracks like she's on rails so I would hope steering wouldn't be affected.

Pic shown has current flopper stopper arms on cockpit bulkhead, further aft than ideal but they work well
Red being proposed arms done in full 6m length of 80mm x 6mm ally tube

Our cruising style wont change, it'll still be waiting for favourable weather for our run.
But allow us to go point to point instead of tacking to our destination.
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Old 01-25-2023, 07:34 AM   #86
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Red being proposed arms done in full 6m length of 80mm x 6mm ally tube.
Simi, I also built my 6 metre flopper-stopper out-riggers out of 80 mm diameter aluminum tubing but mine were only 2mm thick as I didn't want them to be heavier than needed.

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.

When deployed, you may want to aim for the outrigger to be level with the roof of your upper cabin so the forces on the roof are horizontal. You can attach a chain plate to the underside of the roof to avoid having to re-position the solar panels.
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Old 01-25-2023, 04:11 PM   #87
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Simi, I also built my 6 metre flopper-stopper out-riggers out of 80 mm diameter aluminum tubing but mine were only 2mm thick as I didn't want them to be heavier than needed.
Our flopper stoppers are on 80x3
But actual stabilisers/paravane poles I think will warrant heavier tube.

A mate with a 55ft steely has 80x3 in s/s as stabiliser/paravane poles and while they have stood the test of time they do get a bit of flex.

Quote:
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.
I agree
But, I don't want to find out the hard way that 3mm wall was not quite up for the job.

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When deployed, you may want to aim for the outrigger to be level with the roof of your upper cabin so the forces on the roof are horizontal.
That was the direction I was aiming for


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You can attach a chain plate to the underside of the roof to avoid having to re-position the solar panels
.
Solar panels are only an issue if going well aft of centreline.
Not as much structural support - lack of bulkheads- would be more of an issue.
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Old 01-25-2023, 04:24 PM   #88
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That's interesting and valuable.

So that 780 is the case where you're dragging the fish sideways, essentially?
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.
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Old 01-25-2023, 04:31 PM   #89
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Solar panels are only an issue if going well aft of centreline.
Not as much structural support - lack of bulkheads- would be more of an issue.
Yes but bulkheads would be needed for vertical support. But I would think the the roof can handle the horizontal forces involved here.
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Old 01-25-2023, 05:47 PM   #90
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When deployed, you may want to aim for the outrigger to be level with the roof of your upper cabin so the forces on the roof are horizontal. You can attach a chain plate to the underside of the roof to avoid having to re-position the solar panels.
A friend has a setup like this....steel boat but when the paravanes are deployed all of the lines ceom from the top of the pilothouse (this is a Beebe style with an aft raised PH).

I may have some pics of his rig. I'll try and dig them up and post here.
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Old 01-25-2023, 09:02 PM   #91
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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.
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Old 01-25-2023, 09:41 PM   #92
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A few more detail photos. Note: 3/8" 7x19 Type 316 Stainless Steel Wire has a breaking strength of 11,000 lbs
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Old 01-26-2023, 11:11 PM   #93
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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...
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Old 01-28-2023, 04:55 PM   #94
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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.

Quote:
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.
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Old 01-28-2023, 06:39 PM   #95
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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.
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Old 01-28-2023, 06:43 PM   #96
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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.
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Old 01-28-2023, 06:46 PM   #97
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You can also conceivably play with fore and aft positioning. It's entirely self contained.
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Old 01-28-2023, 06:59 PM   #98
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With adequate spacing you have a triangular outrigger hinging down from the bottom of each leg. All loads transferred to the bridge.
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Old 01-28-2023, 07:11 PM   #99
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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

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.
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Old 01-28-2023, 07:23 PM   #100
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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.
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