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Old 09-29-2022, 12:34 AM   #1
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Paravane stabilisers actual loads.

Has anyone actually measured the loads when underway of paravanes in action?

I know in Beebes book it was made mention of around 3 ton but I'm starting to think that can't be right
Reason I say this is because of the plywood paravanes

This being one


And another




From this thread
https://www.trawlerforum.com/forums/...fins-5870.html


My thinking would be if there was 3 ton of load, so 1.5 ton of load either side of the centreline of 3/4 inch plywood fish, it'd collapse

Thoughts?
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Old 09-29-2022, 12:56 AM   #2
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Load in what direction? Vertical to the poles or horizontal drag? I've got 1/2" stainless cable both up to the poles and fwd to the hull.

I'm sure a boffin could do the math. It's enough load to slow 54' and 50t by 1kn at constant power.
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Old 09-29-2022, 03:53 AM   #3
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Load in what direction?
From the direction that wants to break stuff


I had people tell me that flopper stoppers generate a big load and the single 10mm eyebolt through one of the roof deck beans would not be strong enough
Yet, when they are doing their thing, I can grab hold of the dyneema uphaul, pull some belly in it and hold most of it during the upstroke.
To me that says there's not much load.

I wonder if paravanes have a similar "big" load that in reality is not.
Plywood paravanes would suggest it's not that big.
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Old 09-29-2022, 07:46 AM   #4
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I'd expect it varies widely based on the size of the fish as well as the behavior of the boat they're attached to. In a rolly anchorage I've had to carefully time lifting even my crappy flopper stopper cones (not on poles). Depending on the roll, I can either just hold them or not even that much when that side of the boat rolls up, so there's definitely some force on them. Not a crazy amount, but not insignificant. But my boat likely rolls faster than yours, so that would make a difference in how they get loaded.
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Old 09-29-2022, 08:08 AM   #5
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This is from Beebe's first edition (1975).
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2B6A1194-008C-4AE6-90B8-29DA4B0553AB.jpg  
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Old 09-29-2022, 08:32 AM   #6
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A couple of pictures when things fail:
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025.jpg   035.jpg   paravane chain.jpg  
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Old 09-29-2022, 10:40 AM   #7
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I will be following this thread with much interest. My current vessel is a Kadey Krogen 42 that I recently installed paravanes on, our previous boat was a Willard 40 PH all so set up with paravanes. Both of these boats are truly full displacement vessels and both are well known as being very soft chined. I do feel that I’m pretty well experienced with there operation which includes. Half dozen crossings of the Gulf of Alaska. More often than not I hear all about the dangers of paravanes from people that in reality have had no experience with them other having watch the movie “The Perfect Storm” a couple of times. On our previous boat, the W40PH all of the rigging was wire where as on the Krogen all of the rigging minus the shock line and a couple of six foot chains are Dynema. I am actually considering changing the drop lines to the fish from Dynema to stainless out of concern of abrasion from a possible log or something on the surface. Any opinions on this?
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Old 09-29-2022, 11:37 AM   #8
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Quote:
Originally Posted by Simi 60 View Post
Has anyone actually measured the loads when underway of paravanes in action?

I know in Beebes book it was made mention of around 3 ton but I'm starting to think that can't be right
Reason I say this is because of the plywood paravanes

This being one


And another




From this thread
https://www.trawlerforum.com/forums/...fins-5870.html
My thinking would be if there was 3 ton of load, so 1.5 ton of load either side of the centreline of 3/4 inch plywood fish, it'd collapse

Thoughts?
The load on the fish is much smaller than the load on the hull connection points and mast rigging.
The force gets multiplied by the distance from the roll center.
A few hundred pounds on a 25' lever will produce a tremendous righting force.
Do you recall Archimedes' famous quote?
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Old 09-29-2022, 03:37 PM   #9
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A couple of pictures when things fail:
But in fairness, you also said here....


Quote:
Originally Posted by Larry M View Post
Dominique: The picture is what happens after the plywood has been soaking for 5 plus years and fails when fully loaded.
It sounds like it could we'll have been compromised due to water ingress more than a failure from actual load.

Saying that, plywood rudders and dagger boards used to fail over time from rolling shear loads.
I suspect plywood fish could be susceptible to the same over time.
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Old 09-29-2022, 03:50 PM   #10
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The load on the fish is much smaller than the load on the hull connection points and mast rigging.
The force gets multiplied by the distance from the roll center.
A few hundred pounds on a 25' lever will produce a tremendous righting force.
Do you recall Archimedes' famous quote?
Maybe.
But of interest was this snippet I read

Quote:



I started with a straight replacement of wire for chain. I chose 1/8 inch 7x19 with a break strength of 1750 lbs. This is approximately what the chain break strength was, and I wanted this part to be the weak link. I then matched the other parts to this break strength. When I crossed the Caribbean Sea with its large steep chop I found that 1/8 inch wire was not strong enough. The wires broke several times. I have since switched to 20 feet of 3/16 inch 7/19 wire:

Paravanes
Admittedly a smaller Nordy but light wire none the less

I wonder if it was a break with a bang or individual wires breaking more from flex/fatigue?

I have had SS rigging wire break individual strands before and not from dynamic shock loads, more a cyclic load.
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Old 09-29-2022, 04:59 PM   #11
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https://www.engineeringtoolbox.com/d...ent-d_627.html

This gives the equation to calculate the force (in Newtons). No time to do it myself but I'd use a turbulent flow flat plate Cd. You can look up the density of water & all the required unit conversions. You can estimate the area of the plate.

Note that if you want to calculate the drag on forward progress you'd use the frontal area of the fish & probably a laminar flow flat plate Cd.
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Old 09-29-2022, 06:40 PM   #12
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Quote:
Originally Posted by Simi 60 View Post
Maybe.
But of interest was this snippet I read

Admittedly a smaller Nordy but light wire none the less

I wonder if it was a break with a bang or individual wires breaking more from flex/fatigue?

I have had SS rigging wire break individual strands before and not from dynamic shock loads, more a cyclic load.
BTW, that was an interesting book. Also, who knows where he got his wire rope from...

For wire rope, the working load should be at most 1/3 the breaking strength.
Personally, I would use 1/4 of the breaking strength due to the uncertain load.
1x19 wire rope would be better if the runs are in a straight line, too.
The finer the wire diameter the faster it seems to corrode.
Chain certainly solves the problem nicely, though.
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Old 09-29-2022, 06:53 PM   #13
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Call these people, They build them for commercial boats.

https://www.kolstrand.com/
Phone/Fax: (206) 784-2500
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Old 09-29-2022, 06:53 PM   #14
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My drop lines to the fish are constructed with a six foot 5/8 inch three strand built with SS eyes to act a shock lines attached to 3/8 inch Dynema that is attached to six feet of 5/16 galvanized chain. For a total drop of 18 feet below the surface. Fish are Canadian style plywood winged fish. The boat is a 42 ft. Kadey Krogen weighing in at 39K lbs.
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Old 09-30-2022, 07:47 AM   #15
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My drop lines to the fish are constructed with a six foot 5/8 inch three strand built with SS eyes to act a shock lines attached to 3/8 inch Dynema that is attached to six feet of 5/16 galvanized chain. For a total drop of 18 feet below the surface. Fish are Canadian style plywood winged fish. The boat is a 42 ft. Kadey Krogen weighing in at 39K lbs.
I think we met in Kingston this summer. I walked down and looked at the pole setup, very nice.
On the fishing boats we always used the kolstrand all metal fish and galvanized wire. That gear lasted forever. Dyneema is good stuff, but I prefer wire.
Kolstrand makes excellent anchor winches too. As long as you donít mind the workboat look.
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Old 09-30-2022, 09:58 AM   #16
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The Navier Stokes fluid dynamics partial differential equations would be the appropriate way to compute the force on the fish. They are notoriously difficult to solve. One might get a useful approximation by using Newton's F=M*a. Estimate the mass of the water column above the fish that is subject to acceleration and the roll acceleration during extreme movements should get one close. Even better, a small scale model might produce good insights.
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Old 09-30-2022, 10:48 AM   #17
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The Navier Stokes fluid dynamics partial differential equations would be the appropriate way to compute the force on the fish. They are notoriously difficult to solve. One might get a useful approximation by using Newton's F=M*a. Estimate the mass of the water column above the fish that is subject to acceleration and the roll acceleration during extreme movements should get one close. Even better, a small scale model might produce good insights.
One could certainly do that if all the variables were known but if you
want to find the actual loads in real time just use one of these:

https://www.amazon.com/Hyindoor-Digi...2-8997e41410bb

or, if the loads are under 300 kilos:

https://www.amazon.com/Digital-Hangi...%2C191&sr=8-20
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Old 09-30-2022, 01:16 PM   #18
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One could certainly do that if all the variables were known but if you
want to find the actual loads in real time just use one of these:

https://www.amazon.com/Hyindoor-Digi...2-8997e41410bb

or, if the loads are under 300 kilos:

https://www.amazon.com/Digital-Hangi...%2C191&sr=8-20

That's what I am hopeing someone has done
Reality vs theory

If I can get a REAL number I can make an informed decision as to whether or not our existing structure is up for the task
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Old 09-30-2022, 02:35 PM   #19
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I would think that a boat manufacturer like Nordhavn would have this sort of data, after all they do sell new boats that are set up with paravanes. I think that they do there own rigging for such equipment. I would love to see these numbers as well! Are there any other boat boat manufacturers that equip there boats with fish?
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Old 09-30-2022, 02:45 PM   #20
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From the direction that wants to break stuff

I had people tell me that flopper stoppers generate a big load and the single 10mm eyebolt through one of the roof deck beans would not be strong enough
Yet, when they are doing their thing, I can grab hold of the dyneema uphaul, pull some belly in it and hold most of it during the upstroke.
To me that says there's not much load.

I wonder if paravanes have a similar "big" load that in reality is not.
Plywood paravanes would suggest it's not that big.
For a small, lightweight trawler that might suffice. For your boat I think even
12mm might not be adequate. I would use a good quality lifting eyebolt, too.
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