Paravane stabilisers actual loads.

[Simi 60]

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/s31/paravanes-vs-sea-gyro-vs-active-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?

 

[GoneDiving]

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.

 

[Simi 60]

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.

 

[rslifkin]

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.

 

[Larry M]

This is from Beebe's first edition (1975).

 

[Larry M]

A couple of pictures when things fail:

 

[Rob]

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?

 

[KnotYet]

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/s31/paravanes-vs-sea-gyro-vs-active-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?

 

[Simi 60]

A couple of pictures when things fail:

But in fairness, you also said here....

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.

 

[Simi 60]

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

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.

 

[socalrider]

Drag Coefficient

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.

 

[KnotYet]

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.

 

[fgarriso]

Call these people, They build them for commercial boats.

https://www.kolstrand.com/
Phone/Fax: (206) 784-2500

 

[Rob]

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.

 

[Bmarler]

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 don’t mind the workboat look.

 

[gsholz]

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.

 

[KnotYet]

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-Dig...mzn1.fos.08f69ac3-fd3d-4b88-bca2-8997e41410bb

or, if the loads are under 300 kilos:

https://www.amazon.com/Digital-Hang...meter&qid=1664553064&sprefix=,aps,191&sr=8-20

 

[Simi 60]

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-Dig...mzn1.fos.08f69ac3-fd3d-4b88-bca2-8997e41410bb

or, if the loads are under 300 kilos:

https://www.amazon.com/Digital-Hang...meter&qid=1664553064&sprefix=,aps,191&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

 

[Rob]

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?

 

[KnotYet]

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.

 

[Simi 60]

The eyebolt was for flopper stoppers

If going paravane it would be flat bar across roof with epoxy set bolts into deckbeam taking the load but I still need to get an idea on what these actual loads are before deciding to do that.

 

[Xlantic]

Based on the Jenny's Journey experience (post #10) the paravane pulls with a force of more than 1750 pounds.

And based on Rob's rig (post 14), 5/8 nylon three-strand (breaking strength ~10,000 pounds) is strong enough.

So the range seems to be between 1 and 5 tons, I would guess closer to the 1 than the 5, say 2 tons?

The other forces on the rig can be calculated based on the geometry.

 

[MOJO]

Beebe's load calculations for MOJO showed a max load of 7,800 lbs.

 

[Xlantic]

Beebe's load calculations for MOJO showed a max load of 7,800 lbs.

At which point on the rig?

In the diagram in post #5 he suggests 3,900 pounds downward force by the paravane. Much more at other points.

 

[MOJO]

The diagram in post #5 is for a 36' Garden designed boat. MOJO is a 50' Beebe design in steel. On the identical drawing done for MOJO it shows 7,800 lbs.

 

[Capt Dan]

Have you thought about USTA scale in real Life?

 

[KnotYet]

Have you thought about USTA scale in real Life?

Like these?

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-Dig...mzn1.fos.08f69ac3-fd3d-4b88-bca2-8997e41410bb

or, if the loads are under 300 kilos:

https://www.amazon.com/Digital-Hang...meter&qid=1664553064&sprefix=,aps,191&sr=8-20

 

[Airstream345]

Simi, I'm with you and would love to get actual measured data to make informed decisions about rigging, structure, etc. There seems to be a lot of speculative information at best and lore at worst about the loads the fish place on the rig but no real world measured data. KnotYet, I love the idea of hooking one of those crane load scales up to some actual paravanes.

I personally suspect the loads are not as high as some have suggested based on some of the designs I've seen in person and the one James Krogen designed for the KK42. When approching riggers and fabricators about adding paravanes more than one has told me it's like having three automobiles up there swinging around, pushing down on your deck - yet when I press for data they don't have it. That and the designs I've seen implemented are far from that robust.

The issue to solve is how much downward force the fish are applying to the rigging and how best (of even if) you can transfer that load to the deck, hull deck joint or stringers/keel. Posting J Krogen's design here for reference.

 

[mvweebles]

Simi, I'm with you and would love to get actual measured data to make informed decisions about rigging, structure, etc. There seems to be a lot of speculative information at best and lore at worst about the loads the fish place on the rig but no real world measured data. KnotYet, I love the idea of hooking one of those crane load scales up to some actual paravanes.

I personally suspect the loads are not as high as some have suggested based on some of the designs I've seen in person and the one James Krogen designed for the KK42. When approching riggers and fabricators about adding paravanes more than one has told me it's like having three automobiles up there swinging around, pushing down on your deck - yet when I press for data they don't have it. That and the designs I've seen implemented are far from that robust.

The issue to solve is how much downward force the fish are applying to the rigging and how best (of even if) you can transfer that load to the deck, hull deck joint or stringers/keel. Posting J Krogen's design here for reference.

I suspect you're right that loads are much less than many state. In one of these threads, TF member Rpackard, a retired professor of physics from UC Berkeley and longtime owner of a Willard 40 with paravanes, said exactly that. Data would be great but in its absence, an active user who is a physics professor will due, at least for me.

Peter

 

[Jeff F]

My assumption is that in a well designed system the maximum load is dictated and controlled by the fish.

My guess is that with a known speed the fish will have a maximum force that it will exert. If that force is exceeded the fish starts losing effectiveness and allows itself to be pulled up more easily. That's the safety valve for the whole system. Everything else gets engineered on that.

This is entirely an armchair POV. I used to be quite enthused about paravanes, but the failure case in challenging conditions scares me.