Does anyone have a paravane fish I can borrow for a Trawler Forum experiment?

[Airstream345]

People of Trawler Forum!

There is a discussion going on over here:

https://www.trawlerforum.com/forums/s31/paravane-stabilisers-actual-loads-65514.html

...about how much force a paravane fish creates going through seawater at around 8 knots. I won't rehash it all here, if you'd like to add ideas, disagree or otherwise comment on the discussion please do it over there.

This post is to ask if anyone in the San Juan Islands, Anacortes, Seattle area has a paravane fish they would be willing to lend me so I can perform an experiment using a crane scale to measure the actual force a fish creates at various speeds (1-8 knots). I'll provide the boat, you are welcome to participate (bring beer) and forever share in the Trawler Forum Hall of Fame with me as the team that FINALLY measured the ACTUAL force of an ACTUAL fish in ACTUAL water from an ACTUAL trawler! Plus there will be beer.

If you're up for some fun and fame please PM me and we'll arrange some dates.

PS - If this goes well we might take on anchors or single vs twins next.

 

[DavidM]

Realize that there are two forces that a paravane exerts on a boat. The most understandable one is the steady state force that pulls the paravane down when the boat is moving at a steady speed and is not rolling. That force is roughly related to speed.

The other force is dynamic and is additive to the steady state force above. It occurs when the paravane is pulled upwards by the rolling of the hull. It is probably a sinusoidal curve whose amplitude is related to how far the hull rolls on its cycle and the frequency is probably more or less constant. It peaks at the fastest angular speed, then goes negative on one side but positive on the other (but the static force keeps it positive overall).

So try to measure both forces at various speeds and various roll amplitudes. My apologies if this was discussed in the other related thread.

I suspect a hull rolling over to 20 degrees and back and forth has more dynamic than steady state force at 8 kts.

 

[Tad Roberts]

As David states above, the force on the fish or on it's towing line is dependent on more than it's size and speed. The work it's doing (stabilizing the boat) is an additional load. That load is dependent on the boat's stability, the stiffer the boat, the higher the load on the stabilizing system.

 

[ofer]

does your trawler have the spreader bar setup? or the fish will just be towed behind the boat?

 

[Airstream345]

I'll encourage comments like these (good comments btw) over on the original thread to try and keep the wisdon of this crowd in one place

ofer - no, we'll either tow it or run it off our boom (we have an oversized mizzen sail rig with a forward mast and boom.

 

[slowgoesit]

I'm in Port Orchard, WA. I have a spare fish we could use, but we'd have to coordinate a trip up your way.

 

[Airstream345]

I'm in Port Orchard, WA. I have a spare fish we could use, but we'd have to coordinate a trip up your way.

Thank you. I'll see if I can find an option around here first but if not we'll sort something out.

 

[IRENE]

Interested. We have a spare 300 sq. in Kolstrand buried in the bow. We also have two that get used, already mounted on the boat. It might be easier to rig a scale to our mounted fish(es).

Will have to coordinate as the season progresses…lots of projects in the next 6 months as we plan to head south. Maybe we could meet in the islands one weekend and rig your scale to our little boat? Or better yet, come to Sequim Bay!

 

[Airstream345]

Amazing, thank you. Rob from Lady Anne in La Conner has offered up his KK42 as well. I need to get the crane scale up here from Seattle and then at least two of us,if not all three need to meet somewhere. We're in Friday Harbor for another 8 weeks.