Learning how to fly fish (as in paravanes)

[Whodgins]

Thanks to all of the helpful comments and photos in other TF threads from those of you who are using paravane stabilizers on your boats, I am just completing the build of a pair of paravanes or “fish” for our recently completed XPM78 “Mobius” which is a 24m all aluminium Exploration Passage Maker with a fully loaded displacement of about 44T. The hull shape is closest perhaps to a monohull sailboat style similar to the FPB series, with a fully rounded shape and a beam of 5m/19.6ft so she is quite tender and rolls easily but equally easily stabilized and I think that the paravane system will work very well for us. We are both former sailors and this is our first power boat so also our first experience with paravanes. My questions and purpose of this post are related to learning how to “fly” these fish and learning from those of you with first hand experience as to how to adjust them for maximum roll reduction with minimum drag.

I am using the plywood based paravanes that are commonly used in my original home base of Victoria BC and the design which several of you such as LaryM and Cold Smoked have built and shared here in other TF threads. We are currently in southern Turkey and getting ready to head up to Greece in a week or so and hope to have the paravane system ready to test out on that run. Like Cold Smoked I was not able to find any large round lead weights to cut in half and use for the weights up front but I was able to find some large zinc anodes that are discs about 20cm in diameter and 4cm thick and weigh about 7kg/15lbs so I will start by bolting two of these to the round leading edge of the plywood paravane/fish and look very similar to the parvanes that LarryM recently built. A bit more drag than a nice half spherical shape but will do for my first prototype and initial learning curve.

The plywood vane surface measures 76cm/30” wide at the tale end and about 65cm/25.5” long on the CL which gives a total surface area of about 475sq in. Total “bulb” weight of the two zinc discs will be about 14kg/30lbs

I have been doing weekly updates on our Möbius.World blog and the recent ones would show you more details and photos if that would help and I'll attach some photos from previous posts of those building the same type of plywood paravanes I'm building, to add clarity and safe time.

My questions are about understanding how these paravanes work and how best to position the line that attaches to the top of the metal vertical portion of the T-bracket perpendicular to the horizontal surface of the plywood paravane. Typically there are several holes for the attachment of the line coming down from the end of the paravane A-frame boom, and there have been several comments that you use the forward most hole for higher speeds and the ones further aft for slower SOG but I’m not sure I understand why this is the case? What is the relationship between the position of the attachment line and the functioning of the paravane/fish?

As I understand it and makes sense to me, as the attachment point moves aft and further away from the front weighted nose, the paravane would go nose down more and more. This would cause more drag and act as a “brake” which I understand the use of for commercial fishing and trolling but that’s not the application for those of us using paravanes on pleasure craft. In our application I think we want to have the least amount of drag possible and yet still have the weight distribution such that when the tension goes off one of the paravanes as the boat rolls to that side, the paravane “dives” down quickly and smoothly as possible to set itself up for when the roll reverses and you want the maximum resistance.

Said another way, I get (I think) why the commercially made steel paravanes have this row of multiple attachment point holes as their most commonly sold and used by commercial fishing boats who want/need the trolling/braking function of their paravanes. But when you want to use paravanes on a pleasure boat would there not be just one position that is “just right” to provide the Goldilocks sweet spot of maximum roll resistance when needed and minimum drag?

My current plan is to drill multiple holes for the attachment point on the fish I’m building and then do some test runs with the line attached at different positions when running at similar SOG and sea conditions and measure the reduction in SOG and roll when the paravanes are deployed. I have good monitoring of fuel burn, roll, EGT, etc. so I should be able to compile a good log of all this data with the line attached at different positions and see what that tells me regarding the best hole position to use.

A related question is to ask about people’s experiences with different amounts of nose or bulb weights on paravanes. I’m thinking this is perhaps a function of surface area, overall weight and bulb weight but those are just guesses on my part. And what indicators would there be for what the best weight is? Perhaps you just need to run them for awhile and watch how well the fish “dive” as the boat rolls and go with the weight that is just enough to cause the paravane to dive quickly enough to keep the line well tensioned as the fish drops down deeper as the boat rolls?

Very rookie questions to those of you with lots of sea miles using paravanes and my thanks in advance for any tips, tricks and suggestions you have as I get started using our new paravanes for the first time. You have all been extremely helpful with your previous postings on this topic for which I’m most appreciative.

Thanks,
Wayne
mv Möbius

 

[Larry M]

They look great! On Hobo, once we found the sweet spot, we never changed the hanging position of the fish. I played around with it a few times. I did find that if I moved the attachment point too far forward and were in large beam to seas, the fish would occasionally pop out of the water. No danger or damage just a lot noise as the pole unloaded and the rigging shock.

As far as the weight shape, I think that’s just a function of the builder. The guy who originally designed ours catered to the commercial salmon trolling industry off of the Canadian/Washington/Oregon/California Coast. The round lead that was used was a very common 50-55lb downrigger ball cut in half. Kolstrand who use to make (maybe still does) the all metal fish, catered more to the larger commercial craft such as shrimpers, sword fishing (larger) vessels although they were used on Nordhavns when they had the paravane option.

We saw a shrimper once that had to be going 15 knots with the paravanes deployed. The poles were almost parallel to the water. We were in 10’ short, seas and it plowed right through. I know our system couldn’t have taken that high a load.

 

[rslifkin]

They look great! On Hobo, once we found the sweet spot, we never changed the hanging position of the fish. I played around with it a few times. I did find that if I moved the attachment point too far forward and were in large beam to seas, the fish would occasionally pop out of the water. No danger or damage just a lot noise as the pole unloaded and the rigging shock.

As far as the weight shape, I think that’s just a function of the builder. The guy who originally designed ours catered to the commercial salmon trolling industry off of the Canadian/Washington/Oregon/California Coast. The round lead that was used was a very common 50-55lb downrigger ball cut in half. Kolstrand who use to make (maybe still does) the all metal fish, catered more to the larger commercial craft such as shrimpers, sword fishing (larger) vessels although they were used on Nordhavns when they had the paravane option.

We saw a shrimper once that had to be going 15 knots with the paravanes deployed. The poles were almost parallel to the water. We were in 10’ short, seas and it plowed right through. I know our system couldn’t have taken that high a load.

My understanding is the angle change is mostly for different speeds. At higher speeds, you move the attachment forward to reduce the downward angle of the fish. More speed needs less angle to produce enough downward force.

 

[Whodgins]

They look great! On Hobo, once we found the sweet spot, we never changed the hanging position of the fish. I played around with it a few times. I did find that if I moved the attachment point too far forward and were in large beam to seas, the fish would occasionally pop out of the water. No danger or damage just a lot noise as the pole unloaded and the rigging shock.

As far as the weight shape, I think that’s just a function of the builder. The guy who originally designed ours catered to the commercial salmon trolling industry off of the Canadian/Washington/Oregon/California Coast. The round lead that was used was a very common 50-55lb downrigger ball cut in half. Kolstrand who use to make (maybe still does) the all metal fish, catered more to the larger commercial craft such as shrimpers, sword fishing (larger) vessels although they were used on Nordhavns when they had the paravane option.

We saw a shrimper once that had to be going 15 knots with the paravanes deployed. The poles were almost parallel to the water. We were in 10’ short, seas and it plowed right through. I know our system couldn’t have taken that high a load.

Hey Larry, thanks so much for such a prompt response. Your other posts in different TF threads on this topic were extremely helpful to me, especially all the photos. I'm curious as to how you evaluated the different attachment points as you experimented. Other than keeping them in the water, what were you able to observe as you tried different hole location? Amount of loss of speed due to drag? Watching the fish dive down as the boat rolls?

Thanks again for all your help Larry.

 

[Whodgins]

My understanding is the angle change is mostly for different speeds. At higher speeds, you move the attachment forward to reduce the downward angle of the fish. More speed needs less angle to produce enough downward force.

Thanks. Yes, I've read this too. We tend to cruise between 8-10 kts pretty steadily so I guess I'll just have to try different hole locations and see how this affects the amount of roll and try to find the sweet spot that has the most amount of roll reduction with the least amount of loss of speed due to drag.

I had been thinking that when the fish are resisting the roll forces they are level with the WL and not diving or down angled at all and the drag is minimal. Then when the boat rolls the paravane on that side looses some tension in the line, the nose goes down and the paravane dives until it starts to be pulled up and resists. But perhaps I have this wrong and the paravanes are always nose down a bit and so there is always some drag on them and you chose the hole location that has the least amount of down angle hence drag but still provides enough resistance to the rolling.

Sounds like it will be one of those "learn by doing" situations and I'm just trying to do as much pre-learning here as possible to help me evaluate the different hole locations as I experiment.