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Old 02-25-2014, 09:27 AM   #1
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Bi-directional paravanes

Hey!

We are a group of will-be naval architects, studying in the Netherlands. For a reseach-project we are looking for people that have knowledge about bi-directional paravanes to stabilize their ships. With bi-directional we mean that a solid bar will replace the cable that attaches the paravane to the ship. We are unsure if there needs to be joints to make this work or just make a completely fixed setup.

I hope you guys might have some suggestions on reading material or personal experience with this issue.

Kind regards,
Kevin Lute
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Old 02-25-2014, 09:44 AM   #2
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For practicality you need to be able to fit against a dock

I have only seen this done on a crab boat. It that was set up on the port side. The arm was a aluminum truss structure set up rigid with pins at the gunnel and wheel house. It allowed him to work the starboard side of the boat unencumbered for crab pots.
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Old 02-25-2014, 03:40 PM   #3
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Joints, for "break away" points, for removal by parts at least. IMO the rig needs to be able to literally break away from the hull. Best that be via points created by design.
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Old 02-25-2014, 04:46 PM   #4
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I will post some photos later of the vessel beside me.
he has solid struts of his arms. This is reasonably common here in Queensland , Australia especially on commercial prawn trawlers.
They quite often use a universal joint for the connections.

will revert later.
Cheers
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Old 02-26-2014, 05:22 AM   #5
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OK here are the photos.
Sorry about that the photos are darker than I thought.
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Old 02-26-2014, 08:05 AM   #6
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Thanks guys for the information. The photo's show the usage of universal joints, can you tell me if they are free to move in that point when there out in the water? That's how it looks on the photo's. What is the reason they have chosen this configuration with bars on there boat?

Thanks a lot for the effort,
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Old 02-26-2014, 11:23 AM   #7
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It would seem the fish would tend to be bi directional, depending on the angle being pulled as they are weight to point down to dive. So I do not understand the bi directional as long as they are suspended from a cable/rope?

Several of the commercial trawlers have used tubing rather than cable to support the pole arms, but still being able to fold up. I have never seen a boat with fixed solid arms as they would limit docking, so why would somebody what to do that. Maybe one side but not both. I am presently looking at adding paravane and rather than using cable using tubing. Most of the commercial do not use the paravane when fully loaded, and most of the time only one side so they can wok on the other. Its when they are light they use them. The Eagle is stable fully loaded, fuel and water 1600 gallons = 5 tons down low. Its when the tanks are empty that I would use the paravanes.

I plan on install the chain plates under the gunnels, which is about 5 ft off the water, so they do not drag in the water/waves. Also looking at using short poles, 8 to 10 ft which would decrease the angle, so there would be less stress, more of a vertical pull. Being we lift large machinery, 40 tons, in the shop, correct rigging and angle is required. The less the angle the less the stress.

I am not sure what the advantage/disadvantage of having the fish out far from the boat vs.closer to the boat is? It would seem just hanging the fish from the mid cleat would be effective. At our first slip we had roll stopper hanging from the boat, 16 plastic cones that significant dampened the roll, so I was think why not just hang them under way as we only go 7 to 10 mph so there is not that much drag. I definitely do not want the poles much over 10 ft as the angle becomes larger.
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Old 02-26-2014, 03:20 PM   #8
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Solid fold away arms are another very common form of stabiliser arms here in Australia especially on commercial prawn trawlers.
Phil/Fill presently my arms on Tidahapah are approx. 12 ft and to short. Some time in the near future I will extend these to at least 16 ft. This gives a a longer lever for the fish to work on and therefore more effective stabilising and with the arms at approx. 25 to 30 deg and the fish running at approx. 14 ft deep less chance of having them fly and also keeps them away from the prop.

Have a good read of Voyaging Under Power lots of good info there.

Cheers
Benn
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Old 02-27-2014, 11:22 AM   #9
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That is a very good point for increasing the pole length? I was thinking more alone the line of being able to raise or lower the arms depending on the water conditions. Also the angle the fish are dragged, plumb bob, effect also would be a factor. So if the angle of the plumb bob as more vertical the short the poles can be?

What I have read the fish should be down 15 ft so its important to have the correct size fish and the fish down angle for the boat size and speed of the boat. So the heavier the fish and the fish down angle the less the plumb bob effect. You can buy fish of different weight and sizes. 50 to 60 ft is 50 lbs and wind span of 28. So if the plumb bob angle is large either the fish are to small, the wrong down angle for the speed or the boats speed is to fast.

I bought the fish and poles from a 60 ft commercila boat, and I had a new stronger mast installed, so I am sort of getting ready. If you would like some information send me a PM with your email address.
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Old 02-27-2014, 12:27 PM   #10
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On most fish, the down angle is adjustable to match the average cruising speed of the vessel. On ours, you move the shackle forward or aft (3 positions). Our poles are 20' long and the fish are 15 deep at 0 knots. The design prevents the fish/rigging from fouling the running gear in any sea condtion.
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Old 02-27-2014, 01:22 PM   #11
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that is a great picture of how they work and the design of your system. i have never saw a picture of a 'fish' up close.

Just curious did you make and/or design them yourself? After seeing the system up close, they don't look overly complicated to fab or design. Is there an advantage that made you choose to make wing part out of wood(starboard?)?

I'd love to see a system like this in person, or better yet see it in action.
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Old 02-27-2014, 02:26 PM   #12
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Hope you will all have that opportunity as Dauntless comes north in spring.
It will be like a circus and I will sell tickets

I'm still waiting for the fish to arrive in the mail.
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Old 02-27-2014, 02:31 PM   #13
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Keep us posted to both your location and your fish on here as well as your blog. If we are available when you make your way north sounds like a plan. Will you be taking the outside or coming up the bay?
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Old 02-27-2014, 04:23 PM   #14
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Here are some photos of the fish on Tidahapah. I have just fitted a new pair(to me) Aluminium with stainless steel nose weight and larger surface area than the old ones.
The older ones were originally off a boat similar to mine but I feel they didn't have enough surface area. These are aluminium with lead weights attached on the underside.
Once I get a chance to trial the new fish I will let you all know how they performed.
I run mine off 10 mm dynema rope and then to silver rope. The weight/load is carried by the arms/blocks at the end of the dynema a shackle stops in the throat of the block.
I am to fit a new set of springs over the next few days and will post a photo when done.
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Old 02-27-2014, 05:21 PM   #15
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Quote:
Originally Posted by eseyoung View Post
... Is there an advantage that made you choose to make wing part out of wood(starboard?)...
The fish are commercially available on the West Coast either in pieces or complete. The planning surface is 3/4" marine plywood. I know commercial guys who replaced the ply with UHMW. The plywood after several years of full time soaking gets soft. I like the plywood over metal fish. When retrieving if you touch the side of the hull with the plywood, it is more forgiving.

I get the parts from Stano Enterprises, West Port, WA. He sells from Alaska to Northern California. Most commercial marine stores carry the parts or the complete fish.
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Old 03-28-2014, 10:59 PM   #16
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Here is a very simple bi-directional stabilizer, which appears to be hinged to the hull, rather than cable mounted.

Used John Pugh Motor Cruiser for Sale | Yachts For Sale | Yachthub

I don't know how well a system like this performs, but I like the simplicity of it.
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Old 03-29-2014, 02:43 AM   #17
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Auscan,
Quite popular in Tasmania.
I have seen them on a few Tuna Longliners.
Commonly called Dolphin Slayers in Queensland. Apparently they are very effective both underway and stationary.

Some fold up the side very nicely so that there are no protrusions.

Cheers
Benn
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Old 03-29-2014, 08:23 AM   #18
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Here is a very simple bi-directional stabilizer, which appears to be hinged to the hull, rather than cable mounted.

Used John Pugh Motor Cruiser for Sale | Yachts For Sale | Yachthub

I don't know how well a system like this performs, but I like the simplicity of it.
Nice! What an interesting setup. It's the first time I've seen something like these. And I agree, simple.
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Old 03-30-2014, 12:18 AM   #19
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A couple of pictures of different styles of Dolphin Slayers.
Some are nicely set up and some aren't so pretty.
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