Paravanes boom position?

[mvweebles]

Get the load to the gunwales by using an H-frame vs an A-frame.

Peter

 

[Larry M]

Do you keep your fore and aft guy lines on end of the boom attached/rigged all the time, or do you rig these only before deploying the fish?

We don't have any aft guy lines, just forward. They are a fixed length so when deployed they're perpendicular to the hull. The 1' forward diagonal brace (pole) keeps the 3.5" poles from moving forward, aft or rotating when raising or lowing them. Here are a few pictures. The first is at rest. The third is the fore guy attachment point a the hull. The last one is the end of the pole looking forward. The wire is for the top and forward guy. The 1/2" double braid is about 8' in length to give the fish some dampening and to smooth out the ride.

 

[Dashash]

Wow. Thank you everybody! The pictures are worth a thousand words.

I think a load of 4,000lb from one fish at a time is fairly reasonable to expect (assuming 10lb/in^2 and a 300 in^2 fish, with 1,000lb of buffer added).

Presently, the four stays for my mast are 3/16" 316 S.S. Internet says WLL of ~4,000lb. The padeyes they are mounted on are good for just under 2,000lb (a 3x2" padeye). A 4x3" 316 S.S. padeye (with backing plate) has a WLL of around 3,000lb. Still, the limiting factor in my case is that the mast step is on the flybridge only. It looks extremely stout, and I believe it is resting on a large wood crossmember, but I cannot be sure. A 4,000lb compression force on the mast to a 5x7" mounting plate exerts 115psi. Shear strength of a 2"x4" to 4"x4" wood beam is 90-100psi. I could enlarge the mast mounting plate to something quite large and distribute that compression force much better. Again, just thinking out loud.

If I forget using my existing mast (which I think I could make work with some modification), I think some sort of h-frame is the way to go. Based on the advice I've gotten, if I were to go this route I would consider something along the lines of the attached sketch.

 

[Dashash]

We don't have any aft guy lines, just forward. They are a fixed length so when deployed they're perpendicular to the hull. The 1' forward diagonal brace (pole) keeps the 3.5" poles from moving forward, aft or rotating when raising or lowing them. Here are a few pictures. The first is at rest. The third is the fore guy attachment point a the hull. The last one is the end of the pole looking forward. The wire is for the top and forward guy. The 1/2" double braid is about 8' in length to give the fish some dampening and to smooth out the ride.

Larry M,

In your other thread, I noticed your rigging to the fish consists of 1/4" 316 S.S. cable and 1/2" 3-strand nylon. I also understand the rig was built for fish loading of 10psi (and you have a 200ft^2 fish). Is that correct?

I'm running through a loads analysis on the rigging/structural requirements on my own just to get an idea of the forces involved. It appears most 1/4" 316 7x19 S.S. cable only has a WLL of around 1,100 to 1,200lb. There is a 5:1 safety margin on these numbers, so the breaking strength is around 4,900lb. If your fish are exerting 2,000lb through that cable, you're well above the WLL, but about 40% of the breaking strength. Was this understood in the design of the system?

I think a 5:1 safety margin is a bit aggressive, but I just want to see if I'm missing something here. It seems to me that you'd want a "fuse" in the system - a line that would part and release the fish if it got snagged on something underwater. Initially, I thought that's why you undersized the S.S. cable attached to fish. But then released you probably used the same diameter cable in the rest of the system. A 3/8" 316 7x19 S.S. cable has a WLL of around 2,300lb. I would think that all rigging except that going to the fish should be this diameter so that it's greater than the maximum force the fish can exert. The "fuse" is the 1/4" S.S. wire or the 1/2" 3-strand nylon going from the boom to the fish (both around 40-50% breaking strength of the 3/8" S.S. wire). This way, you'd be constantly exercising the fuse wire in-between it's WLL and breaking strength, while the rest of the system would be exercised at some load <100% WLL.

Thoughts?

 

[Dashash]

Well, I'm probably just talking to myself, but figured I'd share a loads analysis I ran just now in hopes it may help somebody in the future. I compared my existing mast set-up to an alternate a-frame configuration. I'm primarily concerned with the downward forces on the singular mast. After running the numbers, it turns out that with a fish pull straight down on the boom of 2,000lb, the force on a singular mast would be over 3 tons, or in my case approximately 180psi. Too much.

The a-frame, surprise surprise, does an excellent job of distributing the loads to the gunwales. Peak loading is just under 2 tons on one gunwale at a time. I can engineer supports/brackets to withstand that, no problem.

The other issue I was worried about was shear at each mounting point. With the a-frame set-up, maximum shear is only 800 lbs. Not a problem.

I think the next step is sizing everything. This will involve guestimating the ship's moment of inertia given maximum roll rate, mass, and approximate C.G. With a MOI, I should then be able to size the fish and boom in order to generate sufficient righting moment.

Edit: I should add, I took a ton of measurements today, so the diagrams I attached are actually quite close to scale. The entire a-frame set-up will weigh 262lb. Total rig height is 20'. Assumed boom length is 18', ish.

 

[DCDC]

Some pictures of our paravane system, which is integrated into the dry stack exhaust risers and instrument arches. 56’ & 42 tons. For and aft guyed with SS cable, 2 speed winch for pole inhaul, 300 sq in Kolstrand fish.

Good luck with your system.

 

[Dashash]

Thanks! Very helpful. Your bracket that mounts the boom to the gunwale is exactly what I had envisioned for my setup.

 

[Jeff F]

Dashdash, I'm following you closely. I am imagining something similar for my boat, though I also know exactly where I'd put a gyro.

DCDC, Stella is gorgeous. I should have asked for a tour when you guys were in Ft Pierce 2 years ago.

 

[Larry M]

Larry M,

I'm running through a loads analysis on the rigging/structural requirements on my own just to get an idea of the forces involved. It appears most 1/4" 316 7x19 S.S. cable only has a WLL of around 1,100 to 1,200lb. There is a 5:1 safety margin on these numbers, so the breaking strength is around 4,900lb. If your fish are exerting 2,000lb through that cable, you're well above the WLL, but about 40% of the breaking strength. Was this understood in the design of the system?

I think a 5:1 safety margin is a bit aggressive, but I just want to see if I'm missing something here. It seems to me that you'd want a "fuse" in the system - a line that would part and release the fish if it got snagged on something underwater...

When the system was built, it was copied from a commercial fisherman’s set up and then adjusted a bit by Tom Davenport. I don’t know of anyone doing a load analysis. I do know there is no “fuse” in the system. We have hit a dead head that blew a fish apart, snagged long lines and gill nets and even hit an unlit 20’ something fishing boat at night. Other than the noise of impact it is not a sudden stop. The half inch nylon acts as a shock absorber plus the distance of the fish from the hull, you seem to pivot around the fish/object if that makes any sense? I think going 7 knots helps. Also, if there was a so called fuse, I’d be afraid that when it was loaded up and failed, when it unloaded, I think it would be like a sling shot and I wouldn’t want to be anywhere near the rigging.

We’ve had three system failures in maybe 14-15000 miles. A swivel between the wire and nylon broke, we blew a fish apart hitting a dead head square on and we had one fish break do to age. The plywood was weak from water immersion. I now replace the plywood every 5 years or so. I know fisherman who have replaced the plywood with HDPE or equivalent.

 

[Dashash]

Very helpful information. Thank you.

 

[offshoreskiff]

We've used a pair of these flopper stoppers while at anchor and they work great. I won't spend a night on a boat without them.

Recently we put them out while trolling and they worked great at slow speeds, 1-3 kts. They were placed 40% forward from the transom and the boat tracked straight and true with little input. The effect they had on roll dampening was magnified multiple times while moving.

 

[DCDC]

Thanks for the kind words Jeff. We are very much enjoying the boat. We were at anchor for that Ft. Pearce get together and missed the last two by a week during our annual migration.

Maybe next year.

 

[trawlercap]

https://www.trawlerforum.com/forums/s68/paravane-set-up-58263.html#post1009993

I'm parting with my set up for a 58' 61ton trawler. Our geometry was bad.

 

[Simi 60]

Over here a lot of working boats run tube with a hinged plate instead of rope/chain and purchased, weighted fish.

 

[Nomad Willy]

ofshoreskiff has it about right from what I read and hear.

I would think CG may have something to do w it but ?
The point (fore and aft) where the boat rises and falls the least or just ahead of that point. Heard that too but I think that would be too far aft. If too far fwd lots of strain is put on the stab system .. cabin, mast and poles, cabin or boat via gunwales while addressing a head sea.
On a fish boat frequently to most of the time fishing activities or fishing gear occupies the ideal place.
And how the stern swings to make turns may not work depending on CG and keel ctr of keel pressure.

A warning that I’ve heard is to not run the fish too shallow. When it gets nasty I’ve heard tales of fish coming out of the water and crashing through the cabin side. Not good and if your fish aren’t deep enough but it can.

First pic is of a very experienced fisherman from Craig Alaska.
Second pic is of a Beebe designed boat.

You would think Beebe would know what he was doing but the stab. rigging looks way far aft to me. The Dixie ll appears to be closer to midship so I'm thinking it may not be that critical. There so far aft on the Beebe boat I wouldn't be too sup- prized to hear tales of getting the gear in the props.

 

[Alaskaflyer]

ofshoreskiff has it about right from what I read and hear.

I would think CG may have something to do w it but ?
The point (fore and aft) where the boat rises and falls the least or just ahead of that point. Heard that too but I think that would be too far aft. If too far fwd lots of strain is put on the stab system .. cabin, mast and poles, cabin or boat via gunwales while addressing a head sea.
On a fish boat frequently to most of the time fishing activities or fishing gear occupies the ideal place.
And how the stern swings to make turns may not work depending on CG and keel ctr of keel pressure.

[…]

First pic is of a very experienced fisherman from Craig Alaska.
Second pic is of a Beebe designed boat.

You would think Beebe would know what he was doing but the stab. rigging looks way far aft to me. The Dixie ll appears to be closer to midship so I'm thinking it may not be that critical. There so far aft on the Beebe boat I wouldn't be too sup- prized to hear tales of getting the gear in the props.

“The proper position for the ends of the poles in the working position is 28 percent of LWL forward of the stern. In all locations appreciably forward of this point, performance grows progressively worse. If located too far forward, when the vessel pitches up, both fish will resist, causing double drag to no purpose.

“The tow wire should be as short as possible while still keeping the fish underwater. Our rig, on a 15-foot beam with 20-foot poles at 30 degrees up angle, put the fish 14 feet underwater at rest. As we skipped one only once in a gale in the Aegean, that was about right. For those who wonder what happens if a stabilizer is pulled out of the water, ours soared straight through the air like a porpoise, dove back in, and went back to work.”

— Voyaging Under Power, 4th Edition by Robert P. Beebe, Denis Umstot
https://a.co/fJO6fug

 

[trawlercap]

This images are a while ago, the guy I got the boat from removed the poles and vanes. He said the geometry was wrong. Too far forward I believe, as it's a double masted boat.

 

[Nomad Willy]

Tcap,
Looks like you could use them aft re the existing mast. Not ideal but if you ran the fish a bit deep should be OK.
You could also use the fwd rig w smaller fish. Since it’s been tested w bigger fish.
Or you could make a midship rig w internal spreader bar over the house roof. Not ideal either (mostly re expense).

Alaskaflyer,
I’m amazed someone calls out a position that specifically. The way it’s nailed down it sounds like 29%is a no no. HaHa
But with too far fwd I think it’s more of a likely/possible structural catastrophe. But extra drag is not good.
But I suspect you could walk most any float in SE and get a wide range of opinions. And they may be good locations. But I’m think’in there are too many variables to be very specific. And I agree being close to 28% as stated would work well for most boats.
My Willard would work well further aft as her ctr of lift and displacement is well aft. But further fwd ???
So I’m think’in too far fwd would be easy to do but too far aft would be harder to go astray.

 

[Simi 60]

I would have thought position would be dictated by supporting structure/bulkheads.

 

[Nomad Willy]

Cap’s boats PO seems to have done that it was problematic.
He used the foremast ... and it’s location.

 

[Simi 60]

Cap’s boats PO seems to have done that it was problematic.
He used the foremast ... and it’s location.

Yep and given Beebes suggested location, aft bulkhead would be more the spot

Plinking a mast in the middle of the proof with no supporting structure under it and then applying a few tonne of load is asking for trouble imho.

 

[trawlercap]

Using 27% from stern comes to 15’. My aft mast is tapered aluminum, stepped through the upper deck to a skookum base. It’s already stayed for and aft with aft shrouds on a wide base. I have to measure but it’s 10’ from mast to upper deck lip aft. The more I read I may be able to rig up a set of poles off the mast aft rather the forward

 

[Alaskaflyer]

The problem I have with the latest edition of Voyaging Under Power is it is sometimes difficult to know what is Beebe's original writing, and what text, opinion, experiences have been added by the subsequent editors. I assume the original calculation was by Beebe, and then Umstot expanded on it with his experiences.

That said, note his calculation is where the working end of the poles should fall in relation to the boat length, not their mounting point. I was really lousy at trig at school but one could assume that the poles could angle forward or aft of their mounting location to accommodate structural and mast considerations, while still managing the loads involved. The potential transfer of forces in such a setup is where my experience, education and intellect fail :lol:

 

[slowgoesit]

The problem I have with the latest edition of Voyaging Under Power is it is sometimes difficult to know what is Beebe's original writing, and what text, opinion, experiences have been added by the subsequent editors. I assume the original calculation was by Beebe, and then Umstot expanded on it with his experiences.

That said, note his calculation is where the working end of the poles should fall in relation to the boat length, not their mounting point. I was really lousy at trig at school but one could assume that the poles could angle forward or aft of their mounting location to accommodate structural and mast considerations, while still managing the loads involved. The potential transfer of forces in such a setup is where my experience, education and intellect fail :lol:

Yeah, I purchased a more recent copy of Voyaging Under Power and read it, then, when on my boat last week, read parts of an earlier edition that came with the boat, and the later edition seems to be just one long advertisement for a specific boat builder, rather than reflecting Beebe's original ideas/principles . . .

 

[ib1810603803]

what is the ratio of boat length, boat beam, mast height, paravane pole length and fish size...thanks