Fishing net/trawl drag

[Alfonso]

Hello,

I'm trying to desig a stern trawler of some 40 m in length. But I have a problem. I need to know the fishing gear drag to determine engine power? Does anyone know how is the fishing gear drag determined?

Also if anyone has plans for similar boats, I would much appreciate it.

Thank you in advance!

[JRMacGregor]

Hi Alfonso

As you know, the fishing gear drag/power depends on the geometry of the gear and the towing speed, and whether it is bottom trawl or midwater trawl.

So no easy answer is possible.

There are some references you may be able to obtain

KOYAMA - A calculation method for matching trawl gear to towing power of trawlers, published in MODERN FISHING GEAR OF THE WORLD 3 (published by FAO a division of the UN)

CREWE - Some of the general engineering principles of trawl gear design, MODERN FISHING GEAR OF THE WORLD 2

These are expensive books. Maybe your library can obtain for you ?

[baeckmo]

In addition to McG, you may also turn to the supplyers of winches and see what force levels they are designing for. They have experience from most types of fishing and vessel size.

Then, of course, why don't you ask the fishermen? They have the knowledge, at least they know the best trawling speed for their gear. As a rule of thumb you can say that the maximum cruising speed, homebound with a decent payload, determines the maximum engine power. That power, applied to the optimum trawling speed determines the rest of the propulsion system.

[gonzo]

I think that asking people with experience and looking at existing boats will be one of your best educations. What kind of experience do you have in marine design?

[Alfonso]

McGregor and Baeckmo

Thank You very much. I know that drag of fishing gear depends on many parameters, but I was hoping for some diagrams as an aproximation. But I found something in ''Fishing boats of the world, vol 2'', it will do for now. Also there is a software called ''Trawl vision''. I also contacted fisherman and fisheries before, so I'm waiting for their answers.

Gonzo

I'm a student of Naval architecture and I'm writing my thesis. Thesis is ''Design of a stern trawler'', but I'm concentrated mostly on hull form optimization ( criteria derived from seakeeping, resistance etc.) The goal is to design a hull to minimize rolling, pitching etc., while trying to lower the drag as much as possible.

[peter radclyffe]

http://www.intrafish.no/fn/

[gonzo]

I was a trawlerman. One of the worse things about them is that they are not seakindly. After a week or two of not being able to sleep, just rest while you are lashed to your bunk, it makes us think the design does not consider the crew at all. There would be thousands of thankful trawlermen if someone designed boats that don't pitch and roll as badly. I know that regulations drive the design parameters. However, you mayb give it some thought.

[Sheepy]

Don't know where you were on trawlers gonzo but here in NSW Aus. the prawn trawlers are very good sea boats.

[baeckmo]

Agree withGonzo, there are certainly some awkwardly moving coffins out there. The problem is, that for certain sizes of boat, the stability requirements make the hull roll exactly in that frequency range, where the adult human has his lowest tolerance for movements!

As for fishing performance, you must remember that yawing movements have to be kept low, ie the trawl must progress in a steady speed in the water, otherwise it will jump up and down, and be impossible to "tune".

[gonzo]

I fished the North Atlantic on the American side.

[Alfonso]

It is the main idea. To design a ship with great seakeeping characteristics.

[Alfonso]

Peter thank You!

[gonzo]

Seakeeping characteristics have to be designed for the target area. Sea conditions, wave periods, winds, etc. are different all over the world. There is not such thing as a vessel that is ideal for all conditions. You have to define the parameters and restrictions for you design before anything else.

[Alfonso]

I know,

My area of choice is Medireranean and black sea. I think it's area 37.

[Alfonso]

Sorry! Mediterranean