Auburn University Marine Extension &Research Center SEA GRANT EXTENSION

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CIRCULAR ANR-791

MASGP-93-005

Trawl Doors And Tickler Chains

Recreational shrimpers are often interested in constructing their own trawl doors or adding tick­ler chains to their shrimp trawls. Both of these items are very critical to successful shrimping. The trawl boards provide the spreading force to open the mouth of the trawl net and the additional weight necessary to keep the net on the bottom. The tick­ler chain acts to scare shrimp off the bottom, mak­ing it more likely that they will be swept into the trawl. The following directions should provide the necessary information to construct a set of trawl doors and add a tickler chain to a standard 16-foot (headrope length) shrimp trawl. A 16-foot trawl is the maximum size that may be used by licensed recreational fishermen in Alabama waters.

'frawl Door Construction Step 1. You will need enough %-inch exterior­

or marine-grade plywood to cut two pieces, each 30 inches long and 16 inches high. You should cut with the grain of the wood on the 30-inch cut.

Step 2. Drill six l-inch holes as shown in Figure 1. The end with two holes is the front of the door; the end with four holes is the back of the door. The front two holes are placed 61/z inches from the front edge, 3 inches from the top, and 2 inches from the bottom. The first set of back holes is placed 11/z inches from the back edge, 3 inches from the top, and 2 inches from the bottom. The second set of holes is placed 7Vz inches from the back edge, 3 inches from the top, and 2 inches from the bottom.

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--------~-------- ----------:,- -~--- - - - -~-1 2-T t I

30"

Figure 1

Step 3. Cut the bottom front comer of each door to make a rounded profile (Figure 2). The curve should be cut on a 4-inch radius.

Step 4. Thread approximately 30 links of gal­vanized chain (V8 or :Y16 inch) through the 7Vz-inch top back hole tmtil the first link reaches the bottom front hole (Figure 2, Chain A). Pin the other end of Lhis chain (top back chain) on lhe outside face of the door with a galvanized 20-penny nail, leaving three to four links beyond the nail. Secure the nail with four staples. Handle the other top chain (Chain B, approximately !Slinks) tJ1e san1e way, from the top front hole to the boltom front hole, leaving three to four links beyond the nail. It is important that these two chains end as close as possible to the bottom front hole. Do not pin these chains at the bot­tom hole. The chains are only placed at this hole to determine the proper length.

Next, add the bottom chains, which must be one link shorter than the corresponding top chain (Figure 3). For example, if the top back chain is 30 links, then the bottom back chain must be 29 links in length.

0

B-+

0 ' ·-r---------------~

4" Radius

Figure 2

Inside face of door

0

0

Figure 3

Again, pin the chains to the outside face of the board leaving three or four links beyond the nail. Attach the free ends of all four chains together with a !fa­or o/winch shackle and a swivel.

Step 5. Bend a 32 x 2 x 14- or %-inches piece of flat iron to fit the bottom of each door and a portion of the front curved section (Figure 4). This iron piece is called the shoe and protects the bottom edge of the door from abrasions. The shoe is attached to the door by welding six pieces (three on each face) of 6 x 1 x 14-inches iron to the shoe and bolting each pair of iron pieces together through the door with two 11/z- to 1 %-inches carriage bolts.

Step 6. Secure the top line (headrope) of the trawl to the top back hole of the board, leaving 2 to 3 feet of line between the door and the webbing of the trawl. Likewise, secure the bottom line (foot­rope) of the trawl to the door using the same dis­tance between the door and the webbing as was used for the top line. Thwlines are then attached to the swivel on the shackle holding the chains together and the trawl is ready for use (Figure 5).

Outside face of door

Nail

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Iron p1ieces -

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T 6"

l 32"1~nbar

Figure 4

Finished inside face

Figure 5

Adjustments in trawl performance can be made by removing the pins and lengthening or shortening the door chains. If the doors are not staying on the bottom, lengthening the two top chains one link can help. Th increase the horiwn­tal spread, the top and bottom back chains can be shortened as long as they are shortened the same amount.

Tickler Chain A tickler chain can be added to any trawl easily.

The only trick is to make the chain the right length so that it will run in front the of the net and on the bottom. The chain should be made of V8- or 3ft6-inch diameter links.

Step 1. Start at one side of the trawl and put the ends of the bottom (footrope) and the top rope (head­rope) together. Holding both ropes together, move hand over hand to the other side of the trawl. As you approach the ends of the ropes, you will see that the footrope is longer than the headrope. This difference in length (footrope minus headrope) is referred to as the setback of the net.

Step 2. The tickler chain is then made the length of the footrope minus one-half the setback as deter­mined in Step 1. A simpler formula states that the tickler chain should be longer than the headrope and shorter than the footrope. The proper length of chain that you have determined is then attached to the bot­tom back hole of each door with a shackle.

Materials List 1 piece of %-inch exterior- or marine-grade plywood,

30 x 32 inches or larger. 37 feet of galvanized chain, 1/8-inch or :lf16-inch . 8 20-penny galvanized nails. 32 staples. 4 shackles, V8-inch or 3j16-inch. 2 pieces of flat iron, 32 x 2 x 1.4 inches. 12 pieces of flat iron, 6 x 1 x 1.4 inches. 24 carriage bolts with nuts 11/2 or 1% inches. 2 swivels, Ys inch or :lf16 inch.

The

E.6.1Aiobomo ~Cooperative

Extension Service AUBURN UNIVERSITY

CIRCULAR ANR-791 MASGP-93-005

Alabama Sea Grant Extension Program Auburn University

Marine Extension & Research Center 4170 Commanders Drive, Mobile, AL 36615

(205) 438-5690

Cooperating Agencies Alabama Cooperative Extension Service Alabama Sea Grant Extension Program

Alabama Agricultural Experiment Station Auburn University College of Agriculture

Department of Fisheries and Allied Aquacultures

This publication was prepared by Richard 1<. Wallace, Ii:~tensioll Mari11e Specialist, and Anthony Serra, National Marine Fisheries Service. This work is partially sponsored by the NOAA Office r Sea Grant, .S. Department of Commerce tmder Granl No. NA16RG0155-02. Issued in furtherance of Cooperative Extension work in agriculture and home eco· nomic:t J\CI~ or Mny 8 nd June 30, 1914, in cooptrohon with tim U. O..:r,g•tmenl of A)J.flCuhurc The Alnl:t.1ma Cooperative Extension !)ciVic~. Aubum ni\·e•"flit)'• Ann E. Thompson , Olrcctor offers educalional proguuns nutl ntnteu-,Ls lo nil peoplt! without n::gurd IU rm:c r.olor, naliona l origin, sex . ugc. 01 hllll~knp ntHJ is"'' C(luAI opJlOr lllnlty <IIIJll )' ·r UI'S 2M08 7:93, ANR ·791