Trunk_Building_Guide.pdf

Combahee River Style

Rice Field Trunk Construction Manual

Bear Island Wildlife Management Area South Carolina Department of Natural Resources

Introduction

Rice field trunks have served to manage water levels along the South Carolina coast for 300 years. Wetland managers today use almost the exact same design as used first by rice planters in the early 1700’s, although materials have changed since those very early days.

This manual provides information and detailed drawings to construct a Combahee River style trunk using 2.5 CCA treated SYP with stainless steel fasteners. Based on these plans, a standard-sized trunk should measure 23 inches by 60 inches by 32 feet, outside dimensions. Georgetown style trunks function similarly but with some design differences especially in the uprights and the doors. Properly constructed and installed trunks may last up to 30 years, but need eventual replacement.

Acknowledgements

The entire DNR staff at Bear Island WMA provided excellent advice and instruction in the preparation of this manual. Manager Ross Catterton along with Matt Smoak and George Todd provided many insights and helpful tips based on their long experience in the construction and installation of trunks. Part-time Bear Island employee Seabrook Platt meticulously reviewed the copy and drawings, correcting many details as well as offering much very useful advice. Terry Cox has also been helpful.

DNR’s ACE Basin Project Coordinator and good friend Dean Harrigal has been very supportive and encouraging in the preparation of this publication.

Karen Swanson provided the design/layout and graphic enhancements. Phillip Jones assisted with the photographs.

Pete Laurie February 2005

Combahee River Style

Rice Field Trunk Construction Manual

Rice field trunks allow water to pass beneath dikes to control water levels in impoundments managed to provide winter habitat for migrating waterfowl.

Preparation of this manual was funded by NOAA Grant NA03NOS4190168, Restoration of coastal impoundments in the ACE Basin.

Constructing the Muzzles

The muzzles provide reinforcement for the ends of the side boards and allow for proper fit of the doors when closed.

Select straight, knot free pieces with as little heart wood as possible for muzzle construction. Each muzzle requires about 17 linear feet of 4 x 8 inch lumber.

The mortises on the horizontal pieces and the tenons on the vertical pieces should be cut as precisely as possible and should slid together easily but snugly. Make sure to cut the mortises exactly 58 and 1/4 inches apart and the shoulders of the tenons exactly 17 and 1/2 inches apart (see figure # 1).

This will ensure a proper fit on an 18 inch by 60 inch trunk.

The front edges of all four pieces of each muzzle must be perfectly flush to ensure the door fits tightly.

After fitting the four pieces together check each muzzle for square, and lay each on edge of a flat surface such as a concrete floor to make sure they have no twist in them. Then carefully drill 5/8-inch diameter holes through each mortise and tenon joint and secure with 8-inch stainless steel bolts and flat washers. Countersink the bolt heads on the front edge to keep them from interfering with the door.

Figure 1

Mortise and tenon joints used to connect the muzzle parts must be cut carefully to insure a precise fit.

Preparing the Side Boards

The two side boards should measure approximately 4 inches by 18 inches with a length of at least 32 feet. Select the better side of each board for the outside and designate any crown for the top edge. Then place the boards flat on their inside surfaces on rollers such as metal pipe to facilitate movement of the finished trunk.

Square one end of each board and measure off 32 feet to the other end of each to ensure that both finish out to equal length. Next, mark the top edge back 5 inches from the squared ends and cut on a diagonal of about 15 degrees from that mark to the corner of the square mark on the bottom edge. (see figure # 2). Then mark a line 6 inches back from cut and cut a 7/8-inch rabbet using a circular saw to hog out the waste and clean out the rabbet with a chisel and a belt sander. The muzzle should fit into the rabbet and secure the side boards at 60 inches apart. (see figure # 2). Note: The set back can be reduced from 5 inches to 4 inches or less to change the angle of the doors and possible reduce turbulence at the muzzles. However, be sure to leave enough space to allow placement of the battens which support the uprights.

Attaching the Muzzles

Slip each completed muzzle over the end of the side boards and clamp each into the rabbet making sure each muzzle fits tightly.

Check the side boards to make sure they are square with the muzzles on each end. Adjust as necessary. Bolt the muzzles to the side boards with four stainless steel bolts, 5/8 x 8 inches, with flat washers.

Figure 2

The muzzles fit securely to the ends of the side boards holding them in place for the decking, making a tight fit for the doors and reinforcing the ends of the trunk.

Decking

After making all the required cuts, stand the side boards on edge, bottom side up. Decking should consist of 3 x 12’s cut to 60 inches in length. If the side boards have any bow or other defects the length of each decking board may have to be adjusted slightly.

Deck the bottom of the trunk starting with the first board on each end. These should be ripped on a 15 degree angle to ensure a tight fit with the muzzle. Nail each board with four 1/4 (no. 4) x 6-inch ring shank stainless steel nails.

Drill pilot holes in the decking boards to accommodate the nails. Add boards from both ends and rip the final board to width to ensure a tight fit.

Once the bottom has been decked, turn the trunk over using a front end loader or other hydraulic implement. Again, start by ripping two decking boards on a 15 degree angle to fit snugly against each end of the muzzle. On one end then add four more decking boards.

Traditionally, wooden pegs were used to secure the decking boards to the side boards and some trunk makers still use wooden pegs or a combination of pegs and nails.

However, in this plan only nails are used for several reasons.

They require less labor to install and require smaller holes protecting the structural integrity of the decking boards. Also, wooden pegs, regardless of treatment, expose end grain to the elements and thus can rot quickly.

In this construction technique the only wooden pegs used are the eight required to secure the uprights.

Building the Spillway Sides

The spillway sides consist of one layer of 3x12’s with a second layer of 3x’s ripped to width and bolted to the first layer (see figure # 3). The 2 and 1/2-inch slot on the inside layer allows for the spillway boards to be added and removed once the trunk has been placed into service. The 2 and 5/8-inch notch on the bottom of the lets the front edge of each side fit on top of the fifth spillway board from the end. Note that the two sides are not identical but mirror images of each other and must be built accordingly. The spillway sides need not be a full 96 inches and can be shortened slightly depending on the width of the back decking boards to eliminate the need to rip the top board.

Figure 3

Install the decking boards from each end toward the middle. The final board will probably have to be ripped to width to fit.

Building the Uprights

Each up right consists of two vertical legs, two horizontal stretchers, constructed of 3x10’s and a 4x8 spindle. Select straight, knot free materials for all five pieces. Cut the two mortises in each upright and the tenons on the stretchers so that they fit smoothly together (see figure # 4). Drill a 4-inch hole in each upright to accommodate the spindle.

Cut the three mortises and make the nipples on the spindles as illustrated in figure # 4. Place the five pieces on edge on a flat surface and assemble. Drill a 11/4-inch hole in each tenon as close as possible to the outside surface of the uprights. Note that the holes in the top stretcher are horizontal and in the lower stretcher vertical relative to the decking of the trunk. Insert a wooden peg (see figure # 6) through each hole and tap firmly into place to complete construction of the uprights.

Figure 4

The uprights hold the doors in place and allow them to be raised and lowered as necessary to control water levels. Note that this trunk does not incorporate a spillway.

Making the Spindles

Select straight, knot free 4x8 material to construct each of the two spindles. Rough out the nipples on the ends on a table saw or with a circular saw. With a 31/2-inch hole saw round off each end and then trim back to the notch with a reciprocating saw and belt sander or with hand tools.

The three mortises for the paddles can be hogged out with a large bit on a drill press and then cleaned up with a jig saw using a 6-inch blade, or with a reciprocating saw or a sharp chisel. Cutting a small 45 degree camber on the shoulders of the notches reduces binding once the spindle is placed between the uprights.

Figure 5

The doors hang from the spindles which allow them to open and close with tidal flow.

Making the Pegs

This design requires eight wooden pegs, four in each set of uprights. Make each peg from 11/2 x 11/2 stock cut to a length of 12 inches. The barrel of the peg should finish out to 11/4 and fit snugly into the holes on the stretchers.

Setting the Spillway

Set the two sides of the spillway with the front edge of each approximately 47 inches back from the back edge of the muzzle (see figure # 7). The notch should fit over the edge of the fifth decking board, counting the first one which was ripped on a bevel to fit against the muzzle. This ensures enough room to attach the uprights.

Make certain each side is square and plumb with the side boards. Plane the ends of the decking boards or the top surface of the fifth board if necessary to ensure the spillway sides are plumb and square. Attach each spillway side to the side boards with four 5/8 x 8-inch stainless steel bolts with flat washers. Use a pipe clamp or a spreader board as necessary at the top of the spillway to ensure the same measurement from top to bottom. Nail the back boards on the spillway using straight lumber that fits tightly edge to edge, using a pipe clamp if needed. With the spillway in place, finish decking the top side of the trunk.

Figure 6

The eight wooden pegs used in this design can be shaped in several ways but turning them on a lathe produces a uniform, snug fitting peg.

The spillway must be set far enough back from the muzzle to allow for the attachment of the uprights but no further in order to leave room for a dike wide enough to drive across.

Setting the Uprights

Using a front end loader or other implement, stand each set of uprights vertically and slip them over the sides of the trunk about 17 inches back from the muzzle. The lower stretcher should rest on the decking. Slide the paddles of the doors through the mortises in the spindle with the lower edge of the door flush with the bottom of the muzzle. Then carefully bump the uprights back and forth until the door closes flush against the muzzle. This is critical to ensure a watertight fit.

With the uprights properly positioned check them for square and plumb to the trunk. Then bolt a 3x10 batten to the side board on either edge of the uprights, leaving a gap of about 1/4 inch on one side to facilitate removal or replacement of the uprights as necessary (see figure # 7).

Once the battens are secure, mark the top edge of the spindle to determine the top hole in each that will allow the door to be fully lowered to the bottom of the muzzle.

Then remove the doors and up rights to protect them during transport of the trunk. Drill the remaining holes in the paddles to allow raising and lowering of the doors with a lever.

Because the uprights are not attached to the side boards they can easily be removed and replaced.

Due to constant exposure to the elements, uprights and doors often need replacement before the trunk itself does.

Figure 7

Install each upright at the correct distance from the muzzle to insure that the door fits tightly against the muzzle. The doors and uprights can then be removed until the trunk is installed.

Building the Doors

First clamp together three 74-inch long pieces of 2x10-inch tongue and groove. Make sure that this assembly remains as flat as possible while clamping. Then clamp the three paddles to the door as illustrated in figure # 8. Bolt the paddles to the door with 3/8 x 41/2-inch bolts, making sure each paddle is perpendicular to the door. Cut the ends of the paddles to length. The necessary pin holes and pry holes will be drilled after the uprights have been secured to the trunk.

Figure 8

Slide the door paddles into the mortises on the spindle to help determine the position of each upright.

Conclusion

Not everyone makes trunks in quite the same way or to exactly the same dimensions. However, the above instructions and accompanying drawings will allow anyone with some carpentry skill to construct a serviceable trunk which, when properly set, will offer years of maintenance free service.

Materials List (add 10-15 percent for waste)

4 x 18 x 32’ - 2 ea

3 x 10 x 16’ - 8 ea

4 x 8 x 16’ - 3 ea

3 x 12 x 16’ - 24 ea

2 x 10 x 16’ - 2 ea

2 x 10 x 16’ - T&G - 4 ea

2 x 8 x 16’ - T&G - 4 ea

2 x 8 x 16’ - 4 ea

Note: Width and thickness of lumber varies slightly with each batch, often requiring minor changes in dimensions shown in drawings.

nails 1/4 x 6” ring shank stainless - 1 50lb. box bolts

flat washers and nuts

Most materials require special order from lumber dealers who specialize in large timber with sufficient treatment to last in an aquatic environment.

The South Carolina Department of Natural Resources, an Equal Opportunity Employer, prohibits discrimination on the basis of race, color, gender, national origin, disability, religion or age. Direct inquiries to the Office of Human Resources, P.O. Box 167, Columbia, SC 29202.

Total copies: 25

Total cost: $113.25

Cost/copy: $4.53

Printed on Recycled Paper February 2005

A finished trunk, complete with doors and uprights, ready for installation.