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Fitting the Chines

On February 25, 2015, in Designer Articles, Plywood Construction, by Glen L. Witt

A chine in a boat is the backing member of the side and bottom planking and is typical on a hard chine hull, meaning an abrupt angle change from bottom to side, not a radius or round shape. In other words, the chine is the usual longitudinal backing typical on vee bottom boats. The backing member is properly a chine “log” but over the years the single word chine has become commonly used.

There are numerous methods of making chines but this discussion will cover the typical solid wood chine on a runabout or sailboat built with sheet plywood or diagonally cold-molded, although the suggestions given will apply to other craft.

The lumber used for chines should be selected with care; good, clear, straight-grain stock, knot free, neither over-dried nor wet. The species of wood can vary widely, but it should accept glue and fasteners well. A chine is highly stressed and soft sugar pines or similar wood should not be considered.

The chine typically extends from stem to stern, preferably is a single piece, and should be at least a foot longer than the installed member. Usual practice is to have the side of the chine parallel to the side frame, although this is not always the case. Sufficient landing must be provided for both the side and bottom planking. Typically, the side planking is lapped by the bottom in the aft section while butting together near the stem. The member will require bending and twisting to force it in place.

Each frame should be notched and beveled so the chine fits tightly against each of the frames and transom. The chine should bend naturally against each frame so that after fairing (beveling), adequate stock is available for fastening the bottom and sides. The bend may be stiff, but should scribe a clean fair line without dips or humps.

Bending and shoving the chine exerts considerable stress on the hull framework so be sure the structure is well braced and won’t move. Bending in the chine for left and right sides simultaneously is desirable to equalize stress. Some, however, feel doing one at a time is preferable and the lesson learned on the first makes the opposite side easier.

fitting the chines of a small boat

A few hints on bending the chine in place. Fit the junction with the stem first leaving overhang at the transom. It’ll probably take several cuts to properly fit the chine to the stem. Use clamps to hold the frames in the frame notches in the aft section. C or bar clamps anchored to the forward portion of the chine will provide leverage and a handle to bend and twist the chine against the stem while fitting.

The actual position of the chine on the stem is not critical. Twisting the chine will alter its ending on the stem. Move the chine at the stem up or down so it forms to the frames and mates flat against the stem contour. This can be visually illustrated by using a 1/4″ plywood strip the width of the chine extending aft of the stem a frame or so to represent what the actual chine must accomplish. The thin plywood will exaggerate what will take place when the solid member used is bent in place.

Sometimes the chine will simply not mate to the forward frame so it parallels the side. A small amount can be faired off, but realize an excessive amount may destroy the member’s integrity. The following assumes the boat is being built upside-down. If the top edge of the chine does not mate solidly against the forward frames, try twisting the chine and letting it land on the stem closer to the sheer edge. If the chine lower edge projects, try moving the chine/stem junction the reverse direction. If you have the chine in place and one of the above conditions still exists, all is not lost. Shims on the inner or outer surface can be used to add material to the chine so it can be faired properly. Finish an outer shim in a long taper so the transition from chine to shim is a smooth fair plane.

build your own boat

The chine sides to the stem in a long compound taper as it junctions against the stem side; typical construction for this type of craft. However, a continuous flat area for the side and bottom planking, stem, and chine must result after fairing. Easier said than understood by most. The stem is usually partially beveled, but final trimming done after the chine is permanently installed. If the chine protrudes too far, it can be faired to a certain extent; if set in too far, a shim will be required.

The photo above illustrates a plywood fixture we have found helpful to determine the position of the chine on the stem side. Keep in mind what has been stated in the foregoing. The bottom and side must mate to the stem and chine on a continuous surface. The chine can’t be located on the stem so that the stem/chine junction cannot be faired to a flat plane. Take small pieces of plywood and simulate the side and bottom joining on the stem to help visualize what the finished junction will look like.

Glen-L fitting chine

After the chine is fitted, pre-drill screw holes for the stem ending, coat all mating surfaces with glue, preferably epoxy. Have a helper hold the chine obliquely away from the boat and position the chine at the stem with a single screw. Use a clamp, rope, Spanish windlass, or braces to hold the chine against the stem if the screw junction is not adequate. Spring the chine around the boat, and when in place, drive a second (or more) screw through the chine into the stem then progressively fasten into the frames. Often, screws holding the chines into the forward frames are omitted at this stage, and the member clamped in place or a finishing nail in a pre-drilled hole or a thin drywall screw. If a large countersunk hole is drilled for a screw, at the point of severe bending, the chine will probably break. After the glue has set and the boat is planked, the screw fastening can be installed. Keep bending the chine after fastening into the frames. Most prefer to leave the chine extending past the transom, trimming to fit, when most of the fasteners are holding the chine to the frames.

fitting the chine on a small boat

We haven’t had to steam chines in place on any of the GLEN-L prototypes. However, we choose the lumber with care and have a big stock to select from. If the member seems difficult to bend, the chine can be forced in place as far as possible. Wrap the area of greatest stress with old towels, pour boiling hot water over the area, and immediately bend in place as far as practical. The process can be repeated several times if necessary; bending the chine progressively forcing it in place. When released, the chine will retain a partial set but can be re-bent in place easier.


small boat plans


chine diagram

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