This term is carried over from wood boats. The garboard strake or plank marks the turn of the hull where it meet the keel. A drain hole at this point can be opened when the boat on the hard to let rainwater out of the bilge. In this case we are trying to correct a problem leak. The bronze rudder shoe which acts as the lower rudder hinge is attached to the keel using bronze rivets. We will be installing two drains. One at the bottom of the keel to drain an enclosed area below the bilge sump and, a second drain near the bottom of the bilge sump.
We started with the lower drain because water filling the enclosed cavity is the greater concern. The weeping in the picture above became more apparent after 18 month on dry land. It was exasserbated by the freeze thaw cycles of the winter and perhaps water is seeping into the cavity from the bilge sump.
Anyway, the first step was to prepare the drain for a bronze fitting with a pipe thread plug that can be removed when Veritas is stored on land.
The keel is about 6" wide at his point and based on the drawings the hollow area is filled with polyurethane foam. I started by routing out a flat area in the fiberglass about 3/16" deep. This allows the lip of the bronze fitting to sit flush with the keel. At the center of this inset I used a 1" hole saw at the center of the inset.
The core removed by the hole saw shows the condition of the fiberglass. The laminates are thick. However, the laminate has separated at about 1/2" and 1" from the outside. We found polyester bog in the enclosed void at this point rather than foam. A significant volume of water began dripping from the enclosed area. It does not flow freely, about 2 or 3 drops per second. However, at this point after two days about 10 liters has been discharged.
We let the opening drip for several weeks and it was still dripping after 4 weeks (although much slower). Once we received delivery of the garboard drain fittings we connected a vacuum pump. The pump is easily generated 27 "Hg negative pressure. However, there is still some leakage that can be observed when the pump is turned off. Initially the 2 quart liquid trap had to be drained every two or three hours.
The more traditional use of the garboard drain is to make sure the bilge stays dry whe the boat is on the hard. Veritas still has a few leaks on the deck and every time it rains some water makes its way in. We added a second drain at the bottom of the bilge. This is just behind the internal keel ballast and about 16" above the bottom of the keel.
We cut the opening starting from the inside and finnished it from the outside once the guide bit passed completely through. Then as before we used a jig to route out an inset area so the bronze fitting will be nearly flush with the hull. This time we had to screw the jug to the hull and then repair the screw holes with epoxy.