Installing a Garboard Drain
in the Bilge

Ever since I acquired Early Light I had wanted to install a garboard drain plug in the bilge. I just had a hard time getting a grip on the fact that I wanted to drill a 1 1/2 inch hole in the bottom of my boat "to let the water out".....but, it certainly makes it handy to just pull the plug once the boat is on the hard for the winter and not have to worry about rainwater coming down the mast sitting in the bilge and freezing.

I decided I wanted a garboard drain that could be mounted flush with the outside surface of the keel stub so as to cause minimum turbulence. I purchased one manufactured by Buck Algonquin from Hamilton Marine. Unlike many of the units that are on the market, this one is 100% bronze. So many of the units I looked at had a bronze body, but the plug itself was made of brass.

This unit is shown in the photo below. The OD of the mounting flange is 3 and 1/8 inch and the flange is 1/4 inch thick. A hole saw 3 and 1/8 inch in diameter was ordered from Jamestown Distributors so the unit could be mounted flush.

Buck Algonquin garboard drain plug

The hole required for the body of the unit is 1 1/2 inch diameter. To locate the unit as close to the bottom of the keel sump as possible, I used my right angle drill to drill a 1/16-inch pilot hole as low as possible from inside the keel stub while keeping the drill bit level. The closest I could get to the bottom of the bilge was 1 and 1/8 inches using my right angle drill. After this hole was drilled I went to the outside of the boat and measured down 3/8 inch from this first hole. This became the center for the second pilot hole which would be drilled from the outside and would become the center for the hole saws.

The next two photos show sketches of how these holes were located.

Drilling from inside using a right angle drill

I marked the location on the outside of the keel sump for the ultimate pilot hole exactly 3/8 inch below the location of the original hole drilled from the inside.

Next I scribed a 1 1/2 inch circle which would ultimately be the mounting hole for the unit.

This unit has a keyway cast into it and therefore must have a matching keyway cut into the keel stub. By taking a 1/4 drill bit and centering it at a convenient point on the circumference of the 1 1/2 inch circle previously scribed with the compass the keyway is almost taken care of in one quick step. All that was left to do to the keyway was to square up the edges a bit with a file once the final mounting hole was cut using the hole saw.

The next step was to mark the depth at 1/4 inch on all the hole saws I had that were between 1 1/2 inch diameter and 3 1/8 inch diameter using blue masking tape. I then started with the largest hole saw (3 1/8 inch) and worked down in size. I cut concentric 1/4 inch deep rings into the feberglass.

Photo showing the concentric cuts 1/4 inch
deep that were made with the hole saws

Once I got down to the 1 1/2 in hole saw, I cut the 1 1/2 inch hole all the way through the side of the keel stub. With this done, using a chisel and Dremel tool, I chiseled and ground the glass that was remaining between the successive hole saw cuts to allow the flange on the garboard drain to sit flush with the surface of the keel stub.

Photo of recess after rough grinding

The garboard drain fitting was then dry fit several times during which the recessed surface received some final touch-up grinding. I had to allow for coating of the surface with a couple coats of epoxy as well as the bedding compound used in the final installation and still get as close as possible to a flush fit.

Photo garboard drain after dry fit was complete It is
approximately 3/64 inch below the finished surface of the keel stub

I then gave all of the raw fiberglass that was exposed two coats of West Systems epoxy to seal it against any possible moisture penetration.

Photo shows all raw glass after two coats of epoxy

Once the epoxy had cured the garboard drain fitting was set in place and three of the holes were drilled and tapped to a depth of 1/2 inch with a 10-24 tap to accept three 10-24 x 1/2 inch silicon bronze machine screws. A fourth hole was drilled completely through the keel stub and then tapped with a 10-24 tap. This fourth hole would receive a 10-24 x 1 1/2 inch silicon bronze machine screw. On the inside it would have a flat washer followed by a lock washer and a nut installed. Since this is the termination for the bonding wire that will electrically tie the garboard drain fitting to the keel bolt to provide bonding it will also have another lock washer and nut to secure the bonding wire. This is done because the entire boat was bonded when it was built.


If your the underwater metal fittings on your
boat are not bonded, then you need not have one
of the fasteners installed all the way through
the glass.

I bedded the fitting and all of the silicon bronze screws with a liberal amount of Fast Cure 3M4200. The screws were drawn up snug and the squeeze out of the 3M4200 was cleaned up. After allowing several days for a good cure of the 3M4200, the bonding wire was fabricated using #6 AWG tinned copper bonding cable to go from the one through bolt on the garboard drain to the central tie point on the keel bolt where all the bonding connections are made.

Photo shows garboard drain fitting bedded in 3M4200

All that remains to be done is to sand smooth after 3M4200 cures and bottom paint.

This completed the work on this project.

Materials Required:

1 ea Buck Algonquin garboard drain plug (Hamilton Marine) $38.99

3 oz tube 3M4200 fast cure caulk (West Marine) $7.99

3 ea #10-24 x 1/2 inch flathead silicon bronze screws (Local Marina) $1.50

1 ea #10-24 x 1 1/2 inch flathead silicon bronze screw (Local Marina) $0.65

1 ea #10 silicon bronze flat washers (Local Marina) $0.10

2 ea #10 silicon bronze lock washer $0.20

2 ea #10-24 silicone bronze flat hex nuts (Local Marina) $0.50

2 ea 6 gauge lugs (on hand) $0.00

6 ft 6 gauge tinned stranded wire (on hand) $0.00

TOTAL $49.93

Tools Required:

Snap-on right angle drill

Set fractional drill bits

Set numbered drill bits

Hole saw 1 1/2 inch diameter

Hole saw 3 1/8 inch diameter

Assorted hole saws between 1 1/2 inch diameter and 3 1/8 inch diameter

Dremel rotary tool

1/2 inch chisel

Small hammer

Tap and die set


1/4 inch drive socket set

File set

Crimp tool for 6 gauge lugs

This project took approximately 5 man-hours to complete

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