PassageMaker - November 2010

Story And Photography By Steve D’Antonio

Seacocks

PART II
INSTALLATION

n Part I of our two-part series on seacocks, we discussed ABYC guidelines and the importance of suitable design and material selection. Now we delve into the details of how to properly install this component, one of the most critical aboard any cruising vessel.

The importance of proper seacock and through-hull installation cannot be overemphasized. After all, the watertight integrity of your vessel relies on these components. Properly selected materials that have been improperly installed may lull you into a false sense of security. While the following information applies to experienced do-it-yourselfers and professionals, a thorough understanding of correct seacock installation techniques will benefit any boat owner who might depend on others to carry out this vital task.

Before beginning installation, ensure that safety gear is used: eye protection, rubber gloves, and a dust mask and/or respirator. Although there are several common installation methods, my preferred approach is as follows. For a new seacock installation in a solid, un-cored hull, select a location and drill a 1/8-inch pilot hole. After confirming that the installation location is correct, use a hole saw to drill a hole that is as close as possible to the through-hull fitting’s outside diameter. A snug fit is desirable; a 1-1/2-inch hole for a 1-inch through-hull fitting is less than ideal, while a 1-1/8-inch hole for the same fitting would be fine.

Replacing an existing seacock with a like unit requires no drilling, provided the existing hole is correctly sized. However, the old through-hull and seacock must be removed, a task that presents its own set of challenges. If the through-hull and seacock cannot be easily separated, the through-hull’s “mushroom” may be ground off using an electric or pneumatic grinder and a 36-grit sanding disc. If this is done carefully, without damaging the gelcoat or fiberglass (heavily masking the area around the through-hull will help), the process may be accomplished quickly and easily. Once the mushroom is gone, the seacock may be withdrawn from inside the vessel.

A backing block, an essential component for any seacock installation in a fiberglass or timber hull, should be fabricated from 3/4-inch AA marine fir plywood or prefabricated fiberglass sheet (the latter is commonly referred to as GPO- 3). High-density polyethylene materials such as King StarBoard should not be used as backing blocks because they are slippery and therefore seal poorly. Solid timber, regardless of species, should never be used as a seacock backing block because of its propensity to fracture under load, particularly when used against irregularly shaped surfaces like the inside of a fiberglass hull.

The size of the backing block should be proportionate to the size of the seacock’s base. In general, a round backing block that shows a minimum of 1 to 1-1/2 inches between its outside perimeter and the seacock base is appropriate. Thus, a seacock whose base measures 4 inches in diameter should utilize a backing block with a diameter of 6 or 7 inches.