Fabricating Pads for New Seacocks (Replacing Thru-Hull Fittings and Seacocks – Part 2)

With work on the exterior of the hull progressing along it is time to fabricate new mounting pads for the seacocks.  I am creating pads to serve two purposes.  First, the pads provide a smooth flat surface for mounting the seacock on the interior of the hull.   Secondly, since I do not plan to thru bolt the seacocks to the hull the pads provide a thick stable surface to which the seacocks can be mechanically fastened.

Morgan used 5200 to adhere plywood pads during the original construction. The image below, taken in January, is of the original plywood pads in the head.

Pilgrim's original plywood seacock pads in the head.

Pilgrim's new seacock pads will be created from fiberglass (FRP) board.  Prefabricated FRP board can be purchased in sheets up to 4’ x 8’.  The material is also available in many thicknesses.  I’ve seen it range from 1/8” to 2” thick.  Commercially the material can be sourced under the name GPO3  or G10 Fiberglass Board. 

Fortunately there is a pile of scrap G10 material left over from other projects here at the boat yard.  Attaching the seacocks to the pads via tapped holes rather than bolting through the hull requires a pad thickness of at least 5/8”.  Achieving a 5/8” thickness while scavenging from scrap pile required laminating 3/8” thick pieces together for the larger pads.  I was able to find scraps suitable for creating pads for the two smaller seacocks.

Cutting fiberglass is brutal on saw blades and drill bits.  Only after destroying two blades on my jigsaw did I discover that there are blades specifically made for cutting FRP

The right tool for cutting FRP 

Having the right tool for the job is invaluable.

Cutting, drilling, and sanding FRP creates a noxious dust.  So… always wear a high quality dust mask.

4 of the 5 thru-hulls we are installing will be located in new positions on the hull.  For these we purchased mushroom (button) style thru-hull fittings.  Pads for these thru hulls were relatively simple round or square shapes. 

Rough cutting the G10 Board.  The two discs at top will be laminated into a single pad.  The two square pieces below are for a recessed thru-hull in the head.

The Morgan 382’s original thru-hull fittings were recessed.  We are replacing one of the original recessed thru-hulls, the head sink drain.  Since the fitting is recessed the interior fiberglass bulges upward around the fitting.  Fabricating a thick seacock pad for this thru-hull required two layers of G10 board.  The initial layer has a circular void in the center to accommodate the hull shape.  The second layer is a solid piece of G10 board.

The pads as they will look when laminated together 

I laminated the pads for the mushroom style thru-hulls together prior to installing them in Pilgrim.  The two layer pad for the recessed thru-hull will be laminated together during the installation process.

Test fitting the seacocks on the completed pads.