How To Make Holes In Your Boat

Making a hole in your hull is serious business, even more so if your hull is foam-cored. Jeff and Anne aboard s/v Pilgrim and in the midst of a complete refit demonstrate how it should be done...

We have added two new 1-1/2” thru-hulls above the water line.  The port thru-hull will serve as the discharge for the upper, larger capacity bilge pump (3700 G/H).    

The starboard side thru hull will act as a drain for the deck scupper.  We did not like the long hose run from the starboard scupper to the torpedo tube drain manifold.  We also wanted to rig a method for collecting water off the deck if necessary. 

Prior to drilling any holes we assembled the new starboard deck drain plumbing.

Test fit of new plumbing for starboard deck drain.  Note old drain hose at far right.

Test fitting the new plumbing allowed us to accurately mark the location for the starboard thru hull.   The port side fitting connects to a single flexible hose so identifying the exact location was less critical.

Since the location of the holes was marked on the inside of the hull, I began the drilling using a ¼” bit to drill a pilot hole from the inside out.  The ¼” hole matches the diameter of the hole saw pilot bit.  Next, I chucked a 1-7/8” hole saw into the drill and moved outside the hull.  Drilling the larger hole from outside allows for properly aligning the hole perpendicular to the hull and creates less dust inside the boat.

We drilled two 1-7/8" holes in the hull.

The Morgan 382, 383, & 384 hull’s have a foam core above the waterline.  This is the first time we have drilled large diameter holes above the waterline and subsequently our first look at the coring material. 

Close up of plug offers a glimpse of Morgan's construction techniques.

The hull is slightly over one inch thick… the outer fiberglass layer is 5/16”; the foam 9/16”; and the inner fiberglass layer 1/8”

Placing holes in cored hull’s or decks requires additional effort to ensure water never reaches the core material.  In smaller, fastener sized, holes this can be achieved by over drilling the size of the hole and then filling it back with epoxy.  Larger holes for plumbing fixtures require a different approach.

Using a small flat screw driver and a couple different styles of picks, we removed all the coring material within approximately ½” of the hole.

Foam core removed from the area around the hole.

The plan is to fill the newly created void around the hole with thickened epoxy.  So the next couple steps are the usual epoxy prep… 80 grit sanding, acetone wipe down, mask area...  We used a syringe to apply the epoxy and a plastic spreader to achieve a nice clean finish.

Filling the area around the hole with thickened epoxy.

After a couple days for the epoxy to fully cure, we returned to the project.  Using a #49 cabinet rasp and some 80 grit sand paper, Anne cleaned up any excess epoxy from the holes.  While I cut down the length of the threaded section of the thru-hull to properly fit the valve on the starboard side.

Prior to applying any sealant we dry fit the two thru-hulls and masked the surrounding area.  For the final install we used 3M 5200 sealant. Anne worked the interior and I the exterior.

New thru hull fittings are just above the waterline and five feet forward of the torpedo tube drain on either side of the hull.

We are still waiting on hose to connect the bilge pump to the new fitting on port, but we wasted no time installing the new starboard deck drain plumbing. 

New deck drain w/ option for filling water jugs installed.

Since the installation we have weathered a couple heavy rains.  The starboard deck scupper is performing much better with the new system.

What was that you said? 

Why yes that is a new battery selector and bilge pump switch panel in the image above.  I’ll post more info on that project very soon.