How Thick Is Your Hull?

It is rare that “good old boat” owners get the opportunity to measure their vessel’s hull thickness in various locations.  Re-locating four of Pilgrim’s thru-hull fittings has afforded us such an opportunity.  With the exterior hull repairs complete the time to drill arrived. 

Drilling holes for Pilgrim's new thru-hull fittings.

The starboard side intake thru-hulls -  a ¾” thru-hull in the wet locker forward of the nav station for the house raw water intake and a 1 ½” thru-hull under the quarterberth for the engine raw water intake – were the first to go under the drill.

Peering through the freshly cut hole into the quarterberth.  This 1 1/2"  hole will serve as then engine raw water intake. 

Of the port side discharge thru-hulls – 1 ½” galley sink drain, 1 ½” black water discharge, and ¾” head sink drain – only the two 1 ½” holes were relocated.

It is worth noting at this time that many, dare I say most, vessels place intake thru-hulls in relatively close proximity to discharge thru-hulls.  By placing all the intake holes on the starboard side of Pilgrim and the discharge holes on the port side I believe we stand a much greater chance of not pulling in our own waste water back into the boat.    Allow me to digress no further down this path and return to my commentary on hull thickness.

Ok – the drilling process went smoothly.  Like polar ice core samples to climate researcher the plugs from Pilgrim's hull offer a glimpse into the history of our hull. 

Generally we were pleased by our findings... all dry, solid FRP with no voids.  Our plugs revealed a surprisingly consistent  ½” thick hull layup.  The plug from the galley drain site, starboard and approx. 6” outboard of the keel is the thickest at 5/8”.

Plugs removed from Pilgrim's hull.  From left to right - head, galley, wet locker, quarterberth.

The image of the plugs is a bit misleading since the ½” seacock pads were epoxied to the hull prior to drilling.  The inner (top in the image above), green section of each plug represents the 1/2" thick seacock pad.

Where is the thickest portion of the hull?  Last winter we removed an old transducer located on starboard just aft of the entrance to the vee berth…

removing the aft of two transducers located starboard and forward of the head.

The hull thickness at this location was 1 1/8”.

A glimpse of the hull thickness at the site of the old transducer

We had no plans to reuse the hole and it was filled during our Tabbing Repairs Project.

The site of the old transducer thru-hull was filled as part of tabbing repairs around the head pan.

My guess is the layup along the midline of the hull is very thick, but my hope is to never have the need to personally assess any additional areas of Pilgrim’s hull.