Thru Hull Backers

Sep 11, 2011
Hunter 41AC Bayfield WI, Lake Superior
Simple question, Is there a reason that most backers are made from plywood vs starboard, or fiber glass etc? Money? The wooden ones inevitably swell during the season, and then while on the hard shrink and dry out. This spring before launch I found a few through hulls that had nuts that could be tightened a bit by hand.

Sep 25, 2008
Alden 50 Sarasota, Florida
Asking what reason people have for doing anything is not a simple question. If you are asking what is the best material for backing plates, I think you answered that by describing your recent Spring experience.
Feb 14, 2014
Hunter 430 Waveland, MS
Simple answer...
The backer plate acts like a washer and must distribute the load of Valve Open/Close.

Stuck valve, strong hands = Break off the thru hull valve.

Look here for better answer...
Seacock Backing Plates - Marine How To


PS: King Starboard flexes too much.


Jun 3, 2012
Hunter 33 Steamboat Wharf, Hull, MA
If you use epoxy to bond the fiberglass backing plate to the hull, be sure it will hold the thruhull mushroom exactly flat against the hull exterior. Once the epoxy cures there is no way to adjust this fit. Alternatively, if you bond the backing plate to the hull with an appropriate sealant, it should square itself with the hull when you install the thruhull assembly and tighten while the sealant is still pliable. Sealant is easier to use than epoxy for backing plates and a seawater leak in this application is unlikely.
May 24, 2004
CC 30 South Florida
Whatever you choose, let it be the weakest link in the chain. It is not supposed to last forever, just approximate the life of the thru-hull.