Sunday, September 22, 2013

Through with Thru-Hulls

I don't know if I've mentioned this before, but we have 21 Thru-hulls.  Yes, 21!!!  17 of which are below the waterline, including the shaft log and the rudder.  That is a lot of holes to keep track of. We created a nerdy diagram using our boat's layout and marked out where every single one of them is located with colored dots.  Frank decided to glass over the thru-hull for the old speed log since we went with a combination unit from Furuno that measures speed, depth, and temperature.  Though this was a straight-forward project, it was a bit more time consuming and itchy than we had thought it would be.  Frank had initially planned glassing over several of them, but after tackling this one, he has decided we should just replace the unused thru-hulls and cap them.  We ended up replacing 11 of them, mostly because the old ones did not have proper flanged bases.  They were just ball valves attached to a thru-hull.  If knocked hard enough, they could easily snap off without support at the base.  Some above-the- waterline ones were made of plastic and had severe UV damage to the point of crumbling upon removal, so these also were replaced with bronze.  Though these are expensive purchases, they rarely need replacing if properly installed and maintained, they are also good insurance that water will stay on the outside of the boat, where it belongs. Defender occasionally runs good sales, and we had bought all 11 during one of their big sale events.  

Thru-Hull Diagram

We went with Groco thru-hulls as we've had bad experiences with the Apollo brand.  Several of the ones we've purchased in past would not open or close, even when brand new.  Even a West Marine representative had tried, in vain, to get them to work after refusing to believe us when we told him what was happening.  I secretly enjoyed watching his neck and forehead veins bulge when he attempted this,  and did all I could to not giggle and say "I told you so..."

Groco Thru-Hull
Installed for our new Furuno combination unit
Fairing block for unit sculpted with West Epoxy and high density filler
Look how thick our hull is!  

When we installed the thru-hulls, we followed this guy's method that we had found online, and replacing them proved to be a piece of cake with 2 people.  Hopefully they don't leak.  Frank tackled plugging up the single thru-hull by first tapering the hole at a 6 to 1 bevel.  He then put a singular layer of glass on the inside of the hull to help support the external lay-up.  From there, he cut concentric circles each approximately 3/4" bigger than the last of 5108 bi-axial fiberglass cloth to fill the void.  Then it was just a matter of rolling on the epoxy and using a laminate roller to squeeze out any air bubbles and excess resin in the lay-up.  Eventually this will be sanded over and painted when we do our barrier coat and bottom job.    

Start with smaller circles and work your way up...
Finished glassing over


  1. I had to replace a seacock. I also went with Groco because of the old ones were like yours with a thru-hull and ball valve with no other support. I have 7 more to change someday. I also want to change them because they are mounted with wood backing and I want to use G10 (fiberglass board) for more strength. I also used the same source of info for replacing them and I was happy that it was much easier than I expected.

  2. You know, it's funny. Everywhere we go, every time Matt gets into a boat conversation, he always goes into Hans Christains and how well they're built. And then goes into "Our friends own boat I've ever seen...". Think about you guys often, we miss you!