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Thru Hull Maintenance or Replacement

Greetings Folks -

It has been some time since I visited the site. I tried selling Patriot but to no avail. Lots of lookers but no offers. I was selling for lack of use, so the solution, use her more. That is the plan anyway.

Got her hauled for a bottom job and am checking the thru hulls. Some are really hard to cycle. Will try lubricant and heat to see if I can get them to cycle freely. I want to check them to see if I can see any corrosion or color differential maybe showing the bronze is compromised. I was going to sand the bottom paint off the flanges to see how they looked and discovered there are no flanges on the underside, just a clean hole thru the hull. I am assuming the flanges are glassed over. Is this standard practice on the 382's? On the inside the flange is also covered by a raised area of fiberglass around the thru hull. See photos attached. Is this standard? It will require grinding down the fiberglass to get to the thru hull fitting, on the inside and outside of the hull. And in such tight quarters under the head sink, I am not looking forward to that task. What concerns me most is with this challenging condition I am guessing these have never been replaced. Can thru hulls last 40 years (1982)?


Marc, mine are much the same on Sonata, a 383 from '82. I am also concerned and have the same questions. No thru hulls on the outer hull of ours too, smooth. Many are also difficult to operate and seems at least one is impossible. Sorry I am no help, but hope to hear of other's experience in "renewing".


Frank Buck

My boat is a 382 hull 80. She is taken out of the water every year due to our location. I will attach a picture of the thru hull valves under the sink in the head (3). I am the original owner so this is how the thru hulls looked when it was purchased new. The thru hulls are separate from the valves. I replaced the original gate valves (non rising wheel and non rising stem) in year 2 and replaced them with ball valves similar to what you have. The rust staining is coming from the handles which are mild steel. I replaced one of the three valves 2 years ago not that the valve was bad, but the handle had rusted to such an extent that it broke off. The others have been in place for 40 years. I lubricate all my sea valves each winter with WD 40 and operate them until they work freely. During the season I cycle the valves once a month. I would not use heat if you can avoid it the ball inside the valve sits on Teflon washers which will probably not do well when heated.

On the outside of the boat the flange was counter sunk into the hull and a plastic insert was glued onto the hull to make the thru hull appear to be only a hole. I am sorry I do not have a picture and I am not near the boat to get one.

I hope this helps




Ken Kurlychek
We had to have all five of our through hulls and sea clocks replaced on our 1984 38-4 as our surveyor believed them to be too difficult to open and close for safety reasons. Fortunately we were in Guatemala where labor is cheap so we didn't have to do the work ourselves. They were glassed in and had to be ground out. The guys did a good job but were not very thorough about dust mitigation. You have to really cover and tape off every nook and cranny because the dust goes everywhere.

But, I imagine that if one were good about the maintenance, bronze through hulls and sea cocks could last forever.20181214_163004.jpg
Thanks for the replies. I got the head outflow and the sink drain valves operable but the head raw water supply, which also supplies my a/c not. What do you think of my idea to cap off the head supply and use the sink drain for the head and a/c (they are both the same size). I will drain the sink into the bilge, or see if I can connect it to the shower sump drain. I know, not best practice but I bet I've only used that sink a handful of times anyway.


Terence Thatcher
My thru-hulls are standards flush mount bronze. Old valves replaced with Groco seacocks. 382, #163. Your valves look dangerously corroded. They should screw off the through-hulls, although given the corrosion, it may be difficult. I have never seen glass piled up round the thru-hull as you show. If you can get the valve off, then using a thru-hull tool (grabs the inside of the thru-hull), you should be able to screw the thru-hull out. I cannot believe Morgan would have glassed over the thru-hull. No need to do so and causes problems in removal.


Dave Ahlers
The fiberglass build up is a production boat short cut. No backing plate or through bolts needed.
To address this correctly you need to go with Ken's solution. There should be an inside backing plate installed after the mound is ground flat with the hull. Fiberglass flat sheets can be hole saw cut and used for proper backing plates as opposed to old school wood plates (which eventually rot).
If you haven't done a lot of glass work, or thru hulls it might be time to hire a pro. This is one of those "mission critical" parts that HAVE to be done right. I have a couple 1 1/2" Marelon flanged ball valves & a few smaller bronze ones I'd like to sell. If interested. Text 904 430 5080 / Dave