Glassed Over Thru Hull?!

[TheWinterSailor]

Hi Everyone,
Last year I bought a 1979 C&C 27 and decided to enjoy the season as much as possible and start dealing with repairs when she was on the hard for the winter. I decided that replacing the thru hull fittings would be a good idea this year because I'm not sure when they were last done and noticed something strange on the bottom of the boat, did the last owner glass them in?! Attached are two images of my cockpit drains, port side you can see the fitting, and starboard side you can only see the drain hole. I'm mighty confused by this and wondering if anyone else has a similar experience.
Theres a few fittings on the boat like this that I want to take care of ASAP.



hmm... Images didn't seem to show up. Attached are two links to the pictures:
https://photos.app.goo.gl/ckmn1LhNHfFrRQVT7
https://photos.app.goo.gl/6agc3SHoVGsbu2i86
Thanks for any advice in advance!

[double u]

https://shakewell.info/
https://www.forespar.com/products/bo...ce-valve.shtml
maybe?

[TheWinterSailor]

Originally Posted by double u

https://shakewell.info/
https://www.forespar.com/products/bo...ce-valve.shtml
maybe?

Those look like some awesome products but definitely not them. Inside are some old gate valves, another reason I want to get rid of them.
https://photos.app.goo.gl/DrixEbhFMc3aBhJx7

[MicHughV]

that one pic looks like a flush depth sounder to me...

[cal40john]

They're not glassed over. Maybe a wooden bung driven in.

[TheWinterSailor]

Originally Posted by MicHughV

that one pic looks like a flush depth sounder to me...

Both of the pics are 100% my cockpit drains, depth sounder is forward of my keel.

[MicHughV]

the second pic doesn't look like a thru' hull at all....just a chip of bottom paint missing..

[TheWinterSailor]

Originally Posted by cal40john

They're not glassed over. Maybe a wooden bung driven in.

Definitely no bungs have been driven into either cockpit drain. The holes are draining freely but they're not round, like someone tried to fair the bottom smooth at some point and partially filled the fittings with fairing compound.

[PerfectPirate]

Hello WinterSailor,
They are unlikely to have been glassed in. C&C used a "flush-mount" style of fitting which is recessed into the hull. Depending on what has been applied over the bottom, the outline of the fitting can simply be totally obscured. After I had applied several coats of Interprotect 2000 epoxy coating to the bottom of my old 27, all of the through-hulls simply appeared to be seamless holes in the bottom of the boat. Same effect when I did that same bottom job on my C&C 25, before owning the 27. It looks as though something similar has been done to the bottom of your boat, at least on one side. If you sand down the area around the obscured fitting, the outline will likely be revealed.


If your 27 still has the original gate valves installed, then replacing them is probably a very good idea. However, be aware that the threads on through-hull fittings are NPS (National Pipe Standard) and the threads on virtually all valves are NPT (National Pipe Tapered). So there is a mismatch, which means that although you can manage to screw the valves on to the thru-hull fittings, the threads do not engage sufficiently for it to be considered truly safe. When I recently replaced all of the valves in my 32, I used either Marelon valves, which have a true NPS thread, or the Groco adapter plates, which screw on to the thru-hull with an NPS thread but provide an NPT thread for the valve to screw on to. The Groco adapter plates are a more ABYC-compliant solution and, in my opinion, preferable to old-fashioned true seacocks since they allow easier replacement of damaged or degraded valves in the future.

In any case, please make sure that you are using marine-grade bronze fittings, not brass ones which will break down from electrolytic action. Or of course, the reinforced polymer valves, such as Marelon or TruDesign. But Ball Valves are definitely the way to go!

[TheWinterSailor]

Originally Posted by PerfectPirate

Hello WinterSailor,
They are unlikely to have been glassed in. C&C used a "flush-mount" style of fitting which is recessed into the hull. Depending on what has been applied over the bottom, the outline of the fitting can simply be totally obscured. After I had applied several coats of Interprotect 2000 epoxy coating to the bottom of my old 27, all of the through-hulls simply appeared to be seamless holes in the bottom of the boat. Same effect when I did that same bottom job on my C&C 25, before owning the 27. It looks as though something similar has been done to the bottom of your boat, at least on one side. If you sand down the area around the obscured fitting, the outline will likely be revealed.

I Think you just nailed it! What you're describing is exactly what I'm seeing on the bottom of my boat. I've been going back and forth on marelon vs. bronze, and as I Millwright have a good grasp on the issue between NPT & NPS, now just to make sure I read the fine print and don't mix the two up.

PerfectPirate, do you recall if you used a barrier coat when you replaced your thru hull fittings or was filling with an appropriate sealant enough to prevent possible blistering from water intrusion on your hull? I'm having a hard time justifying buying a quart of Interprotect or Petit Protect just for 5 thru hull fittings...

Thanks!

[PerfectPirate]

On my boats it was always an integrated project: sand down the bottom, replace the thru-hulls and then Interprotect the heck out of all of it. So my thru-hulls always got covered with barrier coat. In your case, if you are sanding back the bottom around your thru-hulls, you may want to apply fresh barrier coat just to ensure that they get properly sealed and the bottom remains fully protected. If you think that a quart of Interprotect is expensive, just contemplate the cost of the five gallons that I am putting on the bottom of my 32.

My choice between Marelon and Groco valve installations boiled down to this: could I save and re-use the existing thru-hull? Even after 47 years of use, including a trip to the Bahamas, my thru-hull fittings were rock-solid and most of them did not budge even a fraction of an inch when I unscrewed the valves off them. Using a heat gun on the valve helped with that. Those thru-hulls received new Marelon valves. The cockpit drain valves were the worst, one of them had to be cut out and the thru-hull replaced. The other cockpit drain thru-hull simply had to be re-bedded after it shifted while unscrewing the valve. I would have replaced the cockpit drains with Groco installations, but their positions under the cockpit sole and behind the engine were relatively inaccessible, and I did not want to start chiseling out the existing backing plates, which were too small in diameter to accept the Groco fittings. Getting a new, quality thru-hull which would fit flush just like the originals proved to be impossible. The replacement has a much thicker flange, which meant that I had to build up the outside of the hull with epoxy around the new fitting and taper it in. Another good reason for covering it with barrier coat. These thru-hulls then got fitted with Marelon valves. The few completely new thru-hull installations got the full Groco treatment.


When I replaced the thru-hulls and valves in my 27, I did all of them with completely Marelon replacements. In 16 years of service, I never had any cause to regret that choice.

[TheWinterSailor]

Originally Posted by PerfectPirate

If you think that a quart of Interprotect is expensive, just contemplate the cost of the five gallons that I am putting on the bottom of my 32.

You make a very good point, I'll add a pint of Interprotect to my shopping list...

PerfectPirate I have one more question for you, and it's one that often starts fights but I would like your input as a fellow Lake Ontario Sailor. Do you recall what bedding you used for your Marelon Fittings? I'm leaning towards 4200FC, but am open to suggestions.

Thanks!

[MicHughV]

On a whim, I decided to service all my bronze thru-hulls on my previous boat, which was at the time around 15 years old.
Much to my surprise, I noted that all the tapered bronze plugs and the housing it fitted in was pitted, in some cases, quite bad. Though the valve appeared closed, it wasn't, as water could get past the pitted areas. I tried to to "lap" the worn pieces, but the pitting was too deep to have any success.
It was a good argument to go Marelon

[PerfectPirate]

Originally Posted by TheWinterSailor

PerfectPirate I have one more question for you, and it's one that often starts fights but I would like your input as a fellow Lake Ontario Sailor. Do you recall what bedding you used for your Marelon Fittings? I'm leaning towards 4200FC, but am open to suggestions.

Thanks!

I have spent years trying various different caulkings and sealants, spent time discussing their virtues with vendors when I had my own marine chandlery, and after all of that experimentation and research I have settled on one sealant which I use for everything: Butyl tape. The same butyl tape which C&C used to seal all of their hull/deck joints, including yours. Every other adhesive and sealant which I have used has eventually broken its seal and leaked. Anything which I have bedded with butyl tape has never leaked.

When I took the thru-hulls out of my C&C 27, I found that the builder had bedded them with butyl. The previous owner of my 27 had constant problems with leaks around the chainplates. When I remounted them, I spent 20 minutes per chainplate stuffing butyl down into the opening around each chainplate and 15 years later they had never leaked a drop. When I put down inboard tracks on the 27, I was convinced by a friend to try this new Bostik adhesive sealant. Within 3 years the track bolts were leaking into the cabin. I took them up and rebedded them with butyl and never had another leak. When I remounted my cabin windows, I got black butyl from the auto glass shop to bed them and they never leaked again. Recently, when I took the stanchions and cleats off of my 32, I found that they had been bedded with butyl 47 years ago and the all of the core around the openings was still bone dry.

Butyl has a number of virtues, first of which is that it never fully cures. So, if a fixture works a bit, it does not break its seal. The butyl simply yields and then flows back together and reseals itself. If you ever get a leak in your hull/deck joint, just tighten up the screws around the leak a little bit and it will disappear. You can buy a large roll of butyl tape, seal it in a ziploc bag and keep it for years, only using as much as you need at a time. This is much better than throwing out all of those half-tubes of caulking. When the time comes to remove a fitting, a little heat will soften the butyl and help release the fitting with reasonable ease. The residual butyl is relatively easy to clean off by scraping and rolling it away. On the downside, butyl will continue to ooze for years, which annoys people who fuss about having pristine boats.

If you are bedding a thru-hull with butyl, cover the flange of the thru-hull with a thin layer and then wrap a thin layer around the portion of the tube which will be within the hull. It is okay if you go a thread or two past that. Then warm up the butyl with a heat gun so that it is soft and pliable. Insert the thru-hull and screw down the backing nut. Over the next day, or two, take a moment occasionally to tighten down the backing nut a little further, if possible. This will ensure that the butyl has managed to flow into and fill all of the spaces and voids. Then install the valve onto the thru-hull.


I did use 4200 on the Marelon thru-hulls of my 27, back when. Every year, after launch, a couple of them would persist in leaking around the thru-hull for the first week or so after going into the water. That was the final straw in converting me to a true believer in the virtues of butyl tape.

[AKA-None]

I’ve never used butyl below the water line
Sikaflex seems to do a good job