Removing thru-hulls

David Discenza · May 21, 2021, 10:47:05 AM

Hello. I plan on removing, inspecting, and reinstalling my thru-hulls. Before I undertake this, I want to understand how the thru-hulls are mounted to the hull. Are they threaded in place with 3M 5200 providing an adhesive water barrier? Do they just slip through the hull and held in place by the 5200 and a flange on the opposite side? My boatyard can't get to the job for a while because they're understaffed and they have a lot of customers. I've never done this before and I want to avoid making a costly, stoooopid mistake because of my inexperience.

My boat is a 1993 34', hull#12441293

Thanks to all who reply.

Noah · May 21, 2021, 10:56:52 AM

Why do you feel the need to remove them? You can lube them in place. Whatever the reason, if you are intent on removing and reinstalling, with old or new, do not use 5200. Use Sikaflex 291 or 3M 4200

David Discenza · May 21, 2021, 11:08:58 AM

Noah,

Thanks for your reply. When the boat was put in the water, my boat yard inspects to make certain that none of the thru-hulls are leaking. They spotted what they thought was a slow leak. As far as I know, the thru-hulls have never been touched since they were originally installed. After 27 years, it seems like good preventive maintenance to me.

Noah · May 21, 2021, 11:15:04 AM

Depends what leaking means?? Skin fitting or valve? Also, if they are the original Forespar Marelon they should be lubed once a year with Marelube, Lanacoat, or similar grease.

Stu Jackson · May 21, 2021, 11:27:22 AM

David,

1. The better reference source online for thru hulls is this one from Maine Sail: https://marinehowto.com/category/plumbing/

2. The Critical Upgrades has comments about Marelon thru hull valves. Noah's right, it could just be the valve, its handle, or a cranky yard monkey. Have YOU personally checked their claim of leaking?

3. This kind of work is not preventative maintenance. PM is when you lube them properly, not when you replace them unnecessarily. If you can avoid it, we urge you to do so.

4. Mine are older than yours and are doing just fine. I had to have my 1 1/2" head overboard valve replaced because I determined it was leaking. The thru hull fitting itself was just fine.

All the best.

David Discenza · May 21, 2021, 11:31:08 AM

Noah,

I only have what the yard person said. He reported finding water around the base of the seacock. This is the one that serves as the waste line from the sink in the head as well as the source for water for the head. I do know the valve was closed. However....

I had been boiling water to soften the heater hose to connect it to my new hot water heater. Without thinking, I poured the water down the drain of the head sink. Since the seacock was closed, it sat in that line and could have leaked out slowly and making it appear there's a leak when there actually isn't. I'm a "safe than sorry" kind of guy and would rather pull that thru-hull and reinstall it to be certain.

David Discenza · May 21, 2021, 11:35:19 AM

Stu,

Thanks for your reply. If I don't have to do the work, I don't want to. It also saves some bucks. I'm going to reconnect the hose (after I lube the valve), close the valve, pour some water in, and watch it for any leaking.

Noah · May 21, 2021, 12:48:11 PM

David- I am a bit confused as to whether your boat is currently in or out of the water? However, lubing the old-style Forespar valves (not newer Series 93 valve sets) while in the water is NOT easy. Do not dissemble the handle—that could cause you a big problem. Read critical upgrade on this issue. You can lube the valve's ball mechanism from inside the boat while in the water—if you plug the thru-hull with a wood plug and rag, then take off the plumbing hose(s) on the inside, and grease from top down. However, it is a "semi-shaky" operation. You can also lube from the under the boat with a stiff brush dipped in waterproof grease then exercise the valve from in the boat. I have had my diver do this for me. But, lubing is best done when the boat is on the hard.

David Discenza · May 21, 2021, 01:28:40 PM

Noah,

The boat is on the hard.

glennd3 · May 21, 2021, 02:51:12 PM

I did lube my valves this winter for the first time and they are noticeably easier to turn

Ron Hill · May 21, 2021, 03:01:59 PM

David : I haven't done this in years so Noah or Stu will probably correct me, but the "thru hull" in really in two pieces. One is the thru hull which has the rounded flange on the outside (of the hull) and is seated on the inside with a nut on to the threaded portion of the inside of that thru hull. The second piece is the "valve" which threads onto the "thru hull" itself. So any leak can come from the thru hull to the hull ..... or the valve screwed on the thru hull .... or the hose on to the valve.

So now you have to determine which of those 3 places that leak might be coming from. I'd stay away from the thru hull and just back off the Marelon nut and put a thin strip of butyl rubber around the threaded stem and tighten that nut back down. Then I 'd use some thread sealant (most is non hardening) and screw the old or new (lubed) valve on the thru hull thread. Then reinsert the hose and double clamp it.

A few thoughts

KWKloeber · May 22, 2021, 12:35:01 PM

David
>>My boat is a 1993 34', hull#12441293<<

I would've thought with your hull date Dec 93 that it would be a 1994 model. CTY was a little loosely goosey with the model year flip over month but my 30 is Dec 83 and an 84 model.

Ken

Ron Hill · May 22, 2021, 04:50:28 PM

David : You haven't listed your total hull # correctly. There should be 12 digits - 3 manufactures ID , one model letter, 4 hull #s, 2 date of certification and 2 model year!

I'm guessing that you have hull # 1244. (just before the molds burned!!)

A thought

Noah · May 22, 2021, 05:35:48 PM

"Just before the molds burned" should not be confused with "the day the music died"

https://en.m.wikipedia.org/wiki/The_Day_the_Music_Died

KWKloeber · May 22, 2021, 07:44:14 PM

Quote from: Ron Hill on May 22, 2021, 04:50:28 PM
David : You haven't listed your total hull # correctly. There should be 11 digits - 3 manufactures code, 4 hull #, 2 date of certification and 2 model year!

I'm guessing that you have hull # 1244. (just before the molds burned!!)

A thought

Au contraire, mon ami. 12 digits (the factory "P" designation for the 34.)

— as I just wrote to explain to an owner the difference between HIN and what some say is their "hull number."

HIN = MMM (mfgr code); nnnnn (sequence number); dddd (date of certification code; there's 3 different formats since 1972.)

Since my HIN is CTYN3573M84E most typically say, "That's hull number 3573," which is not exactly correct, depending on how one defines "hull no" (not HIN.)

More precisely, my unique hull number is CTYN3573; there's ONE and only ONE hull existing with that number (the 4-digit certification date suffix is irrelevant information.)

My Catalina hull number is N3573; there's ONE and only ONE Catalina with that number.)

My C-30 hull number is 3573; only ONE Catalina 30 exists with that number)