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Catalina/Capri 25/250 Sailor's Forums

General Sailing Forum

Capping off 1-7/8" Thru-Hull

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Justin
Admiral

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502 Posts

Initially Posted - 05/20/2007 : 21:20:08

I ripped out all the previous owner's overboard plumbing and need to seal off the thru-hull which is 1-7/8" diameter at the threads. I cannot find anything in that size that would work. Does anyone have any recommendations on how to seal it off? I was thinking of finding a cap to seal and screw on, but can't find them. I might have to take it out and fiberglass over the hole, but in some ways I would prefer not to.

Any tips?

Thanks,

Justin
Previous Owner of Sapphire Breeze - 1982 Catalina 25 SK/SR
My sail blog site: https://reveriesailing.com/

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ct95949
Captain

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Aruba
300 Posts

Response Posted - 05/20/2007 : 22:29:28

Are you talking about the large waste discharge thru-hull?

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tmhansen
Captain

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USA
397 Posts

Response Posted - 05/21/2007 : 02:15:56

Justin, I did exactly as you are seeking to do. In my case the through hull went directly to a valve. I put a threaded plug in the through valve. I found the part at West Marine. Took me a while to find it though, looking at different stores when I was in the neighborhood. Always made me nervous that the valve on the though hull would get pulled open and I would discover I had an 1 1/2 hole in the boat.

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atgep
Master Marine Consultant

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1009 Posts

Response Posted - 05/21/2007 : 08:29:22

It "should" be 1 1/2 NPT sized. You can get a plastic cap at lowes or HD to try. Once you have the size, find a bronze cap and you are in business. If you are using to to cap a Marelon thru-hull that does not leak, a PVC Cap should be more than adequate. ON my boat the valve was still good so I used pvc parts to make a cap to avoid any electrolysis issues.

Tom.

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Justin
Admiral

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502 Posts

Response Posted - 05/21/2007 : 11:49:01

I was tired last night when I posted so I didn't give many details. Yes, this is the waste discharge thru-hull. The previous owner plumbed the system for overboard pumping only; he cut off the deck pump out. We were able to pump out the holding tank directly through the tank opening without any problems. It is a nylon thru-hull, most likely a Marelon thru-hull, fully threaded with the nylon lock nut against the inside hull liner. I cannot see the outside of the thru-hull because a boat stand is covering it. There was a bronze gate valve attached to it. The previous weekend while on the hard, I loosened the hose clamp on the valve and started twisting the hose off. I barely applied any pressure and the entire bronze valve simply popped right off the thru-hull! I am so lucky that did not happen last year when I tried to close the valve but it was corroded open. The bronze valve was barely attached to the thru-hull!
Yesterday I bought a 2" PVC cap and tested it in case I measured off by an 1/8th of an inch. It was too large and in fact was over 2" in thread diameter. I will try a 1.5" PVC cap to see if it fits. If it does, this would be such a simple fix.
I also stopped by West Marine yesterday but they didn't have any recommendations for me and hadn't heard of any caps in 1-7/8". Their catalogs don't have anything and I haven't found any fittings so far directly from manufacturers of those parts.

Tom, what is NPT size? Are you saying a 1.5" NPT size should equal a 1-7/8"?

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atgep
Master Marine Consultant

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1009 Posts

Response Posted - 05/21/2007 : 14:58:23

Justin,
NPT is National pipe thread. It is a standard plumbing size. It is measured by inside diameter , so a 1 1/2 pipe will be closer to 2" on the outside. Once your are sure of the size, get a bronze cap though. tape over the outside and fill the hole with 5200 from the inside . let it cure for a couple of days. Then wet seal the cap on and forget about it! It will act as an insulator and will cure over time. 5200 will cure even under water. Here is a bronze cap from West Marine. It is not cheap but will not sink your boat!

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Justin
Admiral

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502 Posts

Response Posted - 05/22/2007 : 14:53:15

Tom, why do you recommend the bronze instead of just getting a pvc cap? I just read on a site that a 1.5" pvc pipe has a 1-7/8" outside diameter which is what I need.

I'm going to try a 1.5" pvc cap to see if it works. Now what about sealants with pvc and the marelon? What is recommended? I have Life Caulk (polysulfide) and some WM Silicone sealant. 5200 would be more permanent. Would the WM silicone be fine? Just applying a lot on the threads and in the cap, then tighten it down is what I'm thinking.

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dlucier
Master Marine Consultant

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Virgin Islands (United Kingdom)
7583 Posts

Response Posted - 05/22/2007 : 14:58:12

Justin,

Was there a valve connected to the marelon thru hull for this overboard discharge?

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Justin
Admiral

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502 Posts

Response Posted - 05/22/2007 : 16:35:15

Yes, there was a bronze gate valve that was stuck open. When I attempted to remove the hose from the valve, the entire bronze valve popped right off the thru-hull. I'm trashing that and will just screw on a cap with sealant.

I just got back from Home Depot and found their last 1.5" screw on PVC cap. I measured the thread diameter and it is 1-7/8", so it sounds like this will work!

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atgep
Master Marine Consultant

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1009 Posts

Response Posted - 05/22/2007 : 23:41:44

If you had a seacock on the thru hull, I would suggest a pvc cap. With an open hole to the sea, a bronze cap would be the "coast guard" way to terminate the fitting. Marelon is a nylon product which should be fine with nearly any sealant. 5200 will cure to a solid form given enough time.

PVC is not a "marine" product and can crack. I also do not like using a female threaded plastic cap. The force of the threads trys to crack the cap. The bronze cap is $20. A tube of 5200 is another $14.

Tom.

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Justin
Admiral

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502 Posts

Response Posted - 05/23/2007 : 06:58:15

Thanks Tom, I'll look into a bronze cap. I didn't think about the possibility of having the PVC crack in the future; so to be safe, bronze sounds like a better idea.

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