I purchased an exterior shower unit for my boat, but am having problems. I hooked it up to my freshwater system and have the pipes running to the location where I want to place the shower. Unfortunately, I am having a hell of a time trying to find plumbing parts that will fit the shower. I don’t have a hot water heater, so my plan was to cap the hot water and run my pipe/hose to the cold water only. I purchased multiple size caps for hot water side and none of them work. They will screw on a few turns and then bind up and get very tight and ultimately have started to strip the threads. Is the thread count or distance between them different on marine parts vs. normal plumbing parts? I really thought the hardest part would be running all the new piping, but it has been trying to locate a cap and a female end with hose adapter that work. Any thoughts?
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Pipe threads
There are several pipe thread schemes about - NPT (National Pipe Thread) is pretty much the standard plumbing pipe thread. You will note that your 3/4" garden hose connection will NOT fita 3/4" NPT. Different system - the garden hose having fewer teeth per inch (TPI). I would not be suprisewd to find that plumbing aboard a boat uses a finer TPI than either mentioned. Good plumbing supply stores sell gauges to measure TPI.
There are several pipe thread schemes about - NPT (National Pipe Thread) is pretty much the standard plumbing pipe thread. You will note that your 3/4" garden hose connection will NOT fita 3/4" NPT. Different system - the garden hose having fewer teeth per inch (TPI). I would not be suprisewd to find that plumbing aboard a boat uses a finer TPI than either mentioned. Good plumbing supply stores sell gauges to measure TPI.
You don't need a gauge to measure TPI...
All you need is a ruler and the ability to count 16 or 11 "ridges" in an inch. 16 TPI was common on boats built before 1980, but almost all fittings on boats built after the early '80s are 11. Unfortunately, that makes it VERY hard to find 16 TPI fittings any more...they're all 11 now. I finally had to give up and replace the deck pumpout fitting on my own boat 'cuz I couldn't find a replacement cap that had 16.
All you need is a ruler and the ability to count 16 or 11 "ridges" in an inch. 16 TPI was common on boats built before 1980, but almost all fittings on boats built after the early '80s are 11. Unfortunately, that makes it VERY hard to find 16 TPI fittings any more...they're all 11 now. I finally had to give up and replace the deck pumpout fitting on my own boat 'cuz I couldn't find a replacement cap that had 16.
NPT is tapered, APT is straight thread, etc.
In plumbing/piping there are various profiles: NPT which has a tapered/conical profile - the tighter you screw it together the tigher the interface/joint gets; APT (American Pipe thread) which is a 'straight' thread profile - used to 'push' the pipe ends against flares and gaskets, etc. Finished fixtures such as showerheads, etc. usually are APT (straight thread). Although the threads per inch of NPT and APT are the same, they wont 'fit' together very well ... as you found out. To go from NPT to straight thread APT you need 'adapters' (or APT 'terminal' fittings). If you go to a 'knowledgeable' (certainly not Home Depot or Lowes) harware store or a plumbing supply they will be able to help you - take the connections and fixtures along with you.
In plumbing/piping there are various profiles: NPT which has a tapered/conical profile - the tighter you screw it together the tigher the interface/joint gets; APT (American Pipe thread) which is a 'straight' thread profile - used to 'push' the pipe ends against flares and gaskets, etc. Finished fixtures such as showerheads, etc. usually are APT (straight thread). Although the threads per inch of NPT and APT are the same, they wont 'fit' together very well ... as you found out. To go from NPT to straight thread APT you need 'adapters' (or APT 'terminal' fittings). If you go to a 'knowledgeable' (certainly not Home Depot or Lowes) harware store or a plumbing supply they will be able to help you - take the connections and fixtures along with you.
NPT plumbing parts will fit
I want to thank everyone for your help with this. I have been all over town to HD, Lowes, Westmarine, Boaterworld, and a professional plumbing store and the best advise I recieved was from you guys. I have learned a lot about the different thread configurations and how they work. Since I wasn't completely sure which configuration I had, I called the manufacture and asked. I have a NPT system, so having this information should make it much easier to pinpoint the parts that I need.
I want to thank everyone for your help with this. I have been all over town to HD, Lowes, Westmarine, Boaterworld, and a professional plumbing store and the best advise I recieved was from you guys. I have learned a lot about the different thread configurations and how they work. Since I wasn't completely sure which configuration I had, I called the manufacture and asked. I have a NPT system, so having this information should make it much easier to pinpoint the parts that I need.
Great Link Ross
That was a really great link describing pipe threads! Also liked the detailed drawings. And Auto Cad helps one to see how it looks close-up.
That was a really great link describing pipe threads! Also liked the detailed drawings. And Auto Cad helps one to see how it looks close-up.
Did that same install 3 years ago.
Just added teflon tape to the threads (plastic)and screwed on the cap (galvanized) tightening it with a pair plyers. Installed a "T" connector to the sink hose and extended a hose to the shower with hose clamps. Checked for leaks and there were none. To this day, working fine. The metal cap will mold those plastic threads. No need to tighten to much.
Just added teflon tape to the threads (plastic)and screwed on the cap (galvanized) tightening it with a pair plyers. Installed a "T" connector to the sink hose and extended a hose to the shower with hose clamps. Checked for leaks and there were none. To this day, working fine. The metal cap will mold those plastic threads. No need to tighten to much.
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