Thru Hull thread and ball valve thread??

Odawg753

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Hey guys I need to replace a leaking ball valve for my live well and potentially the thru Hull fitting. After doing my research I’m quite confused since thru Hull fittings are nps (straight thread) and valves and caps that I’m finding are npt (tapered). I’m trying to do this in one weekend so I don’t experience a lot of down time on the boat. Can anyone enlighten me ? Also it’s in a tight spot so no room for adapters.
 

Odawg753

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dingbat

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Two reasons actually
1. To keep people from using brass fittings and valve instead of bronze.

2. Thru hull fittings are designed to be terminated with a seacock inside the hull. The straight threads allow you to screw the two components together on any hull thickness. Sealers is used to water proof the connection
 

Scott Danforth

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to expand on what dingbat is stating, get the proper thru-hull and seacock from a marine store

not a ball valve from a hardware store.
 

Odawg753

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I am buying from a marine store I just always thought that mixing nps and npt was a no no
 

dingbat

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I am buying from a marine store I just always thought that mixing nps and npt was a no no

NPT and NPS can’t and don’t mix. Different thread profiles.

Anything related with a thru hull is NPS
 

Odawg753

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NPT and NPS can’t and don’t mix. Different thread profiles.

Anything related with a thru hull is NPS

On my 1990 wellcraft the factory set up is a valve with npt thread on the thruhull with presumably straight thread
 

dingbat

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On my 1990 wellcraft the factory set up is a valve with npt thread on the thruhull with presumably straight thread

You can buy in-line valves with NPS on one side and NPT on the other but they don't qualify as "seacocks" for the following reasons.

An in-line valve has no means of attachment to the vessel hull or backing block, so the valve can turn or loosen from the thru-hull fitting with vibration or with normal use.

If the connected thru-hull fitting becomes damaged or broken, as might occur if the vessel struck a submerged or floating object, or if the fitting was inadvertently damaged or broken inside the hull, there would be no way to shut off the flow of water into the vessel.
 

Odawg753

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You can buy in-line valves with NPS on one side and NPT on the other but they don't qualify as "seacocks" for the following reasons.

An in-line valve has no means of attachment to the vessel hull or backing block, so the valve can turn or loosen from the thru-hull fitting with vibration or with normal use.

If the connected thru-hull fitting becomes damaged or broken, as might occur if the vessel struck a submerged or floating object, or if the fitting was inadvertently damaged or broken inside the hull, there would be no way to shut off the flow of water into the vessel.

I see, so wellcraft was basically trying to save a buck by doing it that way? Is it possible to do Seacock with 4200 at bottom of flange where it meets backing board instead of screws. I really don’t wanna drill screw holes.
 

dingbat

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I see, so wellcraft was basically trying to save a buck by doing it that way? Is it possible to do Seacock with 4200 at bottom of flange where it meets backing board instead of screws. I really don’t wanna drill screw holes.

Yep....saving a buck.

Grady did the same thing in mine. I swapped it out for raw water strainer with a seacock to mount the live well pump. Added a second intake to feed the raw water washdown pump.

It makes no sense to go through the time and expense of installing a seacock only to cut corner on the installation.

Swapped out all the OEM "plastic" thru hulls and scuppers for stainless while I was at it.
 

Odawg753

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Yep....saving a buck.

Grady did the same thing in mine. I swapped it out for raw water strainer with a seacock to mount the live well pump. Added a second intake to feed the raw water washdown pump.

It makes no sense to go through the time and expense of installing a seacock only to cut corner on the installation.

Swapped out all the OEM "plastic" thru hulls and scuppers for stainless while I was at it.

Thanks for the help
 
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