NPS vs. Combination thread - thru hull intake
 

So I picked up a thru hull intake from west marine that is NPS threads, then decided it would be best to get the "combination thread" fitting from wakemakers as I would be putting a NPT thread ball valve on the end. Allegedly the "combination thread" fitting is suppose to have NPT thread on the very end (or modified to accept a female NPT thread better than straight NPS).

I recieve the "combination thread" thru hull and to my dis-may the ball valve doesnt thread onto it any further than it did on the NPS thru hull. Is this normal?

The threads on the 2 different thru hulls look exactly the same, I have seen some pictures online of the combination thread and there is a distinct difference in the way they looked.

Anyone who can shed some light on this would be appreciated.

oops... posted this in wrong section. Dave, feel free to move this to boat section. Thanks!

Get rid of the ball valve and use a proper sea valve. Not only is it the correct install practice but the whole assembly gets shorter, important on most tow boats where space is an issue. You will find the threads ill mate as intended. I would also suggest going to Marelon Forespar because of their good selection of low profile and appropriate fittings and you can avoid bonding issues if you boat in brine.

On the other hand, people mix and match these thread types every day not knowing any better and very few ever have a problem. Your millage may vary.

Not conflicting what you are saying, more for conversation sake. But do any of the OEM's use a sea-cock for ballast intake? Or do they use a thru hull to ball valve (or thru hull to 90 degree elbow and then to ball valve)??

Most common is a button through hull, elbow, close nipple, ball valve, tail piece. that's allot of $ in bronze hardware. But i believe it is the accepted practice by all builders of tow boats.
Alternatively one could use a sea valve with a 90* tail piece. 3 sections instead of five and certainly more secure to the boat. It also negates backing plates. (I hate backing plates) You will however have to counter sink a few bolts into the bottom. Over kill for a lake boat.
What i described is how we rig off shore boats where things get steep and deep. Lake boats can get away with much less integrity, and most, strike that, all do.

You'll be fine, relax. i am not gonnna survey it!

Cool, thanks for the input.

There is so many different options out there and it seems there is no "industry standard". Or the standard of what is acceptable just differ's that much from each boat type.

I was going to go with one of these, it seemed to be the "happy medium" and its reasonably priced. drilling more holes in the boat is no worry. I became at ease with that by the time i got to the fifth ballast drain/vent :-)

http://www.boatersworld.com/product/MP81125627.htm

I have the 1 1/4" thru hull from wake makers and one from west marine, the wake makers piece is MUCH heavier wall thickness, but it is also longer, so more bare threads.

More bare threads/length with thicker wall or less wall thickness but shorter. Any thoughts there? I know you said a backer plate is kinda useless!

The wake maker stuff looks like Groco. Good quality there.
This is what I had in mind but that will work. In any case you cut / size the button to length.

Have you seen these? Man, i would go this route cause they dont rust and turn easy.

If a marine surveyor says a sea-cock is over kill on a wake boat... then i'm sold on my original plan of bronze thru hull mushroom to bronze thru hull ball valve.