Thru-hull questions - please help me keep my boat from sinking

I thought I had this figured out but I now I'm not so sure...<br /><br />I described in another thread how I have a plastic thu-hull fitting which acts as a drain to my live well. This fitting is BELOW THE WATER LINE. This is connected with flexible tubing to other plastic fittings on the live well. All conected together using plastic n-i-p-p-l-e-s and hose clamps. The key word here is that everything is PLASTIC PLASTIC PLASTIC. My boat is a 2000 model and all this is from the factory.<br /><br />One problem is that in order to keep my livewell from filling up with water when not in use (because the thru-hull is below the water line), I have to put a rubber stopper in the drain (which came with the boat by the way). This seems like a stupid design to me.<br /><br />Also last summer one of these fittings (inside the boat and not exposed to the sun) sprung a pin hole leak and I replaced it (with same plastic).<br /><br />Anyway my plan was to install a bronze thru-hull with a seacock. Well...from what I've read, bronze thru-hulls have straight pipe threads (NPS) and seacocks have female NPS to female pipe (NPT) threads. I also read and I quote "NPS threaded componets will provide free and loose fitting mechanical joints without preasure tightness".<br /><br />It sounds like thru-hull fittings aren't supposed to be under water? What am I missing here? I want to moore my boat this summer but I just don't trust this plastic crap. Suggestions?<br /><br />Thanks,<br />Brian

Re: Thru-hull questions - please help me keep my boat from sinking

Hi,<br />I'm not sure I understand your question but there really isn't anything wrong with plastic fittings. Of course, you don't want to tighten them to the point they crack, etc. There's lots of underwater through-hull fittings on lots of boats out there. I dont see a problem. <br />Backlash

Re: Thru-hull questions - please help me keep my boat from sinking

I personally would not use anything other than bronze on an underwater thru hull. I had regular bronze pipe gate valves on the thru hulls on my 31 Bertram. I didn't buy it new but I believe they were original to the boat. Considering the pressure on a thru hull 12 inches below the water line is only .5 PSI with sealent on the threads leakage is not an issue.

Re: Thru-hull questions - please help me keep my boat from sinking

I would agree except I've had one spring a leak for no apparent reason. My real question is what is the correct way to install a shut off valve on a thru-hull (currently plastic) that I very rarely use. Thanks for the reply.<br /><br />Brian

Re: Thru-hull questions - please help me keep my boat from sinking

Originally posted by Buttanic:<br /> I personally would not use anything other than bronze on an underwater thru hull. I had regular bronze pipe gate valves on the thru hulls on my 31 Bertram. I didn't buy it new but I believe they were original to the boat. Considering the pressure on a thru hull 12 inches below the water line is only .5 PSI with sealent on the threads leakage is not an issue.

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Do you know what type thread was between the thru-hull and gate valve?

Re: Thru-hull questions - please help me keep my boat from sinking

Well...from what I've read, bronze thru-hulls have straight pipe threads (NPS) and seacocks have female NPS to female pipe (NPT) threads. I also read and I quote "NPS threaded componets will provide free and loose fitting mechanical joints without preasure tightness".<br />

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What I Believe this Means is,<br />The threads Aren't Tapered....... They Won't Tighten upon Themseleves.........<br /><br />What they Will Do is,<br />The threads Will draw the Seacock into the inside of the hull,+ the Thruhull into the outside of the hull.......<br />Thus, You get a Tight, Waterproof(with sealant) fit......<br /><br />I Think,... In the Plumbing World this would be called a Bulkhead Fitting.........<br /><br />Make Sense ??

Re: Thru-hull questions - please help me keep my boat from sinking

Originally posted by Bondo:<br /><br />What I Believe this Means is,<br />The threads Aren't Tapered....... They Won't Tighten upon Themseleves.........<br /><br />What they Will Do is,<br />The threads Will draw the Seacock into the inside of the hull,+ the Thruhull into the outside of the hull.......<br />Thus, You get a Tight, Waterproof(with sealant) fit......<br /><br />I Think,... In the Plumbing World this would be called a Bulkhead Fitting.........<br /><br />Make Sense ??

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I think so...looks like a true seacock has bolts which go through the hull -> backing plate -> seacock. These bolts in addition to the straight threads will create a seal (with sealant). I guess using this method you wouldn't have to use the locknut that comes with the thru-hull fitting.<br /><br />I was hoping to just use an inline (ball) valve so I wouldn't have to drill holes through my transom, but they have NPT threads.

Re: Thru-hull questions - please help me keep my boat from sinking

I think I've got this right, but I'm more used to the British system:<br /><br />NPT is a taper thread. Using a taper thread on a thru hull fitting is not a good idea. Reason is, the thread might tighten up before the flanges have gripped both sides of the hull. False seal!<br /><br />So whatever material you choose needs to be a straight thread (National Standard Free-Fitting Straight Mechanical Pipe Thread - NPSM).<br /><br />You might get away with a taper thread if the thru hull fitting is a small one and you test-tighten the fitting first. Taper thread tolerances vary, and some might tighten home on the hull before the taper takes full effect - but it's not worth the risk.

Re: Thru-hull questions - please help me keep my boat from sinking

Originally posted by stillfishing:<br /> I think I've got this right, but I'm more used to the British system:<br /><br />NPT is a taper thread. Using a taper thread on a thru hull fitting is not a good idea. Reason is, the thread might tighten up before the flanges have gripped both sides of the hull. False seal!<br /><br />So whatever material you choose needs to be a straight thread (National Standard Free-Fitting Straight Mechanical Pipe Thread - NPSM).<br /><br />You might get away with a taper thread if the thru hull fitting is a small one and you test-tighten the fitting first. Taper thread tolerances vary, and some might tighten home on the hull before the taper takes full effect - but it's not worth the risk.

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Actually from what I can tell they make a combination thread thru-hull with 1/2 straight and 1/2 NPT with a pre attached nut. Doesn't matter, I'm really reaching here...I'll probably either forget the whole idea or drill the holes to mount a conventional seacock.<br /><br />Thanks for your input.<br />Brian

Re: Thru-hull questions - please help me keep my boat from sinking

Brian – seacocks installed below the waterline come in a couple common varieties. Often you will have 3 set screws that go thru the exterior flange, thru the hull, and thru an interior wooden block* on the other side of the hull. The setscrews keep the seacock from spinning when you tighten the flange on the inside of the hull. Some seacocks (Groco) use a system of notches molded into the bronze and a special tool is inserted into the seacock from the outside. Someone holds the tool and seacock in place while someone else tightens the flange on the inside. It’s a pain in the butt but your not dealing with the three setscrews.<br /><br />The flange you screw on the seacock from inside the boat, not the valve, completes the seacock installation.<br /><br />Any seacock that is installed below the waterline must have an accessible shut-off valve attached to it. In most cases it is a 1/4-turn ball valve. They are inexpensive and maintainable. That means you can take the ball valve apart and clean it, lube it, loose a part and put it back together wondering why it doesn’t work anymore. With the ball valve installed you won’t need that cheesy plug anymore.<br /><br />Ball valves come in a variety of ports on the other side, away from the seacock. You can get threaded or hose nipple, whatever you need.<br /><br />You never want a below-the-waterline seacock with a hose barb/nipple on the inside. Why? Like I said, the first thing that immediately attaches to it is a valve. The valve will thread into the seacock.<br /><br />* The wood backing-block makes for a rigid and distributed mount so if you kick the seacock it won’t break a chunk out of the hull and sink your boat. Also, seacocks are sometimes mounted where the hull curves so the wooden block can be shaped to the hull curve so when the seacock comes thru it has a perpendicular flat surface for the locking flange to tighten down against.<br /><br />Here’s where I replaced an older style seacock with a newer style. This is how it is done BELOW the waterline. This first pic is from outside the boat. You can see where the three setscrews went in. As you look into the hull, the white material is the fiberglass. Right up against it, the light brown material furthest inside is the wood backing.<br /><br /> <br /><br />This shows the hole from the inside. On my boat the original wood backing block was shaped into a circle, like a donut. Looks pretty but isn’t normally done this. Usually it’s just a square piece of wood glassed over and/or painted. That knarly looking green thing on the shelf above the hole is the old seacock. <br /><br /> <br /><br />He’s a close up of that ‘pretty’ wood block. If you image yourself looking at the hole straight on you can kind of see where the setscrews came thru the block at about 10 o’clock, 2 o’clock, and 6 o’clock positions. Sorry, if I make this pic any bigger it will pixelate…turn into square blobs.<br /><br />

Re: Thru-hull questions - please help me keep my boat from sinking

When using a regular pipe thread valve on a thru hull the nut normally used on the thru hull fitting is what holds it in place not the valve. Once the thru hull fitting is installed with the inside nut the valve is put on.

Re: Thru-hull questions - please help me keep my boat from sinking

hello<br /> use only bronze under the water line and inspect all rubber hoses frequently. we have 5 or 6 sink every year due to broken plastic thru hulls and broken plastic bilge hoses. a few years back a dry stack customer bought a 26 wellcraft with a pair of FICHT 225 rudes. he was due in on friday aftnoon so we set the boat in thursday and the local rude tech did some updates and the boat was left in the water. out of 14 plastic under the waterline fittings 4 leaked. also we found out friday morning that with the battery switch in the off position the auto bilge pump does not work. took 9 hours and a boat load of money to restart the engines.<br /> moral of the story is plastic sucks under the waterline, most boat manufactures use it,most also wire the autobilge stupidly and the VHF radio. so change to bronze, rewire your auto bilge ,with a proper waterproof fuse holder, to the battery side of the switch not battery post, rewire your VHF with a proper fuse to the battery side of the switch.that way if you have electrical problems and have to secure the switch you may still have auto bilge and VHF.

Re: Thru-hull questions - please help me keep my boat from sinking

Thanks everyone for the advice. I will print this thread for reference.