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Does anyone know, or know how to figure out, the mean (psi) pressure of seawater 3′ below the surface? In
other words, what is the pressure on a hose connected to a thru-hull 3′ below the waterline?Tor
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Silver Heels, P-424 #17
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Yes. It's easy. Water in a column provides about .49 pounds per square inch. That means for every 2 feet or so, it's a pound (close enough). At three feet, you could say, then, it's 1.5 psi static pressure (dynamic is not taken into account here). It's also the reason that water pressure at 33 feet is twice atmospheric (about 14.7 x 2). This is close enough for government work. If you're building something that will only withstand 2 psi, I'd make it stronger.
You could look up the exact conversion, but half a pound per foot is pretty close.
Bob
On Sun, Sep 14, 2008 at 8:54 AM, Silver Heels < ([email][/email])> wrote:
Does anyone know, or know how to figure out, the mean (psi) pressure of seawater 3' below the surface? In
other words, what is the pressure on a hose connected to a thru-hull 3' below the waterline?Tor
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Silver Heels, P-424 #17
http://www.SilverHeels.us
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Bob Fine
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Wouldn't the pressure have to include atmospheric pressure on the water surface for a total of around 16 psi at the through-hull?
John
On Sun, Sep 14, 2008 at 9:22 AM, Robert Fine < ([email][/email])> wrote:
Yes. It's easy. Water in a column provides about .49 pounds per square inch. That means for every 2 feet or so, it's a pound (close enough). At three feet, you could say, then, it's 1.5 psi static pressure (dynamic is not taken into account here). It's also the reason that water pressure at 33 feet is twice atmospheric (about 14.7 x 2). This is close enough for government work. If you're building something that will only withstand 2 psi, I'd make it stronger.
You could look up the exact conversion, but half a pound per foot is pretty close.
Bob
On Sun, Sep 14, 2008 at 8:54 AM, Silver Heels < ([email][/email])> wrote:
Does anyone know, or know how to figure out, the mean (psi) pressure of seawater 3' below the surface? In
other words, what is the pressure on a hose connected to a thru-hull 3' below the waterline?Tor
~~~~~~~~~~~~~~~~~~~~~~~
Silver Heels, P-424 #17
http://www.SilverHeels.us
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Bob Fine
Fine Software LLC
Your data on the web your way. No kidding—
Regards,
John Stevenson
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Wow, that little?
I’m installing a seawater intake manifold that will draw from a thru-hull 3′ below the waterline. This will let me feed all of the seawater users in the boat from just one thru-hull – except for the engine, which has its own, dedicated thru-hull. Anyway, I wondered if reinforced Series 162 polyester reinforced clear PVC tubing (i.e., the kind of hose you’d normally use for your boat’s pressure freshwater system) would be all right to use between the thru-hull and the manifold. Its burst pressure is 250 lbs, so I guess it is strong enough.
Anyone know if there are there any ABS or USCG regs about hoses from below-waterline thru-hulls (other than the obvious double-clamping)?
Tor
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Silver Heels, P-424 #17
http://www.SilverHeels.us
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I believe I read somewhere that double clamping is not a standard of any
sort but rather just good sense.By the way, the cost of Titan Titanium clamps is worth it. Never
replace your clamps again…Pete
Silver Heels wrote:
Quote:Wow, that little?I’m installing a seawater intake manifold that will draw from a
thru-hull 3′ below the waterline. This will let me feed all of
the seawater users in the boat from just one thru-hull – except for
the engine, which has its own, dedicated thru-hull. Anyway, I wondered
if reinforced Series 162 polyester reinforced clear PVC tubing (i.e.,
the kind of hose you’d normally use for your boat’s pressure
freshwater system) would be all right to use between the thru-hull and
the manifold. Its burst pressure is 250 lbs, so I guess it is strong
enough.Anyone know if there are there any ABS or USCG regs about hoses from
below-waterline thru-hulls (other than the obvious double-clamping)?Tor
~~~~~~~~~~~~~~~~~~~~~~~
Silver Heels, P-424 #17
http://www.SilverHeels.us
~~~~~~~~~~~~~~~~~~
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Hi, John,
In absolute pressure terms, yes, but since the inside of the boat is also subject to the 14.7 psi the pressure you'd be measuring is the delta, or around a pound and a half.
Bob
On Sun, Sep 14, 2008 at 9:32 AM, John Stevenson < ([email][/email])> wrote:
Wouldn't the pressure have to include atmospheric pressure on the water surface for a total of around 16 psi at the through-hull?
John
On Sun, Sep 14, 2008 at 9:22 AM, Robert Fine < ([email][/email])> wrote:
Yes. It's easy. Water in a column provides about .49 pounds per square inch. That means for every 2 feet or so, it's a pound (close enough). At three feet, you could say, then, it's 1.5 psi static pressure (dynamic is not taken into account here). It's also the reason that water pressure at 33 feet is twice atmospheric (about 14.7 x 2). This is close enough for government work. If you're building something that will only withstand 2 psi, I'd make it stronger.
You could look up the exact conversion, but half a pound per foot is pretty close.
Bob
On Sun, Sep 14, 2008 at 8:54 AM, Silver Heels < ([email][/email])> wrote:
Does anyone know, or know how to figure out, the mean (psi) pressure of seawater 3' below the surface? In
other words, what is the pressure on a hose connected to a thru-hull 3' below the waterline?Tor
~~~~~~~~~~~~~~~~~~~~~~~
Silver Heels, P-424 #17
http://www.SilverHeels.us
~~~~~~~~~~~~~~~~~~
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For additional commands, e-mail: ()—
Bob Fine
Fine Software LLC
Your data on the web your way. No kidding—
Regards,
John Stevenson
http://www.svsarah.com—
Bob Fine
Fine Software LLC
Your data on the web your way. No kiddingPost generated from Pearson424 Forum using Mail2Forum
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Hi Tor,
It was a rainy day on Friday so I went to Home Depot and got all the PVC parts and valves to make my own manifold – I have the seawater foot pump for the galley and the water for the head and soon a seawater washdown system so I made a 5 valve manifold (pictures soon, if you want) for expansion – never know what else, like a water maker, will use seawater.
I used the white sanitary hose from the thru hull to the manifold inlet which has a valve and then each provider has its own valve, too, and a cap on the end in case I end up with more stuff. I'll wire tie the unused valves shut.
The hardest part of the job was providing a new hose to the head. That took an hour. the rest of the job took about three hours. Mostly because the thru hull is in a terrible place behind the refrigerator compressor.
Oh, and the hose you're talking about is perfect. ABYC indicates you should double clamp any hose fitting that can be below water in normal heel angles.
Bob
On Sun, Sep 14, 2008 at 10:23 AM, Silver Heels < ([email][/email])> wrote:
Quote:Wow, that little?I'm installing a seawater intake manifold that will draw from a thru-hull 3' below the waterline. This will let me feed all of the seawater users in the boat from just one thru-hull – except for the engine, which has its own, dedicated thru-hull. Anyway, I wondered if reinforced Series 162 polyester reinforced clear PVC tubing (i.e., the kind of hose you'd normally use for your boat's pressure freshwater system) would be all right to use between the thru-hull and the manifold. Its burst pressure is 250 lbs, so I guess it is strong enough.
Anyone know if there are there any ABS or USCG regs about hoses from below-waterline thru-hulls (other than the obvious double-clamping)?
Tor
~~~~~~~~~~~~~~~~~~~~~~~
Silver Heels, P-424 #17
http://www.SilverHeels.us
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Hey Bob,
I originally bought PVC fittings to make my manifold, but heard around the yard that an insurance surveyor might take issue with that. So I returned the fittings to Home Depot and swapped them for brass (photo attached). My end users are: watermaker, toilet, galley sink and deck washdown. The gate valve & barb at the left end are for a bilge rinse hose. I can pull off the feed barb at the other end to clean the length of the manifold occasionally, and can easily add on more T-gatevalve-barb sections for additional end users if I ever need to. I think it’s going to work well.
I put a grill over the thru-hull on the outside of the hull last haul-out. Was tempted to install a plastic Shurflo in-line water strainer (rated 150 psi) between the thru-hull and the manifold, but decided to use a bronze Groco or Raritan raw water strainer instead. They’re a lot more expensive, but I don’t like the idea of a plastic fitting adjacent to a thru-hull. Hoping to find a used Groco or whatever at Sailor’s Exchange next week. (Anybody out there have one they want to sell?!)
As for running hoses, tell me about it! I’ve just about completed a substantial replacement of the original hoses in Silver Heels during the past week or so. All the freshwater system hoses and all the sanitation hoses. Just waiting now for my 1-1/2″ & 3/4″ sanitation hose to arrive, hopefully tomorrow. BTW, I found a really cheap source for Series 148 sanitation hose, less than half the Port Supply price: http://www.hydraulic-supply.com/pdf/196.pdf .
Mounting a new toilet this afternoon. Fun.
Tor
~~~~~~~~~~~~~~~~~~~~~~~
Silver Heels, P-424 #17
http://www.SilverHeels.us
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Be careful with brass fittings in saltwater applications. They can suffer from what is called dezincification. After a few years they will become brittle and may snap off. I had this happen to the engine seawater strainer.
Bronze fittings are becoming increasingly difficult to find. PVC can split open if it freezes. I think nylon or marilon may be the only viable choice these days. The stuff they use for home sprinkler systems might work.
Rich
BlackSheep #47Quote:<.. snip>Post generated from Pearson424 Forum using Mail2Forum
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Hi Tor,
I'm a firm believer that using plastic is way better than metals not designed for the marine environment – case in point, brass (copper and zinc) (see http://en.wikipedia.org/wiki/Brass ). As an alloy, brass is fine for fresh water but terrible for seawater. Bronze is essentially copper and tin, a much more expensive and corrosion resistant metal.
You may not see those fittings fail. But whoever purchases Silver Heels will. Schedule 40 PVC piping is designed for fluids not to exceed 140 degrees F and 120 psi. Since I don't expect to be sailing in waters of that temperature, I'm fairly confident in the fittings. I used threaded valves so that they can be replaced.
I already have a bilge washdown as a 'T' on the engine water intake (which also allows me to fill the engine with antifreeze when the time comes.)
But that's just my opinion. As you well know, I have a million of them.
Bob
On Sun, Sep 14, 2008 at 2:41 PM, Silver Heels < ([email][/email])> wrote:
Quote:Hey Bob,I originally bought PVC fittings to make my manifold, but heard around the yard that an insurance surveyor might take issue with that. So I returned the fittings to Home Depot and swapped them for brass (photo attached). My end users are: watermaker, toilet, galley sink and deck washdown. The gate valve & barb at the left end are for a bilge rinse hose. I can pull off the feed barb at the other end to clean the length of the manifold occasionally, and can easily add on more T-gatevalve-barb sections for additional end users if I ever need to. I think it's going to work well.
I put a grill over the thru-hull on the outside of the hull last haul-out. Was tempted to install a plastic Shurflo in-line water strainer (rated 150 psi) between the thru-hull and the manifold, but decided to use a bronze Groco or Raritan raw water strainer instead. They're a lot more expensive, but I don't like the idea of a plastic fitting adjacent to a thru-hull. Hoping to find a used Groco or whatever at Sailor's Exchange next week. (Anybody out there have one they want to sell?!)
As for running hoses, tell me about it! I've just about completed a substantial replacement of the original hoses in Silver Heels during the past week or so. All the freshwater system hoses and all the sanitation hoses. Just waiting now for my 1-1/2″ & 3/4″ sanitation hose to arrive, hopefully tomorrow. BTW, I found a really cheap source for Series 148 sanitation hose, less than half the Port Supply price: http://www.hydraulic-supply.com/pdf/196.pdf .
Mounting a new toilet this afternoon. Fun.
Tor
~~~~~~~~~~~~~~~~~~~~~~~
Silver Heels, P-424 #17
http://www.SilverHeels.us
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That's what I'm talkin' about. Whatever you do, if you haul or stay in the water up north in the winter, you'll have to make sure the lines are empty. I use a compressor to clear them. But since I live on the boat, the bilge stays warm enough to not freeze.
Bob
On Sun, Sep 14, 2008 at 3:09 PM, Rich Carter < ([email][/email])> wrote:
Quote:Be careful with brass fittings in saltwater applications. They can suffer from what is called dezincification. After a few years they will become brittle and may snap off. I had this happen to the engine seawater strainer.Bronze fittings are becoming increasingly difficult to find. PVC can split open if it freezes. I think nylon or marilon may be the only viable choice these days. The stuff they use for home sprinkler systems might work.
Rich
BlackSheep #47Quote:<.. snip>Post generated from Pearson424 Forum using Mail2Forum
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What Rich described for brass fittings in a seawater environment is exactly what happened to my seawater manifold this past summer. I made it up with a combination of bronze and brass fittings. After 5 years all of the brass fittings had deteriorated significantly. One brass hose barb broke off with almost no effort on my part. I replaced the manifold with a combination of plastic (close nipples) and everything else bronze. I hope this one lasts a little longer.
On Sun, Sep 14, 2008 at 2:32 PM, Robert Fine < ([email][/email])> wrote:
Quote:That's what I'm talkin' about. Whatever you do, if you haul or stay in the water up north in the winter, you'll have to make sure the lines are empty. I use a compressor to clear them. But since I live on the boat, the bilge stays warm enough to not freeze.Bob
On Sun, Sep 14, 2008 at 3:09 PM, Rich Carter < ([email][/email])> wrote:
Quote:Be careful with brass fittings in saltwater applications. They can suffer from what is called dezincification. After a few years they will become brittle and may snap off. I had this happen to the engine seawater strainer.Bronze fittings are becoming increasingly difficult to find. PVC can split open if it freezes. I think nylon or marilon may be the only viable choice these days. The stuff they use for home sprinkler systems might work.
Rich
BlackSheep #47Quote:<.. snip>Post generated from Pearson424 Forum using Mail2Forum
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Sonofabitch! I didn’t know that (obviously). Glad to find out now, though, rather than during an offshore passage. Thank you all – Rich, Bob & John – for straightening me out. Looks like I’ll be returning a bunch of brass fittings to Home Depot.
Just this morning I happened to come across a bronze Groco raw water manifold that will feed 3 users from one source (http://www.groco.net/07-ftgs/07-sb-4-fs.htm and click on the manifold image). A pair of them might do the trick, but they don’t seem to make the size(s) I need.
I guess I’m back to Plan A, which is what you did, Bob. I’m not worried about freezing, either.
Tor
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Silver Heels, P-424 #17
http://www.SilverHeels.us
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Rich,
Marelon would be an ideal material, but do they make the fittings – T’s, coupling nipples, various size barbs, etc – that you’d need to put together a manifold similar to the one I made out of brass?
Tor
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Silver Heels, P-424 #17
http://www.SilverHeels.us
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You must need a manifold in your house for something, eh? Or, you could replace the manifold for the cold/hot water with this so you can isolate either the cold water or hot water source for whatever reason. Or, you could go back to Home Depot – I think my whole set up cost about $64, but since you're using less taps and less valves, you'll save 12 or 15 dollars. I have plenty of pipe left over (6 feet out of 10 because you can only buy a ten foot section). You're welcome to it, but that's only 3.65 or so. Costs more to mail it.
Get fresh PVC glue, too.
Bob
On Sun, Sep 14, 2008 at 4:48 PM, Silver Heels < ([email][/email])> wrote:
Quote:Sonofabitch! I didn't know that (obviously). Glad to find out now, though, rather than during an offshore passage. Thank you all – Rich, Bob & John – for straightening me out. Looks like I'll be returning a bunch of brass fittings to Home Depot.Just this morning I happened to come across a bronze Groco raw water manifold that will feed 3 users from one source (http://www.groco.net/07-ftgs/07-sb-4-fs.htm and click on the manifold image). A pair of them might do the trick, but they don't seem to make the size(s) I need.
I guess I'm back to Plan A, which is what you did, Bob. I'm not worried about freezing, either.
Tor
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Silver Heels, P-424 #17
http://www.SilverHeels.us
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Yes, but it would be VERY expensive. Marelon is a trade name for FRP or fiberglass reinforced plastic, in this case, nylon. Very strong. Very resistant to splitting. Very expensive because it's only used in the marine environment.
Bob
On Sun, Sep 14, 2008 at 5:06 PM, Silver Heels < ([email][/email])> wrote:
Quote:Rich,Marelon would be an ideal material, but do they make the fittings – T's, coupling nipples, various size barbs, etc – that you'd need to put together a manifold similar to the one I made out of brass?
Tor
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Silver Heels, P-424 #17
http://www.SilverHeels.us
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Engineer Bob,
Is the problem with brass in seawater an issue of electrolysis, of the zinc being robbed from the zinc/copper alloy? And if so, would a simple pencil zinc incorporated into the brass manifold solve the problem?
Tor
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Silver Heels, P-424 #17
http://www.SilverHeels.us
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Watch out for the pressure seawater on the washdown system.
I installed pressure washdown in the cockpit, at the bow, and at the galley sink. That is a lot of hose and a lot of fittings all at 75 psi working pressure. Sure enough, one of the fittings let go when I was away at a friends boat for an hour. The pressure washer was out-pumping the bilge pump, and I had water nearly up to the floor boards.
Now, when I turn on the switch for the washdown, a flashing LED comes on. I want it off whenever it is not actively being used. If this is not sufficient to keep me and my crew in line, I will install a buzzer that is on whenever the washdown has power.
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That’s a sobering story, Walter. Not sure what happened to you, or why. It doesn’t seem ‘sure enough’ that a fitting would inevitably fail at 75 psi, although that’s twice what my freshwater pump puts out.
Anyway, my (dedicated) deck washdown pump will be pulling, not pushing, except for the last few feet. It’s mounted just beneath the foredeck virtually at the stem, with a deck hose connection fitting just abaft and in between the anchors. It’s primary function is to rinse anchor chain as it comes aboard, though it can also serve to wash the decks or (heaven forbid) put out a fire.
Tor
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Silver Heels, P-424 #17
http://www.SilverHeels.us
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Hi Tor,
Without knowing the exact alloy of the valving and the zinc, I couldn't tell you. You'd have to calculate the valence of both and determine which is higher. But you'd have to check the zinc pretty often. Brass and seawater is just a bad idea. Bronze is better. Plastic, as far as I'm concerned is best. No corrosion, no electrolysis, no chipping, cracking, crazing. Lasts, conservatively, 1, 000,000 years. Can't beat that. The problem with brass, as Rich indicated, is that the zinc in it is the same as a zinc. Even with a zinc, it will still dissolve at the same rate as the zinc given similar zinc alloys.
The pressure side should be as short as possible as you've done, and I was thinking of connecting the washdown pump to the breaker for the windlass so that it's only on when the windlass is. I never leave the windlass breaker energized to prevent inadvertent anchor motion.
Bob
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Hi
On Sun, Sep 14, 2008 at 6:08 PM, Silver Heels < ([email][/email])> wrote:
Quote:Engineer Bob,Is the problem with brass in seawater an issue of electrolysis, of the zinc being robbed from the zinc/copper alloy? And if so, would a simple pencil zinc incorporated into the brass manifold solve the problem?
Tor
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Silver Heels, P-424 #17
http://www.SilverHeels.us
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