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Bob,
Where in the boat are you planning to put your 6″ PVC pipe seachest? You thinking of about, what, a 2-foot length? Are you planning for at least one end to unscrew to provide access to the inside for periodic cleaning? Any other thoughts on the design?
Here are a few relevant notes from Steve Dashew’s “Offshore Cruising Encyclopedia”:
“… it’s vital that the plumbing be either level or, better yet, plumbed with a slight rise. This prevents air locks. When there are dips or loops, water flow is restricted and centrifugal-style pumps don’t work well.
The attached illustrations represent “three different approaches to PVC-based intake manifolds on a salt-water system. Two-inch (50mm) Ts and elbows are used, then reduced down to the needed size as they run along the manifold. The PVC is quite strong and not subject to electrolysis. However, it does need to be mounted where there is no danger of being stepped on, as it will not survive that sort of abuse.Tor
Silver Heels, P-424 #17
http://www.SilverHeels.us
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Hi Tor,
Seeing those manifolds, I think I could very well do with that, longitudinally along the hull below the show/head area. Even better than a big seachest. Or, longitudinally under the galley.
You’re right about the 6″ thing. It might not be the best idea, or even necessary. Most seawater flows are very low (including the engine cooling). So, a two inch pipe should be more than enough. (remember a 1″ hole in the hull is supposed to provide 1000 gallons an hour, so 2″ should be nearly triple that. Good enough to wash dishes, pump the head, cool the reefer, wash the anchor, etc.)
Your thoughts?
Bob
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Bob Fine
Fine Software LLC
Your data on the web your way. No kiddingPost generated from Pearson424 Forum using Mail2Forum
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Bob,
As fanatical as I am about reducing the number of thru-hulls in my boat, I still opted for a separate, dedicated
thru-hull & seacock for the engine raw water intake. Everything else aboard that uses seawater – the galley sink,
watermaker, toilet, anchor/foredeck wash-down, and anything else I might install in the future – will draw from the
seachest. Of those items, the biggest consumer is likely to be the deck washdown pump up by the bow anchors, a Shurflo
Pro Blaster, and that only pumps 4 gpm during its occasional use. So I’m not too concerned about having a huge thru-hull
for the seachest. What I installed comes down to a 5/8″ ID hose fitting, which I believe will suffice. Remember, Dashew
is accommodating a larger vessel with every imaginable bell & whistle. Our needs tend to be more modest.I’m still not decided whether to just beef up the lid and maybe the rest of the box of the converted shower sump I have
already set up as the seachest, or to scrap it and build a PVC manifold from scratch. As for location of the PVC option,
what you suggest sounds right to me.Tor
Silver Heels, P-424 #17
http://www.SilverHeels.us
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HI Tor,
I agree – the engine and other uses should be different intakes.
I think I’ll use a 1″ thru hull for the manifold and leave the other 1″ for the engine. Still, that only removes a couple of thru hulls. I also have 7 1-1/2″ drains (cockpit-2, deck-4, galley sink 1), 1 1-1/2″ head overboard, 2 5/8″ overboards for head/vberth sink drains. I think I have 19 thruhulls all together.
My head and galley use the same intake thruhull – which I may just use for the whole.
Still there are WAY too many holes in the boat. I’m not sure what the best way to deal with this is- I’ve thought of removing the deck drains and putting in hausepipes for drainage, or moving the thru hull to accomodate a simple elbow and then out the hull 6″ or so below the deck. Ugly, but removes large hoses and valves that are nearly impossible to get at.
That may be next year’s project… Or one of them.
Bob
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Bob Fine
Fine Software LLC
Your data on the web your way. No kiddingPost generated from Pearson424 Forum using Mail2Forum
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I think Tor stated the main advantage of the seachest over just a manifold, which is what I installed. With a seachest you don’t need to size the thru-hull to meet surge demand. With a manifold you do need to deliver the surge demand through the seacock. Otherwise you run the risk of starving one of the connected pumps. The safest way to size the manifold thru-hull is just add up the cross sectional internal area of every hose fed by the manifold then use a seacock with equal or greater cross-sectional area. That will produce a significantly oversized thru-hull, but it will provide capacity to expand the manifold or increase a pump capacity in the future. If you use hose barbs to connect the hoses to the manifold you can use the ID of the barbs to calculate the cross-sectional area,which is significantly less that the hose area.
Of course, an engineer would get the specs on every pump in the system and calculate the thru-hull size to those specs.
I’ve been running all of my non-engine seawater demands (head, AC, Frig, galley) from one manifold fed by a 1″ seacock for nearly 5 years. The only problem I’ve encountered is on the Chesapeake Bay. I need to clean out the raw water strainer at least weekly when the Sea Nettles appear in the summer. In Florida the strainer bowl started to attract barnacles. A bi-weekly addition of a pool tablet in the strainer basket seems to have contained that problem (Tor something you may want to think about for your seachest).
I have a separate manifold for the engine and generator fed by a 1-1/2″ seacock.
The only pump that is not fed by a manifold is the deck washdown. There was a 3/4″ seacock in the forward cabin, originally for the 2nd AC (which is gone) so I lazily used it for the washdown pump. I may move that to the cabin manifold, but that will wait until I decide if I’m going to add a watermaker.
I still have gazillion thru-hulls.
Routing the deck drains to the hull above the water line is a good idea, but you will spend a lot of time keeping the hull clean.John
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Regards,
John Stevenson
http://www.svsarah.comPost generated from Pearson424 Forum using Mail2Forum
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