Raw water manifold for safety?

[captlloyd]

Originally Posted by Simi 60

60 ft trawler.
1 single through hull for the primary engine
1 single through hull for the genset and deckwash.
That is all.

Now we’re talking. One step further, steel hull with keel cooling and and composting head plus enough fresh water tankage= no through hulls.

[boom23]

My Amel 50 has one thru hole for sea water intake. It's in the engine room and easily accessible.

[GordMay]

GROCCO Manifolds ➥ https://www.groco.net/products/fittings/manifolds

Raw Water Manifold ➥ https://www.groco.net/products/fitti...water-manifold
Drain Manifold ➥ https://www.groco.net/products/fitti...drain-manifold

[Coolerking]

The real trick to manifolds on the supply side is the ends of them, no 90s, use tees and plug/cap the ends.
Many bronze fittings are undersized, they fit into the hose size you are using, restricting flow.
Use fittings marked "FF" full flow, and size your seawater circuit to match.

[meirriba]

Amel as mentioned, but I remember from my two visits to Contest yachts that they also had raw water manifolds.
So at least two very respectable brands use this solution.

It goes without question that the manifold MUST be secured to the body of the vessel and not (as someone already warned against) only hung on the through-hull. There is no point taking a good idea and not install it properly.

[mvweebles]

The beauty of the Groco manifold is its typically attached to the sea strainer, not the thru hull. Serves to reduce number of bulky sea strainers. My guess is well designed boats have pumps centrally located in the engine room thus making consolidation of raw water feeds feasible.

[mvweebles]

Attached picture is a raw water manifold I am tinkering with for the refit of my 36-foot Willard Trawler. I have a total of five raw water draws: Engine (3/4"), A/C Pump (one 1" input pump for two A/Cs), 6kw generator (3/4"), washdown pump, and watermaker. The most critical is the engine, but highest volume by far is the A/C pump. The system is sized to easily allow the Generator/AC/Engine to be run simultaneously. The entire assembly is comprised of three sub-assemblies: the Seacock; the sea-strainer; and the actual manifold. It steps-down from a single 2-1/2" Seacock and Sea Strainer; to a 2" Manifold zone, and finally down to a 1-1/4" engine hose that feeds the 3/4" gear driven raw water pump. Having multiple assemblies connected by hose allows each to be firmly secured to a stringer.

As you can see, although there is only a single seacock (good), there are a ton of piping connections (bad). So it's a trade-off. It's probably more expensive than separate seacocks as they get exponentially more expensive as the size increases

[a64pilot]

Originally Posted by sailcrazy

Best I've seen was called a "seachest". It was a quite large diameter tube served by a single big seacock, and had multiple access points (ea with a valve around it and vertically. The one I saw was open at the top, so waterlevels, debris, flow rates, etc could easily be handled/watched/seeviced. I always thought a removable top on it would have been better, for safety, but this one was open.

If your really safety concerned then a seachest is the answer. The reason is a real seachest’s open top is well above water line so it can’t fill up and overflow.
Manifolds in my opinion don’t really increase safety due to their complexity and multiple parts.
In my opinion multiple thru hulls are fine so long as they are all easily accessible. Plus it’s not hard at all for them to be in groups. My engine , watermaker, generator, and rear AC are all in one place for example, my head thru hull is in a watertight compt whose top is above waterline.
I prefer completely independent systems myself, manifolds have a single point of failure and how is a manifold safer than three thru hulls in a row?

But the ultimate answer is a sea chest, stick all your thru hulls in one place, surround it with a tube who’s top is above water line, worst case if something busts, the sea chest fills up is all.

[a64pilot]

If you do the manifold, be sure to support it well, you don’t want it’s long arm levering on the seacock.

[mvweebles]

Good advice. I forget that some boats are built for speed. Mine is a full displacement trawler based on a 1950s Wm Garden west coast design. The main stringers are heavy roving encapsulated 3x14 mahogany that run almost the entire length of the boat plus a second pair of longitudinal stringers outboard that support the fuel tanks. There are plenty of places to firmly affix plumbing

Attached is a great example of a sea chest in an Art Defever designed trawler of fairly recent vintage (1990s). She's a 44-footer. Sea chest is a 12" x 12" column that rises slightly above waterline with all thru hulls visible via the clear plastic lid which is removable if needed. Clearly, this engine room has standing headroom. From the outside, this looks like any other simple Taiwan trawler and not that expensive used. Personally, my boat doesn't have space for this, or I would design one in.

[GordMay]

Weebles: I've never seen such a detailed plumbing diagram, for a specific boat system.

Well done!

[transmitterdan]

Our boat has a single thru hull supplying aux engine, generator and air con via a manifold supplied by a large sea cock and strainer.

A manifold will work if it has a few characteristics:

1) manifold should be well below the water line.

2) inflow pipe/hose should be significantly larger than any exit hose/pipe. This to ensure that there is no negative pressure in the supply line. You don’t want to suck water out of the supply line. It must flow in from the sea freely.

3) valves on all exits from the manifold. This to handle a leak downstream so as to not disable all the other users of raw water.

4) it’s a good idea to have raw water flow sensors on all engines in case the single strainer gets plugged up.

Sea chests are ok but for modest usage such as 50hp aux, generator or air con we have never had a problem with the manifold. I was skeptical at first but it works quite well.

[mvweebles]

Originally Posted by GordMay

Weebles: I've never seen such a detailed plumbing diagram, for a specific boat system.

Thanks - I am having a refit done in Ensenada MX. If I don't provide detailed drawings, it can be a real crap-shot on what the outcome will be. The electrical diagram is my magnum opus with well over 50-hours of design work into it.

For this manifold, I changed the design to split into two manifolds instead of everything on one. I decided I had the room for a second sea strainer, and allowed me to go with 2-inch sea cocks instead 2-1/2", which starts getting pretty big. Also allows me to split the A/C pump from the Generator, the most likely running scenario. My A/C pump is sized to support two A/C units, so is rated at 1050 gph. I simply didn't want contention between it and my main engine. I also decided to use Tee-fittings instead of a "Cross" fitting simply because the system became physically large and difficult to keep well below waterline unless I laid it flat, which had other problems. Attached revised diagram is only the engine-run circuit. I've included the Defender parts list which is missing some Tee's that I need to source from Buck Algonquin. All-in, this is a $1100 system. The other manifold will be sourced from parts I already have, so will cost will be negligible.

This Cruising World article by Steve D'Antonio was very helpful, especially the picture which I included on my diagram. For those who haven't spent time on Steve's site, well, he's amazingly prolific and generous with his time. Very refreshing in these days where no one wants to discuss anything unless you're a "Patron."

[CassidyNZ]

I was involved with a re-power using a new Yanmar 4JH4HTE. The old engine shared a raw water intake with the watermaker. In the new installation we were told that the watermaker would need to be re-directed to another raw supply because if the new engine was installed without a dedicated raw water supply, warranty would be voided.

So either the Yanmar agent was talking garbage or Amel and Contest don’t use Yanmar.

Having one raw water inlet feeding a manifold doesn’t obviate the need for other holes in the boat like sewerage, galley drains, wash basin drains, watermaker brine dumps, cockpit drains. Are there boats that consolidate these via manifolds too? Or perhaps they pump all this stuff out above the waterline?

I’ve read in other threads about some high-end cruising yachts having seperate bilges with water-tight bulkheads between. I also read about those same vessels having pipes running all over the place from a central manifold. I wonder how they achieve both goals. A whole bunch of bulkhead fittings with double clamps in each side? Or perhaps the pipes all run above the cabin sole?

Don’t take me seriously, I’m just musing (although it would be interesting to know). My boat has 9 holes (in and out) below the waterline but very short pipe runs. It wasn’t my clever choice, bought the boat like that but I’m not sure I’d be keen to swap that for a maze of long pipe runs all over the boat.

[mvweebles]

First, Groco makes a drain manifold to aggregate multiple gravity-fed discharges into a single above waterline thru-hull. I have a hard time imagining having that many gravity-fed lines in a nearby place, but it does exist.

By far, the biggest benefit for me in a manifold is not reducing below waterline penetrations - modern seacocks are extremely reliable and require minimal maintenance. The big benefit is reducing space-hogging sea strainers (or going with tiny ones). Over the 50-years my boat has been afloat (I've owned her almost half of those years), she's had some sloppy installations (mine included). When I added the watermaker and again the wash down pump, I repurposed existing holes that were not well positioned in the first place. I just want everything in one place so I can see it easily. Things like thru-hulls get forgotten if they're not easily seen, at least by me.

If I were the one warranting a new engine installation, I would want a dedicated thru-hull too. The Groco intake manifold clearly states - "this is a bad idea, but if you're gonna do it, here's a good product." That said, correctly designed with adequate flow, a manifold makes sense. But I'm with you on questioning whether having tons of hoses running around a boat is a decent tradeoff.