Shared Through Hull Watermaker/Genset

[Dougcole]

Hi All,


I am planning on doing a semi-permanent installation of our AC powered Rainmaker portable watermaker in our lazzerette which will require a pickup at a through hull. The generator is also in the laz, with a through hull and strainer in a perfect spot for the watermaker install. The genset is an 8K Kohler. The through hull is a 3/4" with a 3/4" hose feeding the gen-set.


I'd like to avoid installing another through hull if possible as it involves hauling the boat and added expense.


Do you think the watermaker can share a through hull with the gen-set? Both would be running at the same time.


Thanks

 

[RickyD]

Hi All,


I am planning on doing a semi-permanent installation of our AC powered Rainmaker portable watermaker in our lazzerette which will require a pickup at a through hull. The generator is also in the laz, with a through hull and strainer in a perfect spot for the watermaker install. The genset is an 8K Kohler. The through hull is a 3/4" with a 3/4" hose feeding the gen-set.


I'd like to avoid installing another through hull if possible as it involves hauling the boat and added expense.


Do you think the watermaker can share a through hull with the gen-set? Both would be running at the same time.

Thanks

You could give it try and watch the genset engine temps and the watermaker incoming water volume. If it doesn't work well you can then opt for the addition hole.

 

[tiltrider1]

My raw water wash down pump and my water maker share the same thru hull fitting with no issues. However, I am never using my wash down and making water at the same time so there is never a conflict.

In your case you will most likely be running the generator at the same time you are making water. Not knowing the specs on either piece of equipment I can’t say if there is an issue. You should probably be talking to Rainmaker and asking their opinion.

 

[SteveK]

Shared, only use one at a time.

 

[Dougcole]

Unfortunately, I will have to use both at the same time, it’s an AC powered watermaker.

 

[mvweebles]

You have a generator that is spec'd for a 3/4" thru-hull; and you have a 3/4" thru-hull feeding it. And you want to install another consumer. The answer is no - don't do it.

But if you must, the best route would be enlarging the thru-hull to 1-1/4", replace the sea strainer, and add a decent manifold on the inboard side of the sea strainer such as this GROCO manifold HERE. Note that Groco recommends AGAINST using this, but they sell it anyway. Guessing the lawyers had their input.

If you insist on giving it a try, put a check valve to assure the generator gets priority. Groco makes one HERE. Realize check valves are fallible, but this will protect your generator.

But to be clear, my advice is to NOT share a 3/4" thru-hull.

Good luck -

Peter

 

[Mako]

What's the water feed rate of the water maker? If it's negligible then go for it and give it a try. Like what was said previously, watch the genes temperature in warm water, as you load it up fully for an hour. See how it goes.

 

[wkearney99]

Of the many things that can go wrong, and the steps involved with troubleshooting them, having water cooled systems get deprived of water, or worse, having it sucked out of them, is generally considered a 'bad plan'. I'm guessing the watermaker intake pressure isn't "all that much" but would wonder what kind of reverse pressure the impeller in the generator is prepared to tolerate. Or vice-versa.

If the intake was plugged for any reason you'd then have the devices competing to pull water against each other. I doubt most (if any) systems are designed with that in mind. And intakes DO get plugged from time to time. Growth, stray trash, whatever.

Yeah, it's an annoying add-on of time/expense, but I'm guessing a screw-up from rigging it up the wrong way could likely cost easily that much, if not more, to fix.

 

[O C Diver]

I have a 2" seacock and strainer that feeds a manifold for engine, generator, air conditioning, and raw water washdown. It works very well because there's ample volume and all the plumbing through the manifold is a foot under water. In essence, the system is pressurized through the manifold.

In your situation, I would first determine the total volume requirement. Then, accurately determine the outside water level in your lazarette. If you're going to have 2 or more appliances sucking water, the seacock, strainer, and manifold all need to be below sea level or you will inevitably have problems. I would also shy away from check valves in this application. I wouldn't want a weak impeller on the generator starving it of cooling water. In this type of application, the pumps don't have great suction and vacuum from one pump may increase resistance for the other check valve to open.

Ted

 

[mvweebles]

......but i'm guessing a screw-up from rigging it up the wrong way could likely cost easily that much, if not more, to fix.

 

[Dougcole]

Good info from everyone here, thanks for your help.


I think a second through hull is the way to go. I considered a larger through hull and strainer, but upon further thought that doesn't make much sense. I'd still need a haul out and a second 3/4" through hull is cheaper than taking the old one out and replacing it with a bigger one.


I've also kicked around adding a raw water washdown pump down there, and I think it would be a better candidate for a shared through hull as it would not run at the same time as the watermaker.

 

[Dougcole]

View attachment 140785

I've never been lucky. Not even once.

 

[mvweebles]

.....

In your situation, I would first determine the total volume requirement. Then, accurately determine the outside water level in your lazarette. If you're going to have 2 or more appliances sucking water, the seacock, strainer, and manifold all need to be below sea level or you will inevitably have problems. I would also shy away from check valves in this application. I wouldn't want a weak impeller on the generator starving it of cooling water.....

The challenge for OP is the generator calls for a 3/4" inlet. Thru-hull is 3/4" . Is there spare capacity? Maybe but no way to tell. If the generator is spec'd at 1/2" but installed at 3/4", then maybe there is reserve capacity.

I have a similar setup to OC Diver - 2" thru-hull and strainer and a 1-1/4" thru-hull and strainer. They feed everything on the boat. The only way I could find to accurately assess capacity is to use area of a circle for all inlets (pi x r ^2).

I agree that check valves should be avoided. But if you're going to undersize the thru-hull, some insurance makes sense. Protect the generator and assure it gets water.

Peter

 

[mvweebles]

Good info from everyone here, thanks for your help.


I think a second through hull is the way to go. I considered a larger through hull and strainer, but upon further thought that doesn't make much sense. I'd still need a haul out and a second 3/4" through hull is cheaper than taking the old one out and replacing it with a bigger one.


I've also kicked around adding a raw water washdown pump down there, and I think it would be a better candidate for a shared through hull as it would not run at the same time as the watermaker.

I'd encourage you to reconsider and go with a single larger thru hull and strainer. Easier to maintain a single strainer, and provides more flexibility. Suppose you want to add a washdown pump....
.
Peter

 

[O C Diver]

The challenge for OP is the generator calls for a 3/4" inlet. Thru-hull is 3/4" . Is there spare capacity? Maybe but no way to tell. If the generator is spec'd at 1/2" but installed at 3/4", then maybe there is reserve capacity.

I have a similar setup to OC Diver - 2" thru-hull and strainer and a 1-1/4" thru-hull and strainer. They feed everything on the boat. The only way I could find to accurately assess capacity is to use area of a circle for all inlets (pi x r ^2).

I agree that check valves should be avoided. But if you're going to undersize the thru-hull, some insurance makes sense. Protect the generator and assure it gets water.

Peter

I don't remember which company, but either Buck Algonquin or Groco use to have flow data on their website for seacocks and strainers. It was a graph listing GPM versus vacuum. Obviously if the plumbing was below sea level, the vacuum value would be offset by water pressure.

Ted

 

[ksanders]

I have a 3/4" through hull that goes to a 1" groco sea strainer.

Then it tees off through groco check valves to both the 1000 GPH AC pump, and the 40 GPH watermasker. Both are isolated by a on-off valve for servicing.

Both work just fine at the same time.

Worst case is you need another through hull but you'll never know unless you try.

 

[Flatswing]

I have the same Rainman -used portably on the aft deck. I have a sea water spigot on the foredeck for anchor wash down (which is T’ed off the AC pump thru hull) . Wishing to avoid an expensive or permanent install of a portable system, after discussing my plan with Rainman tech. Support) I just run a 1/2” garden hose from the foredeck spigot back to the Rainman intake hose using appropriate sized Banjo fittings. Works well while underway. I can, but do not usually run the AC when making water. Now I don’t have to listen to the noisy Rainman at anchor, since it has a bubble free sea water source while underway. I forget the maximum intake pressure that the Rainman can accept, but it was above my 50 psi washdown pump.

 

[SteveK]

Curious why sharing another thru hull is not considered. Like for the head, or even the engine, wash down?

 

[O C Diver]

Curious why sharing another thru hull is not considered. Like for the head, or even the engine, wash down?

It depends on the pumps.

If all your pumps have intake and exhaust valves (such as diaphragm and piston pumps) the pumps have the ability to suck into a vacuum until the water reaches the pump.

Centrifugal pumps (such as air conditioning raw water pumps) don't have valves and must be filled with water to prime. As a result another diaphragm pump could suck the priming water out of the centrifugal pump and keep it from priming.

Impeller pumps are designed to overcome a dry pump, but may not prime when another pump is pulling air through the Impeller.

Ted

 

[twistedtree]

The generators and watermakers I've dealt with all prohibit using a shared intake, and some even void the warranty if you do. I suspect there is just too much opportunity for one device starving the other device, unexpected backflow, unexpected air draw, etc.


Another consideration is around the use of a thruhull scoop. A forward facing scoop is often good for a watermaker, ensuring a good air-free flow of water. However a forward facing scoop is prohibited on a generator because when you are underway with the generator off, water can be driven back through the line and flood the generator.


I would take the time to do it right. You will also need a brine water discharge, so can do that at the same time.

 

[SIBERNUT]

If you decide on a bigger thru hull, I have an all bronze 1.5" thru hull AND check valve to sell. Plus an ell & a couple nipples all together.

 

[mvweebles]

The generators and watermakers I've dealt with all prohibit using a shared intake, and some even void the warranty if you do. I suspect there is just too much opportunity for one device starving the other device, unexpected backflow, unexpected air draw, etc.


Another consideration is around the use of a thruhull scoop. A forward facing scoop is often good for a watermaker, ensuring a good air-free flow of water. However a forward facing scoop is prohibited on a generator because when you are underway with the generator off, water can be driven back through the line and flood the generator.


I would take the time to do it right. You will also need a brine water discharge, so can do that at the same time.

Groco makes this handy manifold that is sized so the three consumers are slightly smaller than the supply fitting. However, Groco explicitly states they recommend against it!!!

Peter

 

[jgwinks]

Unfortunately, I will have to use both at the same time, it’s an AC powered watermaker.

I don't think that will work. I once tee'd a galley sea water pump into the engine intake on a sailboat. The engine was about the same size as a genset so similar water flow. The galley pump would not draw water if the engine was running.

 

[SteveK]

It depends on the pumps.

If all your pumps have intake and exhaust valves (such as diaphragm and piston pumps) the pumps have the ability to suck into a vacuum until the water reaches the pump.

Centrifugal pumps (such as air conditioning raw water pumps) don't have valves and must be filled with water to prime. As a result another diaphragm pump could suck the priming water out of the centrifugal pump and keep it from priming.

Impeller pumps are designed to overcome a dry pump, but may not prime when another pump is pulling air through the Impeller.

Ted

Ted what you said, but if a convenient gen thru hull was considered, then why not another where there is no continuous competition. The issue you describe could be applied to the original plan.

 

[jgwinks]

I have a 2" seacock and strainer that feeds a manifold for engine, generator, air conditioning, and raw water washdown. It works very well because there's ample volume and all the plumbing through the manifold is a foot under water. In essence, the system is pressurized through the manifold.

In your situation, I would first determine the total volume requirement. Then, accurately determine the outside water level in your lazarette. If you're going to have 2 or more appliances sucking water, the seacock, strainer, and manifold all need to be below sea level or you will inevitably have problems. I would also shy away from check valves in this application. I wouldn't want a weak impeller on the generator starving it of cooling water. In this type of application, the pumps don't have great suction and vacuum from one pump may increase resistance for the other check valve to open.

Ted

That's more like a sea chest which is like a BIG through hull with all the intakes plumbed into it. They're common in commercial vessels.

 

[O C Diver]

That's more like a sea chest which is like a BIG through hull with all the intakes plumbed into it. They're common in commercial vessels.

Yes, that's why I researched it and did it. Went from 4 seacocks to 1.

Ted

 

[OldDan1943]

On my AT34 one of the first things I did was to change the 2 3/4 ‘plastic’ hull valve to 1’ bronze hull valves attaching them to the bonding system. Per sharing thru-hulls? I have been told, if possible avoid it. Your boat, give it a shot, if it doesn’t woke, another thru-hull will be necessary.

 

[mvweebles]

....... Per sharing thru-hulls? I have been told, if possible avoid it. ....

I went the same route as Ted/OC Diver. A 2-inch sea cock and sea strainer, and a 1-1/4" sea cock and strainer (I also have hydraulic stabilizers with a cooler). More of a sea chest than over-stretching a single thru-hull.

There is logic to consolidating thru-hulls. The obvious one is reducing holes in the hull, but honestly, that's not even an asterisk because thru-hulls are extremely reliable. As a past delivery skipper, one of my challenges was finding and mapping all the thru-hulls which is not always easy. And many are not protected by a strainer and those that are, often have a cheap plastic strainer. It is so much more convenient to have a single large thru-hull and strainer centrally placed vs inside a cabinet or lazarette.

A 2" thru-hull plus hose and strainer is fair size. But it will serve many consumers. There's a lot to be said for just such a setup, but it does have to be over-sized.

Peter

 

[OldDan1943]

Making the thru-hulls oversized has the advantage because if the hull strainer or the sea strainer becomes fouled the ‘over size’ will still provide good flow.

 

[Hippocampus]

As is not unusual TT gave you your answer. There’s usually no issue if the two devices are never (yes I mean never) on at the same time . Otherwise you run the risk of starving the R/O. The intake pump for the genset is strong enough to develop a relative vacuum at the T (or Y) fitting. The water feed pump for the R/ O may not be strong enough to over come it and still supply salt water at adequate volume and pressure to the unit.
If you had a large enough sea chest or possibly a manifold fed by a large thru hull and feeding multi devices where all are never run all at once or of low volume /pressure it would be fine to share. With the sea chest, if of sufficient size, there would be no additional work for the RO pump to do even with multiple devices running.
On a prior boat I had a manifold supplying salt water to multiple devices but they were all low flow low pressure. ROs return more salt water than the fresh water they make. A lot of water runs through them. It’s a high volume device. A lot of salt water comes in , a little fresh water is made, a lot of slightly saltier water goes out. Feed volumes are usually higher for AC than DC units as they make more fresh water per unit time so adequate feed is even more critical.