Shared Through Hull Watermaker/Genset

[Dougcole]

Thank you for all of your well thought out advice. I am a few months from hauling out, so I am trying to think it through before I do anything.


I currently only have a single through hull in the laz, the 3/4" one with a marine hardware bronze strainer that serves the gen-set. In order to use another existing through hull I would have to make a pretty long hose run through a bulkhead into the main engine room. Even then, I only have a few choices; the engine pick ups, the 3/4" air conditioning pick up, and the holding tank outflow (obviously a no on that one). None of them a re really convenient.



Here is a link to installing a rainman water maker for those that may have interest. It calls for a 3/4" pick up.



https://www.rainmandesal.com/rainman-water-maker-installation-manual/


I like things simple and manual. I currently store the high pressure pump and the membranes in the laz when not in use with the pump plugged into a GFI outlet down there that I installed specifically for it. My main reason for the semi install is to eliminate having to pull the membranes up on deck for use and having to have the laz hatch open with hoses running in and out of it while the gen-set runs. It is loud and sort of awkward.


I can easily reach the tops of my two water tanks which are already in the ER, so I am consider installing deck fill caps in the top of them for filling within the laz. I could tee off a hatch scupper drain hose that is located in the laz for the brine outflow hose, so no need for any sort of through hull there.



So my water making procedure would work like this:


1. While in the laz with the gen-set running open the through hull and start the pump then turn the valve to begin making water.



2. Run 3 or 4 gallons of fresh water into a bucket in the laz.


3. Open a deck fill on either tank and put the fresh water hose into it. climb out of the laz, close the hatch and let it run until tanks are full. The tanks feed each other, so I wouldn't have to switch the hose from one side to the other.


4. Close the valve and turn off the pump. Close the through hull.



5. Open a tee on the bucket pickup line and put its hose into the freshwater in the bucket to flush the system. Turn pump back on and open the valve. Run until the bucket is dry. Turn off the pump.


I like that since the membranes mount with just four screws I could still easily pull the entire system out to bring it home with me or for service etc. I also like that I would only have to add one more hole in the boat.


I could also use the through hull for a wash down pump.


As an alternative, I also like the idea mentioned above of just connecting the wash down hose from the pump to the high pressure pump. That would mean I could eliminate the tee fitting for the pickup/fresh water flush bucket. For flushing just unscrew the high pressure pump hose from the wash down hose then put the H.P. pump hose into the bucket.

 

[Simi 60]

Our 240v 150lph watermaker and Genset share the same through hull
Genset goes into auto shutdown after about 30 minutes.

Doesn't matter
We do water on sunny days and have enough solar that it handles the load and battery/inverter picks up the slack.

 

[twistedtree]

A bigger thruhull with a manifold is of course the same concept as a sea chest. It just opens up a lot of opportunity to screw things up if not engineered and sized correctly. I know of a number of "sea chests" and "manifolds" that don't work because they were sized and built seat-of-the-pants without careful engineering. Even things like strainer scoops that face forward, face aft, or are flat can make a significant difference. There are advantages, but you really need to know a lot to design and build one - or you need to get lucky.


The manual for the OP's watermakers says very clearly that using a shared intake is only allowed if the two consumers NEVER operate at the same time.

 

[O C Diver]

In my research on sea chests and what I built for my boat, the first thing to understand is vacuum versus pressure for water flow. The volume of water coming through the sea chest or seacock needs to be sufficient for all devices that outside water pressure is capable of feeding more than enough water. This is in sharp contrast to devices competing for water with vacuum. This is especially true with strainers and external screens. While a device such as an engine may have to lift water to the raw water pump, there should be an ample volume available that external water pressure provides.

Ted

 

[Hippocampus]

A bigger thruhull with a manifold is of course the same concept as a sea chest. It just opens up a lot of opportunity to screw things up if not engineered and sized correctly. I know of a number of "sea chests" and "manifolds" that don't work because they were sized and built seat-of-the-pants without careful engineering. Even things like strainer scoops that face forward, face aft, or are flat can make a significant difference. There are advantages, but you really need to know a lot to design and build one - or you need to get lucky
The manual for the OP's watermakers says very clearly that using a shared intake is only allowed if the two consumers NEVER operate at the same time.

Again +1. Our prior boat’s manifold was well thought out and engineered. Detailed attention was paid to flow volumes and impact of device pumps on pressures. That boat has a total of seven through hulls. One forward as a wash down. Four in a box layout for things like AC, genset , and the manifold.A separate one for the main engine. When a boat is moving there’s a Bernoulli effect lowering the pressure at the intake of thru hulls unless there’s a clam shell facing forward . When still if the thru hulls are close together and volumes high there will be water movement across those close together. Screens and filters cause resistance. As usual TT is correct. What looks simple is really somewhat complex. Liked the Outbound solution as all thru hulls were easily accessible and unnecessary ones eliminated. Very much like the solution on the Northern Marines where one large sea chest serves all salt water requirements except main engine. Very much dislike some boats with hosts of thru hulls and some in difficult to access locations. They don’t get exercised so freeze. A good old school bronze thru hull routinely exercised should last for just about ever.

 

[BevinB]

I tap into the AC inlet with my Rainman. Never been an issue

 

[MaDehn]

Don’t try to use the generator thru hull. If you can use something else that will never run at the same time then might be ok. I would not use main engine thru hull either (personal preference). Everyone seems to be worried about protecting the wrong piece of equipment. Generator probably has a high temp and a high exhaust temp shutdown. Not great if the go off but not Catostrphic either. Might have to replace an impeller at worst. However your water maker high pressure pump will get totally messed up very quickly with even momentary losses of flow Also the membranes do not like pressure surges from interrupted flow and will be damaged quickly. I strongly advise separate thru hull. Your boat your choice. Best of luck.

 

[Flatswing]

I could also use the through hull for a wash down pump.


As an alternative, I also like the idea mentioned above of just connecting the wash down hose from the pump to the high pressure pump. That would mean I could eliminate the tee fitting for the pickup/fresh water flush bucket. For flushing just unscrew the high pressure pump hose from the wash down hose then put the H.P. pump hose into the bucket.

This is essentially what I do except I lug my pump & membranes up onto the aft deck since there is a 110v outlet there. A couple of things:
Do not share the generator sea water supply, definitely use the washdown or a separate thru hull. The Rainman pump is actually 2 pumps. The low pressure “lift pump” that can easily draw a vacuum through the intake hose over the side, which then supplies the high pressure pump that powers the RO.
In my iteration, my boat’s Jabsco washdown pump connects by garden hose to the Rainman intake hose, so actually 3 pumps in series. Not necessary but a simple, quick & effective solution.
Btw, Rainman recommends running the RO for 30 minutes after pickling fir safety. I just use that long 1/4” hose to rinse salt from the boat while I wait.

 

[boatnbump]

It only takes seconds with no water to burn up a high pressure water maker pump.

 

[Dougcole]

This is essentially what I do except I lug my pump & membranes up onto the aft deck since there is a 110v outlet there. A couple of things:
Do not share the generator sea water supply, definitely use the washdown or a separate thru hull. The Rainman pump is actually 2 pumps. The low pressure “lift pump” that can easily draw a vacuum through the intake hose over the side, which then supplies the high pressure pump that powers the RO.
In my iteration, my boat’s Jabsco washdown pump connects by garden hose to the Rainman intake hose, so actually 3 pumps in series. Not necessary but a simple, quick & effective solution.
Btw, Rainman recommends running the RO for 30 minutes after pickling fir safety. I just use that long 1/4” hose to rinse salt from the boat while I wait.

This is great, thanks for your info.


I do the same thing the first batch of fresh water that I run through the hose after pickling. I hose off the deck for a while, then fill a bucket with fresh water for the flush cycle after I am done filling my tanks.


Doug