Watermaker Intake Position

[hummingway]

The intake thruhull I'd like to use was the old head intake but I'm on a composter now. The only other intake on the boat is the raw water intake, in the engine compartment.

The old head intake is about 12 inches below the water line. In all other ways it is beautifully situated for my purposes. Has anyone any experience with using a source so close to the waterline?

[Randyonr3]

Originally Posted by hummingway

The intake thruhull I'd like to use was the old head intake but I'm on a composter now. The only other intake on the boat is the raw water intake, in the engine compartment.

The old head intake is about 12 inches below the water line. In all other ways it is beautifully situated for my purposes. Has anyone any experience with using a source so close to the waterline?

we used the forward head intake for ours.. pulled the head and turned the room into a watermaker closet and a place to hang cloths.. for just the two of us, we didnt need two heads and showers..
something to think about.. If you are using a vane pump on your watermaker, it has a chance of losing prime if the area you speak of will be either out of the water or close to it on any one tack, and most preasure pumps for watermakers dont like AIR in the system..
on ours, we installed a sureflow pump in front of the presure to insure the prime would not be lost and if it was, the sureflow would pick it back up fast..

[svcambria]

You will have problems with air getting into the system while underway one one tack. If you can just use it on the other tack or when stationary, you will be fine. It probably will not work (that is, suck air) even motoring in calm water...

Michael

[hummingway]

It's a Katadyn 80E. They call the pump a positive displacement pump and say it's self priming. It does warn about getting air in when operating it.

[hummingway]

Originally Posted by svcambria

You will have problems with air getting into the system while underway one one tack. If you can just use it on the other tack or when stationary, you will be fine. It probably will not work (that is, suck air) even motoring in calm water...

Michael

I expect to mostly use it when stationary but I'm a little worried that if I limit myself like that it will jump up and bite me!

[mdvick]

Please be VERY,VERY careful when using a water maker when stationary. If you are the only one around and are sure that you are not leaking any fuel or oil - go for it. You will destroy a membrane with ANY hyro-carbon. Docks, etc...

[hummingway]

Originally Posted by mdvick

Please be VERY,VERY careful when using a water maker when stationary. If you are the only one around and are sure that you are not leaking any fuel or oil - go for it. You will destroy a membrane with ANY hyro-carbon. Docks, etc...

Where I am the tidal flow is considerable so I thought that as long as it's an incoming tide I would be alright.

I guess that's the thing. If I come off the head intake the job will be much simpler but I will be restricted when I use it. If I come off the motor intake then the job is more difficult but I'm less restricted when I use it.

Is there any concerns teeing off the engine raw water? For instance can water flow back out of the engine with contaminants in it?

[mdvick]

I have always tried to use a dedicated inlet for a watermaker. I use the engine inlet for the heads so if it is showing any contamination you will see it when you flush! Try to get the inlet for the watermaker as far down the hull as you can and you will avoid the issues mentioned. Good luck. Mike...

[svcambria]

My own rule of thumb is oil and fuel float, so if it's a calm day, I make fresh water, even in a marina or crowded mooring field.
Generally, the lower the watermaker inlet the better off you are, as it can be relied upon when motoring (a great time to make water) or sailing on the tack that brings it closer to the surface. But if you are willing to accept the restrictions, a higher inlet will work just fine - always nice to have fresh water.
Pulling the water in from the engine strainer? Your machine probably wants about 1/2 gallon of sea water per minute, not a huge amount, so it is possible (not guaranteed) that it wouldn't cause cavitation or starve the engine (less problem the larger the inlet hose is), but only setting it up and trying it will tell.
I have a Spectra 380, had it for eleven years, intake about 2 feet below water line on the port side, takes in about 2.5 gallons per minute. It will work on port tack with one pump on whether or not one or two pumps are on, the second pump just gets air...

Michael

[Tellie]

Deeper is always better and a dedicated thru hull is ideal. Several watermaker companies require a dedicated thru hull with a forward facing strainer for warranty reasons. Engine thru hulls are the least favored connections and always discouraged. Attaching to the engines thru hull restricts flow to the watermaker if your running the engine and trying to make water at the same time. Most engines raw water pumps will pull more water volume than most watermakers feed pumps can, thus starving the watermaker enough to reduce it's ability to produce the amount of product water it is designed to make and making the watermaker work harder than it's intended to. But watermakers come in all sizes and designs. You don't mention what unit you are trying to install. Ten inches below the waterline is fine if you're making water at anchor where it's done most of the time. But if you plan to run your watermaker while moving, as most people will from time to time, you'll be sucking a lot of air. As stated above most watermakers do not like air and consistant air will quickly lead to premature failure of most watermaker feed/pressure pumps. Use the old head thru hull for now and make water while anchored in calm water, not while moving. But I'd strongly recommend a dedicated, proper and deeper thru hull installation on your next haul out. It'll be cheaper than what you're going to be saving on joker valves, pump outs, nasty flowing repairs made in 8' seas and replacing sanitation hoses, clamps and holding tanks that always eventually stink up your boat. I'm going on better than two years on my composter and have never looked back. One of the best all time improvements I ever made to my boat.