watermaker air bubbles underway-gctid390570

[ksanders]

Here's an interesting challenge.

My watermaker draws water from the seawater washdown pump through hull. That through hull is located in the lazarette.

While at rest, the watermaker runs fine.

While underway the watermaker picks up little air bubbles, and eventually the air bubbles accumulate enough to cause the watermaker to quit pumping effectively.

Of course I don't want to be limited to running the watermaker at rest. Watermakers are noiser than you might think, and I have to run it for several hours a day on average to keep up with water demands.

I believe that the bubbles are coming from the props since the intake is in that vicinity and the problem is only while underway.

I do not have another through hull to use, and I do not really want to install one.

How do I solve the problem???

One possible solution would be to use a intermediate tank, something like 5 gallons between the through hull and the watermaker. A pump would keep the tank full, and the watermaker would draw water from the tank. There are several technical details to work out for this solution but a tank would work.

Does anybody have a different idea, or any other advice?

Thanks very much.

[Guest]

Kevin

When I installed mine the manufacture and the dealer rep said the pickup had to be forward of the props and have a forward facing scoop to eliminate this issue. This was a real issue for me since I wanted to put mine in the extension

[Guest]

Does this happen at hull speed or faster? I have the same setup and have no problem but I never run faster than hull speed.

Is there any way to check that it is not leaking back through the wash down plumbing?

[ksanders]

JohnWms wrote:
Does this happen at hull speed or faster? I have the same setup and have no problem but I never run faster than hull speed.

Is there any way to check that it is not leaking back through the wash down plumbing?

We only travel at hull speed.

I suppose it could be coming back through the wash down but I kinda doubt it. I could install a check valve in the wash down to be sure thanks.

[Guest]

What kind of through hull do you have? Certain through hulls dont work while under way.

[Guest]

1. A simpler version of a tank could be a large diameter pipe (say 4"-ish) that allows the air to settle at the top. Hook up a vent to allow the air to escape. Mount it horizontally below the waterline so it's always full.

2. Ask Steve D'Antonio.

[ksanders]

Kåre L wrote:
1. A simpler version of a tank could be a large diameter pipe (say 4"-ish) that allows the air to settle at the top. Hook up a vent to allow the air to escape. Mount it horizontally below the waterline so it's always full.

2. Ask Steve D'Antonio.

Kare

Have you seen somethink like this proposed by Steve D'Antonio??? If so, please elaborate, I'm interested.

The tank, or tank/pipe idea is good, but can be challenging to do. I think I'll have to add a pump to keep the tank full. The air would settle to the top and be vented as you indicated. The watermaker would draw from the bubble free water in the tank.

One of the challenges of this is how to keep the tank full. Two methods come to mind. The simplest but least efficient would be to have a tank with a vent at the top, and a pump that runs continously at a rate slightly faster than the watermaker. The excess capacity of the pump would just go out through the vent.

A more complex method would be to use a pump, and two float switches. The bottom float switch would turn on the pump and the top switch would turn off the pump.

[ksanders]

biohazard wrote:
What kind of through hull do you have? Certain through hulls dont work while under way.

This one works great underway for the washdown. It just gets a few air bubbles that eventually build up in the watermaker.

thanks

[Guest]

Your watermaker is getting an alarm in the low pressure feed stage? Is it really air bubbles or a situation where the first stage can't get enough water when under way?

My watermaker is under the cockpit on the starboard side with the pickup the same place as yours on the port side. Pretty short run but the installation includes a very large pump for the first stage. I'll have to look at the specs on the pump but it seems way larger than I would initially think.

My watermaker draws almost 30 amps (120vac).

What happens if you run the washdown pump at different times (with the watermaker off)?

I'd bet the washdown spigot is a pretty good seal so there are probably no leaks there. If there was a leak anywhere else you'd think it would be obvious. Sill possible there's an air leak that only shows up under higher vacuum than the washdown pump can generate.

[cosmo777]

Kevin,

Why not use the washdown pump to fill the tank. It can be dual use for both the watermaker tank and the washdown pump.

Maybe even wire it into the watermaker, so when it turns on then the pump also turns on.

Then use a float switch in the tank to turn the pump off when the tank is full.

[ksanders]

JohnWms wrote:
Your watermaker is getting an alarm in the low pressure feed stage? Is it really air bubbles or a situation where the first stage can't get enough water when under way?

My watermaker is under the cockpit on the starboard side with the pickup the same place as yours on the port side. Pretty short run but the installation includes a very large pump for the first stage. I'll have to look at the specs on the pump but it seems way larger than I would initially think.

My watermaker draws almost 30 amps (120vac).

What happens if you run the washdown pump at different times (with the watermaker off)?

I'd bet the washdown spigot is a pretty good seal so there are probably no leaks there. If there was a leak anywhere else you'd think it would be obvious. Sill possible there's an air leak that only shows up under higher vacuum than the washdown pump can generate.

Wow!, thats a heck of a watermaker. My unit draws 20 amps DC. I looked at a much larger unit of the size your're talking about, and even had a very good deal in one lined up, but I just couldn't get it installed without allot of re-arranging.

The washdown pump works gerat, underway or at rest. I'm really sure the small air bubbles are the result of cavitation from the props.

This build up of air is not an immediate thing. It happens gradually over the course of an hour or two running.

The output goes down then stops. I can see the air bubbles in the hose.

cosmo777 wrote:
Kevin,

Why not use the washdown pump to fill the tank. It can be dual use for both the watermaker tank and the washdown pump.

Maybe even wire it into the watermaker, so when it turns on then the pump also turns on.

Then use a float switch in the tank to turn the pump off when the tank is full.

Thats not a bad idea, I could tee in after the washdown pump and use it to fill the tank using a selonoid valve.

The method I'm leaning towards is a offshoot of the one Kare suggested.

I'm thinking for simplicity sake about going with a tank fed by a dedicated low volume pump. The pump would have more volume than the 1 gal per minute the watermaker needs. The pump would fill a tank that has an overflow overboard through an existing through hull, just like the watermaker does with its brine output. I could even tee into that line.

Kares pipe/tank idea is where this gets really interesting.

I need a tank, and I even have a brand new 18 gallon tempo tank that would work great, but I think I like the pipe/tank better.

If I used a piece of 4" ABS pipe. say 2' long to make the tank out of it would be easy.

The pipe would be mounted vertically.

At the bottom would be a fitting going to the watermaker.

At the top would be a fitting going to the overboard through hull.

Using a tee and fitting, near the top would be the output of my new pump.

The new pump would be powered only when the watermaker is on.

The pump keeps the tank full.

The excess water and air go up and overboard.

The pure water goes down to the watermaker.

I discussed this at length with the head tech guy at Katadyn today.

He told me that even a small amount of bubbles build up over time.

The only way to fix this is to turn a valve to purge the air from the watermaker, then start it up again.

The issue has something to do with how the piston pump works. If there is any air the pump just compresses that air and gets into a cycle where it cannot clear itself.

He's heard about the issue before many times and the solution is to either put in a new through hull or use a small tank system.

[Pacrimrat]

[img]/media/kunena/attachments/vb/694407=28643-bottom.jpg[/img]It looks like the intake is far enough ahead of the props.Could the shaft/zinc be aerating the water enough to cause the problem?Do you have aircon on yours? I have another thru hull forward of the port engine.After looking at the bottom, it could be caused by the turbulence coming off the bottom at the shaft outlet.

[ksanders]

Pacrimrat wrote:


http://baylinerownersclub.org/media/...ttom.jpg[/img]It looks like the intake is far enough ahead of the props.Could the shaft/zinc be aerating the water enough to cause the problem?Do you have aircon on yours? I have another thru hull forward of the port engine.After looking at the bottom, it could be caused by the turbulence coming off the bottom at the shaft outlet.

Nice photo, Thanks!The bubbles could be coming from any number of places. I have no clue.All I know is that they're there, and I need to solve them. Using the watermaker only while at rest is not accpetable.My boat does not have air conditioning, and doesn't have any foward through hulls except the macerator.

[AndrewF]

For what its worth I had the same problem on another boat with the water intake for the air conditioning that I took the water from a wash down pump skin fitting. It brough in air and also they act like a ventury and suck back on the hose itself while underway. The fact is there is allways air under the hull when travelling through the water....it just gets under there and its a good thing as lowers the drag on the boat from the water.

A scoop will fix the problem, simply or not so simply replace the skin fitting witha scoop style one or fit a scoop to the exsisting one and your problem will be resolved I am sure.

Good luck

[Mike3888]

If the 4" "tank" is mounted well below the waterline let gravity fill the tank. Keep the inlet to the tank low as well. A horizontal tank with the inlet and vent on the top of one end of the pipe, the outlet to the watermaker on the bottom of the other end. If underway the thru-hull does not have positive pressure, fit a scoop. No pump required.

Mike