I use a micro air/water pump on my subs to blow ballast tanks on model submarines. It is very small and is equally able to pump air or water. Cost about $15 usd at NautilusDrydocks.Com. Might be worth taking a look to see if it will work for you. Search for micro pump in the shop section of web site.
Hope this helps,
Steve R
windwardcd@gmail.com

"The next thing I'd like is one that runs intermittently like on off on off on off to replicate a real boats exhaust at idle. "
I might suggest adding a riser to the exhaust pie. As the pump pushes H2O up the inboard side of the riser, it finally crests over the top of the riser and spills out the exhaust outlet. The pump meanwhile refills the inboard side of the riser until the H2O again spills over. Very prototypical hopefully. I've never tried it, so let us know if it works.

I bought my pumps off AMAZON.CA, both just the bare pump & also a version that includes a switch. Sorry I don't know how to attach a direction, or link, to the product. But i hope this helps.

Hi Scott,

A few years ago, JB kiwi and I worked on intermittent cooling water with added air/smoke. It was controlled with a custom programmed microchip.

You can find more on what we did here:

(You need to scroll down a bit to “exhaust smoker”)
https://model-boats.com/blogs/60819#63592



Graham93

I wonder if I manage to add air to the outlet line from pump if it will make it splutter?

I believe the on /off would be a separate channel on the radio. I have purchased a small water pump off ebay. It was 7 volt, but I think you may need a valve on the out put. This way you could throttle the output to make it look realistic or a large line on the output side to make it sputter and fart realistically.

I think the valve would give you more options for output. The more experienced folks could give you more info