Sea Nettles Be Gone

Do you have any suggestions for keeping sea nettles out of my intake valve for my onboard air conditioner? The sea nettle infestation in the mid-Chesapeake was particularly heavy this year due to low spring runoff and little rain. Nettles don’t like fresh water. I’ve been polling fellow members at West River Sailing Club about how they handle the problem, and so far everyone has thrown their hands up in defeat.

Refrigeration and air-conditioning intakes seem to take in the most, particularly at anchor or at a slip. My best “fix” to date has been a Wa-ter Blaster water cannon I received as a gag birthday gift. It has a slanted ¾-inch nipple on the discharge end that fits snugly in an intake hose. A short blast of water from the sink clears the thru-hull intake, then I clear the strainer and reassemble it. I have the process down to about two minutes. If I’m lucky, it will stay clear for awhile. Unfortunately, I cannot leave the air-conditioner running unattended. I can’t even take a nap, for fear another nettle will be sucked in and overheat the system. My wife suggests we use the winter de-icer to flush the intake area clear. It sounds like a good idea, at least at a marina. We’ll try that and let you know if it’s successful.

The only other answer we’ve noticed is wait for a good heavy rain that sends the nettles down to a saltier depth. It would be nice to get a full night’s sleep with air-conditioning and wake up to a cold reefer.

Pete and Pokey Emens
Freedom 45
West River, Md.

We assume the Chesapeake scourge you write of to be the sea jelly (“jelly-fish” to the politically incorrect) known as chrysaora quinquecirrha. In some areas this creature and its inveterate invertebrate cousins are simply a nuisance; you might have to clean out the strainer basket every few days. In other areas and during prime season, however, certain locales can prove downright maddening to operators of air-conditioners, water-cooled refrigeration, generators, and other gear that require cooling water while the vessel is stationary (this tends to be less of a problem underway).

It’s not uncommon for the nettles or other sea jellies to clog an air-conditioning strainer on an hourly basis. Fortunately, there are a few tried and true approaches that may offer some relief for vessels and crews suffering from sea nettle overload.

First, an oversized internal basket-type sea strainer will hold more of these critters than the average strainer, giving you longer breaks between basket emptying. Second, an external, perforated scoop-type strainer (sometimes called a “south-bay strainer”) will help keep out sea jellies, seagrass, and flotsam that tend to chronically clog internal strainers. Scoop strainers should be of the serviceable variety, where the screen can be easily removed or opened underwater, for cleaning and service. A scoop strainer has the added benefit of placing slight positive pressure on the air-conditioner’s raw-water system while the vessel is underway, reducing the likelihood of the pump becoming air bound. It’s important to remember, however, that for this very same reason, forward facing scoop strainers should never be installed on sailboat engines or gensets, which like a little air in the cooling stream.

The ultimate solution for chronically clogged sea water strainers is installing a macerating strainer. One such device is Groco’s Hydromatic Self-Cleaning Raw Water strainer. It operates on 12 volts and periodically cleans itself at preset intervals to keep water flowing to your air-conditioner, generator, or other vital equipment.