Fighting bio invasion

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Wider use of electronic-controlled air conditioning systems on voyaging boats in warmer climates has given rise to an insidious, unseen invasion: Barnacles and other marine growth that set up shop in the piping and heat exchangers of marine air conditioning units. If left unchecked these invaders can create an expensive mess.

Solutions to this problem include 1) passive (non-electrically powered) systems that produce disruptive ions to inhibit barnacle attachment and growth and 2) active systems (drawing an electrical current) that use a copper anode to disrupt fouling. One of the passive systems is an ingenious new device called the Bio-Guard water treatment system from Spectra Watermakers ( Employing this system will reportedly greatly reduce the need for cleaning out cooling water plumbing.

This type of bio-fouler invasion was less of an issue before the widespread use of electronic controls for air conditining units. With the rise of smart controls, boat owners can set the A/C unit to one temperature and forget it. The unit then cycles on and off as necessary to maintain that set temperature. The result is mutiple hours of A/C operation. This nearly continuous running sets the stage for the culprits in all this fouling, those pesky little aquatic creatures from the class Cirripedia, more often known &mdash and cursed &mdash as barnacles (for fresh water vessels, zebra mussels have also become a problem).

As filter feeders, barnacles like to live where they can get a steady flow of snack-happy water past their frilly mouth parts. The intertidal zone where the tide ebbs and flows twice a day is a great haunt for barnacles. But as boat owners in southern waters have found, there is an even better place for these hungry critters. When an A/C unit runs for several hours a day it produces a steady flow of sea water moving through the cooling pipes. For a barnacle, that equates to a feast. The barnacle larva, called a cyprid, swims into the cooling circuit and attaches itself. When the A/C is on and cooling water is circulating, its as if the barnacle is living in a smorgasbord. Lots of barnacles join the party and the volume of cooling water drops until eventually the unit can become so starved of water it shuts down.

One way of dealing with this problem is to flush the cooling system with an acid wash. If the issue is not caught early enough, however, the growth can restrict cooling water flow sufficiently that the A/C unit will not operate. In that case only a complete rebuild of the raw water loop can solve the problem of low water flow. That means replacing most, if not all of the plumbing components.

Spectra Watermakers was one company that looked into the problem of fouling of pipes, hoses and heat exchangers. Its solution is the Bio-Guard. This is a unit consisting of a metal tube enclosed in a clear plastic tube with plastic fittings at either end. This unit is installed in the line and cooling water flows through the inner metal tube. As the water does so, the tube releases metal ions into the water. “The metal leaches out and the ions disrupt organisms from starting to grow,” said Ray Carter of Spectra. The result is an unpleasant environment for barnacles and other marine organisms, inhibiting them from growing in the system.

Spectra first developed the device roughly a year and a half ago, providing them to selected boat owners on a test basis. According to Carter, a large yacht in Florida that runs A/C equipment on nearly a 24/7 basis and that had experienced considerable problems with fouling, was fitted with the units. “This boat had such a problem that they would replace their hoses every two to three weeks and acid wash two times a year,” Carter said. Since the Bio-Guard was fitted they have reportedly not had to replace any hoses.

According to Spectra, barnacles and marine growth are even inhibited from growing upstream of the device, which is typically mounted close to the raw water seacock to provide protection to the components downstream. The product has been available for purchase for the last six to eight months.

The Bio-Guard unit is a passive device, which means it requires no electrical current to do its job. Because it is chemically interacting with the water, the Bio-Guard metal doesn’t last indefinitely. The inner tube, which acts as a sacrificial anode and gives up ions, eventually becomes sufficiently depleted for pin holes to form in the tube. The holes leak water into the outer plastic tube which indicate to the boat owner it is time for the inner tube to be replaced. The unit is an ingenious approach to the problem of pipe and hose fouling.

In additon to passive systems like Spectra’s Bio-Guard, there are active pipe antifouling systems generally used on larger boats. One example of this type of system is from a British company called Cathelco ( It has a unit for yachts from 20 to 70 feet in length that consists of a control box that can be powered with either 12 to 2 volt DC or 110 volt AC. The control box is wired to an anode that is placed in the intake strainer or seawater inlet. A current is impressed onto the copper anode and it inonizes the water to prevent marine growth.

Passive or acive, both these approaches are designed to help boat owners fight the battle of the bio foulers.

By Ocean Navigator