Friday, 20 May 2016

Things That Work For Us #8 - Ultrasonic Antifouling

Ultrasonic Antifouling - Two Years On, The Results Are Excellent

In May of 2014, we installed a new Ultrasonic Antifouling system, hoping to reduce or eliminate the problems we had been having with barnacle growth on the hull and inside our water inlets.

At the time we reported on the system installation, and covered some of the basics of barnacle breeding, with the help of marine biologist Glen Burns - read that story here.  We also covered a high tech barnacle removal tool - the story is here.

I should explain that we like to sail for at least two years between each haul out, where possible. This saves us quite a lot in boat yard and paint costs. So Crystal Blues was last hauled and painted with anti-fouling paint back in October 2014.

We applied four coats of our favourite antifouling paint, Jotun Sea Force 90, rolling it on over three days. We added a fifth coat to the leading edges of the keel, rudder and skeg, and around the waterline. That paint system is now 19 months old, and we've covered over 9,000 nautical miles since it was rolled on - quite some distance for us.

At this point the biocides in the paint system are just starting to let us down - the slime on the hull needs to be wiped every month, and green seagrass is now starting to grow where sunlight penetrates the water depth.

HOWEVER THERE ARE NO BARNACLES.  NONE.

Back in Cape Town I paid the local divers to clean the hull - the water there was way too cold for my 3mm wetsuit - and they reported that it was in very good condition, finding only three (3!) barnacles.

Here in St. Helena, where the water is a balmy 23 degrees, I dived to clear some fouling on our folding propeller, and found that the hull needed a wipe, but no barnacle scraping at all.

This is a major improvement for us, as previously we fought a constant rear guard action against barnacle growth on the hull and in our sea water intakes. The raw water intake for the refrigeration, aircon and genset systems had been specially problematic, frequently clogging with extensive barnacle growth. Since installing the ultrasonic system we haven't had a single incident of barnacle clogging.

I'm sold - the package is compact, doesn't draw much power (half an amp at 12 volts) and requires absolutely no maintenance. The only thing I have to remember is to turn it off at the DC switchboard before I go diving under the hull - it does generate some audible harmonics underwater that are quite painful when you get close to the transducer location.

Follow this link for details about the system we have installed, which is sold by Ultrasonic Antifouling Ltd in the United Kingdom.

2 comments:

Daria Blackwell said...

Hi Ley,
Have you experienced any change in how wildlife behaves around you? I imagine the ultrasound could affect cetaceans in the vicinity. I wonder if it would draw or repel them?

SV Crystal Blues said...

Hi Daria, there does not seem to be any difference in the observed behaviour of dolphins and fish around the vessel. Coming in to Ascension Island we had dolphins with us for several hours. In Madagascar the whales moved around us in the anchorage several times. I just read an article by Nigel Calder (in Prof. Boat Builder mag) that said it does not effect sea life, except for the slime and barnacle growth, as the audio power drops off dramatically as you move even inches away from the hull....