May 3, 2016

The propeller's worst friend

IN THE YEARS I have been writing about sailing, I have come across many suggestions for preventing barnacles from attaching themselves to propellers. One friend of mine swore by axle grease that he stole from the marine railway when his boat was hauled out for antifouling. He would smear thick gobs of it on his prop just before launch time.

Other people advise you to use carnauba wax, or zinc paint. I myself have tried two coats of copper antifouling paint. It worked for a while, but eventually wore off. I’m told the backroom boys are working on a way to apply a Teflon coating to a bronze propeller, so barnacles simply won’t be able to stick to it. But so far none of these remedies has worked satisfactorily in all waters. The very action of a propeller working in water quickly abrades whatever coating you apply.

There is one trick that really does work, and that is to tie a black plastic bag around the prop each time you reach your home mooring or slip. Some fanatical racers do that, but I’m sure you can see the problems, not the least of which is to remember to remove the bag before you set off again.

There is a theory that barnacles will not touch a prop that isn’t protected by a sacrificial zinc. Apparently the tiny electric currents generated in the bronze of an unprotected propeller are sufficient to deter them, and convince them to move to the boat next door whose propeller is nice and docile, thanks to its sacrificial zinc.

No doubt you can spot the problem, here, though. The electric currents that keep the barnacles away are also slowly eating the propeller away. Maybe if you can afford a new propeller every couple of years you can live a lovely life free of worry about barnacles. If not, you, like most, will just have to put up with an increasing number of barnacle squatters and a corresponding decrease in motoring speed as time goes by.

You can, of course, dive and scrape off the barnacles from time to time if you sail in warm waters. But if you live in the frigid zone of Puget Sound like me, then grinding your teeth and swearing in a sailorly fashion seems to be all there is to do about it until the next haulout. You might find, though, that the occasional beer or Dark ’n Stormy helps.

Today’s Thought
Though you drive away nature with a pitchfork, she always returns.
— Horace, Epistles, 1, x

“Why has your dog got such a flat nose?”
“He keeps chasing parked cars.”

(Drop by every Monday, Wednesday, Friday for another  Mainly about Boats column.)


Mike Benson said...

I have heard that product "never wet" hydrophobic paint can do well, have not tried. I'm hauling my Westsail 32 on 5/13, and I can try the same on my Bristol 27's long shaft outboard that lives in a well. I will be pleased if it delivers a good result. Even if it does work, the question remains as to how long it will remain effective.

Unknown said...

Can't remember where, now (The Boat Galley?), but I read that egg whites help.

Jarm said...

Has no one copper plated a bronze prop? With sacrificial zincs in place, you should be able to deter corrosion, but barnacles won't attach to a copper lined hull so why not a copper plated prop?

John Vigor said...

Jarm, a copper-plated prop sounds like a good idea in principle, but I have this funny feeling that if it worked, everybody would be doing it already. I have to observe that the material in bronze props is mainly copper and tin to start with, both of which are deterrents to barnacles. Both when they're used together and spun around 1,500 times a minute, barnacles seem to love them. Strange things happen at sea.

John V.