Posted by Darrell Nicholson at 12:01PM - Comments: (14)
A cheap, effective antifouling paint for a propeller is as rare as a good pun. The coating must not only ward off all marine growth, it must present a smooth slick surface that can stand up to the constant water friction when the boat is under power. And in the case of a folding prop, the coating must also adhere in nooks and crannies and, in some cases, even withstand metal-to-metal contact. These demands are well beyond the reach of any run-of-the-mill marine coating. Thus, we embarked on our search for—wait for it—a prop(er) paint.
Yes, you can paint a bronze propeller with conventional, copper-based hull paint, but it won’t do much good, since the more noble metals in the bronze prop will eventually waste away the copper biocide. Don’t even think about painting an aluminum outdrives or prop with a copper paint, or the reverse will occur—the more noble copper will attack the outdrive alloys. Even with the right preparation, regular bottom paint tends to wear quickly on a prop due to increased water friction.
Practical Sailor’s search for longer lasting prop paints has led us down many rabbit holes, we've experimented with several different prop paints with varying degrees of success, although none of the results so far have been dazzling. Some of our testers have had better success with dedicated “slick” prop paints such as PropSpeed. In our testing, however, mostly in Chesapeake Bay, no prop paint had lived up to our increasingly faint hope that the paint repel growth as effectively as our hull paint.
For previous articles on this topic check out our report on the dedicated propeller paint PropSpeed (see PS February 2014 online), and a more detailed report on prop paints in general (see PS July 2010 online).
We also looked at Mussel Buster (see PS October 2011 online), a baked-on powder coating that, like PropSpeed, relies on its slick, hard coating (as opposed to biocide) to prevent barnacles from adhering. Other products our testers tried include Feldtens Nano propeller spray treatment, an inexpensive product that appeared no more effective than others. Like other prop paints we have tested, both the Prop One (formerly Prop Gold) and Velux Plus showed signs of failure after less than six months of use. The Velox Plus (primed, left, and painted, middle) began to flake off the prop (right), but it was still fighting barnacles.
Lately, we have advised sailors to take one of two options:
Option 1: Blast the prop to bare metal, prime with Interlux Interprotect or a similar barrier-coat epoxy, and then paint with a conventional hard bottom paint. (Although the epoxy theoretically prevents galvanic reaction between dissimilar metals, copper-based paints are to be avoided.) The trick with using a conventional bottom paint (sprays like Interlux Trilux 33 or Pettit Alumaspray are easier to apply) is getting it to adhere, thus the epoxy primer. Although there are options other than epoxy for priming a prop, because of health concerns, these etching primers are not considered do-it-yourself friendly (although they were used that way for years).
Option 2: Use Pettit Barnacle Barrier, a spray zinc product that has given us a year’s worth of protection in the Chesapeake. Because the prime-and-paint routine hasn’t delivered dividends commensurate with our effort, we’ve found that applying multiple coats of the relatively inexpensive Pettit Barnacle Barrier is the most practical option for boats that haul out annually. (Readers have also reported unsatisfactory performance with Barnacle Barrier.)
Option 3: Take your pick of the dedicated "slick" prop coatings we've tested. Results will vary (as our tests have shown) but all should provide longer lasting protection than either of the above options if they are applied as directed. However, the added cost might not be worth it to the boater who hauls and paints each year.
If you'd had good (or bad) results with any of these options--or something else--we'd like to hear about your experience. Be sure to include the boat's type, name, home port, and location and pattern of use during the period the paint was in use (i.e. sailed weekly, daily, monthly in San Francisco Bay. . . ). You can respond by email at email@example.com. Comments are also appreciated.