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, 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. Dont 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 Sailors search for longer lasting prop paints has led us down many rabbit holes, and eventually to the Land Down Under. For the past several years, Practical Sailor tester Jonathan Neeves has been conducting a series of antifouling paint field trials on his 38-foot catamaran based in Sydney, Australia. Some of the work is aimed at supplementing our paint panel tests of hull paints, (see Bottom Paint Checkup, PS March 2016), but the main purpose of the most recent trials has been to evaluate the real-life performance of propeller paints.
Paints for Props and Running Gear
For the past few years, Neeves has been trying to find a paint for props, saildrives, and running gear that matches the life of the antifouling on his hull. The seasonal sailor who hauls and paints every year doesnt need this level of performance, but for a year-round sailor, a good multi-season prop paint can yield big savings.
The selection of paints specifically for propellers is limited. Neeves has tested four different products on his boat: Velox, Prop Speed, PropOne (formerly known as Prop Gold), and Interlux Trilux. In separate trials aboard a monohull based on the Chesapeake, weve tested Prop Speed and Mussel Buster, a professionally applied bake-on coating. The results from these propeller paint tests are averaged in the adjacent table. (Another product, Prop Purr, has since entered the market that we will be testing for the first time this spring.)
In this report, we detail the results of Neeves most recent test-a comparison of Velox and Prop One. Like conventional bottom paint, Velox relies on biocides to fight marine growth. Prop One, like Prop Speed, is characterized as a foul-release coating-sometimes called a fluoropolymeric or silicone paint. It contains polytetrafluoroethylene (Dupont brand Teflon). Prop One depends on its rubbery, slick surface coating surface to prevent barnacles from latching on.
The makers of Prop Speed and Prop One discourage amateur application. They prefer their products by applied by professional applicators. One reason for this is that the coating process requires special care. (Neeves went through a training course in order to become a qualified applicator for Prop One.) If you intend to apply either product yourself, we suggest you work very closely with the manufacturer, and ask specifically about any safety precautions to take when applying and removing the paint.
Applying Velox is more straightforward-prep, prime, and paint. An amateur can handle the job himself, although we recommend calling the maker (or qualified distributor) before painting. The instructions in the U.S., Australia, and Europe vary (and even can be contradictory).
Most props require very little paint. Even if you buy the smallest size kit available, youll have some left over, and you might not be able to re-use it. Weve reused Velox after more than a year, and Prop Speed and Prop Gold have an 18-month shelf life. Again, check with the manufacturer regarding shelf life before you plunk down $200 for more paint than you can ever use.
If you are re-applying Prop Speed or Prop Gold you need to strip off the old coating and get down to bare abraded metal every time you apply a new coating. If you are re-applying Velox, you can lightly sand the old paint using 120- grit sandpaper, re-apply primer where necessary and re-coat with the topcoats.
You can use a stainless steel wire brush on an angle grinder to remove old coating. Other PS testers recommend an 80-grit lap wheel. In either case, be sure to wear eye protection. After grinding, wash well with water and apply the primer coat. Do not touch the bare metal with your fingers, it will leave grease and the primer will lack adhesion. Neeves used latex gloves while cleaning and abrading. Do not use turpentine or other paint cleaners, which can contain oils that inhibit good adhesion.
Prop One also supplies an acid wash to complete the prep work, something that the makers of Velox discourage. After Neeves acid-cleaned the prop, he again lightly abraded it and rinsed well with water. (Prop Speed does not mention an acid-wash prep, although this would seem advisable.)
Folding props require special attention. Neeves three-bladed folding Volvo prop needs to be completely removed to replace the sail drive anode. The prop assembly consists of 16 pieces, plus one saildrive anode, two bolts, three segmented hub anodes, and three Allen bolts. Each blade and hinge pin are marked so that the blades are returned to the exact same spot of the hub. Disassembly and re-assembly is not difficult-but does call for patience.
If this all seems excessive, five or six years ago when Neeves did not pay such close attention, most of the epoxy primer (Interprotect) and paint (Interlux Trilux) he had applied fell off within one week. With another silicone product, the paint peeled off like a plasticglove.
The actual painting with either Velox or Prop One is simple: apply the primer and topcoat following the makers instructions. These products can be professionally sprayed. Neeves used one-inch disposable paint brushes-one for primer and one for topcoat.
Velox suggest one coat of primer and two or three coats of the active topcoat. Prop One suggests two thin primer coats and one topcoat. Both require allowing at least 12 hours for the paint to dry before submerging.
One final word on application: Always remember that prop or shaft anodes must be masked and should not be painted over. Shaft anodes must also be bolted to bare, unpainted, metal, so it is best to completely assemble, mask and paint. Using Loctite to secure the anode bolts affords some piece of mind that the anode won't go anywhere.
In early 2015 we treated both sail drives and one prop with Velox and one prop with Prop One (then called Prop Gold). After about one year, Neeves beached the cat for inspection, and could detect no difference between the products. After a quick wipe-down, the boat went back into the water.
After 21 months, the two products again performed similarly. There were a few more barnacles on the Prop Gold, but they were small and isolated. Both props had soft growth that was easily wiped off. In Neeves view, both products lived up to expectations of 24-month protection, with Velox performing slightly better.
The main difference between the two products is when it comes time to re-apply, especially if you do it yourself. Most of the Velox primer was still intact, so after a powerwash and light sanding, the prop was ready for a new coat. The Prop One, on the other hand would need to be stripped back. For more on prop paints and bottom paint, check out the online version of this article, which contains links to past tests and reports.