A sometimes overlooked boat improvement is upgrading your boat's antifouling bottom paint. In this case - applying Interlux VC-17 bottom paint. In this discussion, I will show why I like VC-17, as well as how I apply it.
VC-17 is known throught the Great Lakes as probably the premium bottom paint - at least with most sailboaters, but and a few power boaters are aware of its benefits as well. If there is a down-side to VC-17, its that it is known as primarily a fresh water paint, although Interlux states it can be used in brackish water as well (water somewhere between fresh water and salt water).
The fact is - VC-17 is a paint in a class by itself. It is a thin-film paint, and you can apply paint for dozens of years without the need to remove old paint buildup (as with hard epoxies). Secondly, the paint is smooth, and to hance speed, and it also has what Interlux calls a "fluoro microadditive" in it (what I call Teflon), and is probably the "fastest" bottom paint available, hence its popularity with sailboaters. Third, the paint seems to be particularly effective with algae, which is not always the case with other bottom paints. And lastly, it probably is the easiest paint to apply seasonally, as no seasonal bottom prep is required - other than a clean hull.
Bottom preparation is a must. The first issue is that VC-17 is generally not compatible with any other kind of bottom paint, so if you are switching from a hard epoxy or ablative paint, you are going to have to remove it. So the best time to make the decision to use VC-17 is on an unpainted boat. Also, the recommended practice is to use an intermediate coat between VC-17 and the fiberglass bottom. At one time, a companion product made by Interlux, VC-Tar, was the recommendation. However, it has become popular of late to use Interlux Interprotect 2000 epoxy barrier coat. Regardless of which one you use, I highly recommend using an intermediate layer as it will not only help VC-17 stick, but it will also offer some blistering protection.
Interlux does state that you can use VC-17 directly over fiberglass, and you can, but its my experience that it will not adhere as well. Here is an example; My boat has VC-Tar under the VC-17. A few years ago, I relocated a sensor on the transom, which meant sealing a couple of screw holes. So I filled the holes in with epoxy, and sanded the epoxy down to the hull. When doing this, I removed a small amount of bottom paint, with it's underlying VC-Tar, down to the gel coat. Since this was a small patch; approx 4 sq. in. I didn't bother with the purchase of a $50 can of VC-Tar, so I simply painted over the gel coat with VC-17.
The result is that the VC-17 works over raw gel coat, but not as well as the VC-17 over VC-Tar. If I power wash the boat bottom, I have to be careful in the patched area as I can literally blow the VC-17 off that is over the raw gel coat.
So, bottom prep on a previously unpainted boat would consist of prepping the gel coat (cleaning and sanding), application of several layers of VC-Tar or Introprotect 2000, then finally 2 or more coats of VC-17.
Since there are several choices for bottom preparation, I'll not discuss that further. The remainder of this article concerns the seasonal application of VC-17, as this is one of the reasons you would want to switch. VC-17 (actually VC-17m with Biolux) comes in 0.75 Quart cans for around $50 per can. You cannot buy it in gallon quantities. I have found that one can will cover about 100 sq ft as a seasonal repaint, per coat (Interlux estimates 340 sq ft per gallon, so its at least in the ballpark). Interlux recommends 2 to 3 coats, but I have found that a single annual coat, especially boating in Michigan where the season only lasts 6 months, is adequate. Besides, once you apply a coat a year, there will likely be some residual paint from the prevous season. You can test this with VC-17 by using a Scotch-brite pad on old paint on the hull. If you see bright copper under the oxidized layer, the paint is still in good condition.
Wet paint evaporates quickly. In 70 deg weather, the paint will dry in seconds, meaning it will also dry in the pan as well. One popular trick many boaters use is to mix the paint, then put the paint in a 2 Liter pop bottle. Using the pop bottle means you can keep the paint from evaporating until you need it, as you only need to pour as much as you need in the pan. Typically, we pour just enough paint into the pan to wet the roller. This becomes a two person operation. I paint, and my wife pours paint into the pan. Also by using a pop bottle, you can easily keep the paint shaken.
Fortunately, the paint won't eat through the pop bottle, and foam rollers work well. I am not sure if the same holds true for the thinner, so avoid using 100% thinner on those items.
Mixing the paint. To keep the mess down (as well as keeping paint off our car), I pre-mix the paint at home. The paint is a 2 part paint, with a bag of dry copper stored under that red cap. I mix the paint by inserting a funnel into the pop bottle, then empty the contents of the copper powder bag into the funnel. Do not do this where there is wind present, as it will blow the powder all over (including your car, if you are mixing the paint at the marina). Secondly, if you get powder on anything, do not attempt to wipe it off with a cloth, as the powder will be embedded into whatever it touched. Instead, use a bit of thinner and a cloth to remove the powder.
I have to restate - mixing the paint can be a real mess, so mix the paint in a controlled enviroment out of the wind, like your garage. If you attempt to mix the paint in the trunk of your car or bed of your pickup, you'll be wiping copper off your vehicle for some time to come (experience talking here).
After the copper bag goes into the bottle, pour the liquid from the can into the bottle, cap it off, then shake it up. Thats all there is to mixing the paint. Interlux tech support has told me to use mixed VC-17 within 2 weeks, so I would try to stay within that timeframe. I like to use a different pop bottle for each can of paint, so for me, that means 3 bottles of paint, and I am headed to the marina.
When you apply paint, do it after you have cleaned, washed, and waxed the boat, as well as using any "Lime-Away" type products to remove last season's water stains on the hull. While this is not absolutely necessary, the Lime products will tend to etch the paint, so you might as well avoid that.
When you apply the paint, it goes on a bright copper color. After launching, the color will slowly change to a dark brown/black (original), red, or blue, depending on the color of paint you bought. This typically takes a couple of weeks. I almost kind of wished the paint would stay the copper color, as it really does look pretty cool.
Painting the boat simply consists of using blue masking tape to tape off the boot line, then painting the bottom. There is no need to sand the previous layer. All you need is a clean hull. Its simply incredible how fast the paint goes on, and I often use a chair with rollers to paint along the bottom. I can literally roll the paint on as I wheel the chair along the boat - it goes on that fast. Having a power boat, my boat has a lot of hard chines and angles, which I typically cut in with a foam brush, then smooth out with a small roller. Once that is done, I use the roller and roll on the main areas. Sailboats that have a round bottom and no hard angles is even quicker.
I like to use a 3" foam roller for applying the paint. I buy rollers sold by West Systems, intended for applying epoxy. I buy 7" rollers, then cut then into two 3" long rollers on my band saw. This saves about 75% over buying 3" rollers, and with that amount of savings, I just throw the rollers away rather than attempting to clean them. Using a 3" roller is just about right for getting in and around all of the hard angles of the hull, but becomes a bit tedious for the large acreage of the bottom. I sometimes switch out to a 6" foam roller that you can buy at the big box home improvement stores. The primary advantage of switching to those rollers is the handle is a bit longer, which gives me a better reach. Even then, I have to use an automotive creeper to get under the hull. I would avoid using the 9" nap rollers typically used for latex paint. They soak up a lot of expensive paint; you'll end up using up half a can of paint to soak the roller. And they don't seem to lay the paint down very well.
Even though the paint goes on without a lot of dripping, use gloves and old clothing. If you are painting on a windy day, be sure to hang on to the paint pan, as it is usually mostly empty (you only pour in enough paint to immediately use), and any gust of wind will toss the paint pan. I remember one time, a gust of wind picked up my pan, flipped it a couple of times, and the paint dried so fast that none of it spilled out. To be sure, there was maybe only one ounce of paint in the pan at the time, but this enforces the notion that the paint dries fast.
It should go without saying that its best to paint in a well ventilated area, preferably outdoors. You may wish to use a resperator, but I have not needed one. But you should consult the Interlux website for information on enviromental and health concerns.
It takes me about 3 hours to paint my boat's 300 sqft. bottom, with most of that time painting around the hard angles and chines of the bottom, and trying to paint laying flat on my back on a creeper. If I painted a sailboat of the same size, with round curves and standing up, it could be one in probably an hour. Still, its less time than painting with any other paint choice.
Cleanup is a breeze; take your gloves off, remove the blue tape from the boat, throw away the pop bottles, a couple of foam brushes and rollers, and you are about done. Depending on the temperature, you can launch literally within minutes of painting. If you have any paint left over, leave it in the pop bottle. When your boat is launched, ask the marina if you can have a few minutes to touch up the areas you could not get to (under the jack stands, etc). The paint will dry so fast, that it won't really delay the launching.
In summary, if you have a Great Lakes boat, or boat exclusively in fresh water, you should consider giving VC-17 a try. Other than the initial preparation, the annual cost of maintaining the bottom is perhaps less than with convential bottom paints. I can guarantee that once you have used it, you'll never go back to the other paints.
Interlux Interprotect 2000
Interlux V172 thinner
West System rollers