bigwave said:
Make sure you have a good bottom paint, with a high copper content. This will help slow down the barnical and oysters on the bottom. Once water gets so cold the growth will slow down or stop......come spring they will grow like crazy. Here where I live in central Florida you can get some rapid growth in just a week or so. It is a real PITA scrapping them off.
+1, except for one thing.
It should be noted that the ONLY type of anti-fouling paint suitable for use on aluminum boats is COPPER THIOCYANATE BASED PAINT, NOT CUPROUS OXIDE! If you paint an aluminum boat with cuprous oxide paint, it will destroy the hull. Interlux Trilux 33, or the equivalent must be used. It is also preferable to initially put down 2 layers of Interprotect Primer, or some other 2-part epoxy primer similar to this, and then the Trilux 33.
Reason being, the anti fouling paint is ablative, meaning it wears down with use. If you don't have primer under this, then, any exposed areas are just that, exposed areas of unprotected surface. The Interprotect is a very good primer that is rated for use on all metals above and below the waterline, and will insure that the hull is properly protected.
Additionally, even though there are zinc anodes on your engine, no boat manufacturers provide any galvanic protection, i.e. a zinc anode mounted to the hull. You should install a zinc anode on your boat, and have it connected to the bonding wire of the engine, if one is available. If not, then run a bonding wire between the zinc anode and the negative terminal of the battery. The bonding wire can be made of some stainless wire, such as 1/16" wire rope, or even fishing leader, with ring terminals on each end.
To mount the zinc, you'll need 2 bolts, 6 fender washers, 2 regular nuts, and 2 nylock nuts, all stainless steel. Make sure the bolts are long enough to pass through the thickness of your hull, the thickness of the zinc, and allow for extra thickness for the lock nut, and the nut that will be tightened to the hull, and then also allow for the thickness of a backing plate, which will mount to the outside of the zinc...I'll explain this in a minute.
Drill the 2 holes for the mounting bolts in the transom, below the waterline. The hole pattern should coincide with the mounting holes of your zinc, depending on which one you want to use.
Now, place a fender washer on each bolt, and coat the surfaces with RTV Ultra Black, 5200, or another good sealant, do NOT use regular silicone. Place the bolts through the holes, from the inside of the boat. Then, from the outside, install another fender washer and sealant on the bolts protruding from the hull. Then, screw a nut (regular nut) onto each bolt, and tighten down.
At this point, you should have 2 studs sticking out of the transom. Place the zinc onto these studs. Now, you will need a strip of aluminum about 1.5"-2" wide, by about 1/8" thick, with the same hole pattern as the zinc. This is your backer plate. It is important to use this, because the zinc will first erode around the mount holes. Once it erodes large enough, it will fall off, leaving the boat with no protection. The purpose of the backer plate is to prevent this.
Once you have installed the zinc and backer plate, place the last set of fender washers onto the bolts, and then the ring terminal for the bonding wire goes onto one of the bolts. Lastly, install the lock nuts.
When installed in this manner, you can easily change the zinc, without having to remove bolts and re-seal everything.
For a 16 foot johnboat, you'll need about 32 square inches of galvanic protection, or a zinc about 4x8"
Be sure to regularly inspect your zinc, keep a good coat of paint on the boat, keep a functioning bilge pump (or two) with float switches (but never rely on them, always check your boat after a heavy rain) and haul out at least 3-4 times a year, only if for a day or two, just to give it a good freshwater rinse, flush the engine, inspect zincs, change lower unit lube, fog the engine with some Sea Foam spray, and attend to any other details........... and you will have no problems.
This comes from someone who has kept boats in saltwater for the last 30 years, and has the experience of the right way and the wrong way to do it. Thus, therefore, all the recommendations for the correct bottom paint and galvanic protection.
I've seen what happens when this SOP is NOT followed, and it ain't a pretty sight! Holes in the boat large enough to put your hand through. And that's not an exaggeration.
