From the Bottom
By Tom Neale, 10/20/2006
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Tom free diving cleaning bottom of Chez Nous
It’s hard to describe what it’s like, looking up at your boat in the water. It always seems huge, whether it’s a small boat or a big boat. And it seems so very different from what you think of your boat. You normally think of the deck and cabin and all the stuff inside it. The motor that roars. The sails that clatter. The stereo or TV that intrude into a night at anchor.
From underneath, it’s all quiet. And it seems solid, even though you can see it moving. If there are waves, they splash around the hull making flashes of light. The boat seems like a living island.
I spend a lot of time down there looking up. It’s my nature I guess. But I also like being underwater and I like to not take for granted that bottom that’s keeping me afloat. So I like to go down there for regular maintenance. And the really good part of that is that it saves me haulout fees. I use Interlux Ultra which is, in my opinion, an excellent paint. With periodic diving, I get three years between haulouts.
Usually I go down free diving with mask, snorkel and fins. I do what I can on a lungful, come back up for a gulp of air, and go down and do some more. I’ve even changed props doing that. But if it’s cold or if I have complex jobs or if I want to get the diving over faster, I use my Brownie’s Third Lung Hookah. I have scuba tanks and a compressor, but I prefer the Third Lung because it’s less hassle, there’s less “stuff” hanging on you to get in the way or get snagged when you’re down there, and you don’t need to refill tanks. A Brownie’s Third Lung can be powered by a gas engine (so you can take it to remote areas for fun diving) or electric, which is what I have because of its simplicity. It’ll pay for itself very quickly if you use it for bottom maintenance.
There are some special tools that help when you go down. For example, I use a wide blade paint scraper to clean the prop and strut. Usually I use this to clean the entire hull if there’s a lot of mud and scum on it during the third year after my most recent haulout. I just scrape off that stuff and, if there are any barnacles, they come off with it.
I use a carrot peeler to clean out the inside of smaller through-hull holes, such as those for the air conditioning and refrigerator discharge. I use an old kitchen knife to clean out larger holes. The key here is to be very careful to not cut the hose which is up beyond the through-hull fitting. I hang a heavy duty plastic bucket with small holes in the bottom (you can make these with an ice pick) over the side to hold tools and parts. Several collar zincs in the bottom serve as weights to keep it upright.
Unbolting old shaft zincs is easy. Usually I just knock them off (or most of them) with a hammer. Bolting new ones on is more of a trick because it’s so easy to drop the little bolt or nut. Doing work like this over white sand in shallow water in the Bahamas isn’t too bad because you can often find what you drop. Doing it in murky water over muddy or grassy bottom is a different matter. This is another way in which my Third Lung helps. It’s much easier to do small work like this when you can just take your time and hang there, rather than rushing up and down to gulp air as you work. I always have handy several spare single allen wrenches that fit the bolts to replace the ones I drop, and I always save the bolts and nuts from old zincs and keep those handy for the same reason.
One of the hardest things to do is clean the back of the propeller blades on my bow thruster. (Mine is a “Side Power” from IMTRA and has two blades, which, in my opinion, are more effective than one.) But if barnacles get inside the tunnel or on the blades on any brand of thruster they can cut down on the water flow considerably. If you go down frequently enough you can keep the blades clean with gloved fingers. But if you let a big barnacle grow up on the back side of the blade, you’ll probably need a curved tool, such as a miniature crowbar or bent soup spoon to reach behind the blades to get the critter. Needless to say, all sources of power to the thruster should be disconnected before you get anywhere near them, as is the case for the engine and anything else that could hurt you.
There are special issues that may not be readily apparent when you dive to work on your bottom. One is the exhaust hose. If it’s partially underwater, barnacles can grow up inside it. Often boatyards fail to clean this out when they haul and paint. Check this out regularly and scrape out any barnacles. If you don’t, they can layer and actually cause a partial obstruction, possibly resulting in back pressure in the exhaust, which may impair engine performance.
Tom with Brownie Third Lung
Another example of unsuspected issues is the question of what’s going on behind your clam shell or similar strainers covering your engine raw water intake, air conditioning intake, and others. All you can see is the outside of the strainer. I take a good underwater light down with me and check up inside the exterior strainers, to be sure there’s nothing growing inside. For some reason that I don’t understand, I’ve noticed that usually very little grows between the strainers and the hull or through-hulls. If there’s much in there you’ll need to remove it and this can be difficult. Depending on your type of fitting, an ice pick or table knife may work to clean the small holes. If it leaves large barnacle shells that may be sucked up, be sure to check out and clean your inside raw water strainers (which should be done periodically anyway).
Diving your bottom can be fun, good exercise, increase your boat’s safety margins, and save you a lot of money. It can also be very dangerous if you aren’t physically up to it and don’t have good equipment, training and skills. But it makes you appreciate even more what your boat can—and can’t—do for you.
Copyright 2004-2008 Tom Neale