Usually I can do a good 2/3 of the hull via a long handled scrub brush. Especially when I'm in a
dinghy. Sometimes it helps to lash a small
fender to the backside of the brush, so that it's buoyancy presses the brush up against the hull, when the brush is underneath of the
boat.
Also, it helps to have a few strategically placed lines around the boat's toerail for you to grasp with one hand, to help you remain on station while scrubbing. Some times a "plumbers helper" (toilet plunger) is useful for holding onto the hull as well. And there are some of these which are made specifically for that/for divers, which have 2 suction cups about 1' apart, with a handle running between them.
What I'm saying is that when working from the dink, or while in the
water, you need a reliable way to hold onto the
boat, in order to be able to scrub effectively.
And when it comes to paint, it pays to have a good strategy in terms of what you'll apply, & in what order, prior to heading into the yard to add a few coats of antifouling. Such as first putting on several coats of a hard antifouling, in say, black. And then ovetop of it, put on several coats of something which wears away a bit more easily, perhaps in red.
That way, with the different colors per layer, you get lots of warning as to how much antifouling you have left. And can (loosely) schedule your next
haul out for repainting. Plus it gives you a bit of time to watch for sales/good deals on paint. So that you're not
buying it at the last minute, & having to pay full retail for it.
PS: Of course when you're painting, it's just common sense to add a couple of extra coats near the waterline, as well as on the
keel,
rudder, & bow. Particularly their leading edges. Since those are the areas which will get worn down the most. Both by
water flowing over the boat, & via scrubbing your boat's bottom.