Okay, lot of information required to answer a simple question!
To repaint the bottom, the boat needs to be hauled out of the water. it should immediately be pressure washed - if you don't, any marine growth will set like concrete.
You then need to prepare the bottom. This normally means sanding, and in some places repainting. Some repairs
may also be needed. One catch is that bottom paint
is incredibly toxic, so you will need a special sander that vacuums all the dust, complete body covering (including head/hair), and quality respirator. Your boatyard can probably advise. How long will this take? How fast can you sand! Say 1-2 full days, could be more if you hit problems.
Then, when the bottom is prepped (and any repair
work done, like that pesky through-hull) you can paint
the bottom. Mask first, then paint
. Again, wear protective clothing. Roll on one or two coats - two coats will last longer, but at $250 a gallon for typical bottom paint
, you may just put on one coat! Say one day per coat, depending on temperature. (Don't paint in the rain, or in freezing conditions)
Now ask the boatyard pretty please to lift up your boat and then go to lunch. Why? So you can paint those parts you could not reach while it was on blocks!
After lunch - splashdown! you're done!
(kinda a brief summary)