After a week, soft growth will form a thin layer of slime that will drastically reduce your speed and efficiency through the water. Bottom paint can help retard the speed at which this growth occurs, but it will still happen and it will still slow you down.
Modern day commercially acceptable ways to clean your hull include short hauls, where you power wash the bottom, and hiring a diver who scrapes your hull in the water.
Both of these options are rather expensive after a while, which has led people in high tidal ranges to explore alternative options. One such favorite is to take the boat into shallow water with a leg tied to it. As the tide goes out, the leg keeps your boat from tipping over as it rests on its keel and rudder. With the tide out, you are able to scrape and scrub the hull clean. I have even seen people paint their hull before the tide comes back in!
In Maryland, our tide is much less drastic with a range of 1 to 3 feet. This means that my 6 foot keel will not be coming out of the water by natural means any time soon.
Since the cost of short hauls adds up over time, I have experimented with other methods to clean my hull as it floats in the water.
My favorite, and most reliable method is to use a 12 inch wide wallpaper scraper to clean the bottom. It covers a lot of bottom on each scrape makes quick work of the job. The problem is the water in the bay is extremely murkyat times and I can't see where I am or where the surface is. This makes free diving under the hull less than desirable.
I then tried lashing the wallpaper scraper to a long boat hook. This worked well for the sides of the keel and hull, but was impossible to clean the turn off the bilge! No matter how I positioned the pole, I simply could not reach into that concavity. I also feared dropping the boat hook or having the scraper slip off the end of the pole. They were well tied, but they were not permanently connected.
This led to my latest and favorite method, the hoe. The hoe has a blunt blade that turns ninety degrees with the relation to handle. This angulation places the blade perpendicular to the hull, letting you scrape the hull and reach the turn of the bilge all from the surface of the water.
From the comfort and dryness of the dinghy, the blade is set against the hull and guided by the top of my foot. I push the hoe as deep as I can and then draw up with force. The up stroke is where the cleaning occurs! I like to start deep and work my way towards the surface, continually cleaning and scraping until I don't see any more muck floating off in the water. At this point, I move a few inches over and begin the process over again.
This may seem time consuming, but it's not that bad. In around 20 minutes, I was able to clean from keel to water line on our 45 foot sailboat (with a 32 foot waterline, we have 13 feet of overhangs).
Later that day, I dove in with a mask and snorkel to clean the keel and rudder. The only differences were I was not dry and I didn't use my feet to guide the hoe. Instead, I would float at the waterline and extend the hoe as far as I could. When I felt the bottom of the keel, I knew I was in position and began cleaning the sides of the keel.
I know I did a poor job on the keel and rudder, mainly due to visibility issues. The water was so murky that visibility was limited to 1 foot. I have no idea how the keel looked before or after the cleaning, but I know some improvement occurred.
The reason I didn't dive under the keel with a wallpaper scraper was I could feel barnacles with the hoe near the bottom of the keel. The last thing I wanted was to puncture myself on an unseen spear of a shell in filthy water. If we were in clear waters of the Caribbean, diving under would be the ideal method of cleaning growth off of the bottom of the keel. Dangers under the hull could be located and avoided as the cleaning process takes place.
The final test came when we set sail the next day. On our sail to this creek with a dirty bottom, we were running with 15kn of wind apparent at times while only moving 4kn. Now that the bottom is "cleaner" we were able to ghost along at 3-4kn in 5-10kn of wind on a run as well. Later in the trip, we were broad reaching at 6.5 knots during stronger winds.
While we had minimal hard growth, the soft growth adds a lot of drag to the hull, slowing it's motion through the water.
Morty certainly approved of the cleaner bottom as it meant we got to our destinations quicker and his walks came sooner!