Sailboats are, by their very nature, floating. They are designed to float level and flat by their designer and equipment is placed in the yacht in such a manner that the weights are balanced around the boat to keep its trim level. Too much weight on one side, and the yacht will list toward that side. A slight list of only a few degrees is grossly apparent when you see the mast leaning over towards that side.
Keeping the weight balanced as you load up your cruising yacht with everything you think you might need on your voyages can be tricky. Tools, pots and pans, and canned foods, all add considerable weight to the yacht and must be stowed in a weight conscious manner. If you load everything you own on the port side, your yacht will list significantly.
Sometimes, this means stowing things in the "wrong room". I have met cruisers who keep all their cooking ware in the V berth because the stern was weight down too much by the dinghy in the davits. Every time they wanted to cook a meal, the cook would have to carefully consider what she needed and retrieve it from the forward cabin before she started cooking. This was not a long walk, by any standards, but people on land don't usually think of storing the pots and pans that are used in the kitchen in the bedroom.
While these solid items are easy to stow weight consciously, another important item on a yacht can prove to be a bit more challenging to visualize: Water.
Water weighs approximately 8 pounds per gallon, meaning that if you carry 100 gallons somewhere, you should rather think of it as 800 pounds somewhere!
When your water supply is divided up into various tanks located around the yacht, it is important to consider where the tank is before you start to draw from it. In our case, we have 8 water tanks spread throughout the yacht, 4 on the starboard side and 4 on the port side. Collectively, these tanks hold 160 gallons, or 1,280 pounds.
We were tied up in a marina one day and decided to take advantage of the unlimited water we had access to and chose to flush out our water tanks. The last place we filled up had some unpleasant tasting water, but it was all that was available and we were forced to fill up with it. In an attempt to rid ourselves of the remainder of this water, I began draining the water tanks to then refill them.
As a meticulous person, I naturally began at tank #1, and worked by way through them in sequential order until I reached tank #8. It wasn't until I began draining tank #5 that I noticed we were heeled over! The list was not too severe, only 3*, but it was still very apparent to us inside the yacht. While Maddie instantly knew why we were listing, it sadly took me a moment to realize what I had done!
Emptying all the port tanks meant that the starboard side of the boat weight an additional 640 pounds! Upon filling everything back up, the list was eliminated and we were once again level, but at that moment, it was rather alarming.
The valuable lesson to be learned is, when using your water supply while cruising, be sure that you draw on tanks from both sides of the yacht. If your tanks are located fore-aft, draw in a way that will not cause trim issues. If your tanks are located arthwartship, draw in a way that will not cause heel issues.
Our typical method for water consumption is to draw on one port tank, and then the analogous starboard tank. This will cause very minor listing issues as we cruise, but not enough to justify any alarm.
As far as using your water tanks as ballast while sailing, this can be tricky. If you are going to be on starboard tack for the next few weeks, you might be inclined to use the water on the port side as it will help level out the yacht as you sail. This might be true for the time being, but should you encounter foul weather and need to tack or jibe, your yacht will now be vastly lopsided and this could enhance the negative effects of the storm on your yacht. For this reason, I would still suggest using the tanks evenly so that in the event of a storm, your yacht will respond normally and predictably.