Weight Distribution in Light Displacement Yachts

Light displacement yachts are much more sensitive to weight distribution, as any portion of weight in the hull represents a greater percent of the total displacement of the hull. This means that a light displacement yacht will alter its trim in the water faster than a heavy displacement hull because the same mass represents a greater amount of the total displacement.

Boats in their most basic sense are fancy buckets. As you fill the bucket, the bucket becomes heavier and displaces more water to remain floating. A lighter bucket would be analogous to a light displacement yacht, while a heavier bucket would be analogous to a heavy displacement yacht. If you have 90 pounds in the bucket and you add 10 pounds more, the bucket now weights 100 pounds and that last weight accounts for 10% of the total displacement of the yacht. If you too that same 10 pound weight and added it to a 990 pound bucket, the heavy bucket would now weight 1,000 pounds and the last weight would only account for 1% of the total displacement of the yacht.

The positioning of this weight is much more critical in the light bucket, as the weight accounts for 10% of the total displacement. If it were set far to one side of the bucket, the whole thing would tip in the water! In the case of the heavy bucket, where the weight only accounts for 1% of the total displacement, the positioning of the weight is much less critical. The weight can be located pretty much anywhere in the bucket and it won't shift the bucket very much in the water because it is such an insignificant part of the entire mass.

This catamaran has too much weight aft, which has resulted in the entire yacht being tipped back! The sterns are squatted into the water while the bows are completely clear of the water, you can even see light between the bow and the water.

This may seem harmless, but it could have drastic effects on the safety and performance of the yacht. As the sterns squat, any through hulls that are supposed to be high above the waterline are now closer to the waters surface. Many yachts sink in the winter when snow accumulates on the deck and pushes the boat a few inches into the water. Through hulls that are leaking and located above the waterline are now submerged and water begins to flow into the hull, sinking the boat in the slip.

The other issue is the rudders are now located deeper than you thought, and if you are passing through some shallow water, they may hit bottom and be damaged. 

Lastly, squatting the stern will tip the mast aft and increase the effects of weather helm. This will significantly degrade performance as the boat fights to turn into the wind instead of gliding along the pressure difference between the air and water.

It is very important to maintain proper weight distribution and trim of your yacht, especially if you have a light displacement boat.