Stability Vs. Capacity

Joseph Carro, U.S. Coast Guard Boating Safety

Do you know the difference between stability and capacity when it comes to your boat? You should. It can mean the difference between a safe voyage and potential snags.

About Capacity
Determining your boat’s capacity for carrying passengers and cargo is an important step in planning a safe voyage. Overloading a boat can make it difficult to handle, especially in an emergency or bad weather. Overloaded boats also tend to use excessive fuel and are more likely to swamp or capsize.

The “maximum capacity” or “maximum weight” for a recreational boat refers to the weight, including people, gear and the motor, that can be carried safely. The safe load for a boat depends on a number of factors, including hull volume and dimension, the weight of the engine and the outboard motor (if the boat has one), and its method of steering (console or tiller). The number of seats in a boat is not always an indication of the number of people it can carry safely.

All mono-hull boats less than 20 feet in length (except sailboats, canoes, kayaks and inflatable boats) are required by federal regulations to have U.S. Coast Guard Maximum Capacity information permanently displayed in a location clearly visible to the operator. The information is usually provided on a label or a plate and should never be removed, altered or tampered with. Many states have laws that prohibit carrying people and gear in excess of a boat’s stated capacity, or installing an outboard motor that exceeds the maximum rated horsepower.

You should avoid exceeding the maximum weight or capacity at all times. In fact, in rough conditions or poor weather, it’s smart to reduce your load as much as possible, to make the boat easier to maneuver.

Factors in Stability
Stability, or a boat’s ability to maintain equilibrium, is just as important as capacity for boating safety. Loading too much cargo or too many passengers in one part of the boat can affect its stability, even if the total load is within the boat’s maximum capacity. Load dispersion — spacing passengers and cargo evenly throughout the vessel and not placing too much weight forward, aft or on either side of the craft — is always important, but especially so in bad weather or strong currents. The higher a boat’s center of gravity, the more likely it is to capsize. The same can be said for any loading imbalance to port or starboard, fore or aft. Too much weight in any direction can be a problem.

A recent boating accident involved a large recreational boat carrying more than 25 passengers when it capsized and sank, and three passengers drowned. This boat was slightly more than 30 feet in length and was not required to have U.S. Coast Guard Maximum Capacity information displayed. While this accident is being investigated to determine the specific factors involved, it serves as an example to all boaters that care must be taken to properly evaluate all conditions — including the weather, the total number of passengers and their placement — and a boat’s capacity must never be exceeded, no matter how large it is.

Using a motor that exceeds a boat’s horsepower limit — or making excessive modifications to a vessel — can also lead to vessel instability. The Coast Guard has seen numerous incidents where boat owners have modified their vessels by adding shelters constructed of steel tubing and plywood. These shelters can add too much weight and raise a boat’s center of gravity, creating a stability problem. Owners who modify their boats often fail to account for the resulting added weight, and they continue to load their boats as they did prior to the modification.

When determining the right passenger and cargo loads, remember that any modifications can affect your boat’s capacity and stability. Be conservative in making your estimates — it’s best to err on the safe side.

Capacity and Stability Safety Tips
Consider these tips when thinking about how many people to invite on a boating outing, or when planning any alterations to your vessel: – U.S. federal regulations require all mono-hulled recreational boats less than 20 feet in length to display a capacity plate. The plate is a metal placard listing the maximum cargo capacity, the total persons that can be carried on board and the maximum horsepower rating of the outboard motor used on the boat.

– The maximum capacity plate on a vessel is generally found near the operator’s station or the inside transom.

– Personal watercraft operators should consult the Owner’s Manual, and never exceed the manufacturer’s recommended capacity.

– The number of seats in a boat is not an indication of the number of people it can carry safely.

– The number of passengers listed on the capacity plate is based on an estimated weight of 150 pounds per passenger. Many boaters weigh considerably more than that estimate — be sure to calculate actual carrying capacity accordingly, based on actual passenger weight.

– Loading too much cargo or passengers in one part of the boat can affect its stability, even if the load is within the vessel’s maximum capacity.

– Space passengers and cargo evenly throughout the vessel to balance the weight; avoid placing too much weight forward or aft, or on either side of the craft.

– Remember that any modifications to a boat can affect capacity and stability. Be conservative when determining the maximum passenger and cargo loads.

One thought on “Stability Vs. Capacity

  1. The person capacity is generally calculated by (Length x beam)/15. Why do most fiberglass boats’ capacities meet this formula but most aluminum boats get rated for less than this calculation (usually by 2 or 3 people)? Is it the buoyancy difference of aluminum vs. fiberglass?



Your email address will not be published. Required fields are marked *