: Or does it exclude the kayak weight. What happens if you violate it?
: Hows this nukber arrived at?

: Thanks

: Pete

Generally, payload would be the amount you could safely carry inside the boat.

The toatal weight of the boat and payload would be the displacement. This is the amount of water, measured in weight (pounds or kilograms) or, sometimes, volume (gallons or liters) which is displaced by the boat.

The heavier the boat is loaded the deeper the boat sinks into the water, and the greater the amount of water displaced.

If you put too much weight into a boat (let's say you are adding blocks of concrete) eventually the boat will sink so low in the water that the top edge of the boat goes below the surface of the water. At that point water rushes in, filling the boat with water--in addition to the existing contents. Then the boat sinks to the bottom.

Some boats have built in flotation, and if they fill with water (this is called capsizing) they still stay afloat. Usually this built in flotation is rather modest, and if the boat is heeavily loaded, the boat will be heavier than the built in flotation can offset.

The maximum payload is calculated to allow you keep the sides of the boat high enough above the surface of the water so that mild waves do not spalsh into the boat. In extreme weather (such as a hurricane) the estimated payload is not accurate. In extremely calm conditions you can exceed the listed payload, but if you do, you have to consider what you will do if the weather changes. Will you jettison excess weight? If so, what do you toss out first. That leads to the question: If you can toss it out, then why did you pack that in the first place?

Some boats are designed so that if they turn onto their sides they will come upright again by themselves. The payload for these boats is calculated to allow for this self-righting feature. If you exceed the payload, they will not come upright without help.

Most boats are designed based on a given waterline depth or draft. When the boat's weight is added to the designed weight of the contents, the total weight will displace enough water so that the boat floats at the designed waterline. If more weight is added, the actual water line will rise on the sides of the hull as the boat's depth in the water (draft) increases. Some designers will list the amount of additonal weight you can carry for each additional inch of draft.

The amount of the side of the hull which is above the water is called the freeboard. For a canoe, generally, the safe amount of freeboard is considered to be 6 inches.

Here is an example: Assume I have a canoe with sides which are 12 inches high. It is designed to displace 200 pounds when the draft is 4 inches. (this is a 4 inch waterline, and I have 8 inches of freeboard) ) The boat weighs 45 pounds, so it was designed around a payload of 155 pounds. For every 75 pounds I add to the canoe it will sink an inch into the water. My safe payload will be 305 pounds. With that much load, the total displacement will be 350 pounds (payload plus the boat), the draft will be 6 inches ( original draft of 4 inches plus the 2 inches I get from adding 150 pounds) and the freeboard will be 6 inches (sides are 12 inches high, and 6 inches is now underwater. that leaves 6 inches above water).

Actually, I have a canoe like that, and with two adults and camping gear it carries about 400 pounds. That exceeds the maximum designed payload by 95 pounds, and increases the draft to about 7 1/2 inches, leaving only 4 1/2 inches of freeboard. I accept this overload because I paddle in mild conditions, and a lot of the gear weight is food. As the trip progresses this is consumed and the boat is lighter. Also, I pack a lot of my gear in float bags, which I tie to the canoe's thwarts. Should conditions suddenly get bad, I can toss some of the gear out of the boat, and let it float alongside. It will stay dry inside the floatbags, and the canoe will float higher, but my speed will be reduced as I'll be towing the bags. If I build another boat of this design I'm going to make the sides 13 inches high.

Hope this helps

PGJ