How do you find the water line on a boat without putting it in the water?

Picture in your mind... an empty cardboard box the exact size of 1 cubic foot. Good, now remember this - fresh water weighs 62 pounds a cubic ft. Got it? That means 1 cubic foot will displace 62 pounds of water...

Therefore, if you put 31 lbs (half the weight of the water it will displace) in the box, and set the box in the water... it will float 1/2 in the water, and 1/2 out of the water...

So, if you are making this boat to float you... and you weigh 124 lbs, you need 2 cubic ft of boat (2 x 62 = 124) just to keep you at water level.... Follow me?

Now, since you need "freeboard" to keep the water from flowing over the top and swamping your boat, you need to add plenty of freeboard.

So, lets make the boat bigger...

If you make a rectangle shape cardboard boat, that is 6 feet long and 2 feet wide - you will have 12 cubic feet (12 x 62 = 744 lbs) So, your boat now will float 744 lbs. Therefore, if you weigh 124 lbs, and all your boat making material weighs another 62 lbs. You have have 744lbs over 186 lbs or 1/4th of your hull will be under the water, and 3/4 will be out of the water... and therefore, your waterline will be 3 inches from the bottom (1/4th of 1 foot or 12 inches = 3 inches... and you will have 9 inches of freeboard (which by the way, it not enough... for you to actually float in this thing, you need at least 2 feet of freeboard.

So, a rectangle box 6 feet long x 2 feet wide x 2' 6" tall would make a good boat...

If you are doing this with a smaller, model boat instead of using 62 lbs a cubic foot, you can use

.0362 per cubic inch.

Good luck,

John

it is not easy but you have to calculate the volume of the boat, the water displaced by the vessel. then you take the chassis weight, and compare the two. as long as the two are pretty close to even, then the boat should sit about half way down.