Mary C wrote:I want to build a boat similar in materials to Rosies but I plan to design it differently I am looking at boat designs a lot before I build I am wondering how to figure the buoyancy and how to figure if I build it will it hold me above the water that is the only reason I haven't built one. I will figure it out even if it is by try and see method. what I want is similar to the mouse boat made with lots foam and more designed as short and thinner at the front but 4 inches of foam on the bottom and hold me and a little electric motor and battery along with my fishing gear. I know nothing about boats so I can think out of the box, without prejudices and all the things that can and can't be done. I can build a fishing boat where I will have what I want and it will be very light and can be used in still waters without hesitation. I can also block out the naysayers, and the ones who just like to stir up the pot so to speak. I can do it but it will be a project when I get back from my Big Out West Trip.
See I told you canvas has been used in earlier boat building. what he said!!!
There was a boat retrieved from the depths and the historian was pointing to the little patches of canvas as it was torn from the wood that it had protected the wood so well that it looked like new.
Mary C.
Every cubic foot will displace about 65 pounds of water.
A 4x10 rectangular flatbottom boat with 8 foot waterline (meaning the front of the boat starts to rise out of the water for the last two feet of length, don't want to calculate that into displacement because it isn't displacing).
32 square feet in water contact..... now add the 3rd dem, height. If the sides are 18 inches, let's assume you don't want them sinking more than 6 inches down into the water so you've always got at least 12 inches of freeboard above the water line....
32 square feet times 0.5 feet is 16 cubic feet of water displacement.
16 times 7.5 gallons of water in a cubic foot, times 8.6 pounds per gallon = 1032 pounds. To determine capacity, subtract the weight of the boat itself. I can't imagine such a structure weighing more than 200 pounds, so you would be good to with 800 pounds of people, battery, cooler full of ice and beverages, etc.
Flatbottoms are not only easy to build, they displace alot more water per square foot of deck space. The drawback is they are innefficient for power boats with higher horsepower and very rough riding through waves. For protected waters at low speeds, you can't beat a flatbottom design for ease of build and functionality/comfort. Also extremely stable to move around in.
The one thing to keep in mind is that the boat will take 10x more abuse out of the water than in the water. Make it strong enough to fall off the trailer and roll down a hill.
EDIT for one more tip...
Notice Josey put her battery up front.... this is smart with such a light weight boat.... the lighter the boat, the more attention has to be paid to distributing weight evenly. You don't want to put yourself and a batter in the back, catch a wave and a gust of wind and get flipped over, head over tail, battery going into the water and shocking up every fish within a half acre... which would also be illegal in most jurisdictions....
OK.... one more tip... in GA, if you boat is under 16 feet and it's not powered with a gas motor, you can classify it as a canoe and you don't have to register (pay tax) it.