Boat Buoyancy

[fbWldcat]

I am wanting to make a boat much like the one seen in this video  http://fw.ky.gov/flatbottomboatvideo.asp

I am wondering how buoyant this would be (if someone could figure up the calculations of the boat, I believe the dimensions are in the video along with the wood-type). The boat will need to support me and a couple of friends which would put us at around 750lb with gear. If the figures are not favoring my situation, what other materials could I use to reduce density but also maintain strength and increase buoyancy?

Thanks to anyone in advance.

[Husky01]

I cant believe I just watched that whole video. ha

But it looks like it would hold a person or two? Not sure I would feel safe with more then that.

[fbWldcat]

Well in the video they say "a few people" which in Kentucky means 3-4.... so... I'm not sure about it. I'd love someone who is good with calculations and formulas to figure this out and how much buoyancy this would have

[bozon]

I asked Archimedes once about this and he said that the buoyancy of an object is the weight of water it can push. In other words, figure out the volume of vessel that will be submerged (the volume of water pushed aside to make room for the boat) and then figure out the weight of water filling such a volume. A good estimate is 1 gram per cm cubed, but sea water is a little heavier than sweat water. This buoyancy includes the weight of the vessel itself, so what is left is how much cargo you can put on the boat.

[Ghosth]

Looks to me to be one full sheet of plywood or 8 x 4 plus one half sheet of ply 4 x 4. For a total of 12 feet long. Sides confirm the length as he mentioned using a 12' long 1x12 for each side. That does not give you a lot of extra displacement for more people, gear.

Fine for 2 people, 3 or 4 would really be pushing it. However there are a couple of options for you.

You could Scale this design up, make it 16 feet long instead of 12 which should add the displacement for at least one other person.

Or you could go looking for another design. There are a load of basic stitch and glue type wooden boat designs out on the net for anyone willing to spend a bit of time looking.

There are also some very good books out there about building basic wooden boats like the one in the video. Some of the best designs I've seen come from Harold Payson.
http://www.instantboats.com/index.html

If your going to risk your life in it, best to spend a few dollars and get a boat that will be designed to handle what you need to handle. 

[fbWldcat]

Can anyone give me an estimation of what a boat like this would carry? I've never looked at wooden boats and have always been looking at Aluminum ones. I will work out that calculation, Bozon.

[MrRiplEy[H]]

Buoyancy and stability are two different things. A boat can capsize way way before it's buoyancy is exceeded.

[grizz441]

Well, water weights 62.4 lbs/ft^3.  Bump up the weight to 1000-1200 lbs (safety factor)

1200 lbs / 62.4 lbs/ft^3 = 19ft^3 REQUIRED of boat, displacing the water underneath it.  I don't know much about boats, but would assuming a submerge depth of a foot and a half be unrealistic?  If that was the case, you would need.  19/1.5 = 12.7 ft^2 min. of boat, Maybe a 5'x3' boat?

[Ghosth]

Let me put it this way, I have a 10' aluminum Jon boat with higher sidewalls than that 8' wooden boat, and the makers plate specify's an 850 lb total load limit. It is similar in width, nicely sliding into a standard pickup truck box.

How many people and how much gear is going to depend on how much they weigh.

But those sidewalls are not very high, and if you over load it a single 6" wave will swamp you.
So start small, go light and stick to smaller waters for starters as you learn.

[fbWldcat]

We don't plan on using it in a lake, just a couple creeks/ streams.

[jimson]

Here is a great resource for plywood stitch and glue boat building. Plans, kits, supplies, anything you need for any kind of boat you can imagine.

Not cheap but everything has been engineered by folks that know what they are doing.

http://bateau.com

[grizz441]

We don't plan on using it in a lake, just a couple creeks/ streams.

Start with the numbers I posted.  Submerge depth is how much of the boat will be underwater and you can figure out how much you want submerged and go from there.  You can figure out how much cross sectional area of boat you need based off that.

[fbWldcat]

Thanks guys, this helps a lot. I'll take a look and see what I can figure out.

[greens]

I have a 18' lund v bottom boat w a yamaha high thrust 50 w a standard lower unit n a 13 pitch aluminum prop  gets me where i need to go w a max of 7 person load.

[Shamus]

I watched the video until they got to the gorilla glue part.

Do not use gorilla glue!!!, use a marine epoxy such as West, gorilla glue comes apart after a while in wet conditions.

shamus