Boat Stability?

Question

I am building a flat bottom punt boat. Dimensions: 6ft 5in long, 3ft 6in wide. Can anybody advise me of maximum load weight and if this boat will be stable. Depth of the sides: 14in. Would a 6in keel the full length help stability? I cannot increase the size because I am transporting it in the back of my volvo estate. I would be using this boat for cutting off over hanging branches at a lake, so I would be moving about quite a bit. Would welcome any further advise on stability.

Answer 1

This depends a bit on the material you make it from and how rigid it is. Sacrificing a bit of buoyancy for added weight may allow you to move around a bit more . The buoyancy as noted by another answer will be ok at 1 ton. However the stability will be doubtful. Fore and aft not too bad, but sideways very wobbly. Ok if you sit and use hand tools, but not for standing, and certainly don't even dream of a chain saw. Take care with the freeboard. If you get a bit of water sloshing about inside the stability disappears. (Remember the Herald of Free Enterprise? A big ferry capsized because of a bit of water on the vehicle deck)

Answer 2

Hi Jab

Try this site - it is pretty big and will take a while going through, but I'm sure they'll have something there to suit you.

http://home.clara.net/gmatkin.design.htm

You will also find good boat building instructions.

Good luck -

For me it was one of those projects that I haven't got around to yet.

Answer 3

Sounds small for that kind of moving around.

From standing in a flat bottom dinghies  about same size , I would say not a good idea esp w' a saw in your hands.

If you have already started , might consider adding outriggers that could be  extended while you are working or building another one a little smaller so it fits inside the other & both will fit into your wagon  ,then  joining the two together on site  in a double hull rig w/ a platform across the top.

You double the weight load ,get better working height & stability.

Best regards

Answer 4

Maybe you can buy something that inflates to attach to the sides of your punt once you're at the lake. That may add a little stability. I hope you aren't going to be using a chainsaw for the branches , a doctor here recently slipped off the ladder he was using to reach a branch with his chainsaw and ended up cutting into his chest and killing him.

Answer 5

That's going to be very unstable to work from;  the keel won't make any appreciable difference.  If you're really that restricted in size, how about constructing some form of outriggers that you can slide into the Volvo as well and bolt onto the boat before use?

Answer 6

Good luck Noah!

Answer 7

We would need to know more

Answer 8

dont do it, if u cant swim dont try it. that well not balance you at all. i would suggest outriggers that could be attached when u got to the lake.

Answer 9

Hi Jab

Try this site  -  it is pretty big and will take a while going through,  but I'm sure they'll have something there to suit you.  

http://home.clara.net/gmatkin.design.htm

You will also find good boat building instructions.

Good luck  -  

For me it was one of those projects that I haven't got around to yet.

Answer 10

Have you come across "Sea Otter" boats?

They are small, aluminium boats, light enough when fully fitted out to be trailed.  (see their web site)

They got over the stability problem by using a 'V'-shaped, water-filled ballast tank (cross-braced) welded to the bottom of the boat.  This holds a ton and a half of water when afloat, but when pulled out onto a slipway, the water drains back into the river or canal.

When launched down a slipway, the tank fills itself by displacing the air in the ballast tank with river water.

Answer 11

On pure displacement your punt would displace a little less than a ton of water if loaded to sinking so I would not worry about carrying two people.

As for stability then it will be like any other punt and be relatively unstable if you stood up but not bad if you sat and paddled. Think of it as a wide canoe!! OK provided you do not over reach. Cutting branches should only be done in a sitting position using a pole saw unless you are very good at balancing on a moving platform.

How does that grab you for starters as usage and type of waters and experience of boater will all have a bearing.

Answer 12

It's so small on length and beam as it will be very very unstable for use as a work platform>The keel will have no use as it's for turning at speed> It's not much bigger than a bath tub>Need to re think this adventure >At least a Jon boat is 10' and it has issues>Good luck > It will float but carry little weight>And trying to saw & Cut branches>Unless  you but flots on the sides For stablity>