Hey guys, I am currently collecting materials to make a hot tub

>>987998
See how in your pic there is a rather large gab between the water level and the top of the tub? That's to allow for displacement, just build up the sides high enough to allow for the water to rise without spilling over.

>>987998
Round is the strongest shape for resisting internal pressure.

>>988036
This anon is correct.

We used to have a redneck hot tub out at my Grandparents family farm.

Similar setup to your picture. Used a metal cattle trough for the inside, think it had some ratchet straps to re-enforcement and a wooden surround.

The main issue with it was that there was no temperature control. We eventually stopped using it because one of my young cousins got burned because it had been running for a long time.

Luckily the burns weren't that bad 2nd degree burns to about 50% of the body. Luckily it wasn't that deep.

Don't make it square

>>988053
Just because square isn't the absolute optimal form doesn't mean he shouldn't use it. Ease of construction is a real thing that should be considered, if he ever wants to get the project finished.

Besides, square is more optimal for space, and can fit more people in (plus you can lean back against the wall in the corners which personally is nice).

With some sort of frame behind it, and enough layers, the fiberglass should be plenty strong enough.

File: CedarHotTub1_000.jpg (20KB, 423x346px) Image search: [Google]

20KB, 423x346px

That picture is of a hot hot tub with a metal/ceramic tub insert. Wooden barrel tubs without an insert are made of boards that have a slightly angled edges so they fit together in a cylinder. There are large, very heavy duty steel hoops that get tightened around the tub. A hot tub full of water will weigh around 6000 pounds, so it has to be very sturdy. They are generally made from wood that resists rotting like cedar. You also have to consider the foundation, most hot tubs will need a solid concrete foundation.