I have just purchased a 6-7 person spa with a dry weight of 625 lbs and total weight of 4175 lbs. Dimensions of the spa are 83.5x83.5x37”. I plan on sinking it into a raised deck. I have read several of the postings in this forum but want to make sure I am designing the platform for the spa correctly. The height if my deck is 78". I need to build a platform that will raise my spa up 61". That will give me 20" above my deck as suggest by another posting. I plan on digging 4 footing 48" deep. Each footing will be 72" apart. I will have 6x6s off of the footings with a height of 37". On top of the footings I will have 2 beams made of three 2x12 bolted together. Sitting on top of the beams I will have the platform frame again made of 2x12 at 12" on center. The total size of the platform will be 8' by 8'. Then I will use 1" decking. All wood will be PT. I will notch the top of the 6x6s like a tong and grove for the beams. That gives me 37” (6x6) + 11.5” (2x12 triple beam) + 11.5 (2x12 platform frame) + 1” (decking) = 61”

Is this strong enough to support a full spa?
Is it over kill?
Do I need another footing in the center?
Any other suggestions that I should be looking at?

Thank you for your feedback.

It looks good on paper, although spas off the ground make me nervious. Also are you leaving room to get to all sides of the spa for service
appdoc

Service related- be sure the deck support beams don't cover up screws that need to be removed to provide service acess, and that once screws are taken out, there's enough space to wiggle out the panels.

Thank you for all of your feedback. In the back of my mind I was thinking about access to the panels and screws. One side of the hot tub will be fully accessible which should be the pump side. Devil is always in the details of the execution.

OK here is an update for any one looking to do the same thing I did. I spoke to a few deck guys and to local spa dealers. The design I post works great. However the most important of this design is the 45 degree supports. You must do them on both side of the 6x6's. You should have a total of 8 45 degree supports. Make sure you lag both ends of each support. The lag bolt I used were 6 inches long. This will remove all rocking from the platform. Also you do not need to use 2x12's. It is hard to find 2x12s with no knots is almost impossible. Knots weaken the wood. I ended up using 2x10's. As mentioned above I made some small adjustments so all screws accessible. I am pretty sure I can put my house on this thing never mind a hot tub. I will post final pictures once it is delivered on Thursday.