Installation of Jacuzzi/Spa on the deck

Your taking on a modification beyond factory specs. Not just the weight changing CG, but the supporting decks and underlying structures.
You have not offered the boat model your considering these mods to or location of such mods.
Have you considered an marine engineer or architect? Or the factory?

Sadly, I have witnessed a soft sided tub installed on a couple of boat decks. Scary to say the least.

I saw one of those also on the FB deck of a 65' MY and it ended up cracking a salon window on each side of the boat.....LOLOLOLOL

Hi,

It is a bit difficult to retrofit a few things already mentioned. I do not know the size of the vessel you were thinking of installing, but still the points to think about. Stability, point weight on deck people + water + tub, sewer and water pipes + electricity (all from and to where).

If a boat/vessel manufacturer is still in operation it is best to ask them about the ideas to implement this project or another shipbuilding engineer to figure out the whole thing from every point of view.

"One of the questions is if the jacuzzi should be installed on the deck before laying new teak or after"

After a new teak cover because the lid is quicker and simpler to fit than a handle to fit the tub shape, another viewing angle can be easier to attach the tub slightly off the lid and then the good that the entire area is teak as a ring that collects water and dirt.

NBs

You got the recommendations of the community and it appears you have already made up your mind and are not listening. Without a study by a naval architect or equivalent, such as a top yard experienced in studying such matters, I would not recommend doing the installation. Clearly you don't have the experience or knowledge to design and execute the installation and with that in mind in would be a very unwise endeavor 40'+ in the air. Meanwhile you're more concerned with finding a "marine" model (hint, no such thing) than in studying the structure, support, stability, impact of weight shift, potential impact of water over the sides. This is not something we can advise from distance without intimate knowledge of the boat.

Then there's not just the hot tub, but everything else on the deck as recalculation is needed for all. How does it impact the other fixtures and equipment, any storage of tenders, and anything else there. You're altering significant characteristics.

Simple factors too such as what grade aluminum is the superstructure out of as typically there would be efforts to reduce weight on the upper level and now you're about to do the opposite. Your choices are to get a professional evaluation or to just plop something up there and take your chances. We can't recommend the latter.

The boat is aluminum. Have one made!!!!!!!! Aluminum on the sides and a fiberglass innerliner Jacuzzi.

Given the space you mention, assume about 3,500-pounds weight full of water. That is about the weight of a 21' center-console with 150hp outboard, gear, and fuel, sitting on your deck. That is a lot of weight, then the increased structural components need to be figured out, and the weight of added structure needs to be added.

Jacuzzis on boats are usually drained before getting underway, so you don't need to worry so much about the dynamics while underway. A way to drain, fill, and heat rapidly would be a significant bonus. Compared to a stationary Jacuzzi, extra sturdy mounting of the pump, valving, heater, electronics, wiring, plumbing, will be needed. And all this will need to be stainless or suitable for salt air and water.

The tub itself won't be complicated, a standard fiberglass tub with foam insulation will do. It will probably need a good frame under it to distribute the weight to your deck, or whatever structure gets built to hold it. Jacuzzi tubs aren't rocket science, a lot of places can build you one custom, like Capt J mentions.

If you are thinking about using this Jacuzzi while under way, that gets more expensive, you need to have some more serious engineering done.

Not to mention you have to have a SERIOUS capacity water maker to keep up with filling a Jacuzzi and all of the guests normal water needs as well as a generator large enough to run it.

If it is like most boats that size, it will sit long periods at the dock, and the Jacuzzi could stay full and filtering, like any normal Jacuzzi. Perhaps that is the intent. I'd be very nervous about forgetting to empty it before getting underway.

Hello dikikh.dm would you be able to take some pictures of the space, and boat deck, support structure, plumbing, etc.. you are considering for this and share them with us? That would provide more info for recommendations.

Thanks

Is this currently a Class Vessel? Subject to some Country Flag inspections or COI?
A DIY hot tub on a Flagged or commercial yacht is going to be tuff.