Hot Tub In A Boat

[cyclops]

If it is gutted the way you describe, I am not so sure the hull sides are now strong enough not to cave in with tub, water and 8 to 10 non swimming people in it.

[rhubley]

Hence my original question....What type of framing would be necessary to support
this in a hull?

[Skippy]

You have three tons of cargo sitting amidships. It's not really an unusual problem. The primary stress will be the same as on an upside down see-saw, downward weight in the middle and upward pressure at the ends. The stringers are longitudinal beams that support that load. The hull and deck together act even more effectively as one big beam to do the same thing, so you should replace the deck with something that will take longitudinal compression and athwartship tension, held in place vertically.

Other than that and supporting the tub within the hull, it's a standard problem of reinforcing the hull against the pressure from being immersed. Any contact between tub and hull sides will help equalize the pressure on either side of the hull. I doesn't make too much difference what shape that support is, mostly it just transmits pressure directly.

[Willallison]

www.yachtub.com

[rhubley]

Will, I saw that -- nice concept if you don't mind lots of heat transfer
into the water. Also it would be nicer to have the tub up higher.

Skippy, thanks for the pointers. At first I was thinking of supporting the tub with
C shapped transverse supports but after reading a few responses I see that
both stringers and transverse supports are needed. I am thinking I will use some
large stringers under the tub with plywood C shaped transverse supports placed
in a grid pattern under the tub footprint. The stringers will continue beyond the
footprint and end in a wedge to avoid hard angle effects. Now I am wondering
if I should glass over the stringers. Are there alternative ways of anchoring the
stringers without making them enclosed ( and vulnerable to rot )?

[Skippy]

How can the C-supports form a grid if they're all transverse?
By a wedge you mean tapered ends? That's fine.

The stringers should have a glass outer shell, maybe epoxied, I'm not positive about that, with a lighter core inside. Most people seem to trust epoxy/glass sheathing these days.

You might want to also consider some supports directly between the tub sides and hull bottom fore & aft. They'll support part of the load more efficiently than stringers or the surrounding deck and hull. Of course they take up more space, and they're also stiffer and have to be kept from buckling, so it might help to consult with a professional NA.

[Inquisitor]

Sounds like an interesting problem. Since you said 99% docked...

Remember any portion of the tub below the waterline you don't really have to have structure. i.e. Put a kiddie pool in a pool and fill it up... it just sinks to the water line inside. No appreciable structure required. (You just have to account for those high heel shoes! ) You could do a several inch thick foam core (to house your jet's plumbing, and heat insulation value) and then put several layers of glass inside and out and call it good. It would rise out of the water a couple of inches higher than the waterline inside due to the foam core buoyancy. For placement, hinge it off the stern. Easy to step down into and pull it up for your 1% outings. As someone suggested… if you’re using lake water… you could have a BIG drain in the bottom to let the water in/out while lowering/lifting and it would be self filling/draining as you lower/raise it.

[yipster]

a simple big blow-up pool at the transom heated by the engines may be the pool we all want behind our boat.
a lot of fresh water consumption each weekend though...

[safewalrus]

Two watertight bulkheads amidships some few feet apart defines the ends. stick a few holes in the sides to give a wet well, water runs in, water runs out! solves most of your free surface effects (slope bulkheads into the centre, bottom wider than top also helps,) (holes have to be fairly big), chuck a couple of logs floating in the well sorts out the splashing! Deck over the ends to give bouyancy! Shove a BIG water heater in the bottom and cover the whole bottom with a grateing for standing on. OK you heat a lot of the lake but you don't want it too hot do you? Removable outboard on the back (technical term not used this is a bath that goes out in a lake not a boat). On the odd occasion that you do go out go slowly! Enjoy!

[l_boyle]

Whew, I am glad that you all answered this..... Yes, the boat the way it designed for.. Built a floatie ring of foam, tow it, and be happy... Why, fold a boat..

[rhubley]

Hey everyone. Thanks for all the advice. I figured some of you might want to know what happened in the end. Well here is the result:

http://www.repeatmasker.org/~rhubley...oat/index.html

[marshmat]

Well I'll be damned, it worked!
Looks like you did a pretty good job in the end. All that's missing now is a bar