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Clever idea for a hot tub spacer (to require less water to fill the tub)?

Clever idea for a hot tub spacer (to require less water to fill the tub)?

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  #1  
Old 03-06-14, 09:00 PM
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Clever idea for a hot tub spacer (to require less water to fill the tub)?

I'm building a sort of Japanese soaking tub, meaning a long, narrow and deep tub. I was going to make it smaller to require less water, but then had the idea of making it large (big enough for 5 people to soak) and then having some spacers that I put in so it doesn't require as much water to fill it. In other words, its the same principle as putting a brick in the toilet reservoir.

Can anyone think of a good object to put in the tub? Properties off the top of my head:

- shouldn't float
- should be reasonably large, the size of two people or so (or can have multiple small ones)
- ideally should be compact for storage, but that's not a requirement

I'm sure there's some readily available thing out there that fits the bill, but I can't think of it, so thought I'd throw it out there to see if anyone has any ideas.
 
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  #2  
Old 03-06-14, 09:13 PM
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Welcome to the forums.

Your building a soaking tub for five people but to save on water you want to put the equivalent of two people's worth of ballast in it. Wouldn't that become a soaking tub for three then ?

For anything to be considered for ballast it needs to be heavy. It can't be anything hollow or it will float. Pavers, block, 5 gallon buckets full of sand with lids.
 
  #3  
Old 03-06-14, 09:21 PM
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Your building a soaking tub for five people but to save on water you want to put the equivalent of two people's worth of ballast in it. Wouldn't that become a soaking tub for three then?
Yup, but it gives me the option of fitting 5 (or however many) the next time.

For anything to be considered for ballast it needs to be heavy. It can't be anything hollow or it will float. Pavers, block, 5 gallon buckets full of sand with lids.
All good ideas. Things filled with sand would be great, but super heavy. I wonder if there's not something lighter?

5 gallon buckets with a bit of sand in them so they sink would probably work, I'll give it a try.
 
  #4  
Old 03-06-14, 09:25 PM
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You'd have to experiment with the amount of sand needed to keep it down.
Air trapped inside the bucket will cause it to try to float.
 
  #5  
Old 03-07-14, 05:52 PM
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I would go for a very modular system. If you want to displace water equivalent to several people your filler blocks will weigh more than those people so you're talking about several hundred pounds. Personally I don't think it's a good idea as you're dealing with lots of heavy blocks which are just waiting to crush a toe. Then there is all the surface area of the blocks to clean. It just seems like a lot of work for relaxation.
 
  #6  
Old 03-07-14, 07:10 PM
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> it would be heavy

That depends what you make them out of. There's lots of things that don't float but that are pretty light.
 
  #7  
Old 03-08-14, 05:02 AM
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Uhhhh, no. There is no magic way around physics. You want something to displace a lot of water but does not float. For an object to not float it must be heavier than the water it displaces. If you want to replace the water that a 150 pound person would take up than your blocks will about 150 pounds or more.

One cubic foot of water contains 7.8 gallons and weighs about 62 pounds. To replace one cubic foot of water with something that will not float you will need something one cubic foot that weighs more than 62 pounds. Awfully heavy to be lifting in and out of a tub. You might as well stack a hundred bricks.
 
  #8  
Old 03-08-14, 11:30 AM
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Well for example, I could put a bladder in there that gets filled with water. Light (after emptying it), conforms to whatever shape, and very easy to store. Trying to think of a good source for those. Wake boarders use them in boats to add weight so I should research that.

One issue is insulation. I don't want to lose a lot of heat keeping the bladder(s) warm.

And I wonder it there's some other clever item that displaces water without being heavy and bulky that I'm missing...
 
  #9  
Old 03-08-14, 12:21 PM
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Here's an interesting one, they call the wakeboard ballast systems "fat sacs". There's some really cheap ones on ebay, like this:

550 lb Wakeboard Boat Ballast Bag Wakesurf Fat Sac Wake Enhancement Bladder | eBay

($60 for a 550 pound sack)

Water is about 8.3 pounds per gallon, so that's a 66 gallon container. That's probably a few people worth of displacement, depending on how submerged I can make the sac. Hmm.

And reading up on "diy fat sac" I found some suggestions to use a waterbed bladder, which is pretty funny. The wrong shape for my needs though.
 
  #10  
Old 03-08-14, 12:52 PM
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You said you wanted a big tub... but wanted to put something in so it didn't use as much water... now you want to put the water in bags??? You've still got the same amount of water in the tub.

You said you were building the tub. What if you approached it from a different angle. Don't try displacing water. Make the tub smaller. What if you made your tub big and had a removable partition dam that would block off part so you can fill just a small section. When it's party time you fill the other side then remove the partition/dam.
 
  #11  
Old 03-08-14, 12:54 PM
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Wow I didn't think of that! You're a genius!

Just kidding. Obviously I have my reasons for wanting to build it this way. Most of the time it'll just be my girlfriend and I using the tub. But sometimes, when we have a party for example, I want to be able to fit more people. So I'd leave the spacer in the tub when its just my girlfriend and I, and remove it for parties.

And I'll only be filling the tub when we use it, as opposed to keeping water in it for months at a time, so putting water in bags is a water savings. And once its insulated, it'll also be an energy savings.

And I'm totally not married to the idea of using water bags, its just a possibility. It fits my need of using less water each time I fill the tub, but I'm worried that it'll be difficult to insulate and will absorb a lot of heat.
 

Last edited by wrybread; 03-08-14 at 01:36 PM.
  #12  
Old 03-08-14, 05:35 PM
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Ah, now I'm understanding better.

How are you going to construct the tub? Materials?

Air bags, foam blocks or some other light weight material can be used as filler blocks if you have a way of holding them down. If they are light they will want to float but if you built an overhanging lip on part of your tub you could slide in your filler blocks when the tub is empty. When you fill the tub they would float up a bit and get caught by the lip around the tub which would keep them from floating uselessly and their upward flotation against the lip would securely lock them in place. The lip would not be comfortable on the shoulders and necks of guests when you open the whole thing up but maybe you can think of a construction method that would be more comfortable.

One thing I've noticed with spas is that dead water spaces become nasty. So, I'm not crazy about filler blocks and the water space around them. After each use you'll have to remove your filler pieces to let everything dry thoroughly. With the dam method you don't have so many crevices for dirt and nasties to grow.
 
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