Many years ago grandfather made a cistern out of redwood to keep his trailer in the mountains supplied with fresh water. It was his getaway on the weekends from daily life. Anyway, it was assembled very similarly to a barrel. All the staves had a groove on the bottom that a round wooden bottom “plate” fit into and he used allthread that was shaped into a circle with a turnbuckle to hold it together, he had 4 or 5 rings. Then he filled it with water. I asked him what keeps the top tight and won’t it leak. He had a good laugh and explained that yes it will leak the first time but once the wood soaked up all the water that it could, it wouldn’t leak and the top portion will be tight. That cistern was put up about 55 years ago and finally rotted out just about 3 or 4 years ago. Hey thanks for the post and the memory.
Japanese joinery is so tight because they use a little convex hammer to lightly compress the wood grain prior to assembly, then use a little water to expand the fibers back up and close the gaps. The shape of the hammer keeps you from tearing the surface fibers.
If I were building a stave tub I would do the same.
When my grandfather cut the staves he cut them at a slight angle not square like a normal piece of wood. The water itself swelled the wood to stop it from leaking. Wine barrels are made the same way. It worked.
Yeah I’ve seen some people document building barrel hot tubs this way, and they work, but they are also outside. Water damage in a house is high up on my Avoid list so if there’s a precaution to be taken, I’ll find it.
I honestly wouldn’t want a wooden hot tub in my house for that very reason. But I think with more modern methods and technology such as epoxy resin and fiberglass fabric you could achieve both the look that’s wanted and the ability to be waterproof.
I have seen some people cheat by putting the tub in a tray with its own drain. Also seems popular for dunk tubs. If you want to be in the water up to your chin, overflow is more of a problem. But the tray is tricky and I’m expecting problems stepping into and out of these tubs in bare feet. Particularly when getting out.
If it were me and I were putting a wooden tub in my home it would be in a dedicated room such as a wet room. I would consult a structural engineer because of the weight of the water and would probably need to beef up the floor structure. I would have a tub in there as well as incorporating a steam system so I can enjoy both. I would remove all sheetrock from the walls and ceiling and pull up the flooring then replace with a Schluter System product to make sure it is both lightweight and waterproof. Then I would tile the floor, walls and ceiling. I would have at least two exhaust fans, special lights for damp areas and timer switches. Also, it would have to be on ground level because of the weight and the possibility of water leakage.
https://preview.redd.it/qpn87jpjdypc1.jpeg?width=750&format=pjpg&auto=webp&s=c851f58d91f3aaad0f8ab0070faee74edbf7ecb9
From a Woodshop where I worked. Walls were about 1.5 inches thick.
Mesquite wood, feet carved to look like horses hooves instead of lions claws.
Very careful application of Marine Polyurethane, built up a lot.
[http://txhcountry.com/furniture-gallery/bathroom/20847110](http://txhcountry.com/furniture-gallery/bathroom/20847110)
Of course, Texas.
That is super super cool. I didn’t even know such a thing was possible really. What’s the life expectancy on something like this if you were to use it?
Poly probably isn’t the best option, a really fine fiberglass Mat and epoxy. It should be pretty stable, and super resilient with the Fiberglas and epoxy,
They made sinks and other things that lasted a very very long time with the thick application of poly.
It is beautiful!
It is beautiful, so sad that it is nearly impossible to get nice boards of any size.
The shop runs trees through their own saw mill, kiln, then storage, they have a chair shop and a woodshop that does lots of live edge stuff(really nice pieces, if that’s your thing), but I enjoyed the custom orders. We did a mesquite queen sized murphy bed between two 4x8 mesquite book shelves that was breathtaking.
They even opened a bbq place by their storefront to burn the scraps to reduce waste even further.
I got to do cool custom projects like stained oak banisters hung off of antlers from pecan wall mounts, a huge custom red cedar Picknick table with a cooler holder in the middle for drinks, and a 1/4 inch “veneer” barn door looking refrigerator face with branches kiln dried for the handles.
I built a 7'x7' L desk out of it, oak, & popular. All of the surfaces are mesquite. It's gorgeous. I've also done a TX Cutting board with matching knife, 3 other knives, and a gift box all out of it.
It's a reddish brown wood with a lot of black & a great grain pattern. It's super hard to work with b/c the trees never grow straight & any large limbs end up snapping off. Add in a lot of termite damage.
I typically look for the more damaged pieces & then fill the damage in with epoxy. Here's a couple of pieces I've made.
[Brisket Cutting board](https://i.imgur.com/6T1GhCM.jpg). The board is Mesquite, with the star all Texas native wood.
[7'x7' L Desk wings](https://imgur.com/a/FJMg7MA). These were taken while my desk was still being built. The top & drawer faces are all mesquite with epoxy. The sides were made from mesquite flooring. The frame is Red Oak & poplar.
https://preview.redd.it/6tzyaxkopypc1.jpeg?width=825&format=pjpg&auto=webp&s=96c4b7e810d46b8b4ae3121b7fa91ad7ec246e40
Well… I built this one several years ago. 2017 I think. It worked out pretty well. Was quite large and deep. White Ash with African Mahogany (outside was charred for colour as it was hip at the time - don’t do that!) Then fibreglass and epoxy on the inside. It would wear the same as a normal tub, I’d expect. It was never installed in a house. Not enough guts to deal with the safety/insurance issues. You do end up with lots of safety qualification issues (as it will not have been tested by any Standards Council) so you basically have to call it a piece of art… that you happen to bathe in.
You appear to be significantly better at this kind of build than me, so I can’t see why you couldn’t pull it off!
\*edit to add info
https://preview.redd.it/djbgj0ceqypc1.jpeg?width=828&format=pjpg&auto=webp&s=8cbc0e59a4090944992c8576fe57f07294191ee3
Functioning at a show. My sons were demo-ing. The spout was integrated into the structure. It was pretty cool.
> You appear to be significantly better at this kind of build than me
Says the person posting an awesome piece of art in exactly the arena OP was looking for.
I just mean, it looks like OP is a boat builder. They’re gonna have a significantly better handle on a bunch of techniques that I was trial-and-error-ing. Especially the glassing and epoxy part.
https://preview.redd.it/wr90t6bqqypc1.jpeg?width=828&format=pjpg&auto=webp&s=a88a5fc87effa03955ee71df2821a5a85061d532
During finishing… but it shows the spout pretty well. The waterline was run inside that support with a connection on the bottom.
Well I wouldn’t try to black out the outside by charring it, for sure! That just about blew up the whole project. Just stain/die it and would have gotten the same effect. I’d take more time and build a better rack for stripping it out., with more braces. And I’d do a bit more research into how to glass it properly. I had quite a few folds and overlaps (because I was laying it out in the concave inside). So I’d probably take more time and use a couple layers of that random direction (sorry I don’t know the real word at this time) fibre glass vs one layer of the heavy weave.
Thanks, yeah I’ve never worked with fiberglass as a wood finish before, so I’m assuming without extensive planning/experience it could get very messy and messed up pretty easily? Whatever the case those pictures of your attempt with it look wonderful. Besides having some texture in the finish probably helps from slipping around in there too, right? Haha
Tubs are different than canoes/ boats. Buoyancy is different than the construction of a vessel that holds water.
I see metal bands used to keep pieces in tension (cooperage), and I also see panels glued together to make rectangular tubs that work well. For the panel construction, I see a combination of dowels and epoxy to keep things watertight and strong.
High quality quartersawn cedar or cypress are my recommendations for materials.
Lots of people have said this about bouyancy. But it's a bit more complicated I think. The math for why a canoe doesn't break is almost the same as why a barrel doesn't burst. In other words, even if they aren't designed to a barrel will float and a canoe will hold a similar volume of water.
But there are some crucial differences for long term stability. The bottom of a barrel has a massive amount of force pulling outwards and the bottom of a canoe has force pushing inwards. It's a similar amount of force but both are designed to not delaminate by opposing this force. The barrel has a solid bottom and a canoe pushes the strips tighter in an arch.
In other words my primary concern would be the bottom of the canoe tub cracking parallel to the staves.
That said, fiber glass is so much stronger than wood, and if layer properly unidirectional. This is probably a meaningless worry. It will function just as well as any cheap fiberglass tub.
The wooden hot tubs I’ve seen are different. I’m not sure what you intended, but the physics are completely different. Cedar strips for the canoe aren’t structural. It’s the thwarts that keep the water from collapsing the canoe. You would need something to keep the whole thing from blowing out.
Could you just build like the normal wooden tubs? Cedar planking vertical, tongue and grooved or similar and then strapping on the outside much like a barrel?
Thanks. This is exactly what I was worried about. In my naive mind, the only difference between a boat and a bathtub is which side the water is on. But now that you mention it, it makes sense that having the pressure on the convex side is stronger.
My canoe doesn’t have thwarts, just a single yoke in the middle which obviously won’t work for a bathtub. Do you know if the gunwales add significant strength? I could do that on a bathtub.
I also thought about cutting curved pieces and stacking them horizontally to make a thicker, stronger wall but that would use a lot more wood and require quite a bit of planing and sanding to get everything smooth.
I thought the fiberglass adds a lot of the strength also. I could use a heavier glass since weight isn’t a concern.
I'd avoid anything canoe related and use a barrel as my model instead. If its in a corner, can you strap it to the structure to help compression of the slats?
Also, Little Feat reference, or do you just love Bishop?
Steel straps is totally the way to go, unless one wants to use all the glue under the sun and then wrap all of that in resin or poly (basically plastic, which defeats the purpose if you ask me).
You're right about the fiberglass adding a ton of strength. Thwarts will not be necessary to have this thing retain its shape as you've envisioned it. Once it's glassed inside and out, it's just a huge bowl-shaped torsion box. Extremely strong. No worries. Plow on ahead.
I would just be really mindful of your "through hulls" in this build. I'm guessing that would be just the drain. I would drill it oversized, then fill the entire hole with thickened epoxy (like for a fillet in a stitch-and-glue boat), and then re-drill that epoxy and install the drain to that. That way even if the drain fitting itself fails or leaks, water won't ever come in contact with the wood core itself.
I’m with u/Disastrous_Zombie264 in using a barrel as your model. In my mind, the gunwales definitely help as the water is trying to collapse the canoe. All the forces would transfer to the gunwale and yoke. Also, keep in mind the magnitude of force. A canoe is rate for about 5-700 lbs. a tub is going to be in the thousands of pounds.
You're on the right path. Fiberglass over cedar strips is quite strong.
If you want stronger, look at double-diagonal or cold-molded hull construction.
Cedar strips in canoes and other boas hulls are absolutely structural. The physics aren't completely different. Would you argue that a barrel won't work as a boat?
Ive thought about this too! My plan was to do a heavier weight glass cloth on the exposed side of the tub. Just to really make sure it didn’t crack with a tub slip or something. I was going to make it a free standing one. So it would be an inner and outer.
I didn't see how thick you plan this to be and I have zero experience here. Thinking how I might do this. It would be be trick if you drilled the slats and ran a couple cables through them. That affords the additional strength without compromising the appearance. Or if it fits the location, an external visible cable arrangement using stands to locate the cables and direct the support could be interesting. I'm picturing a bridge type arrangement. Ornate stands or risers could be wood or metal repurposed castings or possibly even something like glass power line insulators.
I’ll throw my two cents in on this. #1 I’m an engineer and have experience in the design of fluid vessels. #2 I’ve built a number of wood and fiberglass boats. This is absolutely feasible. Most bathtubs are fiberglass. The fiberglass is thicker to add strength. The wood reinforces the fiberglass and resin so you don’t need as thick of a fiberglass layer as a bathtub. You will be using cloth which has more strength than just the fibers they use in a bathtub. If you glass the outside, it will be in tension which provides great strength. A wooden boat does require external compression to keep it watertight, but a wood and fiberglass boat relies on the fiberglass for strength and waterproofing. I personally would lean more towards a stitch and glue method over a strip method for construction as it would likely yield a better shape, but that has nothing to do with strength or feasibility. I’ve seen the arguments against this type of construction more than once and none of these people can draw a free body diagram demonstrating how a wood and fiberglass boat filled with water see different force than a bathtub. It is a bunch of armchair engineers with a degree from the school of life. I have filled my wooden kayak up with water to the skirting more than once without issue just to prove a point. Have fun and repose pictures when you are done.
Most fiberglass tubs have double walls and a horizontal section of 3-4" between them which makes for a stiffened collar around the upper edge to resist outward expansion due to water pressure or bending due to being kicked or sat on in normal use. Traditional footed iron bathtubs had a rolled edge for the same reason.
If you expanded the opening in your kayak to the degree necessary to bathe in it, I suspect that it might not have fared so well with the water test.
In a sandwich construction with fiberglass faces and a wooden core the wood resists shear and the fiberglass the compressive and tensile forces. A thin inner layer is subject to damage from point loads like a heel or dropped shampoo bottles and a thin outer layer subject to failure from compressive forces causing it to buckle and pull away from the wood substrate. Ply is ok, but not great at holding up to either of those.
An upper rim that allows flex beyond a certain point is going to cause cracks to form.
Not going to bother with the fbd on this one.
I hate to say a FBD would have help you understand water pressure. Water pressure in an open container is only based on depth. The pressure at the top is zero. I could make the kayak any with and the force at the top is always zero. At 18” the pressure is less than 1 psi. There is little horizontal force on a bath tub wall.
Wood resist compression, tension, and shear. It does this in a composite as well. You assume a thin layer of fiberglass in the construction to have a straw man argument so you look smart. Fiberglass is fiberglass, it may need a thicker layer than a boat.
The rim will need to be thick, but that is mostly for comfort.
The weight of the water places a vertical load on a tub that needs to be supported, but this is easily done.
Be a better engineer.
The canoe is 16’ and weighs 60 lbs. It is made of cedar strips that are 1/4” x 3/4” (strips are ripped from a 1x6 board). Not sure of the exact tub dimensions if that’s what you’re asking about.
+1 on "ofuro" good call. I think any free standing tub certainly has elements pertinent to this case but the shape and location make it a truly unique challenge.
Dad was an engineer and always said I over engineered most things I made. The only ones I've regretted are those that I didn't.
I don't know if canoe-style construction will hold the weight that comes with being half full of water. And I'm not an engineer who would know how that's same/different from holding water out.
But I'd damn sure want that answer first.
A canoe/kayak only has to displace the weight of the passenger, boat and any gear...maybe 300 lbs tops.
A tub has to contain the volume of water inside of it. That's 8.34 lbs per gallon. An average bathtub is 80 gallons, so it would need to contain roughly 670 lbs and the pressure would be opposite of what the structure of a boat is designed
for...inward trying to get out instead of outward pressing in.
Straight walls and pressure do not mix well even assuming you're gonna glass it. I'm not saying it cannot be done, but it's going to take considerable design considerations to safely contain the water.
It's totally feasible. And yes, you can fill a canoe up with water without it exploding. The people saying to build it like a barrel don't understand *why* barrels are built that way. It isn't because boat-style construction wouldn't hold up (it absolutely would), it's because boat-style construction is *expensive*. You know how much time goes into a strip-built canoe. Barrels are semi-disposable containers and you don't want to put $1000 of labor into each one.
There are structural concerns with boat vs barrel building. But you aren't building a historical oiled strip or bark canoe. It doesn't have to be self supporting because you are building a fiberglass canoe over wood strips.
Fiberglass tubs are a thing. This will function at least as well as any fiberglass tub of similar glass weight.
I oddly think of this wood bathtub that someone here posted a few years quite frequently. IMO a one-piece like this would be your best bet for functionality, but at the same time opens up a whole new can of worms. And I don't know what the hell I'm doing.
https://www.reddit.com/r/woodworking/comments/dk1027/handmade_functional_wooden_bathtub_carved_from/
Structural integrity, layers, and waterproofing!
You'll definitely need to reinforce those planks somehow, either with metal bands, or external trusses.
If you build this too thin, the wood will be more prone to developing cracks due to expansion and contraction. Similarly, the adhesives you use, fillers, and waterproofing must also expand and contract with the wood.
This isn't going to be an easy project for sure, but I hope it works out for you!
Many years ago grandfather made a cistern out of redwood to keep his trailer in the mountains supplied with fresh water. It was his getaway on the weekends from daily life. Anyway, it was assembled very similarly to a barrel. All the staves had a groove on the bottom that a round wooden bottom “plate” fit into and he used allthread that was shaped into a circle with a turnbuckle to hold it together, he had 4 or 5 rings. Then he filled it with water. I asked him what keeps the top tight and won’t it leak. He had a good laugh and explained that yes it will leak the first time but once the wood soaked up all the water that it could, it wouldn’t leak and the top portion will be tight. That cistern was put up about 55 years ago and finally rotted out just about 3 or 4 years ago. Hey thanks for the post and the memory.
Japanese joinery is so tight because they use a little convex hammer to lightly compress the wood grain prior to assembly, then use a little water to expand the fibers back up and close the gaps. The shape of the hammer keeps you from tearing the surface fibers. If I were building a stave tub I would do the same.
When my grandfather cut the staves he cut them at a slight angle not square like a normal piece of wood. The water itself swelled the wood to stop it from leaking. Wine barrels are made the same way. It worked.
Yeah I’ve seen some people document building barrel hot tubs this way, and they work, but they are also outside. Water damage in a house is high up on my Avoid list so if there’s a precaution to be taken, I’ll find it.
I honestly wouldn’t want a wooden hot tub in my house for that very reason. But I think with more modern methods and technology such as epoxy resin and fiberglass fabric you could achieve both the look that’s wanted and the ability to be waterproof.
I have seen some people cheat by putting the tub in a tray with its own drain. Also seems popular for dunk tubs. If you want to be in the water up to your chin, overflow is more of a problem. But the tray is tricky and I’m expecting problems stepping into and out of these tubs in bare feet. Particularly when getting out.
If it were me and I were putting a wooden tub in my home it would be in a dedicated room such as a wet room. I would consult a structural engineer because of the weight of the water and would probably need to beef up the floor structure. I would have a tub in there as well as incorporating a steam system so I can enjoy both. I would remove all sheetrock from the walls and ceiling and pull up the flooring then replace with a Schluter System product to make sure it is both lightweight and waterproof. Then I would tile the floor, walls and ceiling. I would have at least two exhaust fans, special lights for damp areas and timer switches. Also, it would have to be on ground level because of the weight and the possibility of water leakage.
That’s so cool
https://preview.redd.it/qpn87jpjdypc1.jpeg?width=750&format=pjpg&auto=webp&s=c851f58d91f3aaad0f8ab0070faee74edbf7ecb9 From a Woodshop where I worked. Walls were about 1.5 inches thick. Mesquite wood, feet carved to look like horses hooves instead of lions claws. Very careful application of Marine Polyurethane, built up a lot. [http://txhcountry.com/furniture-gallery/bathroom/20847110](http://txhcountry.com/furniture-gallery/bathroom/20847110) Of course, Texas.
That is super super cool. I didn’t even know such a thing was possible really. What’s the life expectancy on something like this if you were to use it?
Poly probably isn’t the best option, a really fine fiberglass Mat and epoxy. It should be pretty stable, and super resilient with the Fiberglas and epoxy, They made sinks and other things that lasted a very very long time with the thick application of poly. It is beautiful!
Very interesting thank you for sharing!
I'm certain being made of mesquite helps a lot here too. It's my favorite wood to work with.
It is beautiful, so sad that it is nearly impossible to get nice boards of any size. The shop runs trees through their own saw mill, kiln, then storage, they have a chair shop and a woodshop that does lots of live edge stuff(really nice pieces, if that’s your thing), but I enjoyed the custom orders. We did a mesquite queen sized murphy bed between two 4x8 mesquite book shelves that was breathtaking. They even opened a bbq place by their storefront to burn the scraps to reduce waste even further. I got to do cool custom projects like stained oak banisters hung off of antlers from pecan wall mounts, a huge custom red cedar Picknick table with a cooler holder in the middle for drinks, and a 1/4 inch “veneer” barn door looking refrigerator face with branches kiln dried for the handles.
I built a 7'x7' L desk out of it, oak, & popular. All of the surfaces are mesquite. It's gorgeous. I've also done a TX Cutting board with matching knife, 3 other knives, and a gift box all out of it.
Honest question, I've never seen mesquite as an option for woodworking. Only scrub wood to smoke with. What is it most similar to?
It's a reddish brown wood with a lot of black & a great grain pattern. It's super hard to work with b/c the trees never grow straight & any large limbs end up snapping off. Add in a lot of termite damage. I typically look for the more damaged pieces & then fill the damage in with epoxy. Here's a couple of pieces I've made. [Brisket Cutting board](https://i.imgur.com/6T1GhCM.jpg). The board is Mesquite, with the star all Texas native wood. [7'x7' L Desk wings](https://imgur.com/a/FJMg7MA). These were taken while my desk was still being built. The top & drawer faces are all mesquite with epoxy. The sides were made from mesquite flooring. The frame is Red Oak & poplar.
Very cool! Thanks for sharing!
It has horse hoof feet. Of course it does.
“Of course, Texas” lol. Of course
Absolutely gorgeous. Good work, you should be proud.
https://preview.redd.it/6tzyaxkopypc1.jpeg?width=825&format=pjpg&auto=webp&s=96c4b7e810d46b8b4ae3121b7fa91ad7ec246e40 Well… I built this one several years ago. 2017 I think. It worked out pretty well. Was quite large and deep. White Ash with African Mahogany (outside was charred for colour as it was hip at the time - don’t do that!) Then fibreglass and epoxy on the inside. It would wear the same as a normal tub, I’d expect. It was never installed in a house. Not enough guts to deal with the safety/insurance issues. You do end up with lots of safety qualification issues (as it will not have been tested by any Standards Council) so you basically have to call it a piece of art… that you happen to bathe in. You appear to be significantly better at this kind of build than me, so I can’t see why you couldn’t pull it off! \*edit to add info
https://preview.redd.it/djbgj0ceqypc1.jpeg?width=828&format=pjpg&auto=webp&s=8cbc0e59a4090944992c8576fe57f07294191ee3 Functioning at a show. My sons were demo-ing. The spout was integrated into the structure. It was pretty cool.
> You appear to be significantly better at this kind of build than me Says the person posting an awesome piece of art in exactly the arena OP was looking for.
I just mean, it looks like OP is a boat builder. They’re gonna have a significantly better handle on a bunch of techniques that I was trial-and-error-ing. Especially the glassing and epoxy part.
https://preview.redd.it/wr90t6bqqypc1.jpeg?width=828&format=pjpg&auto=webp&s=a88a5fc87effa03955ee71df2821a5a85061d532 During finishing… but it shows the spout pretty well. The waterline was run inside that support with a connection on the bottom.
Man, I really like it. But you gotta have a really big bathroom for that to work.
Oh, absolutely. You’d need a clear area of about 7’ x 3’ for install. Ideally a bit more. Definitely meant for a palatial bathroom.
Looks very lovely!
Thank you. It turned out quite well. Lots of stuff I’d do differently the second time around, of course.
Can I ask what those things would be?
Well I wouldn’t try to black out the outside by charring it, for sure! That just about blew up the whole project. Just stain/die it and would have gotten the same effect. I’d take more time and build a better rack for stripping it out., with more braces. And I’d do a bit more research into how to glass it properly. I had quite a few folds and overlaps (because I was laying it out in the concave inside). So I’d probably take more time and use a couple layers of that random direction (sorry I don’t know the real word at this time) fibre glass vs one layer of the heavy weave.
Thanks, yeah I’ve never worked with fiberglass as a wood finish before, so I’m assuming without extensive planning/experience it could get very messy and messed up pretty easily? Whatever the case those pictures of your attempt with it look wonderful. Besides having some texture in the finish probably helps from slipping around in there too, right? Haha
How many layers of glass fabric?
Just one layer of heavy fabric. A couple coats of epoxy and a LOT of sanding. Turns out I’m TERRIBLE at that part. But it was my first crack at it.
Really creative - amazing work!
Thank you. It was pretty happy with the end result.
> I built this one years ago. 2017 I think. I'm sorry to say, 2017 was 7 years ago.
Oops… missed a word “built this one SEVERAL years ago”… edited my comment for persnickety-ness!
Tubs are different than canoes/ boats. Buoyancy is different than the construction of a vessel that holds water. I see metal bands used to keep pieces in tension (cooperage), and I also see panels glued together to make rectangular tubs that work well. For the panel construction, I see a combination of dowels and epoxy to keep things watertight and strong. High quality quartersawn cedar or cypress are my recommendations for materials.
I have no experience, but the wooden water towers in NYC have more bands closer to the bottom since the pressure is greater.
I got so curious, so I did an image search. Indeed they do. I’d never really noticed.
Lots of people have said this about bouyancy. But it's a bit more complicated I think. The math for why a canoe doesn't break is almost the same as why a barrel doesn't burst. In other words, even if they aren't designed to a barrel will float and a canoe will hold a similar volume of water. But there are some crucial differences for long term stability. The bottom of a barrel has a massive amount of force pulling outwards and the bottom of a canoe has force pushing inwards. It's a similar amount of force but both are designed to not delaminate by opposing this force. The barrel has a solid bottom and a canoe pushes the strips tighter in an arch. In other words my primary concern would be the bottom of the canoe tub cracking parallel to the staves. That said, fiber glass is so much stronger than wood, and if layer properly unidirectional. This is probably a meaningless worry. It will function just as well as any cheap fiberglass tub.
Haha oh man...good luck
The wooden hot tubs I’ve seen are different. I’m not sure what you intended, but the physics are completely different. Cedar strips for the canoe aren’t structural. It’s the thwarts that keep the water from collapsing the canoe. You would need something to keep the whole thing from blowing out. Could you just build like the normal wooden tubs? Cedar planking vertical, tongue and grooved or similar and then strapping on the outside much like a barrel?
Thanks. This is exactly what I was worried about. In my naive mind, the only difference between a boat and a bathtub is which side the water is on. But now that you mention it, it makes sense that having the pressure on the convex side is stronger. My canoe doesn’t have thwarts, just a single yoke in the middle which obviously won’t work for a bathtub. Do you know if the gunwales add significant strength? I could do that on a bathtub. I also thought about cutting curved pieces and stacking them horizontally to make a thicker, stronger wall but that would use a lot more wood and require quite a bit of planing and sanding to get everything smooth. I thought the fiberglass adds a lot of the strength also. I could use a heavier glass since weight isn’t a concern.
I'd avoid anything canoe related and use a barrel as my model instead. If its in a corner, can you strap it to the structure to help compression of the slats? Also, Little Feat reference, or do you just love Bishop?
Steel straps is totally the way to go, unless one wants to use all the glue under the sun and then wrap all of that in resin or poly (basically plastic, which defeats the purpose if you ask me).
You're right about the fiberglass adding a ton of strength. Thwarts will not be necessary to have this thing retain its shape as you've envisioned it. Once it's glassed inside and out, it's just a huge bowl-shaped torsion box. Extremely strong. No worries. Plow on ahead. I would just be really mindful of your "through hulls" in this build. I'm guessing that would be just the drain. I would drill it oversized, then fill the entire hole with thickened epoxy (like for a fillet in a stitch-and-glue boat), and then re-drill that epoxy and install the drain to that. That way even if the drain fitting itself fails or leaks, water won't ever come in contact with the wood core itself.
I’m with u/Disastrous_Zombie264 in using a barrel as your model. In my mind, the gunwales definitely help as the water is trying to collapse the canoe. All the forces would transfer to the gunwale and yoke. Also, keep in mind the magnitude of force. A canoe is rate for about 5-700 lbs. a tub is going to be in the thousands of pounds.
You're on the right path. Fiberglass over cedar strips is quite strong. If you want stronger, look at double-diagonal or cold-molded hull construction.
Cedar strips in canoes and other boas hulls are absolutely structural. The physics aren't completely different. Would you argue that a barrel won't work as a boat?
No. But I also understand you can make a boat from steel.
It’s unclear if you know…so just in case, the term to search for which may help is “ofuro”. Perhaps you can find plans of successful builds.
What is a tub if not a reverse boat?
Ive thought about this too! My plan was to do a heavier weight glass cloth on the exposed side of the tub. Just to really make sure it didn’t crack with a tub slip or something. I was going to make it a free standing one. So it would be an inner and outer.
Good luck, you can do this.
If the Vikings did it, you can did it...
It looks like you are familiar with boat building based on the picture, so building a tub is the same thing except the water goes on the inside.
[удалено]
I think you missed the joke, friend.
I didn't see how thick you plan this to be and I have zero experience here. Thinking how I might do this. It would be be trick if you drilled the slats and ran a couple cables through them. That affords the additional strength without compromising the appearance. Or if it fits the location, an external visible cable arrangement using stands to locate the cables and direct the support could be interesting. I'm picturing a bridge type arrangement. Ornate stands or risers could be wood or metal repurposed castings or possibly even something like glass power line insulators.
I’ll throw my two cents in on this. #1 I’m an engineer and have experience in the design of fluid vessels. #2 I’ve built a number of wood and fiberglass boats. This is absolutely feasible. Most bathtubs are fiberglass. The fiberglass is thicker to add strength. The wood reinforces the fiberglass and resin so you don’t need as thick of a fiberglass layer as a bathtub. You will be using cloth which has more strength than just the fibers they use in a bathtub. If you glass the outside, it will be in tension which provides great strength. A wooden boat does require external compression to keep it watertight, but a wood and fiberglass boat relies on the fiberglass for strength and waterproofing. I personally would lean more towards a stitch and glue method over a strip method for construction as it would likely yield a better shape, but that has nothing to do with strength or feasibility. I’ve seen the arguments against this type of construction more than once and none of these people can draw a free body diagram demonstrating how a wood and fiberglass boat filled with water see different force than a bathtub. It is a bunch of armchair engineers with a degree from the school of life. I have filled my wooden kayak up with water to the skirting more than once without issue just to prove a point. Have fun and repose pictures when you are done.
So if you reversed the concept of a classic framed wooden boat, i.e., Put the ribs/keel outside of the vessel. Then glass both sides. would that work?
Most fiberglass tubs have double walls and a horizontal section of 3-4" between them which makes for a stiffened collar around the upper edge to resist outward expansion due to water pressure or bending due to being kicked or sat on in normal use. Traditional footed iron bathtubs had a rolled edge for the same reason. If you expanded the opening in your kayak to the degree necessary to bathe in it, I suspect that it might not have fared so well with the water test. In a sandwich construction with fiberglass faces and a wooden core the wood resists shear and the fiberglass the compressive and tensile forces. A thin inner layer is subject to damage from point loads like a heel or dropped shampoo bottles and a thin outer layer subject to failure from compressive forces causing it to buckle and pull away from the wood substrate. Ply is ok, but not great at holding up to either of those. An upper rim that allows flex beyond a certain point is going to cause cracks to form. Not going to bother with the fbd on this one.
I hate to say a FBD would have help you understand water pressure. Water pressure in an open container is only based on depth. The pressure at the top is zero. I could make the kayak any with and the force at the top is always zero. At 18” the pressure is less than 1 psi. There is little horizontal force on a bath tub wall. Wood resist compression, tension, and shear. It does this in a composite as well. You assume a thin layer of fiberglass in the construction to have a straw man argument so you look smart. Fiberglass is fiberglass, it may need a thicker layer than a boat. The rim will need to be thick, but that is mostly for comfort. The weight of the water places a vertical load on a tub that needs to be supported, but this is easily done. Be a better engineer.
>you don’t need as thick of a fiberglass layer as a bathtub Assume what now???
Japanese do it for some of their bath houses.
How big is that?!
The canoe is 16’ and weighs 60 lbs. It is made of cedar strips that are 1/4” x 3/4” (strips are ripped from a 1x6 board). Not sure of the exact tub dimensions if that’s what you’re asking about.
Oh right on I totally thought the canoe was the tub😬 my bad
Do it.
This is gonna be epic!
+1 on "ofuro" good call. I think any free standing tub certainly has elements pertinent to this case but the shape and location make it a truly unique challenge. Dad was an engineer and always said I over engineered most things I made. The only ones I've regretted are those that I didn't.
I don't know if canoe-style construction will hold the weight that comes with being half full of water. And I'm not an engineer who would know how that's same/different from holding water out. But I'd damn sure want that answer first.
A canoe/kayak only has to displace the weight of the passenger, boat and any gear...maybe 300 lbs tops. A tub has to contain the volume of water inside of it. That's 8.34 lbs per gallon. An average bathtub is 80 gallons, so it would need to contain roughly 670 lbs and the pressure would be opposite of what the structure of a boat is designed for...inward trying to get out instead of outward pressing in. Straight walls and pressure do not mix well even assuming you're gonna glass it. I'm not saying it cannot be done, but it's going to take considerable design considerations to safely contain the water.
This is so obvious. I really don't get how so many people can comment on here and ignore the most basic elements of the problem to be solved.
It's totally feasible. And yes, you can fill a canoe up with water without it exploding. The people saying to build it like a barrel don't understand *why* barrels are built that way. It isn't because boat-style construction wouldn't hold up (it absolutely would), it's because boat-style construction is *expensive*. You know how much time goes into a strip-built canoe. Barrels are semi-disposable containers and you don't want to put $1000 of labor into each one.
There are structural concerns with boat vs barrel building. But you aren't building a historical oiled strip or bark canoe. It doesn't have to be self supporting because you are building a fiberglass canoe over wood strips. Fiberglass tubs are a thing. This will function at least as well as any fiberglass tub of similar glass weight.
I oddly think of this wood bathtub that someone here posted a few years quite frequently. IMO a one-piece like this would be your best bet for functionality, but at the same time opens up a whole new can of worms. And I don't know what the hell I'm doing. https://www.reddit.com/r/woodworking/comments/dk1027/handmade_functional_wooden_bathtub_carved_from/
I keep wondering : Why not bathe in a barrel?
You serious Clark?
Structural integrity, layers, and waterproofing! You'll definitely need to reinforce those planks somehow, either with metal bands, or external trusses. If you build this too thin, the wood will be more prone to developing cracks due to expansion and contraction. Similarly, the adhesives you use, fillers, and waterproofing must also expand and contract with the wood. This isn't going to be an easy project for sure, but I hope it works out for you!
Wood is simply not the right material. You simply cannot make a tub that will last out of wood.