Introduction: Saunaboat: Turning an Old Unused Boat Into a Swimming Sauna

Who wouldn't want a sauna. And who wouldn't want a sauna at the lake, if you happen to live at one? But what's even better, is a sauna ON the lake. And since there are a lot of old boats rotting and rusting in backyards, we bought one for cheap and turned it into the best sauna we know...


An old boat nobody wants anymore

Old school insulation material

Beautiful wood for the sauna

A lot of paint

Super expensive high temperature resistent glass for the windows

An awesome wood burning sauna stove


Step 1: Find the Right Boat

For a saunaboat you obviously need a boat. Before you can find the right boat, a couple of questions need to be answered:

  1. How much space do you have on the water?
  2. How many people should the sauna be for?
  3. Do you live in a place where there is a risk of ice in winter?

Depending on the answers, you'll have to find the right size of boat and you have to decide what material the hull can be. If you run a risk of having ice in winter, you need a steel boat. Such was the case where I live. Since you want to use the sauna in winter, it wouldn't make much sense to have a boat that needs to get out of the water in winter.

It took me around half a year to find the right boat. Steel Hull, less than 8m of length, and a cabin that could be turned into a sauna for up to ten people... In the end we paid 550€ for the boat and 250€ for it to be brought to a neighboring boat yard, where we could do the hull and get it into the water...

Step 2: Rip Everything Out You Don't Need

As it says in the title, first let´s get the boat as bare as possible. Basically down to a hull with a deck and the cabin.

Step 3: Getting the Hull Ready

In our case, the boat needed a lot of sanding before we could repaint it, so that it could go back into the water. Since the boat stays in the water all year long, use whatever paint/coating/antifouling that will work best in your environment.

Step 4: Deciding the Inner Design

Once your boat is empty, it's time to see how best to design the inside. A big question is where the stove should go. I would strongly recommend a stove that has its opening not inside the room your sitting in, but can be heated from the outside instead. We got ours from the Estonian company HUUM.

When you know where the stove is, you can decide where to put the benches, windows and so on.

In our case there was one spot that was best for the stove and the window openings were already there.

In the front of the boat was a latch (originally for an extra storage compartement). We kept that latch so it can be used as an escape door, because the stove is next to the door. It was already used once when somebody had poured to much water on the stove and then did not want to pas by the stove to get out. it is also very useful for cross ventilation.

Step 5: Putting in New Windows

One thing that is really important is, that for a sauna you cannot use normal windows. Glass will easily break when heated and cooled regularly and given how exposed you are when sitting in a sauna inside a boat that moves, this could potentially be really dangerous. So we got extra windows made from special security glass (similar to that used in cars). The eight windows actually cost us more than the boat! If you have the possibility to use standard size windows you can probably get them much cheaper. We were only able to do this for the glass window of the door, were we got a simple round shape for around 20€, while the other windows cost around 100€ each...

We used silicone for putting the windows in, you can get specific stuff for high temperatures...

Step 6: Building a Structure for the Insulated Walls

The problem with boats is, they normally don't have straight walls. For a good insulated sauna, it is much easier however if there are as few corners as possible. We already had a lot of corners to deal with, so I tried to make a base for straight walls at least on the sides. For this I used cheap construction wood. Obviously this step will be varying a lot depending on what shape your boat and the cabin have... The advice is: Try to get a simple shape!

Step 7: Insulation

For the insulation choose a material that does not rot when getting wet (cool insulation like hemp, wool, straw is really nice, but may not be the right stuff for a boat). We used glas-wool.

The insulation really needs to go everywhere! However, behind the stove it might be necessary to get additional fireproof material, as was the case in our boat, because the stove is really close to the wall and ceiling.

For a good sauna, it is necessary to add a layer of aluminum foil between the insulation and the wood. This serves two purposes:

  1. The foil keeps the damp and moisture from entering the wall and insulation, it acts a damp barrier.
  2. The foil reflects infrared waves (heat). So the heat from the stove that goes through the wood will then be reflected back into the wood and the room. That way the wood gets hot quicker and stays hotter for longer.

Putting the aluminum foil in every corner und making sure it´s all well taped, takes up much more time than the insulation itself....

Step 8: Preparing the Space for the Stove

As mentioned above, its important to make sure the space around the stove is well insulated and the material here is fireproof. We used insulation, then fireproof wall panels and finished it with stainless steel plates. Especially the ceiling gets really, really hot.

You can see on the photograph, that we added a water tank to the chimney. It has a couple of positive effects. First it cools down the chimney, second it gives you a tank of hot water. We use this water for the infusions (thus cooling the stones less than if we would use cold water). Additionally the hot water is really useful for hot water foot baths when sitting outside in the cold in between sauna sessions...

Step 9: Making a Door

In our case there was already a two wing door for the cabin at the right spot. So I took the two parts and joined them together, insulated the door in put in a window.

Step 10: Finishing the Walls With Wood

There is special wood for saunas, in our case we used alder for the walls and aspen for the benches. I started with the ceiling and then did the walls afterwards. with all the windows it took a long time to get everything finished...

Step 11: Putting in the Stove

In the picture above you see how the stove works. It as a firebox which is surrounded by a steel frame into which you can put your stones. The firebox has an extension that reaches out of the room, so that you can fill it from outside the sauna room. This way you don't need to open the stove inside the room. We had to make a construction that dispersed the weight of the oven onto the hull, but otherwise it was a pretty straight forward job to get the stove set up. Since the boat can move, it's important to fix the oven to the ground. It´s advisable to leave a slot under the oven where air can run through from the outside. We attached a chimney with water tank and then did the first test...

Step 12: Building Benches

The form of the hull makes it logical to have benches on each side. I build a pretty strong basis for the benches and then made five bench parts that can easily be removed for sanding once a year... as said above, we used aspen wood. its important to use wood that is suitable for sauna benches, for obvious reasons.

Step 13: Finishing Works and Add Ons

When the inside is finished you might want to ad a couple of features. In our case we made a little box for donations, a couple of benches and we made a little box that holds the lights we use.

We decided not to run any electricity on the boat, so for the lighting we used solar-powered light-glasses. They look really nice. We take them into the sauna and put them somewhere low, so the don't break. A lot of them broke in the beginning when we had wavy days, so I ended up making a small holder...

We still haven't got a motor. It's something we want to add. Not because we want to go far, but it would be nice to just get out on the lake occasionally. But a good electric motor is rather expensive...

Step 14: Enjoy the Sauna

Once its finished its time to enjoy the sauna. Our sauna runs three to four times a week during winter, in the housing project I live in. Normally someone fires the stove for a round 1,5 Hours and then we take turns. It´s a really nice thing to fire the sauna, get everything ready and then step into a sauna from which to enjoy a view of the lake.

And afterwards we normally take a swim, or at least a dip into the water. Even when there is ice we can use the sauna and make a hole so we can take a nice ice bath (and quickly return to the sauna).

We named the boat "dampfer" (steamer).

It has been the best thing I have build and brings a lot of enjoyment, especially in these special pandemic times, where there are few social activities.

If you have any questions, go ahead and post them here...!!!!

I would be stoked if you build your own and am happy to help find the right boat or help in any other way...

Anything Goes Contest 2021

Sixth Prize in the
Anything Goes Contest 2021