Personal Submarine Build

Finally starting to plan out my submarine project which I've wanted to do for quite awhile. The basic idea is to get some 250 gallon propane tanks to use for the hull. Then with a bit of cutting, rearranging, and welding we're supposed to end up with the worlds smallest fully self sufficient diesel electric submarine. Actually, there are a decent number of mini submarines out there, but most are just battery powered and are meant for staying in one general spot. My plan is to have a Diesel 10hp yanmar clone running a couple alternators and an air compressor. Everything will run on a 12 volt system. I have most of the idea roughed out with solutions for most of the problems I'll run into during the build. At the moment I'm working on a model of what the full sized one will look like. The model won't be exactly to scale, but close. It's mostly to help see where things on the outside will fit. After the model is finished, I'll make a full scale mock up of at least part of the sub from 1/2 electrical conduit. The hull will be about 30" in diameter.

wow ok your builds are just amazingly... well unique and special, cant wait to see the actual thing !!!

Lol man I never know what you're gonna do next. Will be really cool when you finish it!

Your builds never cease to amaze me. What kind of depths and speed are you looking for? You'll have to run a snorkel like a WWII German U boat right?

Thanks! Hopefully I actually finish the thing. As far as a snorkel system goes, I thought about it, but I decided against it for a couple of reasons. 1st issue is that the engine I want to use is air cooled and I don't think I could get enough air flowing through the hull to keep it cool inside. 2nd reason is that out in a lake, if your near the surface snorkeling, boats can't see you very easily and I can't see them easily either, even with some sort of periscope or camera system. So I feel like it's somewhat dangerous to spend a lot of time just below the surface.

So when on the surface, you run the diesel with the hatch open. Couple of fans circulate cooling air through the hull. Some air is pulled through the diesel itself and goes out with the exhaust. The propeller is turned by an electric motor either on the surface or submerged. If you want to dive, you just need to shut the diesel down and close the exhaust valve. The electric motor will then run off a bank of batteries.

Max diving depth I think will be around 100'. Pressure increases with depth. In fresh water 100' depth = about 45 psi. There are various ways to estimate the depth at which the hull will be crushed by the pressure, but they are really complicated (for me at least) and not always accurate. So basically you try to get an idea of where crush depth is, then you only dive half that deep or 1/3rd. I plan on welding in stiffening rings inside for added strength, but I've heard of other people going down as far as 400' with an unstiffened propane tank sub. One guy built a small pedal sub from a propane tank and said calculated crush depth was something like 600'. At 600' the pressure would be about 272 psi.

Speed is almost certainly going to be under 10 mph. I think I'll be lucky to get 6 mph, but we'll see.

Wait so are you actually going to be in this thing? I kinda though it was going to be a remote control tyre deal.

Ok, I gotcha now. You'll only run the diesel on the surface. if you really wanted to, you could use the compressor to feed air to the diesel under water with a pressure regulator that feeds it just the right amount, and build a cooling jacket that runs between the fins on the cylinder out of copper pipe to keep it cool. Then to go a step further, weld a plate to make a wall between you and the engine and you will have even less thermal intrusion.

Just something to think about I guess.....

Man! I'm excited to see this thing being built, very interesting idea!

MattD - Heck yeah, controlling this thing from the inside!

Craftsmanquad - The only way to run the diesel submerged for any length of time is if you had a tube or some sort to the surface. Any air removed from the inside will quickly draw a vacuum on the boat. Towards the end of WWII or just after, some countries did experiment with fuel mixed with hydrogen peroxide with has some liquid oxygen or something in it to run diesels underwater for short bursts. If I could find a liquid cooled diesel small enough that would be best, but I might be able to adapt something. I thought about a divider between me and the engine, but the only thing is it would need to be removable to work on the engine. The hatch will be the only way into the hull once everything is welded. Actually I should be able to run on batteries for an hour or so without much issue if I have enough capacity. By that time I'll need to surface to refresh the air inside the sub anyway. As you breathe, CO2 builds up and also the oxygen is used out of the air.

alliskid - Thanks!

Here's a video of something similar to what I'm doing. This is a Kittredge K-350, there is also a smaller K-250. A guy built and sold them starting in the 1960's but later stopped due to insurance costs I believe. Wonder why.... but you can still buy plans for them and people still put them together themselves.

Oh I meant charge up the air compressor on the surface with the hatch open, then close the hatch, shut off the compressor and dive. And use like a 5 gallon compressor. one of the larger ones. That would run the diesel for a little while...

Like store air in a tank to use for running the diesel? It's an idea but I think the volume needed to run more that a couple minutes would be huge. And I'll already have air tanks taking up a lot of room for blowing the water ballast when you want to surface. For air tanks I was thinking of using four 250 cubic foot oxygen tanks like the ones on an oxy acetylene torch. The air compressor I have has a safety valve set at 160 psi, I was hoping to be able to get 200 out of it. It's tough to find any air compressors rated for much over 150 psi or so. But like the guy in the Apollo 13 movie says, I don't care what anything was designed to do, I want to know what it can do.... I've heard guys say the old cast iron air compressors can handle quite a bit, one guy even said they would put out 300 psi. Once we had a large compressor that had the shut off stick and it ran till the safety valve blew on the tank which was at 200, so it should work ok. The more air I have to work with the better, because you need more pressure to blow the ballast out at greater depths where there's more pressure. Oxygen tanks are usually filled to something like 3000 psi, so they would be good and rugged. Maybe add some moisture drains and check to make sure they are coated inside.

Here's the compressor I was going to use. I have the pulley for it, just missing in this pic.

mr.modified wrote:

Like store air in a tank to use for running the diesel?

Yeah thats exactly what i meant. A 5 gallon compressor at 150 psi is quite a bit of air if you're only giving it like 2 or 3 psi. I don't know how much it would take to keep it running/how much air it uses at any given RPM. I just don't know how to run the numbers...

I got one of those too, I use it for sand blasting, LOL. Should work to 300 psi if you remove the gaskets on the head and resurface it so you don't need gaskets, replace the bolts for stronger ones. I use a 6 hp for 150 psi for sand blasting and barely is strong enough. Will be using every bit of that diesel to reach 300 psi but I can see it happening with a big enough pulley on the compressor.

I'll probably have to do some testing before deciding for sure what to use in the sub. Anyway, a little more progress on the model. Rear deck mostly finished. Mocked up a tail section and rudder from card board before I weld them up from steel. Top section/conning tower welded on.


Some plastic gutter guard looks like mini expanded steel, which is what I expect to use on the real deck. Sides will be covered over except there will be a small gap at the hull to let water through.


What I imagine the exhaust system outside the hull will look like. Somewhere in the line there will be a muffler. I thought it would be neat to just T the pipe to both sides to make it look like the the full size boats with twin engines. May or may not be that way on the real one. There needs to be room for some linkages under the deck also, such as those for the rudder and ballast tank vent valves.


Just a rough mock up of the rear section. The tail will support the rudder and the rudder linkage rod will be inside of it. I imagine something will be needed to hold the bottom of the rudder also and protect the propeller somewhat in the place of that piece of flat steel seen in this pic. I just set that there to hold the rudder for now.


Welded the skids on the bottom of the hull. On the real boat these will be steel I beams. It was easiest to get square steel to use for the model so that's what I did instead. Parts of the I beams on the real boat may be boxed in anyway to hold lead ballast weight, so it may end up looking something like this anyway. In between the skids there will be a safety weight which you can release to add buoyancy and maybe a small auxiliary ballast tank.


Need to finish the rudder, tail, propeller, forward deck/nose, and air tanks on the side. Then it should be ready for some paint and after that I can start on mocking up a full scale model of at least the middle portion of the sub from 1/2" electrical conduit. I plan on welding up a skeleton of pipes in the shape of the hull so I can make sure I'll have enough room inside before I buy any propane tanks.

Lookin' good Mr mod. Model actually looks pretty smart.

Looking good man! Only question i have as of right now:
How is your motor going to get air to run it while underwater? Im sure theres something im overlooking but it is something that puzzles me.

Thanks. While on the surface, the hatch is open and you can run the diesel engine as normal obviously. To submerge, the diesel is shut down and you close a valve that the exhaust runs through to seal it off. Submerged you run on an electric motor powered by a bank of 12 volt batteries. Once back on the surface you can recharge batteries again.

There are two options for getting power to the propeller. One is to have a propeller shaft and clutch either the electric motor or the diesel to the shaft as needed. You could use v-belts I guess, but there isn't much space inside for this setup. German WW2 submarines were sort of like this, with a diesel in line with an electric motor and the prop shaft, with clutches between each.

The other option is to drive the prop shaft from an electric motor all the time, surfaced or submerged and run a generator with the diesel on the surface. Basically a diesel electric setup. This is somewhat simpler to make and use. It would probably be more reliable and fit better also. This is how American WW2 subs were set up.

I guess a third option is to mount an electric trolling motor outside which is how most other mini subs are, but I would rather run a shaft through and keep everything inside. Space is extremely limited. I'll only have a 28"-30" diameter pipe to stuff everything into. Pretty sure one of those yanmar diesel clones will fit ok, but it'll be pretty tight.

Oh ok. That makes a lot more sense i thought you were gonna run it underwater

I could make a snorkel and be able to run the diesel just under the surface, but in that position, I'm almost blind to what's happening top side. I don't really want to spend much time in a lake that way in case I get hit by a boat. The submarine would be tough to spot with only a couple pipes sticking out of the water. For a periscope I was planning on using a camera on a rotating pole, then inside have the image on a small tv screen. I would just need a camera that you can wire up to a tv. Also if I could find one with zoom that would be ideal.

Glue that thing to the top of the jeep when its done.

mr.modified wrote:

For a periscope I was planning on using a camera on a rotating pole, then inside have the image on a small tv screen. I would just need a camera that you can wire up to a tv. Also if I could find one with zoom that would be ideal.

Could use a waterproof action camera with integrated bluetooth and a tablet that can run its app.

Yeah periscope on the jeep would be nice for parking lots. So your saying have a wireless setup? I'd rather have a simple direct wire connection but it's an option. I'll have to see what's available semi cheap. I have a screen from a dvd player that was inside a junk car which I guess runs on 12 volts.

Maybe browse some electronics forums, im sure theres a way to output video from a camera to RCA. Or maybe a webcam.

Yeah I'll have to do some research, I don't know too much about all that stuff. I would just fab up a real periscope, but the limiting factor is space inside the sub. With a real periscope I would have to be able to move my head 360 degrees around it to get a full 360 degree view. And that's not happening in there. Your pretty much sitting in one spot and that's it. A camera on a rod on the other hand, I could just turn and have an arrow or pointer inside so you know which direction your looking in.

If I correct this is going to work like a diesel electric train?

Correct, that would probably be the easiest way to hook everything up and also the simplest to operate.