French Submarine Surcouf

After a very long time out of the hobby, I have moved to Dallas and yesterday joined the NTXBG!

The guys in NTXBG already started pressuring me on what ship I want to build. Honestly, I should just buy a used heavy cruiser or pocket battleship and be done with it! (and I still might) However, I have always wanted to make a sub; and I figured it doesn't cost anything to mock it up in Fusion 360. If it works - Great! If not, oh well!

First question: Which sub?

Size is obviously the biggest factor, and width in particular. The largest sub in our hobby seems to be the IJN-400; which is a 3-1/3" wide aircraft carrier with torpedoes.

The Surcouf is a bit smaller, coming in at 2 1/2" wide and has the 8" cannon from a Heavy Cruiser on top. I think the position of that cannon makes it particularly interesting. If the model works, most of the sub can be submerged and still firing.

I was happy to find some plans on RC Warship Combat from my old pal @Tugboat. Thank you sir!

Frankly, I have a lot of concerns which could kill the project. This ship would simply not have been possible a decade ago, but the technology has changed so significantly!

I do think I will have to make a lot of hard choices to make the ship viable for Big Gun combat. In particular, I think I'm going to need to use the Small-Gun weapon design/style just to get the CO2 canister small enough to fit. NTXBG allows ships to return to port during battle. So I expect hot swappable batteries, CO2 canisters, and small ammo payloads will be key in this design.

Finally, I checked the Big Gun rules from NTXBG and didn't see any showstoppers. So, with that, I got started!

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So, I'll admit I already started drafting the ship a week or so ago; incase the sub became too hard too quickly.

I also want to write this thread in phases, so others can comment on improvements or concerns with my approach.

That said, for transparency on the first thread, here is the current state of the drawing in Fusion 360:

 

Ahoy, Justin, congratulations on volunteering to join the ranks of the Submariners! The challenges you face are many, the rewards few. But if you succeed, the submarine is an absurdly powerful weapon. A few thoughts, based on both the non-combat and combat submarines I've seen in action:

1) How do you plan to dive?
This is one of the most important questions you'll have to figure out, because diving is the only difference between a submarine and a very slow, very squishy destroyer. I am presuming you are already familiar with the basics of dynamic-diving and static-diving systems. My personal recommendation is to use static-diving, with one or more large-diameter syringes driven by a high-torque servo or a small positive-displacement pump to act as ballast tanks. You'll also want to have stern planes to control ship's angle during an attack. What you definitely don't want to do is use CO2-blown ballast tanks. That's messy, and the tiniest of leaks could result in you not having enough gas left to surface.

2) what weapons do you plan to use?
This is the second-most-important question you'll have to answer. The NTXBG is a Big Gun club, correct? If so, you'll almost certainly want torpedoes. A deck gun, even a twin 8" deck gun, just doesn't pack the killing firepower that a submarine-launched torpedo does. You can very easily arm the Surcouf with two or four forward-facing torpedoes. Charge it on shore, blast something, then come back to reload. You also mentioned the possibility of arming the deck guns with Fast Gun style cannons. This is also entirely possible and gives more time between port visits, but doesn't have the same penetrating power and flooding that torpedoes do.

3) how do you plan to access the innards for battery charging, reloading, repairs, etc?
Another difficult question to answer. One submarine I saw had about 40-ish deck screws and a rubber gasket around the top deck. This sometimes leaked, and resulted in sinks. Another submarine I saw put the access hatch on the bottom, with a similar setup. This arrangement was less prone to leaks. Another sub only had access ports for charging batteries and filling the accumulator from a compressor. Any service required removing the sheeting on the sides. Finally, I have seen a few non-combat submarines that would break in half for service. The middle was an interrupted screw, with an o-ring seal. Twist the front of the ship 45 degrees, and you could pull it off to access the guts.

4) What radio do you plan to use?
Since water effectively blocks 2.4ghz radio waves after an inch or two, how do you plan to control your sub? If you don't have an old 75mhz system, it may be worth shopping around. Maybe @Z Boat has a better idea.

It's good to hear the NTXBG is still alive and active. I haven't heard much from them in several years. Good luck and happy sinking!

 

So the first thing I did was I took the original plans, and scaled and aligned them. That was actually pretty frustrating because I think the plans were actually scanned from a book? They were "pretty good", but many lines weren't quite square. I decided not to sweat the details, and made everything "close enough".




So going back to my basics of building ships with wood, I've started the Surcouf the same way... drawing the ribs. The only difference is no sawdust this time!

I needed a way to align everything, and many of the smaller ribs didn't touch the deck nor the keel. So, I simply drew a random line through all of the ribs which would be marked on all the ribs.



I knew that the keel and deck would not match up perfectly, so I was going to have to adjust them. When I did I figured it would throw the curvatures out of whack. So, that random line also gave me a place to anchor the curvatures and many other little things later.

This photo is also showing the penetrable cut outs too, which was a PITA that I'll talk about later.




So here are the ribs in their position, aligned with the line markers on the hull plans.

 

Hey man! It's been a minute! How have you been!!! What you been up to?

My plan is to keep it simple, and iterate. I want to get it battling as my first priority, even if it doesn't work well. I will then add the next most valuable feature, based on what I learn during a battle.

To answer your question; I want to start with dynamic diving then later add static, if things work out well. That said, I would absolutely LOVE to see photos of your setup.

NTXBG is a Big Gun club, yes.

I want to try the top cannon as my priority, actually. It's a dual 3/16" cannon and I want to use some of the techniques that I learned from @GregMcFadden's fast-canister-gun.

My vision is the ship would fight mostly submerged with only the cannon above the surface. I'm hoping the water depth and the hull angle would be as good as extra added armor. The 45-degree inward curvature at the top of the hull makes for a lot of hard area, which I'm seeing as a bonus. If I have to surface the whole ship to fire torpedoes, I'm guessing I would have chunks taken out of me. That said, I have no idea how hard it would be to keep the ship "mostly" submerged, nor do I know how deep 1/4" bearings are still effective.

That said, if you have any videos of your battles; I would love to study them!

My plan was accessing the batteries & CO2 from the bottom, BBs from the top, and printing the hull to break apart across the beam for repairs.

That said, I haven't exactly worked any of it out yet. I'm only today starting to figure out where the internal parts COULD go.

I saw that your ship keeps the radio mast above the water. I thought that was a clever idea that I figure I will steal.

That said, as low as mhz as I can find on eBay.

COVID hurt them for sure. The next battle is planned for October, but I think it's the first in 2022. They also lost their pond and were forced to go to a secluded location which hurt new-members "encountering the hobby". They finally have another publicly accessible pond, and they seem hopeful they'll be able to get the foot traffic back again.

Hopefully, now that the world is getting back to normal-ish, the club will pick back up. TBH - this is my number 1 concern about building another ship. Will I once again have a toy and no place to use it?

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Question for you @Kotori87 -
What are you using for a CO2 bottle? A 3oz is a pretty snug fit in that hull.

 

Joseph and Z Boat are the most recent submarine builders I've seen. Hopefully one of them can add their comments. For clarification - I have not built a submarine myself, but I have seen around 5 or 6 combat submarines built at various times. Three of them even battled! I also attended several Sub Regattas specifically to see what interesting technologies the non-combat submariners use. I have a fiberglass I-400 hull in my garage that I would love to build... eventually... Although, that CAD model is looking mighty fine. And I am very easily distracted...

Gascan and I moved out to Washington state late last year. The Washington Cascade Column was in similar straits - hit by Rona and lost access to all public ponds. We found a privately owned pond over the winter, had a few build sessions, and started having battles a couple months ago. At the first battle, I think half the ships on the water were from my fleet, either operated by me and Gascan or loaned to other captains whose ships weren't battle-ready. Over the past couple months, those loaner ships have brought a number of club members back and got them motivated again. Last battle, a few potential new members got to drive the convoy ships around. That's the most important thing - have a battle, even if not everything is perfect. It's amazing how quickly people forget how awesome this hobby is.

Anyway, one of the nice things about a torpedo cannon is that it doesn't require a CO2 bottle at all. No regulator, either. It's just got an accumulator tank that you charge with an air compressor on shore. Very simple. If you want reloading deck guns, then a disposable cartridge may be best. One 16-gram is good for a 50-round bb cannon. Of course, then you have to worry about lost ballast from CO2 and bbs affecting buoyancy. An ounce of CO2 plus the ammunition is a fair bit of mass to a submarine. I have no idea how much of a problem that actually is, though. From a submersible perspective, you really don't have to run deep. Even if your sail is poking out of the water, you'll still be immune to everything but point-blank cannon fire. Dive a couple inches down and you're untouchable. I think that's one advantage of a Surcouf, it has a nice big sail so it's easy to achieve that not-quite-submerged condition for cruising and attacking.

 

Next step is on to the penetrable areas. I hated this part & I'm really glad I was able to draw it in CAD so I could undo several iterations that I did not like.

The first step is to read the rules, then re-read the rules, then read the rules again.

The first rule is easiest to understand: the penetrable areas must cover 85% of the ship. Some quick math and a couple lines later, I found the layout that I'm going to start with.

I want to keep as much hardscape in the front of the ship as possible, here are my thoughts:

• My vision for how this ship will fight is to point the sub's bow directly at the side of other ships, firing as close as possible, then submerging before I collide.
• The bow is SOO thin, I don't want a lucky shot to find its way through both sides of the ship.
• This is a big gun ship; so I expect the ship will be traveling forward most of the time. Holes in the front of the ship will have water pressure pushing water into the ship, sounds like what I don't want.

As such, I want as much hardscape in the front of the ship as possible.

 

It's been a while my friend! I'd love to catch up!!!!

I will download your new designs & study them, thank you for all the hard work!!

 

OK, so now time for the real PITA... the penetrable windows.

So, the NTXBG rules seem pretty clear, albeit it's still an art more than science. The essential things I'm seeing are:

• No deeper than 1" below the waterline
• No need to have penetrable areas with angles of 45-degrees inward.
• 3/8" cap rail

So, I first needed to find the waterline. From the photos of the prototype ship, it looks like waterline is just under the large curvature. I set it at 0.10" above that magic line that I drew in all the frames.

The large curvature is greater than 45-degrees, as it's almost parallel with the waterline; so I believe that to be all legal hardscape.

There is also a flat shelf about 1/2" below the waterline on many of the frames. I perceive that is additional legal hardscape.

The only question I really have is the top rail. It's like <0.46" before the rail turns to 45-degrees.
---> Frankly, I'm not sure if it make sense to make a cut out for a space which is smaller than a BB.

Here are the NTXBG rules:
a. The maximum combined thickness of the deck and cap rail shall not exceed 3/8 inch except as defined in item b.
b. On ships with at least 1-inch penetrable freeboard remaining the cap rail may be ½ inch thick.
c. The cap rail will be located up to 1/8” below the top-most deck of the hull. On an aircraft carrier, the top-most deck of the hull is defined as the hangar deck.






For the front ribs, I again relied on that magic line to find the waterline.

At the bottom, I also drew a 45-degree 'protractor' to find the tangent where the hull turned 45-degrees back inward. On this frame the 45-degree inward turn and 1" below water line were at the same spot!

Blast Shields
You'll also see that the depth is set to .313" (5/16"). This is for the blast shield. NTXBG states the min offset the blast shields can be from the hull at 5/16".

I have it in my mind that I want to print as much as I can, so at least for now I'm planning to print the blast shields in place. I just don't know how thick of material I'll need against the 1/4" bearings.

At some point, I'm probably going to replace the straight shields with ones that curve with the hull. This should make them stronger and give me more internal space back.

 

After I got the ribs the way I wanted them, the next phase was to use the loft tool to create the body of the hull.

This was the most satisfying of all the steps so far, however it really showed the inconsistencies with the sketches.

I found that allowing the loft to go (nearly) the entire length of the ship created the best shape as it flowed the shape from the front the whole way to the back. Fusion 360 also really had a lot of trouble on this step. I guess it really struggled with all that information. I'm not sure if there is a better approach, but this technique got the job done.

I also wound up going through every rib multiple times finding ways to anchor the shapes and curves to that magic line. This let me iron out the small inconsistencies which created ugly ripples in the loft. You can see much of those constraint in the sketch in the above post.







The bow and the stern were significant changes in the shape, so I created them as separate isolated structures. Otherwise, they changed the shape of the loft from the inner ribs. They were then "joined" to the main hull body.

 

The next phase was to create the penetrable windows. For this to happen all the hard work was done earlier in the sketch phase. So, to create the look, I used another loft to 'cut' the shape out of the new body.

I specifically stopped the cut at a specific depth as an attempt to 'print' the blast shield. I will cut holes or similar to let the water through, once I place the internal parts & know that the blast shield concept will really work out.

















Now that I have a very large channel, it's time to add some support structures for the balsa.. AKA 'Ribs".

For this, I just used a symmetric extrude on the same squares that 'cut' the channel in the first place.

 

Next time, create a grid sketch and use that to make an equal number of spline points. Also attach guide rails. It will make the lofts a lot cleaner

 

I've had difficulties with questionable cross-sections before. I ended up doing something similar to what you did, with big lofts that covered large portions of hull, then massaging individual rib profiles until everything looked nice. Same thing for the cutouts. Gridded spline points can work for some hull shapes, not for others. I still struggle with the bow and stern shapes though. I'm still not truly satisfied with my Mikasa's ram bow.

 

Thanks!

Haven’t encountered a grid sketch yet. Will look in to it. For number of points, I just manually kept it consistent. I didn’t need many for those curves to work.

There was one where I added a second point before I got consistent. When I saw the resultant loft, I immediately cleaned it up.

I thought about a defined guide rail, but couldn’t figure out a way to do it at the apex of the curve - which is where I most needed it. That edge goes inward AND down… It looks good how I have it, but if you can recommend an approach I would certainly do it.

 

I used a lot of constraints on the common shapes, angles, and proportions of each rib to drive consistency.

My favorite approach was the center spline point on the top curve was equidistant between the next two points. Those next two points were consistent-height splint points but moved horizontally. This made the curvature shrink, but the aspect remained constant... just like the prototype ship. My brain was having a good day when I thought of it.

 

I'm glad you figured out a solution. It's looking awesome!

 

The next step was to get the superstructure designed.

Even though cannon rotation is not a day 1 feature; I do not want to prevent it. So, I'm going to cut the hull to allow it. This was a simple sketch followed by a cutting-extrude.





Next, I repeated the same process, instead with a new body extrude. This body will not be joined with the main hull.
- Note: it was not the same sketch this time, I added a couple mm of tolerance between the rotating bodies.





Next it was time to create the superstructure. This was pretty challenging. I couldn't just use a dumb loft because the sweeping nature was too aggressive. It looked more like a witches nose than a sub's superstructure.

So, I decided to build it as a summation of smaller pieces. First I modeled the one dimensional round bulges, For this, I used the loft tool again. The problem I ran into with Loft was that it tried to make these things more like triangles. In the loft tool, you can use the "direction" property on the profiles to give it a more weighted effect, which gave me the nice round curves that I wanted.








After that, I wanted to connect the new bodies with that nice sloping piece in the middle. This was again a simple loft, but this time I used the faces that were created on the round bodies (instead of the sketches). This gave me a nice smooth look as each body transitioned.

Loft tool still tried to create a much sharper transition that I wanted, but the tangent & curvature settings helped create the look I wanted.





Next, I used the same basic techniques to create the front and aft bulge, using the same tangent tool.







Finally, I created a sketch & extrude to create the AA-deck. I just brought it up through the superstructure, exposing it on top.






Lastly, I used a pair of extrudes (join then cut) to create the tower shell that you see in the photos.

 

Now, it was finally time to add the other side of the ship!
- It looks pretty silly as 1/2 ship...




This was as simple as creating a couple Mirror operations on the various bodies.







...and that about catches you up to today.

 

So, now I have my first real problem. I need to find a way to fit all the guts into this ship.

The CO2 bottle is the first problem. I know I can do an accumulator with single shot torps, but that's really not my vision.


Here is a 3oz bottle WITH the BC regulator in the hull. It does fit, kinda. Once I add thickness for the hull/etc; It'll be absolutely way too tight.

I'd really love another option if anyone has any recommendations for a smaller bottle?

 

Maybe something like these ?