Ballast on Submarines + other Sub tricks [Stock].

[Aeroboi]

I wanted to experiment with building subs recently and I know many people like them.

I tried to play with part buoyancies and found a out 2 neat little tricks using the Vector engines and Inflatable airlock (Making history).

Vector Engine

Let's explain...

1. I used vessel mover to locate a Mk1 inline cockpit with 2 Vectors attached fwt and aft (shrouded) with gimbal and thrust put to 0.

2. I dropped the vessel. Watch the mission timer to see it had settled several seconds...

3. In the next picture I staged the Vector engines, and see what happens...

4. Since I created ballast the vessel starts to sink, eventually at a great increasing speed... so 3 seconds later!

Conclusion: In other words, staging Vectors (who would sink by themselves when not staged) you add extra ballast. Unfortunately the process can't be reversed by the looks of it. When staged they have added ballast but if you were to shutdown they do not revert and the extra ballast is permanent. That means ISRU vessels would have to much ballast if they were to refill. Although I haven't tried if you could re-dock vectors to the sub and re-stage them would be a workaround, maybe someone else will see before I do.

This trick is a very good thing since using jet engines underwater you will loose fuel mass and the ship becomes more buoyant. While vectors would sink by themselves anyhow you could add them to adapters or on the sides. The vector shrouds look submarine like anyhow, are very aero/hydrodynamic and you could stage them in sequence to add ballast as you burn off fuel. Of course you'll have to place them so that they re-balance evenly.
There are other ways to alternate buoyancies by close/opening cargo bays. If a cargo bay content is buoyant it will be calculated when the cargo bays are open while open cargo bays themselves are more buoyant when open. You'd think they'd fill with water and would therefore sink, silly developers lol.

Using vectors would be better weight wise since they'd sink by themselves anyhow and using cargo bays you need more weight to submerge so the overal weight of your sub will be higher (that's less speed and less fuel economy)
 

Inflatable airlock

Again I have a Mk1 cockpit with 2 Vectors but 2 on one end with 3 inflatable airlocks at the top.

1. Again I start off with the Vectors un-staged and the Vessel nearly doesn't sink due to the closed airlocks being (slightly) buoyant.

2. I staged the Vectors, several seconds later...

3. I opened all 3 airlocks (requires just only 1 to be slighly buoyant, 3 is more impressive)

4. Several seconds later.

The neat trick is that you can use a vector only Submarine and stage them to add increased ballast. On the other hand you can toggle airlocks to increase/decrease ballast.
A staged Vector may not be as heavy in water as a Ore tank Mass to Mass but you can clip, stack and form factor to 1.25m only for potentially faster more aerodynamic submarines.
Because the effect of a airlock mass to mass and per magnitude of effect using a single airlock you could combine the effect of both to fine tune ballast.
If your intention is to use the airlock fine tuning could be easier if the mass of the Sub is heavier. Try to distribute them evenly for balance.
Put the airlocks on action groups to tune the effect as you burn of fuel.

You may be able to stuff a cargo bay with ore/vector ballast and put the airlocks inside to decrease drag for faster speeds and have free ballast control.
Happy diving

 

 

Edited March 30, 2019 by Aeroboi

[Aeroboi]

Update!

Best solution for hydrodynamics.
 

1. Diverterless supersonic intake.

So I did a few tests and I've come to the conclusion that the "Diverterless supersonic intake" is the best solution when using underwater intakes. It doesn't say "diver" terless for no reason...

This is weird because these tubes have these air scoops sticking out which would increase resistance in water one would presume. Maybe the scoops are scales like on a actual sea animal, who knows...
It seems the Pre-cooler and engine nacelle do slightly worse. The other added benefit is that the Diverterless has the most air intake at low speed, and as we all know, subs are slower so it's the best choice to get the most intake air underwater of all the available intakes. AFAIK you need one per jet engine but you need forward speed for the intakes to function properly so the Sub shouldn't sink to fast at negative velocity to potentiate the effect of a air intake underwater.

2. SM-25 Service module.

So what about the rest of the vessel? I wanted to find the most hydrodynamic way to propel underwater for the fastest speed. The most Hydrodynamic way of doing things known and ducumented is to just stack the large ore tank and make the front and aft pointy using engine plates, adapters and proper nosecones.
Having tested I could never go much faster then ~50m/s underwater.

The large ore tanks have these curves around them and by the looks of it isn't the most dynamic shape of what might be possible, then again, what else is there to sink that is 1.25m or 2.5m wide apart from the other ore tanks and vector engines?

Well, nothing really. However, I tested the submergeability of several parts and found out that the SM-25 Service module (which is buoyant) doesn't require that much added weight in order to submerge.

What's best about this Making history part is that everything within the shroud is protected from drag.
The other benefit is that it seems to be much more Hydrodynamic when submerged then stacking the large ore tanks together. In fact, it is noticeably better.

1. Result (60.6m/s, I did 62.7m/s on the same design with proper balance but forget to screenshot it) That's upwards of 225Kph underwater (which is fast)

2. Another view.

 

What Ore container is best?

I did a few tests to see what Ore container is best, do they all sink similarly fast? Absolutely not and there's a clear winner.

I created this test bed and staged all 3 ore containers filled using seperators at 0 decoupling force for fair comparison...

Result =

Several seconds later...

In other words it is the "Radial holding tank" that sinks fastest" and has nothing to do with it's hydrodynamic effect since it sinks fastest from ~0m/s up to 18m/s until hitting the ocean floor.
Now, if you were to wonder how does the test Sub above sinks? Well, it has the radial holding tanks inside the shroud.
Because the radial holding tank sinks fastest relative to it's mass it means the Sub can be much more lightweight then usual.
While weight in and of itself doesn't matter in terms of speed much it does mean you have more fuel to ore mass ratio so you could make subs that could travel faster as you would have more fuel compared to ore mass when using the radial holding tank instead.

IMPORTANT thing i've learned.

The last added benefit is that you can easily move:tool the radial holding tank inside of the SM-25 service bay so you can freely re-arrange the ore mass over the fwt<>aft of the vessel throwing out many design optimizations to get the heavier then water mass (ore) into the correct position for stability.

Lightweight/compact Sub design...

Using the small holding tank you can create smaller and more lightweight sub designs. You can clip them inside the 1.25m service bay which is a compact design.
Unfortunately the 1.25m service bay seems to induce drag underwater more so then other parts such as ore tanks etc so it isn't as fast (still fast)

 

 

Edited March 30, 2019 by Aeroboi

[KerikBalm]

Intersting...

So far I haven't looked too much into sub design, let alone with only stock parts.

I'm not super interested in faster subs, since the fastest way to move a sub is to fly above the water and use a dynamic diving sub* (hydrodynamic forces to submerge), but I am interested in buoyancy and drag for better and longer range subs.

In particular, unless we get electric fans/ props, ways to make subs stay near neutral buoyancy as significant fuel is consumed.

So radial holding tanks sink the fastest, are they the most negatively buoyant?

For the service bay, doesn't it shield part buoyancy as well as drag? Can you make it sink adding buoyant parts such as fuel tanks inside of it?

* Because I want to be able to leisurely explore the ocean floor, i designed neutral to slightly negatively buoyant subs that can deploy from and recover into the mk3 cargo bays of a seaplane, so I can move submarines fast and over long distances

[Aeroboi]

31 minutes ago, KerikBalm said:

Intersting...

So far I haven't looked too much into sub design, let alone with only stock parts.

I'm not super interested in faster subs, since the fastest way to move a sub is to fly above the water and use a dynamic diving sub* (hydrodynamic forces to submerge), but I am interested in buoyancy and drag for better and longer range subs.

In particular, unless we get electric fans/ props, ways to make subs stay near neutral buoyancy as significant fuel is consumed.

So radial holding tanks sink the fastest, are they the most negatively buoyant?

For the service bay, doesn't it shield part buoyancy as well as drag? Can you make it sink adding buoyant parts such as fuel tanks inside of it?

* Because I want to be able to leisurely explore the ocean floor, i designed neutral to slightly negatively buoyant subs that can deploy from and recover into the mk3 cargo bays of a seaplane, so I can move submarines fast and over long distances

Not sure what you mean by dynamic diving, but just above water it goes faster indeed. IIRC the above Sub does 66 m/s max instead of 62 m/s underwater.

The Vector is slightly more negatively buoyant. The radial holding tank is the heaviest of the ore tanks. Plus points are that they are small and can be dragged inside any cargo container to shift the heavier then water mass. The 1.25m service bay is small and the radial holding tank just fits in to create small lightweight vessels that are hydrodynamic.
The vector has to be shrouded or contained in a cargo bay as it suffers drag underwater more so then a service bay.
The Mk2 and Mk3 cargo bays does also shield the content like in the atmosphere. In a way water is just air but heavier/soupier. But for some reason opening the doors creates a buoyant effect. The same with one landing leg and inflatable heatshield.

So the bottom line is that the service bay contains the mass (buoyant or negatively buoyant) and yes it also shields from drag. That's for the SM-25, 1.25m and 2.5m service bays (The latter though is quite buoyant)

I also create my slightly negatively buoyant. With vectors I can stage to add weight as I burn of fuel.

Edited April 1, 2019 by Aeroboi

[KerikBalm]

I assume that you mean that the radial is the densest.

For dynamic diving, I mean it is positively buoyant, but uses motion and hydroplanes/wings to force it under.

By flying, I literally mean flying above the surface, through air, using wings.

If your sub uses hydroplanes to submerge, such designs are easy