Civilian Vehicles Submarines

R

rust

Mongoose
I just finished my first draft of a submarine with the Civilian Vehicles
design system, and I am not exactly pleased with the result, for exam-
ple the speed.

However, the worst problem seems to be the mass: My submarine has
a volume of 250 cubic meters, but a weight of only 140 tons, and nei-
ther ballast tanks nor enough free space for other kinds of ballast - it
can not dive.

Looking at the design examples in the Civilian Vehicles supplement to
see what I had done wrong, I discovered that all four submarines there
are unable to dive, too:

The Deepwater Sub on page 79 has a volume of 28 cubic meters and a
mass of 6.28 tons, the Research Sub on page 84 has 102 cubic meters
and 22.8 tons, the Submarine on page 88 has 55 cubic meters and 13.6
tons, and the Submersible on the same page 8 cubic meters and 1.5 tons
- in each case the flotation is significantly higher than the weight.

So, either I am missing something important, or the design system has
a very serious problem when it comes to submarines. :cry:
 
So your saying you have no empty spaces? All the ballast tanks, and sewage tanks, would fill in those empty spaces. I assume you built all your internal spaces as squares or rectangles? There should be plenty of spaces to fill with these tanks. Be sure your looking at it 3 dimensionally as well.

Whether the build system takes this into account or not. If it doesn't you now know where its failing.

Plus it may help to be aware subs, at least the type I was on, was built with an inner hull and an outer hull, and most of these tanks were in between those two hulls.
 
Thank you very much. :D

Yep, I see the problem now, and also several ways to deal with it. How-
ever, the design system as written ignores it, and so I missed it when I
followed its steps - and then discovered that the authors obviously had
missed it, too.

One way to handle the problem are the ballast tanks you mentioned, for
smaller submarines one could also use the "deep flight" concept and just
give them a heavier hull (= add armour) or heavier engines to reach the
required neutral buoyancy, and so on.
 
Thank you again, a lot of most useful information for the vehicles of my
water world setting. :D
 
rust said:
Thank you very much. :D

Yep, I see the problem now, and also several ways to deal with it. How-
ever, the design system as written ignores it, and so I missed it when I
followed its steps - and then discovered that the authors obviously had
missed it, too.

One way to handle the problem are the ballast tanks you mentioned, for
smaller submarines one could also use the "deep flight" concept and just
give them a heavier hull (= add armour) or heavier engines to reach the
required neutral buoyancy, and so on.
Click to expand...

You may be right, while searching for those links I saw a very general schematic for deep sea submersibles, and they look densely packed together, so probably need very little in the way of ballast tanks, even though I know Alvin has them because I have watched dives by it on Discovery Channel, and they definitely used Ballast tanks. But likely very small tanks, maybe only 50 gallons.

EDIT: Which would account for over 400 LBS of weight change.
 
I was thinking of these ones, basically "underwater aircraft". The current
versions do not yet have a good diving depth, but the concept seems to
work:
http://www.deepflight.com/
 
Hi folks,

I'm the guy who sort of prevent rust's submarine fleet from submerging. I figured I'd pop around and chime in on this.

First off, what determines if a ship float or not is buoyancy. If a ship weights less than the water it displaces it floats. If not it sinks.

How submarines work is that they use ballast to take on water, changing their weight from less than the water they displace to greater than the water they displace, allowing them to submerge.

Now in metric this is easy. 1 m3 of water mass 1 metric ton (okay, sea water masses 1.026 per m3 but 1 is close enough).

You can tell how deep a sub will sit in the water by how close it's weight comes to it's displacement. For something like the Alvin, I suspect that even on the surface it is barely floats. Considering that they put 4 200 lb weights on the thing to make it sink faster, I doubt it floats normally, and is probably held up by a crane.


You can actually reverse engineer the size of the ballast tanks of a sub by using the difference between submerged and surfaced displacement. For example the Simon Bolivar has a displacement of 8250mt submerged, and 7250mt surfaced. So it's ballast tanks would be about 1000m3. Well actually a bit bigger, since the U.S. Navy lists displacement in long tons (2240 pounds) instead of metric tons (2200 pounds), but again it's close enough.

Since we know the weight of the water is 1000 tons, we can work out that the sub, without ballast, must weigh more than 7250mt but less than 8250mt.

So to make a sub "work" you just need to make sure it's weight is high enough that the weight of the ballast tips it over 1 ton/m3.

Now in a Sci-Fi setting one option would be to use anti-grav in reverse, to increase the gravitational pull on the sub. If they could do that, they could double the effective weight of the sub and make it sink like a stone.

This would not only allow the sub to dive and surface faster than a conventional design, but also has the benefit that if the sub were to loose power it would surface automatically. Infinitely superior to a sub with ballast tanks. If the ballast tanks get damaged, a conventional sub might not be able to surface.

Oh, BTW rust, the Alvin actually uses Titanium armor! It looks like Titanium only needs to be about half as thick as steel, so you might want to half the Armor requirements.


As for the "flying" sub. I doubt they will be able to get it down to 6km. It appears to be a submersible (not entirely autonomous), and I don't think it has a pressurized crew compartment. Many submersibles are not sealed, and require the crew to wear SCUBA gear.
 
The Bolivars hull is a alloy called HY 180 by the US Navy. I am not sure if Titanium was in that or not, but my distant memory wants me to say it was. However, if you really want to know look for a far more reliable source than my 15+ year old memories.
 
atgxtg said:
As for the "flying" sub. I doubt they will be able to get it down to 6km.
Click to expand...
So do I. For my setting I see them as the equivalent of a normal car,
something one uses to move from one seaflloor settlement to another
one, or to take a look at one's kelp fields, without getting wet and cold.
Since the settlements are all less than 300 meters deep, it should work
well enough, at least one the vehicle has got an airlock enabling the
passengers to board and leave it without having to surface.

"Buoyancy" could be a translation problem, it is what my dictionary of-
fers for a vehicle's ability to float at a certain depth without having to
run the engine to keep this depth, so a vehicle with "neutral buoyancy"
could "fly" upwards or downwards with a minimum of engine power re-
quired - the way these deepflight subs move.
 
Just design the sub via Eye and don't sweat the details, only you the GM need know all of them. Design the sub as you want and need it to be for your game, and don't worry about the specs so much. Remember this is SciFi Fantasy and not "Build a REAL sub" game. If something is off, OH WELL. As long as it works for your needs in your game, who cares or needs to know. The whole point is to "Play a Game" and "Have Fun" not build a sudo-real sub guys. So just GM it and MOVE ON!!!

Penn
 
Bygoneyrs said:
Just design the sub via Eye and don't sweat the details, only you the GM need know all of them.
Click to expand...
The problem with this is that we do not play space fantasy, but science
fiction, and that the players expect me to know the important details -
plausible ones - whenever their characters ask for them.

The idea of a vehicle design system is to enable me to design those de-
tails in an easy and fast way. I do not mind minor problems caused by
the necessary simplicity of such a system, but submarines unable to di-
ve is more than a minor bug ...
 
Ok Traveller is a Non-Real Science Fiction RPG, I used the word "Fantasy" because it is "ALL" smoke and mirrors of Fantasy...really!

Now I am a "IT" professionial, and I think in deep details in presenting any Techno-Babble (SciFi Tech that really doesn't exist but only in this game). I have always tried for "realistic setting" but not everything needs to be explained, and you can present all the details that are enough to fill the setting with sudo real tech that fits the bill for the playing experience.

Sorry I don't see the point in crunching the numbers to get a semi sudo non-real tech to seem perfect as to look like the game specs, when a bit of good GMing can gloss over and do the job just as well. Sorry I guess my style has been developed after playing RPG for 32+ yrs and having a running Traveller campaign (non-Stop) for over 20+ yrs with a group of players (5-7) that are all GMs as well and each have their own gaming groups as well. We play every other week my game, and they GM their own gaming groups on our off weeks. These same group of guys and I have been together for over 20+ yrs, and we all do the same thing. So I would say number crunching isn't as important, as the character and spirit and flavor of the game is.

Penn
 
Bygoneyrs said:
Just design the sub via Eye and don't sweat the details, only you the GM need know all of them. Design the sub as you want and need it to be for your game, and don't worry about the specs so much. Remember this is SciFi Fantasy and not "Build a REAL sub" game. If something is off, OH WELL. As long as it works for your needs in your game, who cares or needs to know. The whole point is to "Play a Game" and "Have Fun" not build a sudo-real sub guys. So just GM it and MOVE ON!!!

Penn
Click to expand...

That raises the quest "Why bother to have a design system at all?"

Anybody can just make stuff up. The point of a system is to make stuff up according to some logical guidelines.

Now as a gamer, I concede that it isn't important to get all the details, or for imaginary future tech to work out perfectly.

That said, I do expect some rationality and for the basics to be right. I expect water to be wet, fire to be hot, and such.

I don't think it is too much to ask for subs to have a weight greater than their volume in order to dive (and for surface ships to have a weight less than their displacement in order to float).

Likewise, I don't expect an RPG to work out top speeds to 100% accruacy using wind tunnel or wave tunnerl tests. But a decent ballpark figure isn't too much to ask for, is it?

The problem with design everything "to Eye" is that most people have no idea what good "eye" values are. Or what little they do know, will result in designs that are immediately recognizable as wrong by anyone with a passing knowing of the field.

For example, "by Eye", someone might think that since a typical sedan has a 120hp engine and a top speed of 90mph, the same car with a 240hp engine could go at 180mph.
 
Besides, the use of a design system helps a lot to avoid arguments be-
tween referee and players, because values determined "by eye" instead
of with an agreed upon system suffer from the problem that referee and
players can have very much different ideas of what is plausible - they
may not "see eye to eye". :wink:
 
If you don't tell them, nobody is going to count up the squares and add up all your tonnage, unless you're way off. Just go with what looks good, and is close. If your players don't like it, invite them to design the vehicles they way they like, when they are running the game.
 
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