Surfs and Starships

SSWarlock

Mongoose
Looks like my Forum Search-Fu is failing me; apologies if this question has already be answered in the forum but..do MongTrav star/spaceships float? Or does the M-drive need to be active to keep a ship from sinking (I'm assuming the M-drives are some sort of handwavium-based thruster that plays nice when being submerged)?

Not sure how to decide if a particular ship design will float without the density calcs of TNE but I figured I'd at least post the question and get the thoughts of anyone who cares to reply.
 
I remember seeing the thread, but blowed me if I can find it now either.

Firstly, are we talking fresh or saline water? Fresh, I'd say not - but it depends on quite a few factors in saline and if it can float, I'd say it's borderline. It mainly, IMO depends on the ship dton to weight ratio, fuel load (it all has mass) and whether you're carrying any cargo (since if you're not, a lot of that dtonnage will be empty space, so you'd want to count your cargo space as less than usual).
 
Hi,

I seem to recall a discussion a long time ago on this, and I think (but am not positive) that since in previous versions of Traveller many/most starships were assumed to be able to float, and thus in Mongoose they would as well. (Actually, I believe that in previous versions of Traveller ships like System Defense Boats either would (or could) operate under the water's surface, but other ships were assumed to be able to float in water when refueling).

I believe that in GURPS Traveller: Interstellar Wars they have calcs for both weight and volume and based on those, most ships float, though the sample System Defense Boat only just barely does so, so that if you just fill a small ballast tank or two you could make it into a "submarine").

Regards

Pat
 
I think I'd just keep it simple and compare empty volume with filled volume. Count empty volume as empty cargo space, empty fuel space, empty vehicle/craft space, and all quarters/common space including computer. Every thing else is filled volume.

With 50/50 being neutral buoyancy of course. Ideal for powered submarine operation. For example (because I know it so well) a 100ton ship (the old CT Scout) with:

Filled volume: 15tons drives, 20tons bridge, 1ton weapons, 4tons vehicle, and 10tons fuel

Empty volume: 30tons empty fuel, 16tons quarters, 3tons empty cargo, 1ton computer

Above or below neutral buoyancy will float or sink.

Generally:

Empty cargo ships will float. A 400ton "fat-trader" with 200tons of empty cargo for example will easily float.

Loaded cargo ships will sink.

Warships will sink.
 
I recall a GDW CT adventure called "the drenslaar quest" about a cargo ship that sank in an ocean and the players were hired to salvage it's cargo. If one could find it I imagine it might have a few things to say about the subject at hand.
 
Several prior editions have added mass to vehicle and ship design. The upshot in most cases is that a ship without additional armor will almost always float, if only in iceberg mode (90% submerged), while nearly any amount of armor beyond the default will tip a ship over the limit for fresh water (1 ton per m3) and cause said ship to sink.

Even the ships that float have trim problems. Most starships are not built with buoyancy in mind, and would float nose up instead of deck-parallel.
 
As for deliberately sinking - filling the fuel tanks with (purified) water should do the trick, should it need to - and/or the cargo bay, if (completely) empty. I'm assuming here that the scoops or a hose attachment can purify the water to prevent lifeforms, silt and other debris from being sucked into the ship and you REALLY don't want salt water in there - not unless you want to run the risk of your purifiers rusting up.

Mind you, feel free, if they do so, to penalise them in the form of rust, for any extended duration in water, particularly saline (ie salt) water - having lived on the coast, I know how quickly (and it is very quickly) iron or steel can rust... and since most are Crystaliron... that'll be pretty quick.
 
Crystaliron is a madeupium material - who says it rusts? :P

The name could merely refer to its properties and the material may have no iron in it at all (though some silly author who doesn't understand science fiction could have made it so...).

As to starships floating - if their average density is less than the liquid, they float. Most would be when unloaded, specially if they are 'lifting-bodies'. Liquid hydrogen is only a fraction the density of water (7%, IIRC, but still a lot denser than air) - so being fully fueled wouldn't necessarily raise the average density too high.

Even loaded with cargo, they would likely 'float' - as long as they stay sealed. RW cargo ships do it.

Submarines float. Large deep diving ones have very thick hulls and are full of heavy gear - but they float till their ballast tanks are flooded...

Concerning armoured ships not floating by default - RW battleships do (granted, the 'all or nothing' approach meant not having armour everywhere). Again, the armour material could also be a lot less dense than today's materials (yes, even at same TL - since that does not mean identical to today, only similar).
 
BP said:
Crystaliron is a madeupium material - who says it rusts? :P

The name could merely refer to its properties and the material may have no iron in it at all (though some silly author who doesn't understand science fiction could have made it so...).

As to starships floating - if their average density is less than the liquid, they float. Most would be when unloaded, specially if they are 'lifting-bodies'. Liquid hydrogen is only a fraction the density of water (7%, IIRC, but still a lot denser than air) - so being fully fueled wouldn't necessarily raise the average density too high.

Even loaded with cargo, they would likely 'float' - as long as they stay sealed. RW cargo ships do it.

Submarines float. Large deep diving ones have very thick hulls and are full of heavy gear - but they float till their ballast tanks are flooded...

Concerning armoured ships not floating by default - RW battleships do (granted, the 'all or nothing' approach meant not having armour everywhere). Again, the armour material could also be a lot less dense than today's materials (yes, even at same TL - since that does not mean identical to today, only similar).

Well, I was going by the name... as meaning either crystalised iron or crystals with iron - I've also seen it referred to as Crystaliron Steel, although that may be a typo...

I said the empty cargo hold for submerging purely because I guessed that people wouldn't want waterlogged (and/or rusted) cargo... I doubt very much if anyone bothers to waterproof the ore containers or the timber, for example and may produced goods may be just on pallets with cardboard boxes, for all I know... :)

I will point out two things though - ship hulls are shaped specifically to improve the upwards force, so make them float better than their displacement would suggest - most spaceships probably wouldn't have that advantage. Also, the spaceships, not having to worry quite so much about mass (indeed, they employ gravity manipulation to negate as much as possible - although whether that would negate mass or weight is another discussion) they may be heavier than a surface ship. Also, bear in mind that surface ships only have armour around the waterline and a little above and below it. A spaceship has to have 360x360 armour (except the drives). A ship also has no openings below the waterline or has special precautions against water intrusion if it does - a spaceship on the other hand, may have open weapon barrels, leading to electronic or electric systems and/or missile tube hatches that were designed to keep air in, not water out.

Not saying that you're right or wrong - just pointing out a few issues...

I think, ultimately, the GM needs to handwavium the whole issue and if it seems a little far-fetched, the salinity of the water was extremely high that day... :)
 
BFalcon said:
Well, I was going by the name... as meaning either crystalised iron or crystals with iron - I've also seen it referred to as Crystaliron Steel, although that may be a typo...
Yep - that is why I dislike that name - and, yes, some dolt probably did refer to it as 'Crystaliron Steel' :roll:

Fortunately, 'crystaliron' doesn't exist, so that form of 'steel' can still have sci-fi properties... unfortunately, Titanium Steel is real (for game purposes).

BFalcom said:
...Not saying that you're right or wrong - just pointing out a few issues...
No ego investment here, enjoying the discussion. :wink:

You make good points, we just disagree on the specifics...

Hull shape for ships has more to do with the quality of floating (and movement) than the mere act - i.e. your starship will float if its density is less than the liquid, it just might not float the way the occupants want it to! :twisted:

The reason I am posting this drivel, is that real life doesn't give most of us a good feel for density. Take a 50 pound iron gym weight (at your own risk ;) ). Most people would call it heavy and expect it to sink. Take the same weight, but make it 8 times 'thicker' and most people will still expect it to sink. It will float, of course. (See below)

Most starships, by the nature of their design intent of moving things, typically have a large ratio of gas to solid when it comes to volume (i.e. open space), and so a lower density.

Yep, nautical ships are not armoured on all surfaces - I even alluded to the 'all or nothing' armouring doctrine which eliminates even more armour - but, surface area to volume ratios are generally quite huge. Submarines are often designed, IIRC, to keep their density high enough so that their average density is close enough to water so that submerging is easier.

That said, with game armour coming in % ship volume chunks and Titanium being about 4.5x denser than water (of course, Traveller uses Titanium Steel which most alloys are slightly denser, but one could use a lighter alloy of Ti Steel, still containing iron), an otherwise empty starship could not have more than 22% armour... which actually works quite close to the max armour allowed of 22.5% (9 for TL 9 ship). Since the average density of the rest of the ship would likely be less than water anyway, that means that only maximally armoured fueled ships would sink at TL7 assuming actual density of common Titanium Steel. Since most warships aren't maximally armoured, and assuming higher tech armour 'handwavium' materials are not overly dense (though 'Bonded Superdense' might not qualify ;) ), almost all larger warships would float - on water and anything denser. YMMV - and other versions of Traveller may state densities that counter this. (Thus actually stretching my suspension of disbelief - part of the reason I never played any of these others - more detail, more inconsistencies...).

I speak of liquid rather than water as Traveller yields the opportunity for starships to 'land' on liquid bodies (pools, lakes, oceans, etc.) like methane or aqueous ammonia. Their densities are a lot lower (methane @-164C being .46 that of water) - so most ships may sink, or be easier to intentionally sink, without being flooded.

Speaking of water, salt water, is not really that much more dense than water (1025 vs 1000 kg/cubic m) - but it makes a big difference for us humans. And, liquid water is dense - pure iron is only around 8 times more dense*. One Traveller design ton (13.5 cubic meters) masses 13.5 metric tons if pure water (at max density, i.e. 4 degrees C*).

* - of course, densities are based on averages and impurities and temperature impact that.
 
Yup and don't forget the gravity of the planet - I'm guessing that would impact the metal far more than the water around it... that hull weighing in at 50% more on a 1.5G world would make quite a difference, I suspect... especially with cargo on board removing the "safety margin" of the cargo hold.
 
Not generally. As most liquids and solids are incompressible*. (You have the basic principle correct, but in practice, the results would be insignificant - and sometimes counter-intuitive. I.e. some solids can be more compressible than water.)

This means as the 'weight' of the ship changes, so to does the 'weight' of the liquid by the same ratio - without their volumes changing. I.e., the relative densities remain the same (specific gravity and apparent gravity remain equivalent). Its the relative density that matters in determining float or sink (*neglecting surface tension, of course).

*Liquids and solids can be compressible - but the amount is insignificant for the Gs here. For gases this is quite different as they are compressible and thus their density would change significantly... as pressure increases, some gases might become dense enough to 'float' a starship, especially if the temp was high enough.
 
Hmm... ok - makes sense, I guess - would still feel better if someone had a base on the moon and could test it to be sure. :)

Don't suppose they've done the tests in a descending 747 like they do zero-G familiarisation, have they?
 
(Oops - I edited my prior post to add the 'without their volumes changing' - just to make things clearer.)

I don't believe any size-able body of free standing pure water could exist on the moon - not enough gravity to retain most gases, much less pure water. If pure water was sitting on the surface (if we could ignore temperature - too hot/cold), a starship would still sink (ignoring surface tension), just its rate would be slower due to less acceleration from gravity.

I stated 'ignoring surface tension' since such force could be strong enough to overcome the force of gravity. However, in talking pure water (and starship sized bodies), I feel pretty safe ignoring it.

Any fluid could have dissolved/insoluble materials (gases as well as solids) that change its density and cause such to change more drastically under the right conditions (pressure from atmo, temperature, and gravity) as well as its surface tension. I mention this for completeness and for plot fodder... :)

As to a 747 vomit test - no, I am pretty certain no one's landed a starship inside a body of water in a rapidly descending 747 :lol:
 
rust ? ... rust? !

I have on my list of 'industrial and other non-military' ships to design a shuttle designed to drop from high port, submerge and dock with an underwater habitat. Such a shuttle would be sold to all the starports of waterworlds or near waterworlds. It would save so much time and cost in transhipment of cargos onto submersibles on the world surface....

So I'd be interested in how this thread looks at the problem :)
 
BFalcon said:
Yup and don't forget the gravity of the planet - I'm guessing that would impact the metal far more than the water around it... that hull weighing in at 50% more on a 1.5G world would make quite a difference, I suspect... especially with cargo on board removing the "safety margin" of the cargo hold.
Hmm.The water on the planet would also be affected by the increased gravity. Wouldn't that make the water a bit more dense and thereby balance out the buoyancy?

EDIT: Gah. BP beat me to this. Kindly ignore my post and see his about 3-4 posts above this one.
 
BP said:
As to a 747 vomit test - no, I am pretty certain no one's landed a starship inside a body of water in a rapidly descending 747 :lol:

Ass... :lol:

I meant floating a model in a tank of water... :)
 
Mithras said:
rust ? ... rust? !

I have on my list of 'industrial and other non-military' ships to design a shuttle designed to drop from high port, submerge and dock with an underwater habitat. Such a shuttle would be sold to all the starports of waterworlds or near waterworlds. It would save so much time and cost in transhipment of cargos onto submersibles on the world surface....
We are discussing starships - small craft have a much greater surface area to volume ration - so their hull contributes more to their density. 100 dton plus starships would have a harder time...

Either way - any ship could be designed to submerge. Their density just has to exceed that of the liquid they are trying to submerge into. Of course, with a lifting body (like maybe a shuttle) designed for atmospheric flight, one probably wants a much lower density than water ;)

The traditional way is then to take on ballast. Usually this is the liquid in question, but if the craft is low density and designed to maximize passenger space, this might not be enough. In which case, external ballast could be used in the RW prior to submerging. However, especially in Traveller, there is a better way...

This thread was about floating without gravitics. Powered submersion could happen despite density (i.e. like pushing an inflated ball under water) - and gravitics is the perfect handwave for that. Not to mention, other than rapid pressure change issues (hull) - it would be safer (automatically rises on failure of propulsion system). :)
 
BFalcon said:
BP said:
As to a 747 vomit test - no, I am pretty certain no one's landed a starship inside a body of water in a rapidly descending 747 :lol:

Ass... :lol:

I meant floating a model in a tank of water... :)

Well, we're talking freefall / zero-g for that case, so the question (floating aka density displacement) doesn't really apply. A dense lead ball will "float" with exactly the same characteristics as an air filled beach ball under those conditions. Even in air.
 
Back
Top