Floating spaceships

[Drakon]

Your ship has an intact landing on an ocean world. Will it float?

I have been trying to figure out a means by which I can answer that question, as well as how high up the sides the water will go, but am kind of stuck. I don't know how much the ship weighs.

Floating is simple. Displace more water than the weight of the ship. I know the volume, and the density of water, but not enough to figure out whether the ship will float or not. Equipment is heavy, but interior spaces like berthing compartments are not.

It seems what I need is a density factor, or rather sets of density factors for the various ship components. That, with the volume, will tell you how much that component weighs. Add it all up, you have how much the ship weighs, and, compared with the volume, you will answer the question of whether your starship floats.

 

[Gallowglacht]

I'd say yes, even without measuring. Cargo hold, staterooms and hydrogen filled fuel tanks normally take up a lot of a ship and provide plenty of buoyancy. There should be plenty to hold up a ship.

 

[Drakon]

While I would agree, I was working with one of the spreadsheet design progams, (can't remember which, FF&S2?) and came up with 8,000 tons for a 600 dton ship. Either my, or its, math is bad, or something is wrong there.

Also, how far up the side would the water rise? This is especially important to figure out which hatches would be underwater, and which would be available for exiting the ship. To answer this, will need some real numbers.

 

[Hemdian]

Arrival Vengeance rates an AHL cruiser as having a loaded weight of 775596 tonnes and 60,000 dtons displacement. If I've done the math right that comes to just under 0.96 grams/cm^3. Water is 5.5 grams/cm^3 therefore an AHL would float (less density than water floats, more density sinks).

Regards PLST

 

[Scott Martin]

Ummm

Water is exactly 1 g/cubic cm / 1 metric ton per cubic meter at 4 degreees celcuis (most dense). This number is higher (and can be significantly higher) based on how much stuff is dissolved inthe water, so you can float a lot more in the dead sea than a freshwater lake. Do a search for "plimsoll line" for more info on this topic.

The "standard" mass of a starship using FF&S design is 10 tons per displacement ton (14 cubic meters) so your "generic" ship is about 30% above water.

With my designs, an empty freighter / tanker can be as little as 10% submerged, and (stupidly) heavily armoured warships (most of the ones in "shattered ships of the fighting imperium) will sink in molten steel (density ~8tons / cubic meter)

As a rule of thumb, assume that anything in HG with an armour factor above 4 or 5 will sink

Scott Martin

 

[Rover]

To figure that out accurately you would need to know the mass of the spaceship compared to volume of the ship. So long as the total mass is less than that of an equal volume of water it will float, provided it is sealed of course. There are other complications, like will it list? Is it nose or tail heavy, or worse yet top heavy? It may not float all nice and level like it was on solid ground, it could bob and roll around like cork.

The problem is ships in Traveller do not deal in Mass, only Volume. So we’ll have to make sum assumptions.

1dTon in Traveller equals 14 cubic meters. Water is 1000 KG (2,200lbs) 1dTon masses 14,000KG.

If 5% volume of the ship is solid, not counting fuel in tanks or armour, and the 5% is mostly iron. (I choose Fe because it is a heavy, common and strong materiel likely to be used in ships.)

For a 200 dTon far trader:
Volume 200 X 14 meters cubed is 2,800 cubic meters.

5% = 140 cubic meters of solid iron.
Iron is 7000KG/Meter cubed. Mass of a 200 dTon Far trader is 980,000KG

Or about 980 Cubic meters of water. 980/2800 = 0.35 or 35% of the ship will be below the waterline.

You will have to make your own assumptions IYTU about the material your ship is made of and what % is solid.

Change to aluminum and the mass would be 378,000 or 13.5% below the waterline.

R

 

[aramis]

Depends. In MT, TNE, and T4, it's quite possible for warships to sink readily.

If mass exceeds the mass of the displaced volume, it sinks.

Well, pure water is 1 metric ton per cubic meter... saltwater up to 1.01 metric tons per cubic meter. so if the mass exceeds roughly 14 Tons mass per displacement ton, it sinks.

 

[atpollard]

From my limited experience with Striker and MegaTraveller, I agree with the notion that lightly armored commercial ships will float and heavily armored warships will sink. A simple rule of thumb might be to assume that 50 percent of an armor-0 ship will be above the water and subtract 10 percent for each point of armor (armor-4 will barely float with only 10 percent of the ship above water, armor-5+ will sink).

 

[Drakon]

So, an 8,000 ton (mass)/600 dton ship would float, since the equivalent weight of water is would be 8400 tons. (or 8484 tons salt water). Now assuming we have a flattened sphere (roughly), that means that if I have done the math right, my ship will float with less than a meter showing above water.

Found the spreadsheet I used, I still thought the mass was high. It was the FF&S3 spread sheet version 3.2. The mass is highly dependent on the density of the cargo. I had it set to 1, (1 ton per cubic meter). empty the hold and you get 4100 tons, which works out to being submerged about half way. Which is a good thing, as it means that to ride higher, I need to unload cargo. (Duh)

Thanks for all the responses. They have been very helpful. I had not thought about listing until Rover mentioned it, and when he did, I got this image of a scout floating, tail submerged like the opening of "Planet of the Apes"

 

[GypsyComet]

Pretty much. Of course, "will it float?", and "what's above water?" are two entirely different questions...

 

[TheEngineer]

Actually the way how your ship floats heavily depends on load balancing.
I strongly guess (watching at several deckplans) that most ships will lift up their nose up in the sky
So, if you want to float "flat" on the water, try to keep the center of mass in the center.

 

[Jeff M. Hopper]

What kind of world are you on? Different worlds will have different contaminants in their water and thus different densities. On Earth, the saltwater at the equator has a different salinity than the saltwater at the poles, thus different densities as well. This could easily become a really complex question demanding a spreadsheet answer.

'Course, I'm also thinking that just because something floats doesn't mean that it will be particularly seaworthy. Submarines can control their bouyancy and make great underwater craft, but they make lousy surface ships because of their shape. The natural wave action of the ocean will toss them around, and it just gets worse in foul weather. I think a similar problem would be encountered with a starship, unless it was parked in a bay that could dampen out the normal wave action of the sea.

 

[aramis]

How much is above water is easy enough, too.

Find the float percentage by mass in tons-metric divided by volume. That is the fraction of your volume that is under water.

Applying it to the various non-standard shapes is less easily done, but can be rough figured.

 

[Icosahedron]

Drakon, before everyone ties you in a Gordian Knot of mathematical complexity:
You're the GM. Do you want it to float? Then it floats.
Do you want the hatches above water? Then they're above water.
"This model was designed to float with its hatches above water by having many of its structural components made of <insert material(s) of choice>. It operates its grav thrusters on standby to compensate for the tail-end drives."
That's the CT referee way.

 

[Valarian]

You're the GM. Do you want it to float? Then it floats.

I like this approach. Solves many many problems.

It operates its grav thrusters on standby

I like this too, although you may have problems if the m-drive is damaged. Although, this could just add excitement. Find the saboteur and fix the m-drives before the ship hits crush depth.

 

[TheEngineer]

Hi !

Sure, with m-drives on, this case isn't an issue anyway ...
And, after looking in the MT Encyclopedia again, it really as simple as Aramis noted...civilian craft should float, while military ones tend to be divers.
Anyway Valarians sabotaged military vessel is a pretty nugget.

BTW, Valarian, noticing Your location. Is floating or diving still an issue at your place. Germany news told, that is getting better ....

Regards,
TE

 

[Drakon]

Submarines can control their bouyancy and make great underwater craft, but they make lousy surface ships because of their shape. The natural wave action of the ocean will toss them around, and it just gets worse in foul weather. I think a similar problem would be encountered with a starship, unless it was parked in a bay that could dampen out the normal wave action of the sea.

What this guys says is true concerning submarines. Having ridden them for a number of years, I can confirm his observation. But I will point out that while they make lousy surface vessels, they are far smoother submerged than skimmers are on the surface, regardless of how light or heavy the wave actions are.

 

[Drakon]

Drakon, before everyone ties you in a Gordian Knot of mathematical complexity:
You're the GM. Do you want it to float? Then it floats.
Do you want the hatches above water? Then they're above water.
"This model was designed to float with its hatches above water by having many of its structural components made of <insert material(s) of choice>. It operates its grav thrusters on standby to compensate for the tail-end drives."
That's the CT referee way.

Yeah, yeah, I know. But I am the kind of guy who yells at the TV everytime someone, say, reports that we've been locked out of transporter control by the computers.

"Open the damn breakers! That will shut them down."

What can I say. I am sure there is a name for this particular mental illness. I don't know what it is.

 

[Hemdian]

Water is 5.5 grams/cm^3

Oops, 5.5 is the density of the Earth. As Scott said pure water is 1 by definition. But if a loaded AHL (according to MT) is 0.96 grams/cm^3 then it still floats (just).

Regards PLST