No, I did quite a bit of poking around with this back in the day. It was the amount of liquid Hydrogen that would be displaced by total immersion - ie a measure of the volume of the ship.

Always thought it was H2O but liquid hydrogen (H2??) sounds more apt.

That's where the 14cu m per ton comes from. 14cu m of LHyd weighs 1 ton.

LHyd the magic fuel.  Better to store it as methane and break it down, you get more densely packed H2

Well, 1/14 is about 0.0714 tonnes (or 71.4 kg) per cubic meter.

Pure water masses 1 tonne per cubic meter by way of contrast.

Density for liquid hydrogen is supposed to be somewhere around 70.85 grams/liter, so this 14 cubic meters/tonne doesn't quite scale, but it's close.

A cubic meter is 1,000,000 cubic centimeters.  This is equivalent in volume to 1,000 liters, so by the density, LH2 should be about 0.07085 tonnes per cubic meter.

1/V = 0.07085 tonnes/liter so 1/0.07085 = V = 14.11 cubic meters.  This isn't too far off from the stated approximation in Classic Traveller vol. 3.

Carrying this to its logical extension, a Beowulf-class Free Trader of 200 tonnes displacement would therefore have an internal volume of something like 2,822 cubic meters.  Does that about tally with the advertised specs for the class?

IIRC, they were pretty close - within the bounds of wastage and internal bracing. Much better than the '10dT small craft that has 10dT of internal space, yet fits into a 10dT hold' that the designers gave us to begin with. (They did fix it later, sort of).

However, none of this actually addresses the question I was asking:

Do your starships sink or float in water? And if they float, do they wallow up to their conning towers like a submarine, or bob around on the surface like an Apollo capsule?

And how do you handle weight distribution to maintain an even keel? Do your deck plans take this into consideration?

Antigravity is the magic hand wave :)

A ship with displacements such as we are talking about here would definitely float if subjected to a water landing.

Whether it was able to maintain a proper attitude in water would depend strongly on how it was designed, and whether or not it was rated for aquatic operations.  Such a ship would have ballasting systems that allowed it to maintain an even keel in or under the water.

Speaking of underwater operations, any ship rated for this would have to have a specification for its maximum operating depth, and special design considerations for keeping the reaction control engines (maneuver drive and thrusters) sealed while underwater.

This could open up a whole new branch of naval architecture in Traveller...

Yeah, I pondered about operating depth once upon a time, but the physics was way over my head - even given perfect cylinders.

Eventually, I just handwaved it. I figured a submersible ship must be armoured, and I rated the ships at 100m depth per armour factor. If you went a percentage below your rating, you rolled percentage dice to survive.

Doesn't really work right - for a given AF, a smaller ship should be able to dive deeper than a larger one, but I'd had enough by that time. Maybe I'll figure something better one day, taking account of the ship size factor, or something.

Putting Iris Valves on the exhaust ports is the easy part.

Antigravity only works if you have power. I can feel my GM horns sprouting just by thinking about that...

As much space as is taken up by Lhyd tankage I would think that a Traveller starship would float nicely.

Good point, Montezgvegh, that's the sort of thing I was wondering about. I think the density of a ship needs to be a compromise between lightness and strength.

There are canon descriptions of ships landing in water, so I'm happy to go with ships being lighter than water, but I think Traveller ships, many of which are built with combat in mind (even if only in self-defence) would be tougher than the flimsy 'Coke-cans' we put into space today.

I'm just trying to figure whether starships should be the same degree of toughness/lightness as aircraft (0.2-0.3 tonnes/m^3), or more like wet-navy warships (0.5-0.6 tonnes/m^3)?

I think you're right, submarines at 0.8-0.9 tonnes/m^3 are probably overkill, unless you need to dive, and maybe most ships wouldn't be designed for that - or would they? Would starship armour automatically form a pressure-hull capable of withstanding ocean depths, and would it outweigh the buoyancy of the LHyd tanks?

Are your ships routinely able to dive, folks? As a GM, what would you allow? As a player, what would you expect your GM to allow?

Maybe one day I should try designing a Type S Scout with the Striker rule set, and see what it pans out like...

I would think that military, scout and free trader type ships would be built to frontier refuel which would mean any streamlined ship not only could skim at a gas giant, land in atmosphere but also withstand floating or submerging in water or Fluid as defined by Traveller.  Given the tech at even TL 9 it's probably fairly trivial to make a ship able to submerge as part of streamlining it for operation in atmosphere.

Uh-huh.  Wet-navy vessels seem a more reasonable analog to me.



Any submarine of my experience uses water for ballast to achieve whatever degree of buoyancy is required to submerge or surface.  It might be possible that a sufficently tough hull would work almost as well against pressure as against vacuum, but I haven't done any math yet.



I would not expect the same hull designs to be optimal for water travel as travel in space.  I only had a very few Imperial warships that could submerge in water.  Anyone who could throw enough money at a design and implementation could field a submersible starship, though.



The Type S I'm familiar with has a lifting body planform.  Something with a more tubular/cylindrical/teardrop type shape might be more at home in both vacuum and water.

That lifting body Type S could easily sprout hydrofoils or wing-in-ground effect surfaces (think an Ekranoplan), though for high speed manevering on water's surface.

Yep, that's why submarines are designed with a density close to that of water. It would take a HUGE amount of ballast to sink a surface ship. With a sub being almost the same density as water, it just takes small ballast tanks to change from floating to sinking.

Hence, if a starship was designed to be submersible, it should have a similar density to water, but if it is only designed to land ON water, then its density may be nearer 0.5.

IIRC, water pressure is roughly 1 atmosphere per 10m, and obviously it's working in the opposite direction. Most starships are not designed with an optimal submersion shape and a double hull, so I think you would need quite a bit of armour to make it submersible.

Yeah, thinking as I type, making a starship float is relatively straightforward, and probably standard practice. Making it submerge to any appreciable depth might require a special hull construction.

In which case, standard starships may have a density of 0.5, and submersible starships would need to be built on a submersible hull with a density of 0.9.

Does that sound reasonable?

In reply to Beowulf (msg # 17):

Yeah.  Look at WWII submarines, though.  They didn't submerge to the great depths that more modern types do (at least not by design).

A typical Gato-class submarine's advertised test depth is 90 meters.  The Type VII Unterseeboot's test depth is 230 meters.

I would imagine their hull density figures might be slightly lighter than 0.9 (somewhere near 0.7 to 0.8).

Compare this to more modern craft like the Sturgeon class, with an advertised test depth of 400 meters.

In Traveller terms, as long as the rules governing creation of specialized craft are consistent and consistently applied (i.e., without too many special "edge" cases), yeah, surface and submerged operations should be possible in craft of proper design.  All things for a price, Effendi.  All things for a price.

Some data that may be of interest can be found at:

https://samueldavey.files.word...submarine-report.pdf

This report does have some errors of grammar and spelling/word usage (notably in their statement of Archimedes's Principle), but the basic math is sound even if their assumptions were not always in keeping with the math.

A lesson plan for high school/junior high school students can be found at:

http://usnavymuseum.org/Education_LP0022.asp

Of course, none of this data accounts for the possibilities of vectored thrust in a submersible's design, nor does it speak on shifting from submersible to airborne to spaceborne operations.  That would be expecting too much, I think...

Nonetheless, the basic math is sound, and may be useful to anyone thinking of developing formal rules for the design of submersible starships.

There is one interesting concept brought forth in the US Navy Museum's presentation, namely the use of floating deck mounts to preclude buckling from hull compression.

Keep in mind that star ships will want to have some thickness to their skins. There's dangerous stuff out there! Meteors, radiation, even pirate small arms fire are all things that a ship would want to be safe from.

So, Been looking at Book 2 style ships, for my latest campaign. Other than there, and the Shipyard on Freelance Traveller https://www.freelancetraveller...d/classic/index.html

Are any of you aware of resources for ships in this size range?
This message was last updated by the GM at 07:02, Sun 02 Sept 2018.

Other than some of the commercially available designs at DriveThruRPG.com, I'm at a loss right now.  It looks like Pocket Empires is completely offline, which takes out Fafhrd's Shipyard, and more's the pity.

This link might help:  http://zho.berka.com/tag/deckplans/

I also found several likely hits searching with duckduckgo.com (which I greatly prefer to Google).

Updating this post while I have the time:

The Traveller Deckplan Page

A Tutorial on Drawing Deck Plans with Campaign Cartographer 2 Pro

Paul Schirf's Deck Plan Page

An interesting Pinterest page...

Freelance Traveller Shipyard features ship designs for a wide variety of Traveller rule sets.

A topic on reddit.com about software for making deck plans...

There are many, many, more out there.  These are just some of the ones that came up in my search.
This message was last edited by the GM at 07:27, Sun 02 Sept 2018.

More Deck Plans and other great info on Traveller starships and other vessels can be found at:

Citizens Of The Imperium Forum - The Fleet
This message was lightly edited by the GM at 05:46, Mon 24 Sept 2018.

Using the rules from your favorite version of Traveller, design a "dream ship".  This doesn't have to be a huge extravagant vessel, and can, in fact, be something as simple as an X-boat if that's what trips your trigger.

I'd love to see submissions here that folks could grab and use in their games at need.

It's not needful to show your work, but submitted designs should include any deviation from the rule set used.  Background material submitted with the design may be specific to any Traveller setting, or setting-neutral as the designer may wish.

In the next few days, I'll tackle an atmospherically streamlined 400 tonne Subsidized Merchant (a so-called "Fat Trader") using Classic rules, including Book Two and Book 5 (High Guard).

Join in!  Let's build up this shipyard!

I am commencing a campaign using small ships, so I will submit a exploration and trade cruiser between 300-500 tons using Book Two Classic rules.

Pity my own Shipyard (along with most of my Traveller gear) is in storage just now. However, here’s something from memory (oh-oh!). It’s a ubiquitous craft IMTU. It’s a small craft built using LBB5 (as all my spacecraft are) (I don’t think I deviated, but let me know if the old memory is playing up).



The 10dT Shore Boat is a ubiquitous craft serving the purpose of a lighter or passenger transport. It takes up minimal space in a starship by way of a Fitted Compartment, but allows for regular (and occasionally clandestine) dirtside forays without risk to the mother ship.

It has a wedge-shaped format with external engines, (cough, Star-Trek shuttle, cough) allowing the entire rear face of the craft to provide a full width/height clamshell door. This allows modular fitments to be installed into the cargo bay, including:

a passenger section (up to 8 passengers @ 0.2MCr)
a mobile sick bay (get price from Striker + stateroom cost)
a repair workshop (get price from Striker + stateroom cost)
a 2-berth vehicle bay
an air-raft hold
a 16-space ELB lifeboat module (@0.4MCr)
or even a pair of slide-in passenger staterooms (@0.2MCr).

Alternatively, the bare cargo space is dimensioned to accept a pair of standard 2dT bonded-store cargo containers.

Well, my first foray into High Guard in quite some time has convinced me it really isn't all that useful until one starts designing military craft.  I'm going to do my Fat/Far Trader using Book 2 exclusively.  Back to the drawing board.

Using a 400 ton hull, the Cortez-class Exploration Cruiser is an armed survey and merchant ship. It mounts jump drive F, maneuver drive J, and power plant J, giving a performance of jump-3 and 4-G acceleration. Fuel tankage for 160 tons supports the power plant and jump-3. Adjacent to the bridge is a computer Model/6. There are 20 staterooms. The ship has 4 hardpoints and 4 tons allocated to fire control.  Cargo capacity is 50 tons. The hull is streamlined. The ship requires a crew of 9: Pilot, Navigator, Medic, 2 Engineers, 4 Gunners.

400 T  16McR
Jump F= 35t  60McR
Manuever J= 17+28 = 45t  36+72 = 108Mcr
Bridge= 20t 2Mcr
Comp 6= 7t  55Mcr
hardpoints= 4t .4Mcr
Staterooms 20 = 80t  10Mcr
Cargo= 49t
Fuel= 120+40 = 160t

Cost= 428.4 McR