Starship level system proposal

[Turanil]

STARSHIPS & OTHER VEHICLES CONSTRUCTION.

Here is a system to create vehicles and starships based on level, as for characters. This is similar to the concept of d20 Modern basic classes. To get the idea of what may produce this level-based vehicle system, just compare two boats of the same size (say 40 feet long). The first is a simple liner’s lifeboat with just a hull, basic benches, and rows; while the other is a luxury yacht with powerful engines, luxury crew quarters accommodation, etc. With this level-based system, the first boat is probably only a 1st level ship, while the second could be a 12th level ship. You could say the same about a basic Ford, a Ferrari, and a Mercedes. The Ford is perhaps only a 3rd level car, while both the Ferrari and Mercedes are 17th level cars. However, in this latter case, the Ferrari and the Mercedes have different class levels: the Ferrari emphasizes more on speed and maneuverability, while the Mercedes emphasizes more on luxury and number of passengers.

Another point is that vehicles do not improve in level in getting experience points. It is money that purchase levels. As such, vehicles use the basic level progression of all classes, but the required amount of XP becomes a cost in credits.

A vehicle’s size and level are two different things. In the above examples, both boats are the same size, but their level is different; both cars are the same size, but their level is different. In fact, the size of a vehicle gives a multiplier which affects the characteristics of each level, such as number of weapons added, number of crew, hit-points total, and of course price.

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Vehicles’ Classes:

1) Offensive Capacity: (Loosely based on Strength) d10 hit-die. Starfighters and war vehicles have many levels of Offensive capacity, which gives them weapons of all sorts.

2) Tolerance Capacity: (Loosely based on Constitution) d12 hit-die. This represents both tolerance to extreme conditions of uses, such as in certain planets’ atmospheres, but also the level of armor a vehicle has against attacks.

3) Maneuverability Capacity: (Loosely based on Dexterity) d6 hit-die. To be fast and agile, a ship must have a good amount of Maneuverability Capacity. Of course, the ship’s size also affects this its maneuverability.

4) Opulence Capacity: (Loosely based on Charisma) d4 hit-die. This represents the comfort afforded to the crew and/or passengers, as well as the overall beauty of the ship. Yachts usually have many levels of Opulence capacity.

5) Room Capacity: (Loosely based on Intelligence) d6 hit-die. This can be cargo room, or number of passengers. A liner and a freighter have many levels of Room Capacity.

6) Range Capacity: (Loosely based on Wisdom) d8 hit-die. For how long a ship can function without re-supplying is determined by the Range capacity. The more level a ship gets in Range capacity, the more reliable become its systems, engines, etc.

Each of these classes has 10 levels, so the theoretical maximum for a starship is 60th level. However, in practice it is impossible to have everything at once, whatever the amount of credits you can pay. As such there is a minimum and maximum number of levels a ship may get, that depends on its size.

With each level, come new equipment and improvements of existing equipment (as if it were feats). The ship also gets basics of the level: all get hit-points, but in various amount as relevant to what capacity is gained (i.e.: Tolerance brings d12 hit-points since it designs armored vehicle; while Opulence brings only d4 since it designs elegant vehicles at the expense of practicability). Another basic is the number of crew/cargo gained each level with the Room capacity, while Offensive capacity will bring an overall increased amount of firepower (which must be then transformed into various weapons).

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Vehicles’ Sizes:

1 - Size: 5 m /18 ft. long. Credit and Hit-points multiplier: x1. Other factor: 1

2 - Size: 10 m /33 ft. long. Credit and Hit-points multiplier: x5. Other factor: 2

3 - Size: 20 m /70 ft. long. Credit and Hit-points multiplier: x10. Other factor: 4

4 - Size: 40 m /135 ft. long. Credit and Hit-points multiplier: x25. Other factor: 8

5 - Size: 80 m /270 ft. long. Credit and Hit-points multiplier: x50. Other factor: 16

6 - Size: 150 m /500 ft. long. Credit and Hit-points multiplier: x100. Other factor: 32

7 - Size: 300 m /1000 ft. long. Credit and Hit-points multiplier: x200. Other factor: 64

8 - Size: 500 m /1700 ft. long. Credit and Hit-points multiplier: x500. Other factor: 128

9 - Size: 800 m /2700 ft. long. Credit and Hit-points multiplier: x1000. Other factor: 256

Comments are welcome, if only to tell if you like it or not. Blackjaw, what do you think about it ? Is this what you had in mind yourself ?

 

[BlackJaw]

first of all it's not using the standard size system in D&D. it's also not adapted for easier use on a larger grid size (if vehicles are big and move fast, then a 1 inch = 5' grid does not work well). We've already got rules put made for handling all that, and its a minor thing.

Other then that it's basicaly the system I made, each design focus the vehicle has (weapons, armor, special systems, etc) a seperate "level" (not real levels... something based losely off levels)

Range of the craft has everything to do with the setting's tech. jet fighters are not the same as a zepplins or fire elemental powered magic-steam-tech. Special systems can be used to increase the time a vehicle can operate befor running out of power (and thus range)

Limiting a class doesn't make a lot of sense to me... you can only devote so much to engines before you can do something else? I was going to make an infinite progression (these are not real levels!) so you could put anything you want given a reason.

Beyond that the only issue I have is with mulitply instead using hit dice...
why does 1d10 x 100 work better then 100d10? It's the same thing and one of them is standard D&D notation and the other hasn't been done before.

 

[Blacksad]

It might be good for a specific game, but in a generic environment tying hit-point to size is a bad idea, during the forties german zeplins were big and very fragile.

This system assume too many things in the design to fit my taste.

It's seems quite hard to be universal without point-buy method, I do not know if it can be done.

 

[BlackJaw]

It might be good for a specific game, but in a generic environment tying hit-point to size is a bad idea, during the forties german zeplins were big and very fragile.

Actualy my idea for deal with derrigibles (blimps, zepplins, hot air balloons, etc) is that they are a "special system" that increases the size of the vehicle without increasing the hit dice, but lets you hover. thus your Hit dice and hit points are much lower then other vehicles for your size, and yoru armor class and "usable space" and speed, and manuvering is likely much weaker. I've even considered making it a 2 size increase to better reflext the massive size and delicate nature of derrigibles.

Special systems are something you get a few of when making vehicles, and that you can get a lot more off depending on the focus ranks of the vehicle.

As far as duplicating the exploding hydrogen filled zepplings of germany... well that's a hard one to do with or without point buy (untill recently I was trying to make a point buy system). The germans only did it because they couldn't get ahold of enough Hellium.

No sane player to select the option to have massive explosive blatters straped to their craft. It would be come something only NPCs (and poor or non-combat oriented ones) would do. That said, it isn't that easy to blow up a hydrogen zepplin. They could be shot by enemy aircraft without exploding or taking serious damage. Allied fighters on missions to attack them were given burning phosphurus (tracer) ammo so they had a chance to ignite the hydrogen. The explosions mostly happened in their hangers where equipment for construciton and repair is. Electrical equipment and welding etc. If they had been that easily destoryed with only a single attack, no one would have been so foolish as to make them or use them, let alone in times of war or as military vessels!

That said, its a cultural & historial icon so I will need to come up with a way to deal with it. Most likely causing the zepplins to explode when it hits half hitpoints or maybe 0 hitpoints? Maybe make it a 1 size increase for "unstable" derrigible designs and a 2 size increase for "safer" designs.

This system is intending to be about as generic as D&D is. D&D right now supports Dragonstar through Spell jammer with just a little tweaking. The same holds true for the flight rules I'm making. with just a little tweaking you should be able to cover most things, maybe even d20 modern type stuff. That's the goal of my system. giving out hit dice by size isn't any less realistic then a 20th level fighter that can take tons of damage standing next to a 1st level commoner with 2 hit points that can be killed in one round by a house cat.

Basicaly game systems are game systems I'm trying to get the Cosmo to match D&D core. Point buy isn't D&D. I tried making it D&D but it wouldn't stick.

I've only recently switched to a class/level dynamic for ship building because the point buy type system I had been working on for so long was incredibly complicated, massive, and hard to use. I was thinking about how to best start over on a point buy system that wouldn't end up being that complciated or hard to build and blanace with when I hit upon the idea of levels and classes as a system to base it around. It works a lot like character creation. each class in D&D has its focus, and you can mix them by multiclassing (d20 modern is built around this).

What is it you want in a vehicle construction system? I'm still working on it and willing to make adjustments as it needs to be done. What kind of setting are you thinking about? What is it you want it to do? If size isn't a good starting point for number of hitpoints/etc then what should hit points be based off?

 

[Blacksad]

Actualy my idea for deal with derrigibles (blimps, zepplins, hot air balloons, etc) is that they are a "special system" that increases the size of the vehicle without increasing the hit dice, but lets you hover. thus your Hit dice and hit points are much lower then other vehicles for your size, and yoru armor class and "usable space" and speed, and manuvering is likely much weaker. I've even considered making it a 2 size increase to better reflext the massive size and delicate nature of derrigibles.

That's what bother me, exception to the system. If their is only one, there is no problems. But it's probable that there is other, vehicles that do not fit well in many vehicles construction system:
-motorcycle (medium size vehicle which can carry two medium size passenger)
-submarine (more a problem with vehicles rules than construction, but still: an easy target when on the sea, a very fragile vehicle when under the sea, plus the cover rules which work strangely with mines and the like).
-rocket (a vehicle which destroy itself in its use)
-cart (or any muscle or wind powered vehicle: how do you determine maximum charge and speed, etc...)

Special systems are something you get a few of when making vehicles, and that you can get a lot more off depending on the focus ranks of the vehicle.

As far as duplicating the exploding hydrogen filled zepplings of germany... well that's a hard one to do with or without point buy (untill recently I was trying to make a point buy system). The germans only did it because they couldn't get ahold of enough Hellium.

No sane player to select the option to have massive explosive blatters straped to their craft. It would be come something only NPCs (and poor or non-combat oriented ones) would do. That said, it isn't that easy to blow up a hydrogen zepplin. They could be shot by enemy aircraft without exploding or taking serious damage. Allied fighters on missions to attack them were given burning phosphurus (tracer) ammo so they had a chance to ignite the hydrogen. The explosions mostly happened in their hangers where equipment for construciton and repair is. Electrical equipment and welding etc. If they had been that easily destoryed with only a single attack, no one would have been so foolish as to make them or use them, let alone in times of war or as military vessels!

I thought that they weren't used as military vessels

That said, its a cultural & historial icon so I will need to come up with a way to deal with it. Most likely causing the zepplins to explode when it hits half hitpoints or maybe 0 hitpoints? Maybe make it a 1 size increase for "unstable" derrigible designs and a 2 size increase for "safer" designs.

This system is intending to be about as generic as D&D is. D&D right now supports Dragonstar through Spell jammer with just a little tweaking. The same holds true for the flight rules I'm making. with just a little tweaking you should be able to cover most things, maybe even d20 modern type stuff. That's the goal of my system. giving out hit dice by size isn't any less realistic then a 20th level fighter that can take tons of damage standing next to a 1st level commoner with 2 hit points that can be killed in one round by a house cat.

Yet, this fact does not disrupt suspension of disbelief, because it means easy play and it is used in many games (CRPG, CCG, RTS, etc...).

While not being able to cover some vehicles, or only with special rules, could disrupt the faith in the system.

Basicaly game systems are game systems I'm trying to get the Cosmo to match D&D core. Point buy isn't D&D. I tried making it D&D but it wouldn't stick.

Well, d20 BESM and d20 Mecha did something close (even if movement is too cheap for D&D in those books)

I've only recently switched to a class/level dynamic for ship building because the point buy type system I had been working on for so long was incredibly complicated, massive, and hard to use. I was thinking about how to best start over on a point buy system that wouldn't end up being that complciated or hard to build and blanace with when I hit upon the idea of levels and classes as a system to base it around. It works a lot like character creation. each class in D&D has its focus, and you can mix them by multiclassing (d20 modern is built around this).

Perhaps I wasn't clear, but I think that this is a good idea. Though I think that building such a system to be generic is harder than building a generic point buy system (The easier it is to use, the harder it is to design).

What is it you want in a vehicle construction system? I'm still working on it and willing to make adjustments as it needs to be done. What kind of setting are you thinking about? What is it you want it to do? If size isn't a good starting point for number of hitpoints/etc then what should hit points be based off?

I do not know how to present all of my needs in a pleasant to read form, but I'll try. Here are my needs and their motivation:

-a good presentation and index: Babylon 5 use the Dragonstar's vehicle system, but the repair rules the combat rules and the ship stats were spread all over the rulebook (which had no chapter heading) making it really hard and unpleasant to use.

-an easy way to assess the relative combat strength of vessel: I used the Archipelageo ship system in an over the top campaign, ships were described using monster statblock, so you could compare the ship statblock to other monster to assess its strength (they were given CR). Ships fighted each other on their specific scale (which maked direct interaction from PC a bit hard).

-a guide or sidebars to prevent stupid design: when I used mecha crusade I designed a mecha which was unable to deal damage due to the default damage reduction of other vehicles (it was in the same over the top campaign, in which they modified an undead ship to become a spaceship akin to the one from Captain Harlock).

-ease to reverse engineer stats produced on the fly: in a planescape campaign set in the Ethereal plane, I used a mix of Spelljammer: Spidermoon and Alternity rules to produce ships stats and have interesting interaction, those stats were produced in less than 30 secondes, but I abandonned all attempts to form a coherent system based on it.

As you see, the kind of setting I tend to play can vary wildly, but I use the d20 system with little variation for most (and I plan to test d20 Mecha rules once I've bought the Heavy Gear 3rd edition book). So I would like a system which can be easily used with any setting provided that the rules do not vary wildly (no need to have any compatibility with M&M, Godlike or Star Wars, though compatibility with Star Wars would means compatibility with Spycraft and I would like it, but that goes a bit too far IMO).

The ease of creation with steps is interesting, it means that the system could be easily put in players hands. But I also need that the system can support my habit of assigning stats on the fly. Because once I'm acustomed to a system I do not need the steps anymore to produce balanced encounters.

This is somewhat counter intuitive in D&D (it used to be easy in 2nd edition), given the number of variables, that's why there is those pre-made NPC in the DMG, and all those monster and templates available on the market. Producing balanced NPC and monster being quite hard, those ensure that it is still easy to play.

That's why I'm not even sure that a class/level system is desirable if it makes it hard for the GM to design vehicles when he has the final stats already in mind (while player try to find what they can buy with their money). Though if it can be done without bothering the GM it would be better.

On hit points, is there any inherent reason to tie it to something?

edit: I've lost the PDF of the first 4 chapters and the link seems broken
can I find it anywhere else? There was a lot of good things, and I was willing to see if a different perspective could lend to something.

 

[BlackJaw]

That's what bother me, exception to the system. If their is only one, there is no problems. But it's probable that there is other, vehicles that do not fit well in many vehicles construction system:
-motorcycle (medium size vehicle which can carry two medium size passenger)
-submarine (more a problem with vehicles rules than construction, but still: an easy target when on the sea, a very fragile vehicle when under the sea, plus the cover rules which work strangely with mines and the like).
-rocket (a vehicle which destroy itself in its use)
-cart (or any muscle or wind powered vehicle: how do you determine maximum charge and speed, etc...)

I don't think of them as exceptions. Using the character building analogy I thought of them more as feats. basicaly everything you describe were already exceptions to the rules of vehicles I was using in my point buy system. Point buy or a class like system, it is still an exception. Yah the sails one is complicated because speed is attached to wind (although it works well for solar, psychic, etc) Rockets are best built using 2 seperate vehicles. One is the rocket the other the capsul (or attached shuttle, etc). I have a system for crafts that are connected to others... although its a simple system it does work. submarines and mines are more to do with the medium etc, and I agree with you on that one. Motorcycle... I don't see the complexity here... it all has to do with basic design dealing with the number of people a vehicle can hold/etc. Now the animal pulled/powered crafts... ugh. That is hard stuff to deal with. I'll level with you, I have no idea how to pull that off right now. I remember talking about it once and I think I blanked it all out after the last time I worked on it.

I thought that they (hydrogen filled blimps) weren't used as military vessels

I never said they were used in military blimps (or I shouldn't have said that). I said no sane PC would want to use it. Germans did use them, but I recall it was because they couldn't get the Hellium that the USA latter used in it's airships. (Did you know the US had 2 flying aircraft carriers in the 30s!)

Yet, this fact (2 hp commoner next to a 200+ hp 20th level fighter) does not disrupt suspension of disbelief, because it means easy play and it is used in many games (CRPG, CCG, RTS, etc...).
While not being able to cover some vehicles, or only with special rules, could disrupt the faith in the system.

I have yet to see a system that covers all vehicles in a good way. Yah my system has some holes in it, but reality is a very complicated thing, I can't imagine it covering everything well. somethings will work fine with odd rules if they are needed. How often would single use break away rockets come up in flight combat system?! The animal power system is more likely and something I may have to think on a bit.

Well, d20 BESM and d20 Mecha did something (Point buy) close (even if movement is too cheap for D&D in those books)

I'll level with you: I loved the point buy system of Alternity. I loved making robots and space ships in that system. loads of fun had with that. i started out trying to make a point buy system for ship building (I argued againts systems that were along the lines of vehicles being base craft types + templates... which isn't a bad idea either but makes it hard to build truly custom ships) and we tried working with point buy for a long time. we had a lot of problems with it. I was trying to remake alternity point buy for things that were just space crafts. It was hard because flight is treated difrently in D&D and in our system then it was in alternity. One thing that was always bad in Alternity vehicles was that power sources fueled things, and engines once powered provide movement points, which in turn provide speed... adjusting power levels or engines (one is shut down or destoryed or over or under powered... or god forbid you use power sails etc) ment recalculating all the vehicle's movements etc. That slows down play a lot. I tried to avoid that for faster play. i was also have trouble applying a system with all powered ships to a setting that likely won't etc...

Perhaps I wasn't clear, but I think that this is a good idea. Though I think that building such a system to be generic is harder than building a generic point buy system (The easier it is to use, the harder it is to design).

I'd say building a good system is hard. I was having a hard time with point buy, and I'm having an easier time with the level system as design goes... the fear I have is that making it simplier to build a vehicle system might be to simplified... something that point buy is not in danger of doing at all (I figured it was too complicated!). You sort of put a voice to fear... I might have taken a bit of an agressive reaction to that, but then I've also been told I'm just a bit agressive in general. Sorry if was attacking you. Rest assured I don't know you enough to attack you, and you are helping me out with each post you make (even if we arn't seeing eye to eye on all of it.)

I do not know how to present all of my needs in a pleasant to read form, but I'll try. Here are my needs and their motivation:

-a good presentation and index: Babylon 5 use the Dragonstar's vehicle system, but the repair rules the combat rules and the ship stats were spread all over the rulebook (which had no chapter heading) making it really hard and unpleasant to use.

-an easy way to assess the relative combat strength of vessel: I used the Archipelageo ship system in an over the top campaign, ships were described using monster statblock, so you could compare the ship statblock to other monster to assess its strength (they were given CR). Ships fighted each other on their specific scale (which maked direct interaction from PC a bit hard).

-a guide or sidebars to prevent stupid design: when I used mecha crusade I designed a mecha which was unable to deal damage due to the default damage reduction of other vehicles (it was in the same over the top campaign, in which they modified an undead ship to become a spaceship akin to the one from Captain Harlock).

-ease to reverse engineer stats produced on the fly: in a planescape campaign set in the Ethereal plane, I used a mix of Spelljammer: Spidermoon and Alternity rules to produce ships stats and have interesting interaction, those stats were produced in less than 30 secondes, but I abandonned all attempts to form a coherent system based on it.

Thanks for the guide lines here... the bits of interesting examples made it clear to see what is going on in your style of play. I'll see what you have:
1) good layout and index so when you need a rule you can find it. I personaly hate the 3.5 DMG because I have a hard time finding the topics I need. I'll be sure to look at the book I have durring the editing and try and and make it cleaner and well layed out because it's just a good idea to do.
2) I was hoping to balance the vehicles mostly as an equipment thing because giving CR (or ECL) to a player in item for is just such a bad idea under basic D&D DM type rules. On top of that, a vehicle's power is tied to it's pilot's and gunners' skill. a nice ship with a bad pilot, or a big gun with a commoner level 1 as a gunner is not that so bad... on the other hand a deth star with a bad pilot and crappy gunners is still a death star. I'll likely use price as a balancing factor for PCs, but list a CR for use by NPCs (enemies). I'll also take another look at the Dragonstar & DMG rules for modifiying a CR/Encoutner level based of extra or powerful gear.
3) The danger of Stupid design is part of the reason I was moving away from point buy... it was quickly becoming apparent that you could all to easly make vehicles that could not fly in gravity! UGH. It reminds me of how you could make ships in Alternity that didn't have enough power to use more then half it's systems (like engines or life support but no guns)... in a few situations it was cool, but it got real complicated real fast. The advantage of the character like system is that it's like making a PC: Sorcerer Half-orcs in full plate are not a good idea, but it's not like they can't walk or don't have enough magic power or have no spell slots... ships system is the same way. You can make a lot of vehicles... some won't be all the powerful or effective, they will all fly and do the basic stuff. Side bars are still a good idea though (side bar: don't make wizard half-orcs in plate male unless you like casting lots of still spells!)
4) Ok, this is a hard one to do, but it should be easier then using an alternity-spider moon combo (wow!). Still building a system that would be easy to reverse would be hard. Mostly it comes down to picking a size, Hit Dice, and picking a number of Engine levels. Faster and more manuverable vehicles have more ranks of Engines. (Sails are special systems!)

As you see, the kind of setting I tend to play can vary wildly, but I use the d20 system with little variation for most (and I plan to test d20 Mecha rules once I've bought the Heavy Gear 3rd edition book). So I would like a system which can be easily used with any setting provided that the rules do not vary wildly (no need to have any compatibility with M&M, Godlike or Star Wars, though compatibility with Star Wars would means compatibility with Spycraft and I would like it, but that goes a bit too far IMO).

I've been working on getting it to work well in D&D, and I recently looked at D20 Modern's built in vehicle rules (no creation rules but vehicle rules) and they are remarkably similar to the vehicle rules we have ended up making here. Only thing needed to make the system compatible with d20 modern would be purchase DCs. Beyond that I haven't worried about it. I looked at and talked to d20 starwars players to learn what they liked and didn't like about that system. I also looked at Dragon Star (I own a lot of it) and felt it was ok for spacecrafts but wasn't all that great outside that and was bad if you wanted to usign anything other then space crafts (dragon vs space ship, or space ship vs wizard in a tower, etc) I haven't worried about making it combatible with starwas d20's existing vehicles or stats... but I did worry about dragon star's teleportation magic system because it affects the setting. I've found that Sci-Fi settings with faster then light travel systems are effected by it's rules. Alternity had a chapter talking about that in it's ship building book. instant travel takes have a diffrent effect on designing a culture (and military tactics) then one that involved more time to get somewhere. the stardrive system is diffrent then space folding etc. Dragon Star has it's teleport system which I figured was about the only Dragon star thing I needed to be able to deal with on Dragon star terms.

The ease of creation with steps is interesting, it means that the system could be easily put in players hands. But I also need that the system can support my habit of assigning stats on the fly. Because once I'm acustomed to a system I do not need the steps anymore to produce balanced encounters.

Once your acostumed to this system you could mostly do it on the fly. I present it in steps to make it easier to understand becuase right now I'm the only one with it all in my head right now. It should be fairly easy to make stuff on the fly (just like with making D&D npcs on the fly) guess a size and a HD then figure out how much of a focus it has in various things... gun ship? lots of weapon levels. high AC? lots of armor levels. Lots of high-tech or magic systems/powers? lots of support levels. Fast and/or manurable? lots of engine levels. Figure the details latter. I can't imagine it being any harder or easier then making just about anything else, but I don't make things on the fly that much myself. (I figure stuff in and adance and if I do make someting on the fly I don't worry about how much it fits latter when I rebuild it correctly. I'm not even sure how to build a system that is easy to reverse build unless I make it so simple it becomes hard to build interesting or complex ships.

That's why I'm not even sure that a class/level system is desirable if it makes it hard for the GM to design vehicles when he has the final stats already in mind (while player try to find what they can buy with their money). Though if it can be done without bothering the GM it would be better.

I'm sort of thinking this won't be any worse then a making an NPC... I felt the point buy made it too complicated. I don't figure this will be bad on GMs. It's a good point to bring up though. DMs often go into something with a target concept in mind, and it should be easy to build this in reverse. I figure it will be ok because we arn't talking about true levels, but something simplier then that. Simple things shouldn't be hard to judge? Did the builders focuse on engines, armor, weapons, or special systems... and in what amounts? Assign levels accordingly. Easier then trying to figure how to connect a target monk undarmed damage with a target rogue sneak attack bonus damage and ability to cast invisiblity with out making an NPC too far over your NPC's character level!

On hit points, is there any inherent reason to tie it to something?

Is there any reason to not tie it to something? If hit points have a bassis that is done entirerly on price (in say points in a point buy system) you could make massive ships with small hit point amounts or tiny ships with massive hit points... that breaks my suspension of disbelief and making players buy hitpoints is just another thing to get complicated. I tied it to size because it seemed like a good idea, a larger vehicle would have more hit points. Other have argued that it should be tied to thickness of hull (the material per inch rules for objects in D&D says that hitpoints for a material is based off the thickness in inches x the hitpoint value for the material) but I figured that didn't work so well for vehicles as it did for static objects like walls, doors, and floors.