Lately I've been toying around with a custom ship design ruleset for MTU, mostly to combine what I like in a single place and leave out what I won't use. It's a hybrid of LBB2 and LBB5 -- generally the rules of the latter applied in the spirit of the former -- with no regard paid to other versions of Traveller (which I don't even own). I thought I'd post what I've been thinking about it here to get suggestions.
* Hull Size
I want the rules to work (fairly) seamlessly for making small craft. So hull sizes are 10, 20, 30, ... 100, 200, 300, ... 1000, 2000, 3000, ... I thought of a cute 'size code' for a USP: a 300-dton hull has a size code of 23, meaning "two zeroes with a three at the front", though it's hard to see 28 and think of that as 800-dtons. So perhaps it's too cute and should just be the first number. Small craft are size 1, small ships are size 2, etc. Vehicles are size 0. Hull price is a flat MCr 0.1 per dton, with no engineering/main compartment worries.
* Streamlining/Configuration
No partial streamlining, I think, but I might go back on this. I'm thinking streamlining will cost hull space, about 5% for aerodynamics, avionics, landing gear, fuel scoops, etc.
I'm torn on configuration. I like the simplicity and freedom of just noting streamlined or not, but I love the specificity and color of the HG configurations if not their actual numbers.
So configuration are hull price and volume modifications which may or may not include streamlining. A needle/wedge hull is streamlined for free but loses 10% of hull to wasteage (yes, the ISS is cheap). A saucer/disk is streamlined at the normal 10% / -5%. Cylinders are 20% / 0% (more efficient to streamline in terms of waste space, but more expensive to build). There will be "Other, streamlined" and "Other, unstreamlined" entries to opt out of the system entirely.
* Drives
I like the LBB2 drop-in drive code system, but I'm afraid the tables get too big to scale from 10-90 dtons up to 1000-9000 dtons. So with a bit of reluctance I'm going with the HG system with % of hull required to get a certain rating. I'd like to be convinced otherwise though..
For maneuver drives, I don't like the disconnect where small craft seem to have an enforced TL of 7-9 (minimal gravitics, lots of thrusters/attitude jet action) while ships have pretty extensive gravitics (TL10). I want it to be an exclusively TL thing where you can make a small craft with grav drives or a 1000-dton ship with thrusters and acceleration couches. So probably two sep. tables for M-drives.
I'm going with power plants not needing to match jump drives, and halving the tonnage needed for jump fuel, which frees up a lot of space for higher jump ships (although see the next item).
* Electronics
I'm combining (over-detailed) computers and (barely covered) senors into a general electronics system and rating, which is bought like a HG drive to produce an electronics rating for a ship, a single number from 1-9ish. The ship's E-rating must meet or beat the ships J-rating.
I like this idea, even if it takes away the fun tough choices one had to make with computer size and program loads. I hope that the E-rating can be tied to the combat system in such a way to add back interesting tactical choices there; I plan on ransacking the awesome simple sensor and sensorlope ideas for that
Bridges are about half the size, although I might forgo it entirely in favor of buying 'control seats' for each crew position (2 dtons each).
* Life Support?
Crew/passenger accommodations sort of assume this but I thought it might be interesting to peel it off and make it an explicit system. Like say taking 1 dton and MCr 0.4 for a person-month with some recharge rules, but then allowing to buy cheaper range for smaller ships (person-days) and longer for the big ships. Might make it cheaper and longer-lasting across the board just to lower its profile a little bit.
* Weapons
I haven't decided yet whether ot use HG's energy points. They do add an extra dimension to picking weapons...
* Hull Size
I want the rules to work (fairly) seamlessly for making small craft. So hull sizes are 10, 20, 30, ... 100, 200, 300, ... 1000, 2000, 3000, ... I thought of a cute 'size code' for a USP: a 300-dton hull has a size code of 23, meaning "two zeroes with a three at the front", though it's hard to see 28 and think of that as 800-dtons. So perhaps it's too cute and should just be the first number. Small craft are size 1, small ships are size 2, etc. Vehicles are size 0. Hull price is a flat MCr 0.1 per dton, with no engineering/main compartment worries.
* Streamlining/Configuration
No partial streamlining, I think, but I might go back on this. I'm thinking streamlining will cost hull space, about 5% for aerodynamics, avionics, landing gear, fuel scoops, etc.
I'm torn on configuration. I like the simplicity and freedom of just noting streamlined or not, but I love the specificity and color of the HG configurations if not their actual numbers.
So configuration are hull price and volume modifications which may or may not include streamlining. A needle/wedge hull is streamlined for free but loses 10% of hull to wasteage (yes, the ISS is cheap). A saucer/disk is streamlined at the normal 10% / -5%. Cylinders are 20% / 0% (more efficient to streamline in terms of waste space, but more expensive to build). There will be "Other, streamlined" and "Other, unstreamlined" entries to opt out of the system entirely.
* Drives
I like the LBB2 drop-in drive code system, but I'm afraid the tables get too big to scale from 10-90 dtons up to 1000-9000 dtons. So with a bit of reluctance I'm going with the HG system with % of hull required to get a certain rating. I'd like to be convinced otherwise though..
For maneuver drives, I don't like the disconnect where small craft seem to have an enforced TL of 7-9 (minimal gravitics, lots of thrusters/attitude jet action) while ships have pretty extensive gravitics (TL10). I want it to be an exclusively TL thing where you can make a small craft with grav drives or a 1000-dton ship with thrusters and acceleration couches. So probably two sep. tables for M-drives.
I'm going with power plants not needing to match jump drives, and halving the tonnage needed for jump fuel, which frees up a lot of space for higher jump ships (although see the next item).
* Electronics
I'm combining (over-detailed) computers and (barely covered) senors into a general electronics system and rating, which is bought like a HG drive to produce an electronics rating for a ship, a single number from 1-9ish. The ship's E-rating must meet or beat the ships J-rating.
I like this idea, even if it takes away the fun tough choices one had to make with computer size and program loads. I hope that the E-rating can be tied to the combat system in such a way to add back interesting tactical choices there; I plan on ransacking the awesome simple sensor and sensorlope ideas for that
Bridges are about half the size, although I might forgo it entirely in favor of buying 'control seats' for each crew position (2 dtons each).
* Life Support?
Crew/passenger accommodations sort of assume this but I thought it might be interesting to peel it off and make it an explicit system. Like say taking 1 dton and MCr 0.4 for a person-month with some recharge rules, but then allowing to buy cheaper range for smaller ships (person-days) and longer for the big ships. Might make it cheaper and longer-lasting across the board just to lower its profile a little bit.
* Weapons
I haven't decided yet whether ot use HG's energy points. They do add an extra dimension to picking weapons...
Like 1% of hull tonnage supports 4 weeks of full life support. But keep the costs (perhaps adjusted if you find them too high) for actual passenger and crew feeding as the replenishment costs for life support. So a long range mission ship might devote 5% of it's hull tonnage to life support gear and be good for 5 months between port calls, as long as they packed enough food for everybody 
