CT-Compatible Vehicle Maintenance in GT

Kenneth Witt:


As far as I'm concerned the vehicle maintenance rule in GURPS Vehicles, second edition (VE2, p.146, sidebar) is seriously broken. It may give reasonable answers for tech level 7 gas powered vehicles, but maintenance hours for Traveller starships compared to Classic Traveller crew levels are way off. The rule is overly simplistic in that it is based solely on the cost of the vehicle (Square Root of the cost actually) and makes no account for the type of power system, its power output, the type of drivetrain or the vehicle's tech level. Without consideration for any of these important factors, it is not surprising that the VE2 maintenance rule sometimes produces results that are just plain silly. When I designed a drop tank for a starship last year and the design program told me the hull plus tank required 14 man hours per day for maintenance, I threw up my hands in disgust and made up my own system for calculating maintenance requirements.

Part of the problem is the different assumptions made in Classic Traveller (CT) and VE2. In CT, most of your heavy duty maintenance work is done during the annual maintenance at a port where you have facilities to thoroughly check out all the ship's systems and you have spares available to replace consumables and worn parts. In the time between annual inspections the engineering crew on the ship just monitors the operations and makes minor repairs as needed. In GURPS VE2, the assumption is that large expensive vehicles need constant daily intensive maintenance from a dedicated staff to function. GURPS Traveller has merged these two systems together so you need an annual overhaul plus intensive daily maintenance work. Can you say "The worst of both worlds"?

Since I think of my campaign as more Traveller than GURPS, I have little problem with throwing out broken VE2 rules and substituting something that fits the feel of CT better. So I based my vehicle maintenance rule on the power plant output of the vehicle with modifiers for the technology level, the type of power plant and the type of drivetrain. So steam engines require a lot of maintenance per unit of output, gas and diesel engines somewhat less, and electrical systems (including grav vehicles and starships) have a still lower factors. I assume that improving manufacturing techniques, better designs, and improved material technologies make higher tech level equipment more reliable and need fewer man-hours for maintenance than lower tech level equipment of the same type. Starting at early TL8, (about now) I assume that built in self-tuning, self-test and diagnosis systems will reduce the need for routine monitoring and maintenance. At higher technology levels, limited ability to self-repair also reduces maintenance requirements. This leads to the somewhat counterintuitive situation where at higher tech levels, a more complex and expensive machine may well be easier to operate and require fewer man-hours to maintain than a simpler and cheaper, but lower tech system. This could provide a good reason to pay extra to buy the higher tech level version of a vehicle. Note that my system factors in maintenance for power generating and power using equipment in the vehicle. The external fuel tank I mentioned above and any other vehicle systems with power requirements of "none" or "neg." would require no daily maintenance and only need to be inspected/maintained during the annual overhaul.

The System

Using the maintenance formula in VE2, The man-hours required per day for maintenance will vary directly with the square root of the cost of the vehicle. This has the advantage of simplicity but will sometimes produce some very unrealistic results. My system is more complicated, but I believe it produces more reasonable results for a wider range of propulsion technologies and vehicle types. I start by taking the square root of the power plant output (in kilowatts) and multiplying it by a factor (see Table A) based on the tech level of the vehicle. My formula is normed for Traveller starships, so if you're calculating maintenance for a starship then this is all you have to do. If the vehicle is not a fusion powered reactionless drive starship then there are two other factors to add to the formula. A factor based on the type of power plant (see Table B) and a factor based of the type of drivetrain (see Table C). The full formula is

Man Hours per Day = SQRT(KW) * TF * PP * DT


KW is the output of the power plant in kilowatts.
TF is the Tech level Factor from Table A.
PP is the Power Plant factor from Table B.
DT is the Drive Train factor from Table C.

Table A (TF)
Tech Level Multiplier
5 0.040
6 0.035
7 0.030
8 0.025
9 0.020
10 0.016
11 0.014
12 0.012
13 0.011
14+ 0.010

Notes: Steam engines, the earliest type of vehicle power plant, are introduced at tech level 5, so factors for tech levels 0 thru 4 should not be needed. The factors for tech level 13 and higher assume conventional structures. If a tech level 13 or higher vehicle is made of living metal, it requires no maintenance and the factor becomes zero.

Table B (PP)

Power Plant Type Multiplier
Steam Engine 2.0
Gas Engine 1.5
Gas Turbine 1.4
Diesel Engine 1.4
MHD Turbine 1.3
Fission Reactor 1.2
Fusion Reactor 1.0
Fuel Cell 0.7
RTG or NPU 0.6

Notes: RTG's and NPU's are essentially maintenance free power plants with no moving parts. They can operate for years, or even decades, with no attention from an engineer. This is one of the reasons NASA uses RTG's to power all its long duration probes to the outer solar system. The explanation for why the Multiplier is not zero for these power generators is because the vehicle's power using equipment (such as the drivetrain) will still need maintenance even if the power plant does not.

Personal Note: When my players asked what a NPU looked like, I told them "it's a very heavy completely sealed metal box with rounded corners and various fittings for securing it in a vehicle and tapping it for electricity. It has large radiation warning symbols printed on several of its surfaces with a text message in galanglic that reads, "This unit contains no user serviceable parts. Breaking the seal by anyone other than a factory trained technician will void the manufacturer's warranty." There is also the implied but un-stated addition, "opening this unit is dangerous and really stupid."

Table C (DT)
Drivetrain Type Multiplier
Wheeled 1.1
All-Wheel Drive 1.2
Tracked 2.5
Leg 3.0
Marine Screw Propeller 1.3
Marine Ducted Propeller 1.4
Marine Hydrojet 1.4
Aerial Propeller 1.3
Ducted Fan 1.4
Helicopter or Tilt Wing 2.0
Turbojet or Turbofan 1.5
Reactionless Thruster / Jump Drive 1.0

Notes: This is the most problematic and troublesome part of the system for me, The drivetrain factors are critical for calculating reasonable maintenance requirements for vehicles, but I made up all the multipliers for the currently available real world drive systems based on anecdotal information from mechanics I know, with little in the way of hard data to back them up. I know that a 4-wheel drive is more complicated than a 2-wheel drive system and should require a little more maintenance. But how much more? And what about an electric all-wheel drive that eliminates all the mechanical drive shafts by using a direct drive electric motor built into each wheel? Should that take more, less or about the same maintenance as a conventional 4-wheel drive? I know that tracks are the most complicated and maintenance intensive ground vehicle drivetrain in common use today, but is 2.5 a reasonable multiplier? I didn't want to set the factor so high that a tracked ATV is useless, but there is a huge real world difference between wheels and tracks when it comes to the man-hours required to keep a vehicle operational.

About the only thing I can say in defense of the Table C factors is that they seem to produce fairly reasonable results for the sample vehicles below, so while someone more knowledgeable than I could probably tweak this table a bit to increase its accuracy, the current values are probably good enough for game purposes.


GURPS Traveller Ships

The following table shows a side by side comparison of the VE2 maintenance values and this Variant for all the ships in GURPS Traveller (second edition) book. Note that the power output figures were multiplied by 1,000 to convert them from megawatts to kilowatts before taking the square root.

To see the effect of the tech level adjustment on maintenance, compare the two yachts. Using my system, the TL12 Shallot requires slightly less maintenance than the TL10 Vanderbilt even though it has a much higher power output. Using VE2, the Shallot would require more maintenance than the Vanderbilt simply because it costs more.

The Broadsword, Rampart, and Iramda in the table below all include the standard weapon loads as described in the GURPS Traveller book. All other vessels are unarmed. Installing weapons in any of the unarmed ships would increase their cost and power plant outputs, so maintenance requirements would increase using either system.

The small craft and ground vehicles in Traveller are typically not operated continuously like starships. For vehicles designed for short term operation, you need to know the maintenance interval rather than the man-hours per day. The maintenance interval is the number of hours you can operate the vehicle reliably between servicing. If the maintenance interval is exceeded then the vehicle must start making health rolls to check for break-downs. The maintenance interval in hours can be calculated using the following formula:

Maintenance Interval = 96 / Man-Hours per Day

The following table shows the small craft and vehicles from the GURPS Traveller book comparing the calculated maintenance intervals in hours from VE2 and my Variant system. Note that a longer interval indicates a more reliable vehicle that requires less maintenance.

  GURPS Traveller - Second Edition

Maintenance Interval

TL Vehicle Name VE2 Variant Notes
12 10-ton Rampart 6.1 27.0
10 10-ton Iramda 8.9 33.4
10 10-ton Launch 11.0 82.7
10 10-ton Lifeboat 8.7 82.7
10 20-ton Gig 8.4 44.1
10 30-ton Ships Boat 8.0 44.0
10 40-ton Fuel Skimmer 6.0 24.0
10 40-ton Pinnace 6.8 21.7
10 100-ton Shuttle 5.5 16.5
10 100-ton Interplanetary Shuttle 6.3 21.1
10 50-ton Modular Cutter 7.7 26.7
6 Ground Car 282.4 166.2 Gas Engine(×1.5), Wheel(×1.1)
7 ATV - Tracked 28.8 40.9 Gas Turbine(×1.4), Tracked(×2.5)
8 ATV - Wheeled 16.6 217.7 NPU(×0.6), All-Wheel Drive(×1.2)
12 Air Raft 88.6 1703.1 NPU(×0.6), Reactionless(×1.0)

To see where my system really diverges from VE2, look at the two ATV's in the table above. The TL7 ATV uses a Gas Turbine engine and a Tracked drivetrain. Both are high maintenance items in my system, especially the tracks. The TL8 ATV uses a very low maintenance NPU power plant, an All-Wheel drivetrain, and the vehicle is one tech level higher. All of these factors reduce its required maintenance (or increase the maintenance interval) compared to the Tracked ATV under my system. But since the TL8 Wheeled ATV is the more expensive vehicle, VE2 has it requiring more maintenance. This is another example of the silly results that the overly simple VE2 maintenance rule can produce.

Note that the TL12 Air Raft has the best of everything as far as maintenance is concerned. It is a very high tech level vehicle with a small, very low maintenance power plant and a solid-state electrical low maintenance drivetrain. That makes it by far the most reliable of all the sample vehicles and is a good justification for it to be ubiquitous in the Traveller universe.

VE2 Sample Vehicles

The following table shows calculated maintenance intervals in hours using both systems for some sample vehicles from GURPS Vehicles, Second Edition. The Scout Ship below should probably be considered a long term (continuous operation) vehicle so the man- hour per day figures for it are VE2: 18.30, Variant: 7.16

GURPS Vehicles - Second Edition

Maintenance Interval

TL Vehicle Name VE2 Variant Notes
6 Jeep 319.4 240.9 Gas Engine(×1.5), All-Wheel Drive(×1.2)
6 Transport Aircraft 34.3 33.2 Gas Engine(×1.5), Aerial Propeller(×1.3)
7 Family Car 200.1 199.0 Gas Engine(×1.5), Wheeled(×1.1)
7 Motorboat 253.0 258.1 Gas Engine(×1.5), Marine Propeller(×1.3)
7 Motorcycle 366.7 354.1 Gas Engine(×1.5), Wheeled(×1.1)
7 Main Battle Tank 13.7 27.3 Gas Turbine(×1.4), Tracked(×2.5)
7 Utility Helicopter 43.9 35.3 Gas Turbine(×1.4), Helicopter(×2.0)
10 Scout Ship 5.2 13.4 Fusion Power(×1.0), Reactionless Thrust(×1.0)

Vehicle Quality and Maintenance

An optional multiplier for the vehicle maintenance formula could be a factor for materials and construction quality. If a buyer pays out lots more money for a vehicle made with the best materials available using precision manufacturing techniques performed by the most skilled workers, my base formula will at least not penalize the vehicle with extra maintenance due to the higher sticker price. However, such a vehicle might well require 20%, 30% or even 50% less maintenance than a standard vehicle of the same type. So to reflect this, an additional multiplier of 0.8, 0.7 or even 0.5 could be added to the man-hours formula to reduce the maintenance required for this type of high-quality machine. On the flip side, a shoddily built machine slapped together using cheap materials and substandard manufacturing techniques might easily result in a vehicle with maintenance requirements 50% or 100% (use ×1.5 or ×2.0 of course) more than a standard vehicle. As an example, we could say the ships produced in the General Products facility on Regina in the years leading up to the Fifth Frontier War were of low quality and require 50% more operational maintenance than the imperial standard. Older vehicles, or ones with a history of sub-standard maintenance, may also develop this flaw. Because this factor can vary wildly and could be difficult to quantify, I did not put it in the general formula above and leave applying it to the game master's discretion.

Operational Style

Just because your fusion reactor has all the latest built-in self- test and diagnostic devices available and has a control program capable of operating it more efficiently than any human could, doesn't mean that they will always be used. In the Traveller universe, the Third Imperium has a long history of distrust for automation, especially in the military services. It would be very much in keeping with that tradition if the imperial navy set up Standard Operating Procedures (SOPs) that required their engineers to manually check settings and perform diagnostics that the machinery could easily do automatically. In this case, the operational style of the organization might cause a 100% increase (×2.0) or more in man-hours required for routine maintenance. This would result in military ships with engineering staffs twice as large as merchant ships with the same size power plant. Military leaders might well see this as desirable so as to have more trained engineers available to perform damage control in combat situations. As with quality, I leave the style factor to the game master's discretion.

If you are using both of these optional elements, the full maintenance formula becomes

Man Hours per Day = SQRT(KW) * TF * PP * DT * QF * SF


KW is the output of the power plant in kilowatts.
TF is the Tech level Factor from Table A.
PP is the Power Plant factor from Table B.
DT is the Drive Train factor from Table C.
QF is the Quality Factor - GM's discretion.
SF is the Style Factor - GM's discretion.


This variant method for calculating vehicle maintenance requirements is more complicated than the standard VE2 method, but I do not believe that anything as simplistic as the VE2 maintenance formula can produce reasonable answers across the wide range of technology levels and propulsion types found in the Traveller universe. So if you want more realistic numbers in this area, the additional complications are required. I wanted a system that would produce engineering crew requirements for player character ships similar to those in Classic Traveller and adjusted the factors, primarily in Table A, to produce the desired answers. Specifically, I wanted it to be possible for a single talented individual to operate a Sulieman-class scout ship by himself for an extended period of time. If you want a different outcome in your Traveller universe, you can just tinker with the factors until you get the results you are looking for.

If you find any of the ideas or information presented in this essay to be useful, feel free to use it in your own campaign and reproduce it for personal use.


This page originally found at http://www.elvwood.org/Traveller/Maintenance.html
Last updated: 25 July 2007