The following was cobbled together from various sources (from here and eleswhere). Assuming Table 1.11 Starships book list the Engines as tandem.
SINGLE WARP ENGINES
Space Cost: 1/2 Size(rounded up)
Maximum Size: Size -1
-1 to all Warp Factors and -1 to Reliability Rating (cannot go below Reliability Rating A)
Starships with Single Warp Engine automatically gain Design Defect (Warp)[Flaw]
EXAMPLE: Lets say you want to mount a single PB-32 mod 3 on the starship you want to build. Looking at Table 1.11(p.13) of the Starships book, a PB-32 mod 3 has a Space Cost of 4+ half-size; Standard/Sustainable/Maximum speed 6/7/8, Maximum Size 6 and a Reliability Rating of a D.
Now, that is for Tandem PB-32 mod 3. To mount this as a Single Warp Engine on the Starship you want to build, The Maximum Size that a PB-32 mod 3 mounted singlarly would be Maximum Size of a 5. The Space Cost would be 4 (5/2=2.5(rnd up)3, 3+4=7,7/2=3.5(rnd up)4) The WF would be 5/6/7 with a Reliability Rating of C.
NOTE: Single Warp Engines are possible by 2227-2229. After 2269 Single Warp Engines on starships drop the Design Defect(Warp System )[Flaw]. Also, TNG Single Warp Engines drop the -1 to all Warp Factors and -1 Reliability Rating penalties.
SPECIAL NOTE: Any starship that has Tandem mounted engines half of the Maximum Size allowed, the ship gains a +1 benefit to all warp factors.
EXAMPLE: Lets say you want to build a ship that is Size 3 and you mount Tandem PB-32 mod 3 warp engines. Your Standard/Sustainable/Maximum speeds would be 7/8/9 instead of 6/7/8.
Look up Doppleganger Warp Drive on the Star trek Expanded
Also, take into account that that the USS Kelvin is canon. I have modified the date in which single engines become available __________________________________________________ _____________________________
THREE WARP ENGINES
THEORY: A three nacelle configuration gives a 1/3 more power to the warp drive, thereby giving greater acceleration and faster maneuverbility.
NOTE: However, in the first experiments*, the third nacelle accentuated discrepancies in the warp field causing warp vibrations. This creates diffuclties in steering, and would have resulted in the ship shaking itself apart at higher warp speeds. It was however noted that if the design was constructed perfectly it is possible for it to deliver what it promises.
*(Wasp-class 2178, Tritum-class 2200, Siegfried-class 2235, Federation-class 2249)
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Side Note: With the operational failure of the transwarp drive propulsion system(2284). Federation engineers went back to improving basic warp technology. Conventional wisdom held that warp drive technology had reached its limits and that no major breakthroughs would occur. As has been the case since time immemorial, conventional wisdom was wrong.
A research team headed by Dr Katherine Ballantine created a computer model that postulated; "Using two "mated" pairs of warp engines, with a total of four separate warp field generators, each casting a single warp field ahead of an ongoing craft in a perfectly timed sequence of events. Resulted in a vessel moving continually from one warp field into another with the constant "shifting" acting as a multiplier effect."
The results were astounding. Warp technology had never been able to propel an object faster than Warp 14(2,744c). Using this model, Federation engineers were able to construct vessels using three or four warp engines. As with three warp engines the problem had been resolved by a simple timing of the three warp fields.
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Space Cost: Place an additional 1/2 Size(rounded up) to the normal cost.
+1 to all Warp Factors
Starships with Three Warp Engines automatically gain Design Defect (Warp System)[Flaw] Next Gen ships drop this Flaw.
SPECIAL NOTE: Three Warp Engines configurations are available by 2284.
FOUR WARP ENGINES
Space Costs: Double the cost.
NOTE: Four Warp Engines configurations are available by 2284.
