GURPS Sailing Vessels=>http://www.bakal.hr/incanus/gurps/sailing.html
 David Pulver's Weapon and Armor expansions=>http://www.io.com/~pulver/weapon.html
 David Pulver's Customized Ammunition rules=>http://www.io.com/~pulver/custom1.html
Alternate Starship Construction and Combat=>http://www.io.com/~pburns/gurps/shipcon/index.html