Wireless signal weak from access point to laptop cause of distance. Are there antennas, boosters for laptop?

Laptop/PC user trying to reach free access point from a distance, wherein signal strength is weak (1-2 bars only), but wish to increase capture range of wireless adapter via an antenna, or some kind of booster adapter to network signal as no control over network signal or distance from access point (on sailboat in marina). Can and/or how can you plug in an omni directional antenna to your computer and/or wireless adapter. Thanks