Readme:
Once unzipped, place the entire Ship of the Line folder in your art/units folder. Then copy and paste the SOTLLarge.pcx and SOTLSmall.pcx into your art/civilopedia/icons/units folder. Then open up the SOTL32.pcx with an image editor, back-up your units_32.pcx and open it with an image editing program. Paste the image into a square at the end of the other icons, be sure to line it up correctly. Finally, backup your PediaIcons text and Civilopedia text. Then copy and paste the text below into its respective places (feel free to change the Civilopedia description, this is only my version). Finally, open up your scenario in the civ3-editor and add the unit (if you need help with this part, look around in the tutorials forum, I made this quick tutorial because some people organize their units differently).

Enjoy! 

Note: There are four attack animations, Attack A-D. Each can be arranged as you wish, the default is Attack A, Attack B and Attack C. To change this this, simply change the letters under the "Animations" section and in the "Sound Effects" section of the ini file (make sure the changes match in each section!).

PediaIcons

#start units
art\civilopedia\icons\units\SOTLLarge.pcx
art\civilopedia\icons\units\SOTLSmall.pcx

# Unit animations
#ANIMNAME_PRTO_Ship_of_the_Line
Ship of the Line




#PRTO_Ship_of_the_Line
^
^
^A [Ship of the Line] is a dangerous sailing-era adversary, more powerful than $LINK<frigates=PRTO_Frigate> or the $LINK<Man of War=PRTO_Man-O-War>.
^
^A coastal city needs both $LINK<iron=GOOD_Iron> and $LINK<saltpeter=GOOD_Saltpeter> in its
$LINK<Strategic Resource=GCON_ResourcesS> box to build a Ship of the Line.
#DESC_PRTO_Ship_of_the_Line
^
^   
^ As cannons became the primary weapon of naval combat, new naval tactics were required. Boarding an enemy was only important if you wanted what was aboard their ship, otherwise a few cannon holes below the waterline would do. The solution was simple, have more firepower than your enemy. With the extensive rigging for the sails above deck, the only place for a lot of guns was along the ship's sides. Thus the term 'broadside' was coined, when the majority of the ship's firepower would fire simultaneously. Of course, if your ship is in a fleet, the only way to fire two or more broadsides is for your ships to stay in a single-file line. And to have as many guns hit the enemy as possible, they must be in this formation as well.
^ This 'line of battle' tactic required ships that could dish out a good beating, but also take one in return. Thus the Ship of the Line class of vessels were born. By the time of Napoleon, one wouldn't dare put a vessel with less than two decks and 74 cannons into a line of battle. Flagships could have well over 100 main guns on three, even four decks, reaching the limits of sail power. In Europe the Ship of the Line lasted a while inthe face of steam power by retro-fitting the ships with steam-powered screw propellers, however the fully armoured and completely steam reliant ironclad vessels eventually ushered in the new era of engines, armour and massive guns.