The H16 main will not fit the P16, The luff of both sails may be the same but that's it, the H16 has 218 sq ft of sail area and the P16 has only 189 sq ft, the difference is in the foot of the sail, the H16 main sail has a longer foot. The H16 has a fixed foot sail meaning that you slide the bolt rope in the foot of the sail into a sail track (curf) on the boom, the P16 has a loose foot sail, it only attaches to the boom at the outhaul car on the rear of the boom.
http://sailboatdata.com/v…record.asp?class_id=3860
http://sailboatdata.com/v…record.asp?class_id=3852
To make the H16 main fit, you would have to take a dremel to the boom to route out a larger opening on the sail track at the front of the boom to slide the foot of the H16 sail into the sail track, but the clew of the H16 sail would stick out past the boom by some 12-18". To attach the H16 sail to the outhaul car you would have to punch a hole through the sail and maybe put a grommet
How do I know this? When I pick up my current P16 it came rigged with a H16 sail as above, a hole has been punched through the sail using a screwdriver, the seller forgot to mention this when he sold me the boat. Always, always, roll out the sails when buying a used boat, worked out great for me, sold my H16 sails for $200 and found some awesome Randy Smyth P16 sails on CL for $200.
If you can borrow a H16 boom to go with the H16 main sail, that should work, as long as you can get the gooseneck on the H16 boom to fit the sail track on the P16 mast, will give you almost 30 sq ft of extra sail area, will make your P16 a
rocket.........
oh yeah!