i thought there were only 2, (cause when i bought it, it only came with 2 plugs), but i took the boat out and it wasn't driving normal, the rear looked like it was going under when i put it at full throttle and the front was going way up. and at full throttle it was going really slow. so when we got back to the boat launch and put it on the trailer i saw a third hole on the bottom and it had water gushing out. so i figured that's why we weren't going anywhere, cause we were sinking and didn't realize it! so i assume we have 3 on the boat, are there anymore like on the sides or underneath i am unaware of? or is it different with all boats? i have a 1989 proline 17 cc outboard..