I'm teaching my 13 year old step son Max how to spearfish. Today was the first day he has ever shot a speargun. My gun is for sure to big for him, but I wanted to see if he was able to get down there and know how and what to shoot. I took the first shot only a couple of minutes in the water to give him the idea of what to do with different types of fish. I shot a nice sized goat fish we call a Moana Kali. I then turned the gun over to Max and had him go down and take a practice shot at nothing to get the feel of the gun and it's kick. He soon got the idea of how to hold it and fire off shots. He did a few dives on some fish and took a few shots, but no luck. He did a dive on a fish in about 20 ft of water and missed his shot the shaft got hung up on a peice of coral so he had to dive back down to unhook the tip from the coral. He came back to the surface and started pulling up the line. Meanwhile I was floating off to his left debating on doing a dive to look for shells. We were both face out to the deep when I looked over at him to see how he was doing with the pile of line that he had pulled up. He was having a bit of trouble with the tangled mess and I was breathing up to do my dive when I looked over at him again. This time there was something just not right about the picture. There was something large and grey behind him and getting bigger every second. As I turned toward Max the grey object also turned only 15ft away from Max it was a 12 to 15 foot Tiger Shark. I've lived and dove in Hawaii for 11 years now and have never seen a Tiger so this could have been a great experience, but because it was so close to Max and I was unarmed I was a bit unnerved. I swam toward the shark first and it veired away a little, but was still to close for comfort. I surfaced yelling at Max to give me the gun. He gave up the tangled mess and turn to look at what I was excited about except he was looking the wrong way, he thought there was a big fish. I had turned with the shark towards shore and watched as the shark swam between us and the shore which was only about 20 yards away and only about 10 to 15 ft deep. I was scrambling to get the shaft back into the gun and the gun loaded. It circled around and head off to where I could no longer see it. The visibilty was about 70 to 80 ft and the beast disapeared into the grey. Max still had no idea what I was excited about and I kept telling him to get close to me. I finally told him there was a large Tiger Shark and he started looking around trying to find it. I was looking for a place to get him out of the water. Now don't get me wrong, I love to see sharks and have had many encounters with many different types except a Tiger. I think I would have been much more calm had we both been armed and both had seen it. Now looking back on it, it was quite the experience, my first Tiger Shark and at such close quarters. I really wish Max had seen it, but he was looking in the wrong. Max said he was kind of glad he didn't see it he thought he might have paniced, but he had a great time spearfishing.