Pretty much this. Oh, but I was not so lucky to have anything that would be used to attack it. My first playthrough of the Wind Waker, I tended to procrastinate with a lot of things--not just that Triforce quest near the end of the game. So, I went to the Forest Haven, where I was supposed to get Farore's Pearl... but when I got there, I got distracted by the forest fireflies. So, after I received the Deku Leaf, I set back off for Windfall to give the firefly to Lenzo.
When I was on my way down to Forest Haven, I just jumped over those random octoroks that would appear on occasion, but remembe that I still have nothing to throw or launch at marine enemies (the first item for that was the boomerang in the Forbidden Woods, which I left behind). But, on my way back to Windfall Island, I was clueless on what I got myself into. While in the sector of Fire Mountain, I sailed right into the Big Octo's domain. I had no clue what was going on... I was just like, "Oh, a whirlpool... hmm..." Then to seeing the Octo itself kind of startled me. The only thing I could think to do was to L-target it with the grappling hook, but I just ended up salvaging... so I was helplessly sucked in.
That had to be, like, my scariest moment... I think after that, my experience with Big Octos wasn't good at all. I think this whole thing was the reason I procrastinated so much with the Triforce Quest. When I had to sail around the cursed ocean, I seriously went on the internet to find the Big Octo locations so I knew which regions to avoid... I was that freaked out. I think after I got to Jabuun, I got so paranoid, I had to get my sister to get me to Outset for me.
Now, I kind of find it ridiculous, but there are still traces of that fear when I go back to replay the Wind Waker. Whenever I pull enough courage together to actually kill one, I feel all awesome afterward. xD