I went to the summit of Chinamna's Hat once maybe 5 years ago. Some of us walked in the waist to chest deep water while others used a boogie board to paddle across. The boogie board might be a good idea in case the tide decides to rise while you are in the middle of the walk.
One thing I would like to note was that once we reached he island, we were greeted by TONS of red ants. THere were ants everywhere. On the rocks, on the ground, on the sand, in the bushes. There was so much that there were ants all the way to the shoreline, some were even getting swept out by the small waves. This is no exaggeration. We wore slippers on the island and the ants were always on our feet. We would have to brush off an ant or two that approached our upper thigh every 1-2 minutes. You learn to live with the 50 ants cruising on your feet and lower legs. Just stomp hard when you walk and most of them fall off. But stand still for 10 seconds and they start to approach your shorts. The good news is that the ants didn't bite. Cool dudes.
Keep in mind that my experience was around 5 years ago. I read about Dayle's more recent trip to the island and he didn't mention anything about ants so things must be different now.
In any case, the trek to the island summit is a memorable one, just to say you've been there. I thought it was a pretty scary climbing those cliffs, but maybe it was because I was in wet slippers.
Don't remember being swarmed by ants when we were there. Speaking of ants, though, Halape in the HVNP on the Big Island is THE domain of ants (big kine flying cockroaches too). Before I went on my first backpack to Halape, Ken Suzuki of the HTMC told me, "Ants will be your best friends" there. The same sentiments were echoed by Grant Oka, Carole Moon, and others who'd been there.
Well, they were right.
That aerosol bug spray that Ken suggested I take along worked wonders, though. :-)
I heard the story went something like this:
Some elementary schools used to go on outings to Chinaman's Hat. But one time, a whole class was crossing when the tide rose. Some kids couldn't swim, so it caused a panic, and quite a few students and teachers drowned that day. All schools stopped the Chinaman Hat outing after that horrible incident. I think it must have happened more than 15 years ago.
Thats why I think if you plan on going across, a boogie board would be a good idea. And fins would be good too. It can be a life preserver, and it gives you something to kick and paddle with if you get tired of walking. But I would not recommend a person crossing if he/she can't swim. That would be way too dangerous.
I remember another incident that happened maybe 5 years ago. Some people were in a inflatable raft (2 of the 3 couldn't swim I think). And none had paddling experience too. From what I understand, they tried to paddle to the island and they missed it. But since they couldn't paddle well, and some couldn't swim either, they couldn't paddle/swim back in and they eventually drowned. YIKES! But I think that was pretty dumb of them to try it if they haven't rowed a boat and since 2 of them couldn't even swim. Not too smart.
I think you just need to use some common sense if you plan on crossing. I personally feel that it isn't too dangerous. But if you are an inexperienced swimmer, you should not go. I would be very hesitant to cross if I did't have some kind of floating device either.
I don't recall the currents in between in the channel. It wasn't throwing me around, but I can't say for sure that the currents are weak enough to swim against if you had to. Something to consider.
Talking about Chinaman's Hat (Mokoli'i), just another a little different story:
A few years ago, a friend of mine decided to get married on top. The bride climbed up with her wedding dress in her pack. She discreetly changed and then the rest of the wedding party arrived including the groom's 83-year old mother. The ceremony took place, and the party then adjourned to their waiting kayaks to head for Kualoa and the reception. Maybe a first for the island?
Kayaking is a good way to go there as there is a natural kayak-sized landing spot on the northeast corner. People also wade/swim/surf or bodyboard without much problem usually as it's shallow especially at low tide without any real currents. I remember a couple of years ago when waves were really big outside the reef and a scheduled race on the 1-man canoe/kayak circuit was changed so that it went around the outside of Mokoli'i and finished at Kualoa. There were some sizable swells off the island but nothing breaking except for some smaller stuff on the inside especially off the northern end. Possible problems for inexperienced people under those conditions but basically it's a pretty safe place to visit. Never really seen any ants or hammerheads.
Have fun, gang!