This is the only day trip, which I do not organize. I do not have the time, to hold your hand during snorkeling. Instead, i will give you advise, how you easily can arrange for a day trip to the islands.
All boats in Kota Kinabalu, start from the Marina at STAR (Shangri-La Tanjung Aru Resort), or the Marina from Sutera Harbour, or in downtown KK at “Jesselton Point”. So, if you stay in the Shangri-La Tanjung Aru, or in the Pacific Sutera or Magellan Sutera, then go to the Marina and ask for the scheduled boat departures.
For all of you staying in Kota Kinabalu, you probably can walk to the Jesselton Point. Go inside the first building, and.. all goes automatic from here.
Expect to pay a RM34 for return boat ticket, RM7.20 for tax, and RM10 upon arriving at the island (Parks Fee). Of course, you can also do island hopping, then the boat fee will be more expensive, you only pay the Parks Fee at the first island, all other islands are free (if you keep your tickets).
Boats are like taxis, they go fast, and don’t care about waves. Please.. be angry at the driver if he is speeding, this helps. If you stay quiet, they go faster.
Enjoy your day snorkeling on the islands, I hope that i can arrange the rest of your holiday ;).