Island connection from Honolulu

What ferry? No ferries between the major islands. I believe there are a couple of little ferries running between one or two of the smallest inhabited islands, ie between Maui and Lanai (Lanai is pretty small and doesn't get a ton of tourists) but nothing between the major islands. The major islands are probably too far apart for a ferry-based day trip anyway, even if there was one. So I think your only practical options for inter-island travel would be flights, which don't have to be super-expensive. I'm sure there are lots of tours you could book pretty much everywhere (although plenty of people visit without booking a tour and just travel independently - Hawaii is pretty easy to do and easy to like).

Doing another island as a day-trip would leave you with very little time there and not seeing much, but I'm sure it's possible if all you want is a very quick glimpse. But if you've got 10 days in the islands, why not split your time between a couple of them? That's quite easy to do. You could easily do part of your trip on Oahu, and another part on one of the other islands - any of them, in fact (including Maui or the Big Island).

But if you want waterfalls, head for Kauai, there are oodles - and to many people (myself included) it's the most beautiful Hawaiian island and as a bonus, the one major island that's not so heavily dominated by mass tourism (there are certainly plenty of tourists on Kauai, but large parts of it are relatively undeveloped and uncrowded) . It's lovely, the most green, most wet of them all (for waterfalls, you need some rain - Kauai gets plenty of that, but check seasonal weather....it does rain in all the islands, Kauai gets more than the others). Oahu and Kauai would make a very nice trip; go to Oahu first, go to Kauai second, you'll appreciate the unspoiled nature and relative lack of tourist crowds on Kauai more after being in Honolulu.

As you probably already know, things in Hawaii can be expensive (this is a gentle understatement).

You can easily fly. Last time I checked there were no ferry options. I would consider doing 5 nights Oahu and then 5 nights Maui, then fly home from Maui. Rent a car on each island. From Maui we have done a day trip with a tour company on their boat and overnight visit to Lanai using the public ferry. There is one for that short stretch. I have not done any research on how this is working since the fire.

Norwegian Cruise Lines has a fantastic cruise of Hawaii that visits several islands, check it out.

We were on Maui once, and some friends made a day trip from Honolulu. Given the timing of their flights, we pretty much only had time for a nice lunch, a look at some beaches, and a drive to and from the airport. It might look very small on the map but it takes a lot of time to get around. And they do have traffic.

Only ferry I know of, as mentioned, is the Lanai-Maui ferry. There used to be a Maui-Molokai but that has been closed down. All other inter island travel would be flights or a cruise ship. The Big Island is our favorite.

We have a friend who lives part time on Kauai. They typically fly to other islands to meet friends for lunch, participate in sporting events, see medical professionals, etc. Once you get to the island of your choice for waterfalls, and I too recommend Kauai, you’ll need to rent a car. It’s easy driving on Kauai.

Honolulu is just a big crowded city and Hawaii, in general is a very expensive place to visit. I would suggest for 10 days, to pick one of the other islands such as Kauai or the Big Island (depending on your interests) to experience Hawaii, rent a condo within walking distance to the beach, visit Costco for food supplies and relax and enjoy. As someone already said, no ferries (the islands are quite a distance apart) and flying between islands eats up your time. Kauai is green and lush and has a lot of easily accessible waterfalls, Waimea Canyon and Hanalei. The Big Island has the volcano national park, the Kona coffee plantations and Kailua-Kona.

debbiefischetti,
We are planning a short (5 day) trip to Oahu in January. As far as that island goes, with research and info from the wonderful people on this forum, we chose not to rent a car for most of our stay. Car rental and PARKING are very pricy there. We will rent for just one day to drive to the north shore and environs for a day. We have learned that public transportation in the Honolulu area is affordable and efficient, so we will use that for all the places we want to visit. That said, the suggestion to split your stay between two islands is excellent. The inter-island flights are quick and frequent. (I don't know how expensive they are now.)
As far as Kauai is concerned, having a car is the way to go, but you probably won't have the high-priced parking problem there. We have been there twice, and to the big island once, and love both places. Kauai is, as they say, truly the garden island, and beautiful. But Hawaii Island itself is also beautiful and full of things to delight the senses. We especially like the Hilo side.....more rain (therefore more lush surroundings), but much more "old" Hawaii. I recommend having a car there as well.
Whatever you decide, I am sure you will have a great time.

As has been mentioned there is no inter-island ferry service.
There is frequent service to all of the neighbor islands via Hawaiian air, taking an hour or so to get from Honolulu to Lihue (Kauai), Kahului (Maui) and either Kona or Hilo on the Big Island. Any of those would satisfy your curiosity about local waterfalls. We lived on Kauai for 13 years and I can certainly recommend the island, though our personal favorite for our frequent re-visits to Hawaii is the Big Island - lots to see and do and not quite as expensive as the others if you do a little homework beforehand.
You could conceivably day trip to any of the neighbor islands from Honolulu but it would be a very long day. As an alternative you could consider an open jaw (or multi-destination) itinerary by flying into Honolulu and then home from Kauai, Maui or the Big Island. There are flights back to the mainland from any of those which would save you a day of backtracking.

Another vote for kauai, for waterfalls and the Spouting Horn and there is a small coffee plantation there and feral chickens 🐔 abound

We did the NCL Hawaii cruise several years ago for a first visit and enjoyed it very much. We got to see the four main islands and spent two days on each. We rented cars in some ports and did a few ship tours. We spent a few days in Honolulu pre-cruise. After Oahu I probably liked Maui the best but of course things have changed since then. Actually, I liked all the islands and would be happy to return to any of them.

We did a trip of about ten days to Hawaii many years ago. We flew from the mainland to the Big Island, spend about five nights there in two different locations, flew to Kauai for another five nights in a single location, then flew back to the mainland. At the time, the only way to get between the islands was to fly through Honolulu. It was actually fun because the nice airline employee at check in on the Big Island (this was before checking in on apps) gave us seats with the best views for each leg of the trip.

The point I want to make is that you don't have to use Honolulu as base. It would probably be cheaper, and certainly less stressful, to focus on the other islands. The two island trip was our first trip to Hawaii and even after later visiting Honolulu, I don't regret skipping Honolulu the first time.

I agree with the comments above about waterfalls on Kauai and would encourage you to include that island on your trip. If you really want to see Honolulu or another part of Oahu, you could spend some time there and then fly to Kauai for the balance of your trip.