Nautilus UnderSea CR

The Nautilus Under Sea is the former Undersea Hunter of Cocos Island fame and now back in Costa Rica for part of the year. This brave small ship is one of the most loved dive boats in the world with a huge reputation and following. The Under Sea underwent renovations in 2016 and gained a full-width superstructure and premium suite on the upper deck. She is a 90-foot liveaboard originally built in Florida in 1968 for Perry Oceanographic as a submarine support vessel, working primarily in the Bahamas and the Caribbean. The boat is now completely refurbished for serious diver comfort while maintaining its vast fresh water tank – never a shortage of hot and cold water, even on longer voyages!

The excellent vessel has seven cabins for the maximum of fourteen passengers. All cabins have private bathrooms, plenty of storage, 110-volt outlets, portholes and individually controlled air-conditioning. Five of the cabins have a queen-size lower and a twin-size upper, one has upper twin and a lower twin, and one – the only one on the main deck, the rest are on the lower deck – a queen-size lower.

The large dive deck is also convenient for swimming, kayak launching and, at night, shark viewing. There is a dedicated camera and dive gear storage for each diver, and the very large dive deck turns into barbecue under the stars. The partly covered sun deck is perfect for relaxing. The airy and light-filled dining area and the adjoining lounge are made for socializing and enjoying the excellent food onboard. Nautilus Under Sea offers free Nitrox and Rebreather Support.


95' x 24' ocean-going dive boat

Steel with teak deck

Engines: Twin Caterpillar 240 HP

Tenders: One 25ft. heavy duty fiberglass dive boat. One 32 ft. custom high speed aluminum dive skiff.

Generators: Two 65kW + 1 emergency genset

Voltage: 110/208 VAC 12-24 VDC

ISM safety certified audited by Bureau Veritas, VSAT, Satelite Phone

Compressors: 2 x water cooled Coltri MC-30

Full oxygen, Nitrox and rebreather service
19 guests, six staterooms, one quad stateroom, one premium cabin.

Cocos – Island of the Sharks

Join us this summer for an unforgettable adventure to Cocos, the Island of the Sharks. This 6,000-acre UNESCO World Heritage site is the only island with a tropical rainforest in the eastern Pacific. It holds great fascination for divers, as it serves as the first landmark encountered by the north equatorial countercurrent and acts as a confluence point for marine currents. This unique combination creates the perfect environment for large migratory pelagic species, including hammerhead and tiger sharks, as well as all the other critters that Cocos is famous for.

The diving will be led by our Captain Beto, formerly of the Okeanos Aggressor, who boasts 29 years of experience. He has personally hand-picked a crew of Cocos veterans to ensure an exceptional experience. Our trips take place during peak season when the density of hammerhead sharks is at its highest, giving you the best chance to encounter whale sharks, humpback whales, and much more.

Update – We have gained permission from the Costa Rican authorities to use our 132-foot flagship, the Nautilus Explorer, on our Cocos Island and near-coastal ocean and rainforest adventures. Our beautiful ocean stabilized Explorer features 4 levels of accommodation, huge back deck and camera tables, separate dining room and salon with million-dollar views and of course a fresh water hot tub.

Sample Itinerary - Cocos

On arrival, a 90 minute shuttle transfer from San Jose airport to a resort close to where your ship will be berthed. We recommend arriving early to enjoy what Costa Rica has to offer!

Day 1: 7:30 pm board at the marina and depart.

Day 2: At sea. Travelling to Cocos Island.

Days 3 – 9: Dive, dive, dive plus go ashore on the “real Jurassic park”!

Day 10: At sea. Travelling back to port.

Day 11: Morning arrival at the marina. Disembark 8:30am for resort stay or shuttle back to San Jose airport.

What dive experience is needed?

50 logged dives and advanced open water is the bare minimum experience required to safely dive around Cocos Island. More experience is better and all divers should have good buoyancy skills. The diving can be challenging. There could be strong current on some dives. Some of the dive sites are in open water and exposed to the swell. The difference between Cocos and a destination such as Socorro is that there is no navy base or airstrip on the island which means that airplane medevac is not possible. If you have a medical issue, the boat will have to return to port or at least be met part way by fast boat. For all these reasons, these trips are best suited for good experienced divers. Don’t worry if you don’t feel that you are quite ready yet for Cocos!! Come and visit us in Baja, Sea of Cortez and Socorro and we will get you all tuned and tweaked up for this great adventure!!!


Ocean & Rainforest Adventures

Join us for an exciting adventure that combines peak season diving with exploring the rainforests of Costa Rica. Could there be a better combination? Reminiscent of the old days when we were exploring and adventuring in Alaska and Haida Gwaii, there will be ample opportunity for diving, kayaking, relaxing on pristine white sand beaches, and hiking into the rainforest that is home to a range of monkeys, lizards, parrots, toucans, hawks, sloths, and iguanas. We will see dolphins for sure and hare hoping for Manatees. Summer is the best diving visibility of the year, and it’s prime time for visiting humpback whales and for nesting turtles. Guided with local expertise, we plan on diving at Bat Island (famous for its bull sharks), Catalina, and Cano Islands.

We have been reading about local crocodiles and are excited to try and find them. Which is exactly the point – these first trips are expeditionary in nature. Captain Mike will be leading the first trip, and while we will research the heck out of the area, we are not sure what we are going to encounter. We’ll have our eyes open, have drinks ready for sunset cocktail hour, and we have discounted these first trips to ensure that no matter what, they are a great value.


Hola Costa Rica!
Special Cocos Expeditions
Aug 30-Sep 9, 2023
* 10 night trips from $4995