FeMO2 Dive Cruise 2007
Report Day 16 -- Friday 26 October 2007 -- Last Day Aboard the SWATH Ship Kilo Moana

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Kilo Moana is a twin hull SWATH ship

Today is my last day aboard the Kilo Moana. About half the science party will disembark at Kona today and the other half will remain aboard to arrive in Honolulu early Saturday morning. Anthony and Hubert and I are scrambling to finish our work in the ship’s computer lab and to organize and backup files from the ship and the Jason team. The Kilo Moana has been a great ship to work on – the crew, the techs, and the officers have all been friendly and helpful.

At first the Kilo Moana was a little strange for me due to its unusual twin hull design. It is much wider than any other research ship I’ve been on, almost twice as wide – and that width is accentuated by the “house”. Most ships have a long narrow house in the center of their long narrow hull, and you can walk around the house on the weather deck. But the Kilo Moana’s house is the full width of the ship; to go forward of the work deck you must first climb a ladder, to walk from the port bow to the starboard you must pass through the house. The way the house dominates the design of the ship makes it seem more like an office building than other ships I’ve been on. It takes a while but once I’m used to it I begin to really enjoy the Kilo Moana. The wide house protects the work deck from the wind so it is a nice place to sit and enjoy the sun. And the large weather deck atop the house is high above the water making it great for sunning, exercising and the BBQ dinner.

The Kilo Moana’s twin hull design is intended to be a stable research platform – to resist the rolling that single hull ships feel in a swell. With its twin hulls Kilo Moana is wider than half its length (88’ x 186’) – roughly the proportions of a brick. In contrast, the Moana Wave, which it replaced, was only about 1/6th as wide as it was long (36’ x 210’). But width is not the only stability feature of the Kilo Moana. It also has very little hull at the surface of the water – most of the volume of the hulls is below the surface. The reason for this will be obvious to you if you have ever swum in waves. At the surface you bob up and down with the waves (and if they are breaking you tumble) but if you dive below the surface the motion of the waves is much less. Submariners know this and dive to escape storms on the surface. The Kilo Moana is built so that most of its floatation is below the waves. The hulls look like two submarines floating just below the surface. Struts extend up from the backs of the two submarines and the ship’s house is built on the cross-structure between the struts tying the two together.

One canard of the Kilo Moana shows
nicely in the clear blue ocean water

Despite the twin hulls Kilo Moana is not a catamaran. A catamaran gets much of its buoyancy at the sea surface due to the width of its hulls. When “submarines” and struts replace the hulls surface waves have very little of the ship to push against resulting in a ship that is even more stable than a catamaran. Ships of this design have been designated “SWATH”, a tortured acronym for Small Water-plane Area, Twin Hull.

A welcomed BBQ on the one-level deck

When I first learned I would be working on the Kilo Moana I was aware that it was a SWATH ship but SWATH ships are so unusual I did not expect to see others. Yet the Kaimalino, a much smaller SWATH ship was tied up just around the pier. With its tall tandem struts and apparent lack of weather deck the Kaimalino looks much more radical than the Kilo Moana. I wondered if it were an abandoned prototype SWATH ship and took several pictures of it. An internet search finds a picture of the Kaimalino at sea with a large helicopter tied to the top of its flattened house and reveals that the Kaimalino had been used as a research vessel by University of Hawaii scientists. On leaving the harbor the next morning I was surprised to see a third SWATH ship, slightly smaller than the Kaimalino but looking more conventional. Topside it looks like a large motor yacht, but below the deck the hull form becomes struts that extend down to two torpedoes. The canopies and handrails give the impression that it was once used as a tour boat, but its location and faded paint give the impression that it is no longer used.

Like a submarine the engines and steering machinery are all contained in the submerged hulls of SWATH ships. On the Kilo Moana, in addition to the main engines and rudders, this machinery includes bow thrusters, generators for electricity, water distillers and the sewage treatment system – all contained within the submerged hulls. I’ve been calling the hulls “submarines” because of their size (188’ long), but the first mate calls them torpedoes. Sticking out from the front of the torpedoes is the need for more machinery, two large horizontal fins that look like small wings or a submarine’s dive planes. The fins are called canards and can be controlled like rudders to give the Kilo Moana added stability or to adjust trim. If required for high speed in rougher water the canards can be adjusted to cause the bow to ride higher.

As we leave the ship in the small boat I ask if we can pass under the house between the hulls, but we are out of time and the Kilo Moana must depart for Honolulu. A little later, standing on shore Craig Moyer and I take some pictures as the Kilo Moana sails into the sunset. It’s been a great adventure and I’m sad to see her leave.

Shawn Doan onboard the R/V Kilo Moana
26 October, 2007

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