PHOTO: The ducktail on Viking Ocean Cruises' Viking Star. (Photo by Jason Leppert)
Not to be confused with the popular Disney animated television series from the late 1980s, “DuckTales” (although I’m sure the theme song is now stuck in your head), ducktails and interceptors on cruise ships are those somewhat unsightly additions to a stern that jut out beyond, usually with a flat portion of structure. These relatively new elements may be a bit ugly, but they make for a far more efficient ride.
Examples of ducktails you may be familiar with on brand new vessels are the ones aboard Viking Ocean Cruises’ new ships like the Viking Star and Viking Sea, and variants that have been grafted onto existing ships include the more architecturally pleasing ones on Disney Cruise Line’s Disney Magic and Disney Wonder. Whereas most are flat, almost brim-like extensions to the aft section of a ship, Disney’s do the best job of masking their appearance with a more shapely curvature and pinched center line that matches the bulk of the stern above.
Just what is the purpose of these new add-ons you may ask.
Well, the website gCaptain gives a good technical description: “A ducktail is basically a lengthening of the aft ship. It is usually 3-6 meter long. The basic idea is to lengthen the effective waterline and make the wetted transom smaller. This has a positive effect on the resistance of the ship. In some cases, the best results are achieved when a ducktail is used together with an interceptor.”
The website goes on to cite that a ducktail can lower propulsion power requirements by 4-10 percent, resulting in a 3-7 percent enhancement in overall energy consumption, at least on a ferry. That is there are great fuel savings to be had.
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Meanwhile, the aforementioned interceptor is an additional element of trim planes at the stern. gCaptain again explains, “The Interceptor is a metal plate that is fitted vertically to the transom of a ship, covering most of the breadth of the transom. This plate bends the flow over the aft-body of the ship downwards, creating a similar lift effect as a conventional trim wedge due to the high-pressure area behind the propellers. The interceptor has proved to be more effective than a conventional trim wedge in some cases, but so far it has been used only in cruise vessels and RoRos.”
The resulting numbers from an interceptor, according to the website, are a 1-5 percent reduced propulsion power demand and an up to 4 percent improvement in overall energy expenditure, again on a ferry. As an interceptor is occasionally used in conjunction with a ducktail, the resulting combined element on a cruise ship will likely appear one in the same.
In fact, it has become common practice to add these to new and existing cruise ships. In some cases, they are more architecturally integrated and less obvious, and in other cases, they stick out quite a bit beyond a typical stern. Of course, it’s one thing to plan such an addition on a new ship when everything is considered as a whole with an overall size that is generally much larger these days, but existing ships have more to consider.
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In the case of the first pair of Disney ships, they already filled out the dimensions of the original Panama Canal locks, so when the Disney Magic first added its ducktail, it was no longer capable of transiting the canal. As the Disney Wonder relies heavily on the engineering marvel to bridge Central America to head to Alaska from the Caribbean seasonally every year, it had to wait to lengthen the ship until the larger new locks were ready. Now it can utilize the newest facilities and has added its own stern extension accordingly.
It’s also understood that ducktails add stability to a ship as former spoon-shaped sterns are flattened out for a wider base. Especially as more weight is added to the decks above when introducing new features, it’s particularly important to ensure rolling is kept to a minimum. Another great website discussing this effect is CruiseInd.
Over time, you’re bound to see more and more of these ducktails and interceptors. Viking Cruises’ founder and chairman Torstein Hagen often speaks of how he knows they are unattractive, but he also admits that the fuel conservation is nothing to sneeze at. After all, savings to the cruise line is ultimately a savings to you.