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More about the Marindus Integrated Tug-Barge Concept

Catug sketch
Catug sketch

By Mike Waters 2018-11-27 15:50:56

This article is a follow up to the article by Harry Valentine, entitled: Reconsidering an Innovative Integrated Tug-Barge Concept, that was developed by the now closed shipyard Marine Industries (MIL) of Sorel, Quebec, Canada, now 40 years ago. The writer is the originator of the design (see U.S. Patent #4,356,784).

Here are the basics of the concept and how it came to be developed. In 1978, we were invited to submit a bid to build one of the new CATUG’s for Occidental Petroleum. In order to assess what was involved, I travelled to the Gulf of Mexico to inspect the first vessel of that type. While the tug itself is of catamaran form, the barge is not. The central bridge of the CATUG slips over a large steel “tongue” and hugs the rear of the barge with its two hulls laying externally over and around the tongue. This effectively creates a vessel that is almost indistinguishable from a one-piece ship and for the same power, the speed was only a little less - roughly 15 knots in lieu of 16.   

While this was all very positive, there were/are some negatives to overcome. Firstly, a catamaran ship form (the tug in this case) requires two divided and narrow engine rooms that make the boat expensive to build. The barge also required a complex shape to accommodate the catamaran… adding further to the cost.

Secondly, as the tug hulls become the exterior of the final vessel, one is left with the bows being very pointed, and as they are also at the area of maximum beam, this makes them vulnerable to damage when the tug is disengaged. The end result of this is that the Catug and its barge, tend to remain “locked together for life” or most of it, defeating the versatility aspect of the integrated tug-barge concept.

Thirdly, as a by-product of the above, the Catug became physically very difficult to separate from its mated barge, so maintenance between the two hulls was easy to neglect. 

As these things became clear following my visit, I felt we could do better with a monohull tug, yet retain the solid, one-piece linkage that enabled the Catug to perform at sea far better than a tug-barge with more typical linkage, which at that time was mostly a conventional tug lashed into a large barge notch using steel cables (a method still used successfully today in inland waterways).   

Since that time, most integrated tug-barges use systems that pin the tug bow to the inside of the barge wings, so that the two vessels pitch individually. However, this can result in excessive accelerations in the wheelhouse of the tug, as the pitching barge is now wagging the tug up and down in rough water.

As all in-house designs from Marine Industries Ltd  became known as “Marindus” designs, the integrated tug-barge we developed became known as the Marindus-ITB or MITB for short. 

While some areas are detailed in the patent document, here is a brief description, based on how we chose to meet our list of design goals:

The tug was to be able to operate independently in calm and moderate conditions, but become solidly linked to whatever its front-end was to be. We thought of this concept as a marine “tractor with multiple front ends” and the complete boat “as a spade” with the handle (barge) being able to lift the heavy blade (the tug) as one piece.    

To achieve this, the notch was made quite deep, so that the aft end of the tug could be locked into the long jaws at the rear of “the forward unit.” That connection was achieved with a very solid triangular boss (welded inside each jaw), sliding rearward into a receptacle on the tug, formed by two steel fender rails that also served to limit the relative vertical displacement as the tug moved forward into the notch. Upward movement of the tug on entry was limited by four or six truck wheels (mounted on strong pedestals) that rolled along the straight deck-edge of the tug, outside the bulwark.   

At the forward end, the wide forefoot of the tug would interface with a sloped docking ramp on the barge (lined as needed with greased wood or Teflon), using propeller power to thrust forward – just enough to reach an articulated arm (or two), that is powered by a large hydraulic ram. Using mechanical advantage, this ram pulls the tug the last few centimeters to remove all slack. Additional chains and/or links would be added for ocean voyages.     

The same ram is designed to apply a separating force when needed, so that the two vessels can be forced apart, aided of course by the tug thrusting in reverse. Of course, many small details still need to be worked out, but the concept seemed quite feasible and our local Lloyd’s office felt so also. 

(For full disclosure, the bow ram detail was created by designer Jacques Fortin who worked under Andre Taschereau, explaining their names on the patent).

If anyone is interested in taking this concept farther they can request my contact information from Wendy Laursen (wlaursen@maritime-executive.com).

Mike Waters N.A., retired Director of Engineering and Ship Design, was responsible for the design of some 60 ocean-going vessels while at Marine Industries Ltd until it was purchased by a Quebec competitor in 1988 who then closed the yard. Now in retirement, Waters returned to his passion of small sailboats and is currently author of the website www.SmallTriDesign.com

The opinions expressed herein are the author's and not necessarily those of The Maritime Executive.