By Stuart S. Peters and Richard A. Spellacy*

The supply and anchor-handling vessels that are deployed on the east coast of Canada are basically a transfer of equipment, technology and experience that evolved in the northern parts of the North Sea in the middle to later 1970s. The North Sea as a whole tends to compare environmentally with the east coast of Canada as f a r as supply boat operators are concerned. The northern parts of the North Sea are similar to those off Newfoundland and the southern part of the North Sea.

Anchor-handling/supply vessels were becoming to be recognized as an integral part of the North Sea exploration activity by the late 1960s. Their appearance was coincidental with the use of the semisubmersible d r i l l i n g rigs.

These rigs required to be towed from one drilling site to another, and each site had its particular anchor pattern. The support vessels were used for transporting supplies, towing and anchor handling.

The early vessels engaged for these tasks were of modest horsepower (2,000-3,000) and encountered difficulty in anchor handling because of the low horsepower. It often required two vessels working together to drag out the anchor chains and place anchors.

As drilling programs moved to deeper waters by the early 1970s, vessels of 4,000 to 6,000 horsepower were appearing in order to provide the required support services and h a n d l e g r e a t er lengths of chain and cable.

The North Sea area soon became dominated by Norwegianbuilt vessels that demonstrated that the northern areas of the North Sea required vessels of 7,000 to 8,000 bhp and with greater freeboard. By 1978 a few vessels with over 9,000 horsepower were appearing, and shipyards responded to the required new capacity and capability of anchorhandling/ supply vessels. By now the low-horsepower vessels were obsolete except for the purpose of supply only.

By the mid 1970s the charter rates reflected the change in vessel technology and demand, and many shipyards were capitalizing on the situation. There has been a steady climb in charter rates that reflect a reasonable spread between horsepower categories.

Unfortunately, this reasonably encouraging situation did not last.

By 1975, the oil and exploration activities on a worldwide basis entered a downturn. This was caused by various factors, most of which were related to international politics. By 1978, however, a full-scale recovery was being experienced, which for Canada's east coast was extremely exciting.

Now, again through political disputes between levels of government and an apparent unacceptable national energy policy by some oil companies, we are in a reduced stage of exploration. The effect that politically motivated alterations of policy with respect to energy is serious and plays havoc with industrial growth and to the attainable objective of this nation's energy self-sufficient position.

In view of the uncertainty facing oil companies in the exploration activities, it is not surprising that over the past few years very few vessels of any p a r t i c u l ar horsepower class have been built, and there are now no vessels at all available.

Based on our operations, commencing in 1979 with 14 OSA vessels, we are satisfied t h a t these vessels have performed reasonably well in our waters. These vessels range from 146 to 258 feet long with horsepowers ranging from 4,000 to 13,000, and deadweight tonnages from 936 to 2,480.

The horsepower for east coast support vessel operations appears to be in the 8,000 range with additional specifications and reserve capabilities requiring up to 13,000 horsepower. Along with this horsepower r a n g e , ice-strengthened hulls are required for ice and the heavy seas frequently encountered.

Fuel consumption for vessels in this range could amount to as much as 20 tons per day, and with the present and expected cost of fuel, consideration must be given in designing vessels for the utmost economy.

For ease of maneuvering and especially in the "hover" situation, which occurs frequently under quite extreme weather conditions, joystick control is considered a standard. This single control, through an analog control system, transmits the required signal and thrust strength to the main p r o p e l l e r s , bow thrusters and rudders. The next control development will be a requirement for automatic digital computer control using radar reference to maintain the distance from the rigs when loading or discharging personnel or goods.

There is, however, some general opposition to this system because of the danger of the captain becoming less alert in his monitoring role rather than being physically responsible for the position of the vessel.

Weather-protected triple-drum and closed winches are now being favored over double-drum systems.

This is to facilitate the additional pendant wire for deep waters, and thus, increases the speed of the anchor-handling activity.

There is also a trend toward deeper vessels that would permit 5 to 6 feet of freeboard and the capability of carrying 1,200 to 15,000 tons of cargo.

It does not appear conceptually possible to have one vessel designated that will meet all requirements.

However1 the paper does give an outline specification for a vessel that the authors feel would come as close as possible to the ideal vessel to operate off Canada's east coast.

This vessel has a length of 64 meters overall, a breadth of 14 meters, a depth of 7 meters, and a loaded draft of 6 meters with a deadweight of 1,400 metric tons.

The bollard pull would be 120 metric tons. Propulsion would be provided by two diesel engines having a continuous rating of 8,000 bhp total and a total maximum rating of 8,800 bhp.

In addition to the features listed in these specifications, the following recommendations are suggested, based on the authors' experience, using the basic vessel as the 8000 type OSA: 1. Increase the brake horsepower to 8,000 bhp/120 tons bollard pull (preferably four 2,000 bhp engines with two engines on one gear box).

2. Increase the draft and wat e r / f u e l c a p a c i t y (interchangeable tanks) (100-150 cubic meters of more water would be sufficient).

3. Increase freeboard by 0.30 to 0.50 meters.

4. W i t h i n c r e a s e d d r a f t , a stronger bow thrust unit will be necessary.

5. Cooling water outlet to return outboard and to the seachest (to keep clear f r om ice) with two-way valve.

6. Thermal oil boiler for heating device (preferably steam) to be big enough to heat water tanks, void spaces, s e a c h e s t s, vent pipes and bilges. If steam, connections to be fitted on deck for deicing with flexible steam hose.

7. Vessel to be ice strengthened with icebreaking capability.

8. Bridge windows to have defrosting capability and the bridge to have two separate heating systems, i.e., steam and electric, with each system with the capacity to provide sufficient heat.

9. If avoidable, vessel should not have lifeboats but instead liferafts, to be installed in a place protected from freezing spray (behind the funnels) or releasing device to be heated. If lifeboats are necessary, the boats and davits should both be heated.

10. One storage winch to be capable of accommodating 1,200 meters of polypropylene rope for iceberg towing.

11. Avoid all unnecessary rails, wire stays, m a s t and a e r i a l s, sounding pipes, vent pipes, etc., on the forecastle and forward structure.

12. Winch room to be heated.

13. B e s i d e s air-conditioning, each cabin/messroom should have separate heating systems (steam/ electric).

14. Deep-sea mooring to be limited to one winch.

Other stories from June 1981 issue


Maritime Reporter

First published in 1881 Maritime Reporter is the world's largest audited circulation publication serving the global maritime industry.