Ships – Ice breakers – Rams
Patent
1994-01-24
1995-10-24
Swinehart, Edwin L.
Ships
Ice breakers
Rams
114 56, B63B 3508
Patent
active
054601100
DESCRIPTION:
BRIEF SUMMARY
The object of the invention relates to a method for improving the seakeeping characteristics such as the rolling characteristics of an icebreaking ship and a hull form of an icebreaking ship.
One of the problems is shipbuilding is that the hull form of the ship usually is a compromise solution of the required characteristics. If the hull form of the ship is designed to benefit one particular use area only, other characteristics may get worse. One of these objects is the breadth of the ship's hull. There are use areas that require a relatively wide hull. This, however, results in worse seakeeping performance of this kind of vessel.
The above mentioned problem occurs especially in modern icebreakers. Nowadays the main characteristics of an ice-breaker are, in the first place, determined by the breadth of required channel to be formed in the ice. Therefore the aim is to make the icebreakers wide in order to achieve the required breadth of the waterway in ice. There are also cases that the necessity of changing the breadth of the hull can be changed just the opposite. In particular conditions instead of narrow hull a wide hull would be more advantageous for stability reasons.
Eventual draught restrictions and displacement of the vessel also have influence on the hull form of a modern icebreaker. Furthermore, for improving the icebreaker capability and manoeuvrability of the vessel the sides of icebreaker are made sloping and the length-to-breadth ratio of the ship as small as possible. This results in the fact that icebreaker is always relatively wide.
Due to the above, modern icebreakers have developed into effective special vessels showing their best characteristics especially in the winter in icebreaking operations. On the other hand, this kind of specialization in one use area only has also led into disadvantages. Hull of modern icebreakers is much too wide for open water operations, which makes the seakeeping performance considerably worse in open water.
The poor behaving patterns of icebreakers in open water are caused in the first place by too big initial stability of a wide hull. The consequences of this are increased tendency to roll and the fact that rolling has very intensive accelerations in beam seas. Furthermore the hull form of an icebreaker is not apt to dampen efficiently the rolling motion because the side form in an icebreaker is round at bilge.
With bilge keels the seakeeping characteristics of an ordinary sea-going ship can be improved, but in icebreakers they can't be used. Ice causes so much ice loads to the hull of an icebreaker that bilge keels wouldn't withstand it. Without bilge keels a ship with wide hull rolls heavily on rough seas and therefore, accordingly, accelerations of ship are in beam seas one magnitude bigger than in a ship designed for open water use. Thus on rough seas it is difficult, often even impossible to carry out operations on an icebreaker. This essentially limits the open water use of an icebreaker.
On the other hand, however, the operating time of icebreakers in winter is so short that it should be able to use them also in summertime in open water. Suitable tasks would be, for example, towing and supply operations. Good behaviour in open water would be needed also in normal operations of an icebreaker because icebreakers must be able to move long distances also in open water during transfers. On modern icebreakers these transfers are, however, extremely inconvenient. Accelerations onboard can then be so intensive that it's intolerable for human body. So rough seas can make the transfers of an icebreaker impossible to carry out.
The object of the present invention is to eliminate the above mentioned problems. It will be achieved by means of a method according to the invention characterized in that for improving the seakeeping characteristics of an icebreaking ship the hull breadth of the ship will be decreased on the aft side of relatively wide foreship at least in part of the ship's length so that in this area the hull will be narrower mainly in the vicinity of
REFERENCES:
patent: 1710625 (1929-04-01), Kapigian
patent: 3727571 (1973-04-01), Devine
patent: 4831951 (1989-05-01), Liljestrom et al.
Eronen Harri
Harjula Arjo
Mattila Reijo
Insinooritoimisto Lehtonen & Siirila Oy
Kubovcik Ronald J.
Swinehart Edwin L.
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