When I saw this in the discussion on Subs I was tempted to disrupt the conversation with a tangent, as is my wont.
But I decided to go here instead.
The AOPS has its origins in the Norwegian ship Svalbard. The key difference between the Svalbard and Harry de Wolf is the propulsion. Harry uses conventional propulsion. Svalbard uses Azipods. Azipods can swivel 360 degrees and the propellers can be run forwards or backwards in any orientation. That means that the ship can drive forwards with the Azipods pointed forwards or backwards and can drive backwards with the Azipods driving forwards or backwards.
That allowed the Svalbard to optimize its bow for blue water transits and its stern for ice-breaking transits. This is known as Double-Acting technology and it has been applied to freighters and tankers operating in the Baltic and across the top of Russia. It is the technology that is referred to in the latest Manitoba report on extending the shipping season for Churchill.
In blue water the Svalbard uses the Azipods the same way that the Kingstons usee their Z drives and Svalbard drives forwards bow first.
In ice she reverses in place and drives through the ice stern-first, presenting her stern to the ice and uses it to ride over the ice like a conventional breaker and crack the ice with her weight.
But the Azipods give her couple of other advantages that a conventional breaker doesn't have.
The props can be rotated to face the bow or the stern while turning backwards or forwards.
If facing the bow the props are protected from the ice by the faring of the Azipod while pulling the Svalbard towards the ice. That action also drags the water out from under the ice, removing support from the ice and making the crushing and cracking of the ice when the stern leans on it that much more effective. That gets Svalbard through 1 m ice, or so. First year ice as typically found in the Baltic and Hudson Bay.
But, as noted, ice keels. They present an additional obstruction and can appear in first year ice. 2 to 5 m deep.
Svalbard has a solution.
She rotates her Azipods so that the blades of her props are presented to the ice and proceeds to use her blades to physically grind, mill and chew her way through the ridge.
The Norwegian Coast Guard vessel KV Svalbard Nordpolen has become the first Norwegian ship to reach the North Pole. Built in 2001, the KV Svalbard is a relatively small icebreaker...
gcaptain.com
"The 1,400 nautical mile voyage to the North Pole came just seven days after the ship’s departure of Longyearbyen. At times the vessel travelled through polar ice packs at speeds of up to 6 to 7 knots.
"ABB’s Azipod system is an electric propulsion system that uses electric drive motors located beneath the hull in a submerged pod, which can rotate 360 degrees to deliver thrust in any direction, making Azipod-equipped vessels highly maneuverable. ABB says its Azipods are capable of breaking ice up to 2.1 m thick and have proven to reduce fuel consumption by up to 20 percent as compared to traditional shaftline marine propulsion systems."
.....
This was the opportunity missed when the Canadian Navy opted for conventional drive over Double-Acting Technology.
As noted it is also the technology that enables year round operation in Hudsons Bay and Churchill.
en.wikipedia.org
During winter tests of the Artic tanker UIKKU, it was found that a ship with an Azipod and well designed stern generally performs much better in heavy ice condition when going astern.
www.wartsila.com
Two innovative 106,000 dwt crude carriers TEMPERA and MASTERA were built by the Yokosuka shipyard of Sumitomo Heavy Industries Ltd. for the Finnish group Fortum Oil...
www.wartsila.com
.....
Proposition
svalbard double acting azipods originally designed with the intention of chewing or grinding through pressure ridges
AI Opinion.
Yes, that is correct. The Double Acting Ship (DAS) concept and its heavily reinforced icebreaking ABB Azipod systems were fundamentally designed to
mill, chew, and grind through thick underwater ice accumulations and pressure ridges. [
1,
2,
3]
When a vessel like the Norwegian Coast Guard's
KV Svalbard operates in "double acting" mode, it navigates
stern-first (backwards) through heavy ice. [
1,
2,
3]
How the "Ice-Chewing" Mechanism Works
- Propeller Milling: Instead of relying purely on the weight of the bow to crush ice from above, the ship turns 180 degrees. The massive, heavy-duty stainless steel Azipod blades act like a giant blender, physically milling and grinding down the submerged "keel" of Arctic pressure ridges. [1, 2, 3]
- Water Flush Lubrication: As the pods rotate 360 degrees, they generate a powerful, high-velocity water stream (propeller wash). This water flow flushes the chopped ice fragments away and lubricates the ship's hull, dramatically lowering friction and preventing the vessel from getting wedged or stuck in compressed ice fields. [1, 2, 3]
- Hull Optimization: This design allows the ship's bow to be perfectly streamlined for high-speed, fuel-efficient travel in open water, while the stern is specifically shaped and reinforced to handle severe ice-grinding loads. [1, 2]
This precise capability is what allowed the
KV Svalbard to make history as the first Azipod-powered vessel to successfully navigate through dense polar ice packs all the way to the
North Pole. [
1,
2]
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