Naval Icebreakers

[Ex-Dragoon]

Ok you will have to explain how a hovercraft manages to break ice. Correct me if I am wrong but hovercraft ride a cushion of air trapped in their plenum....besides I thought all the CCG hovercraft were based out west and used for navaid and rescue missions.

 

[Neill McKay]

Ok you will have to explain how a hovercraft manages to break ice. Correct me if I am wrong but hovercraft ride a cushion of air trapped in their plenum....besides I thought all the CCG hovercraft were based out west and used for navaid and rescue missions.

They produce a wave (similar to the bow wave from a ship).  They approach the ice over open water and ride up onto it, causing the wave to undermine the ice -- a bit like a torpedo displacing the water from under the hull of a ship.  I understand that it's only effective on first-year ice.

 

[ChopperHead]

basically Ice is not solid, it has millions of tiny little holes in it anyway when the hovercraft goes over the ice it disterbes the water beneath the ice and cause a sort of wave and the ice breaks. you can do this at very fast speeds.

 

[Ex-Dragoon]

Thanks guys that makes sense.

 

[Torlyn]

Lt, when you say it's only good on first year ice, is that becaue 2nd year ice is thicker, or because the ice itself has an increased density and won't transmit the wave anymore?  Just curious.  Wish I still had the Discovery channel... 

T

 

[ChopperHead]

the ice doesnt tranmit the wave. the ice has nothing to do with it. it's the water under the ice where the wave is. second year ice would just be thicker.

which what Im wondering if a large Hovercraft could do it. the ones the coast gaurd use are relativly small. 4 man crew I think.

 

[Neill McKay]

which what Im wondering if a large Hovercraft could do it. the ones the coast gaurd use are relativly small. 4 man crew I think.

Here's a link to the Coast Guard fleet list.  The hovercraft are at the bottom.  There are two in Quebec and two in BC.  (I don't think the ones in BC do a lot of icebreaking...)

http://www.ccg-gcc.gc.ca/vessels-navires/main_e.htm

 

[ChopperHead]

ya I was right. 4 man crew. those are awefully small. I think they just use them on the saint lawrence sea way.

Still I wonder if one say 5 times as large would be able to tackle thicker ocean ice.
Im not an engineer or Nautical in anyway so I have no idea. Just something to consider though.

It's not written in stone that we have to approach icebreaking in the convential means. Im sure that if we gave some funds to R&D they could probably come up with something viable. Maybe a giant ice melting laser for instance lol  ;D

 

[Neill McKay]

ya I was right. 4 man crew. those are awefully small. I think they just use them on the saint lawrence sea way.

Still I wonder if one say 5 times as large would be able to tackle thicker ocean ice.
Im not an engineer or Nautical in anyway so I have no idea. Just something to consider though.

Sometimes an outside perspective helps to solve a problem -- people who do something for a living can sometimes get into a limited mindset and forget to think "outside of the box".

Speaking very generally, it isn't always possible to scale machinery up.  It could be possible to build a hovercraft, say, one and a half times the size of the current ones, but it might become impracticable to go beyond a certain size because the size of the required engine might become unreasonable (for example).  Another hindrance to breaking heavier ice by hovercraft might be that the ice would close up before the ships could get through (since the hovercraft would be zipping along many miles ahead of the ships it was escorting).

 

[Colin Parkinson]

The CCG uses the AP1 –88 hovercraft in two different sizes each craft has two lift engines and two thrust engines. The larger 400 class will carry a fully loaded pumper truck.

The hovercraft creates a depression in the surface of the water and will create it’s owns bow wave up to around 15-20 kts after which the hovercraft can break through the wave and become a truly “dynamically operated craft”, we call it “hump speed”. It is this effect that is used for breaking the ice, the craft stays just below hump speed, creating a significant bow wave, the wave travels under the ice both lifting the ice and removing support from it and the weight of the craft contributes to the cracking process. This is used to prevent ice jams in the rivers back east, but I seem to remember that the effect is limited to a certain thickness and would have to be new ice. Hovercraft can not operate in an area with heavy ice ridges. But Hovercraft do benefit from scaling up as they can carry significantly more weight, but the limiting factor is your ability to jack it up to do skirt repairs.

The drawback of this effect is called “shallow water effect” where the bow wave becomes significantly higher in shallow water and will prevent the hovercraft from breaching it’s own wave. This effect was more prevalent in the older, smaller SRN6 hovercraft with one engine and if you watched them you would notice that the pilot will climb up onto the beach to pick up speed before crossing into the water. Hovercraft will actually go faster over land, ice than water, but the SRN6 was limited to 30kts (max speed when new was 60kts) over land in case of engine failure  I spent most of my time in SRN6 hovercraft and the AP1-88 came in just as I changed jobs.

The Royal Marines use the Griffion, about the size of a SRN6

By the way real men drive SRN^’s the AP1-88 are for pussies!!!  ;D ;D

 

[Kirkhill]

Colin:

Could you comment about the use of air bubblers on conventional icebreakers,  and also about the use of the Azipod propellers on these double-ended ice-breaking tankers?  I believe in both cases the idea is to undermine the ice, just as the hovercraft does, weakening its supports so that it is more inclined to break.  Were these technologies available in the 1980's when the Polar 8 Class icebreaker (8 feet or 2.2 m?) was proposed?  Do they make a given ship more capable now?  I note that the Polar 8 was budgeted at about 450 MCAD in 1980s dollars while the Norwegian and US boats designed to work in ice about half that thick seem to be more in the 100 MCAD current dollars range.

Cheers.

 

[Colin Parkinson]

I don’t know anything about the azipods and ice, but the purpose of the bubblers built into the hull is to reduce friction between the hull and the ice, allowing the vessel to maintain momentum. I think the first version of this came from Finland. Some countries have also used “ice breaking” barges that strapped onto the front of a regular ship.

Here in Canada we use “bubbler systems” which are plastic pipe strung underwater which air is pumped into and then bubbles up through holes to hit the ice above, this helps corrode the ice and slows the forming of ice. This is normally done to keep ferry routes open, I think the longest is in Williston lake and is over 4 km long.

The last time I looked at cost, the money we spent on the “Louie” could have built a new breaker in Finland, I did see a model of the Polar 8, it had a SRN6 hovercraft on davits on the Starboard side I think. Tried to find a picture, but no luck so far. I did see the only “real part” of the Polar 8, a chunk of hardened steel that sat in the back 40 of the hovercraft base approx 4-5” thick that was used for testing.


A couple of interesting links

http://www.dieselduck.ca/library/articles/russian.htm

http://www.looksmarteurope.com/p/articles/mi_qa3760/is_200210/ai_n9130313

http://www.msc.ec.gc.ca/crysys/education/photogallery/photogallery_edu_e.cfm

http://en.wikipedia.org/wiki/HMCS_Labrador_(AW_50)

 

[Cdn Blackshirt]

The Norwegian Coast Guard Vessel Svalbard: 

General Characteristics
Displacement: 6500 tonnes
Length: 103.7 m (340.2 overall
89 m (292 ft) waterline

Beam: 19.1 m (62.6 ft)
Height: 8.3 m (27.2 ft)
Draft: 6.5 m (21.3 ft)
Power: 4 x 3390 kW BRG-8 diesel generators
Propulsion: 2 x 5 MW Azipod electric motors
Speed: 17.5 kn
Range:  ?
Complement:  ?
Aircraft: Capacity for two helicopters;
one Lynx carried initially, NH90 from 2007

Radar: EADS TRS-3D /16 ES with IFF
Gun: Bofors 57mm, 12.7mm
Cost: 575 million NOK (80 million USD), radar and helicopter not included

Importantly, how is it the Norwegians were able to build a single vessel for $80 million and as soon as we start talking about building (3) in series that suddenly the base price is $400 million per vessel?  Are our defence contractors just picking out numbers they think they can get away, or is the $400 million a combination of life cycle costs, radars and helicopters?


Matthew. 

Note:  Reference Information gathered at:  http://en.wikipedia.org/wiki/KV_Svalbard

 

[Armymatters]

What can of ice can she handle?

 

[Cdn Blackshirt]

Up to 1 meter....although if that's not enough, if were ordering (3), you could probably get that specification bumped.


M. 

 

[Kirkhill]

http://forums.army.ca/forums/threads/38894.0.html

Here you go Matt. 

 

[SeaKingTacco]

Importantly, how is it the Norwegians were able to build a single vessel for $80 million and as soon as we start talking about building (3) in series that suddenly the base price is $400 million per vessel?  Are our defence contractors just picking out numbers they think they can get away, or is the $400 million a combination of life cycle costs, radars and helicopters?

We tend to thru-life cost our kit up front.  In other words, we try to figure out how much in training, spare parts and infrastructure HMCS XXX is going to cost us for the next twenty years. 

I seem to recall from a post by Duey (who spent a tour in NDHQ trying to buy helicopters) that a quick rule of thumb for a twenty-year thru life cost on an item is to triple it's original cost.  Therefore, $80 million USD, converted to Cdn and mulitiplied by 3 is getting awfully close to $400 million...

I apologize to Duey in advance if I have misquoted him...

Cheers

 

[GAP]

Keep any vehicle, etc for 20 years, use & abuse a bunch, and you probably realistically looking at 3x the original cost. Sounds about right

 

[GAP]

A not too original thought, but when capital purchases like this are made for major components, are the total funds allocated (eg: 1.2 billion for 3 icebreakers even though original cost is 80+ million x 3 in allocating for 20 year lifespan) and the changes/repairs/upgrades done out of that money? Or each time there has to be major work done, they have to go through the budget system to allocate specific funding, then wait for approval?

I guess what I am getting at, does the government generally give them the basic units and then make the department chase the $$ for future projected work?

 

[SeaKingTacco]

This is getting a bit out of my lane, but my understanding (from OPDPs, way back when...) of defence spending is as follows:

Program X is budgetted at $1 billion for the next twent years.  You get a portion of that this FY to pay the contractor as they deliver your kit and build your infrastructure. This money would be delivered to DND in the Captial expenditure portion of the defence budget. Follow on years (as the equipment is used in service) is handled through the O+M portion of the budget.  The problem of course is that each FY is a standalone unit and money allocated for that year has to be used that year.  If not enough money is given to DND overall (pretty common occurence), the O+M budget usually gets shorted.
At the beginning of the project, some smart guy figured out the to keep Program X going for 20 years, you need to spend $10 million/years in spare parts and overhauls (just rectally extracted those numbers for argument sake).  Because money is in short supply, the O+M budget gets divided up as far as it can go.  Your project only gets 5 million dollars.  You do the best you can...the kit gets run down and misses overhauls and updates...it costs even more money than budgeted now...death spiral begins...

Cheers!