Frigate Helge Ingstad Design - Damage Survivability


The nature of warfare has changed significantly since the 1930s, and the ships being built today are a reflection of that. When ships were fought in a line of battle things like armor mattered. Ranges of thousands of yards made a tactical difference for side armor and deck armor penetration. In the era of over-the-horizon weaponry, detection and weapons range make the difference. There is no armor plate to protect AEGIS radar arrays and all of the sensitive electronics that modern weapons systems rely on. The premise is that it is far better to kill the archer than try to intercept the arrows. Much of modern missile combat can be explained by the work of Captain Wayne Hughes and his salvo combat model (

I don’t know how much punishment anyone expects a ship to absorb in a collision with a vessel 12 times her displacement. Battleship armor couldn’t have protected against tonnage like that.


The question is why a hollow shaft? That is because the inner material to a large extent is not needed for the torsional rigidity of a shaft, that comes exclusively from the material near the outside. Therefore to keep the weight down the hollow propellor shaft can be made much lighter than a solid one with the same strength and stiffness.

A disadvantage is that a hollow shaft is more expensive to make and balance than a solid shaft. If money is more important than weight than the obvious choice is a solid shaft. It is unforgivable that the shafts, at hardly no cost, were not closed at both ends to prevent sea water from entering the ship via that way.


While a controllable pitch propeller requires a hollow shaft between propeller and the pitch control mechanism, I have never heard of a full-length hollow shaft - is it really used in frigate-sized naval ships? Perhaps there’s a translation error or misunderstanding somewhere, and they are referring to the tube where the shaft is running through the compartments? edit: Some articles refer to “hollow propeller shaft tubes”.

As for the lack of photographs of the underwater damage, to my knowledge the damaged part has been resting against the seafloor. In addition, following the sinking, it may be difficult for a layman to differentiate between collision damage and grounding damage. What would the Norwegian Navy have to gain from publishing photos at this stage, especially of an active-duty naval ship class?


So what happened to my post? And the figure I made! Aha, it is still there. So the damage was mainly in the superstructure side above main deck, which does not affect buoyancy. Ships do not float on superstructures! They float on the hull below.
Anyway, Only two compartments of the hull were initially up-flooded - the aft generator room causing immediate Black Out and the cabins/store room aft at two levels. The aft peak, complete double bottom and compartments forward were not up-flooded. No efforts to start bilge pumps were made.
Then we are told that the stabilizers/gear room between the two engine rooms was progressively flooded via two shaft tunnels? Sounds strange! And finally, both the fwd and aft engine rooms were progressively flooded through leaking shaft penetrations in the bulkheads. Three undamaged compartments were progressively flooded from a leak aft.
So, the HI war ship was completely knocked out by a little leak into the aft generator room. And nobody had thought it could happen.


It’s not that unusual for a CPP system to use a hollow shaft with the pitch control rod running within from the actuator (built into the reduction gear or bolted to it) to the propeller hub and crank gear to move the blades. But all such systems I know of are not open at either end. This would suggest big damage to at least one propeller on the outside to let water in and further damage at the actuator on the gearbox to let it out.

Tupsis has a good point in that perhaps they are trying to refer to the stern tube itself and the seals at either end of that failing. Difficult to tell from such a generic section but the inner seal might not have been located in the “gear room”.


The invention of the torpedo led to the development of the torpedo boat as an offensive weapon against capital ships and in defense against the torpedo boat the destroyer was developed (first called a torpedo boat destroyer).

These developments tipped the scales away from heavy battleships to a degree however it wouldn’t be reasonable to expect either the destroyer or the torpedo boat to be built to survive collision with a large tanker.


There are many versions why KNM Helge Ingstad HI sank in a collision. In my opinion it seems HI turned port in front of Sola TS, so the starboard anchor of Sola TS contacted HI superstructure and ripped it open. HI for some reason heeled away from Sola TS, so the anchor then also ripped open the HI hull below main deck but above waterline:

Then two watertight bulkheads were damage below the main deck. This lead to flooding of two compartments - the aft generator room and a cabins/store room aft above an intact double bottom. No big deal. HI should survive it.
But then it is suggested that the gear room between the two engine rooms was progressively flooded through shaft tunnels. And then both the fwd and aft engine rooms were progressively flooded from the gear room via leaking shaft seals in the watertight bulkheads.
I have seen many leaking shaft seals between aft peaks and engine rooms and the easy solutions is to tighten the seal and pump out the sea water in the engine room using a bilge pump. I have never heard of a ship sinking due to a leaking shaft seal.
So it is very good the wreck will be removed and put on a barge for examination.

Tanker Sola and Norwegian navy frigate Helga Ingstad collide off Norway

I’d be shocked if a ship of this size and vintage was using a stuffing box type stern tube shaft seal that you could “tighten up”. On the other hand some naval vessels have an inflatable seal as a last chance seal installed inside the lip seals. Use of which would assume the shaft had not been displaced sufficiently to render it useless though.

It’s not hard for me imagining a ship sinking from uncontrolled leakage from a shaft seal.


It’s not hard for me to imagine it at all; it nearly happened in 2000.


Normally lubricated shaft seals are fitted on stern tubes passing through aft peaks to prevent sea water entering the engine room. In this case plenty shaft seals were fitted in bulkheads of dry engine/gear compartments, where better solutions are available. Anyway, if there is a leak, there should be several bilge pumps available to pump out the water. Maybe the crew didn’t know how to start them? I look forward to the accident investigation report.


So a Norwegian war ship KNM Helge Ingstad (HI) collided with a Malta registered tanker (fully loaded) M/T Sola TS (Sola) in Norwegian VTS waters last month and sank soon after. It was discussed here at gCaptain but then the link was closed = not to be discussed, so I create a new topic about it KNM Helge Ingstad in collision with M/T Sola TS bis 1. That thread was closed immediately.
It seems HI crew was confused. HI then turned port in front of Sola, there was a collision, HI was damaged and sank a little later. It happens all the time. The HI collision damages were 80% above waterline … as expected and was 80% in the deck house and superstructure. No big deal! But it is suggested that some damages were also below the main deck and damaged some HI watertight bulkheads. One way or other some damaged HI compartments were uploaded with seawater.

It is suggested that the HI aft generator room was up-flooded first = Black Out. HI was dead but floating. But later three undamaged compartments were progressively flooded through openings in three alleged watertight HI bulkheads. It means that HI was not seaworthy! Watertight bulkheads must be watertight and not fitted with openings. If you go to sea with three watertight bulkheads not watertight, you should be put in prison 50 years.
For the moment nobody is put in any prison anywhere. The topic is under investigation at Norway so we have to wait for developments.


At the risk of displaying my ignorance…

The two diesels are aft here, with the gas turbine all the way forward. Between is the reduction gears etc.

So this shows the shafts terminating at the gear box which would have been in the gear room.

I assume the diesels would have been in a separate space?


Looks like the diesels here are in their own compartment with a solid bulkhead forward of the engines.


Geeze, thanks for giving concrete imagery to my nightmare scenario. Get that sick in the stomach feeling looking at that.


The leakage through the shaft seals explanation makes sense.


  1. The two most aft compartments, steering gear and and the store room flooded from being open to the sea.

  2. The gear room, the forth compartment from aft, flooded via the propeller shaft. as shown above.

  3. Both after and forward machinery spaces flooded through shaft seals. The gear room has a shaft fwd running to the gas turbine and aft running to the diesels.

The images are from this site which was linked to upthread.
At that site it says the image of the CODAGs is an example.

The Helga Ingstad did have CPP as would be expected; “two shafts driving controllable pitch” propellers so the shafts would have been hollow for the control mechanism.

If the stbd prop or the strut got moved in the collision that might open the shaft to the sea. The prop end of the shaft moving might have twisted the gear-box on it’s mounts which would could have opened up the other end of the prop shaft and the shaft seals both forward and aft of the gear room.

In other words the force of the collision was transmitted through the shaft to the gearbox.

This is the Fitzgerald in drydock - shows the prop and shaft in relationship to the hull


Nansen Class Frigates under water arrangement (3D Model):





I’m going to bet when the ship gets raised the stbd prop is either going to be heavily damaged or gone.


This could be or perhaps not that extreme.

Let’s say the stern tube terminated in the RG room. This would put the outer stern tube shaft seal on the aft side of the strut outside the hull and the inner stern tube shaft seal in the RG room.

Without even opening up the propeller hub/blade/hollow shaft leakage path, if the impact caused the shaft to moved radially and axially it could cause damage to both the inner and outer seals and assuming an oil lubricated stern tube, would have displaced the oil into the gear room followed by the sea. Of course this means a number of bearings would have to have been damaged as well.

If the stern tube terminated in the aft machinery room then the failure of the inner seal should have flooded only that space. Flooding of other spaces would have meant failures of bulkhead seals or other penetrations or from above.

Are the reports of flooding from the hollow shaft from crew interviews or desk jockey speculation?


Yeah, inside the shaft itself or shaft tube.

Either way force transmitted via that path. Or an unbalanced shaft running at high rpm could have just tore things up?

I believe that the info originated from the crew. It seems more likely than making it up from whole cloth while knowing the fact are going to come out soon.

If the gear box torqued it might have damaged the other shaft seals, The gear box was connected to shafts which ran thorough bulkhead to the compartment both fwd and aft (to the diesel aft and the turbines fwd).

That’s my assumption at least. Based on the names of the compartments; gear room, aft machinery and forward machinery and the photos and the diagram of the layout of the CODAGs

This is from the Wikipedia article about the loss of the Prince of Wales after a torpedo explosion near the prop:

Turning at maximum revolutions, the shaft twisted and ruptured the glands that prevented sea water entering the ship via the broad shaft tunnel’s interior bulkheads. The flagship promptly took in 2,400 tons of water and her speed dropped to 16 kts (30 km/h, 18 mph).[35] Testimony from Lt Wildish,[39] in command of ‘B’ Engine Room, indicated the shaft was stopped successfully, but upon restarting the shaft, water rushed in through the damaged shaft passage, flooding B Engine Room and forcing its evacuation. Also flooded from this hit were the long shaft passage itself, ‘Y’ Action Machinery Room, the port Diesel Dynamo Room, ‘Y’ Boiler Room, the Central Auxiliary Machinery Room, and a number of other compartments aft.[40]


No need to wait, this is from the Norwegian Accident Investigation Board (AIBN)

Next, the crew found that water from the aft generator room was running into the gear room
via the hollow propeller shafts and that the gear room was filling up fast. From the gear room,
the water then ran into and was flooding the aft and fore engine rooms via the stuffing boxes in the bulkheads.

And the ship didn’t black out, from the video while the tugs were pushing some deck lights are still on, presumably from an emergency generator.

Ship was abandoned at about 4:50 hrs, lights went out around 0800 hrs,

Here’s a photo of the Helga Ingstad aground with deck lights on



I use the term Black Out when normal electric power is lost and when only emergency power is available, e.g. deck lights. We are told that progressive flooding of many watertight compartments took place and that the crew didn’t use the bilge pumps to stop it, etc, etc. Maybe the bilge pumps were not connected to the emergency power? There are four sister ships probably with same defects. Anyway, nobody is going to attack Norway so the whole purpose of these ships - submarine hunting or escort - is complete nonsense. Imagine 130+ persons sailing around looking for submarines that are not there. What a boring job.
BTW - the ship’s name is not Helga …