Frigate Helge Ingstad Design - Damage Survivability


precisely, the force of impact probably rolled HI on side, exposing its underbelly to hawsepipe.

Also, we have to remember that there come three elements in play: a) hawse pipe, b) anchor chain, and c) anchor itself. As far as I know the anchor and about 20 meters of the anchor chain got lost and hadn’t been found so far. It very well might be possibility that once we raise HI we find the anchor and the chain embedded into side of HI (apart and in addition to the damage done by hawse pipe alone). Think of fish which broke fishing line and ran away with hook.


Given the reports of initial flooding 3 compartments abaft the engine room, this seems like a very plausible theory.


You are right there are no pictures of HI underwater, below waterline hull damages available. When Sola TS contacted HI from starboard, I would expect HI to heel to port being pushed away from Sola TS. Of course HI does not roll back afterwards to submerge the gash in the side several meters above waterline. Pictures/films of HI afloat after collision, apparently without propulsion, show HI upright with no stern trim for several hours. The gash was then above water.

I cannot understand why HI was later pushed against the shore to submerge the starboard damage above waterline.

I doubt any Sola TS anchor/chain damaged HI. Anchors normally drop straight down and do not get caught into warship propellers and rudders in high speed collisions. Anchor chains are normally locked when nor used and cannot be ripped off in collisions.

Re stabilizers, I doubt warships have them and use them transiting in protected inland fjord waters. They are fitted on pax ships at mid length below water (of course) and are used in open seas, so Sola TS bow flare could not touch them in any case. But, divers should inspect HI hull to clarify question of stabilizers.

Interesting case. Divers should inspect the HI wreck or salvors should lift it on a barge and remove it somewhere.


Um, I think you may want to revise your picture with the hand-drawn guesstimate of where the HI was gashed. If you examine that picture of the actual damage, there is a very straight line at the edge of the gash that is steeper than what you drew.
Consider this as well - the HI was doing 17 knots, M/T Sola approximately 5 knots, for a combined speed of 22 (or so) knots. 22 knots = 37.1 feet/sec or 11.3 meters/sec. The visible slash is approximately 40 meters long to the point where it disappears from sight, so the two ships were in contact for at least 3-4 seconds. In that time, the M/T Sola (at 5 knots) would have moved forward approximately 8-10 meters - more than enough to continue that slash well around to the underwater parts of HI if she was being rolled to Port. Given the lightweight nature of HI and the high mass nature of M/T Sola, I consider that a distinct possibility. That slash may well extend around underneath the hull to below the waterline.

Regarding stabilizers, I believe that it has already been established that HI had them (to assist in air operations), but not whether they were deployed at the time.


I believe that HI was lifted on the bulbous bow of Sola, her side was HI ripped open by the anchor of Sola TS. She sank because the way the tugs later pushed her. Slowly she gained weight as the water continued to fill her up and finaly the wires broke.


A bit OT but here is a detailed description of the Nansen Class frigates with all their armament and some equipment, incl. machinery arrangement:


This was in the comments


Electric bow thruster


A retractable 1MW electric bow thruster provides precise manoeuvrability when the ship is in confined areas. The bow thruster can be used as an auxiliary propulsion unit in an emergency if the main propulsion system is compromised.


The stabilizer fin is located about 3-4 meters below the gash and was probably torn off by the sheer force of the collision resulting in possible hull damage on the HI. This of course if the fins were extended and not in the retracted position but somewhere it was mentioned that they were out.


So the collision side damage was above HI waterline but for some reason first the aft peak (AP) was down-flooded via this damage when pushed below water, then the compartment ( AP+1) fwd of the aft peak/steering gear room was progressively up-flooded (the AP bulkhead was not watertight!), and then the third compartment fwd of the aft peak (AP+3) was also progressively up- flooded (the shaft tunnel in AP+2 was not watertight or the stabilizer fin was ripped off?) and finally the second (AP+2) and fourth (AP+4) compartments were finally progressively up- flooded one way or other (the bulkheads were not watertight). Later compartments AP+5, 6, 7, … 15, fore peak, also filled up). Which remind me that there are no rules how to build watertight bulkheads in a warship. In the navy you can do what you like. Nobody cares about safety. Main purpose is to wipe out the enemy! So there are no watertight bulkheads!!! On my merchant ships the ISM instruction is simple, when in collision/grounding occurs, one seaman sounds all tanks/compartments to establish what is dry and what is leaking and reports to the Master. I doubt HI had such instruction, because it didn’t matter anyway. There were no watertight bulkheads on HI! That’s why warships are so expensive. There are no rules to control the costs. And as taxpayers pay, nobody cares. I cannot complain – I was paid 500 days watching the nonsense on the scrap back in 1960/70’s in the Royal Swedish Navy.
It seems the HI wreck has to be removed ashore for examination. It is a joke!


This is an assumption, not proven facts.
Even if it is based on statements from crew,(??) there may be confusion about the order the compartments flooded.
The stabilising fins are situated in the gear room. Could it be that the first flooding was there and spread to the other spaces initially through the propeller shaft tunnel?


…as with the Costa Concordia, where a 80-ton-piece of the famous rock was wedged into her hull.

Big tankers create an important wave in front of the bow, like here >>>

Bulbous bows are optimized to reduce the wave at cruising speed; I don’t know how the wave would look at the true speed of Sola.

When HI crossed the bow wave, before contact with Sola’s anchor, she must immediately have heeled to port and exposed her starboard wall to the anchor.

Then, the initial gash prolonged aft and downwards, probably due to further heeling under the collision forces. On photos, it is not visible how far, aft and down, the gash continues.


It seems the structural damages are mostly above waterline and involve several watertight bulkheads ending at the main deck … subject to diver inspection. Another question is if HI had a double or single bottom. A 2 m deep double bottom would not have been damaged and would provide plenty buoyancy.
And it had guaranteed structural resistance to a missile impact, whatever that means.
The square, flat stern like a box is very ugly but probably very easy (=cheap) to weld together. Most yachts today have a platform welded on the outside of the stern today to simplify boarding.
We are told that the HI deck house is gas tight but there are big air intakes on both the forward and aft funnels so that the engines can run! Maybe they can be closed from inside? Anyway, no ship floats on its funnels.
My ferries have permanent, horizontal steel fenders fitted at main deck level for protection when moored along side. Maybe it was too costly to fit anything like it on HI? Doesn’t a ship like HI spend most of its time in port?
Anyway, pushing HI against the shore submerging the side damage allowing progressive flooding was a mistake. They should have turned it around and pushed it so the hole was above waterline.


Found this dwg on the Shipbucket forum with the following text:
The damage to aft section are sever, FN-class have to power-generator room for electricity, it’s clearly the aft generator room is damaged, and cabins that are aft in the ship-section. Question is how many of the water/air tight bulkhead have been closed. This bulkhead was build in a way the ship could survive in a chemical/gas/radiation area. I estimate at about 6-8 bulkhead is damaged (2, under water line, 6 above water line.) No wonder she was laying so heavy on her stearn, after that collision.

But that she managed to stay afloat for so long means that bulkheads in front of torpedo rooms must be intact, if not, she would just had gone immediately down, after a crash like that.

Wonder if the anchor did this damage and got caught on initial impact and while partly paying out under the force pulled the ship up and over and ripped it open like a can opener and displaced the starbord propeller shaft causing the upflooding. That anchor might still be embedded in the stern.


So HI has no double bottom and the aft peak is connected to the aft generator single bottom room, which in turn is connected to the aft engine room via two shaft tunnels. So three compartments fill up at once due to non-watertight bulkheads. And then two undamaged compartments fwd/aft of the aft engine room fills up!
On top of this the ship has no bilge pumps to pump out water from any compartment.
Imagine that I dreamed about being safety officer aboard a similar destroyer 50 years ago. It had an open bridge on top of the wheel house, from which the ship was run. No risk to fall asleep there. Unfortunately I was ordered to stay ashore and occupy myself with R&M. It was quite fun though because the girls loved my uniform.


The gash across the hull is askew. First point of impact is high on the right where the hull is penetrated. As the ship is gradually pushed over, while moving forward, the gash is opening up in a can opener fashion from that point and moving in a slanted way further down the hull until the contact at the lowest point left is lost. After that the HI will veer upright again but that probably causes flooding at the left of the gash that is now submerged.

The tangent of the slant angle can be measured and the resulting angle is about 9 - 10° what more or less could be the heel of the HI caused by the collision.


No. The M/T Sola TS anchor contacted the HI deck house several meters above main deck and more meters above waterline. HI heeled port due to contact, while Sola TS ripped open the deck house down to the main deck, and then the HI hull side downwards towards the waterline. We don’t know the extent of HI hull damage below waterline.
I doubt the M/T Sola TS anchor ripped open five HI watertight compartments below waterline and above the HI double bottom in the 5 seconds collision. So progressive flooding of intact HI compartments took place after the collision = HI sank! Like all warships HI was never seaworthy as per rules and regulations, because there are no such rules.


Wasn’t the progressive flooding to non-damaged compartments initially blamed on faulty stuffing boxes? That would explain the slow sinking even if watertight scuttles on the bulkhead deck and watertight doors on the bulkheads (if fitted) were closed properly during damage control efforts. I would also assume that such highly-deforming damage could easily compromise the watertightness of adjacent structures that may look intact from afar.


You need to stop this ridiculous ranting about warships not being built to rules. You really seem more crazy with every post. Of course warships are built to rules, just like every other ship. All American war ships are built to rules (currently ABS class rules for Naval Vessels or High Speed Vessels - depending on the ship). Recently, in addition to building to these rules, the ships are then classed by ABS. The only difference between this practice and commercial practice is that warships are not generally maintained to class due to the cost and lack of perceived value.
As a rule, naval vessels are built to much more stringent damage stability criteria than any commercial ships - just due to the nature of service. So please shut up.


It should also be noted that there are other rules than classification society rules. For example, the US Navy has their own requirements for damage stability and survivability which are not maintained by ABS. I would presume that prior to the development of classification rules for naval vessels, navies had their own standards for e.g. steel construction.