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  • The sea ain't flat in a storm, there are waves and swells. Think of your automobile and standing water on a road. If you drive through the water, a puddle, you will notice your auto will slow down and create a bg splash. Its the same with a snow drift. its more techinical than this, but its the easy explanation to a land lover. On a ship the propellers are the ship's wheels.
    Sea Toby
    Private 3*
    Last edited by Sea Toby; 9 January 2008, 23:29.

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    • HMNZ Cantbury,
      The report is interesting but leaves a lot of unanswered points.
      The RHIB was probably carried away by hydraulic pressure created in the alcove when the vessel rolled excessively and the RHIB alcove became submerged. The Netherlands ship model basin ,who did the origonal model trials, could probably tell why this happened. One way to prevent in happening again would be to fit a hydraulically operated covering plate, hinged on top. I am surprised the door from the alcove to the cargo deck opened under sea water pressure, I would have expected a strong WT door to be fitted.
      The stabalizers ceased operating when the rolling period was quicker than 11.9 seconds (it was 11.5), this means the fins stick out and don't move, I'm assuming the vessel has fin stabalizers.Surely the information was on board to load and ballast the vessel down to prevent the vessel being so stiff that she rolled so quickly, 28 degrees in 11.5 seconds is a lot of rolling and puts great stress on the hull and machinery not to mention the crew!.
      I'm amazed they were sailing along in such weather on shaft alternators ( driven by the main engines via the gear boxes). The most basic rule is never but your electrical supply at risk. When the prop dug down into the water the engine slowed and the electrical breaker connecting the alternator to the switchboard opened on under frequency trip.Fortunatly they had the main switchboard split in two, maybe they have two seperate boards but they probably lost that engine for a few minutes. could the other engine have been close to coming off the switch board as well? Could this have caused even more excessive rolling and resulted in the RHIB been carried away?
      Lots of questions, no need to rush out and buy a sister ship just yet.

      Comment


      • A propellor is designed by its nature to cope with different forces, namely those when it turns, and the force caused by it pushing water from front to rear. Submergence is when the turning prop is forced further underwater due to excessive rolling. A propellor is only designed to operate in a certain depth of water. Submergence forces it into heavier volumes of undisturbed water , reducing its thrust and then the same rolling removes it from the water where it suddenly finds no resistance. This can cause damage to the Blades, and the shaft, and cause severe vibration in the stern area.

        This is my understanding of it. Hopefully the resident marine engineers will correct me if I am wrong.


        Catch-22 says they have a right to do anything we can't stop them from doing.

        Comment


        • Originally posted by Stoker View Post
          HMNZ Cantbury,
          The report is interesting but leaves a lot of unanswered points.
          .........
          The stabalizers ceased operating when the rolling period was quicker than 11.9 seconds (it was 11.5), this means the fins stick out and don't move, I'm assuming the vessel has fin stabalizers........
          Lots of questions, no need to rush out and buy a sister ship just yet.
          From the Tenix website



          No stabilisers? "...The Tenix MRV is fully equipped for EEZ patrol and response. Specifically, the design provides for a gentle roll period when empty at loiter speeds through the inclusion of active anti-roll tank stabilisation, bilge keels, and the wide beam and hull lines of a passenger ferry..... Benefits of the wide beam include a gentle roll period.."

          Teething troubles, or back to the drawing board? And Tenix is now up for sale...

          Comment


          • No fin stabilisers, however she does have Tank stabilisiation.

            One wonders about the quality control at the Merwede shipyard if they identified these difficulties during sea trials, but chose not to do anything about them. I also believe there is a single engine room, for both main engines, which seems unusual.


            Catch-22 says they have a right to do anything we can't stop them from doing.

            Comment


            • The area behind the the highest superstructure would look to be far more sheltered from a boat storage point of view and would possibly be more stable given it seesm to be closer to the centre of the ship..assuming thats where the centre of gravity would be.

              The idea of a single engine room from a damage control point of view is pure madness.

              I would have assumed a military spec in line with modern doctrines would have specified two engine rooms.

              I am now assuming that the vessel is indeed registered as a Warship rather than a civilian type vessel in grey paint?
              Covid 19 is not over ....it's still very real..Hand Hygiene, Social Distancing and Masks.. keep safe

              Comment


              • Looking at the Canterbury, despite the grey paint she isn't a warship. It has never been the intention of the New Zealand government to consider her an LPD. The government has considered her a cheap multi-purpose ship capable of being used as a training ship for her recruits, as a patrol ship in the Ross Sea, as a resupply ship for the conservation corps, and as a transport ship for a company group of her army. She didn't have near as much problems slamming and propeller submergence when loaded during the expercise. She carried the army admirably. Whatever her problems are as a patrol ship, steaming empty, and losing her RHIBs will most likely be sorted out. Its more of a teething problem, and some misguided design flaws, but she can do her missions she was designed for.

                If the New Zealand government wanted an amphibous ship they would have probably bought the 8,000 ton Enforcer. Instead, the government wanted a ro-ro ship for strategic sealift, and with the capability of tactical sealift when a port wasn't available. It was never intended the ship ever be involved in a opposed landing. Back in late September almost all of the army she carried for the first time had never been to sea before.
                Sea Toby
                Private 3*
                Last edited by Sea Toby; 10 January 2008, 23:23.

                Comment


                • Originally posted by Goldie fish View Post
                  A propellor is designed by its nature to cope with different forces, namely those when it turns, and the force caused by it pushing water from front to rear. Submergence is when the turning prop is forced further underwater due to excessive rolling. A propellor is only designed to operate in a certain depth of water. Submergence forces it into heavier volumes of undisturbed water , reducing its thrust and then the same rolling removes it from the water where it suddenly finds no resistance. This can cause damage to the Blades, and the shaft, and cause severe vibration in the stern area.

                  This is my understanding of it. Hopefully the resident marine engineers will correct me if I am wrong.
                  A Marine engineer tells me:

                  "well ideally props are designed to work in the disturbed water caused by the wake of the vessel......hang on, naval arc book coming out....erm naval arc book on the missing list, but your right in saying the prop will have more friction and therefore greather thrust in deeper water caused by rolling resulting in incosistant loads on shafts bearings and eventually gearboxes and engines/turbines.

                  twin shaft ships are prone to this but are designed with this in mind and the problems usually manifest themselves in an auto slowdown of the engines or a stepped down response on the govorners."


                  Catch-22 says they have a right to do anything we can't stop them from doing.

                  Comment


                  • This magazine article has more on the engines:

                    http://www.rnzncomms.net.nz/navy/doc...agazine%20.pdf

                    Comment


                    • Wasn't the Canterbury's Captain worried that the propellors would 'emerge', rather than 'submerge'? Presumably if they were to emerge - come out of the water due to an excessive pitching motion - they would suddenly spin much faster and possibly damage the shafts, bearings, engines or whatever?

                      Comment


                      • Same problems caused by submergence and emergence.


                        Catch-22 says they have a right to do anything we can't stop them from doing.

                        Comment


                        • HMNZ Canterbury

                          No fin stabilisers, however she does have Tank stabilisiation.

                          Well that tells us why she rolled so badly, I should have known when the report kept referring to the Anti Roll system that they had a tank system not fins.

                          When writing the design philosophy the NZ Navy put more emphasis on reducing rolling when the vessel was at anchor or loitering than when she was underway in heavy weather.(I expect the NS will have it the other way around.) Fin stabalizers do not work when the speed is under 6 knots. obviously tank systems don't work too well when the vessel is rolling badly. I sailed on two ships which were fitted with Flume tanks (anti roll systems), we did not use them much as they were not considered worth the trouble, but we did not go to anchor or do any loitering.It is not a big deal to house the fins if you were doing any boat work, not something you would want to forget though.

                          Comment


                          • Feedback from a couple of old RNZN hands over Christmas beers is that the new Canterbury is another Govt disaster like the previous sealift ship HMNZS Charles Upham, should be painted white with a blue and green funnel and have the words Interislander Ferry painted on the side or at least renamed the HMNZS Chunderbury and class it as a Multi Roll Vessel. But the real views of CPO's with 15+ years service are not the endorsement that Govt wants the public to hear about (especially when they are on the grog and in good form). Funny how the MoD press release of the inquiry came out on the Friday afternoon before Christmas. Since there is an election later this year down here maybe the press might pick up on it.
                            Last edited by Te Kaha; 12 January 2008, 12:56.

                            Comment


                            • Well it must be said that it was noticed over here, and not by just us on this site.
                              Combined with the death of a crewman, the future is not good. The inquiry into his death could coencide with the election.

                              Its not even a useful ferry any more. The bow visor thats on Ben Ma Chree was removed for Canterbury.


                              Catch-22 says they have a right to do anything we can't stop them from doing.

                              Comment


                              • I take it Goldie that the NS have been scratching there heads over how this ship has ended up as well and are at pains to avoid making the same mistakes. From what I have heard (RSA Gossip) the RNZN actually wanted a different ship to what they got and were pushing for a vessel in the 300 - 400 million range.

                                The good news (looking on the bright side of things) is that because the RNZN is now way short of EZZ Patrol days ( at least 100) and that two Anzacs have been trying to do the work of three (since the original Canterbury was decommissioned in 2005) - there is now a clear cut case come election time for the Conservative opposition (who are way ahead in the polls by the way) to get the third blue water vessel they have long promised. So it could be a blessing in disguise. What that will be or could be is a moot point.

                                The new Canterbury with some expensive retification probably will suffice as a straight sealift and support ship. As a patrol vessel in the Ross Sea and sub-antartic fishing grounds - nada.

                                The locally built 55m Lake Class IPV's have been well received which is good news. The RNZN has retained the HMNZS Kahu one of the old Moa class IPC's. This is likely to be replaced circa 2011 with a 5th Lake Class. Also in the early half of next decade the fleet supply ship Endeavour and MCM/Dive ship Manawanui are due for replacement.

                                So lets hope Project Protector Part 2 is driven by operational and strategic realities and not the fiscal and ideological constraints imposed by the Veitnam era hippies and feminists who have been running my country of late. Thats were I put the blame.

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