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foeth

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  • Birthday 10/10/1975

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  1. Certainly very interesting! A first-hand account on an incident is better than a report of "several incidents". I did find not much on the Table Bay in our archives, other than a general paper (in German) on twin-screw single-rudder maneuvering by Brix, also found in his later work in the reference in the opening post.
  2. Not directly, only that a series of incidents happened, but the ships with poor steering behaviour with having an open skeg and diverging shaft lines are Liverpool Bay class, Table Bay class, Helderberg class and Sea-land Market class. Ships with a closed skeg apparently did better at smaller rudder angles with no grounding in Suez but one in the Panama canal (Again no specifics but either Hamburg or Tokyo Express as only two are named? ). Barndoor rudders behind a closed skeg behaved well, with the rudder hitting a prop race at very large angles (Bremen Express, Hong Kong Express, Nedlloud Dejima/Delft/Houtman/Hoorn and Transvaal) (All from the Vossnack paper). Gawn is very well known in the hydrodynamic community; the data of several of the Haslar propeller series are still being used. Just a few months ago I also used some data by Gawn and Burrill on old propeller data (added mass & inertia). Fifty year-old data and approximations that held up remarkably well against a computational re-analysis by your truly.
  3. It crossed my mind; from what I recall she did loose control when accelerating to a higher speed. Some links say yes https://swzmaritime.nl/news/2021/04/01/container-ship-ever-given-grounding-could-it-happen-again/ My focus was now mainly on the twin-screw single-rudder setups, which I hope was not the configuration of that container ship. Regarding Getty/Alamy: I once found an image from my collection uploaded to a forum for sale for $450.... (now in the public domain). Now I always add a small link to my images in an inconspicuous location but there's always some low-life that will even edit that out (for instance); a minor side effect of sharing I suppose.
  4. Blog post update; couldn't resist talking about work Rudders and manoeuvring aren't my subjects but we do have a large database with many useful papers, one of which by a colleague of mine analysing a tanker in a shallow channel. The papers I found on container ships in the 1970s discussing both manoeuvring and propulsion are quite interesting, as these ships match the larger battleships quite well. Many were built as double and triple crew ships and literature is quite rare on the latter. Hope to dig up more. Will the right hon. Gentleman in any event ask the captain to steer this extremely expensive craft a little more carefully? “ Reproduced from Gawn (1950) On January 12th 1934, HMS Nelson was just leaving the Portsmouth harbour entrance at a speed of 15.5kts assisted by three tugs. That is, the rpm of the propellers was set to an equivalent speed of 15.5kts but by the combined effect of shallow water and a following current of about 1-1.5 kts her actual speed over ground was estimated by tracking fixed positions on land at about 7-9kts. As she was about to pass Blockhouse Fort speed was ordered to reduce to 12 knots, the tow of one tug was parted and she was ordered to wheel to port by 15 degrees. Before her rudder execute she was close the east embankment; shortly after Nelson started steering to starboard—against her rudder—and proceeded about 2.5 lengths before grounding herself on Hamilton bank on the opposite side of the channel. Fuel and shells were offloaded, the anchor lowered in a lighter and shoal removed by a dredger; destroyers were ordered to pass her at 20 knots hoping the wash would raise her. I was even attempted to free her by having the crew jumping in unison on the quarterdeck for about an hour. Nelson would be refloated by the next tide. She suffered no physical damage and soon continued with her spring cruise, but the entire affair must have been an embarrassment for the flagship of the Royal navy, immovable for all to see and well captured by onlookers on nearby Southsea beach. The irony of HMS Nelson hitting a bank called Hamilton was impossible to miss by the British press. It may appear a trivial navigation mistake that was initially attributed to wind conditions, but as with all things hydrodynamic—especially in shallow water— the matter is more complex than it appears. I found a paper in our archives by Gawn (1950) describing a follow-up studies explaining what had happened. A series of model tests were performed at the Admiralty Experiment Works at Haslar—opposite to Portsmouth—starting with a small unpropelled 4ft model in a model of the channel; the mass of the model and mass distribution were set to the relevant deep draft conditions as for the ship. These tests were performed with the model in the centre of the channel and various offsets to east and west, at speeds from 7 to 15 knots. The model followed the channel when sailing through the centre with a slight turn to port and responding to the rudder favourably. When the model was more towards the east side of the channel—as was the case on the 12th of January—the model turned to starboard for all observed speeds even with the rudder fully to port; a speed less than 7 knots and a rudder angle of about 20 degrees was required to avoid grounding. When the model was on the opposite side of the channel towards the West the model turned to port, though not as strongly as on the East side. Increasing the depth in the channel reduced to effect of steering against the rudder. Reproduced from Gawn (1950) A second series of test was performed with a medium-sized self-propeller model of 16ft at the large No2 ship tank. A false bottom at a 6.25 degree inclination was added to the tank. The model was tested at speeds of 6 to 14 knots and the rudder angle was set such that the model kept a course parallel to the bank. Reproduced from Gawn (1950) From these tests it followed that the rudder needed to keep a course parallel to the near bank increased with both speed and water depth. At the depth and speed corresponding to the conditions in Portsmouth harbour a rudder angle of 35 degrees was not sufficient to avoid the model from veering away from the shallow region. Using a rudder about 20% larger in area would not have helped in avoiding Nelson grounding. From these test it was concluded that Nelson sailed too much off centre in the channel at a speed at which grounding on the opposite side could not be avoided; a conclusion rear-admiral Macnamara—captain when the incident happened—regretted not having sooner. He also commented that while the Nelsons were reported to have good steering properties that he found them to handle badly especially in shallow water or wind, although this opinion was not shared by other officers. Mr Stanley who worked on the design of the Nelsons as an assistant director of naval construction and who was also aboard when Nelson grounded was of the opinion that the grounding was not to be accounted for by any defect or deficiencies in the steering qualities of the ship; in fact, the Nelsons were known to handle better that the battleships of the Queen Elizabeth or R-class. The cause of Nelson’s course instability is bank suction; in the restricted channel the flow cannot go under the bottom freely and the presence of the wall causes an asymmetry in the flow; the bow experiences a small apparent lift angle forcing it outward, while the stern experiences a low pressure region on the bank side pulling the ship in; a ship will typically yaw and then move away from the bank. The rudder must be moved towards the near bank to stay the course and then the ship can sail at a drift angle in a channel. Nelson’s model test also showed the thrust of the port propeller was about twice that of the starboard propeller as her stern swung towards the near bank. From a more modern analysis we find that the flow in shallow water runs under the keel from the outboard towards inboard side and may even separate running over the skeg resulting in a region of ‘dead’ water. The inner propeller operates more as in bollard-pull conditions where propellers produce more thrust, forcing an even lower pressure on the stern making the situation worse (the contribution of the force imbalance to the yaw moment between the two propellers is most likely very small). Reproduced from Vossnack (1979) The rudder arrangement of the Nelson’s is a semi-balance rudder on an open skeg; these rudders offer good steering properties at high speed with relatively small turning circles and low resistance but are (now) known for their poor steering properties at low speed, particularly in shallow water and more so when their shaft lines diverge when running aft; modern twin-screws container ships with a semi-balanced rudder were reported to hit the side walls of the Suez canal (Vossnack, 1979). A closed skeg may have been a better choice; however, a twin screw-twin rudder arrangement that allows for the propeller race over the rudder offers far better steering properties as the rudder’s effectiveness increases with the flow speed squared; it remains effective in the slipstream even at low ship speeds. It comes as no surprise that increasing Nelsons rudder by 20% had no appreciable effect. Placing the rudder in the slipstream does incur a resistance penalty, partially offset by increased propulsion efficiency as the rudder acts as a preswirl stator recovering rotational energy losses by the propeller. A news clip can be found here A wonderful serious of aerial shots of Nelson Aground are held by de Daily Herald archive and can be viewed via the image thievery website Getty Consulted sources Brix, Manoeuvring Technical Manual, Seehafen Verlag, ISBN 3-87743-902-0 Hamburg 1993 Burt, R.A., British Battleships 1919-1945, ISBN 9780 1 84832 130 4, Seaforth Publishing, 1993 Garthune, R.S., Rosenberg, D., Cafiero, D, & Olson, C.R., , The performance of model ships in restricted channels in relation to the design of a ship canal, David W. Taylor Model Basin report 601, 1948 Gawn, R.W.L., Steering and propulsion of HMS Nelson in a restricted channel, Transactions INA, volg 92, pp82-106, 1950 Hoydonck, W., van, Toxopeus, S., Eloot, K. Bhawsinka, K. Queutey, P. & Visonnea, M., Bank effects for KVLCC2, J. of Marine Science and Technology 24(9), 2015 McNeil, Nelson & Rodney 1927-1949 The big battleships, Maritime Books, 2005 Vossnack, E., Good steering properties of container ships, the Motor Ship, November 1979 https://api.parliament.uk/historic-hansard/commons/1934/jan/31/his-majestys-ship-nelson-grounding
  5. Ah that would would sense; not sure where the 2nd pair would be for the forward pair, might be just below the mounts. Perhaps as random detail...
  6. I would assume it it "somewhere" but the PS aft quarter of the boat deck is not sufficiently well photographed (as are other areas of the ship ). We know at least one locker is not where it was supposed to be according to the plans, so some artistic license is in order as it would be strange to be one locker short. Most RU lockers for the pompoms are largely below the boat deck, against the bulkhead near where the 5.5in guns used to be.
  7. Did you find: http://godfreydykes.info/Directors Various Part I.pdf ?
  8. Incidentally, I just uploaded a new post with previously unseen pics (well, to me at least) of KGV in Australia with a link to the famous Alan C Green pics https://ontheslipway.com/hms-king-george-v-visits-melbourne/
  9. Alright, I managed to upload one of my frets with eyebrows in 1:350 scale here https://ontheslipway.com/wp-content/uploads/2022/05/fret11.dxf It's lines only, needs filling etc, and is in my old drawing format (top, bottom, holes, bridge links). The set has large, small and covers, added for someone who made an Ark Royal. Hope it helps!
  10. Thanks Maarten, same here Unfortunately, it hath pleased the Lord to knock over one small tree in last week's storm so some gardening was in order. I celebrated this hard work and will probably not be hungover when the F1 race starts to help the wife support Max. Meanwhile, in this weeks episode of How often can you look at a photograph and find something new The aft Quad Vickers are supposed to have two ammo lockers on their pedestals, but as the lower images show one of these lockers is stored on the boat deck. I concluded that only one locker was therefore fitted to the pedestal, but the top left image---that I acquired a few years later---shows two lockers; the other side (top right) remains inconclusive. And, it seems that one additional locker is placed on the boat deck with its back against the at searchlight platform, so that the total number of RU lockers for the machine guns is raised to four. With a fellow Hood enthousiast we were also discussing the total number of RU lockers for the 4" guns. The AOTS Hood seems to be based on this official 1940 plans that almost matches the photographs. The colour coding is as follows - Bright green: clearly spotted on a photogrpah - Dark green: vaguely spotted on a photograph but in the right position - Orange: no photograph found of the locker / area - Red: clearly spotted to be not present. - Yellow: one location spottted on a photograph but not on the plans - Blue: ammo hoist (as fitted to the part seen in previous post) - Magenta: location of the Quad Vickers RU lockers. So that also means that if all 4" guns have 5 RU lockers we are one short.
  11. For about 20-25 EUR you can have your own set done at https://www.etchworks.eu/ . I can send you my eyebrow design as an example, if you wish...
  12. Good progress These drifters are fascinating little ships.
  13. So these three are for HMS Hood and are painted in her hull colour, AP507B (Much to my regret, a DIY mix before SovereignHobbies new paints hit the markets). I painted the floor dark deck grey, and some pics of Hood also show the chute below the main barrels in a darker colour, so I copied that. Not entire clear if that persisted, but it seems so. I have not actively searched for any (C)AFOs specifying how to paint the pompoms though! The barrels are a light gun metal with darker metallic cooling sleeves. Hood was painted in a uniform grey, so I used that for all directors and such as well, though you do see colour variation. For instance, the 4" mount in the background is markedly lighter than the rest of the ship...
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