The Ship Model Forum

Hi All,

Hello EJ and JosephR, great work on the wave pattern and the models too!

I've been working on the gunnery calculations for the Denmark Strait battle lately and speed is a required input, however actually knowing the exact speeds is difficult. I've seen the Suffolk reports that note the dials read one speed but with current wind and wave action they were actually going much faster.

The official speed of Hood and Prince of Wales on track charts etc during the battle is generally 28 knots, they may have actually been going flat out, but what effect the wind and waves had on that speed is the unknown.

But for your calculation I'd try 28 knots as that is the only official speed given. I do have the logs of Prince of Wales but the speed noted is averaged over an hour and so the rapid course changes and speed losses that occurred during the battle are effectively hidden in that average figure.

By the way JosephR I'm still working on what flags we're flying at certain points during the battle, but might at some point need help from more knowledgeable forum members!

Hope that helps a wee bit
Best wishes
Cag.

At 28 knots the trough moves forward a bit and remains present.



From 28 to 30 knots the trough keeps position and descents from about 40cm to a full meter.



(Better images will follow, eventually)

Intensely fascinating. The calculations must be quite complex.

For comparison purposes, here's a bit of "trough inspiration" from another contemporary long-hulled ship, originally designed as a battlecruiser, travelling at high speed on a calm sea. Views include the ship as she turns to port. The wave patterns look very consistent with your computer model.

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Hi EJ,

This is truly fascinating work. Suffice to say I think you have demonstrated a strong correlation with CFD. I've only ever used ANSYS but I know we were always taught never to use the stuff by itself - but I suppose the scale-testing the RN did, those decades ago, probably still stands up by itself as covering the other side. Like you, I also wonder about the effects of a port turn and the non-linearities and periodic instabilities with seastate interference etc. Also, I gather that turning to port would have brought the portside trough further forward as the ship turned into it (she was obviously hit to Starboard - but I say this because am painting her from Port). While nobody could ever ever say it is absolutely the only correct theory that an enemy shell dived a short distance and struck below HOOD's 12" armour strake - the subject of understanding her wake patterns is fascinating by itself. Also illuminating to me because I am just putting the finishing touches on my painting of her, which I which I will post here in > 3weeks' time come May 24th.

Concerning theories as to how HOOD was lost - it also occurs to me that most of the conversations I am seeing are ignoring the fact that heavy shells don't always crash through ships in perfectly the same direction as their incident trajectory. Actually, there are some interesting accounts of shells impacting ships and deflecting at odd directions as they crashed through them - with one very notable story I think from HMS LION involving a shell eventually coming to rest between the legs of a poor terrified sailor (a stoker? I will have to re-check) somewhere deep within the ship. Must have given the poor guy a true fright.. but I shouldn't dive off on this tangent.. to quote a certain movie about something pertaining to gravity and black holes : "some things just weren't meant to be known".

At any rate I am impressed that you actually modelled where the peaks and troughs might be forming.. Regarding the below-attached I have built a grand total of three seascapes now, having experimented with these techniques for a little while; I usually just guess at this information with as much photo reference as I can find.. so there probably are some errors (although as you point out, water is forgiving).. SO here's a nice little ad for Grandpa's Cabinets.. Ron Baluch made these oak trimmings for me. He's been a great guy to deal with.. the Prinz Eugen model is very old.. and needs its boot topping repainted higher.. and please don't get me started on my green HARUNA.. I realise that she possibly never painted up this way but this adult-sized kid has wanted one ever since his former child self first saw that very old (1970's) Fujimi boxart of the green leviathan with its anvil-shaped tophammer.. it is also very unlikely HARUNA could have actually made high speed by this stage of the war.. but I am just having fun.. actually.. all these ships can be removed from the seascapes and are not permanently attached to them anyway - so I may yet put an earlier KONGO into that one..

Hi Cag,

Thanks for your post.. I seem to recall that Admiral Holland had limited his formation speed to the maximum which PRINCE OF WALES could make, being circa ~29kts? HOOD had had machinery repairs by this point - and that stripped turbine blade having been fixed - and she probably might have achieved more - but POW was slower.. I will agree with you that true speed probably moved all over the show. At least the TWA was off to Starboard - so probably wouldn't have factored too much..

I do appreciate your input on flags however. Since we first started talking about this subject I have added a foremast Battle Ensign to PRINCE OF WALES (it's off in the distance, but still there) - and I will not be adding a second Ensign to HOOD, per FW Allen's advice regarding conversations he had had directly with Ted Briggs. My HOOD is just initiating her turn and is making the well-known "two-blue" signal on her Starboard lower signals yard.. I figure Starboard is a safe bet given that POW was in tow on her Starboard Quarter and Portside is leeward - with quite a mass of smoke obscuring any signal made from Port..

Fwiw I really appreciate having a 3rd party sanity check before I take the piece to the printmakers for proper scanning..

Hi Steve,

Those are lovely pictures of Sara (and Lex at the top? or just an older picture of Sara?) - thank you kindly for posting those. I will agree the flat surface makes the effect much easier to observe.. By the way we were in touch many years ago.. It is nice to see your business has evolved and grown. I picked up some parts from you last year which I really like..

But the other hullform coming to mind which makes a pretty big mine in the water is obviously that of the KONGOs.. this seems to be the most severe case of the effect I have ever seen (anybody is quite welcome to upstage me on this one though).. I mean, check out HIEI running speed trials..

Cheers, J

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The trough midship doesn’t look at that deep. Measure the height of the freeboard exposed below the casemates relative to the height of the casements and compare that to the ship at anchor. seems to me the impression of the deep trough is created by perspective of the breaking bow wave:

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Hi Chuck,

Of course you may be right.. it could be that the bow & stern waves are just particularly high.. but wave height relative average sea surface can be difficult to ascertain from photographic perspectives.. and then there are obviously questions around load condition and resultant draught.. I just get the feeling that, extrapolating the converging fall lines to a point of intersection, gives us a bit of a dip.

Agree to disagree?





Regards,

Joseph

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EJ Foeth, Joseph R, Cag and Chuck,

As fascinating as the investigation into whether or not the 'midships wave trough had anything to do with HMS HOOD's demise is, I have some doubts as to what it will prove. I assume that all will be aware that HMS PRINCE OF WALES (PoW) suffered an underwater hit below the belt during the Denmark Straits action: I have never seen any claim in print that a trough had anything to do with it. That aside, it was known by the Germans as early as 1933 that diving shells had the ability to travel like an un-powered torpedo below the surface of water but whether or not a wave trough, would have had any bearing on the matter is debatable.

If an under-water hit was a factor in HOOD's demise, surely a shot falling "short" would have received comment during the investigation afterwards. However, I can't recall reading about such a thing in Mr Jurens's article on the HOOD website. What interests me is the somewhat mysterious comment attributed to Captain Leach that he had the impression that something had arrived onboard the flagship early in the action, there was then a massive fire aft followed thereafter by the loss of the ship.

I don't want re-start anyone going back over old ground: it won't prove anything, so I will end with a comment on the speed of the formation on going into action.

Cag reports that the speed was 28 knots. I can't disagree save to say that it sounds about right. The maximum speed of the KGV's was around 29 knots, HOOD was by 1941 getting on for being an old ship, so she may not have been good for more than 29 knots.
A prudent flag officer would have been mindful of the maximum speed of his slowest ship, PoW and ordered the appropriate speed. That would be that.

Concerning speed gained/lost as a result of weather/wave action. Yes, it can happen but I doubt if it had much, if any, effect on the action in the Denmark Strait that day. The sea appears to have been relatively calm from photographs/film that I've seen, thus the wind speed will have been fairly low: nowhere near enough to have affected the speed of the formation. A ship does lose speed in a turn but I doubt if this had any effect on the factors involved either.

I am probably being patronising here and guilty of preaching to people who know more than me anyway but as I understand it, the midships trough is the result of a combination of factors associated with speed, draught and hull design; which can be affected by depth of water. A projecting bow forward can go a long way to eliminating trough formation and is known to do so but I am now getting into the realm of the naval architect now and I know little about it and so will leave it to someone else.

Right, I have to ask a few more questions at work about the output of the wave pattern analysis; the results indicate that at 28 knots there is a sinkage of about 0.58cm, but the hull in my output files isn't moving.... that's a huge error when trying to estimate the effect of wave elevation wrt the armoured belt.... perhaps there's a simple option or I'll have to write my own post processing using all the output files. I have a ton of tools to do that, but all for propeller... To be continued, but for now please forget about that one meter deep trough I mentioned earlier until I verified what I have been doing! Haven't used this tool myself before

This code I am running is not what people would now consider CFD (I would disagree), such as Ansys' Fluent, as this wave code is not able to capture viscous effect and so on. But this method offers the best bang for buck, especially in the design phase and for some scouting with HMS Hood. We have a code like Fluent too (called ReFresco) but that requires a few days of preparation to run plus access to our calculation cluster... all doable but if the early analysis doesn't hint at a deep trough then it is most unlikely the more demanding calculation will. IIRC, Bill Jurens mentioned that the admiralty considered a hit below the belt and studied the wave pattern of HMS Hood. These results are probably (hopefully) somewhere at Haslar (QinetiQ) and concluded the wave pattern theory was unlikely. We do have meetings there every so now and then and I already did ask them politely to kindly send me everything they have on Hood... but they didn't....

The images of Saratoga and Kongo are indeed fascinating; with a wave length nearing the length of the ship you can tell they're approaching their hull speed. From that colourization monstrosity of Kongo a quick & dirty estimate yields 30.5 knots, slightly above what she could actually do. I collected a few other images of wave patterns as a reference for modeling but never go around to doing anything with them...

Followup: the water surface in the file is corrected for trim & sinkage keeping the hull in place in the 3D file; if you (well, I) look closely at the undisturbed surface in front of the vessel (the 'grain' in old sailing terms?) you can see the change in sinkage showing up with a change in water level. So, ship-fixed coordinates it is & all is well; the presented images show the estimated waterline level properly.

While this calculation takes less than a minute on my laptop, one (!) viscous calculation would take about 8 hours running on 240 CPU cores. (20x Intel(R) Xeon(R) Gold 6126 CPU @ 2.60GHz ($2000 each) with a total 960GB of RAM available.. ). This nicely illustrates how quickly CPU demands ramp up with more modern codes and that calculation clusters are as much a part as our facilities as are our towing tanks.

Hi EJ and others,

I trust you have more than ample scientific background to get the wave patterns cracked!

I however recall a very practical article published on the Steelnavy website: http://www.steelnavy.com/WavePatterns.htm

This at least gave a easy first estimation of the wave pattern of a ship in deep water, given the speed. At least this was a great improvement over the simple but much exaggerated V-patterns sometimes created by modelers with total ignorance of the basical fysics of the matter.

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Indeed, it's all straightforward linear theory. But a slightly more accessible video is here: https://fyfluiddynamics.com/2021/04/kelvin-wakes/.

The concept of group versus phase velocity that you need to explain why there are no waves outside the Kelvin wedge area is conveniently & wilfully ignored, but that video does a very good job at covering a lot of distance fast. Again, basics physics teach us that the speed of the wave is really not the speed of the crest but exactly half that speed; a wave is really only travelling half as fast as it appears to be travelling. I have yet to see a video that explains (explain, not show) that very well without going into theory.



An image I made a while ago shows a travelling wave and as time passes (top to bottom) you'll notice that the wave crest at the front (if you follow it top to bottom) will actually disappear at it reaches that red front, just as a wave crest at the rear will appear out of nothing. These red lines are the actual group speed of the wave, or, the speed at which a 'packet' of waves will travel. Within this packet the speed of the crests is twice that. It's really weird... but while it appears that the waves of a ship travel at the same speed they really do not; at most half that speed, most of them far slower.. You can see it here if you look closely (around 30s)

Interesting discussion! I have been procrastinating about doing the water for my 1:192 Alaska for many years already, but should work on accumulating enough "Roundtuits" to budge the coefficient of static friction to get it at least started. The trough of course is generated as a result of a ship pushing water ahead of it as a result of wave making. The speed of a wave will be related to it's wave length. I was pleased to spend some times on tug boats and destroyers, a contrast in wave making resistance. A tug is perhaps a great example of this effect as it's short length results in a very low natural hull speed and obviously to the observer pushes a wall of water in front of her at "speed". The design HP calculations for US treaty limited Battleships was a trade off between hull weight and machinery power, the longer hull permitted a certain speed (say 27 knots) with less power, but increased the hull and armor weight.

POW, straight out of the builders would at least have a clean hull, as would Bismarck. Hood I cannot say as I have not researched this. Krishima, at her encounter with Washington, was devastated by a number of below the waterline hits which penetrated the side protective system. POW similarly somewhat defeated Bismarcks side protective system by a below the WL trajectory.

USN had access to the David Taylor model basin, but the as built at sea results did not always match the test estimates. Some of the cruisers had speeds a bit below the estimates and Alaska in service had better turning performance than the estimates, being almost identical to the Iowa's and Fletcher's.

It will be interesting to see what you folks come up with. Having never done "water" I'm a bit cautious about this for my project!

Cheers: Tom

Interesting discussion about waves and how much of the Hood's hull could be off the water.
These photos are taken from https://www.maritimequest.com/warship_directory/great_britain/pages/battleships/hms_hood_page_5.htm and show Hood at high speed:





The waves a quite a big and pretty much of the hull is exposed. Not an expert on the Hood, but isn't it already below the armor belt?


66misos

The plate you see above the black boot topping is the 7" upper belt. The boot topping is where the 12" main belt is, and it extends down inside the hull as the torpedo bulges flare out. There's an additional lighter armour plate below the 12" belt outside the torpedo bulkhead extending to approximately the point where the torpedo bulges turn vertical again. Note than in both photographs above HMS Hood is heeled to starboard, which will be exposing more hull below the boot topping on the side photographed whilst the other side will be deeper in the water.

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Actually, the Hood in these photos appears to be going quite slowly, judging by the absence of large wake and characteristic bow wave. What is exposing her underwater hull and also making her roll quite a bit appears to be tall sea swells.

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Chuck,

She also appears to be in a turn to Port which will have slowed her down.

...... and would also have resulted in a heel to Starboard! Sorry, forgot that bit but the situation could well have meant more hull below the waterline being shown than was usual.

I would agree with Chuck that she is in a seaway. A large design issue with Battleships and Cruisers was their increasing draft as "stuff" got added during their lives which actually tended to leave less and less belt above the waterline. This was particularly true of Hood! The main issue was retention of "armored freeboard". USN, and I believe RN ships would have fighting instructions, one of which items would be an optimal combat displacement. Additional factors would be fighting range, which is why Holland was attempting to close the range, concern about Hood's deck armor. At the range she was fatally hit I'm not sure she or POW had immunity for hits against the vertical armor either, though the angle of approach is figured in here. Cruiser immunity zone calculations often assume a degree of approach angle.

I remember seeing these two pictures of Hood as a boy, and have always thought they were the best of her. On another note, the Drakenfel series did a forensic piece on the sinking of Hood, and thought a shell from Bismarck arriving at approximately 30• hit in the area of the trough just aft of the main mast, passed underneath the main belt, penetrated through the hull blister, passed through the crushing tubes, and exploded in the 4” magazine, destroying the bulkhead with the main magazine, blowing her up. An extremely lucky hit.

My Naval Aviator friends had a saying, "Lucky beats Good, any day". The most dangerous thing aboard a battleship in combat is her own munitions. I think some of the CVE's off Samar absorbed more Yamato 18" shells than Hood did hits from Bismarck. Shells would go right through without initiating the fuzeing.

Holland didn't play his tactics very well, but then that was very common in all nations.