Battle Tracks at Denmark Strait

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Re: Battle Tracks at Denmark Strait

Post by Karl Heidenreich » Wed May 06, 2009 12:22 am

Is still somebody paying atention at all? If you want Science Fiction you go next weekend and enjoy Star Trek...
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Re: Battle Tracks at Denmark Strait

Post by Bill Jurens » Wed May 06, 2009 3:18 am

Mr. Dale wrote:

"An important point to consider is the rate of train of the 14 inch turrets at just 2 degrees per second. Very likely the hard turns were made at a rate faster than the turrets could train, but in order for salvoes 17 and 18 to be fired the turn had to decelerate or fire would not be effective."

This is an interesting statement. The training rate of the main turrets of the KGV class is well documented at 2 degrees per second, but although I have no specific figures for this particular class immediately at hand -- I'm pretty sure I have them somewhere, though -- experiments with similar ships would suggest to me that a turning rate in excess of 2 degrees per second at high speed even under hard helm would be unusually high. Vanguard, for example, at 15 knots, would take about 4.25 minutes to turn through 180 degrees, i.e. about 0.7 degrees per second, whilst Eagle, under similar conditions with TWIN rudders could still only manage 0.75 degrees per second. Admittedly, turning rates at 30 knots are typically in the vicinity of 1.5 - 1.75 times higher than those at 15 knots, but this still only gives something in the vicinity of 1.3 degrees per second for a 30 knots full helm turn.

Your statement that a turning rate in excess of 2 degrees per second is not only possible, but in fact 'very likely' suggests that you have a good deal of material on that particular subject, i.e. you not only know the turning rates of various battleships, but have enough on file to identify a less than 2 degree per second turning rate as unusual.

I wonder if you could, then, perhaps pass on some primary source documentation that supports your contention that battleship turning rates -- or at least turning rates in the KGV class -- were indeed very likely to have exceeded 2 degrees per second in high speed full helm turns.

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Re: Battle Tracks at Denmark Strait

Post by Vic Dale » Wed May 06, 2009 5:33 am

dunmunro wrote:
Vic Dale wrote:

Well the statement also begs the question "When after salvo 18?"
Vic, you have PoW running for ~3 minutes after salvo 18, and despite the fact that PoW has 3 functioning main battery turrets, and 2 functioning DCTs, she doesn't fire at shot! C'mon, this is a complete departure from reality. If this had really occurred then there would have been some very pointed questions asked and probably a few court martials. PoW was turning hard, and after salvo 18 this wooded the director and the forward turrets, any other explanation implies that Leach falsified his report.
I don't do fiction and nor do I think Leach falsified his report.

The hit on the compass platform came in at "green 48" so there is no getting away from the fact that PoW was "running roughly parallel to Bismarck" at this time. A succession of hits came in subsequently which convinced Captain Leach that he must turn away. Those hits had to strike and reports about them had to reach him in order for him to make his decision.

I have no difficulty at all with PoW taking 2 minutes 30 seconds to begin the turn away and an equal delay in reopening fire after salvo 18.

In his report, Leach fully justifies problems with PoW's gunnery performance. Her FC was not point and fire, it required some very sophisticated computing and with her instruments in disarray and the target displaced from the prediction, adjustments needed making. I am not at all surpised that she did not get any further shots off before the turn.

PoW had just completed a hard turn to port and would need to steady before a workable gunnery solution could be completed and the necessary observations regarding the target would also take time. PoW's last salvoes all fell short and some shot was out for line, so there was clearly something which had not been observed in PoW about the target. That Bismarck had turned away was only realised on checking gunnery results sometime after the battle. The ships at 7.5 nm were still little more than smudges on the horizon and haze would still be causing problems for target observers. Also Bismarck and PG were to the darker side of the battlefield whilst Hood and PoW had been silhouetted.

If for any reason the gunners could not get target inclination they could not work out the prediction and it has to be remembered that gunnery rules in force at the time, stated that fire should be correct for line, before firing for range. This is because until line has been discovered shorts and overs cannot be distinguished against the target. They would also need to know that Bismarck herself was on a steady heading, or the first shots would go wild. There is no point shooting and hoping - everything must be in place or fire must be held.

If PoW was hit in the ship's command whilst on the turn she would continue to turn until the wheel house was given a new heading (course to steer). I have not factored this possibility into my chart because I have no information on it and am unlikely to get it, but if the ship did need to steady onto a new heading after that hit this would add to the time necessary to get the guns on target.

The last salvo fell ahead and salvo spreads were in the order of 2,000 yards, the ship had made heavy turns and vibration had cause instruments to stick. All of this had to be firmly established before the next salvo could be got off, otherwise the target might be straddled by a salvo spread 2000 yards long and 500 to 1000 yards wide - virtually useless with just five shells. Something had to be done to bring the gunnery department back under control, establishing the correct conditions for a 300 yard spread and in line with the target. In effect they would virtually have to begin again. Instruments would have to be checked and turrets themselves checked to see that they were able to follow pointers, also that the pointers themselves were indicating correctly. Again all of this takes time.

The last salvo (No.18) would fall at 0602:18 and as it was observed short and with no idea of spread for elevation little could be learned from it. It appears that salvoes 15 to 18 were fired on a prediction of Bismarck's last known course and as they all fell short something had been missed. This is a clear indication of the difficulties faced by the Gunnery Department in PoW that morning. They must have missed the target's alteration away, firing a zigzag at 15 and 16 and a regaining up ladder at 17 and 18. They have to have been firing on results of fall of shot and not on anything known about the target, or the last salvoes would not have been off ahead as they were.

Incidentally, has anyone considered how it is possible for a ship to fire a zigzag at 15,000 and 15,100 and then fire a "regaining up ladder" with both salvoes fired at 14,100 yards - 1000 yards shorter - when the ship is heading away? This is what is shown on the Salvo Plot and is a clear indicator that the gunnery table was stopped between salvoes 16 and 17.

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Re: Battle Tracks at Denmark Strait

Post by Vic Dale » Wed May 06, 2009 1:17 pm

Bill Jurens wrote:Mr. Dale wrote:

"An important point to consider is the rate of train of the 14 inch turrets at just 2 degrees per second. Very likely the hard turns were made at a rate faster than the turrets could train, but in order for salvoes 17 and 18 to be fired the turn had to decelerate or fire would not be effective."

This is an interesting statement. The training rate of the main turrets of the KGV class is well documented at 2 degrees per second, but although I have no specific figures for this particular class immediately at hand -- I'm pretty sure I have them somewhere, though -- experiments with similar ships would suggest to me that a turning rate in excess of 2 degrees per second at high speed even under hard helm would be unusually high. Vanguard, for example, at 15 knots, would take about 4.25 minutes to turn through 180 degrees, i.e. about 0.7 degrees per second, whilst Eagle, under similar conditions with TWIN rudders could still only manage 0.75 degrees per second. Admittedly, turning rates at 30 knots are typically in the vicinity of 1.5 - 1.75 times higher than those at 15 knots, but this still only gives something in the vicinity of 1.3 degrees per second for a 30 knots full helm turn.

Your statement that a turning rate in excess of 2 degrees per second is not only possible, but in fact 'very likely' suggests that you have a good deal of material on that particular subject, i.e. you not only know the turning rates of various battleships, but have enough on file to identify a less than 2 degree per second turning rate as unusual.

I wonder if you could, then, perhaps pass on some primary source documentation that supports your contention that battleship turning rates -- or at least turning rates in the KGV class -- were indeed very likely to have exceeded 2 degrees per second in high speed full helm turns.

Bill Jurens
Dear Mr Jurens.

We discussed this at length on the Hood site some while ago and the same applies now as it did then. There is no more material available to me and your request for further information from me has failed - as I expect you well knew that it would.

Figures derived from a full 360 degree turn cannot be applied directly to a turn of just 70 degrees, or even 2 turns making 140 degrees in all.

The turns cited for Hood, Vanguard and others resulted in about 4.5 minutes to 5 minutes to complete 360 degrees, but that takes no account of the rate of decline in the ship's speed as she drags her way around the full circumference of the turn. This is about 1 knot for every 30 degrees but is not linear. I believe there is curve for decay of ship's speed, at given rudder settings for each ship, but I do not have access to them.

Effectively the ship is traveling much faster when the turn begins and will swing faster than 2 degrees per second under full helm initially. There being two elements to a turn: the hull following it's natural curve around the turn's circumference and the tendency for the hull to pivot about a point one third from the bow, a position which is variable according to heel and trim. With hard rudder, reaction from thrust of the screws will push the after part of the hull sideways and the head will slew round much faster than the ship could steer around the turn. However this acceleration of turn is bought only at expense of the ship's speed which will drop off dramatically. Again this is not a linear decay of speed. A good turn keeps pivoting and slewing to a minimum and maintains a good speed.

As speed drops off, the ship's head will come around more slowly though at a given point the turn will tighten slightly, so that the vessel comes up on the inside of her own wake. The amount of heel will influence the ship's speed also.

This extract from Raven and Roberts Battleships of WWII on Vanguard's Trials may be of help;

"During high speed turning trials, at 30.8 knots with full 35 degree rudder, the ship turned through 360 degrees in 4 mins 55 seconds. The turning circle of the ship, on this occasion was 1,025 yards and the maximum angle of heel recorded during the turn was 4 degrees."

30.8 knots translates to 1047 yards per minute and 17.5 yards per second.

The turning diameter on this trial worked out at 1025 yards making a total circumference of 3220 yards. It took 4 mins 55 seconds to complete and that works out at about 650 yards per minute or 18.9 knots - a 38% drop in speed.

Vanguard was going much slower on the second half of this turn than on the first. Also as speed dropped off progress ahead would diminish in relation to reaction to sideways thrust from the screws. This was also a rudder only turn and there was no counter-thrust from the screws on the inboard side of the turn as would be expected with an emergency turn.

We need also to take account of the fact that PoW was shorter and therefore handier than Vanguard or Hood. I have taken the wheel of a 26,000 ton carrier myself (same shape and size below water as PoW) and had no difficulty in making 2 degrees per second once she responded to her helm. I never made a complete turn, though I do have experience of such turns and they do take a long time to complete. They usually begin much quicker than they finish.

The turns made by PoW at 0600 to 0601 were made with full rudder and as I understand it they were made also using counter thust to get the ship's head round quickly. The fact that the ship's gunnery instruments were so badly upset during these turns testifies to their extreme nature.

A possible way to understand this is to consider a turn in a car, put the wheel over correctly and traction will take the car around the curve in the shortest time. Put more wheel on that is required and the car will slew and go wide.

The Admiralty Manual of Seamanship 1964 in regard to use of the helm says; "Success lies largely in using as little as possible and the higher the speed of the ship the less rudder she requires."

I would suggest that the trials using hard rudder at high speed were more to do with seeing what would happen rather than examples in ship handling

Vic Dale

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Re: Battle Tracks at Denmark Strait

Post by Antonio Bonomi » Wed May 06, 2009 9:05 pm

Ciao all,

@ Bgile,

here the explanation on how Jasper managed the order NOT to fire over the Bismarck,... on real facts of course,.. not imagination.

http://www.hmshood.org.uk/forum/phpBB3/ ... p=944#p944

Ciao Antonio :D
In order to honor a soldier, we have to tell the truth about what happened over there. The whole, hard, cold truth. And until we do that, we dishonor her and every soldier who died, who gave their life for their country. ( Courage Under Fire )

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Re: Battle Tracks at Denmark Strait

Post by Karl Heidenreich » Thu May 07, 2009 1:50 am

Antonio:
Ciao all,

@ Bgile,

here the explanation on how Jasper managed the order NOT to fire over the Bismarck,... on real facts of course,.. not imagination.

http://www.hmshood.org.uk/forum/phpBB3/ ... p=944#p944

Ciao Antonio
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Re: Battle Tracks at Denmark Strait

Post by Karl Heidenreich » Thu May 07, 2009 1:54 am

Vic:
A possible way to understand this is to consider a turn in a car, put the wheel over correctly and traction will take the car around the curve in the shortest time. Put more wheel on that is required and the car will slew and go wide.

The Admiralty Manual of Seamanship 1964 in regard to use of the helm says; "Success lies largely in using as little as possible and the higher the speed of the ship the less rudder she requires."

I would suggest that the trials using hard rudder at high speed were more to do with seeing what would happen rather than examples in ship handling
Am I crazy or Vic´s is explaining how a Battleship works to Bill Jurens? I remember when I was dumb enough to try to explain foeth how a propeller works just to found out he design them! :think:
An appeaser is one who feeds a crocodile, hoping it will eat him last.
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Re: Battle Tracks at Denmark Strait

Post by jazsa80 » Thu May 07, 2009 4:42 am

Simply taking the degrees turned and dividing by the number of seconds it takes to complete the turn does not give an accurate turn rate. Vic is right, ships start the turn alot quicker then they finish it. Anyone seen the one of the Nimitz carriers do their hardover turns on trials. Very cool. As they start to 'hook in' they create a massive 'tidal wave'. http://www.navsource.org/archives/02/026824.jpg

You even notice it on the Yahct. The turning of the wheel seems to do nothing for a split second but then she starts to lean over and cut through the turn. I would imagine Vanguard would have slowed her turn rate right up to finish the turn at 180. That part would eat a fair bit of time.

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Re: Battle Tracks at Denmark Strait

Post by Vic Dale » Thu May 07, 2009 3:46 pm

jazsa80 wrote:Simply taking the degrees turned and dividing by the number of seconds it takes to complete the turn does not give an accurate turn rate. Vic is right, ships start the turn alot quicker then they finish it. Anyone seen the one of the Nimitz carriers do their hardover turns on trials. Very cool. As they start to 'hook in' they create a massive 'tidal wave'. http://www.navsource.org/archives/02/026824.jpg

You even notice it on the Yahct. The turning of the wheel seems to do nothing for a split second but then she starts to lean over and cut through the turn. I would imagine Vanguard would have slowed her turn rate right up to finish the turn at 180. That part would eat a fair bit of time.
Precisely!

A hard turn throws the stern in the opposite direction to the turn and shoves the head round. Momentum will keep the ship moving ahead until drag due to the lateral movement of the hull slows it. The first 90 degrees can be acheived at good speed but thereafter it will drop off rapidly. I tired to find the table for this decay in speed in the Admitalty Manual of Navigation last night but unfortunately I have the wrong volume. I'll see if there are any on-line resources.

That is a lovely photo of the Nimitz and illustrates something of what was going on in PoW after Hood blew up.

I did a mathematical simulation factoring in a loss of 1 knot per 30 degrees using a turning diameter of 960 yards which is consistent with Repulse and Renown, whose hull dimensions are comparable to those of PoW. Just steaming around the circumference at 28 knots decaying to 26 knots it worked out at 1.8 degrees per second for 90 degrees, but as you have said ships make the first 90 degrees much faster than the last 90 degrees, due to the slewing effect, which is present to a marginal degree in even a gentle turn. Hard wheel in a big ship would surprise some people I feel.

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Re: Battle Tracks at Denmark Strait

Post by JtD » Thu May 07, 2009 4:38 pm

There is turning data for the Hood on the Hood site.

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Re: Battle Tracks at Denmark Strait

Post by Vic Dale » Thu May 07, 2009 8:43 pm

JtD wrote:There is turning data for the Hood on the Hood site.
Yes I have seen it, but although it is interesting it doesn't tell us much.

15 degrees of rudder gives a slowish turn, but has the advantage that ship's speed does not drop greatly. 35 degrees of rudder pulls speed off like lightening and is not the best way to make a turn anyway. I wouldn't expect more than 25 degrees of rudder and I believe there was a protocol in force which prohibited more rudder than this at high speed.

If you check the figures you will see that as speed degrades, the rate of turn slows as the turn progresses;

Using 35 degrees of rudder
from 90 deg. to 180 deg. takes 108 seconds
from 180 deg. to 360 deg. takes 224 seconds (112 seconds for each 90 deg.)

The turn slows during the last three quarters, yet the first 90 degrees takes 145 seconds, meaning that somehow the rate of turn has accelerated during the second quarter. I think the figures for the first quarter include the delay in the ship answering the helm which at 20 seconds + and with extreme rudder-drag, the ship's speed would be well and truly knocked off. That would probably account for the excess time taken for the first 90 degrees.

I would suggest that the only situation which would call for a turn like that would be to avoid collision, when dramatic loss of speed would be considered a good thing. It is unlikely that more than 25 degrees of rudder would be used when the ship was making high speed and that would make for a reasonably good turn, maintaining speed relatively well and getting the head round.

Having made a brief study of results with destroyers, it seems clear that turning circle results will be specific to a particular ship with variations even between vessels of same type. 35 degrees of rudder tends to ensure the tightest circle, but the ruinous loss of speed will lengthen the time of turn.

The turns I have shown on my chart are no more extreme than those shown on PG's track and at similar length and speed PoW would have no difficulty matching them.

Vic Dale

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Re: Battle Tracks at Denmark Strait

Post by lwd » Thu May 07, 2009 10:54 pm

I note that none of those are anywhere close to 2 degrees/second. Even cutting in half the time it took to do the first 90 degree turn yields less than 1.5 degrees/second.

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Re: Battle Tracks at Denmark Strait

Post by Bgile » Fri May 08, 2009 1:19 am

Vic Dale wrote: We need also to take account of the fact that PoW was shorter and therefore handier than Vanguard or Hood. I have taken the wheel of a 26,000 ton carrier myself (same shape and size below water as PoW) and had no difficulty in making 2 degrees per second once she responded to her helm. I never made a complete turn, though I do have experience of such turns and they do take a long time to complete. They usually begin much quicker than they finish.
Vic Dale
As far as I can see, there is no evidence to show that PoW was likely to achieve a 2 deg / sec turn at Denmark strait. Quite the contrary.

Also, being shorter is not necessarily an indication that a ship can turn sharper than a longer ship. I Believe the Iowa class could out turn the KGVs by a significant margin. In fact, their escorts had to be warned so they wouldn't get run down.

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Re: Turning...

Post by Bill Jurens » Fri May 08, 2009 1:35 am

Whilst it is well known that ships often undertake some rather spectacular gymnastics as they run through various instabilites at the beginning of a turn, especially at high speed and under heavy helm, these usually damp out quite quickly, and are usually not indicative of performance over the turn as a whole. The ship does go through a transitional stage immediately after the rudder goes over and exhibits atypical heeling and rotational moments as she sets up into what is thereafter usually a fairly stable regimen thereafter. Indeed, the rapid onset of what is commonly called the 'drift angle' often cases momentary changes in heading which can be fairly dramatic, and the result is that that the ship will sometimes exhibit a very temporarily (and anomalously) high turning rate during this transient period.

Although only one component of turning must be considered after an angle of about 60 degrees has been reached, there are two components of turning that must be superimposed before that time. The first is the actual change in direction of the ship's center of gravity, and the second is the pivoting of the hull around the so-called 'pivot point', which tends to rotate the bow towards the inside of the turn. The difference between these two angles is typically known as the 'drift angle'. In that regard, even once the ship is well into the turn, it does not point in the direction of the turn but inside the curve. Once the drift angle comes on, i.e. once stability is re-established, the offset between the course of the ship and the heading -- i.e. the aforementioned drift angle -- which is usually something between 5 and 12 degrees -- remains fairly constant. The turning rate usually also remains fairly constant thereafter --although the radius of the turn typically decreases as the turn proceeds, the time to pass through successive angles increases in compensation, leaving things in near-equilibrium.

The Hood information posted on the Hood website, referenced earlier, demonstrates some of these phenomena quite well, as do other illustrations of typical ship turning motions, many of which can be accessed in various and sundry locations on the internet. Plotting the Hood data --which I assume to be official and reliable -- in the form of a graph of angle turned vs time elapsed indicates a very constant turning rate of about 1 degree per second after an angle of about 90 degrees has been reached. There is, as might be expected from the discussion above, a 'hook' at the bottom left hand corner of the graph, i.e. during the beginning of the turn where the turning rate is first anomalously low -- this as the ship first moves into the turn, and then anomalously high as the ship reaches equalibrium in the turn. It is during that phase that the rate of rotation of the hull around the pivot point gets larger quite quickly, while the actual locus of the pivot point through the water changes direction only slowly. Even so, these in effect, compensate for one another, as shown below.

Here, in numerical form, are the raw turning rates derived from the material in the chart for Hood:

First 45 degrees = 0.82 degrees per second
Second 45 degrees = 1.15 degrees per second
Third 45 degrees = 1.05 degrees per second
Forth 45 degrees = 1.02 degrees per second
Last 180 degrees = 1.01 degrees per second

Clearly, the change of course, i.e. the locus of the pivot point never approaches 2 degrees per second. The Hood data It takes 55 seconds to turn the first 45 degrees, but this (very probably) represents the change in course of the ship as a whole and does not include the additional rotation due to the superimposition of the drift angle. In the absence of other information -- and detailed information regarding this transitional period in ship turning is difficult to come by for any ship designed before about 1980 -- it would seem reasonable to assume that this drift angle might be in the vicinity of 10 degrees, giving us a hull rotation of 45 + 10 = 55 degrees (instead of 45 degrees) in the first 55 seconds. This comes out to about about 1 degree per second as before. In truth, the drift angle typically comes on more quickly than this, perhaps establishing itself in twenty seconds or so, which would mean that during the very first part of the turn the transient total rotation of the hull might be somewhat larger, e.g. something in the vicinity of (0.82 x 20) + 10 = 26.4 degrees in the first twenty seconds, i.e. 1.32 degrees per second, but this is still well below the 2 degrees postulated by Mr. Dale.

Assuming, in the absence of other immediate information suggesting otherwise, that Hood would and KGV would behave in a roughly similar manner, it would appear clear that a turning rate in the vicinity of 2 degrees per second would be anomalously high, and -- even if it were attained -- such a turning rate would be extremely transient.

Although I haven't bothered to do so -- time limitations intervene -- one can confirm most or all of the above via purely theoretical methods. Modern turning calculations are mostly done by computer programs now, using numerical integration techniques. That being said, these computer programs are often difficult to obtain unless one has a fairly large budget at hand. Older methods, though more tedious to use, are nearly as reliable -- perhaps more so for older ships -- and can be found in a number of sources. My favorite treatment (am I dating myself?) appears in Comstocks "Principles of Naval Architecture", published in several editions by the Society of Naval Architects and Marine Engineers in the 1970s - 1980s. Another very good source, which contains convenient closed form solutions in a fairly acessible form that do not require higher levels of mathematics to apply, is "Estimation of Ship Manoevering Characteristics in the Conceptual Design Stage" by Aamzan Mainal and Mohd. Kamil, published in Jurnal Mekanikal, July 1996.

In closing, although I have no way of formally proving this,I would be quite surprised to find that the naval architects involved in the design of a battleship would allow her to steer fast enough to 'out-turn' her guns at anything resembling typical battle ranges.

Bill Jurens

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Re: Battle Tracks at Denmark Strait

Post by Vic Dale » Fri May 08, 2009 1:33 pm

Bgile wrote:Vic, are you saying that there is a 20 second delay from the time that the rudder begins moving to the ship responding to the rudder? That sounds really strange to me. I would think that at high speed in particular, the ship would begin to respond instantly. It might turn slowly at first, but wouldn't you see some change in heading the instant the rudder started to move? Of course, the ship would take some time to actually move in a new direction (inertia), but I would think the stern would start swinging out immediately, slowly at first and then faster and faster until the turn rate limit was reached.

A good helmsman will not overshoot a turn, but will apply opposite rudder as he approaches the ordered course so as to stop the turn on exactly that course. You can expect the leading helmsman to be on the helm at battle stations.

In US practice, which is all I have personal knowledge of, you first get the order "Left fifteen degrees rudder". Then when the OOD figures out what he wants for a new course he will say "Steady course 160 degrees." At that point the helmsman is expected to maintain 15 degrees rudder until he has to meet the new course, and he will use his own experience to decide what rudder to use to stop the turn on exactly 160 degrees. That often requires at least some reverse rudder near the ordered course to keep from overshooting the turn. You can tell a rooky by the zigzag wake behind the ship.
It is a fact that large warships take time to respond to the helm and battleships being heavy and ponderous even more so. The Admiralty Manual of Seamanship 1967 P.394 para 4;

"When the wheel of a ship is put over the ship does not begin to swing for some time."

The wheelhouse of large warships in the Royal Navy is usually sited several decks below the bridge and often below the armour. In heavy warships largely they are blind positions, certainly in the older vessels with which I am mostly accquainted.

Vic Dale

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