Acceleration, Manoeuvres and Related Points

[Steeltrap]

For some time now I've been bothered by the performance characteristics of the vessels we and the AI are designing.

This came to a head for me when I attempted the scenario where you're the German side in a very loose version of the Battle of the Denmark Strait.

Why? Because I encountered something that was clearly HMS Hood-like yet was stampeding around at truly astonishing speeds, doing remarkable pirouettes, and all the while proving impossible to hit (more on gunnery later).

I thought I'd lay out my concerns and see what others might have to say.

As things stand, it appears to me that acceleration is linear. The shipyard shows you numbers for acceleration, both positive and negative, and they seem to apply regardless of your current speed.

That last bit is the problem as it's simply physically impossible.

As we all know from our Newtonian Laws of Motion, acceleration results from the application of a net force upon a mass. In fact the definition of the SI unit of measurement for force (the Newton, N) is couched in those terms, namely that 1 Newton is the force required to produce an acceleration of 1 metre pre second per second on a mass of 1kg.

While ship design and acceleration via propellers and hull motion through water are horrendously complicated subjects, for our purposes we can simplify them to the basic principle that as the ship starts to move through water, the water provides a force against the motion. Acceleration is a result of net, or unbalanced, force.

In crude terms, provided the propellers are providing greater combined force to push the ship forwards than the combined force of the water acting against that motion, the ship will accelerate.

On the other hand, the simple fact is the force of the water 'resistance' increases as the ship's speed does. That means the NET force for the purposes of acceleration decreases as the ship's velocity increases. As the net force gets smaller, the resulting acceleration MUST, too.

All of which is a rather long way of getting to the point that acceleration of ships cannot, and must not, be linear.

I've made reference to the following chart on several occasions. It's the performance curves to be used in theoretical exercises as stated by the Royal Navy in 1929 (courtesy HMS Hood Association website )

 

Even it is questionable in the sense it is largely linear but in two distinct sections, it still illustrates the point.

Looking at the curve for HMS Hood it shows 10 minutes to reach 20 knots, a further 6 minutes to reach 25, and a whopping 24 more to reach 30.

From 20 to 25 knots we see 60% more time (6 more  minutes over 10) to add 25% more speed (5 knots on 20).

From 25 to 30 knots we see 150% more time (24 more minutes over 16) to add 20% more speed (5 knots on 25).

If you go to the same page I listed as the source above, you'll also find details of Hood's performance in terms of speed changes resulting from turning through various degrees (45/90/135/180) based on speed before the turn and the amount of rudder applied.

OK, so what's the point of all this?

It's that the ability of ships, and capital class ships in particular, to reach (frequently ridiculously, unrealistically high) top speed is highly exaggerated.

Regardless of how well the game may model speed loss through degrees of turn based on rudder used, something I've not looked at particularly, that speed loss is not especially important IF the ship can be back at its maximum speed very quickly.

I am NOT proposing that the devs need to research every class of capital ship ever built and accurately model their performance curves. I DO recognise they've given thought to the issue of loss of forward speed based on application of degrees of rudder.

What I AM proposing is the acceleration curves of ALL ships need to show a significant rate of diminishing return, which is to say their rate of acceleration DECREASES as a function of their CURRENT SPEED (because "you canny ignore the laws of physics, Captain"; sorry, couldn't resist 😎).

It's probably worth noting this works for all acceleration, be it positive or negative, with the difference being negative acceleration (i.e. against the current velocity) is the inverse. Ships slow down more rapidly from a higher speed than a low one, and their loss of speed ought to be greater if the engines are cut v simply ordering a lower speed.

As I said, this is particularly relevant while the gunnery model grossly rewards the ability to maintain crazy high speeds in a straight line over anything else. I've watched as the enemy's gunnery solution gets WORSE as I go into a straight line and pick up speed v turn with 20 degrees of rudder on with speed reduced as a result, yet an accurate gunnery solution on a ship that's turning at speed ought by definition be significantly more difficult to achieve than one travelling in a straight line even if 5 knots greater.

Even once that is addressed, as it clearly needs to be IMO, it doesn't change the current issues when it comes to the general performance of these ships.

There's another game that models them as ridiculous sports cars. Let's not go anywhere near that, please.

If doing so causes people to get upset and complain about "how sluggish my ships are", then they are getting educated. We continue to see what I consider to be unhelpful consequences of grossly inflated hit rates for guns, but I can see NO need for manoeuvrability and acceleration performance to be unnecessarily inaccurate.

In particular I've said the acceleration is linear in the game because that's what I've observed. If anyone disagrees, please comment.

As usual, interested in any comments/suggestions/ideas.

Cheers

Edited May 5, 2020 by Steeltrap

[Dan Dare]

totally agree with your point of view, in fact the curve you show is quite significant cause Hp/Speed curve of a ship use to act exactly identical (looks as if power/time is linear).

Based on the relation of Hp/Knts i will dare to say that the relation Speed/time could be better represented as logaritm...which one..well then we are complicating things...;)

[DougToss]

Great post. I'd like to see this pinned. 

I'm reading about engineering and propulsion in DK Brown's books (must read to anyone here!) and that is definitely one area that needs developer attention.