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Modifying Ship Stability

carmenara

Pandora's Kitten
Storm Modder
Dear shipwrights,

I noticed a fair amount of issues related to gunnery in bad weather, and seaworthiness in general pertaining to operations in the Caribbean.

Of concern is the large amount of pitch and roll exhibited by vessels on the high seas, be they large or small, they seem to all handle quite identical to each other in sea states 3 and above - they bob and pitch like boats floating in a bathtub!

Now, shallow draft vessels and coastal boats definitely aren't supposed to sail in the open Atlantic (and escorts like the Flower corvettes of WW2 suffered accordingly), but I started noticing even some of the Class 7 boats having very deep draught (some having very very deep cargo holds below the waterline) and rolling as much as a shallow draught yacht!

Hence the following suggestions for your consideration:

1. Is it possible to "upgrade" a ship for roll stability? Not sure if hydrodynamics were a part of 17th Century ship design and I understand ships of the line with their massive topweight were quite poor in seakeeping, but it does make sense to provide handling better than bathtub toys! And so picking the right ship for the job becomes important for the player - shallow draft, high payload for coastal ops, etc. Then again I notice from this game engine that there isn't a "stability" rating for any ship meaning they will be bathtub toys in the 3D simulation..

2. Might it be possible to dynamically alter the ships' waterline based on load? I have, or had, a Class 7 boat that sat so low in the water one could barely navigate at all much less fire in anything more than a calm sea, and the same for a Fast Caravel that could benefit from a keel extension (for stability) and which I was forced to fire grapeshot only in a high seas battle because her high velocity cannon with standard shot couldn't clear the wavetops. If I could have some control over loading and/or ballast I would dump cargo to raise her waterline to permit effective direct fire.

3. Remembering stock POTC, ships tended to roll with rudder applied, especially the fast ones in high winds. I might think that if we were able to mod the "roll stability index" for individual ship classes, we could make ships appear more natural in high seas and also in battle (MoW with poor seakeeping, for example, yet is not entirely at mercy of the seas due to her big tonnage). Currently I think the lack of roll in maneuvering makes for some unrealistic tactics on my part, what with gunnery being unaffected by maneuvering, while merchantmen and the like appear to be stationary fortresses maintaining an even keel even when doing 10 knots hauling downwind 3000 tons of gold with the rudder hard over... And YES I want my ships to capsize doing that if I picked the maneuverability related feats! One cannot defy nature!

4. The above suggestions wouldn't even be possible if the game engine didn't support the relevant seakeeping model settings.
 
It would definitly be interesting to do something with this, but I have no real idea on how to do it.
These are the values used for the seakeeping model:
Code:
	refShip.WaterLine = 0.5;
refShip.SpeedDependWeight = 0.3;
refShip.SubSeaDependWeight = 1.3;

refShip.InertiaAccelerationX	= 0.2;	refShip.InertiaBrakingX		= 2.0;
refShip.InertiaAccelerationY	= 7;	refShip.InertiaBrakingY		= 6;
refShip.InertiaAccelerationZ	= 4.0;	refShip.InertiaBrakingZ		= 3.0;
I'm not at all sure what each value does.
We have added a "Ship Upgrades" mod in Build 14 Alpha 10, so it is possible to change some of the values.
It might be possible to change the waterline even, but only between loading scenes (eg. going to shore/worldmap).

I'm a ship's officer in real life and as such know a fair bit about stability.
Additionally I worked half a year at the MAritime Research Institute Netherlands,
where I learned a fair amount of stuff on the subject of realistic behaviour modeling as well.
As such, I can safely say that whatever Akella did with the seakeeping model, it is not a truly realistic one.

I don't know how much of the model is in the PROGRAM folder and how much is hardcoded.
Somebody should have a look through the files and see what he can find.
Not me though; I have no time. :facepalm
 
Ahhh inertia values. That might be all I need to get something started.


refShip.WaterLine = 0.5; Waterline shall be "1/2" of the ship's model - unfortunately it doesn't seem to suggest a dynamic tonnage based model. Yet. I swear I could remember something like a high tonnage = ship sits lower feature in an earlier Build mod but I might be mistaken (in my dreams, probably)
refShip.SpeedDependWeight = 0.3; Implies how "max sailing speed" of this class is affected by loading
refShip.SubSeaDependWeight = 1.3; Ok this one requires testing to figure out what it does but I'm hoping its a seakeeping factor vs tonnage

refShip.InertiaAccelerationX = 0.2; refShip.InertiaBrakingX = 2.0; This is exactly what I'm looking for, 3 axis momentum values
refShip.InertiaAccelerationY = 7; refShip.InertiaBrakingY = 6; I will leave the coordinates (which is roll, yaw, pitch) to experimentation
refShip.InertiaAccelerationZ = 4.0; refShip.InertiaBrakingZ = 3.0; Even if it doesnt affect weather or seakeeping, having ships move like they actually weigh a few hundred to thousands of tons would be much appreciated.

I can say from experience that most physics features in games are usually set to very conservative levels for purposes of controllability (often making things too controllable and look unnatural). With some work one could setup, in a Homeworld type space combat game, ship movement that appears based on Newtonian thrusters, which is way better than the typical Star Wars "atmospheric flight in space" presentation and opens up way more realistic tactics... off-axis engagement, even setting up capital ship ramming because massive inertia overrides the game's collision avoidance AI.

The keyword is appearing realistic, but understandably some of our players will be irritated at how movement affects gunnery and that they can't just play a 20 knot Xebec barreling downwind like a WW2 destroyer, thus a "realistic inertia" setting, if created, should be an optional feature. But I am confident that I will be very happy to see a huge galleon keeling over in a hard over on the high seas, where suitably equipped and larger, more advanced ships are able to plow through the waves to some degree retaining combat capability while said 20 knot shallow draft attack ships pretty much get swamped.

OK the small boats do suffer in high seas now, because their gunwales are not sufficiently high to permit direct fire anymore (and I like the realistic gun arc limitations), but the inertia mods, should they allow larger ships to plow through the waves and not just ride like a bathtub toy, may make for some interesting presentations. Then again (disclaimer) while I am confident on affecting maneuvering with the provided code, weather is another thing altogether and nature's interactions with 3D ships may or may not be hardcoded.
 
A toggle is required, of course, or make it a part of the current realistic sailing mode.
The main thing that'd need to be figured out is how to tweak this at all.
I hope you get somewhere with it; your ideas certainly sound interesting. :onya
 
Will start on this after 2 things:

1. A fraction of the manual (gameplay tutorial)
2. Recommended options
 
Well its the Islamic holidays here this weekend so I'm loathe to waste the good recreational time...
 
Seakeeping is a broad term used to define a ships ability to handle the various weather conditions. I served in the US Navy aboard a Forrest Sherman class Destroyer DD940 back in the late 70's. She was a good sea boat. She didn't roll to badly as long as they kept her nearly full of fuel and out of the trough (parallel to the wave pattern). She had a high bow and a fairly good freeboard. Nothing like Peter's Cruise ship mind you. We sailed with some Knox class Fast Frigates, boy was I glad to be aboard the destroyer. Those frigates rolled even in 4 foot seas, a real bronco ride. We were stopped in the middle of Mediterranean to transfer a crewman from a Knox frigate. Within a couple minutes of stopping, I swear the frigate was rolling through a 60 degree arc. The frigate ended up getting under way so the boat could hook up alongside.


A sailing vessel stability is dependent on several factors such as wind speed, direction, weight distribution, center of gravity, center of effort, center of buoyancy and likely a few others. Another good site is :Multi-hull vs Monohull. Another link to look at: Sailboat Design and Stability
I am not an expert, but Hope this helps.
Greg.
 
Sure did !, now that you mention it... i've seen a you tube video showing a cargo ship of sorts (not a tanker) in very VERY bad weather rolling up to 45 degrees...

Is this your lady ?

File:Uss_Hull_DD-945.jpg
 
Synchronous rolling? That's a fun effect: waves from dead astern and the ship suddenly starts rolling like mad.
Impossible, you say? I've seen it with my own eyes! On a model in a tank, that is... At the MAritime Research Institute Netherlands. :cheeky
 
Sure did !, now that you mention it... i've seen a you tube video showing a cargo ship of sorts (not a tanker) in very VERY bad weather rolling up to 45 degrees...

Is this your lady ?

No never got a chance to sail on the Lady Washington. That would have been fun. I just like the picture.

Here are a couple shots of the destroyer I served on.

PreModification

What she looked like when I was aboard

Sorry after a bit more research it seems the other ship was a Garcia class frigate not Knox. Sorry about that. It's been over 30 years.
 
This looks really pretty
http://www.youtube.com/watch?v=mzveUz-WRGQ&NR=1

And I watched some of cargo ships in high seas; they seem to roll really badly in higher sea states even fully loaded.
 
That does look sweet. Those Burke class cans are really nice. Did you notice there were no parasitic waves. The bow wave stretched all the way to the stern. Talk about efficient hull design.

Here is another cool vid.
High Speed run
We made a high speed test run in Med on the USS Manley DD940. The old girl got up to about 32 knots. We were throwing up about a 20 foot rooster tail. That video is not jumpy because of rough ride. When we made the run, one of the gunner's mate put a wrench on the deck back by the fantail and we watched it jump about 6 inches in to the air for a couple minutes. He grabbed the wrench just before it was about to go over the side.

Greg.
 
Wow, that is really impressive, cutting through the sea and very, very stable as evidenced by the gentleman just sitting there enjoying coffee.
 
refShip.SpeedRate = 28;
refShip.TurnRate = 68;
refShip.Price = 4000000;
refShip.HP = 150000;
refShip.SP = 100;

Ripped these ship stats out of another thread. These figures spur a bit of inspiration for my ship handling project.

I noticed the "SP" most likely means sail hitpoints. Has any thought been given to increasing this amount dramatically? Right now it seems unbalancing that a lugger or schooner with 6 pdrs on rapid fire could pretty much take out any ship's sails from a very long distance leaving an opponent completely helpless.

Historically, this was not the case as evidenced in the Russian brig Mercury's example where a 20 gun brig was engaged by not one but two Turkish MoWs. The brig's sails were holed by over a hundred enemy shot but remained not only in navigable condition but managed to damage the large ships' sails enough that she herself could get away.

So I vote for increasing sail hitpoints if only to say that yes, you can reduce an enemy ship's mobility by targeting her rigging but not destroy all their sail area with a single salvo, thereby taking into consideration that POTC gunnery is way easier than handling historical cannon.
 
I think every single ship in the game has 100 sail hit point. I have no idea why.
That's not quite logical, of course. Try increasing and see what happens. :doff
 
Currently damage to sails is modeled by something like "percent of sail area punctured" which correctly gives square rigged vessels with tall masts the advantage (until the masts collapse). However it means that a (imaginary) clipper would have as much sail integrity as a xebec, which of course isn't logical as you noted.
 
An update, and closure to this topic of interest:

It's possible to radically alter gameplay by modifying inertia values, but there are certain AI limitations that prevents the ship from carrying too much momentum. Despite that, the ship handling experiments were a success. It's not difficult to create some kind of quasi realistic ship handling that also caters to fast-paced gameplay. You just need to know exactly what you want to do, and keep that objective in mind.

It is not possible to modify, at this point, the amount of roll generated when a vessel is turning. This may require tweaking some values deeper in the recesses of the game's scripting (some sort of roll modifier), as ships DO roll when you execute the 180 degree turn character feat.
 
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