Post by Neil Thapen in Sailing model feedback thread

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I found some more data on drag/inertia.

The build now has a drag coefficient of around 0.0025, based on what I see about modern ships (one of the debug menus says 0.008, but that slider does not actually do anything at the moment). But I've found that the original book on the subject, "The Resistance of Ships" by William Froude, is available at archive.org:

https://archive.org/details/resistanceships00frougoog/page/n13

The first part describes tests done on HMS Greyhound on 1871. Greyhound was a wooden screw sloop, launched in 1859, about the same size as the frigate in APO but lighter - it's listed as around 1000 tons displacement in the tests, while the frigate is around 2000. I think it's reasonable to expect it to behave similarly to the frigate . Presumably 50 years of technical improvements give it a lower friction skin, but on the other hand there's the screw sticking out (I'm not sure what this was doing in the tests - the ship was towed).

The download is missing the diagrams, but there's a description of the results on page 16. At speeds where wave resistance is not an issue, the drag in lbs is 88*V^2, where V is the speed in knots. At 1m/s (very close to 2kts) that gives about 1500N of drag. Taking the weight as 1000 metric tons, that's a deceleration of 0.0015m/s^2. So to reduce the speed by 0.5m/s would take at least 330s, more than 5 minutes, and that's ignoring the big reduction in drag as you slow down.

The drag in the released build of APO is pretty close to this, but the ship will take longer to slow down as it's heavier. Greyhound had a wetted area of 674m^2, giving a drag coefficient of 0.0044. Putting this into APO will give a bit higher drag (I need to think about how I am calculating wetted area), but still on the order of minutes to slow down.

It might be interesting to play with yaw instability here. Increasing the instability should tend to make the ship turn from straight, slowing it down a bit faster, but also making tacking easier.

MartesZ5 years ago (4 edits)

There is some experimental data from the Black Sea Fleet reports of the Russian Navy made in 1828-1829:
https://cyberleninka.ru/article/v/analiz-hodkosti-ostoychivosti-i-upravlyaemosti...
for several ship types ( from 110-gun first rate to small brigs). Unfortunately it does not contain acceleration or deceleration times, but there are speeds and heel angles for various wind conditions as well as times recorded for tacking and wearing.

For example a 44-gun frigate (table 1, col. 4, and it should be noted Russian ships were in general more heavily armed and slower then their French or British counterparts, even if they shared a hull form):

Wind rate 5
- Close-hauled 7 kt
- Beam reach 9.5 kt
- Broad reach 11 kt
- Running 8 kt

Wind rate 7

- Close-hauled 4 kt
- Beam reach 9.5 kt

Heel angle
- Wind rate 5 - 11 deg
- Wind rate 7 - 7 deg
- Wind rate 9 - 8 deg

Wearing (wind 5): 2.5 min
Tacking (wind 5): 2 min
Tacking (wind 7): 3 min

P.S. Found in the text a description of sails set during the trials:
- At wind 5 (up to 10 m/s) running & broad reach all sails (sic) were set.
- At wind 5 beam reach & close-hauled royals & skysails taken in.
- At wind 7 (up to 15 m/s) courses, topsails (double-reefed), t'gallants and fore-staysails were set.
- At wind 9 (up to 20 m/s) fore-course and fore-staysails were set.

P.P.S. Corrected the wind 5 close-hauled config translation and wind 7 close-hauled speed.

Neil Thapen5 years ago

Thanks! That's really good stuff.

MartesZ5 years ago

There must be similar British reports somewhere, but the only references in the "Frigates of the Napoleonic Wars" list only top speeds and general impressions of the captains.

ppitm5 years ago

What page says they set the topgallants in Beaufort 7? (I speak Russian)

MartesZ5 years ago

Look at page 4 on the left.

При ветре 7 баллов (до 15 м / с) корабли с прямым вооружением несли нижние паруса, брамсели, фор-стень-стаксель; брали два рифа у марселей.

ppitm5 years ago

Yikes. I wouldn't recommend flying topgallants in 36 kts of wind in the simulator.

MartesZ5 years ago

Maybe it wasn't that bad over double-reefed topsail. That makes the t'gallant significantly lower, doesn't it?

ppitm5 years ago

Yes but the mast is still spindly, and it's a gale. 35 kts of wind is TWICE as much pressure as 25! I can only imagine they were saying 'look what I can do!' for the sake of the experiment.

MartesZ5 years ago

Judging by the speed table it didn't help them much, but there is definitely something rakish in this.

Lieste4 years ago

I know you refer to the Lively as the basis, but the broadly similar Leda class has a bit more information available... and she is a 1091 tun BM ship, displacing only around 1496 ton.

2000 is closer to the displacement of the much larger US superfrigates such as President/Constitution - 1576BM, 2200 tons.

Neil Thapen4 years ago

Thanks for noticing this. I looked in the editor, and the mass of the ship is 1923 tons. 1800 tons of this is the hull (the guns are 90). It looks like this 1800 figure is one I wrote in by hand, rather than calculated, and I don't remember where I got it from.

I can see the relation displacement = about 1.5*burthen in a few places. I have one source, "The Command of the Ocean" by N A M Rodger, on the 18th century royal navy, that says "for a fully stored warship" the displacement is about twice the burthen. Do you know what the state of storage is for your figures?

This is something I am reluctant to mess with, as I am happy with the way the acceleration, stability etc. are tuned at the moment. But I will have to look at this stuff again if I ever get around to flooding and sinking.

Lieste4 years ago (1 edit)

I assume it is at the load waterline. Sadly I don't have the table of lading, nor an accurate set of curves to integrate. It could be the ship fitted out, but with few stores. On a different point, ordnance seems to be relatively weak vs the structure of the hull (and guns on the engaged side or on the upper deck in general). I had to station within ~100yds to see hulling or a very few 9lb gun losses (and the majority on the unengaged side hit over the rail). While these are "only" 18 and 9lb long guns, the expected performance of the 32lb gun was 1200yds to penetrate the gun deck of a 74, 400 when fired double (with reduced charge). This level of performance should be seen from an 18lb (short pattern) long gun as used on the frigates at around 700yds (0 yds for double) The frigate is more lightly built, so there should be a small useful distance for double (with it's necessary reduced charge), but also an significant extension of the useful range of the single shot with distance charge (full 1/3rd weight proportion). (Similarly the 9lb single shot from the typical pattern of gun should give a useful penetration of the 74 at around 400 yds, but no useful penetration of double). Rigging seems to fall apart a little too quickly compared to damage to the hull systems (crew/guns/hulling) accruing. (A 12lb shot penetrating the side was considered a minimum to be useful in disabling guns, the lighter ordnance being taken as only useful for damaging wooden structures and rigging, or wounding crew. Rate of fires seem a touch high (I interpret the 3 rounds in 5 minutes to include the first loaded shot, and to not include restoring the ordnance to a loaded state at the conclusion - so ~2.5 minutes for the (complete) cycle for each of the first three shots - later shots are limited by heating, with no more than 20 shots permitted per hour if premature discharges (from heat of the bore), excessive recoil and bursting being a risk with higher rates. This makes coming into the wind less obviously a bad idea than with a 30-60 second reloading cycle, as you pass your head or stern across the direction to the opposing vessel.

Neil Thapen4 years ago

I looked at the shot damage code (possibly for the first time since 2014). I'm tracking the kinetic energy of a shot. According to a comment in the code, an 18 pounder shot at 500m/s penetrates 2ft of oak, and I call it a hulling if the energy is more than that (with some randomness). For damage to crew and rigging etc. I just came up with some numbers that seemed reasonable, which shouldn't be hard to tune.

I set the rate of fire at the maximum plausible one. I agree it's a touch high. It would be good to model this better, and change it over time with crew strength and morale etc. Some of the code for this is there already but I'm afraid I'm unlikely to get around to fixing this up.

(And sorry, it looks like the 9 lbers are actually firing 18lber shot.)

Lieste4 years ago

Minor adjustment to the statement on rate of fire (gunnery manual suggested 5 minutes for the first three discharges as stated - my interpretation is loaded to unloaded). the first 20 rounds in the first hour, five minutes between shots after one hour at that rate of fire. This for naval pattern iron guns.

itch.io

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