IRL: big ships go faster than little ships!

[Brigand]

I played around with the data some more:

 

Some scatter plots:

Graph 1: C (block coefficient)

Graph 2: Displacement as a ratio of Length on the Water line

Graph 3: Sail Area as a ratio of Displacement

Graph 4: Displacement as a ratio of tuns Burthen

While the data may not be above discussion, it does show some clear trends, which I think is interesting enough. and may even be useful as a guideline for assigning values to the ships in the game.

Cheers,

Brigand

Edited March 1, 2015 by Brigand

[Destraex]

i think because this is complex we are better off going with captains logs for agility, speed in various wind types with and without loads, clean hulls etc.

But I would hate for this game to defy the basic laws of physics just for balance. To get something out of this game other than useless role play I need to know

that things even though perhaps exaggerated a little are in a basic sense RIGHT,

[Brigand]

While that is a better correlation between length and displacement, it shouldn't be confused with the DLR, which has a relation to resistance to motion.

DLR = Displacement/(WL/100) ^3 proportional to resistance for similar speed ratios and hull entry angle (Kts/(WL)^0.5).

Your Ratio = Displacement/(WL/100)^2 (good correlation of the presented data for a simple® fit).

 

 

That was simply my error, I thought I used the formulas as described in your previous post. I've updated the diagram and data (correlation is not nearly as nice).

 

~Brigand

[K1lbane]

An interesting discussion, however, for NA I think you are all trying to turn the game into a full blown simulation.  Ultimately if you want to go down the line of realistic acceleration, top speed and drift during turns etc. you would surely have to consider the fact that many naval battles would last hours.  Secondly, open world travel would take days if not weeks to travel to other ports.  Imagine spotting sails on the horizon,  would you want to spend half a day trying to out manoeuvre your rival in order to engage in a battle?  

 

I agree that the handling of the ships are unrealistic, but i think it sits well with what NA is trying to achieve.  

[Tom Pullings]

While I agree that the ships in the game need to be balanced for good game play, the general laws of physics should be followed and the OP has those essentially correct. A lot of factors affect how close to hull speed a ship can get when sailing, and how quickly a ship will accelerate to its max speed, but the general rule applies. Waterline length is the primary factor for determining max hull speed, which on these displacement vessels, will almost always be top speed. Ships can be slower than expected hull speed due to poor design (so more friction) and other factors, but the longer the ship, the faster it will potentially be able to go. Physics are physics.

So, although a given small ship in the game might be able to get closer to its hull speed than a given bigger ship, and may even sail faster than that bigger ship, it should not exceed its hull speed, which the above corrected formula provides.

Brigand's "correction" is based on "actual" values that I assume were offered from first person report and so MUST be viewed with a tablespoon (not a grain) of salt. There weren't exactly accurate ways of measuring speed, or even distance made good, for that matter for these vessels.

Edited March 1, 2015 by Tom Pullings

[Brigand]

From what I read in the numbers, big ships where underpowered: the total sail area did not match the sail area required to push the ship all the way up to where the maximum hull speed is attained.

 

Having said that, these large ships, sailing a fair percentage less speedy than their long hulls would allow, may still be faster than small vessels doing sailing at maximum hull speed.

 

We can see that the Lady Washington with her 58 ft length on the waterline manages to reach 93.09% of her potential hull speed, which results in a tops speed of 9.5 knots.

 

On the other end of the scale, HMS Victory with her 196 ft length on the waterline manages to reach only 58.64% of her potential, which results in a top speed of 11.0 knots. In other words, HMS Victory is performing 34.45% worse than the Lady Washington and still 1.5 knots faster than the smaller vessel, due to her length at the waterline.

 

Ships may beat their theoretic maximum hull speed, because the 1.34 number used is only an estimate. Some hull (such as the shapes USS Niagara) have a better performance than the estimate.

 

~Brigand

[Hipparchia]

So the real question is : can i still dream to play a little smuggler (fast ship) ? It's true i was thinking a small ship had to be faster than a big one (because he is heavier)

If this is not about the speed, i hope i'll be able to sail in shallow waters, and still win a race if i sail close to the wind !

 

Anyway it's nice to read you guys, even if i don't understand everything

[Brigand]

I'm guessing (but the data that could prove or refute this guess is missing) that big ships need more wind to reach their maximum speed. If this idea is correct, than smaller vessels could possibly outrun their bigger cousins up to certain wind speed and at certain points of sail.

Maybe @Ryan21 or @Baggywrinkle can shed some light on this? or maybe @maturin has an idea on this?

 

~Brigand

[Thomas Cochrane]

Another point for the smaller ships being faster in some circumstance counterpoint is land breeze.

As land and water heat and cool at different rates you generally have some wind onshore or offshore near the land, especially in the mornings and evenings. This is true even when there is no/little wind at sea. And often the wind near the coast is stronger or at least blusteryer than further out. They are reports, for example, of people winning races by taking a longer route to hug the coast and I've seen this myself in the course taken in the Rolex Middle Sea when the wind fails.

In any case the point is that smaller ships may be able to get closer in land with less risk of being grounded (they draw less) and also fore and aft rigs have less to fear from a leeshore as the can more easily beat out to sea. This might give smaller ships another edge when it comes to speed - taking advange of land breeze when big ships cannot, or dare not.

[Portsdown]

Be careful with more modern vessels, no longer limited by the restrictions imposed by wooden construction.

 

Atlantic is designed to racing rules which limit Static Waterline Length. The key word here is Static - it is measured in harbour with no sails set. When she heels, which she will do when sailing, her elongated bow and stern enter the water, making her waterline length greater. Look at all modern monohulls and they will all use this 'trick' to some extent, unless the rules of their class specifically prohibit it. She is also probably semi-planing at her maximum speed, rather than acting as if she has a Displacement Hull.

 

BTW, Atlantic crossed in 12 days 4 hours, which is an average speed of around 8 to 9 knots, depending on the exact start and end points. 20 knots is the maximum achieved under test in calm waters.

Edited March 1, 2015 by Portsdown

[Brigand]

Most interesting discussion. I'm learning a lot of new things here :-)

Would anyone by any chance maybe have a list of maximum speeds for more ship for say 1720 till 1780? I would love to have more data on this!

~Brigand

[Tom Pullings]

But that data would be mere guesses. They used equipment for measuring speed that had no real accuracy, and then reported speeds that included no small amount of boasting (since speeds couldn't really be checked). So any "data" would lead to conclusions bearing very little resemblance to real life.

I think the takeaway for the developers is to play with speeds to balance game play, but do so within the restrictions of hull speed. Make heavier, under canvassed vessels slower, not lighter fully canvased ships faster than they should go. And slow acceleration for larger ships relative to sail area.

It would also be nice if ships with deeper drafts could ground, allowing shallow draft fore and aft vessels to use islands and reefs and shoals to elude faster vessels, as mentioned above and as actually happened.

As far as chases on the open sea, schooners and cutters should be able to escape into the wind given current dynamics, so unless they are caught out dead downwind without escort, they should have a chance.

[Thomas Cochrane]

But that data would be mere guesses.They used equipment for measuring speed that had no real accuracy...

 

This is true when it comes to sailing away from the knotted rope, but there are some things we can verify like daily fixes of position. They give a reasonably accurate position and we could check passage times too.  For example there must be some way of knowing how long a common journey would take so that we find a good average. 

 

If someone could be bothered find them there may be resources of scanned contemporary ships logs, we could enter the daily fixes into Google maps and see how far they come in a day's sailing. A solar fix at local noon with a reasonable chronometer should be considered very accurate (though not up to GPS standards) but accurate enough to make landfall across the Atlantic within a few hours of error (if O'Brian is to be believed).

 

Of course this is always speed over land not speed through water (the latter is affected by length, the former not (obviously) ).

[Tom Pullings]

Yes, but that would also merely give you average distance made good over a fairly long time (a day) and so wouldn't give you much sense of maximum speed, I shouldn't think, particularly since the fastest passages are influenced by the current as well.  Although average speed on good sailing days would give some idea of shortest passage times for various ships, if that's something we're wanting to know.  

 

And daily fixes are accurate if the chronometer is accurate (which did vary).  Sightings can tell you your latitude with pretty good precision, but for longitude to be determined, an accurate timepiece is required.  Again, such fixes were much more approximate than modern equipment provide.  So navigators often plotted a course to intercept the correct latitude and then sailed along it until reaching the desired goal.  

 

Here's a lovely description of navigation aboard the wonderful "Old Ironsides": http://www.captainsclerk.info/speaks/book18.html

[SueMyChin]

This is true when it comes to sailing away from the knotted rope, but there are some things we can verify like daily fixes of position. They give a reasonably accurate position and we could check passage times too.  For example there must be some way of knowing how long a common journey would take so that we find a good average.

 

This also wouldn't take into account the wind speed or direction either.

[Axralis]

Crossing Atlantic ... that really say nothing .

How can you measure boat speed by crossing atlantic and then compare to other boats...you get no data from that is relevant to anything...

The only true way how they could do it to be sure is that they get relevant data is... example > At the same day same time and place 2 boats are there Bellona and Cutter

same sea and wind condition and sail whole day and measure the speeds . Another day with diff.. wind and sea condition and again measure etc.......

And then they will have true data how those 2 ships are behaving in diff.. conditions and their max and average speeds also.

[IonAguirre]

Hi all:

The accurate measurement of a ship of those ages can only be performed from a model built from plans (If good plans are available, of course).

As it has been pointed above, each contry, each region and even each builder used different procedures for displacement calculations, that were always approximative.

Another thing that is in this thread, goes about the mathematical modeling of ships behaviour. There are many rough formulas, but the real way goes through computing the RAOs (Response Amplitude Operators) from the ships shape, rigging and weights distribution for different sea states and entrance angles.

Roughly explained, RAOs compute angular and linear accelerations of a hull when moving through waves.

 

May look very complex, and in fact it is, but once the RAOs are done, they can be tabulated in polar forms and applied as constants to the Ship response to the sea.

The "ideal" ship will reach the speed given by the Froude formula (hull speed formula pointed above), but as no ship is "ideal", other factors will make her slower.

 

Roughly speaking again:

The more breadth, the slower. But ... stability will be better.

The less wetted area, the better. But the minimum surface for a given volume is achieved by a sphere. The closer to a sphere, the slower due to breadth/lenght relation, the less "form stability" and the less heading stability (Round ships do no hold the rhumb line)

The more sharpened ahead and astern the better, but the lower displacement. At the same time, hull pitching would be too big .... and hence the hull, on waves would result slower.

 

For "our" ships, decks shape must be designed in order to allow for guns arrangement, hence they cannot be too narrow or sharpened .....

 

As you can see, many factors are playing at the same time. Some of them working against others.

 

If it was me .... for motion and behaviour modeling,  I would compute a few RAOs, a power/speed curve, a stability one and a Sails polar, I'd set all of it in a table and interpolate for intermediate conditions.

 

Regards

Edited May 26, 2015 by IonAguirre

[NorthernWolves]

Some while back I did some calculation on this (historic data):

		      LWL	Hull speed 	Actual	   C	   % of Hull speed
Lady Washington       58 ft     10.2            9.5        1.25    93.09%
USS Niagara           111 ft    14.1            15         1.42    106.25%
HMS Surprise          114 ft    14.3            12         1.12    83.87%
USS Constitution      175 ft    17.7            13.5       1.02    76.16%
HMS Victory           196 ft    18.8            11         0.79    58.64%

There is more to this whole discussion than just length of the waterline. As you can see, the fastest vessel in reality turns out to be the USS Niagara, she is almost 4 knots faster than the USS Constitution which has a significantly larger length at the waterline.

I wondered for some time where the differences in C come from, they are quite important and, as shown, most often not 1.33 as suggested on wikipedia.

 

~Brigand

Edit:

I thought it would be a good idea to post this quote from @admin earlier today:

 

USS Constitution's ship logs have her recorded at 15 knots on several instances and 14 even more than that. 

[maturin]

USS Constitution's ship logs have her recorded at 15 knots on several instances and 14 even more than that. 

Source please.

 

I've been looking all over the place and can never find claims of her going more than 13 knots. The excellent Loglines blog that is run by the scientists and historians at the Constitution museum state 13 knots as her maximum recorded speed.

 

14 and 15 strike me as extremely unlikely, unless someone was estimating her speed as she surfed down a wave in a storm. Endymion easily ran down President, after all, and President was decidedly faster than Constitution.

[Malachi]

One minor thing to add: Endymion set the record for the RN (14.4 knots) in our timeframe with 18-pounders onboard instead of her wartime armarment of 24s. With 24s her max speed was 13.6  in ideal contiditions (which, curiously, makes her a slower 24-pounder frigate then Forte/Egyptienne or the swedish Bellonas).

Edited October 17, 2015 by Malachi

[maturin]

Endymion was a lot smaller, admittedly, so her performance is not necessarily a constraint.

The fact that Boudriot reports no outstanding speeds from the very solid 30-pdr frigates of the post-Napoleonic era makes me more skeptical.

[Malachi]

Yeah, that´s kinda curious. But he suggests that the 30-pounders suffered from over-sparring, bad distribution/quality of canvas and too high upper works, which required additional ballast. And I wonder if the french also shortened the distance between knots on the log-line. French sailing reports, if they actually have speed measurements, usually report speeds 1 or 2 knots slower then britsh reports for the same ship.

 

Btw, the Bellonas were 5 feet shorter than Endymion.

[maturin]

Yeah, that´s kinda curious. But he suggests that the 30-pounders suffered from over-sparring, bad distribution/quality of canvas and too high upper works, which required additional ballast.

Hmmn, I remembered a more positive impression of those ships from Boudriot, but looks like you are right.

 

He states in the frigate and 74-gun books that the French knot is 47.5 feet, by the way.

 

 

And I wonder if the french also shortened the distance between knots on the log-line. French sailing reports, if they actually have speed measurements, usually report speeds 1 or 2 knots slower then britsh reports for the same ship.

 

 

This is a very interesting issue! According to Robert Gardiner, our lord and savior and provider of manna from heaven (that is, sailing quality reports), the British used log lines that were only 42 feet long. That means that a speed through the water of 11.5 knots would be read as 13 knots, which is the difference between a slow and a fast frigate, a successful or unsuccessful design.

 

This blew my mind last year, but in the meantime, I have been pretty well convinced that it isn't true. Or rather, that the British knew very well how long their loglines were, and did the basic arithmetic to convert their measurements to actual nautical miles/hour.

 

The implications of Gardiner's theory are just too hard to swallow. First of all, it means that the American clipper-built privateers were radically faster than any other vessel afloat, seeing as our current Niagara and Pride of Baltimore I/II can go so fast. Additionally, L'Hermione hit 13 knots in her journey back across the Atlantic this summer. To my knowledge, the Concorde-class was not regarded as exceptional in the French navy, but if we solve for Gardiner's 42-foot logline, that means she went 14.7 'period' knots. I've heard that the HMS Rose replica (which admittedly had her lines modified aft) hit 13 knots once, and 11 knots closehauled with some of her ballast out. And she was supposed to be a pokey little post-ship (Seaworth class)! These replicas are all authentic enough that modern sailcloth, rigging and bottom paint can't plausibly provide such a dramatic performance boost.

 

Which French reports are slower than their British counterparts?

[Malachi]

I based my statement on the 18-pounders by Coulomb, as there seem to be the biggest differences. For example, they´re described as 'indifferent' sailors close-hauled in french reports, but managed 10 1/2  knots (Impérieuse and Sybille) and 10 knots (Melpomène) in british service.

 

The implications of Gardiner's theory are just too hard to swallow. First of all, it means that the American clipper-built privateers were radically faster than any other vessel afloat, seeing as our current Niagara and Pride of Baltimore I/II can go so fast. Additionally, L'Hermione hit 13 knots in her journey back across the Atlantic this summer. To my knowledge, the Concorde-class was not regarded as exceptional in the French navy, but if we solve for Gardiner's 42-foot logline, that means she went 14.7 'period' knots. I've heard that the HMS Rose replica (which admittedly had her lines modified aft) hit 13 knots once, and 11 knots closehauled with some of her ballast out. And she was supposed to be a pokey little post-ship (Seaworth class)!

 

 

Rose with 13 knots. jessssassss....

 

And I just try to forget what Gardiner wrote about the logline and keep my sanity

[maturin]

I based my statement on the 18-pounders by Coulomb, as there seem to be the biggest differences. For example, they´re described as 'indifferent' sailors close-hauled in french reports, but managed 10 1/2  knots (Impérieuse and Sybille) and 10 knots (Melpomène) in british service.

 

I see that she was captured in 1794, so seamanship could have been the issue there. I've seen quite a few lackluster British sailing reports of French frigates, sometimes by Sane. Of course, I always assume that the British stuffed them full of stores and drove them into head seas off of Brest until they were hogged six ways to Sunday.

 

 

Rose with 13 knots. jessssassss....

 

And I just try to forget what Gardiner wrote about the logline and keep my sanity

Rose was somewhat ridiculous in her youth. Apparently when she was brand new they sailed her from the Maritimes to New York with only 2/3 the necessary ballast. When they had to beat up into the harbor, they realized that the shrouds were too taught to brace the foretopsail yard around, so they furled the topsail and set the t'gallant with main t'gallant staysail instead. After hitting 11 knots they snapped the foret'gallantmast in half.

 

 

But yeah, I asked a naval architect of my acquaintance (not a period expert) what he though about the log lines, and he said he couldn't imagine them building the margin of error into the measuring tool. And regarding the ability of 18-th century hullforms to go so fast he just remarked, 'put a ton of sail on it and sail that sucker till you break something.' And with L'Hermione, the proof is in the pudding. Wheeeeeee!