Seeking information on determining load waterline

[trippwj]

I am working on a paper concerning the process used to determine the load waterline in the 16th through mid 19th centuries and could use some help.

 

I have found an abundance of information concerning the application of Archimedes' principle on buoyancy and displacement, but to date I have only been able to find where it was applied to determine the actual displacement of a vessel when already in the water.  The primary sources I have checked thus far (such as Sutherland, Steel, Humphreys, Mungo Murray, Stalkart etc. - still working through many, and have not gotten far in the works in other languages such as French and Italian, though they were far ahead of the English in adopting scinetific methods) all discuss the waterline but, rather than describe how to determine the level, they provide a set value.  I came across this from The Sea-Man’s Vade Mecum: Containing the Most Necessary Things for Qualifying Seamen of All Ranks. Printed and Sold by James Woodward behind the Royal-Exchange (1707):

 

...the true way of Measure, must be by measuring of the Body and Bulk of the Ship under Water, for if one Ship be longer in the Floor than another of the same Breadth and Length, she shall be more in Burthen than the other; as a Flemish Ship shall carry more than a French or Italian Vessel of the same Length or Breadth; therefore, I say, the Measure of a Ship is known by measuring her, as a piece of Timber may be measured of the Form, to the draught of the Water, assign'd her, the weight of the same Body of the same Water that the Ship swimmeth in, shall be the exact Weight of the Ship, and all things therein, Loading, Rigging, Victuals included therein: then if the Ship be measured to her light Mark, as she will swim at being launched, the Weight of so much Water being taken or subtracted from the Weight of the Water when she is laden, the Residue shall be the Weight that must load Ability of carrying, called her Burthen. By this means you may know the Weight of the Ship light, and what she will carry to every Foot of Water assigned to her, which can be done by no general Rules in Arithmetick, because of their great Irregularity, according to the differing Forms of Ship; you may, if you please, first measure the Content of the Keel, Post, Stem and Rudder, all of it that is without the Plank, and under the Water-line, and note it by it self; then measure the Body of the Ship in the Mid-ships, by multiplying of the depth of the Water-line, and the breadth; then you may find the Content of the Want by the circular part of the Ship under Water, being narrowed downward, and subtract this from the whole Content of the Body found, by the depth of the Water-line and breadth of the Ship, and this shall be the solid Content of that part of the Ship, I mean, of solid Foot Measure, of 1728 Inches to the Foot; then proceed to the fore part or after part of a Ship, and to 3 or 4 Timbers more, find the mean Breadth at the narrowing aloft at the Waterline, and allow at the Floor and the mean Depth, and measure that piece of the Ship, as I told you of the middle part of the Ship, and so measure the whole Ship by pieces, and add them together; and so many Feet as it maketh, so many Feet of Water shall be the Weight of the said Ship, and the Reason may be considered thus: There is a Ponderosity in the Water, but there is a greater in the Air; and there is a Ponderosity in the Water it self, but not so much as in other things more solid, as in Iron: Suppose a Gun or an Anchor of Iron it sinketh in the Water, but yet is not so heavy in the Water as in the Air, by the weight of so much Water as shall make a Body equal to the Body of a Gun, or an Anchor in Magnitude; which Weight substracted [sic] from the Weight of the Iron Body weighed in the Air, and so much must be the Weight of it in the Water.

 

While it encompasses both Aristotlean (for example, There is a Ponderosity in the Water, but there is a greater in the Air; and there is a Ponderosity in the Water it self, but not so much as in other things more solid, as in Iron: Suppose a Gun or an Anchor of Iron it sinketh in the Water, but yet is not so heavy in the Water as in the Air, by the weight of so much Water as shall make a Body equal to the Body of a Gun, or an Anchor in Magnitude; which Weight substracted [sic] from the Weight of the Iron Body weighed in the Air, and so much must be the Weight of it in the Water) and Archimedes concepts (then if the Ship be measured to her light Mark, as she will swim at being launched, the Weight of so much Water being taken or subtracted from the Weight of the Water when she is laden, the Residue shall be the Weight that must load Ability of carrying, called her Burthen.), I have not found where designers, in crafting the model and plans, applied these concepts. 

 

I find some reference to this in works by Deane and Chapman, but most of what I find is actually descriptive of finding the stability of a vessel.

 

Have any of you come across any treatises prior to the late 1700's where the principle of buoyancy was applied during the design stage to find the load waterline, or was most of it based on institutional knowledge?

 

Appreciate any leads or insights - and THANKS!

 

 

[druxey]

Wayne, do you have a copy of Ships and Science by Larrie D. Ferreiro? There is great discussion on the evolution of naval architecture in Europe and England during the scientific revolution in the time period 1600 to 1800. The content of this book is germaine to your enquiry.

[trippwj]

Wayne, do you have a copy of Ships and Science by Larrie D. Ferreiro? There is great discussion on the evolution of naval architecture in Europe and England during the scientific revolution in the time period 1600 to 1800. The content of this book is germaine to your enquiry.

 

I do, and have been using it extensively.  I am trying to go from the info there and find where some of the notable shipbuilders and designers actually applied the methods during the design stage but thus far not finding much. 

 

Ferreiro also has an interesting paper that looks specifically at the influence of Aristotle on naval architecture:

Ferreiro, Larrie. 2010. “The Aristotelian Heritage in Early Naval Architecture. From the Venice Arsenal to the French Navy, 1500-1700.” Theoria 68: 227–41.

 

The challenge is the transition from scientific inquiry to practical application.  Steele has some wonderful description of the use of these methods to determine the volume submerged, but then rather than calculating it for a given design suggests using a ratio of depth of hold to the moulded breadth (for example 7/16 for a line of battle ship).  Sutherland, about a century earlier, likewise provides detailed mathematical instruction yet then states a specific height for the waterline with no description.

[Jaager]

I have always thought that they went at this from the opposite direction.  The hull form developed to work from the waterline that designer drafts (or from the Dutch style -had in his head) and then when a float, blasted to meet that waterline. 

[trippwj]

I have always thought that they went at this from the opposite direction.  The hull form developed to work from the waterline that designer drafts (or from the Dutch style -had in his head) and then when a float, blasted to meet that waterline. 

 

That is, actually, the way it usually worked - I am trying to get to how they determined that waterline since, from all indications, the use of the mathematical methods was not common prior to the late 1700's (not to mention the relative low mathematical abilities of most shipbuilders). 

 

It's been interesting moving through the literature (mainly written in ye olde Englifh, including the relatively random punctuation and spelling of the times) to try and discern a methodology.  Even many of the secondary sources seem to move from the development of the science to the use for stability calculations but little on the interegnum of ship design.

 

For me, the search for information is certainly a pleasure - just wish I could read Dutch, French, Spanish, Italian and Venetian (not to mention Latin) so I could get into the works by Duhamel du Monceau, Pierre Bouguer and others that had some of the earlier works on the topic (the English were particularly tardy in adapting scientific methods to design ships.  I suspect that their colonies in the America's were likewise slow to implement).

[michaelpsutton2]

All of the old methods produced rough approximations. Some were rougher than others. Shipbuilding was an art not a science until the middle of the eighteenth century.The ships were built to displace something more than the actual weight of their intended contents and could then be ballasted down the design load water line for stability. If you want a snapshot of just how well this worked in the real world, consult "Great ships" by Frank Fox. See how many of the ships, particularly the 1st, 2nd, & 3rd rates required girdling or padding the frames to increase the displacement. So many ships could hardly open the lower tier ports when they were at anchor much less at sea.

 

This subject interests me and I would love a chance to read the paper when you are done

[jbshan]

... how many of the ships, particularly the 1st, 2nd, & 3rd rates required girdling or padding the frames to increase the displacement. So many ships could hardly open the lower tier ports when they were at anchor much less at sea.

It has always seemed to me that they made a best guess based on experience during the design phase then, when a ship was determined to be ineffective a fix was made.  Vasa was the extreme where it was not possible to bring her back for the fix based on sea trials.  The problem persisted up into at least the mid-1700s, ships being lost at the battle of Quiberon Bay (1759?) because of hauling up their lower port lids.

Supposedly a yacht for Queen Victoria was so altered while being constructed that she capsized still in the dock.  If a courtier suggested the Queen might want to listen to a fiddler playing chanties atop a capstan, a capstan was added.  Finally so much was added that stability was lost.

I suspect they had to wait for calculus to be invented before they had any sort of chance to work it out on paper beforehand.

[roach101761]

Wayne

 

This topic is intriguing.  This is a quick reply this morning, only after about 20 minutes of research.  I am leaning toward the replies that the shipwrights and builder's relied on tried and true methods and experiences to build the hull, and then when it was afloat could then actually determine the load water line and best sailing trim.  The shipwrights and naval architects might have had a good idea where it was supposed to be, but for the times there were to many factors that influenced the final product that few would want to commit themselves officially on paper to be so easily judged for a failure.  It is very high math to calculate and perhaps there were to many variables in materials,(wood)(availability), methods, and skills at building wood ships to determine for sure.  The advancement in Ship design was very slow and conservative. 

 

I am drawn to my conclusion by the review of several known successes and known failures.  Failures include Wasa, Mary Rose, and the US ship of the line Independence and William Doughtys design of his mid size revenue cutter plan of 1815/16. (Dallas) This little cutter was off.  It had great difficulty carrying its ballast and supplies for 30 days.   When all was on board it was found that that with a 10 draft, less than 2 feet of free board remained.  The plan in the archives does not have the water line marked.(unless I missed it)

 

Successes include Constitution and Essex.  Hacket's plan of Essex is available.  Maybe I have missed it but I can not find where he marked the Load Water line on the plan.   I did not have time to locate or  carefully examine Humphry's or Fox's Plans of the first US frigates, but I bet if you look at the DESIGN plans the LWL may not be on them(This could be my failure to understand all those lines, please let me know if it is).  Make sure you are not looking at as built plans after the ship was afloat.  Chapelle in his reconstructed plans seems to have added the LWL and Best Sailing Trim.  I am curious how he knew as he only had the archives available, not the ship(Constitution an obvious exception,but I do not know if he visited the ship for his reconstructions).  Did Chapelle calculate the LWL more than a hundred years after the fact?

 

When did LWL's actually appear routinely on design plans?

 

Hope this helps.

 

Phil

Edited March 5, 2015 by roach101761

[michaelpsutton2]

Mathew Bakers famous sail plan for a galleon of 1596 seems to show where he wanted her to float. The earliest named plan in the NMM the Tryumph of 1698 has a load line indicated

[roach101761]

In my office, I have framed and hung on my wall, Howard Chapelle's reconstructed plan of Essex.  From my review of Hackett's design plan that I looked at this morning it seems the LWL and best Sailing Trim has been added by Chapelle.  I will look at those Hackett plans again tonight.  I thought I had a copy of Hackett's plan from the Archeives. (it is of course huge compared to the ones reproduced in my books). 

 

Phil

[jbshan]

While she did indeed capsize and fill through the ports, Mary Rose was some 25 years old at her sinking, so not that totally unsuccessful of a design.  Just to keep the record straight.

[mtaylor]

From the anecdotal readings I've done, it appears the designer had in mind how the ship should float, etc.  After launch and fitting out with guns, ballast, rigging etc. there was more checking and testing.  Finally, sea trials where the Captain and/or the Master would adjust mast rake, ballast distribution, etc. to sort out the WL;s, along with the rigging.  However, it is also somewhat apparent that each Captain took it upon himself to tweak things including the waterline and trim due to provisions, armament changes, etc.

 

it kind of reminds of the the early days of aircraft design... design it, build it (with changes due to a 1000 and 1 factors), and then fly it.  Re-tweak and fly again.

[roach101761]

Joel you are of course correct, perhaps a bad example.  Mark, in air craft building you only get to re-tweak and fly again if you survived the first flight.

[roach101761]

Same story different day.    Could not find those plans last night.  I must have put them somewhere safe so I could be sure to find them.  Oddly, they may be in my office.  I will keep looking.

 

Phil

[trippwj]

Same story different day.    Could not find those plans last night.  I must have put them somewhere safe so I could be sure to find them.  Oddly, they may be in my office.  I will keep looking.

 

Phil

The copy of the Hackett draught that I have (from Frigate Essex Papers: Building the Salem Frigate, 1798-1799) does not show a load water line.  The plans drafted by John Stevens in 1952 as well as the sets from Portia Takajian do show a LWL but it is not clear how they determined the placement.

[roach101761]

I found those plans right where I put them.  I have been collecting Essex stuff for years so I was a little panicked.  I put the box in my son's room behind his TV.  They were safe and sound.  I did not have the Large Hackett plan from the archives.  I think I must order it.

 

However I own the last volume of the Naval Documents set of books published in 1945, covering the years  1801-1807.  In the back pocket are 21 plates of vessels belonging to the US Navy for the time period. The Preface states that the plans of vessels are all taken from the Archives or the The Library of Congress. They are represented to be repaired facsimiles of the original documents.  All the plan sheets fold out to about 20 inches.  The Essex plan is Hackett's plan.   No Load water Line.  I will look at he other plans later today.

 

Phil

[amateur]

I used to know someone (died long ago) working in the Rotterdam harbour, His job was in putting the famous plimsol mark at the hull of newly build freightships.

According to him, in the fifties and sixties there used to be a rather large difference between the loadline dring design, and the actual allowed load-line after the ship was completed.

 

Jan

[trippwj]

IT is a challenge, for certain!  Came across this quote from the Director of Naval Construction, The Admiralty, London, England entitled The Influence of Mathematics on the Development of Naval Architecture. in Proceedings of the International Mathematical Congress Held in Toronto, August 11-16, 1924

 

"The employment of ships for various purposes dates back to very early ages, but the science of Naval Architecture is of comparatively modern growth. Ships have advanced in size, speed, equipment and structural strength, but the progress from the primitive log or bundle of reeds used by the ancients to the 100-gun ship of the eighteenth century was effected wholly by methods of trial and error.

 

It was then impossible to predict the draught at which a new ship would float, or ensure that she would possess sufficient stability and satisfactory seagoing qualities. In consequence changes in design frequently proved to be the reverse of improvements, and it was commonly necessary to add girdling around the waterline of ships found defective in stability."

 

So much anecdotal information, and so few contemporary sources!  Still digging and parsing - stay tuned for more!

 

Please keep those thoughts, observations and suggestions coming!!!!

 

 

[Walter Biles]

Wayne,

I once read something which used the area of the stations along all the length of the ship or boat, and converted it using the average spacing between the stations, to find the approximate displacement of the boat hull at that point.  I believe that using that, the average center of displacement was calculated  up or down, and fore to aft to find the Water line and the point on the hull where the hull was balanced fore to aft, which also incorporated all the calculations based on expected weight of the structure when it was loaded.  This also compared the overall height of the boat's structure and how high the center of gravity of the structure would affect the stability for righting itself.  Eventually this brought about a calculation that gave a recommendation as to how deep the hull must set in order to maintain an upright position against the forces acting upon it which included wind and wave action and the motion of any contents such as cargo, crew, fuel or other liquids in the hull, which meant that the loaded condition might be different than the unloaded condition.  I kind of understood it at the time, BUT

I never actually put these things into action for my own models, for somewhere in the course of things my loss of mental capacity interfered with implementation.  I am not sure if this will help you, but I hope that it may give you an idea of the complexity of the calculations.  On my Meridea, I eyeballed the cross section of the hull based on lighter boat hulls, hence I have made external expansion downward to bring back the boat to the waterline I marked proportionally in my initial drawing.  

 

I direct your attention to Mr. Mott's pictures of his 'Maria' when he was checking her out for stability after redesigning her.

 

Walt

Edited March 7, 2015 by Walter Biles

[roach101761]

I have continued to review the facsimile plans from the last vol. of the the Naval documents book referred to in post number 16 above.

 

Wasp                                     No load water line.

 

Vixen schooner, later brig      No load water line.

 

Siren  brig                              No load water line.

 

Philadelphia                           No load water line.  

 

New York, Frigate                   No load water line.   

 

Constitution                            No load water line.

 

Constellation                          No load water line

 

Boston Frigate                       No load water line

 

Argus Brig                              No load water line

 

Various gun boats                  No load water line.

 

I believe all these plans to be design plans, NOT as built plans.  There are lots of water lines, shear lines and the like on these plans, but nothing marked load water line, or best sailing trim.  

 

For American ships it is looking like the shipwrights did not want to commit on paper where the ship would float, until it floated.  However, they must have had a good idea because the super frigates were designed to keep the lower port sills out of the water so the whole battery could be fought in a heavier sea than a three decked ship.  This means Humphries, Fox and Doughtry were no dummies most of the time.  This is what I have for now. I will keep looking.

 

Phil

Edited March 7, 2015 by roach101761

[roach101761]

I have identified some design plans above.  What other well know design plans are there?  Also, do the original as built plans of ships acquired by the admiralty indicate a load water line.  Somewhere I have seen the survey of Bethia(The Bounty before she was  Bounty)   Also the cutter Lady Hammond before she was Lady Hammond.  Do these surveys have Load water lines on them?

 

I say, lets identify known plans or surveys and where they are published and take a look at what was recorded originally upon acquisition by the admiralty.

 

Phil

Edited March 7, 2015 by roach101761

[trippwj]

Looking through volume I of the Humphreys Papers, there are numerous references to the draught of water, but I only find the following that hints at the process (note that the upper drawing was added by the transcriptionist to aid in understanding the process):

 

 

There are also indications that either Joshua or Samuel did utilize mathematical techniques during the 19th century:

 

The Franklin left Philadelphia June 24th 1817 at 8 o’clock AM. July 17 the Franklin took in 29 long 32 pdrs which weighted 1781 cwt. This weight settled the ship 3½ inches. Her draught of water after these guns were taken in was Aft 23 – 1, forwd20 – 3. At this depth it required 19½ tons to settle the ship 1 inch.

 

The originals can be viewed at the link below.  Note that this volume is a long term set of notes for use by the builder - starts with the 1719 Establishment and includes a bit of everything from brief descriptions of vessels to a design for a new ships steering wheel.  Some interesting stuff!

 

Humphreys, Joshua. “Volume 1: ‘Principal Dimensions.’  Joshua Humphreys Papers (Collection 0306).” Text. Philadelphia, 1770-1838. Historical Society of Pennsylvania. http://digitallibrary.hsp.org/index.php/Detail/Object/Show/object_id/10371and the description is at http://www2.hsp.org/collections/manuscripts/h/Humphreys306.html.

[rybakov]

I went throug Nautical Sschool at a time when calculators were not programmable and computers were room sized affairs.

Sometimes in Naval Architecture we were asked to determine the displacement of a ship, at a given immersion, from the lines plan.

We would start by determining the areas of the sections, then plot the obtained results along the x axis of a graph, and then

calculate the area of the graph and that would be the immersed volume, wich multiplied by water density would give us the buoyancy.

To undertake all those calculation we used Simpson's Rule, so named ater an English mathematician Thomas Simpson (1710-1761)-

So I think that from approximately 1750 on the shipwrights would be quite able to figure out immersions and displacements.

 

Anyway, that's just my feeling.

 

All the best

Zeh

[jbshan]

"Simpson's Rule"

That's certainly the first half of the equation, but they then have to get the weight of the ship, guns and stores, etc. correct, enlarging the hull if necessary.  The first US ships of the line sat fairly low in the water, if I recall, so the ports were too close to the water, and those were 1820 and later.

I have seen methods where you mark out squares of a curved enclosed shape, then little squares, then littler squares, until you have covered all of the shape, to measure the area.  Is this similar?

[trippwj]

Mr. Berry (see my above post on the 1924 conference) offers the following:

 

The method used by Mr. (afterwards Sir Anthony) Deane of calculating the displacement of ships is unknown; but it appears that about 1700 this was effected by dividing the body by equidistant sections, calculating the area of each and thence obtaining the displacement by some rough process of quadrature. There is, however, no record of any such calculations, and it is probable they were but rarely performed.

 

Nowacki and Ferreiro, in their 2003 paper “Historical Roots of the Theory of Hydrostatic Stability of Ships”, offer the following:

 

Deane demonstrates two methods to calculate the area underneath waterlines at each “bend” or frame of the hull; using either (1) an approximation for the area of a quarter-circle or (2) by dividing the area into rectangles and triangles. Deane then sums the areas for each frame, multiplies by the frame spacing and multiplies the volume by the specific weight of water to obtain the displacement. He does this for several different waterlines, including the desired waterline below the gunports. When a ship is launched, he can immediately determine the light displacement, and then calculate how much weight should be added to arrive at the design waterline.

Edited March 7, 2015 by trippwj

[trippwj]

Continuing to ponder and contemplate, let me ask whether anyone has found any contracts from, say, prior to 1750 that include the draught of water? 

[jbshan]

They put into the specs where they *wanted* the ship to float, but if wishes were horses ...

[roach101761]

I reviewed my materials, and although I have no contracts from prior to 1750 I did review the Sloop of War Peacock contract found in the History of American Sailing ships.  No mention of the Load Water Line.  It gives the general specifics of the ship in the contract and advises it will be  built according to the plan provided by the Navy Department.  A William Doughty Plan.  This contract is with Noah and Adam Brown of New York.   The Dallas revenue cutter was built to the Doughty Mid sized revenue cutter plan and was also built by the Browns. See Post #      above. 

 

Maybe its time we think in a different direction.  My observations.

 

The Math was there to be able to determine the Load water line. However, there may have been relatively few mathematicians up to the task, and fewer who were shipwrights.  As time marches forward and more scientific principals are applied to ship design, more designers have the math skills and have a more formal education. 

 

In the design plans I have seen, no load water lines appear.

 

It is likely that the ship designer and shipwright has a very good Idea where the ship would float but did not put it on the plan.

 

If you look at the plans we have, even us ship modelers can look at the plan and see where the ship should float, or was meant to float probably within a foot.

 

Although ships have sunk at launching due to stability problems, I know of none that sank because the were too heavy and settled below their maximum sustainable load.

 

They always floated High and Dry as light ships.

 

The test for the new ship comes after it was fully outfitted with Masts, equipment and Ballast for stability.  I think in most cases the ship still floated High and was a light ship.

 

The test becomes whether it can carry the load that was intended.  Such as the stores for a 400 man frigate crew for a cruize of 3 to 6 months or longer together with all its guns.  I think the ship fails if it can not carry its intended load to be useful.

 

Achieving the Load Water line I think was easy because ballast and stores are a very flexible thing. If stone takes too much room, use Iron bar.  If Iron bar takes too much space use Kentledge.  In the end it comes down to how much beef, pork, peas, water and rum you can carry to support the crew or how much usable space you have for cargo storage.

 

Thinking about all that I have read, in warships , best sailing trim and the load water line was subject to constant management during a cruize. Every meal eaten by the crew changed the draft of the vessel.

 

Let us not forget that, depending on the Ocean, salt water densities vary.  In some waters you can carry more, in others you can carry less.  I pulled down my Nicholls's Seamanship and Nautical Knowledge, C.1942 together with a Blue Jacket Manual or two.  I reviewed Plimsoll lines and load marks.

 

In the merchant service the crews were smaller.  We know that many companies and their captains ignored loading conventions. After all if he can get it in the ship, the ship must be able to carry it.  Right?  On a trip the load line did not vary by much as the crew was too small to have an impact.  We all have seen the pictures and read the stories.

 

Saying all of this perhaps the load water line was not a primary design concern.  In fact, it might have been a minor thing.  The ship will float where it will.  You must add or subtract weight to make it sail correctly and efficiently.

 

Perhaps Load lines came much later as safety at sea regulations?

 

I reviewed all the posts above.  Many make the same points I am making here.  It looks like determining a load water line in an existing ship was learning exercise to determine if you could apply the knowledge to build the next ship.

 

Wayne, in any of your research do you have any references to load water lines as part of a design parameter, or is calculating it always an exercise on and existing ship?

 

Phil

Edited March 10, 2015 by roach101761

[trippwj]

Phil -

 

I have come across secondary sources that indicate there were some calculations of displacement done as early as ~1634 in Britain (see, for example, the contract for HMS Sovereign of the Seas (later Royal Sovereign), pages xcii-xcv in The Autobiography of Phineas Pett, ed. by W. G. Perrin (1918) available at http://archive.org/details/autobiographyofp00pettuoft) where both a "draught of water" (fully loaded WL) of 21' 3" and a "swimming line" (light WL) of 18' 9" are provided (these did change during development of the ship).  In the same year, two of Phineas Pett's relatives (his son and nephew, both named Peter) were building ships in Woolwich and Deptford, and providing accurate estimates of their draft and freeboard to gunports, well before launch.  See Trinity House of Deptford Transactions, 1609-35 London Record Society 19 pages 135 & 142 for details ( http://www.british-history.ac.uk/london-record-soc/vol19 ).

 

While these ships indicate that there was an ability, they are more the exception than the rule. By the 1600's, the importance of designing ships of war such that the lower gunports had adequate freeboard when the ship was fully loaded was a key consideration.

 

From several centuries earlier, in Venice, the Capitulare navium (Maritime statutes) of 1255, established load waterlines according to the age of the ship, using an iron cross fixed to the hull.  The Republic of Genoa (100 years later) adopted a statute that established freeboards for different routes based on sea conditions; higher for the open waters of the Bay of Biscay, lower for the protected Mediterranean (from Ferreiro, Down from the Mountain, 2004).

 

 

[michaelpsutton2]

Tonight, I have spent a little time looking at a number of plans from the NMM website of ships from the latter half of the 1700's. The majority seem to indicate a load waterline.

 

On an awful lot of them the load waterline is parallel to a line drawn between the lower edges of the first and last ports of the lowest gun deck. It is set so that it is very near to the lower edge of the main wale at it's lowest point. On some ships it may be slightly above or below that spot . An example shown below is the 3rd rate HMS Alfred of 1778. It might be said to be a good representative of most but not all the draughts of this period.

 

The question though becomes .....were these ship designed in advance to float at this level or was the line arbitrarily placed on the plans in this position simply as a formality.

 

One reads time and time again that there was difficulty with getting the lower deck guns high enough out of the water.The plans show plenty of freeboard. 

 

Maybe the ships were designed to use these waterlines but their captains overloaded them.

 

Somebody with access to more of the archives than myself might compile a list of how much water the vessals were known to have drawn. This could be compared to the plans.

 

Obviously the ships rose and fell with the amount of supplies ballast etc.

Edited March 11, 2015 by michaelpsutton2