Frames built vertical or perpendicular to keel?

[Smile-n-Nod]

When a wooden ship was built on a slipway, was the keel put on blocks so that it was level (before launch) or was it declined slightly and thus matched the slope of the slipway? 

 

If the keel was declined, were the frames installed vertically or were they installed perpendicular to the keel (to match the station lines on the sheer plan)?

 

Or were the the angles involved so small that it didn't make much of a difference?

[Jaager]

I do not have a wayback machine, so I cannot ask the naval architects and builders directly.  I have had hands on practice with a lot of plans - pre 1860.  This covers about a 200 year span -1660 - 1860.

These are my conclusions from the available evidence.

 

The Stations define the frame shapes and orientation.

The Stations were the portion of the plans that were enlarged to full size on the mold loft floor.  The timber patterns were the Station shapes and had marks to define the intermediate frame shapes.  

If there were 20 stations and 80 bends - 160 frames - there would have been 20 sets of patterns made for the actual ship. For a model, we have been making 80-160 patterns. 

It would probably have been crazy making to have tried to have used an angle jig with a plumb line to erect the frames.

The keel is easier to shim than to try to deal with vertically canted frames.

Large ships were not usually designed to have much if any drag.  The captain and sailing master (?) (the technical non-com) would have adjusted the sailing trim prn anyway - regardless of what was designed.

Smaller craft (schooners - sloops - etc) tended to be the ones that could have had significant drag.  The scantlings were less, so a sloped keel on the ways would be easier to build.

The sides of the ports were defined the frames.  With a significant drag and the frames erected perpendicular to the keel, the angle of the sides of the ports would have been .... strange - funky - disorienting.  It would have been a laughing stock.

 

As an aside,  the ports sills and lintels followed the sheer of the deck.  The gun trucks rolled on an angled deck the farther aft or fore was the port. using a rectangular stick as a support for gun port framing is only valid for two or three ports at the midship.

 

[druxey]

I'm afraid I have to contradict you. Look at this contemporary plan of a vessel with considerable drag:

 

https://collections.rmg.co.uk/collections/objects/85907.html

 

As you can see, the frames are at right angles to the keel, not the waterline. There are many other similar archival examples. This is not unique. 

[Roger Pellett]

The results of my attempting to answer this question are inconclusive.

 

Here’s what I think that I know.

 

Wooden ships were built on keel blocks set up on a slight slope.  Maritime history researcher Eric Ronnberg says that this slope was typically 3 degrees.

 

William Carothers reinforces this conclusion in his book on American Packet Ships.  He explains a procedure where a setoff dimension was calculated for each frame.  With the plumb bob landing on this calculated distance from the frame heel the shipwrights would know that the frame was vertically square with the keel.

 

He then goes on to say that ships were not always built with the frames arranged vertically square to the keel.

 

I also have a book published in the early 1900’s where a marine surveyor named Carr discusses construction methods used in Great Lakes shipyards where vessels are side launched.  He points out that a great advantage of side launching is that it allows construction on a level area, unlike ships built elsewhere.

 

While I am confident that ships in American coastal yards were built on a declivity and not jacked up before launching, the question of disposition of frames relative to the keel is not clear.  (The jacking that did take place immediately prior to launch was only to transfer the weight of the vessel to the launch cradles.)

 

In his book, The Practical Shipbuilder, Author  Launchlan McKay, includes a drawing of a New York pilot boat, c1820.  These boats were built with considerable drag.  The stations on the lines drawing are not drawn square to the keel.  

 

McKay’s book also includes a procedure for making a lines drawing for a vessel with drag.  Without actually going through the process with pencil and paper I have been unable to follow it.  It’s on my to do list.

 

I’ll leave examination of British Admiralty draughts to others.  As far as American Practice goes, many of the lines drawings by Howard Chapelle were either developed from half models or by the British measuring captured American ships.  Many half models do not show station lines, and British techniques for taking off lines in a dry dock would not necessarily capture actual disposition of frames.  Chapelle, therefore, drew his lines to illustrate the development of American hull forms, not necessarily to illustrate exact construction techniques.

 

This is an important topic as more and more ship modelers want to build models that display actual construction.  Hopefully this thread will inspire more discussion.

 

Roger

 

 

[vaddoc]

I would think:

The construction should follow the plans. If a frame is meant to be perpendicular to the keel. it must be placed as such. Even a few degrees off in a long frame will lead to problems. The shipwrights would need to think of a way to get the ship to water but keeping the frames as per plans-perpendicular to the keel.

EDIT: or perpendicular to the waterline like my current boat that has a sloping keel or whatever the plans show

Edited April 1, 2021 by vaddoc

[Jaager]

58 minutes ago, Roger Pellett said:

many of the lines drawings by Howard Chapelle were either developed from half models or by the British measuring captured American ships.  Many half models do not show station lines, and British techniques for taking off lines in a dry dock would not necessarily capture actual disposition of frames.  Chapelle, therefore, drew his lines to illustrate the development of American hull forms, not necessarily to illustrate exact construction techniques.

Guilty! as to my sources.

[cotrecerf]

Taking the contemporary launching plan from Frederic H.Chapman's  "Architectura Navalis Mercatoria 1768" as a valid pattern I see the frames mounted in right angle (90 degree) to the keel timber. In the ship plans of this first scientific naval architect the frames are always shown at right angles to the keel even with ships having an extreme  difference of drought between stern and bow.

 

Joachim

 

 

[Smile-n-Nod]

Is ship No. 2 above (in cotrecerf's post) built with an intentionally hogged keel?

[Roger Pellett]

Chapman’s drawings were intended as a survey of hull forms; both to illustrate generic vessel types and more unusual foreign types.  Except where he actually shows structural details his projections would be intended to best show hull form, not actual framing.

 

The waterline is important to Naval Architects as other waterlines drawn parallel, stations drawn perpendicular to it, and especially buttocks based on these projections help them to visualize flow around the hull.  On the other hand there is no structural or construction reason why frames needed to be perpendicular to the  design waterline.  

 

There is also no important structural or construction reason why frames needed to be square with the keel.

 

My conclusion:  Frames in wooden ships were erected square with the keel except when they weren’t. 

Edited April 2, 2021 by Roger Pellett

[Roger Pellett]

Vaddoc,

 

Keep in mind that wooden ships were not actually built from plans.  A draught showing hull lines was drawn or a half model was carved.  A table of offsets, a digital table of xyz coordinates was then prepared fromthe drawing or model.  This table was then sent to the mould loft.  The loftsmen were experts at turning the offsets into a full sized “drawing” on the floor of the loft.  The actual full sized patterns of the frames were taken from the floor of the mould loft, not the drawings.

 

Roger

[vaddoc]

6 hours ago, Roger Pellett said:

The actual full sized patterns of the frames were taken from the floor of the mould loft, not the drawings.

Indeed Roger. This actually was what the Mediterranean shipwrights were also doing. I have no expertise or knowledge in this matter but what I meant was that, after the frames were produced, whether perpendicular to the keel or waterline or other, these angles still had to be maintained building the boat so the shipwrights would have to know beforehand how the boat would lay for building and how it would go in the water. I assume that those very heavy frames would make sense to keep vertical and not at an angle where they would need pretty substantial support.

[Roger Pellett]

Yes, the loftsmen would need to know the frame disposition for a number of reasons, and of course the orientation of the frame in relation to the keel affects frame shape.

 

During the years when large wooden ships were routinely built there was great variety in building techniques, depending on tradition, environment, availability of materials, etc.

 

While there is a rich treasure of detailed construction information for British, some European and some American ships built in organized shipyards, much less is known about the construction techniques employed by artisans in the small yards.

 

[uss frolick]

Check out the Admiralty Draught of the 1814 American prize Schooner Grecian:

 

https://prints.rmg.co.uk/products/grecian-1814-j7988?_pos=1&_sid=fea7772ac&_ss=r

 

 

 

 

[Jaager]

On Grecian, note that the sides of the ports do not line up with this "as built" plan.

If they wished to copy the design, I do not envy their version of an intern who would have gotten the job of reorienting the stations for the new version.

 

Oh, and HIC did not completely redraw lines plans to his particular style.  He duplicated and cleaned up the plans as he found them.  He used the style of the original NA.

Edited April 5, 2021 by Jaager

[jud]

Gravity is a constant within limited areas so a water level unless effected by friction and wind will always show true at both ends. Plum Bob strings will also hang parallel unless disturbed by air movement within the area of a hulls construction. Those two things provide the repeatable constants for building anything and they are perpendicular. Suspect they, with few exceptions were the only constants in old or current ship building. KISS principle comes to mind.

en.wikipedia.org › wiki › KISS_principle

KISS, an acronym for keep it simple, stupid, is a design principle noted by the U.S. Navy in 1960. The KISS principle states that most systems work best if they are kept simple rather than made complicated; therefore, simplicity should be a key goal in design, and unnecessary complexity should be avoided.

 

Edited April 6, 2021 by jud

[Roger Pellett]

The current issue of WoodenBoat Magazine includes an interesting column about this subject.

 

The column’s author, Tom Jackson notes that 40 of Howard Chapelle’s drawings in his American Small Sailing Craft Book of boats with drag are drawn with the keel level and with body plan sections perpendicular to the keel.  He argues that these drawings would better describe the true shape of the hull if drawn with the waterlines level.

 

He then includes a number of reasons why Chapelle might have drawn these the way that he did:

 

For many of the boat’s that he measured (and half models too) the keel was the only fixed reference as there was no waterline visible.

 

The load waterline would vary depending on ballast, cargo, etc.  

 

Builders back then were much less concerned with the concept of “load waterline” than they are today

 

The easiest way to build a boat is with the moulds and frames set square to the keel.

 

He also has discovered that Nathaniel Herreshoff who did not draw lines drawings but took measurements directly from a half model built boats upside down with frames and moulds set square to a construction reference line that approximated the slant of the sheer.  This allowed the hull to be at the lowest possible working level during construction.  Permanent hull frames would not be perpendicular to either the keel or the waterlines.

 

Roger

 

 

 

[amateur]

Hi Roger,

 

you write: the easiest way is to build frames square to the keel.

that sounds rather straightforward, but looking at the Chapman-drawing above (large ship, build on a sloping floor) I sometimes wonder: how did they set up their frames: no laser equipment, and the most simple (piece oflead to a string) not working, due to the sloping ramp.....

 

Jan

[Roger Pellett]

Jan, 

 

In Nineteenth Century American shipyards, they calculated a standoff or offset dimension for each frame that took  into account the slope of the keel on the keel blocks.  A mark was put on the top of the keel at a distance from the heel of each frame equal to the calculated dimension.  When the frame was erected a plumb bob was hung from the cross spall at the top of the frame.  When the plumb bob landed on the mark they knew that the frame was erected correctly.

 

Roger

[georgeband]

This topic has been quiet for a couple of weeks so I will risk extending it at a slight tangent. I am building a British schooner using the Haddock drawings that Druxey mentions above on #3. The Admiralty drawings clearly show that the frames are perpendicular to the keel and this is not surprising given that plumb bobs are and were a readily available technology. What I am surprised by is that structures on the deck and below deck follow these same vertical lines when perpendicular to the water line would be the natural solution. 

 

This snippet from the Admiralty drawing shows the officer's cabin and an entrance lobby with ladder, just aft of the main mast. The waterline is the blue-green line that slopes across the centre of the picture. 

 

I can accept that the end walls of the cabin were built using the frames. However, the ladder has steps that are nearly parallel to the waterline but its sides are perpendicular to the keel. This can be built and a carpenter might scoff at the design but still finish the job. The companionway box above the ladder looks like a dog's dinner. If it has hinged doors facing one bulwark then the shapes of those doors will be compromised by the angle between the sides of the companionway and the deck. Even the skylight above the cabin has sloping ends. 

 

My guess is that the carpenters who built the deck fittings did their jobs after launch and used their own plumb bobs. The walls that they built would be vertical compared to sea level and not the keel. (The sides of the gunports are at 90deg to the deck.) If this is the case then the lines taken from Haddock at Portsmouth might not be correct and the draughtsman simply extended the frame lines by mistake or for expediency. I do not like this conclusion because it throws doubt on the drawings that we use for our models. I do not want to say that the Admiralty drawings are mistaken because it opens a plethora of excuses where we say that drawings are wrong if they do not match our expectations. But I do not want to build a companionway cover that leans back. 

 

George

[Roger Pellett]

George.

 

Before the current system of modular construction, ships were built in two phases.  Construction before launch, and Outfitting after launch.  Construction was done by shipwrights.  Outfitting was done by joiners.  Building ladders, cabin partitions deck furniture etc. was the job of joiners.  My guess is that you are correct.  In doing their job, the joiners would build their structures level and square to the ship afloat.

 

The disposition of frames is a different matter, as they determine the shape of the hull.   If the frames were not arranged parallel to the body plan sections on the draught,  the entire draught would have to be redrawn to shift the orientation of the body plan sections to match that of the frame orientation.  Otherwise the shape of the hull would change.

[georgeband]

Roger,

 

Thanks for your comments and advice. Ultimately I will make a judgment call about what I think is right or wrong on an Admiralty drawing and it eases my conscience when I hear opinions such as yours. 

 

George

[georgeband]

Here is a contemporary piece of information to add to the discussions. Falconer's Universal Dictionary of the Marine (I have a scanned copy of the 1784 edition, readily available on the web) spells 'launch' as 'lanch' and has the following entry. 

 

 

We are all able to make our own interpretations of these words and I do not expect all to agree. My opinion follows the comments from Vaddoc and Jud above and simple engineering expediency - I would expect the frames to be built vertically, and the angle of the keel would be adjusted on the ground with blocks and wedges to enable this to happen. When it comes to launch the vessel, Falconer says that two slipways are laid and a cradle is built to support the ship. The supports for the keel are then knocked out and the vessel either moves immediately or is given a push to start her slide.

There are no definitive words here that the keel is parallel to the slipways in the vertical plane, so it is plausible that the keel is horizontal while the ship slides down an angled slipway while sitting in a cradle. This interpretation could resolve some of the discussions above. Bear in mind also that practice in different parts of the world may well have been different. 

 

George