# Shipbuilding - slipway angle and perpendicular frames?



## ianscales (May 17, 2006)

Ship profiles drawn on paper often show hull framing and deck house frames drawn perpendicular to a horizontal keel, i.e. truly vertical.

Yet, when the ship is being built, the keel is resting on a slope - the slipway. So setting up frames and superstructure to be perpendicular to the keel would present a problem. Just using a plumb-bob like in housebuilding won't work.

How was this done in times past? I'm particularly interested in what the practice was for traditional wooden shipbuilding.


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## Keltic Star (Jan 21, 2006)

ianscales said:


> Ship profiles drawn on paper often show hull framing and deck house frames drawn perpendicular to a horizontal keel, i.e. truly vertical.
> 
> Yet, when the ship is being built, the keel is resting on a slope - the slipway. So setting up frames and superstructure to be perpendicular to the keel would present a problem. Just using a plumb-bob like in housebuilding won't work.
> 
> How was this done in times past? I'm particularly interested in what the practice was for traditional wooden shipbuilding.


90 degree level and good working drawings


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## John Paul (May 27, 2007)

never worked in a building yard but I believe a board giving the angle was placed near the slip way so everyone could see the required angle and all vertical work worked from that

I think the board was the "Declivity Board"


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## Pat Kennedy (Apr 14, 2007)

Deadrise and declivity, good info and graphics here;
http://lumberjocks.com/GnarlyErik/blog/33307


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## stein (Nov 4, 2006)

A plumb bob from cross spall will work fine, just measure the length from the frame where it touches the keel and the length from the spall. As regards traditional wooden shipbuilding at least, I do not think you would measure the inclination of each frame separately, you would set up a cord, parallel to the keel or the waterline (which might not be meant to be parallel), and mark off the position of each frame as with the same distance to the next as it has along the keel or the waterline. A "keel staff" was also used I read, with the spacing of the frames marked on it.


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## ianscales (May 17, 2006)

Great, thanks for the various answers. I did not know about declivity boards; the Lumberjocks article is a good introduction.


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## Duncan112 (Dec 28, 2006)

To further complicate matters the declivity can alter along the length of the ways to avoid excessive hull stress when the stern takes to the water, which transfers weight to the fore poppet, the lower part of the way is less steep - I've also got a feeling that the ways are not truly straight slopes but form part of an arc. Think it is all in Rawson & Tuppers books - in the attic at the moment


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## Alistair Macnab (May 13, 2008)

*Declivity....*

On joining my first ship in Belfast, the "Fleetbank" built in 1953, I crossed in front of the big building slips which I think were the "White Star" slips with the extensive top structures. There was a notice board which I now know was the "Declivity Board". In my ignorance, I took this to mean that the ship that was then building was for Everards! But then, the second building slip had the same notice so I thought: "My goodness! Everard are building two big ships!".


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## Duncan112 (Dec 28, 2006)

Alistair Macnab said:


> On joining my first ship in Belfast, the "Fleetbank" built in 1953, I crossed in front of the big building slips which I think were the "White Star" slips with the extensive top structures. There was a notice board which I now know was the "Declivity Board". In my ignorance, I took this to mean that the ship that was then building was for Everards! But then, the second building slip had the same notice so I thought: "My goodness! Everard are building two big ships!".


(Applause)(Applause)

They appear to have had two "Acclivitiys" but no Declivity (or Futility come to that - which was the title of Morgan Robertson's presentient novel about "Titanic")


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## stein (Nov 4, 2006)

You might try page 53-54 etc in this book (The Practical Shipuilder, by L. McKay) and see if you can understand anything. I have to say I was much confused and little enlightened, but I have the excuse that I am Norwegian. http://babel.hathitrust.org/cgi/pt?id=wu.89090041534;view=1up;seq=53


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## ianscales (May 17, 2006)

Stein, well spotted to find the edition of "The Practical Ship-builder" by McKay - only available at Hathi (as per your link) and not Google Books or elsewhere. Good stuff.

Like you however, I am finding it a very dense read, not helped by the lack of diagrams. A lot of concentration is needed to visualise the spatial frame of reference he is using. 

I had a look through my copy of Rawson's "Basic Ship Theory" volume 1, but found naught. Perhaps vol. 2 has something. 

You'd think this topic would be something covered in the various books on wooden ship building published between 1918 to recent, but I haven't come across it (as far as I can recall). 

Apart from the hull framing, this topic bears on how one would deduce how different shipwrights in different parts of the world erected their deckhouses, and hence their visual appearance. Since deckhouses might be erected on the ways that are horizontal with a declivity; or erected after launch on a ship evenly trimmed or perhaps down by the stern; or even walls erected perpendicular to the sheer, perhaps there is nothing one can say in general.


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## stein (Nov 4, 2006)

See David Steel, Shipwright’s Vade Me***, page 239, from top of page. https://archive.org/stream/shipwrightsvade00steegoog#page/n250/mode/2upe:


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## kewl dude (Jun 1, 2008)

I cannot speak to wood shipbuilding, but during the 1973-74 recession I worked as a Marine Pipefitter at Todd's Shipyard, aka Todd's Los Angeles, in San Pedro. Todd's had an order for five 35,000 ton product tankers for a commercial tanker company. However the ships were going on a long term Military Sea Command contract and as such were finished in MSC colors. I cannot speak to what was done on the ways. Regardless once the ship is in the water at a berth, the natural weight of the propulsion system aft ensures the ship has a definite rake. The waterline may be at the propeller hub depth aft while the bow is out of the water. 

All of the work we did involved reading the correct construction plans, always making sure you had the most recent revision. The plans provide required angles and dimensions. You lay out the piping using a combination of a six foot metal folding ruler and you're Yo-Yo, as we called the spring powered retractable steel tape measures we all wore clipped to our belts. 

I attach two images:

Pipefitter-1400.jpg (161.9 KB) 
Tanks-1600.jpg (176.9 KB)

The tank isometrics are for a T2 tanker. Note the keel in the two center tank images labeled CVK -- Center Vertical Keel. All dimensions grow from the keel. Pipefitter is a sturdy 200 page pocket size reference which I carried in my pocket everyday. It has a lot of short cuts including providing directions to measure to obtain usual angles.

While I worked there a local Los Angeles Pipeline Pipefitters union went on strike and many of their members were hired by Todd's. Despite them specifically being told that their pipeline methods will not work on a ship and to leave their plumb bobs home; many ignored those rules and 'attempted' to use plumb bobs. I came down in a tank one day to find these guys with their personal plumb bobs hung all over the tank. 

I called them together and had a brief instruction course on how to run shipboard pipe by reading the prints. The prints showed how far off the existing structure the piping would be installed always with at least two dimensions such as to the bottom shell plating and the side shell plating. Measurements were to the center line of the outside of the pipe.

I mostly worked on the fifth ship in the series Hull # 13. While attempting to install port tank piping we found that the plans did not agree with what we had. Seems some how or another, after building four before it, Hull 13's bulkhead between the port and center tanks was an even ten inches too far outboard. That whole bulkhead was removed then replaced in the proper place while the vessel was in the water. Then the plans and what we had agreed.

As an aside when I went to Todd's to apply the HR department did not know what to do with me. I had brought along my C/E License and discharges from tank ships. Anyway after awhile I was escorted over to the Pipe Foreman's office. He recognized my license and asked me if I could read plans, he reached to a side table and pulled a sheet over on his desk. I looked down and said "Ah, pump room." And the Foreman said "You're hired."

Greg Hayden


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