Shop Tips & Tricks #3: “Declivity” - a trick for dealing with things out of level or plumb

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Blog entry by GnarlyErik posted 12-05-2012 11:13 PM 8515 reads 2 times favorited 10 comments Add to Favorites Watch
« Part 2: Dividing a line or space into equal parts Part 3 of Shop Tips & Tricks series Part 4: Centerlines - Finding, Marking and Using Them! (Part One) »

With shipbuilding in the past – and for some larger vessels even now – boats were built ‘on the shingle’ (beach), meaning they were built on a slope, sometimes quite steep. In fact, before the days of modern machinery, the slope of the building site enabled the builders to move and launch a vessel of many, many tons. And, unless the builder compensated for the angle of the shingle, many items could end up out of kilter once the vessel entered its working environment after launch.

This was dealt with in at least two ways: “deadrise” and “declivity compensation”. (‘declivity’ means ‘down slope’ in its Latin origins).

First, and most obvious is the use of ‘deadrise’ in the keel and bottom to make the working part of the vessel more or less level during construction, while the keel itself rests at the angle, but still have the vessel float level and properly after launch. This works up to a point, but can get excessive, producing too much ‘drag’ to the keel (depth at the stern), especially if the slope is steep. Many vessels were built with their framing square (perpendicular) to the slope, with decks, superstructures, etc., so arranged to become level and plumb to ‘earth’ after launching. This made for interesting and difficult intersections and transitions, but I digress. See image #1.

Compensating for the slope of the building site.

The subject of this post, is the use of ‘declivity boards’ during construction. While not many are building boats on the shingle these days (you never know!), a declivity board can come in handy for other things at times – anything needing to be built (or repaired) at an angle to earth, or leveled and plumbed when your base is not. These adaptations can be quickly made on the spot, for any angle, as needed.  

In its simplest form, a declivity board is a wooden wedge about as long as your level, at a taper to match a particular slope, as required. This is then placed against the side of the level to compensate for the departure from level the slope makes, in either a horizontal or vertical direction. See image #2.

A declivity board in use

A somewhat easier-to-use-and-make version is a simple batten tacked to a piece of thin stock at the required angle. But, this also then makes the declivity board ‘handed’, so the batten must be on both sides to make it both right and left handed. In use, the main issue is to be sure it is being used in the right direction, as it is easy to get things confused! See image #3.

A simplified declivity board

I know this is mere trivia and of little use to many, but you still may find it interesting.

If you Google “ship launching’ on YouTube, I guarantee you will find some fascinating videos to watch. There is nothing quite like seeing many thousands of tons of ship moving from dry land to its natural element. Once it starts, little on earth will stop them – and more than a few end up in disaster. If you ever have a chance in life to actually watch a ship launching, do yourself a favor and don’t miss it – just be careful where you stand!

-- "Never let your dogma be run over by your karma!"

10 comments so far

View OldKranky's profile


142 posts in 3418 days

#1 posted 12-06-2012 12:12 AM

Thanks! I love learning new things like this.

-- Better looking at it than for it....

View patron's profile


13720 posts in 4427 days

#2 posted 12-06-2012 12:26 AM

that comes in handy for construction too
like for roof repairs
where some add on’s are slightly different pitch
or to follow a slope for gardens and grading

-- david - only thru kindness can this world be whole . If we don't succeed we run the risk of failure. Dan Quayle

View HillbillyShooter's profile


5811 posts in 3378 days

#3 posted 12-06-2012 12:40 AM

Thanks for the information.

-- John C. -- "Firearms are second only to the Constitution in importance; they are the peoples' liberty's teeth." George Washington

View jap's profile


1251 posts in 3140 days

#4 posted 12-06-2012 03:06 AM

Thanks for taking the time to write this blog, i’ve enjoyed it so far.

-- Joel

View Gpops's profile


248 posts in 4531 days

#5 posted 12-06-2012 03:35 AM

Fascinating, never stopped to think about that. Thanks, Don

View shipwright's profile


8717 posts in 3884 days

#6 posted 12-07-2012 12:38 AM

We used to build right on the launch ways and there were always levels around with declivity boards taped on through the holes in the level and corresponding holes in the board. We had two sets of ways back then and when two boats were being built at the same time , the boats’ names would be on the boards. Woe be the lad that used the wrong one to set a galley counter top.

These are great posts to read Eric.

-- Paul M ..............the early bird may get the worm but it’s the second mouse that gets the cheese!

View GnarlyErik's profile


344 posts in 3220 days

#7 posted 12-07-2012 12:56 AM

Yes, we used to drill a couple of 1” holes through the declivity board and use hose clamps to bind them to a spirit level. They were dedicated to the boat being built or repaired.

-- "Never let your dogma be run over by your karma!"

View eddie's profile


8565 posts in 3700 days

#8 posted 12-07-2012 03:10 AM

find it very interesting ,thanks Eric

-- Jesus Is Alright with me

View greg48's profile


633 posts in 3844 days

#9 posted 12-07-2012 04:07 AM

Your a lifesaver, my eyes are getting to weak to read scales to the nearest 1/32”. Thanks for the post(s).

-- Greg, No. Cal. - "Gaudete in Domino Semper"

View Boatman53's profile


1081 posts in 3283 days

#10 posted 12-07-2012 04:42 AM

Thanks for sharing this tip. I have used a plumb bob and a framing square for quick jobs and for comparing different parts that I might be working on.

-- Jim, Mid coast, Maine home of the chain leg vise

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