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 get run over by your karma!"