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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 623 days ago 2264 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!

-- Candy is dandy and rum sure is fun, but wood working is the best high for me!



10 comments so far

View OldKranky's profile

OldKranky

121 posts in 956 days


#1 posted 622 days ago

Thanks! I love learning new things like this.

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

View patron's profile

patron

13000 posts in 1965 days


#2 posted 622 days ago

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

HillbillyShooter

4475 posts in 917 days


#3 posted 622 days ago

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

jap

1225 posts in 678 days


#4 posted 622 days ago

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

-- Joel

View Gpops's profile

Gpops

245 posts in 2069 days


#5 posted 622 days ago

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

View shipwright's profile

shipwright

4898 posts in 1422 days


#6 posted 621 days ago

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 ..............If God wanted us to have fiberglass boats he would have given us fiberglass trees. http://prmdesigns.com/

View GnarlyErik's profile

GnarlyErik

205 posts in 759 days


#7 posted 621 days ago

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.

-- Candy is dandy and rum sure is fun, but wood working is the best high for me!

View eddie's profile

eddie

7197 posts in 1238 days


#8 posted 621 days ago

find it very interesting ,thanks Eric

-- Jesus Is Alright with me

View greg48's profile

greg48

274 posts in 1382 days


#9 posted 621 days ago

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.

View Boatman53's profile

Boatman53

836 posts in 821 days


#10 posted 621 days ago

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

-- Jim, Long Island, NY Ancorayachtservice.com home of the chain leg vise

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