Lapstrake table of offsets

I received a request for the table of offsets for a lapstrake chebacco. Here I have posted an Excel file with all of the offsets in Feet-Inches-eighths and also mm for both the 19’6 and the 25’4 versions. I found it easier to work in mm here in Australia (Inch rulers and tape measures are […]

I received a request for the table of offsets for a lapstrake chebacco. Here I have posted an Excel file with all of the offsets in Feet-Inches-eighths and also mm for both the 19’6 and the 25’4 versions. I found it easier to work in mm here in Australia (Inch rulers and tape measures are available but not so common) so I created these spreadsheets to make the conversions. It will probably require a bit of studying to work out what you are looking at.

The first table for each boat shows the height above a base line of the buttockline at each station. You will need to refer to the drawing for the location of each station – you may notice that Phil numbered his stations in different directions for the 19′ and the 25′ versions. We will never know why. The base line is the bottom of the keel for the 19′ version and 2 inches below the bottom of the keel for the 25′ version (I assume Phil changed his mind somewhere in the design process about the depth of the keel – but kept the table of offsets.) The buttockline is the line where a vertical slice would go through the hull. The vertical slices are 12″, 24″, 30″ and 36″ from the centreline for the 19′ version, but only the 24″ buttock is given for the 25′ version. This table also has the height of the deck and bottom panel. It looks as if I have found a small error in Phil’s deck height at station 1 during my analysis.

The second table for each boat shows the width from the centreline (so-called “half breadth”) of the waterline at each station. The waterlines are the lines where horizontal slices meet the hull. This is just like the line where the water meets the hull when the boat is afloat.

In theory you could build a hull using only one of these tables – but in practice you need to cross reference some little details that can’t be worked out with only 1 table.

Andrew