R&J Baker Company

Using Excel Graphs to Loft Fair Curves
for hard chine boat design

After looking for several months on the internet and trying various CAD programs, I had failed to come up with a simple way to lay out the lines for my fishing vessel to check the fairness of the design.  My building technique involved setting molds on a strongback, and laying plywood over the molds, FRP (Fiber Reinforced Plastic) on the plywood, then popping the hull off the molds, and FRP (Fiber Reinforced Plastic) inside the hull on the plywood for a composite FRP (Fiber Reinforced Plastic) Plywood hull.  My FRP consisted of stitched biaxial cloth and cold cure,  17 oz below the waterline, and 12 oz above.  My design ideas came from the FAO Fishing website using the 7.4 M hull there, taking the widest frame, and coming straight back to the transom with the keel and chine for a planing hull.  However I still needed more stability and lift so I had to modify the hard chine vee to lay on ski's hence the search for a CAD program that would allow me to lay in my own lines and check for fairness.  Applying the formula for when all else fails, return to simplicity brought me to try excel graphs.  The example below is just that, an example.  To get a better idea of what the lines will look like you will need to add columns for every 12 inches of hull or so and then, if the molds are on 36 inches, only use every 3rd one

I use 0 for the Baseline and Centerline and measure in cm

Using sequential columns for the molds starting from the stern as below, 
with mold #1 being the transom;


I found you can then highlight the measurements themselves, as such;


then click Insert/Chart


Select "Line" for type, and highlight "Line with markers" exactly as below

chart 1

click next then make sure you select "Rows"

Chart 2

click next and give it a title

Chart 3

click next and make sure "As new sheet:" is selected

Chart 4

 and viola

Chart 5

You then have a graphical representation of your lines for a hard chine boat.
You can grasp each marker with the tip of your mouse and move them up and down to adjust for fairness.

Another neat trick is to use excel to make a scale model.
Once you get your lines, pick a cell in your first mold column,
a few rows below and enter the formula for the scale you want to build. 

For 1/7th scale, enter "  =b3/7  " without the quotation marks of course.  Then press Enter, and click anywhere outside the cell.  Go back, highlight the cell, grab the black plus sign, and drag it along the row to get the numbers for the rest of the row. 

Then do the same for each column, 

and you will have all the measurements you need to build,
a bang-on accurate 1/7th scale model of the lines you've arrived at.

scale 5