I thought I’d share what seems to be a quick and easy way to measure the area of a fin. This could just be easily be used the area of a hydrofoil.

Futures fins typically lists the dimensions of their fins in the specification section. In that you’ll find Area, Height, Base, & foil. I find this very useful when comparing different fins. But not all of my fins are futures. How do you find the area of a fin that is not published? There are countless ways of measuring area. But in the computer age, I wondered if there was an easy way to do this using a computer, that may actually be quicker.

If you work with microscopes you may be familiar with a program called ImageJ. In that program, you set a reference length, then you take a measurement. Here is an example video:

https://www.youtube.com/watch?v=Qsxvnby7aCMAvailable free here:

https://imagej.nih.gov/ij/download.htmlTo measure the area of a fin we need: a picture with a reference length.

To test this program, I took a picture of a fin on graph paper (10 squares/inch).

#If you have a printer, you can print your own graph paper, see

https://print-graph-paper.com/#note graph paper isn’t necessary, just convenient.

I pre-measured the height of the fin, and the length of the base with a ruler. I opened the picture in Image J.

With the straight line tool, I drew from top of the fin to the base (base is where the fin meets the glass, ie. Top of fin box).

Analyze/Set Scale, I type in the known distance (height of fin).

With the straight line tool, I drew from the front of the fin to the back of the fin along the base.

Analyze/Measure: Look at the length of each measurement to see that it agrees with base length.

To measure the area, you select the freehand tool and trace the fin.

Since my fin is on graph paper, I have reference for area. I traced around blocks of 10 squares by 10 squares. I used the zoom feature for this.

Analyze/Measure: This gave me the area I was expecting, cool.

Next measure the area of the fin:

With the freehand tool, carefully trace around the perimeter of the fin.

Analyze/Measure: Look at the Area in the units of your measurement. Mine was in the ballpark of what I was expecting compared to fins of known area.

Next I looked at an online picture of a Need Essential fin. They only publish the height and base lengths, but do have a picture of the fin next to a scale (i.e ruler). Can Image J be used to measure the area of a screenshot?

https://www.needessentials.com/collections/accessories/products/8-single-finI took a screenshot of fin with the scale. I opened the screenshot in image J. With the straight line tool, I measured from the top of the fin to the base.

Analyze/Set Scale, I enter in the known distance (height of fin).

With the straight line tool, I drew from front of the fin to the back of the fin along the base.

Analyze/Measure: Look at the length of each measurement to see that it agrees with base length.

Next I selected the freehand tool and traced the fin (don’t include the area of the fin that is inside the fin box.

Analyze/Measure: Look at the Area in the results measurement. Again the measurement was in the ballpark of what I was expecting.

If you want to easily convert units, check out:

https://www.convertunits.com/from/sq+mm/to/square+inch#At first I looked into programs like vector drawing programs like Inkscape. Too complicated and takes too long. Then I looked at CAD programs like Librecad, same problem.

If you have an easy way of measuring area that you like to use, please feel free to share. And happy new year.