More on Foils - Foilstrip  
By Tom Hamernik - Chicago, Illinois - USA

Note: Tom Hamernik has contributed a custom made spreadsheet which you are free to download (link at bottom of page) and use to calculate segments for making foil section rudders and centerboards. We are very grateful to Tom for this contribution to boatbuilders everywhere. Feedback solicited.

Thought you might like to see the spreadsheet I am using to calculate the strip widths for my Pathfinder's rudder and centerboard. It's based on the NACA four-digit foil with no camber (Section type 00XX).

It could easily be adapted for Warren Messer's approach, (Part-1 & Part-2) where the plies run forward and aft, as opposed to athwartships as JW shows.

I have it calculate the width of the strips so that when assembled, you plane off the corners, rather than fillet the low spots like in WM's approach.

Screenshot from Spreadsheet

The reason I created it was to:

1. Check/reverse engineer JW's rudder and centerboard foil designs

2. Calculate the precise widths of strips needed to buildup the foil in an attempt to lessen the work needed to shape the foil by eliminating some of the wood prior to glueing. This information can be scaled directly off the print. But, it's easy enough for me to generate a table of values.

3. Educate myself on NACA foils (at least the 4 & 5 digit series)

I dressed up my spreadsheet a bit to share with others. With it, you can calculate virtually any four- or five-digit NACA foil with zero camber (symmetrical NACA foils). In this regard, it may be more user-friendly relative to the approach WM suggests. But, it would have to be modified to produce a table of ply sizes for plies running parallel to the centerline of the foil, rather than transverse (like JW's foils).

It could also be modified to produce a table of strip widths to be filled, rather than cut down, if you really like that approach.

The bottom line - if you think it's interesting, use it however you like.

Click HERE to
download the free
spreadsheet file


Via the link below, you will find a large (3 MB) excel file that has the new version of FoilStip. There are two new tabs to play with - one will calculate lengthwise strips that will require planing to final foil shape. The other will calculate lengthwise strips to be filleted (like the Warren Messer approach; Part-1 & Part-2).

Sorry about the file size. Because the solution to the lengthwise strips approach requires solving an eighth-order polynomial, it requires a hell of a lot of calculations, yielding a large file size.

Click HERE to
download the updated
spreadsheet file

Screenshot from Updated Spreadsheet - Ply-Fillet

Screenshot from Updated Spreadsheet - Ply-Plane

Also by Tom Hamernik: