keel foil design x-y graph

[Tad]

This is not a great picture but the general idea is to use a heavy flat bar as the trailing edge if the keel. Weld the stern tube into the flat bar, and add the keel side plates (notched around the tube as required).

The leading edge of the box keel (stem) should be tapered as well. If it's 100mm total width it should taper to 20mm at the waterline and for some distance below. Just cut the corner off the box and fit a "bevel" plate.

[Tad]

Stem detail.....

[Arvy]

Hi Tad,

Thanks for the 2 ideas, I guess that will be the easiest way to do it. And have the welder notch the keelside plates at the job instead of cutting them with the CNC cutter.

The "bevel" plate will have to be cut with the cnc cutter, but I guess it is not to hard to draw that correctly so that I can make expansions of it, I will keep the start of the bevel just below the waterline simply for esthetics's when not sailing.

[viking north]

After some thought I realized my proper approach to this design was to develop a foil based on the width of my keel mold and not take some abstract width and simply fit the leading, parallel and trailing sections together at the matching widths. The problem I discovered was if the foil width at it's max. point 35% from the leading was wider than my keel it would create sharper than desired changes in width at the intersect points of the foil shaped leading edge to the parallel section and again from the parallel section to the foil shaped trailing edge. I know this should have been a common sense approach to begin with but what can I say Old Dogs are slow to learn. Here's how I approached it. I chose the lowest effective percentage of effective foil width to length ratio, 10% width to chord length based on 72in. 10% of 72in. = 7.2in. Close enought to my finished keel width of 7in. Using the "B" foil form in the chart above posted by TAD here's the resultant foil shape. By using this as my pattern i can now easily splice together the foil leading edge--the parallel mid section and the foil trailing edge with smooth flowing joins at the intersects. Thank you again for the help--Geo.(Oops-forgot to mention that 7.2in. foil max. width is as per "B" foil design at 35% back from the nose)
P.S. While the photos show what looks like a 30% width to length cord ratio, it is just camera perpective error, in actuallity it is only 10%. 7W on 72L

[viking north]

As shown the idea is to keep the keel end as narrow as pratical where the flow feeds to the prop blade area and build in a wider raised section where the flow can be directed around the shaft and cutless bearing or stuffing box. Note also the water intakes to cool and lubricate the cutless extend out past to capture sufficient water. Building in steel, simply cut a pipe longitudionally on a diagional and weld in place to duplicate what has been done here in fiberglass.

P.S. I intend to modify this keels area above and below the cutless to narrow it up even more than shown .