Full Keel Cross Section Question

[hamburg113]

Hi,

Thanks very much for this comment. It help me to think about my ideals.

Tks again and pls keep posting.

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Best regards.

[viking north]

Hamburg--where are you located in Canada-- Are you presently planning a build, into a build or modifying---Geo.

[viking north]

Just to explore a little more on my keel possibilities I have attached my rought sketch drawing and some photos. The sketch showing the two part keel is not to scale, the skeg will actually have less profile width. The beginning point of the deepest forward point of the new keel to be attached is approx. 6 to 8 in. aft of the displacement waterlines station #4(waterline being divided into 10 equal stations,(sloop rigged)) In the photos this point(waterline station #4) is indicated by the small red plastic bottle placed on the existing keel. The existing keel's max. width is constant from where it widens out from the bow forward of the bottle to about 3/4 's of it's length at 9 1/2in. From there it tapers down to 4 in. wide at the end of the existing keel. The top of the new keel (root) is approx. 10ft. the bottom is approx 6ft. If my calculations are correct I do have the ability to install a close naca foil shaped keel. At .8 cord width to length on 10 ft. it would be 9.6in. wide at it's widest part but blending in to the existing keel thru out the rest of the cords length could be a pain in the neck and possibily cause more turbulance and drag than the gain of a foil. My other choice is to go with a naca foil section leading edge, a parallel ships body and taper to a naca foil section wnd tailing edge. Anyhow while i am tending to lean toward the latter choice (simplicity) I would also appreciate any and all input on the pros and cons as this keel research so far has been a great learning experience for me and I know there are others out there (from e mails) that are really interested in the info. Thanks Geo.

P.S. also input on the idea of bolt on scheel type wings re. my post #30 page 2 would also be much appreciated --Tnx. Geo.

[MikeJohns]

Originally Posted by viking north

.......If my calculations are correct I do have the ability to install a close naca foil shaped keel. At .8 cord width to length on 10 ft. it would be 9.6in. wide at it's widest part but blending in to the existing keel thru out the rest of the cords length could be a pain in the neck and possibily cause more turbulance and drag than the gain of a foil. My other choice is to go with a naca foil section leading edge, a parallel ships body and taper to a naca foil section wnd tailing edge. Anyhow while i am tending to lean toward the latter choice (simplicity) I would also appreciate any and all input on the pros and cons .......

Geo
I've been through this before including tank testing some full keel shapes and misinformation abounds, even from people who are expert on higher aspect foils.

Aerofoil shapes reduce drag by promoting attached laminar chordwise flow, however with long low aspect keels the whole concept of using a aerofoil section is invalid. You would get no benefit.

What you should do is fair that keel into the curve of areas rather than try and adopt a chordwise foil shape. Match the existing base and don't worry about section shape, even a flat leading edge on a keel like this for the applicable flow velocity is fine so long as the corners are radiused.

As for the Scheel it's marketing that makes it prominent, there realy is no benefit over a simple tapered section, and as I said before it's a very draggy for any keel form and particularly so for a longer keel where spanwise flow is more common. Any end plate or similar appendage can have a large vortex production unless it's aligned with the flow. Then two factors are significant, the flow has a high spanwise component on a long keel and secondly flow over a keel is far from chordwise and laminar in anything other than smooth water.

You are much better off just making the keel base wider and having the sides sloping inward and having a flat bottom which has advantages for haulout too. Then simply round all the corners even if it's only by a 1/2 inch radius.


[Added]
Recently I posted something relevant here:
Vacanti keel question - nose diving

[viking north]

Great info and very appreciated, My research on this topic is over, I know it's only a conversion and into a motorsailer at that but wanted to give it every chance, too late once the lead is poured--Plus I have learned new info--Thanks again Mike--Geo.

[viking north]

To those following this thread, re keel design, I will do a follow up( in a few months) on my boat build under Boatbuilding--(The Nancy G) once my proposal has been fine tuned by my designer. Tnx. Geo.