HQ35/12 Airfoil

[Happy Days]

Very interesting Peter, thanks for posting that link :clap:

[Ron]

Yes thanks for that link Peter.
I instantly hit the 'bookmark' button.
Interesting bit on kites too.

I find sailing very like flying turned 90 degrees.
The foresail acts like slots when going to windward, allowing the mainsail to have a much greater angle of incidence without stalling.
And many people don't appreciate that you can stall a keel, when the side pressure becomes too great with little forward motion. This is especially so on these modern 'plastic bathtubs' with wing shaped keels, and is why the old sailing fishing boats had large flat keels to use the 'barn door' effect when hauling nets.

[Peter]

Hi Ron,

Yes - the gist of the article was that sailing was just like flying. The keel is a symmetrical airfoil and will not work if the boat is pointing in exactly the same direction as the boat is going.

[Ron]

HI Peter,

Yes that's it.
Leeway it's called.
If you're pointing, say, north, and the wind is from the west, there will be perhaps 5 to 7 degrees of leeway. So you're actual course will be 005 to 007.
So the leeway angle is the angle of incidence.

Mind you, there are lots of other considerations for keels, like righting moment due to ballast, performance when heeled, and even "will it fall over when dried out against the quay". :lol:

[Peter]

I guess you can add me to your list of glider fliers who also like to sail!  Although in my case all I have access to is a very old Heron dinghy that I resurrected and redecked a few years ago.  Good to get out on the water though.  Looks like you have a nice boat there.  Can't beat wooden boats (and gliders!) - although both are a lot of work!

[Ron]

Yes it's amazing just how many sailors also fly, either full size or models.
Like the owner of Rossbrin Boatyard where my boat is at the moment. He flies model gliders.

There must be something about Herons.
My boat is a Purbrook-Rossiter 'Heron'. Built 1960 of Mahogany on Oak. 22' 3" LOA. Needs a lot of work doing this year. Well it's needed doing for many years, but this summer she's staying ashore so I get some dry/warm weather for the work.

Can't say the keel is exactly 'airfoil' shaped though. More 'barn door' principle.