- I think that you are right about flat boards. In my experience the shape of the sail has more to do with windward ability than the foils, at least on small boats that do 5-6 knots upwind.
--- In Michalak@yahoogroups.com, "prairiedog2332" <nelsarv@...> wrote:
> My apologies Bill,
> My post was not intended to refer to the racing crowd which I know you
> are a member of.
> At the sailing speeds you PDR guys goes at - Mr. Bolger mentions you
> "may" gain several seconds per mile with foil shaped blades. Plus of
> course having a 6-part down-haul and cunningham on your 65 sq, ft.
> I certainly would not dare post this to the pitchfork crowd for sure. I
> actually get a kick out of how the Bolger Brick has been elevated to a
> world championship sailing class. NACA foils tend to stall out at high
> angles of incident and is why they have slots in aircraft wings. Our
> slow boats benefit from flat surfaces on the foils to help prevent
> leeway. Just enough rounding to prevent chattering of of the board.
> Otherwise flat is better.
> Bolger also found on his Micro keel design , having a square edge helped
> in going to windward rather than rounding it off. It provided more
> resistance to sideways motion upwind. So it is related to sideways
> pressure against the keel as well as the hard chines helping it hold on
> from slipping sideways.
> <br>--- In Michalak@yahoogroups.com, BGN5731@ wrote:<br>><br>> My
> goodness Nels! Are you suggesting that all those hours of work making
> <br>> a leeboard look like a control surface off a jet fighter is a
> waste of time?<br>> <br>> I can see and hear the villagers lighting
> their torches and picking up <br>> their pitchforks...getting ready to
> run you off this site!
> [Non-text portions of this message have been removed]
- Yes, you are using just the end of the ellipse to shape the leading edge.
From: Anders Bjorklund <andersbjorklund5@...>
Sent: Friday, June 21, 2013 8:08 PM
Subject: Re: [Michalak] Leeboards
I think I got it. Thanks. It looks like the tangent line back to the 20%
chord would meet the ellipse VERY near its forward tip then. Interesting.
On Fri, Jun 21, 2013 at 2:10 PM, Samantha Roberts <
> A 30 deg ellipse is a circle viewed at 30 deg from the plane in which it[Non-text portions of this message have been removed]
> lies (if viewed at 90 deg, it appears as a full circle). This makes a 30
> deg ellipse twice as long as it is wide. So if your plate thickness is 1",
> the ellipse you need to draw is 1" long and 1/2" wide (50% of plate
> Now draw a smooth curve that lies tangent to the ellipse and reaches full
> thickness at 20% chord. Since John does not specify either this curve or
> the one from 60% chord to the T.E., I assume he means that those shapes are
> not critical. On the general principle of not trying to make water flow
> around sharp corners, I would make those two curves come smoothly into the
> flat section from 20% to 60% chord, but I am not sure how important that
> might be.
[Non-text portions of this message have been removed]