Subj : Re: Skeg Design
To   : rec.sport.rowing
From : carl
Date : Fri Sep 10 2021 12:41 pm

On 10/09/2021 09:44, Andy McKenzie wrote:
> On Friday, 10 September 2021 at 05:18:50 UTC+1, Matt C wrote:
>> Like Carl, I don't know of a standard fin shape. Perhaps we could revert to
the well documented standard aerofoils? Here's a nice site on the basic NACA 4
digit profile:
http://airfoiltools.com/airfoil/naca4digit?MNaca4DigitForm%5Bcamber%5D=0&MNaca4
DigitForm%5Bposition%5D=40&MNaca4DigitForm%5Bthick%5D=5&MNaca4DigitForm%5BnumPo
ints%5D=81&MNaca4DigitForm%5BcosSpace%5D=0&MNaca4DigitForm%5BcosSpace%5D=1&MNac
a4DigitForm%5BcloseTe%5D=0&yt0=Plot
>>
>> Just as an opinion, I think something like the NACA 0006 would be a good
start.
> 
> Scary to enter a conversation on fin design with Carl in the room, but
aerofoil sections might not be the best option for a fin. You want a fin to
resist turning forces up to a point to keep you straight, and then stall, so
the boat can be slewed easily when you want to turn. In general the more the
fin resembles an aerofoil the more angle will be needed to get that stall.  I
also  think aspect ratio is a design criteria where you are making engineering
tradeoffs. From a hydrodynamic perspective a long narrow fin (think glider
wing) should give less drag than a squat fin of the same area. But equally the
risk of collecting floating debris and of damage from impacting the river
bottom or solid objects on land goes up with aspect area, as does the stresses
at the fins base - so we compromise. The extreme end of this compromise is the
'restricted' or touring boat designs which dispense with a fin and have a full
length keel.
> 

Agreed in every particular, Andy.

Cheers -
Carl

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