[Public-List] Mainsail Foot Shelf

[americo silva]

is there a rule that states how big a main sail can be


On Sat, Apr 10, 2021 at 2:16 PM Mike Nikolich via Public-List <
public-list at lists.alberg30.org> wrote:

>
>
> Jonathan,
>
> I held off on writing this sooner as I thought others on this list had
> previously expressed detailed views on a shelf foot and would speak up
> again.  Maybe it wasn't here but on the Facebook page (and I'm rarely on
> Facebook).
>
> I would let your sailmaker determine the dimensions and shape of the
> shelf.
>
> There is nothing in the class rules that constrains it other than that the
> sail must be attached to the boom for the full length of the foot and that
> "no device such as zippers may be placed along the luff, the foot, and/or
> the body of the sail for the purpose of adjusting the draft or the set of
> the sail" (i.e. you can have a shelf foot but not one that you can zip
> closed).
>
> Without a shelf foot, the lower panels of an attached-foot mainsail are
> cut flatter and flatter to provide a fair transition from the airfoil shape
> of the sail to the straight line that is the foot along the boom.
> For a loose-footed main the design airfoil shape is maintained all the way
> down to the foot for better performance.  A sail with a shelf foot is
> essentially a loose-footed main with a lightweight dacron "shelf" attached
> to connect between the bottom main panel and the foot rope that still has
> to be a straight line in the boom slot. The bottom line then is that the
> size and shape of the shelf is driven by the shape your sailmaker has
> designed into the bottom of the airfoil portion of the sail.
>
> (There's a really bad joke somewhere in that last paragraph but I don't
> know if I can find it....)
>
> I know that my mainsail has a shelf foot but I don't know it's dimensions.
> I can measure it but it will be sized based on the overall shape of the
> bottom portion of my main. If considering a shelf for a new sail I would
> let its dimensions be driven by your sailmaker's overall design.
>
> Cheers!
> Mike
>
> Mike Nikolich
> S/V Skybird
> Alberg 30 #550
> mike.nikolich550 at gmail.com
>
>
> On Mar 16, 2021, at 9:40 PM, Jonathan Bresler via Public-List <
> public-list at lists.alberg30.org> wrote:
>
> Dear Albergers,
>
> By class rules our mainsails must be connected to the mast and the boom.
> Loose footed sails are disallowed.   One the methods for dealing with the
> resulting shape
> is to remove the bolt rope and  sew a half lens (half ellipse) to the foot
> of the sail.
> The curved side of the lens is sewn to the foot of the sail and the bolt
> rope is moved
> to the flat side of the lens.  This way when the outhaul is eased the
> bottom portion of
> the sail takes on a airfoil shape.  Then the outhaul is tight the bottom
> portion of the
> sail is much flatter and less powerful (better for heavy air).
>
> How deep should the shelf be?  Wondering who has a foot shelf and what the
> depth
> of the shelf might be at 25%, 50%, and 75% aft along the foot.
>
> Jonathan
>
> --
> Jonathan M Bresler
> S/V Constance Alberg 30 #262
> Annapolis/Eastport MD
>
>
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