[Public-List] Mainsail Foot Shelf

[Gordon Laco]

Yes, the size and shapes of all the sails are closely defined, as well as construction.  Full battens and loose footed configurations are illegal in the class.

Gordon Laco
426 Surprise






> On Apr 13, 2021, at 11:51 AM, americo silva via Public-List <public-list at lists.alberg30.org> wrote:
> 
> 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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