PY Lag Time

Originally posted by transient ....Mmm, unmeasured sail area.

Now be fair, its not really unmeasured sail area, is just a stupid rule... Best to think of the measured "sail area" as being a number that the measurement system spits out in order to compare sails rather than an actual measure of how big the rags are. As Rupert says its quite irrelevant for PY handicapping.

Edited by JimC - 14 Mar 14 at 6:33pm

Merlin Rocket Class Rules
August 2011
(d)

9
SAIL AREA
(a)
All measurements, provided they are not outside the allowed max
ima
or minima, shall be taken to the nearest 1mm and areas shall be
calculated to the nearest 0.01 of a square metre.
(b)
TOTAL SAIL AREA in square metres is:
13.80 – (0.60 x (L + 0.680))

but shall not exceed 10.20 square metres.
(c)
MAINSAIL AREA. T
he mainsail in square metres shall be measured
as:

(L x F) / 2
where L and F are luff and foot measurements in metres as follows:
(i)
The luff, L, shall be measured along the mast from the upper
edge of the lower band to the lower edge of the upper band
.
(ii)
The foot, F, shall be measured along the top of the boom in its
normal position from the fore edge of its measurement band to
the aft side of the mast and the dimensions, F, shall be marked
legibly and indelibly in metric units of not less than 20mm
in
height on the boom adjacent to its measurement band.
The measured MAINSAIL AREA shall not exceed 80% of the total sail
area.


MAXIMUM FORESAIL AREA is the total sail area less the mainsail
area measured in 9(c) and shall be marked legibly and ind
elibly in
metric units of not less than 20mm in height on the boom adjacent to
the band.
(e)
ACTUAL FORESAIL AREA shall not exceed the maximum foresail
area.
The actual area in square metres shall be calculated as:
(L x P) / 2
Where L is the luff and
P the perpendicular in metres (see rule 12).
(f)
Sails shall be measured in a dry state, laid on a flat surface, with just
sufficient tension to remove wrinkles across the line of measurement
being taken.

This is what I get *IF* I understand the rule correctly:
- the measured sail area is in green
- the red lines are the measurements which control the sail shape
- the blue is an approximation of the actual sail shape, controlled by the measurements and the rules on corner reinforcement. The actual permissable length of the red lines is controlled by a formula which relates one to another and basically means you get to choose between a smaller, thinner taller sail and a shorter, fatter and slightly larger one. Its a very 1920s way of measuring sails, but if they moved to a modern method of measurement that measured real area without the complicated formulae and strange restrictions then they'd all get to throw all their sails away and their rigs would look quite different.

There's nothing really wrong about it: the sails are compared equably and consistently and the measurements are reasonably quick and easy to do. You just have to be aware that the sail area total is a fiction that has little to do with the real area.

[and, added later] I hadn't even noticed sugmeister had left off all the important stuff. I worked the drawing out last night from reading the rules on the RYA website. As Craiggo says, measuring crosss widths is common enough in one designs, the MR system just puts a formula on top of it which spits out an area.

Edited by JimC - 15 Mar 14 at 8:40am

Originally posted by JimC [and, added later] I hadn't even noticed sugmeister had left off all the important stuff. I worked the drawing out last night from reading the rules on the RYA website. As Craiggo says, measuring crosss widths is common enough in one designs, the MR system just puts a formula on top of it which spits out an area.

All I did was cut n paste from the RYA PDF...

http://www.rya.org.uk/SiteCollectionDocuments/technical/Web%20Documents/Class%20Rules/MerlinRocket%20CR%20090811.pdf

It's just a fancy way of saying the luff should be 5.32m basically.