YTC Handicap Spinnaker % Formula Correction application

[Fraz]

Has anyone understood how to apply the YTC Non Spinnaker correction formula please??
i.e 1.75-(DSA/SA) THS IS WHAT IS PUBLISHED BUT IS THERE AN ERROR MAYBE?
Example to test it
Dehler 34 1.76 (101) DSA 103.6SQM (Downwind sail area) SA 55.90 SQM (Upwind sail area)
so you get 1.75 - (103.6/55.90) = -0.1046366 do i then need to add 1 to this number to make 0.895 ??

But 0.895 is wrong i need to get approx 2.59% difference to apply to the YTC rating for 2023 is 925 and white sail is 949 (24 points difference)
So ideally i need to multiply 925 by 1.025 = 949, but i cant get 1.025 from 1.75 - (103.6/55.90)

I have got the 1st part of the formula working well, then i apply any Propeller change from fixed 2 blade and this works fine.
I just do not understand how to calculate the Spinnaker % change and apply it....

Can anyone help please and show me an example based on the above that works out to give 949 from 925 the based value.
Also noted the formula for calculating YTC has changed from 2023 to 2024, but i have that all working fine except the spinnaker correction

 

[alanhanna]

Hi I worked it out as
YTC * 100-PA * 1+(SA/100)
for white sails (YTC/100) * ( 100+PA+2.5)

YTC = base YTC before adding all the allowances
PA = prop allowance
SA = spinnaker Allowance

All the * and /100's that appear in me working out are to convert to % These formula work out as I have checked about 10 different YTC certificates in our fleet. The bit I cant get working is the Keel type. Nothing I try seems to work for that.

 

[st599]

Hi I worked it out as
YTC * 100-PA * 1+(SA/100)
for white sails (YTC/100) * ( 100+PA+2.5)

YTC = base YTC before adding all the allowances
PA = prop allowance
SA = spinnaker Allowance

All the * and /100's that appear in me working out are to convert to % These formula work out as I have checked about 10 different YTC certificates in our fleet. The bit I cant get working is the Keel type. Nothing I try seems to work for that.

I think you just run rand()*4.

Having calculated ours, the only value that worked was 3.98 on a 1 to 4 scale with 4 being a wing keel. (I promise you our cruising caravan of a school boat definitely doesn't have a wing keel)

We even sent in a photo of the keel, didn't make a difference.