I am trying to calculate a theoretical PHRF base rating for my 1983 O'Day 19 sailboat using the following Schell Regression Formula:
R' = 610-8.36*(SA/Disp^.333)+0.0000511*(SA^2)-55*(P/(J+E)) -30.8*(LWL^.5)-602*(DR^2/SA)
where SA= .5*(I*J)+.5*(P*E), and DR is the draft depth
One of the measurements needed for the calculation is for the draft depth (DR) of the keel/centerboard.
Here lies the rub: How to calculate the DR of a keel/centerboard sailboat with 9' long stub keel having an average depth of 4.5" , and a 4.3' centerboard with a 15" width along the center line of the boat.
My first feeble attempt at a DR calculation produced:
DR = 0.5'
by taking the average of the addition of the average stub keel depth x stub keel length
and centerboard length - 4.5" average stub keel depth x centerboard width, then dividing by the average stub keel length.
Is there a more accurate method for determining DR for a stub keel/centerboard sailboat?
P.S. My O'Day 19 is a short mast with rig parameters of :
I 20.68
J 7.00
P 21.50
E 8.30
The first iteration of the O'Day 19 tall mast (built from 1979 to 1980 1/2) has a Portsmouth rating (D-PN) of 95.2, which would give a theoretical PHRF base rate of 241 using the following conversion formula: PHRF = 6 * D-PN - 330.
The scuttlebutt is that no O'Day 19 tall mast has been able to sail to its 95.2 D-PN rating, causing many to speculate that DR used in the Schell Regression Formula to calculate a theoretical PHRF rate matching that extrapolated from the D-PN rate (DR = 2.5', how its calculated is a mystery) is not accurate.
Its rig parameters are:
I 22.00
J 7.00
P 24.50
E 8.30
Both boats share the same 19' LOA, 16.67' LWL, 1350 lb. displacement, 7.75' beam, and 4.3' draft maximum and 1.0' draft minimum.
R' = 610-8.36*(SA/Disp^.333)+0.0000511*(SA^2)-55*(P/(J+E)) -30.8*(LWL^.5)-602*(DR^2/SA)
where SA= .5*(I*J)+.5*(P*E), and DR is the draft depth
One of the measurements needed for the calculation is for the draft depth (DR) of the keel/centerboard.
Here lies the rub: How to calculate the DR of a keel/centerboard sailboat with 9' long stub keel having an average depth of 4.5" , and a 4.3' centerboard with a 15" width along the center line of the boat.
My first feeble attempt at a DR calculation produced:
DR = 0.5'
by taking the average of the addition of the average stub keel depth x stub keel length
and centerboard length - 4.5" average stub keel depth x centerboard width, then dividing by the average stub keel length.
Is there a more accurate method for determining DR for a stub keel/centerboard sailboat?
P.S. My O'Day 19 is a short mast with rig parameters of :
I 20.68
J 7.00
P 21.50
E 8.30
The first iteration of the O'Day 19 tall mast (built from 1979 to 1980 1/2) has a Portsmouth rating (D-PN) of 95.2, which would give a theoretical PHRF base rate of 241 using the following conversion formula: PHRF = 6 * D-PN - 330.
The scuttlebutt is that no O'Day 19 tall mast has been able to sail to its 95.2 D-PN rating, causing many to speculate that DR used in the Schell Regression Formula to calculate a theoretical PHRF rate matching that extrapolated from the D-PN rate (DR = 2.5', how its calculated is a mystery) is not accurate.
Its rig parameters are:
I 22.00
J 7.00
P 24.50
E 8.30
Both boats share the same 19' LOA, 16.67' LWL, 1350 lb. displacement, 7.75' beam, and 4.3' draft maximum and 1.0' draft minimum.
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