[Rhodes22-list] Mast Bending & PHRF Rating
Roger Pihlaja
rhodes22-list@rhodes22.org
Sat, 24 Aug 2002 13:27:58 -0400
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Ed,
No way! It's attached to the boom all along the foot with a bolt rope =
running in slot on the boom. That's the way the standard mainsail is as =
well.
Roger Pihlaja
S/V Dynamic Equilibrium
----- Original Message -----=20
From: Ed Kroposki=20
To: rhodes22-list@rhodes22.org=20
Sent: Saturday, August 24, 2002 10:04 AM
Subject: Re: [Rhodes22-list] Mast Bending & PHRF Rating
Roger:
Those of us using the IMF are loose footed. Is your standard =
main loose footed?
Ed K
----- Original Message -----=20
From: Roger Pihlaja=20
To: rhodes22-list@rhodes22.org=20
Sent: Saturday, August 24, 2002 7:23 AM
Subject: [Rhodes22-list] Mast Bending & PHRF Rating
Alex,
Yes, the effect of bending the mast & having a fully battened =
mainsail, which is cut to respond to mast bend, is in those PHRF ratings =
somewhere. But, It's difficult to separate out the effects of =
individual changes. I really couldn't do back-to-back comparisons =
between my present mainsail & my original partially battened standard =
mainsail, because the original was pretty much worn out when I bought =
the new mainsail. Comparing an old worn out cruising mainsail with a =
new racing mainsail isn't a very useful exercise. But, the =
seat-of-the-pants feeling between the two is like night & day.
I had the backstay adjuster & standing rigging setup to be able to =
reproducibly bend the mast while I was still using the original =
mainsail. Bending the mast had a noticible flattening effect on the =
original mainsail shape. However, the sail cloth was so blown out that =
the point of maximum draft was too far aft no matter how much luff &/or =
foot tension I cranked in. When the wind piped up, the point of maximum =
draft moved even farther aft, so the whole exercise became rather =
futile. I don't know if a crispy new standard mainsail would behave =
better. I suspect it requires full battens to really get control of the =
mainsail shape.
If you take a mainsail, which has been designed to respond to mast =
bend, & lay it out on the ground, you will see the luff is not cut =
straight. Instead of being straight, the luff bows outward in the =
middle. When this curved luff sail is flown from a straight mast, this =
"extra" material from the curve allows the airfoil shape to get deeper =
just aft of the mast. The sailmakers refer to this sail shape as having =
"deep draft" & it is what you want for light air performance. Now, when =
the mast is bent, the "extra" material from the curved luff fills in the =
bend. This results in the airfoil shape getting flatter, which =
desireable for heavy air performance. My rig tuning procedure sets up =
the standing rigging to enable the backstay adjuster to simultaineously =
take the sag out of the forestay & flatten the mainsail shape as the =
wind speed picks up. Thus, the backstay adjuster becomes a very =
important sail shaping control, almost like the flaps on an airplane. =20
If someone has a standard mainsail, which is in good shape, & they =
are willing to loan it to me for a couple of weeks, I would be willing =
to do some back-to-back testing & report back to the list.
Remember, none of this discussion has any relevance for those of you =
with IMF mainsails. Don't try to bend your IMF mast or you may damage =
your IMF mainsail &/or the furling mechanism. =20
I used my old mainsail for a paint tarp once & then threw it away. =
FYI, old sails don't even make good paint tarps. Man are they ever =
slippery, especially if you ever get a fold of cloth where there is =
Dacron on Dacron!
Alex, thanks for putting this whole rig tuning discussion into some =
kind of perspective.
Roger Pihlaja
S/V Dynamic Equilibrium
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<DIV><FONT face=3DArial size=3D2>Ed,</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT> </DIV>
<DIV><FONT face=3DArial size=3D2>No way! It's attached to the boom =
all along=20
the foot with a bolt rope running in slot on the boom. That's the =
way the=20
standard mainsail is as well.</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT> </DIV>
<DIV><FONT face=3DArial size=3D2>Roger Pihlaja</FONT></DIV>
<DIV><FONT face=3DArial size=3D2>S/V Dynamic Equilibrium</FONT></DIV>
<BLOCKQUOTE dir=3Dltr=20
style=3D"PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; =
BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px">
<DIV style=3D"FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV=20
style=3D"BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: =
black"><B>From:</B>=20
<A title=3Dkroposki@innova.net href=3D"mailto:kroposki@innova.net">Ed =
Kroposki</A>=20
</DIV>
<DIV style=3D"FONT: 10pt arial"><B>To:</B> <A =
title=3Drhodes22-list@rhodes22.org=20
=
href=3D"mailto:rhodes22-list@rhodes22.org">rhodes22-list@rhodes22.org</A>=
</DIV>
<DIV style=3D"FONT: 10pt arial"><B>Sent:</B> Saturday, August 24, 2002 =
10:04=20
AM</DIV>
<DIV style=3D"FONT: 10pt arial"><B>Subject:</B> Re: [Rhodes22-list] =
Mast Bending=20
& PHRF Rating</DIV>
<DIV><BR></DIV>
<DIV><FONT face=3D"Courier New">Roger:</FONT></DIV>
<DIV><FONT face=3D"Courier =
New"> =20
Those of us using the IMF are loose footed. Is your standard main =
loose=20
footed?</FONT></DIV>
<DIV><FONT=20
face=3D"Courier =
New"> &n=
bsp; &nb=
sp; =20
Ed K</FONT></DIV>
<BLOCKQUOTE dir=3Dltr=20
style=3D"PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; =
BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px">
<DIV style=3D"FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV=20
style=3D"BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: =
black"><B>From:</B>=20
<A title=3Dcen09402@centurytel.net =
href=3D"mailto:cen09402@centurytel.net">Roger=20
Pihlaja</A> </DIV>
<DIV style=3D"FONT: 10pt arial"><B>To:</B> <A =
title=3Drhodes22-list@rhodes22.org=20
=
href=3D"mailto:rhodes22-list@rhodes22.org">rhodes22-list@rhodes22.org</A>=
=20
</DIV>
<DIV style=3D"FONT: 10pt arial"><B>Sent:</B> Saturday, August 24, =
2002 7:23=20
AM</DIV>
<DIV style=3D"FONT: 10pt arial"><B>Subject:</B> [Rhodes22-list] Mast =
Bending=20
& PHRF Rating</DIV>
<DIV><BR></DIV>
<DIV><FONT face=3DArial size=3D2>Alex,</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT> </DIV>
<DIV><FONT face=3DArial size=3D2>Yes, the effect of bending the mast =
&=20
having a fully battened mainsail, which is cut to respond to mast =
bend, is=20
in those PHRF ratings somewhere. But, It's difficult to =
separate out=20
the effects of individual changes. I really couldn't do =
back-to-back=20
comparisons between my present mainsail & my=20
original partially battened standard mainsail, =
because the=20
original was pretty much worn out when I bought the new =
mainsail. =20
Comparing an old worn out cruising mainsail with a new racing =
mainsail isn't=20
a very useful exercise. But, the seat-of-the-pants feeling =
between the=20
two is like night & day.</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT> </DIV>
<DIV><FONT face=3DArial size=3D2>I had the backstay adjuster & =
standing=20
rigging setup to be able to reproducibly bend the mast while =
I was=20
still using the original mainsail. Bending the mast had a =
noticible=20
flattening effect on the original mainsail shape. However, the =
sail=20
cloth was so blown out that the point of maximum draft was too =
far aft=20
no matter how much luff &/or foot tension I cranked =
in. When=20
the wind piped up, the point of maximum draft moved =
even farther aft,=20
so the whole exercise became rather futile. I don't know =
if=20
a crispy new standard mainsail would behave better. I =
suspect=20
it requires full battens to really get control of the mainsail=20
shape.</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT> </DIV>
<DIV><FONT face=3DArial size=3D2>If you take a mainsail, which has =
been designed=20
to respond to mast bend, & lay it out on the ground, you will =
see the=20
luff is not cut straight. Instead of being straight, the =
luff=20
bows outward in the middle. When this curved luff sail is =
flown from a=20
straight mast, this "extra" material from the curve allows the =
airfoil shape=20
to get deeper just aft of the mast. The sailmakers refer to =
this sail=20
shape as having "deep draft" & it is what you want for light air =
performance. Now, when the mast is bent, the "extra" material =
from the=20
curved luff fills in the bend. This results in the airfoil =
shape=20
getting flatter, which desireable for heavy air performance. =
My rig=20
tuning procedure sets up the standing rigging to enable the backstay =
adjuster to simultaineously take the sag out of =
the forestay &=20
flatten the mainsail shape as the wind speed picks up. Thus, =
the=20
backstay adjuster becomes a very important sail shaping control, =
almost=20
like the flaps on an airplane. </FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT> </DIV>
<DIV><FONT face=3DArial size=3D2>If someone has a standard mainsail, =
which is in=20
good shape, & they are willing to loan it to me for a couple of =
weeks, I=20
would be willing to do some back-to-back testing & report =
back to=20
the list.</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT> </DIV>
<DIV><FONT face=3DArial size=3D2>Remember, none of this =
discussion has any=20
relevance for those of you with IMF mainsails. Don't try to =
bend your=20
IMF mast or you may damage your IMF mainsail &/or the furling=20
mechanism. </FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT> </DIV>
<DIV><FONT face=3DArial size=3D2>I used my old mainsail for a =
paint tarp=20
once & then threw it away. FYI, old sails don't even make =
good=20
paint tarps. Man are they ever slippery, especially if you =
ever get a=20
fold of cloth where there is Dacron on Dacron!</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT> </DIV>
<DIV><FONT face=3DArial size=3D2>Alex, thanks for putting this whole =
rig tuning=20
discussion into some kind of perspective.</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT> </DIV>
<DIV><FONT face=3DArial size=3D2>Roger Pihlaja</FONT></DIV>
<DIV><FONT face=3DArial size=3D2>S/V Dynamic =
Equilibrium</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT> </DIV>
<DIV><FONT face=3DArial size=3D2></FONT> </DIV>
<DIV><FONT face=3DArial size=3D2></FONT> </DIV>
<DIV><FONT face=3DArial=20
size=3D2></FONT> </DIV></BLOCKQUOTE></BLOCKQUOTE></BODY></HTML>
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