Randy:
The drawing for my boat does not show perfectly plumb – that was the point.
The drawing showed a slight rake. It would be easier in a drawing to draw a
mast perpendicular to the side view, but the drawing for the 42 shows a slight
rake. We surmised that C&C must have had a reason for expending the
extraordinary effort of showing a slight rake on a drawing. By doing a little
math, we were able to figure out from the drawing what that rake is, which I
duplicated in the field. I’m sure it’s not perfect, but I think we got close.
The reason it was so important to get it right with the Spartite plug is
that once you make one, the mast is pretty much staying there. With wooden
blocks at the partners, you can move things around to make adjustments,
including adjusting the rake for various conditions if you want. With a
Spartite plug, once it’s done it’s done. I also made Spartite chocks in the
mast step box, so nothing moves from the deck down. When I’m going through
8-10 footers on Lake Erie, I like it that way.
It’s Matt by the way. Hope your project is going well.
MLW
From: RANDY via CnC-List
Sent: Saturday, March 25, 2017 1:24 PM
To: cnc-list
Cc: RANDY
Subject: Re: Stus-List Mast Step Pitch & Helm Balance
Thank you all for the excellent responses.
Matthew, figuring out what C&C's intentions were, for aft mast step elevation,
is what I'm trying to do. I assume they intended for the mast to perfectly
plumb when the boat is sitting on her designed waterline in perfectly calm
water and calm air. Then rig tuners would set the rake from there. Of course,
those aren't the conditions I'm working in, so it's all guesswork (levels are
useless with the boat on the trailer).
Michael, interesting point about heel at the foot of the mast. I'll check that
out today. I assumed the foot of my mast is flat, and makes contact all the
way around the mast box. I agree the side-to-side level is critical - from rig
tuning last year, I believe Grenadine's is off (the aft end of the mast block
lists to port, requiring more halyard tension to touch the starboard rail than
the port rail, and I couldn't correct that via upper shroud tension without
bowing the mast). That should get corrected by the new aft support, assuming I
cut it and install it correctly.
Rick thanks for the reminder about the owner's manual rig tuning instructions
cautioning against forward rake. I follow those instructions to the letter for
rig tuning, and you're exactly right, I set 8" of rake on Grenadine. Regarding
my 30-kt experience, it was on June 22nd last year - see archived wind graph at
http://wx.iwindsurf.com/map#39.548,-105.08,14,1,!11170,7. We had
light-to-decent wind for our race at 6:30, so I was flying all that sail. Then
after the race the wind really piped up and I wanted to learn how Grenadine
would behave under that press of canvas. At the moment of that 30-kt (true)
gust just after 8:00, I was on starboard tack close reach, trimmed for that
point of sail, going 7.6 knots according to GPS (with fixed 2-blade prop even),
with five people on the rail, and my genoa tore before I got a rail in the
water. That's how stiff a 30-1 is. Of course I had a hell of a lot of weather
helm in those conditions, and I was within about an inch or another degree of
heel of burying the rail. I've yet to learn what it takes to bury a rail on a
30-1. If Grenadine had had a folding prop at the time, I believe she could
have touched 8 knots. Will find out this year :)
Given all these great responses, I think I'll split the difference and cut the
aft support to the elevation indicated by the dashed line in
https://drive.google.com/open?id=0B-NqAxQ6JxFTU3hRNmZoMUU1MFk. Thanks again
everyone.
Cheers,
Randy
--------------------------------------------------------------------------------
From: "Rick Brass via CnC-List" <cnc-list@cnc-list.com>
To: "cnc-list" <cnc-list@cnc-list.com>
Cc: "Rick Brass" <rickbr...@earthlink.net>
Sent: Saturday, March 25, 2017 9:27:38 AM
Subject: Re: Stus-List Mast Step Pitch & Helm Balance
Randy;
I could have sworn that I have seen a table that lists the initial mast rake
for various C&C models built in the 70’s, but I’m not able to find it.
The rig tuning information on the Photo Album, and the information in the
owner’s manuals that came with my 25 mk1 and my 38 mk2 all show the same
information about setting up the mast rake:
On a 24, the target for initial rake is 6” measured at the gooseneck. For the
38, the target is 10”. Looking up the I dimensions and doing a little math says
the initial target for your 30-1 would be 8” of rake. But the instructions
indicate (and this could have changed over time) that some sailmakers prefer no
rake when they make the sails, and caution against having any forward rake in
the mast. The process recommended in the manuals is to set the mast up (close
to vertical is implied) and then adjust the forestay and backstay to achieve
the target rake. Then put in the mast wedges, go sailing, and do any
appropriate tweaking.
Your post indicated weather helm in 30 knots (I’m presuming apparent) with full
main and #2 genoa. I’m not surprised. With wind that strong and a full main I
would expect the boat to be standing on its ear and rounding up unmercifully ,
or to see that the main was trimmed almost fully out and basically flogging. I
find that both of my boats are fastest and most comfortable with a max of about
18-20 degrees of heel, YMMV, so I tend to reduce sail in the following pattern:
About 15 apparent – reduce genoa (starts from 155 on the 25 and 135 on the 38)
About 20 – 1st reef in main
About 24 – reduce genoa again (which brings me to a 110 Lapper on the 25 and
about 100% on the 38)
Depending on conditions but around 26-27 – 2nd reef in main
Remember that the force generated on the sails is proportional to the square of
wind speed, so wind at 20 apparent generate 4 times the force of wind at 10,
and wind at 30 generates 9 times the force at 10. So the boat will go just as
fast with smaller sail up in higher winds.
Anyway, in response to your initial question, my recommendation would be to set
up the mast step so the mast was vertical – or nearly so -for an initial
position and then adjust the rake with fore and aft stays per the C&C
instructions.
Rick Brass
Imzadi C&C 38 mk 2
la Belle Aurore C&C 25 mk1
Washington, NC
From: CnC-List [mailto:cnc-list-boun...@cnc-list.com] On Behalf Of RANDY via
CnC-List
Sent: Saturday, March 25, 2017 3:12 AM
To: cnc-list <cnc-list@cnc-list.com>
Cc: RANDY <randy.staff...@comcast.net>
Subject: Stus-List Mast Step Pitch & Helm Balance
Listers-
Seeking your input here. I'm in the middle of the mast step rebuild project a
la http://cncphotoalbum.com/doityourself/maststep/maststep.htm. Lots of
pictures of the project at
https://drive.google.com/open?id=0B-NqAxQ6JxFTSzRLbFo0NDl6U1E.
I'll be cutting new supports from laminated GPO-3 slabs Saturday night or
Sunday morning. Before installing the new supports, I have to decide on the
elevation of the aft support. Of course I took careful elevation measurements
from the cabin sole before removing the original supports. But the question
is, what was the original shape of the top of the aft support?
I believe the middle of Grenadine's aft support, under the mast step block, was
compressed down from its original elevation due to a combination of weakness in
the support and standing rigging tension (especially backstay). Have a look at
the pictures and you can clearly see what I mean, e.g.
https://drive.google.com/open?id=0B-NqAxQ6JxFTLXZuXzd1T1pkR28. This
compression has the effect of pitching the mast step aft, thereby moving the
masthead aft, thereby increasing weather helm (which I've definitely noticed
under enough wind and sail - it was strong under full main and #2 genoa in 30
kts, not surprisingly).
However I also believe that the original elevation of the aft support may have
been carefully tuned for helm balance, prior to compression below the mast step
block due to weak wood and standing rigging tension.
The reason this elevation question matters so much is because, using
trigonometry, I can calculate the distance by which different elevations of the
aft support will move the masthead forward or aft, which in turn will affect
helm balance. Each quarter inch of aft support elevation difference could move
the masthead about three inches I believe.
The last picture
(https://drive.google.com/open?id=0B-NqAxQ6JxFTU3hRNmZoMUU1MFk) in the Google
Drive folder linked above shows the templates from which I'll cut the new
supports, traced from the original supports removed from Grenadine's bilge. I
hypothesize that the dashed line I drew at the top of the aft support template
may have been the aft support's original elevation.
I'm halfways tempted to split the difference and cut the new aft support to
have that elevation. Of course, I could be full of crap, because I tune the
mast rake using the stays after all, which probably influences helm balance
more than mast step pitch. And of course I can control the sail selection and
sail trim, which probably influence helm balance more than mast step pitch.
However, for a given sail selection close-hauled, with neither the backstay nor
forestay over-tensioned, the mast step pitch would certainly influence the
masthead position and therefore the combined center of effort of the sail plan.
What say ye? Does anyone out there know if the top of the original aft mast
step support on a 30-1 was flat all the way across, or did it come from the
factory with a little elevation drop to tune helm balance? I'll be committing
an assumption about that to a GPO-3 slab with my jigsaw in the next day or two.
Thanks in advance,
Randy Stafford
S/V Grenadine
C&C 30-1 #7
Ken Caryl, CO
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--------------------------------------------------------------------------------
_______________________________________________
This list is supported by the generous donations of our members. If you wish to
make a contribution to offset our costs, please go to:
https://www.paypal.me/stumurray
All Contributions are greatly appreciated!
_______________________________________________
This list is supported by the generous donations of our members. If you wish to
make a contribution to offset our costs, please go to:
https://www.paypal.me/stumurray
All Contributions are greatly appreciated!
