[Alberg30] tunning, shroud tension
Gord Laco
gord at transatmarine.com
Mon Jan 14 03:54:24 PST 2002
Hi,
As usual, I have a more sinister opinion as to why successful A30's have slackish aft lowers. Mike is right, fwd pre bend is good, and to achieve this we must tighten to fwd lowers and ease tension on the after ones. But if the aft lowers have to be slack to achieve this the mast will "pump" in and out of column when the boat is pitching On the A30's I've worked on including my #426 the lowers are too long. (or stretched) Consequently it has been tough to get fwd pre bend on the mast with any tension at all on the after lowers. I can't believe they have stretched - I do suspect that they were often made a bit too long. To add to the seriousness of this - my late uncle Con Costas was the mastmaker who supplied much rigging to Whitby Boatworks during the 60's and early 70's. Sorry Unc!
On my list of things to do is to make new lowers about 1.5" shorter. That way I can tune in the right minute curve and hold it there with tight lowers all around.
Gord
#426 Surprise
----- Original Message -----
From: Mike Lehman
To: public-list at alberg30.org
Sent: Saturday, January 12, 2002 11:29 AM
Subject: Re: [Alberg30] tunning, shroud tension
Tightening the forward lowers puts a little pre-bend in the mast helping to flatten the main and reduces some of the weather helm. The aft lowers really aren't contributing and having them loose allows the mast to bend forward sligghtly as the wind increases. They are acting essentially as preventers to avoid too much forward bend in the middle. What you want to avoid is having a reverse bend because when the mast comes out of column forward, that is when bad things happen.
Mike Lehman
"Gilleleje" #505
(410) 544-9067
----Original Message Follows----
From: Brian and Elaine Timmins
Reply-To: public-list at alberg30.org
To: public-list at alberg30.org
Subject: Re: [Alberg30] tunning, shroud tension
Date: Fri, 11 Jan 2002 23:07:44 -0500
The only reason I can imagine to have the after lowers loose would be that
when the mast does flex, it will go forward in the mid section, which will
have the effect of flattening the main sail some. More wind, more flex,
flatter sail.
Maybe some more experienced Albergers have a different reason?
Brian #497
----- Original Message -----
From: "Dave Terrell"
To:
Sent: Friday, January 11, 2002 1:41 PM
Subject: Re: [Alberg30] tunning, shroud tension
> Thanks for the info. When I looked at my Loos I came to the same
conclusion. If a person went for the 10% figure the 1/4 inch stays/shourds
would be set at about 850 pounds, the 3/6 shourds at about 500 pounds, and
the forestay/backstay as you indicate.
>
> What I do not understand is why there seems to be a tendency(based on the
figures provided) to under tension the Alberg 30 rig (by Loos standards).
What really puzzles me is the tendency to have little to no tension on the
aft lower shroud.
>
> Right now I would have to assume that tensioning practice is based upon
experience, but I really would like to know why it works if that really is
the case. Any insight on this would be appreciated.
>
> >>> timmins at optonline.net 01/09/02 11:38PM >>>
> Sorry about taking so long to respond. It took a while to locate the info.
> From my Loos Instructions, 1/4" wire breaking strength is 8200 lbs and
3/16" is 4700 lbs. Additionally, Loos recommends 1/4" forestay set to 1300
lbs, 1/4" shrouds set to 850 lbs, and 3/16 shrouds set to 500 lbs.
> The relationship of forestay / backstay is something I can't comment on
directly since I've got roller furling on the forestay and therefore can't
easily measure the tension there. Loos makes the statement, "Since the
backstay makes a greater angle to the mast, the backstay tension will be
lower than the forestay tension."
> ----- Original Message -----
> From: Dave Terrell
> To: public-list at alberg30.org
> Sent: Thursday, January 03, 2002 2:51 PM
> Subject: Re: [Alberg30] tunning, shroud tension
>
>
> How do these numbers fit with the general guidelne that shrouds should
be tensioned between 10 and 12% of the breaking strength the wire? This is
what the instructions for my Loos tension guide said and that has been my
guideline in the past. That worked on my old boat, a CAL 27 T-2. If the
application of the rule to my "new" Alberg 30 is different, I would like to
know. I appreciate having this source of informatioin avaliable.
>
> >>> timmins at optonline.net 12/28/01 06:37PM >>>
> These are the conclusions I drew from the list when it was published in
May
>
> Average tensions of the whole list:
> Forestay/Backstay............733
> Backstay only...................726
> Forestay only....................735.6
> Uppers.............................685
> Fwd Lowers.....................495
> Aft Lowers........................0 (loose)
>
> Race Boats Only Averages:
> Forestay only....................811
> No backstay only
> Uppers..............................862
> Fwd Lowers......................679
>
> Based on these numbers and info taken from Brion Toss's video on rig
tuning
> (and his web site), This is how I set up my mast.
> Starting with the mast vertical, tighten the forestay to snug/tight but
not
> to pull the mast forward of vertical.
> Tighten the backstay to 625
> Tighten uppers to 750
> Tighten Fwd lowers to 620
> Tighten Aft lowers to slack/100
>
> After sailing a bit, I reset the backstay to 700
> These numbers worked very well for me and the boat was nicely balanced.
>
> Don't ask me to explain my logic anymore (this was done in June). I just
> happened to come across my note sheet from doing the job.
> All tensions were done with a Loos Model B, part # 90 gauge
>
> Regards,
> Brian
> #497
> ----- Original Message -----
> From: "George Dinwiddie"
> To:
> Sent: Thursday, December 27, 2001 11:41 AM
> Subject: Re: [Alberg30] tunning, shroud tension
> snip
> > If anyone can draw some general conclusions from this list,
> > I think we'd all like to hear it.
> >
> snip
>
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