[Alberg30] backstay adjusters
Don Campbell
dk.campbell at sympatico.ca
Wed Oct 8 06:20:37 PDT 2003
The reason the backstay adjusters are expensive is because of the loads they
carry. The moment for the force is the distance from the base of the mast to the
point of adjustment , - the back stay chainplate, which is over 19 feet. You will
not have a smaller bill if you use blocks to do the job because of the load
bearing you will need on them. Most of the examples in the Harken catalogue are
at 12 : 1. Thus, if a person can pull a maximum of 75 pounds, then the pull on
the stay is 900 lbs and the downward load on the mast ( or upward load on the bow
and stern) is over 17,500 pounds (900 x 19.5). There was an article in Sailing
World when the Aussie America's Cup boat split in two, and, as I recall, the load
on the mast was over 500,000 pounds. Whatever the pricefor an adjuster, it is far
cheaper than having a mast crash to the water and having to scramble to save it.
Split backstays are not allowed for the one design aspect of racing, and I
suggest you consider at least a 1/2 " pin ( the same as is already on the
backstay) for any backstay adjuster. With blocks, you will need to have the main
system that will support a working load of 18, 000 pounds. That gets to be
expensive line too! There is no way to stop spending $ if you want a safe boat
and all the toys.
Don
Jeanne wrote:
> Stephen,
>
> Sorry about not being clear. The question relates to what type of back
> stay tensioner works w/ an A30. The turnbuckles with wheels are
> expensive ($300+) and I do not want to split the back stay to use one of
> those triangular pull down adjusters. Hydraulic adjusters cost more
> than a new set of sails. Does anyone use a block and tackle (similar to
> a strong boom vang) to twang the back stay?
>
> Roger Kingsland
>
> sousa, stephen (ENG) wrote:
>
> >Roger,
> >
> >I follow your entire string with the exception of the last sentence. What is
> >the question concerning back stay adjustment hardware?
> >
> >Stephen
> >#114
> >
> >-----Original Message-----
> >From: Roger L. Kingsland [mailto:rkingsland101 at ksba.com]
> >Sent: Tuesday, October 07, 2003 3:41 PM
> >To: Alberg30
> >Subject: [Alberg30] Twin Headstays
> >
> >
> >Albergers,
> >
> >Several "Pagers" have responded to inquiries about double head stays saying
> >they are problematic because they necessitate doubling the head stay load.
> >I diligently went about designing a system to make the head stays
> >independently adjustable which I thought was simple and elegant but probably
> >would be expensive.
> >
> >I made inquiries to both Mike Kaufman (the Annapolis N.A. that surveyed my
> >boat) and the head rigger at West Marine. Both indicated that, if the
> >inactive (at rest) load on each stay is equal, the additional wind load
> >placed on the active stay while sailing is sufficient to slack the inactive
> >stay to the point where it essentially has no load on it. This is true
> >regardless wind speed. The point seems to be that the length differential
> >between full load and minimal load is so small that any additional load on
> >the active stay increases its length sufficiently to cancel the load on the
> >inactive one.
> >
> >Of course, the problem is, unless you want to rename your boat "Banana," it
> >is not practical to set both stays (at rest) to the tension appropriate for
> >a single stay loaded for heavy air conditions. So, the issue boils down to
> >being able to increase active head tension as the wind increases. The
> >solution suggested to me by the West guy seemed beautifully simple and
> >inexpensive, adjust the back stay tension. This will not only increase head
> >stay tension but will create mast bend that will flatten the main as well.
> >
> >I recall some past missives on back stay adjustment, particularly mast
> >pumping. My brief survey of past postings uncovered info on stay tension
> >but nothing on mast pumping. So, the three obvious questions are. Does the
> >above explanation make sense or am I missing something? Are there any
> >problems associated with increasing head stay tension by adjusting the back
> >stay? Lastly, what back stay adjustment hardware works on an A30.
> >
> >Thanks,
> >
> >Roger
> >
> >
> >Roger Kingsland
> >Chief Financial Officer (AKA, check writer)
> >Mahina Manu, A30 #148
> >N40° 29.288'
> >W79° 54.228'
> >
> >Author's Disclaimer; This email was produced exclusively by the sender and,
> >in the interest of expediency, without the benefit of editing by others.
> >The sender, thank goodness, is a much better architect/sailor than
> >speller/editor and, frankly, constantly laments an obvious flaw in "spell
> >check," it does not know what the author is thinking. Please accept the
> >sender's sincere apologies for any "typos" that may appear in this document.
> >If present, they are certainly unintended and hopefully do not cloud the
> >message, or spawn any unnecessary lawsuits.
> >+---------------------------------------------------------------+
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