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Author Topic: Twin Backstays on a Mark 1.25?  (Read 903 times)

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Patches

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Twin Backstays on a Mark 1.25?
« on: November 30, 2021, 01:57:24 PM »

The factory back stay set up my Mark 1.25 bugs me, and its time to replace some standing rigging too.  I'm constantly bashing into the the split backstay when standing or climbing onto the swim step.  I'm also going to be adding a bimini in the near future, so I would like to plan for that.

I'm aware one solution is to move the location of the "split" higher, which is getting close to having two separate backstays. Most newer boats (I have a C355 in my marina) seem to have twin backstays which allows movement of the deck attachments further outboard on either side.

Has anyone gone to two separate backstays?

Does the original masthead configuration support doing this?

Any opinions on whether this option makes any sense, or is just nutty?

For those who have gone with a higher "split", did you change the location of the turnbuckle(s) to deck level?  The turnbuckle for my split backstay is above the split.

Thanks!

Patches

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Ron Hill

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Re: Twin Backstays on a Mark 1.25?
« Reply #1 on: November 30, 2021, 02:36:37 PM »

Patches : The back stay was only made for one backstay, but It should be no big deal to adapt the mast head for two back stays.

A thought
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WBev

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Re: Twin Backstays on a Mark 1.25?
« Reply #2 on: November 30, 2021, 02:57:55 PM »

Patches - on my 1992 the back stay splits about 10' above the cockpit floor, and each side of the split has its' own turnbuckle.  Looking at the masthead, I agree with Ron it would be easy to run two separate ones from the masthead, but you would need to adapt the masthead with a bracket.  Doesn't look to hard to do. 
The twins at the bottom introduce other issues which may or may not be troubling to you such as sitting in the corners with the wire going in front of you, which is worse when you put pushpit seats on the back.
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Wobegon II
1992 C-34 MK 1.5
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Diversion

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Re: Twin Backstays on a Mark 1.25?
« Reply #3 on: November 30, 2021, 03:45:10 PM »

I've thought about replacing the back stay with appropriate sized spectra with blocks pulling down, smaller blocks, and cleating off on both sides of the cockpit (dual control) rather than a pinch method to get those heavy blocks from banging on my head, especially while sailing or coming in from back of the boat.  I've seen this more on racing boats, not sure it would work here...but a thought!
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KWKloeber

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Re: Twin Backstays on a Mark 1.25?
« Reply #4 on: November 30, 2021, 05:28:25 PM »

The mast truck (as it is) doesn't "support" two backstay.  There's a (horseshoe-like) clevis that swivels on a clevis pin that fits across the truck.  The single backstay pins to the open end (horseshoe legs) of the clevis.   But there's no reason that the connection couldn't be "adjusted" to allow two stays.

There are a couple of ways to do it.

1) Move the split plate for the bridle up to the truck, so that it (instead of the main backstay) swivels on the clevis (you might need a longer clevis shackle (horseshoe) but that's no big deal.)  That's an easy "proper" way because at each pull point there are pinned (hinged) connections, so the stress is absolutely perpendicular to each clevis pin -- no twist or skew can be introduced at any connection.

2) Get Garhauer to make a slightly different clevis with the leg opening of the shackle sized to fit two backstay connections -- essentially double the open-width of the end of the shackle "horseshoe" so it accommodates two stay fittings.  You might find an on-the-shelf clevis shackle that could be opened up to accommodate two stay fittings.  That method exerts all pull perpendicular in one plane on the clevis pin connection but **could** introduce a skewed pull and wear in another plane (albeit with such a large distance to the transom, the angle between the two stays is really insignificant.)

Or
You might be able to use the current clevis shackle and substitute a longer clevis pin that will pass thru it and catch the two backstay connections on the outside of the ("horseshoe") legs.  In the center of the shackle place a spacer on the clevis pin to hold the "horseshoe" legs separated/parallel.  An issue that way is that one backstay connection would constantly ride/wear against the cotter that holds the clevis pin in place (although you could put a washer between them.)  But a more secure fix is: use a clevis pin threaded on just the end, a nylock nut, and (belt/suspenders) a cotter to keep the nut captive.

It's easier to diagram it than explain it.  :shock: :shock: 

An option of course is to simply lengthen the bridle and move the split plate higher.

A decent rigger can figure it out, but unfortunately, it eliminates the ability to add a backstay adjuster (on the bridle.)
« Last Edit: November 30, 2021, 05:29:05 PM by KWKloeber »
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Twenty years from now you'll be more disappointed by the things you didn't do, than by the ones you did.
So throw off the bowlines.  Sail away from the safe harbor.  Catch the tradewinds in your sails.
Explore.  Dream.  Discover.   -Mark Twain

Noah

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Re: Twin Backstays on a Mark 1.25?
« Reply #5 on: November 30, 2021, 05:55:27 PM »

Wobegon—My guess is your two turnbuckles (one on each leg on the “V” split) is NOT a factory set-up. Not sure what the reasoning is behind that solution. Mine is a single turnbuckle above the split. I can just reach it standing on the helm seat. I used to be 5ft 9in. :?  8)
 
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waughoo

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Re: Twin Backstays on a Mark 1.25?
« Reply #6 on: November 30, 2021, 06:30:01 PM »

Patches... if you dont have the walk through transom, i find that the split stay for that era of c34s to be WAY too low to be at all helpful.  I have a 91 with a rather tall split backstay on my walk through transom and find this solution to be quite workable.  I shouldnt be too hard to adapt the higher split backstay to an older split backstay.
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Alex - Seattle, WA
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Stu Jackson

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Re: Twin Backstays on a Mark 1.25?
« Reply #7 on: December 08, 2021, 12:24:35 PM »

I posted these photos before the site server was upgraded and they disappeared.  They're baaack!!!

The turnbuckle should be relocated to the transom.  I didn't, and after a decade when it came time to adjust it, it wouldn't move.  A ladder and my son's strong arms got it to move.  If you can't access it, consider it useless.  The single turnbuckle should be relocated to two at the transom, one on each leg.

I used a Garhauer split adjuster, raised the split and used a Garhauer vang for adjustment.  The split legs are connected to the chainplates with large D shackles.  This eliminates the issue with lining the backstay up with the essentially offset plates.

I got the height change from this sketch, I think Dave Davis posted it in a tech note eons ago.
« Last Edit: December 08, 2021, 12:26:26 PM by Stu Jackson »
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Stu Jackson, C34 IA Secretary, #224 1986, "Aquavite"  Cowichan Bay, BC  Maple Bay Marina  SR/FK, M25, Rocna 10 (22#) (NZ model)

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Dave Spencer

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Re: Twin Backstays on a Mark 1.25?
« Reply #8 on: December 08, 2021, 12:36:13 PM »

Reposting for the same reason Stu did... I posted this a week or 10 days ago but it disappeared along with several other posts. 

Here are some pictures of the masthead showing how the backstay is pinned to the mast. 

Before proceeding with twin backstays all the way to the masthead, you might want to think about the leech of the mainsail chafing on two backstays instead of just one.  It's usually not a big problem for me but when I'm tacking or gybing in light air the leech sometimes hangs up briefly on the backstay. 
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Ron Hill

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Re: Twin Backstays on a Mark 1.25?
« Reply #9 on: December 12, 2021, 11:08:01 AM »

Guys : I made my back stay adjust similar to the diagram that Stu posted. 
Bill Felgenhauer (Garhauer marine) made me two small blocks that held the sheave in place with a removable pin.  Then all you do is add a 4:1 short vang, a short length of 7/19 cable and you are in business.  Made that back stay adjuster in the early 1990s.  I believe that I even wrote a Mainsheet tech note article on it!

A few thoughts
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Ron, Apache #788

Ron Hill

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Re: Twin Backstays on a Mark 1.25?
« Reply #10 on: December 12, 2021, 11:16:45 AM »

Patches : Looking at the above mast head here is an idea to attach 2 back stays:
Purchase a longer pin so the swedged fittings of the back stays would be on the outside of the head stay bracket .  I'd also make a sleeve to fit in the center to insure the head brackets could not compress.

A few thoughts
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Patches

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Re: Twin Backstays on a Mark 1.25?
« Reply #11 on: December 13, 2021, 07:11:29 AM »

Very useful photos and diagrams!  Thank you.

From the looks of it, the masthead "truck"--as designed and manufactured--doesn't support twin backstays at the pin through the truck. 

However, it appears possible to have the split in the backstay--currently too low for me--higher, to include "a lot higher." Maybe within a foot or so of the mast truck.  Ken covered this in his possible solution no. 1.  By doing this you make inspection of the split hardware part of your regular trip up the mast.  Might actually be easier the higher it is--at the mast head-- instead of further down the backstay.

The important thing is to move the turnbuckles down to the the stern for adjustment and inspection.

In my research on this, I came across some Brion Toss comments where he said he did not like the twin backstay set-up (stern to masthead).  Sort of like God telling you its a bad idea, but I'm going to try to figure out why and how moving the split higher up makes a difference.

Many thanks.  I have the next month or so off for boat maintenance/upgrades, so I am going to get to the bottom of this.  Just got the new mainsail on and Strong track system.  Rigid vang goes on this week.  Then the marine head comes out while I fit and build a platform for the new Airhead composting toilet.
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Noah

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Re: Twin Backstays on a Mark 1.25?
« Reply #12 on: December 13, 2021, 09:01:56 AM »

Patches- I will be interested in hearing about how your charter guests react to using the composting head.
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KWKloeber

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Re: Twin Backstays on a Mark 1.25?
« Reply #13 on: December 13, 2021, 10:57:49 PM »

Though I'm neither a rigging nor Toss expert, if you look at his issues about the twin backstay there really are no valid (or at least significant) cons.  His whole point is, he shoots holes into the premis(es) that owners use to justify doing it. 

In other words, when looking at his reasoning critically, they don't support that it's a BAD idea, or an unsafe configuration, or similar -- just that whatever reason(s) justifying doing it, could be "worked around" instead of adding a stay.

His two actual honest-to-goodness "negatives" against it are:
(1) additional weight aloft (ok, technically valid but c'mon, really???) and
(2) the masthead connection could be improperly done. 
Well duh, of course the connection could be improperly done.   And so could it be done properly and safely, so that "negative" is not a valid argument. 
So, a single backstay can't be done improperly?? 
A corollary would be "Soldering on boat wiring is bad" -- the true statement is: "IMPROPER soldering on boat wiring is bad."

-k
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Twenty years from now you'll be more disappointed by the things you didn't do, than by the ones you did.
So throw off the bowlines.  Sail away from the safe harbor.  Catch the tradewinds in your sails.
Explore.  Dream.  Discover.   -Mark Twain

Patches

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Re: Twin Backstays on a Mark 1.25?
« Reply #14 on: December 14, 2021, 06:54:48 AM »

Noah:  You're exactly right about the charter guest concern.  No, I don't trust them to properly use a composting head and to make sure the separate waste streams make it into their dedicated chambers.  Although most guests are pretty good about following use instructions on a marine head, some have a hard time remembering not to place paper in the toilet.  I'll be fitting the composting head now and making the extended platform to support the liquids container.  But it is likely a permanent install once we make the big left turn in a couple of years.  Will free up a lot of space under the port settee for other things.

By the way, after considerable research and measuring, only the Airhead seems to have a small enough footprint to go into the space given over to a toilet in the Mark 1 head compartment.  I went with the "hull shape" solids tank to gain that much more room for installation.  We'll see how it goes in once I get these other projects knocked out, and I'll report back.

Ken:  Thanks for your deeper dive on the Brion Toss comments.  I have to admit, I didn't understand how he was OK with a split backstay but seemed opposed to a twin backstays.  I'm going to run it by my rigger to get his thoughts as well.

Patches
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