Backstay on the M

Highlander · Post by **Highlander** » Wed Apr 15, 2009 9:06 am

Hi G
Calling for a nice sunny wk-end +19C I think she's

coming out of my shop this Fri.

give me a call if ya want to drop by

so as I can hide the beer before you get here !

Cheers J

delevi · Post by **delevi** » Wed Apr 15, 2009 11:13 am

Can't see how the mod you have helps to flatten out the main also. I get the head sail, no doubts there, just can't get my head around how it affects the main. If you take any right angle triangle and move the vertical line back so that it is 89 deg instead of 90, to avoid slacking up the roach, one must tighten up the main sheets. It should not matter, again in theory, where the vertical line is in that triangle. Move the mast fwd, you would have to slack off the mainsheets to allow for that, move it back, you would have to tighten them up to keep the sail flat. Guess seeing will be believing this May. Looking fwd to that as always.

As Bob & Rich have already noted, the entire mast doesn't come aft, but rather the top and the rest of the mast arcs forward, pulling the luff of the mainsail with it, thus flattening it. This is old school sailor stuff, not a concept I invented. The whole deal works better on a fractional rig with respect to flattening the main. On a masthead rig, the backstay is more effective in tightening the forstay vs. flattening the main. My setup, however seems to work well in doing both. Perhaps becuase the forestay on the Mac is relatively loose compared to most keel boats and the backstay takes up that slack when needed.

Leon

beene · Post by **beene** » Thu Apr 16, 2009 4:04 am

Makes perfect sense to me now. Due to the fractional rig of our macs, I can see how your mod will also flatten out the main.

Can't wait to see it all in action.

I hope we get some serious 30+ kt winds.

Would also love to go out in 45+ to try out that 3rd reef of yours.

Lets hope SFO has some gales in store for us to test her out.

See you soon.

G

Inquisitor · Post by **Inquisitor** » Thu Apr 16, 2009 4:30 am

I was out flying full sails the other week in 25 knots just so I could ride at 50+ degrees. I just wanted to "get used to" the boat at its limits so I wouldn't be surprised later. And I thought I was running on the wild side.

But... then Momma always tought me to just say no to drugs.

Inquisitor · Post by **Inquisitor** » Thu Apr 16, 2009 4:40 am

...But I do want one of these backstays.

What do you think about running a pair of side stays from the spreaders to this masthead plate to help with lateral loads...

... and maybe allow a mast head A-Spin?

beene · Post by **beene** » Thu Apr 16, 2009 9:16 am

And I thought I was running on the wild side..............

http://s166.photobucket.com/albums/u119 ... 0_4561.flv

http://s166.photobucket.com/albums/u119 ... 0_4555.flv

http://s166.photobucket.com/albums/u119 ... 0_4078.flv

Got to get out there and just do it!

G

Highlander · Post by **Highlander** » Thu Apr 16, 2009 4:37 pm

Inquisitor

Here's something I drew up for leon

J

delevi · Post by **delevi** » Thu Apr 16, 2009 9:55 pm

Looking good there G! Haulings some serious tail. Your reefing work is a bit sloppy though

And on that third vidceo...are you trying to blow out your main? I know you just need a good reason to get a new one

Try out the jib. You'll like it. And the backstay will get rid of that sag real nice like. You'll see. Was out for a few hours today near SFO. Wind was howling 30's to maybe 40. Had the main tripple reefed with about 2/3 to 3/4 jib. Yeeehaaa! Tried to slack off the backstay before tacking but she would bear off almost 10 degrees and heel over at least another 5. Truly amazing. Cranked it back up and just tacked. Mast rotated through just fine, then switched the backstay to the windward side after I was on my new course and in the groove. Amzaing how the forestay just sags off when the backstay is released. Makes a huge difference, particularly pointing in heavy air. Going to gdet a second 6:1 block and tacke and have one on each side with heavy duty snap shackle on the forestay cable. Will make the switch a breeze.

John & Inquisitor,

I totally don't get the whole rig through the spreaders. Just can't see it. Sounds like trouble.... but maybe I'm missing something.

LD

TRIPPLE REEFED!

Highlander · Post by **Highlander** » Fri Apr 17, 2009 1:16 am

Leon

you'd be pulling the masthead backwards via the spreaders just like running backstays but without the need to switch as they would be applying equal pressure on both sides & attached to the new stationery swivel top brkt they would not interfere with the mast rotation

J

Highlander · Post by **Highlander** » Fri Apr 17, 2009 1:23 am

Here's my Alum masthead swivel brkt in the making , with leon's approval

http://i235.photobucket.com/albums/ee20 ... 0007-1.jpg

http://i235.photobucket.com/albums/ee20 ... 0006-1.jpg

http://i235.photobucket.com/albums/ee20 ... 010005.jpg

http://i235.photobucket.com/albums/ee20 ... 010002.jpg

More pic's to follow

J

Highlander · Post by **Highlander** » Fri Apr 17, 2009 11:27 am

ready for mounting this wk-end I hope

http://i235.photobucket.com/albums/ee20 ... 0009-1.jpg

http://i235.photobucket.com/albums/ee20 ... 0012-2.jpg

http://i235.photobucket.com/albums/ee20 ... 010016.jpg

J

delevi · Post by **delevi** » Fri Apr 17, 2009 3:24 pm

John,

Are you sure the spreaders would hold up to those loads? They are flimsy little aluminum pipes after all. Also, not sure if this setup would actually tighten the forestay, or in your case, four of them

Personally, I would opt fo the simpler option. Switching sides is really not that big of a deal and really optional. I just do it to stay on the safer side of rig intergrity and to max out performance. Would love to see the setup though if you go through with it.

Cheers,
L.

Currie · Post by **Currie** » Fri Apr 17, 2009 4:40 pm

Hi John,

I'm confused about (but very interested in) the drawing with the new shrouds. They seem to connect to the mast at both the top and the bottom. What does that do? Forgive my ignorance.

~Bob

Inquisitor · Post by **Inquisitor** » Fri Apr 17, 2009 6:10 pm

John will probably reply… but…

I should have elaborated when I originally mentioned it. And John picked up on it right away. The added shrouds from the masthead to the spreaders WON’T help forestay tension one-bit.

HOWEVER

Let me first say, I think this backstay is a great idea! But from an anal-retentive engineering perspective, here is something that will make it a little better.

First and mainly – We want higher tension in the forestay. Well this backstay is the best way… period. No debate about that.
Second because of the fractional rig – we get bending (causing an arc) in the mast which also flattens the main. GREAT… double benefit.

And this is where anal-retentive engineering comes in. We only gain performance from the bending in the plane of the main sail.

Any bending out of plane is not helping performance. In fact, it is also the weakest direction of the mast. At some load we could put a permanent bend in the mast. With high enough load AND repeated cycles, we could cause a fatigue fracture. Guess where it would be… It would be right at the top of the current shrouds around all those holes which form stress concentrations in the mast. We obviously don’t want this.

The shrouds from the spreaders to the mast head keep the top portion of the mast from bending out of plane. The primary lateral loads are taken by the shrouds instead of the mast. Thus, the mast only bends fore and aft while tightening the backstay.

My original comment glossed over all this thinking... going strait to the aspect... MORE SAIL... GO FASTER!

By adding these shrouds in addition to the backstay your masthead is fully supported... fore and aft with this backstay and laterally with these added shrouds; there is no structural reason (of the mast... at least) for not having a masthead spinnaker.

With some of the great bowsprit designs on this forum, you could hoist one kick-ass spinnaker. Probably DOUBLING the area of the cruising spinnaker. So the backstay could help downwind as well as upwind performance!

Currie · Post by **Currie** » Fri Apr 17, 2009 7:31 pm

Got it, thanks!

When I looked at the diagram today, I had it in my head that *additional mast bend* was somehow being controlled with the new shrouds, and I thought - that can't work

duh me.

That being said, aren't jumper shrouds on mini spreaders more the norm?

Cheers,

~Bob

MacGregorSailors.com

MacGregorSailors.com

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