Double Spreader Mod

A forum for discussing topics relating to MacGregor Powersailor Sailboats

Moderators: Catigale, Paul S, Heath_Mod, beene, Hamin' X, kmclemore, tangentair

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Signaleer
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Double Spreader Mod

Post by Signaleer » Wed Feb 07, 2018 9:39 am

Hello all you worthless sea monkeys...

So, owned the X now a few years, and admittedly, did not get out on it last year. Someone should shoot me. :( :cry: :|

However, part of the reason, for those of you that wait for me to post - is that I have a damaged mast. I know some of you can relate.... However, I have a new mast off a SOL CAT 18. It is the EXACT same height! Cost me 100 bucks. I actually think this may be a bit of an upgrade. The mast 'feels' a bit stronger, but not much heavier. Maybe that's just wishful thinking... you know, physics and all... However, I'm excited.

Here is my question: I think the X mast/rigging is not optimally designed. By only 'eyeball' measurement, the upper shrouds look like they do not go far enough up the mast even for a fractional rig design. When I was under sail, I could noticeably see the stop of the mast stressing port and starboard. And trust me, if anything, having come from a traditional sailing background, my rig was probably too tight by Mac standards... but wow, it pointed :)

So, here is my thought: I think the Mac should have the uppers 'higher' and a pair of 'mids'. Not because of the massive stresses on the small mast, but because this is (best I can tell) one area where it was lightly designed for trailering and handling purposes.

I will would keep it a fractional rig, but modified. I think I would like to add a second set of chainplates and use synthetic rigging.

Anyone feel similar?

I know the old nut that keeps adding sails to his :macm: has a second set of spreaders - but he is also flying more canvas than a 80-foot square rigger.

TIA,

Ed

P.S. Why haven't we seen Peaches in a long time? I hope she is ok.

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Ixneigh
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Re: Double Spreader Mod

Post by Ixneigh » Wed Feb 07, 2018 10:19 am

I'd skip the 2nd set. I haven't heard of many rig failures from just sailing. Something broke or in one case, they hit a marker.
Maybe upgrade wire. Im experimenting with synthetics before I commit to full wire replacement. I replaced my shroud adjustor plates with synthetic lashings. Jury is still out. Imho upgrade existing rigging components before adding new ones.

Ix

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Re: Double Spreader Mod

Post by sailboatmike » Wed Feb 07, 2018 4:25 pm

Stiffer spreaders may assist, the old broom handle down the spreader trick would certainly stiffen them up, while the shroud is supposed to run freely though the end of the spreader its hardly a frictionless design, this may put bending force on the spreader and thus decrease the rig tension.

Just a thought, but Macs are known for weak spreaders and I know many have used the broom handle to stiffen them up

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Re: Double Spreader Mod

Post by Highlander » Wed Feb 07, 2018 11:37 pm

sailboatmike wrote:Stiffer spreaders may assist, the old broom handle down the spreader trick would certainly stiffen them up, while the shroud is supposed to run freely though the end of the spreader its hardly a frictionless design, this may put bending force on the spreader and thus decrease the rig tension.

Just a thought, but Macs are known for weak spreaders and I know many have used the broom handle to stiffen them up
U r wrong about the shrouds they r not suppose to run freely thru the spreader end caps . they r suppose to b firmly clamped at the spreader end caps at a specified distance from the mast hound connection as per ur Mac Manual ! , if ur shrouds r running freely thro ur spreader end caps u have one or two issues either ur spreader end caps r worn out & or ur shrouds r stretched beyond their spec,s or frayed , either way u have a serious rigging issue that can lead to ur mast pumping side ways that could cause ur mast to snap at where the spreaders attach to ur mast !
check & read ur Mac Manual

Just sayin That,s All

J 8)

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Re: Double Spreader Mod

Post by sailboatmike » Thu Feb 08, 2018 12:01 am

Highlander wrote:
sailboatmike wrote:Stiffer spreaders may assist, the old broom handle down the spreader trick would certainly stiffen them up, while the shroud is supposed to run freely though the end of the spreader its hardly a frictionless design, this may put bending force on the spreader and thus decrease the rig tension.

Just a thought, but Macs are known for weak spreaders and I know many have used the broom handle to stiffen them up
U r wrong about the shrouds they r not suppose to run freely thru the spreader end caps . they r suppose to b firmly clamped at the spreader end caps at a specified distance from the mast hound connection as per ur Mac Manual ! , if ur shrouds r running freely thro ur spreader end caps u have one or two issues either ur spreader end caps r worn out & or ur shrouds r stretched beyond their spec,s or frayed , either way u have a serious rigging issue that can lead to ur mast pumping side ways that could cause ur mast to snap at where the spreaders attach to ur mast !
check & read ur Mac Manual

Just sayin That,s All

J 8)
I'm not sure about that, many boats only have holes for the shroud to go through on the spreader end caps, there is no clamping, we just finished rerigging a JOG boat and there is just a hole for the shrouds to go through. After doing some research seems there is confusion about this very point, but all the reading I have done suggests that the spreader floats on the shroud, maybe different for different boats

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Re: Double Spreader Mod

Post by kadet » Thu Feb 08, 2018 2:51 am

I'm not sure about that, many boats only have holes for the shroud to go through on the spreader end caps, there is no clamping, we just finished rerigging a JOG boat and there is just a hole for the shrouds to go through. After doing some research seems there is confusion about this very point, but all the reading I have done suggests that the spreader floats on the shroud, maybe different for different boats
Actually it is the opposite most boats have the stay fixed on the spreader at a specific angle to the mast to prevent the spreader going out of "column" and thus inducing side loads that could break the spreader or collapse the rig.

Some small boats have free running stays as the loads are not strong enough to break the spreader but it is not the norm especially on keel boats. Inside the spreader is normally an adjuster plate or even rigging screws to secure the stay.

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Re: Double Spreader Mod

Post by sailboatmike » Thu Feb 08, 2018 3:12 am

I have looked and looked on Google images and in the HUGE majority the shroud is not clamped to the spreader end cap, the end cap is just there to stop the shroud from coming off the spreader.

This is my reference https://www.google.com.au/search?q=shro ... veL2XzP2kM:

But as I stated, reading through the forums about this topic some say it should be loose some say it should not move, I would say the answer is somewhere between depending on your boat and rigging, seems to be specific to certain boats and rigs (on the cruisers forum the ratio is about 4 say it should be able to run through to 1 saying it should be tight)

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Re: Double Spreader Mod

Post by kadet » Thu Feb 08, 2018 4:23 am

This is my reference https://www.google.com.au/search?q=shro ... veL2XzP2kM:
And just about every one them is fixed to the stay either by clamping or seizing wire so :?: :?: :?: :?:

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Re: Double Spreader Mod

Post by sailboatmike » Thu Feb 08, 2018 7:07 am

kadet wrote:And just about every one them is fixed to the stay either by clamping or seizing wire so :?: :?: :?: :?:
Seizing wire would allow the shroud to run through the spreader end cap, the wire is only to ensure that it doesn't come out, as I said about 1 in 5 shows the any sort of clamping of the shroud to the end cap that would not allow movement as the mast bends.

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Re: Double Spreader Mod

Post by Tomfoolery » Thu Feb 08, 2018 7:58 am

If a spreader is not clamped to the stay to prevent movement along the length of the stay, then the spreader would normally be angled upward to subtend the angle it induces in the stay. That way the spreader is 'balanced' where it contacts the stay, and there are no force components pushing the stay in either direction (downward if the spreader is horizontal and the upper part angles inward, as they usually do) that have to be reacted by friction between the stay and the spreader tip, or resisted through bending in the spreader.

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Re: Double Spreader Mod

Post by Signaleer » Thu Feb 08, 2018 9:45 am

First, we are obviously ignoring Peaches, which troubles me. ...


But second - this is not the question. My point is that the design is flawed in that the upper shrouds attach too low on the overall mast allowing too much mast above the attachment of the uppers. (That's point 1) and point 2 is that this mast is simply a lb or 2 light for the loads put on the boat. The loads are not a problem for the standing rigging, and I believe the end caps do not allow shrouds to 'move' through the end of the spreader.

I'm trying to get a relatively stiffer (and safer) mast.

My mast began to suffer the classic 'pinch' at the single spreader location and would have failed in the future.

I am recommending that the uppers be attached higher on the mast, but still, allow for a fractional rig design. I would add a second set of spreaders part way up the mast to spread the loads out more evenly. If you are going to carry more sail - I'd like to carry a cutter-like rig sail and the spinny. I think this mast is the one weak link in this design that I have seen.

Thoughts on that?

Ed.

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Re: Double Spreader Mod

Post by BOAT » Thu Feb 08, 2018 10:24 am

Signaleer wrote: 1 we are obviously ignoring Peaches

2 second - this is not the question.

3 I believe the end caps do not allow shrouds to 'move' through the end of the spreader.

4 My mast began to suffer the classic 'pinch' at the single spreader location and would have failed in the future.

5 I'd like to carry a cutter rig. I think this mast is the one weak link in this design.

Thoughts on that?

Ed.
Okay, your right on all points:

Yes. the end caps MUST be secured to the wire or the spreaders will walk right up the wire and flatten out against the mast! ALL spreaders work that way. Always make sure the ends of the spreaders are securely attached to the shroud. The pinch in the mast is shock loads slamming the spot where the spreader attached to the mast - some riggers call that "hammering" - the constant back an forth of tacking makes the spreader snap down hard on the mast at that point on one side of the mast and the pressure is relieved on the other side because the shrouds go slack on one side and tight on the other - the constant back and forth 'hammers' the spreader into the mast. It's not the strong pressure of high winds that fatigues the mast at the spreader mount - it's the constant 'hammering' of loose shrouds banging away at the mast - you could just take your nail hammer and keep banging away at the side of the mast and sooner or later the aluminum will develop a deformity or stress crack.

If you want to carry a cutter rig then two spreaders really is a good idea - but I would recommend you switch to the M mast if you do that - the M mast is shaped a little bit differently - the M mast is designed to bend more than the X mast.
The X mast is stiffer. If your going to a cutter rig I would use more spreaders and a mast that can take more bending. (Usually a mast that is flatter - the X mast is more rounder)

The set up that Highlander has is the perfect set up for running a cutter rig - it has a good mast shape that can bend before it cracks and has all the spreaders and rigging needed to support it. If your gonna do it go with a system that is already tested and working - use the M mast and rig it the way Highlander has.

I too wonder what happened to peaches. I hope all us guy talk did not scare her into one of those 'me too' moments - I wish we had more females on-board here - but I understand we men are insensitive and crude and hard to be with but I hope she might overlook our failings because we want her here.

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Re: Double Spreader Mod

Post by Seapup » Thu Feb 08, 2018 11:39 am

What does the solcat 18 use for support as far as spreaders and standing rigging on that mast?

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Re: Double Spreader Mod

Post by topcat0399 » Thu Feb 08, 2018 11:53 pm

Sooooo, after reading all of this and applying deep thought and consideration of the views allowed minus the ones I dismiss outright and adding the ones with highest post count I'm down to heads I attach and tails I don't.....:P


I love forums.....

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Re: Double Spreader Mod

Post by Tomfoolery » Fri Feb 09, 2018 8:40 am

Here's a cross section of the :macx: mast, with section properties. The items of interest for bending resistance are the moments of inertia, Ix and Iy.

Image

And for comparison, here's the cross section with properties for the :macm: mast.

Image

Both masts are about 3" across (the Y-direction), but the :macm: mast is around 3/8" larger in the X-direction. That makes the :macm: mast about 18% stronger sideways, but around 23% stronger in the fore-aft direction*, assuming the same material strength, and 42% stiffer fore/aft and 18% stiffer side-to-side.

It should be noted that putting holes in the sides for stay tangs and spreader bases weakens the masts right where it can't afford to be weakened. That's why the flats are there in the :macx: mast, I'm sure. Those are big holes, and a known weak point. Those holes weren't taken into account in the above.

*I didn't draw the :macm: mast section, so I don't know where the centroid is, and therefore had to make an educated guess where the neutral axis is. But I'm sure it's close. Close enough, at least.
Last edited by Tomfoolery on Mon Feb 12, 2018 3:06 pm, edited 1 time in total.

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