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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NiceAft
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Re: Double Spreader Mod

Post by NiceAft » Wed Feb 14, 2018 7:30 am

sailboatmike wrote:
Signaleer wrote: Sell me the 19?
Highlander has a 26M
Also a :mac19: , but the photo is an :macm: . I am not aware of a blue :mac19: .

John,

Did you also take your :mac19: with you when you moved, or did you sell it?

Ray

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Re: Double Spreader Mod

Post by Capt Smitty » Wed Feb 14, 2018 8:02 am

Hi Sailors
Macgregor changed the :macx: mast during it's run. My 2002 spreader brackets are fastened to mast with screws. The early models had a bolt thru the mast to attach the spreader brackets, I think that was a weak point they corrected.
I suspect other changes, too. I recently tried a mast gate, 3D printed, insert by MastGate, from Shapeways Marketplace (online), unsuccessfully. They showed 2 different sizes for :macx: , and 1 for the :macm: . I tried one for the :macx: , it did not fit my mast gate (I recieved an easy, quick refund). After seeing how it is supposed to fit, and checking the other sizes spec's, I think I have a :macm: shaped mast gate.

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Tomfoolery
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Re: Double Spreader Mod

Post by Tomfoolery » Wed Feb 14, 2018 9:47 am

Signaleer wrote: Now another piece of data: empirical data...

1. X masts break at the spreaders (does everyone agree to this?) I believe my rig was adequately tight, perhaps over tight (and may have caused a pinch at the spreaders) and this is the impending failure.

I don't remember exactly what my spreader brackets look like, but I believe they are the two individual units with screws, like what BWY shows on their site for the X. High upper stay loads would put high compression load into the spreader, but that's mitigated by the lower stay, which is pulling the mast in the opposite direction the spreader is pushing. How balanced those forces are, I couldn't say, but I made a force diagram a few years ago just to see what's going on in there, and it looks like if the upper and lower stays have the same preload, which they normally don't, there shouldn't be much if any compression of the mast. If you relaxed the inner stays, the force component through the spreaders would only be taken by the mast that connects the two together.

The sketch is in two dimensions, and actual hardware is in three, but I found it interesting nonetheless.


2. I also believe I have visually seen more mast flex than I am comfortable with vs. my 105 lb Pearson 26 extrusion on that boat (which was also a masthead sloop). This flex makes me think this is a weak link.
3. When we calculate stresses are we accounting for headsail? mainsail? perhaps mainsail & Spinnaker? (I tend to be a conservative sailor, and respect the environment, but still enjoy sailing in good conditions). Because the flex in the forestay, this often creates a non-flat sail that is definitely stressing that mast. (again, my was as tight as I've seen on Youtube and tighter... but still our foresails have a ton of flex)

I made no attempt to account for actual sail loading into the mast; I was just playing with the mast sections and their mechanical properties. Actual sail loads into the mast would be distributed along the luff, and not uniform along the length I wouldn't think (force per unit length near the top would be much less than in the middle or near the foot, it would seem to me). Plus the forestay load in three dimensions. And maybe the outhaul, boom, and possibly leach load at the headboard. I'm not a boat rigger, and maybe they use simplifications and rules-of-thumb to make it more manageable, but it looks fairly complex to me. I might try modelling a mast with rigging just to see what it does under various loads, though.

I could be wrong but I don't think double spreaders will add additional windage worth worrying about and may help the mast stay rigid port and starboard. but I don't want to do that if it is dumb.

I don't know if more rigging aloft will make that much difference in the performance of these boats, as they're hardly racers. Jumper stays would stiffen up the cantilevered top 4 or 6 ft of mast, but add weight and windage up there. If mast crushing is an issue, perhaps a compression tube around the bolt that holds the tangs for the inner stays would be practical, just long enough to be flush with the outside of the mast, allowing that one bolt to be cranked tight without risk of squeezing the mast. You'd have to drill the mast slightly larger to fit the tube, or figure out a way to insert it all the way from the top or bottom (ugh), but it's doable.

Thoughts on my analysis?

Ed.
Just a few things that come to mind. But I'm no sailboat rigger, so take all that with a grain of sea salt. :wink:

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Re: Double Spreader Mod

Post by BOAT » Wed Feb 14, 2018 10:11 am

Just look at a picture of the Highlander under full sail in high wind conditions - he has posted lots of pictures.

The Highlander is a heavy boat - the heaviest boat in the fleet - and he has two head-sails. Under full sail you can see the nose of the boat is digging into the water. The boat is being pushed forward at tremendous force - all that force is pulling on the boat through the side shrouds and the main sheet. Most of that mainsail force is in the lower 2/3rds of the mast. It's the head-sails that are adding so much force to the upper mast. That force up there pulls hard on the top of the mast and makes the nose of the boat go into the water. Then the least force unit is the jib sheets - force so light you can pull them in by hand. There is a balanced load on the forestay that is concentrated at the bow. It's a good thing that the forward hull on the M boat is deep with a deep V. Most of the ballast on the M is also carried well forward - The M ballast is closer to the bow. Almost EVERYTHING on the M used for sailing is closer to the bow than the stern.

Because of the arrangement like this - where all the "stuff" is well forward of the middle it gives the rigging tremendous leverage on the boat - if the big green incredible hulk monster came along and grabbed the boat by the mast and tried to pull it off he would just pull the entire boat out of the water - because the entire boat is really in the first third of the boat - the entire aft section and most of the midships is just going along for the ride. That's the "hybrid" design - as a sailboat it's only using the forward third of the boat that's all it really needs to sail, but it needs the entire rearward 2 thirds to be a motor boat that can plane on top of the water. That's how Roger accomplished the whole trick. The boat is one thing in the front and another thing completely in the back.

The back portion is VERY light and puts very little strain on the rigging

You guys are thinking traditional sailboats with lots of well balanced centers weight and heavy spars - yes - those boats need a LOT of rigging - think of the M boat as a 13 foot sailing skiff - because as a sailboat that's really what it is - only the front half does any of the real sailing and has any of the real weight.

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Seapup
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Re: Double Spreader Mod

Post by Seapup » Wed Feb 14, 2018 10:42 am

I broke my :macx: mast. It was 100% operator error, I caught a sidestay on a marker. When it pulled the mast down the spreaders connection was the weak link where it broke. I don't think there is any other rigging combo that would have prevented it breaking though. I feel the stock setup is fine, the answer is not to run into stuff.

I broke my mast around 11pm on a weeknight (learned a few things that night :wink: ) and was back on the water sailing that weekend. Hindsight it was one of my easier mac mods/repairs. $200 for a used beachcat mast and swapped the hardware over to the stock macgregor locations in an afternoon, didn't even pull the boat from the slip. We sailed the heck out of it for 5 years afterwards. Point is even in a worse case scenario its really no big deal on such a simple boat.

My buddy did a similar oops in his mac 22 catching a stay while docking. Difference was the mac 22 mast has hinged spreaders so it hinged back allowing some slack in the side stay while the boat lost its momentum. If anything his "weaker" spreader design saved his mast. My rigid spreader pulled my mast and broke it. I posted up pics of how we were able to quickly straighten his mast while the old salts nay sayed and overlooked begrudgingly at the marina.

For decent headstay tension a winch has to be used when raising the mast. It should be easy to see the prebend in the mast. On the :macx: the mainsheet can be used to load the backstay after the rest of the rig is setup if you still want more tension.

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Signaleer
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Re: Double Spreader Mod

Post by Signaleer » Wed Feb 14, 2018 11:08 am

Seapup wrote:For decent headstay tension a winch has to be used when raising the mast. It should be easy to see the prebend in the mast. On the :macx: the mainsheet can be used to load the backstay after the rest of the rig is setup if you still want more tension.
Tensioning a backstay on a fractional rig does little to nothing for headstay tension on any boat.

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Seapup
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Re: Double Spreader Mod

Post by Seapup » Wed Feb 14, 2018 2:26 pm

Tensioning a backstay on a fractional rig does little to nothing for headstay tension on any boat.

Understandable opinion. To say it does nothing is not my personal experience adjusting it on an :macx: though.

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Ixneigh
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Re: Double Spreader Mod

Post by Ixneigh » Wed Feb 14, 2018 10:17 pm

The spreader fittings need a compression stud. Else it will compress the sides of the mast.
I prefer masthead rigs. With twin back stays. I may eventually convert my M into such by making a rotating plate with a thrust bearing under it for top of the mast. Boat is correct when he promises us the mast as is will be strong enough the lift the whole yacht.
A possible dodge might be to reinforce any weak spot in the mast with an inner sleeve. If the tend to break at the speakers, insert a 3 foot long sleeve or plug into the mast and secure it with fastenings. I might be inclined to use an epoxy saturated soft wood plug.

Ix

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Highlander
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Re: Double Spreader Mod

Post by Highlander » Wed Feb 14, 2018 10:39 pm

NiceAft wrote:
sailboatmike wrote:
Signaleer wrote: Sell me the 19?
Highlander has a 26M
Also a :mac19: , but the photo is an :macm: . I am not aware of a blue :mac19: .

John,

Did you also take your :mac19: with you when you moved, or did you sell it?

Ray
Hi Ray
I converted my :mac19: mast from my modified 28ft mast back to it,s original 24ft size but still left it as a cutter rig & sold her , but i kepted the upper jumper struts kit :wink:

J 8)

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BOAT
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Re: Double Spreader Mod

Post by BOAT » Thu Feb 15, 2018 9:52 am

Ixneigh wrote:The spreader fittings need a compression stud. Else it will compress the sides of the mast.
I prefer masthead rigs. With twin back stays. I may eventually convert my M into such by making a rotating plate with a thrust bearing under it for top of the mast. Boat is correct when he promises us the mast as is will be strong enough the lift the whole yacht.
A possible dodge might be to reinforce any weak spot in the mast with an inner sleeve. If the tend to break at the speakers, insert a 3 foot long sleeve or plug into the mast and secure it with fastenings. I might be inclined to use an epoxy saturated soft wood plug.

Ix
I just don't understand the logic for trying to make the M mast stronger - it will not break - numerous accidents at launch ramps have already shown that the M mast does not break - it BENDS. There is no real reason to try to strengthen it because it's not going to break anyways.

As for the question of bent masts there are several options - some people buy a new mast - others cut the mast and add a sleeve and put on a new section, and some send the mast to a rigger who jigs it back in line.

Your not going to bend the mast at sea. What are you worried about?

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Ixneigh
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Re: Double Spreader Mod

Post by Ixneigh » Thu Feb 15, 2018 12:11 pm

Well boat, that is a valid question. It all comes down to what make me feel comfortable with the rig. And a little bit of instinct gained from other boats.
Take that pivot point on the spreader mount. There are the metal holes that the bolt dropped through. I'm sure you know it. Of course you do. I looked at that one-day and I looked at metal around those holes and I said. Well its strong enough NOW of course. But how much will those holes wallow out under hard sailing? What will happen if one gets a crack from fatigue? So, I had a block of stainless drilled, and fitted between the two tongues of metal, and welded in place. Now there is a lot more bearing surface on the pivot bolt and it can even be greased. Is it overkill? Yes, for someone who sails casually. No, for me. I have never regretted any upgrades regarding making the boat or rig stronger. Its the way I use my boat. I have a 60 lb anchor I use daily. Overkill for most. But not for me when I'm anchored in a tidal cut 100 yards way from a low bridge. Or on some horrible hard coral bottom. Or when I can only use a short scope. I carry four anchors in fact. That 60 pound, an fx 25 a small delta lunchnhook and a 25 pound plow. The experiences I have had in the past tell me that's the correct number.
The running back stay is similar. Just a cheap way to add a bit more to the boat for who knows, maybe I want to run the boat back from Chub Cay in a lot of wind with just a jib. Ill feel much better with those runners set. Does the boat need it? No.
Also note:
The modern boats, macs included have little or no redundancy built in. Single lower, high tech rigs, thin wires. I grew up sailing boats that had a lot of redundancy built in. Two lowers plus an intermediate twin back stays, twin headstay. 3/4 inch fiberglass. Giant compression struts OR keel stepped wood spar.

Ix

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BOAT
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Re: Double Spreader Mod

Post by BOAT » Thu Feb 15, 2018 12:50 pm

Yeah, I know – big chicken heads on the top of the mast to give the backstay enough leverage to bend it backwards and strain the crap out of a short stiff mast with multiple spreaders with multiple side stays and on and on it goes – yes – most of the boats we sailed were ballasted boats with thousands of pounds of lead in their belly and big keels sticking way down 6 feet into the water with bulbous lead weights on the ends of really long keels that can break off and if that happened (and it did – A LOT) you were a dead man – all that weight and stress hanging out there by a thread all over the place is just a catastrophe WAITING to happen!

The M boat does not have enough weight to destroy itself like a regular boat does. Just the ballasted keel alone on a “normal” boat puts INCREDIBLE stress on the hull and the rigging because it’s cantilevered so far away from the boat thus MULTIPLYING it’s stress on the hull and shrouds! The water ballast on the M boat is way up high in the hull and you can hold the M boat on it’s side forever and the ballast will never break the boat.

Hold a regular sailboat on its side for too long and the keel will crack and break off under its own weight!

Yes, a traditional sailboat is indeed in need of a lot of redundancy. The wood spars can’t bend – they break – The fiberglass is thick and heavy and cracks because it can’t bend – and the chain plates are not even strong enough to hold the full weight of the boat.

Those were all the things I wanted to get away from – I knew I was not going to cross any oceans so I could not see the need to have all that risk on board anymore so I was drawn to the simplicity and lightness of the MAC.

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