Mini-Lathe

rev. 1-12-2025, rev. 1-17-2025

I'm kind of a shop junky. I use my tools a lot, but yes, by normal standards I'm not the average credit card sailor.

I built a metal lathe in junior high school from washing machine parts, a few things I cast, and a few things from the hardware store. It vaguely resembled a Uni-mat, and it turned out some bicycle and skateboard parts. A few things for work. However, it was non-standard and wore out 30 years ago. I've been wanting to replace it, but they're expensive. I learned a lot of good drill press and hole saw hacks to get around it when making the odd bushing. But I just wanted one, and now I'm retired, basically, so why not?

 

I settled on an 8x16 lathe from Vevor. The reviews were mixed, some saying that it could do some good work after some adjustments, tuning, and slight modifications. Others said it was a boat anchor that couldn't do shit. After about four hours of adjusting, tweaking, tiny changes, and testing, I'm firmly in camp one. I think it is going to be just swell.

 

 

 Normally I hate unboxing photos. So typical of You Tube. But hauling it around to the basement entrance in the snow and then opening the plywood crate really reminded me of the "special award" scene in "A Christmas Story." I kept saying in my head "Careful! It's fragilee."

 

They ship them loosely assembled. If you can't adjust and tune a lathe, you are going to be disappointed. Since I built my last one from washing machine parts, and have some practice on real machines, tuning it up was just a few hours of plesant tinkering. The only real "fix" was re-grinding the tailstock slide, which was botched at the factory, but that took only minutes and not it is tight. I added a few spacers and washers here and there, and a few shims where they were needed. Now it seems to turn plastic, aluminum, and steel to a pretty good finish and precision, with minimal fuss. Another problem some people have, judging from the you tube videos, is that they don't use cutting fluid. Well, that's just a mistake on a lathe or mill unless you are working plastic. Technically, you don't need it, but you get a better finish and precision with it. I use a water/oil emulsion type by Anchor Lubes. A spray bottle is all you need. Flood systems are for mills and for CNC production environments (the flush helps move the chips to a collection point).

My Scan wall unit base is perhaps not the sturdiest, so I mounted it on a 1-inch marine ply sub-base and used backing plates inside. I weighs about 85 pounds, I think. Not too hard to pick up.

 

There is a wood lathe I use on the bench to the left, (hanging on the wall in storage at the moment), so I have a handy switched outlet (curiously, the wood lath does not have a switch).

 

 I got a set of carbide insert tools to go with it. They seem good, with enough shapes for most things. Several boring bars and parting tool was included, as well as right and left cut tools, several radiuses, and threading tips. They work well. I have some HSS tool stock, so I can grind a few custom tools for thimbles and pulleys. I had to make a set of shims to go under the tools, of course, to get them to the correct height. Just a standard thing that perhaps some of the buyers didn't anticipate. I remember some complaining that they should have come with and they they didn't have shim stock. Whiners. 

I've heard complaints about the slide gibbs on the Vevor machines, but they were actually pretty good. Perhaps eventually I will make a new set from brass, but that's down the road. Meanwhile, they adjust up nice and snug with no wobble. A little more friction than I like, but we'll see how the bed in.

The run out on the chuck is about 0.005. I'm not going to work over it. The spindle bearings came snug with no meaningful runout. I'll have to check the lube and adjustment after a few hundred hours.

At one point I was experimenting on a stub of thick walled aluminum tubing, and it finally just folded up. It seems I had turned the wall thickness down to 0.010 inches, which was OK, but 0.005 inches was too little. But that is pretty impressive, to me. That's thin.

The cross slide angle adjustment is under the slide, which makes it slightly annoying to adjust (you have to back the slide far to the right). But it's not something you use that frequently, and once you get the gibs set right and replace the handle it spins out quickly.  

 

Which reminds me. I did have to alight the tailstock alignment. There is a mechanism, but it is clunky, and I will probably pull it apart and clean it up when I need it.

I got a set of carbide insert tools to go with it. They seem good, with enough shapes for most things. Boring bars too, which seem to work well. I have some HSS tool stock, so I can grind a few custom tools for thimbles and pulleys. I had to make a set of shims to go under the tools, to get them at the correct height. Just a standard thing that perhaps some of the buyers didn't anticipate. I remember some complaining that they should have come with and they they didn't have shim stock. Whiners.

I did some test drilling from the tailstock. No problems. I did purchase a chuck for that (Morse #2 taper).

 

I turned aluminum, steel, and plastic. All good. The surface finish kept improving as I learned what each material liked with these tools. No chattering and nice long chips, often many feet long, even with steel.

The motor and speed controls seem good. Enough power, and I didn't notice bothersome bogging down with any depth of cut that made sense. The power feed works fine. I did not play with threading yet. I'm sure I'll mostly used taps and dies. But it does come with change gears.

I've got a few small boat projects in mind. I'll knock those out after it gets warm enough to go sailing (the snow needs to melt). After that ... no idea.Did I really need this? No. Do you? Probably not. But it's a bit of fun.

---

Later, after dinner, making a quick test jig, and grinding a cutter for 1/4-inch radius grooves....

One of my first projects is to be some wheel thimbles for my shroud tensioners. The Dyneema line is secured around a pin through two sharp-edged stainless plates. Chafe has been an issue, and the small radius of the pin is a concern. I could use a conventional thimble, but it would not center the line on the pin and thimbles can cut the rope. A wheel thimble solves both problems. I hacked this out of a bit of cutting board, so it is crude, but it proved the jig and the groove cutter. The cutter, BTW, was one I ground when I was 13, a full 50 years ago. It was still razor sharp and just right. I think it was originally for a bearing groove.

The grooves are intentionally deeper than a pulley, to keep the rope in place and to protect from chafe. The width is wrong--this was just a quick test. This is probably the correct width for the pin on the boat, but I need to measure.

It's working! It was so easy. I could make 10 of these in 30 minutes, each identical. The breaking load tested to be 700 pounds, and the WLL is probably about 200 pounds.

The once I ended up using on the boat (shroud tensioner tackle) are a little larger and have a WLL of about 250 pounds. Since the maximum load on this tackle is about 200 pounds, plastic works.  But for any high load application, I would use aluminum, which should match the WLL of the Dyneema.

 

 A metal lathe makes these easy, but you could make them with a drill press and a few files, or with a drill press-to-lathe conversion kit. The trick is to make a chisel that matches the groove bottom curve.

 

 

 

The final product:

• Centers the load (rope) on the pin.
• Protects the rope from both side chafe and pin chafe.
• Increases the pin radius. The D/d is increased from 1:1 to 3:1.

Much better than a thimble. Why there is no US distribution I can't guess. They are available for very heavy lifting applications.

 

 

 

  

Deadeyes Vs. Lashings

Rev. 1-18-2025

I recently got a new metal lathe. My last metal lathe crashed about 20 years ago and I;ve been bodging by with a wood lathe and drill press tricks. I have a few small projects in mind, and in addition to those, deadeyes caught my eye. Not the lignum verta sort of square riggers, but something small for Dyneema.

 

 

 

 

 

A halyard applied the tension and a single leg was tied off above the top block.

 

Aluminum should be the trick, or even Nylon for light load applications.

or what about Low friction rings or even big thimbles? Even high-end boats use these.

 

 

A turnbuckle on the Lagoon, vs. the thimble lashing on an Outremer 51.

But what I can't get my arms around, if Outremer and other high-end makers are OK with lashings, is what is the advantage of bespoke deadeyes? My gut is that they are a little easier to tension, but is that even true, if the lines all run the same way? Some mini-deadeyes would be cool and trick, but is there no point?

Some years ago I tested lashing efficiency for PS, comparing Colligo eyes with LFRs.  I couldn't measure enough difference to publish.

---

So I made some up on the lathe to investigate the strength of materials. HDPE is about as weak as you can get. I basically copied the Colligo dimensions and pull tested them first to 2200 pounds and then to failure at nearly 5000 pounds (the HDPE began to creep--no dramatic failure).

 

Easy enough to make on a lathe, but you will need a jig to hold them on an arbor using the deadeye holes. I can see why Colligo went with the teardrop shape; it reduces rotation when tightening the lashing.  Not a problem with a little more care, or if I had made the eye a little tighter (it was just a test stub of line with a preexisting eye, not one made up for this test).

 

If made from nylon they would be stronger than the Dyneema line. If I wanted to go from lashing to pin, without the encircling Dyneema eye, then aluminum would be required for the pin stress.

 

I may make some for some rigging mods down the line. Although I am sure nylon would work, I'll probably use 1/2-inch aluminum plate.  A little slower to turn, but not bad and permanent.

 

 

WAGO and pull out strength

 A little while ago the loss of control of a ship and destruction of the Key Bridge in Baltimore implicated a WAGO connector. It is not clear whether the connector failed or whether it was an installation error, which is actually far more likely (we all make mistakes). However, I do get questions about the suitability of Wago connectors for yachts. I tested them, along with several other types, and they answer is yes and maybe. They are good for some things, but not for small wires and not as good as some other things. Strain relief is is still vital.

I use Wagos for some things. I also solder very small wires, use crimps, and use pressure plate- and eye-type terminal strips. It all depends. And contrary to popular belief, USCG does permit wire nuts inside weatherproof enclosures. In fact, it is always a good idea to use an enclosure if ...

• There is any chance of loose gear coming in contact with the confections.
• If splashes are possible.
• To provide strain relic and vibration damaging.

Over Jammer

12-19-2024, rev. 12-20-2024

My PDQ had 6 winches; there were jammers, but also enough winches so that redirrecting lines was minimized and there were multiple options for many tasks.

 

 Everything except the traveler is on one winch when on port tack. 

 

A single A single turning block faces off with seven clutches. There is a second winch just below, but it has five clutches of its own to deal with.  You don't put sheets in clutches on a performance multihull (Dragonfly).

 

True, I can't trim the jib with the loop over the winch, but the halyard trims easily. I could run the jib sheet through a clutch, but I really don't like jib sheets in clutches, and locating the clutch would be tricky. 

 

If I were to run the halyard through the groove instead I can avoid threading the tail. Lay a loop sling over the winch, place the rope over the sling, thread the LFR onto the end of the sling, slide the rope into the groove, and drop the other end of the sling over the winch. The only downside is that the rope could fall out of the groove if there is not tension, but that is not really likely.

 

Another option would be to cut a groove in the LFR and run the loop sling in the groove, bonded in place. A bit like this, below.

Antal Open Low Friction Ring

 

 

My challenge is trivial by comparison, and is sort of solved with a low friction ring on a loop. But I am considering a turning block so that I don't have to thread it. But they are $300! I may have to machine one.

 

 

I could put a turning block here, or maybe an inch farther aft.

 

Not all Winterizing Products are the Same

3-2014

As part of an up-coming Practical Sailor article I tested the anti-corrosion properties of a number of leading winterizing agents:

The test rig...

 

Ethanol Based                                  Glycol Based

The coupons after 2 months...

The left hand column, all ethanol-based.

1. Water
2. Vodka
3. I won't tell... just avoid ethanol.
4. I won't tell... just avoid ethanol.

 The right hand products I like, all propylene glycol-based. I forget the order, but they were all perfect.

1. Starbrite
2. Camco
3. Pure Oceans
4. Sudbury Marine
5. Southwind/Dow Frost

The clear point is not to be a cheapskate. Stay with something reputable, and stay with glycol.

The best chafe sleeve, and why a cover is NOT a chafe sleeve.

After a little more time spent with the chafe machine, a champion emerges. as well as the observation that weave is as important as the material.

What? Being Spectra is not enough? A it turns out, there is an enormous difference between braided covers and tightly woven tubing. In fact, our lowly nylon tubular webbing typically out-wears Dyneema and Kevlar rope covers. No wonder we have been so happy with our experience using nylon webbing as a chafe cover for docklines.

Top to bottom:

New England Rope ARC. 10 minutes against grindstone.

New England Rope Dyneema Chafe Sleeve. 10 minutes against grindstone.

For reference:

New England Rope Regatta Braid. 1 minute against grindstone.

New England Ropes StaSet (not pictured). About the same as Regatta Braid.

9/6-inch 7x19 rigging wire parted in 13 minutes.

But I hadn't tested nylon webbing in the same run, or plain Amsteel...

Top. ARC, as before.

Center. Plain Amsteel, Dyneema Sleeve, 9/16" nylon tubular webbing, all for 10 minutes.

Lower. Regatta braid, 1 minute, as before.

Notice that the nylon webbing outwore the high-tech cover by a mile (it's still running, at just over 30 minutes, and not through)! Notice that plain Amsteel is 30% through the first yarns, worse than the webbing.

Which is not to take anything away from this Dyneema webbing sleeve that wears like iron. Wow.

Before we question why New England Ropes even make the cover material, realize they serve a different purpose. ARC makes a nice cover, holding in jammers, minimizing core slip, and not stiffening the line. The Spectra sleeve and tubular nylon does none of these things. All it does is wear hard.

----

But this was all tested dry. What about the effect of water? We retested the same materials, and ...

I've never really thought too much about nylon chafe when wet, since it didn't apply to my experience; my mooring lines are well-protected, my anchor rode is chain, and my bridle rigged from cleats with good chafe protection (I suspect this is generally less of a problem for cats--we must always use bridles, but they are easier to rig chafe-free).

Wet vs. Dry Chafe
(2 reps each, only a few minutes variation)

Material                                    Wet vs Dry      Time to Chafe Through
Nylon webbing                          Dry                   45 min.
Nylon webbing                          Wet                   14 min.
NER Dyneema chafe sleeve      Dry                    50 min.
NER Dyneema Chafe Sleeve     Wet                   40 min.

I expected a difference, but 3x caught me by surprise. It is more than a simple change in strength, probably beyond simple analysis. I need to see how much difference Maxijacket makes; there are applications like chain-to-rope splices where Dyneema's not an option. I'll also expand this to include ropes and polyester.

The nylon webbing still makes sense many places, where availability in large sizes and price matter. For comparison, the cover on a typical line fails in 1-3 minutes.

Bare Feet or Shoes?

 I'm firmly in the shoes camp. I've stubbed to many toes and even on my beach cat, years ago, I prefered wet suit boots if the wind was up at all. Better grip. But iron sailor in past went barefoot in the rigging around the Horn (leather soles were more dangerous than cold toes--I bet they would have scooped up rubber-soled trainers in a heartbeat) and the debate continues in some circles.

I wonder if this has ever been systematically tested.

• I'd bet dinner that the correct sole will out grip skin on every surface. I doubt it even merits serious discussion.
• I've heard of studio dancing, but always with the caveat that the feet can't be sweaty. Boats get rain and seawater on them, so forget that.
• Surfing feels better with bare feet, but the reason is nerve endings. You can feel the board better. I've surfed with wet suit boots, and the traction was the same or better, but the feel was less. But I was also not cringing with fear every step, wondering if I was going to cream something. If you slide on a board you just fall, so toe protection, pain, and fear don't enter in. Also, the deck of a surfboard is optimized (soft wax) for bare feet. I doubt anyone spreads surf wax on the their side decks. Without a good coating of surf wax, a board is slicker than eel shit.
• I've heard you can "feel" more with bare feet. I sailed a beach cat for a decade, winter and summer, and I can honestly say I never felt bare feet were better. If there was serious wind, boots for 100% certain. Better traction. The only reason for bare feet was casual days of beach bumming or incinerator heat and light winds.
• I've known of a rock rock climbing problems that are done bare foot, but only because a toe needs to fit in a very specific hole. Weird stuff, climbers consider it very, very fringe. 99.999% of the time shoes are better.
• Deck shoes should be thin-soled for feel and so that they conform over and around ropes. Not the best for tennis or miles of walking, but that is what true performance deck shoes are. "Boat shoes," as distinct from deck shoes, never appealed to me. I'm not into style. Multi-court shoes and trainers can certainly work on decks, but the soles are thicker than optimum to allow padding for running and jumping. I don't run or jump on a boat, at least not the the point where additional padding is required. I do wear orthodics for flat feet. I have multiple pairs, some for higher impact sports, including hiking, and some thin for sailing, cycling, and skating/skiing.
• There is always the matter of skin cancer and covering up. Some are deniers. I admit to wearing multi-strap sandals on some of the hottest days ... with thick sunscreen.
  

December is just a few days away, so I'm not going to be testing any of that anytime soon.

Stove Top Heater

 Every fall someone re-posts the idea of heating the cabin with a flower pot on the stove. I was smart enough to test this at home, where the pot shattered, throwing hot bits around the kitchen. It is an unsafe idea that might wok sort of and might get you burned or your boat damaged. Just no.

 As long as the link stays live, here is the article I wrote for Good Old Boat about an improved stove top heater. This was written about 5 years ago, and I would not change a thing. It works. Stove Top Cabin Heater

 

The concept was simplicity itself:

• We already have an engineered heat source with fuel supply, regulation, and a safe base.
• The Dickenson Cozy Cabin Heater was/is nothing more than a burner, heat transfer space, and a properly sized flue.
• A stainless stew pot serves for the heat transfer space, though perhaps not quite on the stoves highest setting.
  
• A 1-inch flue is a good match for a typical burner, though perhaps not on the highest setting. 
• All of the exhaust will go up the flue. If the flue is the correct length, it will be no more than 100C where it penetrates the deck. No problem. Test and insulate as needed. The highest setting might allow some exhaust to go under the pot and out into the cabin. You can feel this with your fingers near the edge. Adjust.
  
• You can still cook, though more slowly, on the top of the inverted pot. The aluminum skirt conserves heat, for the pot, helps heat the room (more surface) and keeps the cooking pot safe. 
• A very low fan (I use one made to run off the USB port of a PC) helps distribute the heat. it will cook my F-24 in 20 minutes after which I turn it down. This is at about 35-40F.
  

I would turn it off before leaving or sleeping. But if the cabin furniture is warm, the cabin will stay warm for a while. Getting the furniture warm is important.

• The interior volume is about 300 ft^3, or about twenty pounds of air. The cabin furnishings weigh several hundred pounds. It is the furnishings that absorb the heat and keep the cabin warm. Kind of obvious, even though common sense tells us that the air is what we must heat.
   

Deck Level Wind Indicators

Rev. 11-27-2024

Eagles have landed on my boat and eaten three Windexes. They play with them, like a cat.For now, I'm done giving them toys.

 

 

 

So I've started testing deck-level flies. I've been using pulpit flies for years on all of my boats (beach cat, Stiletto, PDQ, and F-24) and like them. The location has to be careful chosen and I used something different on each boat.

Now I'm looking at shroud ribbons and flies. I didn't like them on other boats, but they seem to suit my F-24. 

 

 

Two DIY versions, top, then Nautos and Davis Wind-Tel.

We after a few sails we trimmed the long ribbon to about 10 inches, more like the others. The excess length just made it flutter more and harder to read.

In fact, I'm liking all of them at first blush. I imagine I will stay with the one that holds-up best.

---

The top DIY is on with Velcro. It does not spin, so it can wrap, but it always unwinds when the wind drops in a jibe. The second uses a DIY polyethylene spool (10 minute lathe project for the pair) for easier rotation, making it slightly more sensitive than the Nautos ribbon, but maybe not enough to matter. 

 

The Davis Wind-Tel ($65 per pair) is out of production, but there is lots of old stock around.  The Nautos Tell Tails are cheap ($10 for two sets) and though potentially fragile, work pretty darn well. Being able to spin vs. tied on really does help.

 

Any ideas? I'll test anything.

The Goofy X-Spread Rig on The F-24 MKI

10-26-2024, rev. 11-6-202, rev. 11-27-202, rev. 12-7-2024

The failure of an F-24 mast at the lower diamond wire junction this week (not my boat) started me thinking about the odd rig on this boat. It was not used on any other F-boat, and in fact, no other boat that I can find. Supposedly Gino Morreli designed the rig, but he's a smart guy and he never used this design on any other boat. I'm think it's far more likely this was a John Walton (son of Walmart founder Sam Walton) design choice, one of many that Ian did not approve of. Oops.

 

 The failure point was just above the lower (forward) diamond wires. Note also that it was sideways (as typical), not in the direction of the forward wires, suggesting to me that they are not helpful.

Mono-hulls are typically rigged with spreaders and shrouds anchored to the deck. This provides side support with no added compression load. The proportional stretch of the uppers and lowers insures that the mast remains accurately in column, even as it is slightly deflected to the side under wind loads. Masts, when they buckle are failing in compression. Occasionally a jumper diamond is provided on the front to control the bend of a very slender mast, though larger mast sections and those stabilized with pre-bend typically do not require this extra support.

 

One the left (F-24) rig there are two sets of diamond wires on each side. The drawing omits the outer set on the left and the inner set on the right for clarity. Those are not loaded when the mast is pressed to the side and forward reaching.

 Re. Center of effort.  According to calculations based on ABS (American Bureau of Shipping) documents, the force on a sail is primarily concentrated on the head, clew, and tack. A quick look at the reinforcements and the arraignment of fibers in load path sails makes this obvious. Consider how the luff is relaxed when the sail is backwinded. In fact, about 65% of the sail force above the boom is concentrated at the head, with the balance spread along the luff tape. The load is NOT uniformly distributed along the mast, as commonsense might first suggest.

 

The weird F-24 X-spreaders. The forward spreaders hold the shorter wires. The aft spreaders are about the typical rake angle and provide the pre-bend. 

 F-24 manual image.

 

Multihull masts are often rigged with big rotating masts for several reasons. A big main is advantageous, as it provides accurate heel control through twist and easing the mainsheet. They can tolerate a heavier mast (rotating masts must be heavier because the staying is less efficient) because they heel less and as a result, the mast is not outboard, contributing to heel. They have a wide shroud base, reducing the need for spreaders to create angle. Often multihulls cannot sustain high mast base compression loads because there either is no center hull, or in the case of trimarans, because it is lightly built, without the need for structure to support a keel.  For the same reasons, rotating masts are nearly non-existent on monohulls. Because there can be no fixed spreaders to carry side loads, rotating masts use diamond wires, and it works out well that they rotate with the mast, supporting the weak side of a thin, aerodynamic wind section. Forward support isn't needed, because the mast is wide in that direction. The diamond spreaders are angles aft to help create some pre-bend, which helps with mast stability (resists inversion and pumping) and with draft control (you can de-power by de-rotating the mast which pulls cloth out of the sail, reducing draft).

 The combination of diamond wires, aft-swept spreaders, and aft-angled cap shrouds also helps eliminate the need for a fixed backstay, something that is problematic with a high roach mainsail, the other half of the quick-heel-control formula. It's hard to maintain enough forestay tension without a backstay, and savy multihull sailors quickly learn to compensate with a tight mainsheet.

But the F-24 MKI mast does not rotate, so why the diamond wires, instead of fixed shrouds? It's easier to step the mast when trailering, since no tensioning is required. The center hull is relatively narrow and very light, with no good place to anchor the shrouds. There is also the need for aft-raked cap shrouds to replace the backstay. Of course, many cruising cats have either conventional shrouds or diamond wire stays with aft raked cap shrouds and no second set of diamonds.

There are several problems with the willy-nilly addition of stays without working through the design. When a mast fails, it fails in compression. Like buckling a drinking straw, the tensioned side does not tear, it is always the compressed inner side that buckles inwards. Every additional wire and its associated pretension adds compression, so unless it provides needed support, it actually weakens the mast. The more wires, the more compression. Calculations of buckling strength for this mast sections give a compression working load of 6,500 pounds. Rough calculations based on wind pressure and heeling force (the boat was reefed and very close reaching) and bending moment at the failure point  show that the mast failed under a compression load of about 12,000 pounds (if distributed--this reflects the probable stress on the side that failed). This is well over the safe working load of the section, but less than the expected failure strength.

If we total up the compression loads from the shrouds, diamond wires and other rigging ...

• Forestay. 2200 pounds
• Shrouds (only one is under much tension sailing under full load). 1200 pounds
  
• Mainsheet. 300 pounds
  
• Halyard, jib. 300 pounds. Note, jib halyard tension does not change forestay tension + halyard tensions at the mast, only between the mast and the anchor point at the furler. The total is fixed by shroud and mainsheet tension contributions.
  
• Halyard, main. 500 pounds
• Cunningham. Does not count, since it just offsets friction in the mast groove, from head to foot.
  
• Forward diamonds. 1000 pounds total (but not included at failure point)
  
• Aft diamonds. 2400 pounds total

... and adjusting for angles (only part of the tension is directed in-column) we get about 6,500 pounds total. That does not allow a lot for bending moment. Curiously, 36% of this is from the diamond wires and 10% from the forward diamonds, which we don't need; there is very little forward load on the mast, and the center of the force is near the head of the sail (forces perpendicular to the luff tape are very low, except near the head and tack--not the wrinkles, the luffing when backwinded, and the lack of significant reinforcement on the slug grommets).

The rigging guide gives 500 pounds max for the forward diamonds and 1000 pounds max for the aft diamonds. But what if they really don't need pretension for stretch, since the mast is not bending? Then the pretension for the aft shrouds needs to be just enough to establish the prebend (0.8% of length), and forward diamonds just enough to keep them from going slack, since we probably do not need them at all. But I'm disinclined to remove them entirely, and going slack might allow them to jump out of their fittings. 

10-29-2024. I checked the tensions on my F-24 MKI.

Wire                  Observed (pounds)              Maxium Spec (pounds)            Re-set to (pounds)

Shrouds             800  (may reach spec in strong winds)  1500                       (adjusted each sail)

Forestay            (same as shrouds by geometry, except as increased by mainsheet tension)

Aft Diamond     1400 (over spec, below)      1000                                           800

Fore Diamond    800  (over spec below)       500                                             350  ____________

Total Diamonds  4400                                    3000                                           2300

 This represents a (4400-2300)/6500=32% reduction in mast compression, which translates dirrectly into a 32% increase in strength. 

Data source: from the 1992 F-24 manual

 

 Worse, exactly where the reefed main applies it's greatest force (65% of the drive above the boom), just above the forward diamond wire anchors, the lee diamond wire is pulling down and to leeward. And that is where the mast buckled to leeward with a reefed main. The smoking gun. Removing or slacking the forward diamonds also reduces this stress. 

What if the mast raising stays were snugged and perhaps reinforced in the deck (Lower shroud)? This is a conventional rigging solutions? This stabilizes the lower mast with less compression in the critical area. It would also help to move the anchor point slightly aft and outboard, while staying inside the jib track.

Takeaways? The forward diamond wires increase compression and pull in the wrong direction without providing any useful improvement in mast stability. Best would be a re-designed mast with only one set of aft-swept spreaders. The less drastic solution is to reduce the tension on the forward diamonds; I judged 300 pounds to be sufficient preload and sailing observations confirmed they do not go fully slack.The aft diamond wires should be just tight enough to create 2.5 inches of pre-bend (as specified by Ian Farier)  and no more. These serve a purpose, but extra tension does not help. 800 pounds appears to be sufficient, and I may reduce this, based on further sailing observations in strong conditions. 

Will I reinforce the deck and improve the lower shroud? Undecided. No. The wires are too small to bother.

Time will tell, but I'm comfortable with my calculations. The mast should now be 30-35% stronger, no small improvement.

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rev. 12-7-2024

 

A few more ideas. I could support the center by running a second set of shrouds to the same anchor point. In this way, they would move together.  In addition, they would be tensioned along with the cap shrouds. My gut is that fixing the diamond wires makes this unnecessary. I have to address the diamonds anyway.