Next up, testing fenders ... but not like this.

 

Maybe more like this. I'm thinking about low freeboard and flat fenders, since they are more applicable to my F-24.

Wrinkles

 I've sailed with polyester sails lots and understand adjustment by stretching. I understand rotating masts and bendy masts and how they affect shape. If you ease off the main halyard in light air, for example, the sail becomes for full and powerful. There are some wrinkles across the bottom, but they do little harm and the sail is faster than if you stretched it tight.

But this is less applicable  to laminate sails. They stretch, but far less, and most of the shape is baked in when they are made. For example, if I really yank on the downhaul to eliminate these wrinkles (basically balancing the mainsheet and outhaul tension) I don't expect to see much change in draft or draft position. Thus, I assume the goal is normally to reduce wrinkles, since they are not the result of any beneficial shape manipulation by stretching (or not stretching) and they will disrupt air flow. In fact, eliminating wrinkles probably takes you closer to the original design shape. Smooth seems fast.

With and without Cunningham tension. A slight difference in camera angle. but if you lay a straight edge on the battens, they are the same. Without a trial horse sailing next to me, I can't honestly, accurately say which is faster because of wind and wave variations.

 

If I measure the draft and position of draft with a ruler I see no change. It seems like sheet metal. It will wrinkle if the fit is poor or if we ask it to make a compound curve.

• Jib. When the sail is first hoisted the luff was straight. When the wind comes up the luff is curves (sags), reducing the straight line distance between between the head and tack. If we don't pretension the sail it will bunch up on the forestay. These wrinkles are primarily horizontal and don't hurt much. We need to be cautious of over tensioning the sail if there is a furler; they don't like rolling under high load.

• Main, square top. The leach is falling away, requiring the top of the sail to take a potato chip shape if there is any design fullness (broadseam). Unless the sailmakers cuts this area very flat, the molded-in compound curve is violated. 

• Mainsail, tack and sliders. Often wrinkle radiate from these (polyester too), and the cause is often that the tack or reef grommet is not tight forward, but has been pulled aft by the outhaul. Even sheetmetal would wrinkle, because you have pulled it out of square. The tack and Cunningham tackles need to pull forwards as well as down. Reef tackles too. A very common shortcoming.

While I'm sure there is some bias stretch, these specific wrinkles can exist without stretch.

The question is whether stretching a laminate sail to remove wrinkles has any material effect on shape, or whether the wrinkles are generally the result of either poor fit or incorrect installation/rigging.

(I've intentionally skipped a lot of factors for brevity. It's just a forum tickler. Mast bend. Rotation. Headboard misalignment. Forgive me.)

---

I'm ordering a new laminate main, not because I don't like my current one, but because it is showing signs of delamination. It's old but still has a nice shape. Until it blows ....

Fender Washers--Basically Worthless II

12-10-2024, Rev. 8-17-2024

This spring I spent several weeks replacing a bunch of rotted deck caused by the use of flimsy fender washers.  That encouraged me to dredge up this old post. There are longer versions, with more data, in Practical Sailor and Good Old Boat.

As ramp-up for some Practical Sailor testing, I thought I would share a preview.

First, unable to secure scraps of deck material for which I could be sure of the pedigree, I laid up some of my own. The testing will based upon 1/2-inch balsa core with (1) 6-ounce cloth and (1) 17-ounce biaxial layers on the deck side and (1) 17-ounce biaxial layers on the under side.

I drill a 1/4-inch hole (no epoxy plug, block of wood on the back side) and tightened down a fender washer against it. At 10 in-pounds (about 675# load) the washer had distorted and the laminate was failing. for comparison, the bolt working load of a Lewmar 40 winch (1/4-inch bolts) with a strong grinder is about 500 pounds each. In other words, without an epoxy plug the bolt will fail under working load and standard ASME bolting load, with no safety factor for aging and fatigue. It is about 5x weaker than good design suggests. It also explains why I had a PO installed winch rip out.

By 18-in-pounds the fender washer was buckled and the nut was well into the core. For comparison, this is about 50% better than a plain pine board in each case.

I repeated the test with only lock washer. The same result! The fender washer resulted in no increase in strength. The point being, that the bolting washer provided better support in close, the end result being the same.

Testing for the actual project will involve proper epoxy plugs. However, since under the load the bolt will NOT be supported on the other side (the winch or cleat will be lifting) in the real world, the top side support will be supplied by a 4-inch diameter ring spacer, allowing the washer to pull through, if that is what it wants to do. I've tested this without the epoxy plug; not surprisingly, it lowers the failure load and creates top side damage much like I saw on my failed winches.

We'll see. But for now, the moral of the story is that fender washers are basically useless; they fail as soon as they are actually needed.

 You can buy extra thick fender washers that are double the thickness, 4 times the strength, and 8 times the stiffness (that's the way increased thickness works). Bolt Depot has , them, as well as many others. This is what the chandleries, including West Marine and Defender should carry. But they would be higher in price and we would buy the cheap ones. Which is why chandleries don't sell crappy rope. They shouldn't sell crappy washers.

[From Bolt Depot. Buy the extra thick ones.]

 

 

How to Pronounce Kamala

At my last job too many employees made a joke out of mispronouncing a Greek employee's name. It was insulting and said much about those employees.

It's really very easy. 

Comma-La

How to pronounce Kamala

Getting it wrong is embarrassing and disrespectful. It's not "former president Tramp." I guess it could be ... but that would be an adjective related to documented behaviors and I wouldn't capitalize it. Never mind, that's off the point. Donald Trump was elected President from 2017 to 2021, and I can respect that as the will of the people.

Use it up, wear it out...

Rev. 8-14-2024

... make it do, or do without.

I love projects put together from the left-overs pile.

This boat hook and fishing rod holder was cobbled together for nothing from some scraps of line and a
heavy aluminum channel that used to reinforce the inside of a fuel oil tanker. A few minutes with a port-a-band, grinder, and drill press made for a holder that should outlive the boat. Most of the time I simply through the hooks on the tramp, and they've stayed there in near-gale conditions though bouncing quite a lot, but sometimes it still seems worthwhile to tame them a bit, or simply to give them a proper place.

Like wise this chain lock came from scrap channel.


My pilot berth came from a leftover shelf.

My kayak tie-off points were purchased bolt hangers, sure enough, but at only $2.75 each and the bolts were salvaged from shaft zincs found lying in the yard, since I don't have shaft zincs on outboards.

This immensely strong genoa sheet came with the boat. Must have, since Kevlar core went out of fashion some years ago... for good reasons. Kevlar will fail from fatigue far below its rated strength if bent to sharply or flexed to often. I have used Kevlar core halyards for many years without trouble; they are sized for stretch not strength, they pass over long radius wire rope blocks, and there is little motion. However, when used as a genoa sheet at high load, secured to the clew with a cow hitch, and occasionally allowed to flog while furling, the fibers crack. In a 15 knot breeze the core let go, leaving only the badly sunburned sheath to carry the load. How it came to fail internally without snapping completely is something of a misery to me; just the right combination of winds and flogging such that it gave up from fatigue when the load was not actually great. I cut the line at the failure and sailed home with bowlines; after all, it's not worn out yet.

Note the thin spot to the left--the core is failed and bunched up to the right. The failure was right at the tack, where the rope exited the knot. This is NOT the highest stress location in the knot, that is always the first turn. It was the harsh flexing while flogging that did it.

This sheet--and a second genoa sheet for my new inside track--came from discarded halyards in the marina recycle bin.

This tablet holder was cobbled together in an hour from the might-need pile. very light and a better fit than anything I could find on the web; custom for my tablet.

• 2-ball joint mount from my first car phone (before pocket cell phones, before I got married) about 25 years ago. When I sold the car I kept it, thinking it might make a good GPS mount. A good solid annodized aluminum model.
• 4mm water proof glued plywood scrap.
• Scrap aluminum angle. Just the right depth.
• White spray paint left over from the kitchen remodel (repainted all the hinges).
• Assorted saved screws and machine screws.

My electronics are comically out of date but the they work and I'd be satisfied with map and compass. That's how I learned.

At first glance, without my glasses, this WW II poster bothered me.

I've certainly restitched the dodger and sail cover a few times each.

I've never bought line for a bridle or snubber; there is always some retired anchor rode. Same for dock lines; I either splice some up or... I've found there are folks that will throw away barely used lines if one of the matching set gets rubbed.

My dingy under-the seat-box is a milk crate. Takes the strain off the tubes, holds a few things, never rusts, and was found on a beach.


Towels and the like come from home cast offs. If I use one to mop out the bilge, no one cares.

And then there are a thoughts that fall under the general heading "Cheap Boat Keeping."

Most of use would rather put money in our 401-K or the kids' college fund than pour it in the water. I spread my maintenance funds thin as paint, using every trick I've learned over the years. It helps that my dad is a painter (watercolor artist, but also a house painter in college), my grandfather was a mechanic, and I've tinkered since I was a kid and worked around chemical plants for years. Perhaps some of these ideas will be of use to others.

1. Use your engine. Never let it sit for over a month in the winter; the lube needs to circulate and the electrics need to dry. Run it enough in the summer to turn the fuel over a few times each season; we change the oil twice each year, so why would we expect the gasoline to last longer? Engines don't wear-out so much as deteriorate from disuse. I've done lots of fuel testing in my "real" job, so I'm neither quoting from a book nor guessing.
2. Cleanout every locker twice each year. You'll find stuff and reduce repeat buying. You'll gain space and stow things smarter. You'll save weight and clutter by pitching old rubbish or at least taking it home. It will remind you to maintain a few things. Remember, carrying junk costs $20/pound.
3. Save bits and pieces of materials. Some aluminum or FRP plate, a bit of stainless tubing, some left over wire, scraps of good wood, a bit of gasket material, and leftover old fasteners; never old junk parts, but bits that might be found in a hardware store or West Marine. Keep it neat.
4. Learn sail repair (hand work). A stitch in time saves nine. Really.
5. Find a good thrift store, one that carries some marine stuff but doesn't realize it. Small towns near the water. Also a great source for Gore-Tex foul weather gear; mostly the sorters don't know the difference between a worthless windbreaker and the real deal.
6. Stay at a working marina. Often 1/3 the price of a recreational marina.  Also look for houses with a few unused slips out back, or maybe a rusted up marine railway.
7. Use a good 2-year bottom paint.
8. Learn painting and composite repair. Really, you can be very efficient with these things, given the proper tools and some practice. I figure I save a good $100/hour pre-tax; I've learned speed and quality over the years.
9. Get a book book on marine wiring. Buy a good ratchet crimper. I'm an engineer by trade, which is a good start. However, even if you only apply your knowledge to troubleshooting, it's a blessing when somewhere remote. Do professional quality work the first time or you'll lose reliability, endanger your boat when you're away, and mostly do it over some day.
10. Anchor out. Even if it means adding solar and upgrading a few things, you can save $50-$150 per night. Enjoying increased freedom is priceless.
11. Waterproof grease. Electrical connections and anything that comes apart. Teflon pipe dope is good too, particularly where aluminum meets stainless.
12. Watch chafe and wear. Lines--running and mooring--can last for many years if you don't let them rub or slap.
13. Stay in the water all winter. Of course, this depends on the area--not practical in the Great Lakes--but for most of us it's a great saver. The season can be stretched, and the boat suffers less disuse, the hauling and storage fees go away.  You will need a good 2-year paint.
14. Learn small engine repair. They're really simple. Even if all you learn to do is change plugs, rebuild a carburetor, and change the impeller, there's real savings and less chance of being stranded. You'll need some tools and parts, of course.
15. Fish! It's free and nothing is better.

In 25 years of boat ownership, I've only used contractor services for:

• Major sail work and new canvas.
• Hauling. But I do the painting and hull work!
  

As a result, I know my boat inside out; that's a good feeling and an important part of seamanship.

Stagger When You Anchor

rev. 8-14-2024

Sounds like I've either been drinking to much or sailing too long. But bear with me....

I'm convinced the average person cannot see in 3 dimensions when they look across the water. They can recognize right and left, and to some minor extent distance, but they cannot accurately relate what they see to a map-view.

Anchoring is the classic case. They move the boat to what seems like a good spot and lower the anchor,  without being able to visualize where the boat will be after they stretch out scope, or how boats may swing. They end up anchoring either very close in front of you or exactly beside you, neither of which they actually intended. They just measured wrong.

1. Calculate how much rode you will use, including an allowance for adding scope if a storm arrives. For example, if the water is 7 feet, you bow is 3 feet, and you like 7:1 scope, (7+3) x 7 = 70 feet.
2. Lower your anchor 1 rode length +1  boat length off the bow of your neighbor. This might be 1.5 to 2 mast-heights, a simple way to gauge distance if you are reproaching from astern of your neighbor. By the time the anchor tips, digs, and sets, particularly in softer mud, it will be off the beam of your neighbor.
3. Need to anchor in front?  You need to be about 2 rode lengths + 2 boat lengths (about 210 feet). Simple come up beside the boat, note the lon/lat, and move 0.039 minutes forward (a minute is 1 nautical mile, and GPS typically displays 0.001 increments). Or time the distance; 1-knot ~ 1.5 feet per second. At 3 knots, 210 feet will take about 45 seconds. The point is, do something better than just guess.

You have now achieved the optimum stagger, which will allow the maximum number of boats in a minimum space, with minimal need to visualize the geometry.

Simple.This, along with every detail of single and multi-anchor rigging that I could test, is described in "Rigging Modern Anchors."

Lazy Figures of Speach

We're all guilty of it (an example, right there!). Generalizations or truisms that contain little information are used to defend a position. False analogies and straw men that are use to tear a position down.

I'm going to stick to sailors. Politics would take a book.

Just a few from today's forum morning read:

• "I was taught to do it [this way]." I was taught that 2 + 2 = 4, but it did not become a part of my knowledge base until I was shown or figured out why it was true. I would certainly not tell you 2 + 2 = 4 unless I had some basis, other than I was told, that it was true. As you know, I do a lot of testing. That is NOT because I do not believe what I read. I always start with literature research, because many really smart people went before me. But they didn't go down every alley, not everything was published, and things do change.
• I've been [doing X] for 30 years, and [this] has always worked for me." Often used to resist something newfangled. An adding machine works, but an electronic calculator works better. A CQR anchor works, but a Rocna (or other new generation anchor) work better. This can also be used to defend practices that were never very good, but were good enough, since they were never tested in a real crucible.
• I've heard it said that.... This precedes and opinion offered without any support. The writer may not remember the reasoning, he may not have understood it, or it may not exist. We are offered no opportunity to examine the argument, and not convinced that the speaker reviewed it either. It is likely nothing more than parroting, unless followed by support.
• Non-corrosive, when what is meant is corrosion resistant. For example, this from ABYC standard relating to bilge pumps: "h. Hose connections shall be secured with a non-corrosive type of clamp."Standards are supposed to be written using the standard english meanings of words, and new words are only to be defined if you can't find it is a standard (Websters or Oxford) dictionary or if the meaning is necessarily different. Since all of industry refers to stainless steel as "corrosion resistant," this is sloppy writing. What it literally says is that the clamp should not corrode the hose, which is not what they mean.

How Long Should a Tether Be?

7-02-2016, rev. 8-8-2024

The 3' / 6' split has become a defacto standard, since these are the lengths in the ISAF standard. Well, sort of. What it actually says is that:

• 30% of the crew (or everyone if you single hand) must have a tether leg of no more than 3'.
• Every tether must be less than 6'6".

First off that means you can, and perhaps should have tethers less than 3'.

This tether is only 30 inches, is attached well in-board, and I'm well outboard. Of course, I had to climb over the high lifeline.

 At the mast in lump weather I sometimes go even shorter. How about a vertical jackline. Every boat should have these available in the form of halyards, though mine are fixed (they serve an unrelated tangle-avoidance function).

Additionally, I see no reason they cannot be longer in certain cases. My other leg is 8', bout right for the broad bow of a cat. I can imagine much longer on bigger boats. You just have to use the length intelligently.

What about smaller boats? I was fooling around on this 27' mono, using Amsteel jacklines, and concluded that the longest leg should be 3' and the shorter perhaps less than 2'. A 6' tether has no place on a smaller boat. If you would like a longer tether for the cockpit, then have a separate dedicated tether there.

I like custom sizes. I fabricate mine from 8mm climbing rope using sewn splices, but climbing webbing and knots will do nicely.

rev. 8-8-2024

The 3'/6' split is perfect for my F-24. The jacklines run along the inside edge of the tramp lacing and end 4 feet from the bow and 5 feet from the stern, and the large wing nets make it practical impossible to reach the edge. There are no lifelines, other than small sections at the bow and stern. 

 

 

 

High Lifelines

6-4-20216, rev. 8-8-2024

Standard lifelines are only slightly above the knee; helpful, perhaps, but not reassuring. For example, reaching over the side to add a sheet to a sail clew can be a little unnerving.

While researching jacklines materials I came a cross a lot of references to high lifelines, rigged to the shrouds. I poo-pooed the idea for years, but now that I have actually tried, it, I think I was wrong, at least for this boat. Yes, they are in the way just a bit, but they make going around the side without a jackline that much safer, they make it safer with a long tether, and they make it better when rough or for those with balance problems.

I used a length of old Kevlar genoa sheet (you want something non-stretch). I investigated all manner of fancy shroud attachments, but a clove knot worked best, with a little tape under it to prevent sliding. Attach it to the lifeline in such a way that the tension is carried by the lifeline, not the stanchion (it looks like I tied the forward end to a stanchion, but there is actually an eye for a gate). The aft end is tensioned with a lashing to another gate terminus.

Reaching out feels casual with a lifeline at your waist.That water is only 45F. Falling in under spinnaker, even on a calm day like this, could be life threatening. Note that I am also clipped to a short tether.

The high line makes a good handline that doesn't stress the stanchions.

Dynamic Tethers

 rev. 4-19-2014, rev 8-8-2024

Stitched Splice Warning. Based on limited testing we have found that nylon rope is much different to sew than polyester rope. Because of the extreme elongation prior to break, the stitching at the tail must carry nearly all of the load, while the stitching near the throat carries no load. It is rather like tug-of-war with a bungee cord; only the 2 men nearest the center can do any work.

Because of this difficulty, I strongly suggest all dynamic tethers be knotted rather than sewn. Climbing ropes have very high knot strength and are drop-tested with a figure-8 to attach the mass. A double overhand noose has also been drop tested. 

[Since this article I switched to a webbing retracting Proline tether by Wichard. I don't like the clips quite as well as the  Kong Tangos, but once you get used to them they are very good. The webbing has a bit more stretch than the prior polyester webbing and can pass the ISO drop test, but with a terrible jolt. After 5 years, the elastic is about shot, so the long tether droops dangerously. It has a quick release on the harness end, but I have mixed feeling about something that can release when I don't want it to. This winter I will either buy a new tether or build a new dynamic tether with Kong Tangos on for all three clips (On my F-24 we detatch the rope end as well, rather than leaving the tethers on the jacklines.]

This subject is a little too esoteric--for most sailors--and so magazines aren't much interested.   Fatalities due
to tethers breaking are rare. On the other hand, bruised ribs and back injuries are more common, but wrongly accepted as a part of rough weather sailing. However, if  we simply apply what we know from climbing about falling--lots or real world experience and lots of lab testing--it just doesn't need to be that way. Let's see if I can sweep away a few bits of conventional wisdom that are just plain wrong. Though you may never sail the Sydney/Hobart, capsize your boat and test the limits of  the human body, routine bumps against tethers don't need to hurt either. We can make our sailing experience more comfortable and safer at the same time. My tethers don't hurt.

____________

Dynamic tethers spliced from 8mm ice climbing rope. Knots would serve just as well. 10mm climbing rope works, but it is heavier and a little rolly if you step on it.

I started my investigation into soft tethers and impact forces years ago, but honestly, my boat is not the ideal
test bed; catamarans don't heel, I don't sail in big waves, and I'm not as willing to risk physical trauma as I used to be. I hold on and I don't fall. However, I've let myself slam into tethers intentionally a few times, just for testing, and I'm not happy with the current state of design. My back is too old.

Let's step back for a moment, before we charge forward, and state the limits of our investigation. We're not discussing jackline and energy absorption. I've covered that before and common experience indicates that a jackline will absorb enough energy to safely slow the sailor. I am discussing only the case of a sailor clipped to a rigid point.

While the Screamer/webbing combination is a huge safety improvement over the typical non-elastic tether, it is really engineered for a different purpose; to catch severe impacts in a survivable way for climbers and workers wearing hip or full body harnesses. Sailors, on the other hand, have a chest harness, which is lousy at distributing force. The screamer is just too hard.


A little backyard testing

I do NOT suggest this as you can easily hurt your spine. I've climbed enough to know what I was getting into.

• Anchor one end of the tether to an immovable object, in this case a large tree wrapped with non-stretch line.
• Create several tethers, 6 feet long from test materials: 1-inch nylon webbing,  1-inch webbing with Yates screamer, 10.4 mm dynamic rope (UIAA single), 8.2 mm dynamic rope (UIAA double).
• With increasing amounts of slack in the line, run at the end of the tether as hard as you can back first.

Results:

1-nylon webbing with Screamer. A very tough stop. With about 3 feet of slack I was able to just get the Screamer to trigger and it hurt. My back will complain for a few days.
10.4 mm rope. Firm stop. I didn't go further than 4 feet, not wanting injury. I'm sure I could have run from 6 feet with no harm, though it would be a jolt.
8.2 mm rope. Even at 6 feet and with a sore back, the stop was practically fun. It might take you off your feet, but was no harder than hitting a well padded couch. At 2-3 feet it was only amusing, with about 1-foot of stretch.
1/4-inch Amsteel. I was smart enough not to try. It would be worse than webbing without a Screamer.

General Observation. I wear my harness high, nearly in the armpits and definitely on my lats. If the harness had been worn lower, where catalogs show them or where combo PFDs fit, I would have injured my ribs.  Whiplash is also a problem. Wearing a harness down near the solar plexus and lower ribs, where so many are located, is plainly dangerous.

In the end, only the 8.2 mm rope felt good, thought the 10.4 mm was livable.


Data and Calculation

Is it strong enough? 8.2 mm line is not 5000-pound rated, but as we will see, it is far tougher (can absorb more energy) than 1-inch webbing.

What do we know from laboratory and real-world fall data? For new products....

• Webbing tethers are just adequate: They occasionally fail at forces near 4000 pounds. Rare, but we can use that as a design point. 
• 1-inch webbing can just manage a 6-foot fall with a 185-pound rigid mass; this is generally considered as equivalent to a 200-pound person, since the harness and body absorb some energy by deforming (data from DMM, a climbing equipment manufacturer).
• 10.4 mm UIAA single rope can manage more than 10 falls from nearly twice this distance.
• 8.2 mm UIAA double rope can manage more than 10 falls from nearly twice this distance with a 242 pound rigid mass (261-pound person) using 2 strands.
• 8.2 mm UIAA double rope can manage more than 10 falls from 6 feet with a 242 pound rigid mass (261-pound person) using 1 strand. Thus, it is more than 50% tougher than 1-inch webbing.
• 8.2 mm UIAA double rope can manage one fall from nearly twice this distance feet with a 242 pound rigid mass (261-pound person) using 1 strand. Again, it is more than 50% tougher than 1-inch webbing.
• 1/4-inch Amsteel is the worst material that could be used. While strong, its energy absorption capability is negligible. Its only advantage over chain or cable is light weight.

I created data using well-used products. Why used? Because they will become so, obviously. Less documentable and less repeatable by others--science is all about reproducible results, be they real-world or not--but ultimately more practical.
 

 Percent Elongation (left) vs. Pounds Stress, pounds (bottom)

Webbing is 3-5 times stiffer than dynamic rope. Amsteel is very stiff.

I took the samples and pull tested them up to 2500 pounds; I didn't feel like destroying my tether just yet. I used on-line data  to extrapolate out to the breaking point of each material. In dynamic situation, the breaking strength and the elongation to break is typically 30% less and energy absorption about 3 times less, but for blog post purposes, the above data at least allows comparison on an equal basis.

What matters is the area under the curve.

Static Energy Absorption, 6-foot tether, ft-pounds (left) vs. Stress, pounds (bottom) 

Static calculated energy values are greater than fall values for 3 reasons:

• Ropes are tested with figure-8 knot, weakening rope by ~ 40%.
• Dynamic testing does not allow for heat dissipation and reorientation of fibers.
• Dynamic ropes survive 8-12 falls, the webbing only 1 fall in our test data. Dyneema survived zero test falls.

Dynamic Energy Absorption, 6-tether, ft-pounds (left) vs. Stress, pounds (bottom) 

 At lower stress, 8.2 mm rope absorbs more energy for a given impact force, but eventually 10.4 mm rope has greater capacity. Both dynamic ropes have greater energy storage capacity than webbing. 8.2 mm rope is more than twice as tough as 1-inch webbing.

Both this data and UIAA drop data thus confirm the following:

• 11mm rope can absorb many fall factor 2 drops.
• 8.2 mm rope can absorb 1 fall factor 2 drop.
• 1" webbing can absorb 1 fall factor 1 drop.

What happens in a 6-foot test fall?

• 1-inch webbing: At 4000 pounds impact, 1100 ft-pounds energy. We know from fall testing, however, that 1-inch webbing can only absorb about 1100 ft-pounds (sometimes passes, sometimes fails), so we will use 1100 ft-pounds as the design point.
• 10.4 mm rope:  If we accept the design point only 1100 ft-pounds of energy, impact force is about 1400 pounds. New rope fall data indicated significantly less.
• 8.2 mm rope: If we accept the design point only 1100 ft-pounds of energy, impact force is about 1100 pounds. New rope fall data indicated significantly less.
• 1/4-inch Amsteel: Only 236 ft-pounds of energy were absorbed by the point 5000 pounds of stress were reached, and only 677 ft-pounds of energy were absorbed at the break strength of 8600 pounds. Amsteel will kill the sailor and pull the harness apart before surviving a 6-foot fall. This has been duplicated in real-world fall testing with spectra products; Dyneema is worse.

If we limit the fall to something more reasonable--a 2-foot fall is similar to wave strike and 6 knot stumble, and more severe than my backyard testing--the energy for me is only165# x 2' = 330 ft-pounds, which can be absorbed by a 500-pound impact; you'll feel it but not get bruises. With a webbing lanyard it would be 3 times that pressure and you will be injured. A Screamer will trigger but not be fully spent (though they are single-use).

How much energy can a Screamer absorb? About 270 foot-pounds according to several testing sources, or about 25% of a 6-foot fall; in combination with the stretch of the webbing, enough to reduce the impact force below 2000 pounds. And then you bottom out and the force goes up, though less so.

Other Factors. Does the extra stretch bother you? Probably personal. Is stepping on rope a greater hazard than webbing? For 8.2 mm rope, not much, but on a monohull (sloping decks) that may be more of an issue. Construction? Either knots (testing assumed figure-8 knots) or sewn eyes are practical.

A critical biometric factor, not easily relayed by a machine or simple data, is that a force that comes on gradually (the dynamic rope) allows the muscles time to tighten and resist. A sudden 500-pound kick before a screamer gives is painful and damaging, like a blindside blow, even at the same force level. You truly feel the difference. 

Dynamic rope or a screamer--The best solution? For smaller, more routine falls on the deck, the rope is
kinder. For that once in 100 sailors' lifetimes, torn from the cockpit by a rogue wave impact, the screamer/webbing combination is competitive, though the climbing rope tethers are still survivable without serious harness impact injury; both could have impact forces of 1000-1500 pounds depending on the force of the wave, and it would hurt, but not break ribs or vertebrate. A climbing rope, even 8.2 mm, has greater energy absorption capacity than a webbing/Screamer combination. Thus few climbers use Screamers, but they ALL use dynamic ropes.

The only disadvantage of rope over webbing is the  potential for rolling under foot. A dynamic webbing would be nice, but I could not find any. On a catamaran this is a limited problem (level decks), and the roll-under-foot potential is reduced by the small size of 8.2 mm line (5/16-inch).

What have I done? I've switched to 8.2 mm dynamic tethers. It is kinder on the back for minor falls and even over the edge. It is lighter than the webbing/Screamer combination and easier to hold on to.

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Where to get limited quantities of dynamic (climbing) rope?
MEC sells both single and half rope off spools, by the foot.
Half Rope,
Single Rope.

Testing of Stitched and Seized Eyes

11-15-2013, rev. 12-31-2013, rev. 8-5-2024

A few weeks ago I posted that stitching and seizing an eye was a viable alternative. I've had stitched eyes outlast the line and no failure, but given the high load on the genoa sheets, I though some back-up calculations were in order. I broke out and old rock climbing gear testing rig and did some breaking.

All testing with used 1/2-inch Sta-Set polyester double braid. All tension figures refer to a sewn or stitched eye. Stitching was hand work, round stitching with sail makers needle and doubled 50-pound waxed whipping twine, about 3/16" apart and about 25% of the distance to the rope centerline, staggered slightly. All seizings were hand tight (about 1-pound, allowing for slippage) and side-by-side, about 40 per inch. Three trials of each fabrication, the minimum of which was used for all calculations. The whipping twine was tested to confirm the 50-pound rating. The angle formed by each eye where it was slipped over a beefy eye was 20-30 degrees; certainly realistic. If for some reason a wider angle is needed, a sturdy throat whipping is in order, with sufficient thread count to keep the throat closed. On 1/2-inch line this should amount to about 25 turns, or a 1/2-inch whipping, just to be safe. However, we did not use a throat whipping during the stitched eye trials.

Rounds Stitching on the Outside Quarter. At 4500 pounds tension a maximum of 9 round stitches on each side (total of 18) of doubled 250 pounds per round stitch (2 passes of doubled twine) . At 2000 pounds 4 stitches on each side (total of 8) also carried 250 pounds per round stitch. This is with the end of the thread unsecured (I cut the last stitch with a razor knife) to simulate wear. Over 8 trials, the variation per stitch was less than 10 pounds. Each time the failure was abrupt, the line only slightly distorted around the stitches, and no line damage resulted even from repeated stitching and testing to failure. Thus, I have no reason to believe that the the eye should be significantly less than 100% line strength; probably 90% like most splices. I will test some smaller line to failure to confirm this.

This works out to 62.5 pounds per strand or about 125% of thread strength. Some of the load is carried by friction around the eye and some by line to line friction, while at the same time the angle of the stitches increases stress. Anyway, it all works out to 62.5 pounds per strand. Thus, 20 round stitches on each side of doubled 50 pound line should give a failure strength = 80 passes *2* 62.5 = 10,000 pounds. A nice safety factor. Hard to believe on a gut level, but watching those few stitches holding 4500 pounds set the mind at ease and proves the engineering.

Stitching Through the Core. This time I simply ran  a plain stitch through the core about every 1/4-inch. Over the course of 3 trials up to 2500 pounds, the result was the same; 50-60 pounds per strand. Advantages or disadvantages? On smaller line, 5/16-inch and smaller, this is easier and perhaps less likely to damage the line. However, the problem is the distance needed for the required number of passes. Assuming we sew two lines, rotating the rope 90 degrees, the maximum stitch count is 16 per inch of line or 800 pounds of holding per inch. The second pass can be difficult (the line is compressed) and could be damaging (the fibers are more likely to be cut by the needle, as they cannot move out of the way). Neglecting that factor and ignoring the last 1/2-inch or line....

• 1/4-inch, 2000 pounds:    3 inches
• 5/16-inch, 3000 pounds:  4.25 inches
• 3/8-inch, 4000 pounds:    5.5 inches
• 1/2-inch 8000 pounds:   11.1 inches

So for larger line this gets a bit impractical; my Warp Speed sheets I would need 28 inches of stitching! Of course, they can be combined. Sew the center line first, as the line will be compressed if the edges are sewn first and the needle very difficult to pass through.  A positive is that the stitches pull down into the weave and are thus partially protected from abrasion. If the tail is to be tapered to keep it smooth, a few round stitches will be need to hold the cover down.

Myths:

• The failure of one stitch due to wear can cause zippering. Not true. In fact, in some cases, aft the eye would not break at the full capacity of the test rig (5ooo pounds) I would cut stitiches with a razor until it did fail.While this reduce the average load per stitch to some extent (20-30%), they were still immensely strong. the first example (18 stitches at 4500 pounds) was obtained after cutting excess stitches away under load!
• Pre-compression with clamps or basting down the center helps. Nope, not what we found. As stitching progresses the rope gets quite compressed (round stitches do that). Pre-compression makes it very difficult to get the needle through and results in more fiber damage.
• Even stitch tension is vital. Nope, I'm not a machine and I don't do particularly neat work. While we didn't go around leaving slack in the stitches,  an obvious corollary of the stitch cutting experiment is that moderate tension variation doesn't matter. The waxed twine merely slides a little, like a lashing, and the stress is still carried evenly.The zig-zag shape of a round stitch probably promotes this, one of the reasons a zig-zag is always used in sails, even back in the hand stitching era.

Seizing.
Plain Seizing. Surprisingly, seizing was very hard to quantify. It seems to depend very strongly on the surface of the rope and it seems clear to me that it made more sense on the 3-strand rope of old, where the strands could lock together.

Since the seizing were drawn up about 1 pound with 40 passes per inch, about 80 pounds per inch of

Pre-load. On the other hand, the line shrinks under tension, so there is probably no actual preload.

Instead of counting strands I measured the length of the line-touching-line seizing. The failure was not The force to start sliding varied from 800 pounds per inch of seizing, so a 2 inch seizing should hold about 1600 pounds as a loop. Apparently not much additional clamping force is generated by the strain as the load comes on. Not much value here, compared to stitching. Perhaps the value of seizing was different back in the day of laid natural fiber ropes, but now it is more a matter of protecting the stitching and perhaps reducing fatigue; it would keep stress off the stitching at stress below the point of sliding.
by breaking but by sliding, so there is no point in using heavier thread for strength (UV and abrasion are another matter).

Would a second layer of seizing help? Mostly a second lay prevents abrasion and UV damage. That is the way the old-time sailors saw it.

What about shrinkage with wet dry cycles? That is the greater concern, as a loose seizing is undependable.

And yet, I have used seized-only eyes a few places for many years. Why no failures? I seriously doubt they ever saw stresses above the sliding point. In fact, one of the lines I tested with was an old seized bridle line and it held without apparent strain to 4500 pounds. There were 3 inches of seizing,which brought the capacity to 2400 pounds, plus there some stitching under the seizing, used to hold things tight while working. The 2 acting together shared the load, most likely never passing 50% capacity, and the construction probably matched the breaking strength of the line. Knowing what I do now, I would have added more stitches!

An historical note: 1/2-inch hemp rope had a breaking strength of 2350 pounds. 3-4 seizing totaling 3 inches would have constituted a 90% efficient termination and could have been used make exactly shaped eyes, and tarred and made with linen thread, would have lasted as long as the line. They knew what they were doing. It just does not apply to double braid.

Wracked Seizing. 
I went back a few weeks later and tried a wracked seizing. In this case, instead of simply wrapping the line , the wraps for a figure-8 around the twin strands. I tried #4 whipping twine, #8 whipping twine, and mason's twine (equivalent to #16 unwaxed whipping twine; 1/12 of line diameter is generally recommended (1/2-inch Staset), in this case, #8 whipping twine. No change, it slid at 800 pounds/inch. Perhaps wracking turns made a difference with laid rope, they don't with double braid.

Note on photos, to right: The line broke right at it's rated strength, not at the knot (modified fugure-8), not at the splice, but in between. Both the splice and knot are very near line strength. Just 10 stitches and a small throat whipping held 2100 pounds. The knot is a modified figure-8.

 

Nylon rope is even more difficult to seize than polyester. The problem is that nylon shrinks when it stretches and the seizing comes loose. In fact, even seizing a nylon rope o protect stitching is difficult in high-load applications, because it comes loose when the rope is highly loaded. You could seize when the rope is under high tension, but it's easier to cover it with webbing  or even heavy duty heat shrink.

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The moral of the story? Stitched eyes can be quite strong and reliable. They are even quite forgiving of poor technique. They are far more common in industry than spliced eyes. However, they do not have the same abrasion and UV resistance and should be protected with chafe gear. Seizings look strong but are best thought of as protection for the stitching underneath.

Because of variability in stitching method and rope, and the greater exposure of stitched eyes to UV and wear, it is certainly good practice to apply at least 3x the calculated number of stitches. It's easy to and gives a margin for wear.

My stitched and whipped eye (100-pound Kevlar thread in this case) should have a strength near that of 1/2-inch Warp Speed (stitching and whipping = 25*4*(100/50)*62.5 + 3,000 = 15,500 pounds), although the winch would fail, clew pull out and forestay collapse long before that!