Low Friction Rings: like a donut, but sweeter

ring block dyneema

pinterest low friction ringsAs the quotable quote demands, “ask not what your vang can do for you, ask what you can do for your vang”. OK, maybe that’s not exactly how it goes – but after a few months on a pace through the islands to relative weather security in Grenada, there’s time to catch up on projects aboard Totem and tweaking the vang crept to the top of the list. Swapping that weighty block for low friction ring– the pair pictured above– is a sweet upgrade.

Boom vang improvement

When we bought Totem in 2007, she had a 4:1 tackle vang. No hydraulics, no springs, and also, no good. Thus began a series of efforts to improve the situation.

Totem’s vang upgrade history:

  1. Evaluated new vang hardware. Choked on cost. Evaluated contents of rigging locker instead.
  2. Refastened boom vang tang, with new larger fasteners (old ones were pulling out).
  3. Converted 4:1 vang to cascading 8:1 vang with a block we had and $10 of Dyneema line.
  4. Boom vang tang pulling away from boom AGAIN. Just say NO to more holes in Swiss cheese boom! Removed tang and replaced with strop around the boom, made from $10 of Dyneema line.
  5. Mast vang tang broke. Replaced with strop going around the mast, made from $10 of Dyneema line.
  6. 8:1 was good. 16:1 is better! Added another cascade with a block we had and $10 of Dyneema line.

$40 worth of ¼” Dyneema line and the vang was powered up! Ten years later, our vang is a refined simpleton of rigging goodness.

vang setup before

Why is the vang important?

It adds performance when reaching, by controlling mainsail twist (shape of the upper leech). It helps mainsail longevity by reducing chafe against rigging caused by the boom’s rise and fall when running. Also when running, the vang keep the boom from lifting and possibly inducing an unintended gybe. What happens if the boom lifts, is the upper leech collapse towards the luff, and can “back” – gybe! We run with a boom preventer, but the vang cuts the risk further.

To hang a thrifty vang left me wondering if the dang vang would go bang! Well: 46,000 nautical miles later, it did, sort of.

During those years and miles, our cockpit shrank. We blame the children. They just keep growing! Shifting the fiberglass hard top dodger forward about one foot succeeded in opening up the human space…while taking away from the vang space. And this made the vang go BANG! When the vang was eased, the upper block drooped and smacked the dodger front.

vang goes bang

Enter the low friction ring. Modest and elegant. Simple and thought provoking. What the heck does it do? It’s a type of block, but with no moving parts. And a block without moving parts means, FRICTION! Huh? To address this minor inconvenience, marketing geniuses confronted the problem by naming a frictiony block – a Low Friction Ring.

Replacing the heavy block with a 21mm internal diameter, lightweight low friction ring was the elegant solution to fixing Totem’s vang…no more bang. Let’s not talk about the Swiss cheese boom feature, but you can see why we opted for a strop some time ago. This was a no-brainer fix, and Ronstan low friction rings were stashed before we left the USA earlier this year for just the purpose.

This view brought to you by Mt Hartman Bay, Grenada

This view brought to you by Mt Hartman Bay, Grenada

What’s the deal with Low Friction Rings?

Why choose a block with more friction and a sneaky name? Several reasons.

  1. No moving parts! Yes, more friction, but no shattered sheave, chipped cheek, or busted ball-bearings.
  2. Really strong! Alloy construction and geometric shape result in far higher working loads per block size.
  3. Lightweight and tough! No maintenance required, just inspect now and then for rough edges or chafe.
  4. Low cost! As rigging and blocks go, it’s cheap. The one we used in the vang tweak is under $20.

Sounds fantastic, but… isn’t friction not so fantastic on a boat? Well, yes, and no; despite having some friction, low friction rings are a great choice in two types of applications.

Small line deflection

A line going through a block changes angle. This is called deflection. As deflection increases, so does friction. Moderate and big line deflection is the place for blocks with moving parts. Lesser line deflection has less friction, so may be perfect for low friction rings. Possible applications are: furling lines, parts of a lazy jack, foreguy, afterguy, and don’t forget the inhauler! There is no fixed number on maximum angle of deflection, because the amount of line load and type of line affect the amount of friction.

Static and slightly dynamic lines

A mainsheet has a lot of deflection and changing line loads. This is friction soup with a need to make adjustments – so it stays in the realm of blocks with moving parts. Other application can have a little or a lot of line deflection, but not require dynamic adjustment. Set it and forget it. This is the place for low friction rings. And this is where our upper vang block comes in. The line deflects 180 degrees and carries no load or a lot of load, and not much adjustment. My sailboat racing brain scoffs at the thought, but it works for cruising. Tighten the vang, secure, and enjoy the ride.

Other static and slightly dynamic line applications include preventer, leech reef, check stays, running backstays, and barbour hauler. Since this application can have big deflection and line load, the important part is that the adjustment amount must be minimal. There will be FRICTION, so if the line requires much adjustment use a conventional block. When it doesn’t, try a low friction ring for a fraction of the cost.

How a low friction ring is setup is easier to understand in pictures than my clumsy writing: here are some examples of use on Totem.

Mainsail reefing

frictionless ring

The leech reef line forms an acute angle passing through the leech reef ring in the sail. Consequently, the reefed portion of sails gets scrunched by the unreefed portion of sail and reef line, which can make reefing harder and cause sail chafe. The solution is low friction rings lashed to the leech reef ring. Use 3mm Dyneema line for the lashing, with 6 inches of separation between reef ring and low friction ring. Now the leech reef line passes through the low friction ring giving enough separation so the reefed section of sail isn’t so scrunched. The low friction ring is smoother and has a wider turning radius then the reef ring, making reefing a little easier with less chance for chafe. (More about reefing in this post.)

Furler line lead

Totem’s furler line had been lead after through blocks on the toe rail. See where Siobhan’s hand blithely rests on that Andersen winch? Trace the furler line forward from there, and see the inset zoom for where two low friction rings (orange circles) are used.

furler line- inset

The blocks previously in that spot banged on the deck, they were subject to wear/tear, and were generally just toe stubbers. You can use fancy blocks with a spring, but have you looked at what they cost? Right. That’s most of our monthly food budget! So instead of spendy blocks, Jamie lashed low friction rings as leads: a temporary setup, you know, just to trial the solution. It’s been a YEAR, they work great, and are still in their “temporary” position!

furler lead

Preventer turning block

Swapping out turning blocks used in our preventer setup is on the shortlist for low friction rings on board.  The blocks can flail around, banging the deck, and we know at least one of them shows signs of wear. The blocks in question: one on each side, at the forward point.

preventer turning block

There are a few ways to do this, but swapping the block for a low friction ring just feels like the obvious solution. Here, the fact it won’t bang as much is actually secondary to an even more desirable benefit: the ring is a stronger piece of hardware. More robust? cheaper? that’s easy! And let’s talk about systems on board we don’t want to break… the boom preventer is up there. For a more detailed description of our preventer setup, see Safety on Board: preventer setup on Totem.

Other uses of a low friction ring are climbing their way up the project shortlist. Got any to share? Add in the comments or share on Totem’s Facebook page.

Low friction rings: a sweet treat on any cruising boat.

Safety on board: preventer setup on Totem

downwind offshore ocean sailing sailboat

Boom preventer. Boom brake. Whatever you do, whatever you call it, having a way to prevent or dampen the force of the boom to prevent accidents while sailing deep downwind is important. A lot of cruising IS downwind, so thinking through a smart setup is critical! I’ll never forget learning about a boat some miles ahead of us on the Pacific crossing where a crew sustained life-threatening injuries after a crash gybe. Even a planned, controlled gybe tends to give me the willies due to the tremendous force involved: a violent, unexpected gybe can cause significant damage.

The sliver of a new moon wil set before we pull up Totem’s anchor tonight. Ahead is a challenging passage, one we’re not sure how far we’ll take: hopefully, all the way to Puerto Rico, if all goes well (follow our progress at our tracking page on PredictWind). Breeze expected is all forward of the beam, so there’s no need for a preventer– but recently someone asked about our setup. Jamie wrote it up, I took a few pictures to illustrate.

whale spout sailboat sailing ocean mountains

Whale-watching as we sail away from South Africa – preventer in place

DSC_7708What works for us will not right for every boat, but is a safe, strong, and reliable method on Totem. and I’m sharing here in case it helps others install or improve their own preventer. We like it because:

  • Simple approach
  • Side decks left uncluttered
  • No specialized/dedicated gear purchase necessary
  • Puts loads at points able to withstand them (mast/vang/midpoint of boom not intended for the shock loading involved- outboard end of boom is much better)
  • Quickly/easily released from the cockpit if necessary

Totem’s setup: Component Parts

  • 1 x boom lanyard – Dyneema single braid, with ¼” (6mm) diameter.
  • 2 x preventer lines – polyester double braid, diameter depends on sail area (Totem uses 1/2”). Polyester gives a little stretch, but not too much. Length depends on preventer block location and center or aft cockpit. Lines should be long enough that preventer set on one side can remain in place through a gybe.
  • 2 x Preventer blocks or low friction rings – we have blocks, but low friction rings are a great choice: they are more robust and lower cost.


A preventer must bear considerable loads; in the worst scenario, shock loads that will cause a weak link to fail. For this reason it’s safer to secure the preventer to the aft end of the boom. A middle boom attachment point is more likely to break the boom in an extreme situation.

End of boom attachment can make setup awkward/hazardous or require fixed preventer lines that will cross the deck and get in the way. This preventer setup splits the preventer line into two sections. One line is the boom lanyard; and the others are the preventer lines (1 on each side of the boat). The lines are out of the way when stowed and easy to deploy.

Boom Lanyard

sailboat boom

The boom lanyard is shown above as the line running below the boom. The aft end is spliced around the boom. The forward end has an eye splice to secure to the boom when not in use, as shown, and to use as an attachment point to the preventer lines. When stowed, it’s important to keep the boom lanyard tight along the boom because a drooping line can catch on something or someone.

Eye splice rope line lanyard

Eye splice at the forward end of the lanyard…and around boom on the aft end

This shows one end of the boom lanyard spliced around the boom and the eye splice in the other end. Boom lanyard length should be set as follows:

  1. Easy to secure to the vang attachment when not in use.
  2. Easily reaches the side deck when the boom is out, so it’s safe tying to the preventer line.
  3. Another use for this line is to secure the boom from swinging back and forth when not sailing.

Preventer Lines

sailboat deck

This view down Totem’s side deck shows one preventer line, stowed and ready for use. Things to note, besides those lovely clear side decks:

  1. One end of the preventer line is secured to the lifeline. The other end leads back to the cockpit and is coiled and ready for use.
  2. Fair leads are important! Note that one side of the preventer line runs outside of the lifelines. The other side runs aft along the deck and is NOT fair in this picture. You’ll see that in a later picture I reran this side to go between shrouds so it doesn’t chafe.
  3. The next picture shows me (Jamie) getting ready to connect the boom lanyard and preventer lines together. Note that I am pulling the boom outward for the picture; normally I would be sitting in an easier and safer position when underway. (Behan: you bet he would, or I’d be unhappy about it!)


Secured to the toe rail with a Dyneema loop is the preventer line turning block. Friction is not an issue with the preventer, so consider a low friction ring instead.


Location matters:

  1. Setting the block too far forward increases preventer line length and is hard to run fair.
  2. Setting the block too far aft makes a bad angle when the boom is all the way out.

Our blocks are set about 2 feet forward of the forward lower shrouds, a position that gives a fair lead and good angle to secure the boom.


Above is a snapshot of the boom lanyard and preventer line, tied together and ready to use. Do not use a shackle! The knot is much gentler should it hit something or someone. This is especially true when you do gybe (by choice). Simply ease the preventer line to allow the boom to swing over.

andersen winch

The other end of the preventer line, ideally, goes on a self-tailing cockpit winch: ours goes to one of Totem’s spiffy Andersen secondaries. This approach makes a quick release easy if needed. If you don’t have an open winch here, you can cleat the line. Either way, be sure to coil the end of the line, and keep it clear to run freely in case you need to quickly release the preventer.


Here’s the completed setup, much as it can be from our Bahamian anchorage! Notice how the preventer lead has been moved to run fair between the shrouds.

Boom brakes

For some boats, a brake makes sense. These don’t prevent the boom from crossing over, but dampen the movement. We’re not fans of this on Totem because it would place tripping-hazard lines on the side deck. But for other boats, other layouts, they’re a great option: the setup at our friend’s boat Akira, anchored a few boatlengths away, is a great example of this. Keeping it all on the coachroof means there’s no dangerous deck clutter, and they can handle it right from the cockpit.

green line runs to brake on boom, and clutch in cockpit


I’m looking forward to having a passage that requires setting up the preventer, not this upwind stuff! But for now, will tackle the upwind days ahead by cooking up a storm, checking and re-checking all stowage, and loading books on the kindle from our hometown library.

Another cutthroat game of DogOpoly with crew from the Manta 42, Akira

Another cutthroat game of DogOpoly with kids from the Manta 42, Akira: having a lot of fun with this crew.

Adults in the cockpit, kids in the cabin, paparazzi mama.

With thanks to Bonnie,  for the question and for the kind donation to our cruising kitty!