How to Choose & Optimize Sailboat Clutches

Clutches are designed to hold highly loaded lines that can be hauled in and released with the aid of a winch.  Choosing the proper clutch for a given application on a sailboat is determined by two main criteria:

  • Line Diameter
  • Maximum Line Load Holding Rating

Additionally, there are other factors which can affect a clutches’ performance and influence which you may choose.  In this article, we will walk you through how a clutch works, how to choose a clutch, and how to mitigate potential performance robbing issues.


Clutch Basics

How to Operate a Clutch

A line running through the center of a clutch is cleated or held when the handle is closed. While closed, a clutch will allow you to haul in lines although this causes friction, making the task more difficult and reducing the life of the internal parts.  Also, clutches will grip line better (more immediately) if they are eased closed on a loaded, stationary line.  So ideally lines should be hauled in with the clutch open (handle cocked open).  Once a line is completely hauled in, the clutch can then be closed to engage and hold the line optimally.  The clutched line can then be removed from the winch, freeing the winch for other tasks.

To release a clutched line, fully load the line up on a winch first; otherwise, the line will ‘grate’ and abrade on the holding surface of the clutch upon release. Zero line movement when the clutch is released is ideal to preserve the cover on the line).  Once open, ease out the line as desired using the winch.

NOTE: Although most major clutch manufacturers state that their clutches can be released under load, this should only be an emergency backup to property releasing a line.  Emergency releases (unclutching under load) of a line from a clutch causes destructive stress to line covers.  Repeated releases can literally tear the cover apart.  The higher the line is loaded, the more possible damage to the cover.  Always take the load fully up on a winch before opening a clutch if possible.

Jammers Verses Clutches

Jammers are also designed to hold highly loaded lines that are usually hauled in and released with the aid of a winch, but there are two main advantages to clutches over jammers.  First, lines can be adjusted in, if need be, with the clutch closed, and the clutch will automatically hold the line when tension is released from the winch (still better for wear and tear reduction on the clutch parts and rope if you can adjust the line with the clutch open).  Classic jammers require you to shut the jaw manually, after hauling the line in before taking the load off of the winch (Note: a few ‘new generation’ jammers will auto-engage).  Secondly, jammers cannot be opened under load, and the load must first be taken off using a winch before you are able to open the jammer and release the line.  In an emergency, fully loaded lines can be released from a clutch by simply opening the handle.

How Clutches Hold

The key to clutches holding a highly loaded line securely, and with no slip, is about maximizing the line holding surface area of the clutch that comes into contact with the line’s outer jacket.  Second is the amount of friction the holding surface can generate, without damaging line.


Spinlock’s clutch uses a serrated aluminum cam that compresses the line against a serrated, slightly curved aluminum bottom plate.

Antal’s clutch uses a ‘V’ shaped serrated stainless cam that wraps partially around the line to engage more line surface area.  It compresses the line against a curved, narrow, moderately serrated section of the bottom plate.  This narrow strip is able to penetrate into the ‘V’ of the cam, to aid in encapsulating more of the line all the way around.

Lewmar’s clutch uses a series of ‘domino’ plates that the line runs through, which are pivoted forward, and down onto the line.  This compresses the line, causing it to snake up and down, and through the plates, which locks the line.  Because the line and its cover are being compressed over a larger/longer area, this type of clutch generates the least amount of cover wear.


Lines & Clutches

Considering Line Diameter when Choosing Clutches

Most clutches will have a range of line diameters they are designed to hold.  If you take a clutch rated for line diameters from ¼” to ½”, the ½” line will provide the clutch substantially more surface area to ‘grip’, compared to the ¼” which is half the size/surface-area.  The clutch will have a maximum holding load based on the larger ½” line.  If you are using ¼” in the same clutch, you can expect a much lower holding load.  Most clutches will lose between 25% – 60% of their holding ability as you move from their maximum line diameter rating to the smallest line diameter in their range.

Tip: When matching clutches to line diameter, be sure to choose a clutch where line diameter is at the top of the clutch’s designed diameter range to ensure no slip holding when the line is highly loaded.

Considering Line Types in Relation to Clutches

There are three basic categories of line when considering clutch performance:

  1. Classic double braid polyester
  2. Lines with high tech cores (Dyneema, Spectra, Technora, etc.) with polyester jackets
  3. Lines with high tech cores and high tech, abrasion resistant covers (Technora, PBO, Kevlar blended with polyester).

Classic double braid polyester

Low stretch double braid polyester lines were the first to be used in clutches. They were large in diameter (compared to high tech lines available today), so they presented ample surface area for clutches to hold.

Although these polyester lines are a low stretch line, they do have a lot of elastic stretch compared to today’s high tech lines – up to 4 or 5 times more.  So, if a highly loaded polyester halyard were to slip one or two inches in the clutch, the elastic recovery of the line would make this virtually unnoticeable and would not substantially change the load on the line.  Polyester lines are less demanding of clutches and perform well in them.

High tech core with Polyester Jacket

High tech cored lines with polyester jackets present the biggest holding challenges for clutches, and are the most prone to damage by them. These line types are by far the most popular performance line upgrade and can perform exceptionally well when spec’d, installed and used correctly.

Clutch adjustments

High tech lines provide higher strength and lower stretch (recoverable elongation) than double braid polyesters.  The higher strength means a halyard (or other control lines) can be of a smaller diameter (saves money, less weight aloft) than a polyester line doing the same job.  This smaller diameter presents less surface area for the clutch to hold.  So if you upgrade a halyard to a smaller diameter high tech line, clutch holding often becomes a new issue.

Spinlock Replacement Cam

Spinlock Replacement Cam

With Spinlock clutches, there is the ability to change out cams in their XAS, XTS, and XCS clutches that are optimized for the smaller diameter line. Antal clutches have the ability to change out the base plate in all of their V-Cam clutches to better hold smaller diameters lines too.  Additionally, if the existing cam or baseplate serrations are worn, you should replace them with new to regain high holding load performance.  For non-cam clutches, you may need to replace the entire clutch with one that is optimized for the new, small diameter line.

Antal Base Plate



Line bulking adjustments

Another option is to add diameter to the line where it is clutched.  This can be done with the addition of a second cover, or a core bulk splice:

Cover bulk splices take a larger diameter cover-only which is slid over the line area to be clutched.  The ends of the second cover are tapered and buried back into the line’s existing cover.  Note: Mainsail halyards – for reefing, this may need to be done in multiple locations.

Core Bulk splices take a Dyneema single braid and insert it in the high tech core of a line, which will intern increase its overall diameter. It’s preferred because it will not be affected by any core slip. The limiting factor for this splice is the tightness of the line’s existing cover.  A few covers are so tight that this type of slice is not possible, Most lines will allow for a 1/8” core insert, while others with a looser woven cover, may accept a 5/32” or larger insert.

Cover adjustments

The second issue with this type of line material/construction is in the cover.  This is especially true when racing, as lines are aggressively downsized, highly tensioned, and may not always be properly released from the clutch.

Double braid polyesters carry the line load in both the cover and the core, and both have equal stretch properties; so the cover stays attached to the core (stationary).  High tech lines carry all of the load in the core, and the much less strong polyester cover struggles to stay attached to the core under load.  When the cover slides on the core of a highly tensioned line in a clutch, this is interpreted as halyard stretch, or clutch slip.  In reality, the cover is staying stationary in the clutch (not slipping), but the core is slipping inside the cover.  This creates loss of line tension and creates huge stress on the cover, which is now bearing line load it was not designed for.  Preventing cover slip is the key to performance and longevity with these types of lines.

If you think of the Chinese finger trap as the cover on a line, and your fingers as the core of the line…  If the trap is wide and open, your fingers slide in and out easily (slip in and out).  If you pre-tension the trap on your fingers, then the harder your pull, the more trapped your fingers are (and the trap holds your fingers without slipping).  It is the same way with lines.  If the cover is loose on the core, the core can slid through it and appear to be stretching when the clutch is closed.  If the cover has all excess material ‘milked’ out of it (pre-tensioned) and has been properly seized at its end to keep it that way, the cover will more likely stay attached to the cover when clutched.  After a break-in period with new halyards, it is not uncommon to experience the cover loosening, or bagging up.  If this happens, cut off the seized bitter end of the line, and tie the working end of the line off to a strong fixed point.  Then with gloves (we use sticky Nitrile gloves in the APS rigging shop) or a rag, you want to repeatedly pull the cover, under as much grip/tension as you can, down the entire length of the rope (from working-end to the bitter end).  Once done, cut the excess cover away at the bitter end, and seize the end in place.  This applies to cover bulk spices (second covers) too.


Lastly, to further aid in preventing cover slip (and help reduce cover chafe damage), for both racing and cruising sailors, treat lines with Spinlock’s RP25 in the area(s) that are clutched.  The PR25 coating is a chemical with a low viscosity that penetrates the outer cover, coating all the fibers as it goes on into the core bonding the two together. This action not only assists in preventing cover-to-core slip by 10%, but also improves resistance to both internal and external abrasion by 40%.  It is a simple process to apply, and highly recommended.  It only needs to be applied in the clutched areas.  For main halyards, you may need to apply it in multiple areas for clutching with reefs in.

So, polyester covers serves to protect the high tech cores, and make them grip-able, clutch-able and winch-able.  Clutch manufactures walk a fine line with designs that are good at holding these lines (aggressive grip), while not abrading the cover.  In fact, Antal states that these types of lines ‘prove to have poor resistance [to clutch generated abrasion]’.  With this said, you should not be dissuaded from using these types of lines by any means.  They are extremely popular, and great performers.  The key is to make sure you follow best clutching and unclutching practices as mentioned earlier, and consider applying RP25 to the clutch areas.

Tip: to dramatically increase the life of polyester covered high tech lines, winch in lines with the clutch open, and always use a winch to fully unload the clutch before opening it.

Tip: order your halyard a few feet long.  If it begins to show wear in the area that is clutched, pull the halyard from the mast, cut the halyard shackle off, have it spliced to the opposite end, and rerun the halyard.  Presto, a like-new halyard in your clutch.

High tech core & cover

High tech cored lines with high tech abrasion resistant covers are designed to hold up to and perform well in clutches. Even at very high loads, and with the occasional loaded release from a clutch, they have substantial resistance to clutch wear.  Due to the low stretch properties, and tightly woven construction, cover slip is not usually a major issue.  As long as clutches used with them are properly matched, the only real downside is that they come at a substantially higher cost than other lines.  For some high-performance race boats, this type of line may be the only choice for dependable performance.  For cruisers, this type of line is not usually considered necessary.

Spinlock Ceramic Base & Cam

Spinlock Ceramic Base & Cam

Additionally, Spinlock has a ceramic coated cam and base plate upgrades for their XTS and XCS clutches (sold separately) that are designed specifically for these types of covers.  They resist wear on the serrations and last longer, they have higher holding loads, but the largest benefit they offer is in the initial ‘take up amount.’  Once a line has been hauled in and the clutch closed, the load is eased off of the winch and transferred fully to the clutch.  As this is done the line travels slightly back, to fully engage in the clutch (the take up amount).  The ceramic parts do a far better job of reducing this distance, as they engage with the cover more quickly.  This is substantial performance enhancement for racers who require highly loaded lines to stay fully loaded, and right where they set them.


Choosing Clutches – Line Diameter & Holding Load

Use the charts below to compare the line diameter ranges and maximum holding loads from clutch to clutch.  If you line will be highly loaded, look for clutches with high holding loads (red) that show your line diameter at the top of the clutches’ diameter range (blue).

Clutches for Small Boats (27’ LOA and Below)

Clutches for Medium to Large Boats (28’ – 54’ LOA)

Clutches for Large Boats (50’+ LOA)


Cleaner Decks, Fewer Winches

Image courtesy of Harken

If you have an older cruising boat with dedicated winches on the mast for halyards, boom for outhaul, and multiple deck top winches, you can greatly reduce the number of winches you have, and simplify your deck layout with these controls lead aft to the cockpit.

Spinlock Clutch Bank

Having banks of clutches with deck organizers behind them will allow you to use two cabin top winches for all of your halyards and major control lines, and all of this from the safety of the cockpit.  When purchasing double or triple banks of clutches, be sure you are clear on the line diameters they will be used with.  You may mount a double clutch with a diameter range for your smaller control lines, and a bank of three clutches optimized for your large diameter halyards (or another combination that works for you line needs).

Tip: When re-leading lines aft, be sure to group like line diameters together such that they lead to clutch banks optimized for their diameter.


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