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Jib Reefing & Furling Q&A

Designed for Cruisers

How do I select the right furling system for my boat?
To choose the correct furling unit and accessories, you will need to know the clevis pin diameter as well as your headstay length and diameter.

What are the differences between Harken's MKIV and MKIV Ocean cruising furlers?
Both are designed for longevity and ease of use, but the MKIV has additional features that make it more suitable for performance cruising and racing.

Foils Aerodynamic foil profile. Double grooves for faster hoists, douses, and sail changes.

C-shaped open connectors with low-friction plastic isolators slip onto the headstay wire and into foil for easy installation.
Single groove, round foil profile for easy rolling.

Pass headstay wire and marine eye through foils. Cut top foil to fit. Bottom foil adjusts to fine-tune unit length.
Halyard and Tack Swivels Independent swivels for improved sail shape. Fixed swivel.
Drum Split drum removes for racing. One-piece fixed drum, spool, and guard.
Line Line is included. Line is not included.


I am an avid cruiser. Occasionally I cruise with my wife and kids, and sometimes I sail alone. Do you have a simple furling system that my family and I can operate easily? One that is dependable and doesn't cost an arm and a leg? 
Art Schmickter, Great Lakes cruiser
The MKIV Ocean furling system is simple and affordable, but has the same Harken engineering durability as MKIV and free-rolling, low-maintenance ball bearing system. You will be able to reduce and increase sail area quickly to keep your boat balanced and moving. - Rick Wilfert, Harken Technical Service.

I plan to keep my boat for a long time. Will the MKIV Ocean furler hold up long term without a lot of maintenance?
The round foils are aluminum and are clear-anodized for durability. Foil joints are extremely strong and will withstand years of heavy reefing loads.The one-piece drum, spool, and guard are molded from composite which is better for the application than metal because it won't dent. Guardposts are stainless steel for a dependable, long-lasting system.

How can I reduce heel and get better control with a reefed sail?
For best results, use a sail designed specifically for reefing with your MKIV Ocean furler. Reefing sails should be designed to have good shape from about 5 to 40 knots. Additional sail shape adjustments can be made by increasing or decreasing halyard tension and by changing genoa lead car positions. After reefing, simply move the car forward so the sheet between the car and clew points to the middle of the luff.

Why do I need more than one jib if I can just reef?
Experienced seamen rarely sail without a heavy-air jib because even the best all-around reefing sails can fail. In a blow, you should change to a reefable heavy-air sail before leaving the harbor. A storm jib is vital for offshore passages because of the possibility of hurricane weather. In light air, having a large, lightweight genoa can make sailing a lot more fun.

Can I change sails with my Harken jib reefing and furling system?
Yes. Changing headsails is simple. Just attach the head and tack to their shackles, pass the luff tape through the feeder, and hoist. The feeder smooths out wrinkles and minor twists in the sail so you can easily raise sail while at the mast or in the cockpit.

What is the proper luff tape for my furler?
MKIV Ocean Units 0, 1, 2, and 3 use #6 luff tape. #6 luff tape is 0.1875" in diameter (about 5 mm).

Should my new sail be made with a high or low clew?
Most furling sails are designed with a high clew to give the lower part of the sail a better wrap around the foils, and to improve visibility under the sail. A sail with a moderately low clew has the greatest efficiency and will maintain good visibility because the tack of the sail is raised off the deck.

Do I need to alter my sails to fit the MKIV Ocean furler?
That depends. If you are replacing another furler, check your sails to see if they have #6 or 5 mm diameter luff tape. With a new installation, specify #6 or 5 mm luff tape when you take your sails to your sailmaker. In addition to adding the luff tape, the sailmaker will also add a cut-back above and below the sail to allow room for the halyard swivel and lower unit. The installation manual gives all require dimensions in the appendix.

Can I assemble the MKIV Ocean myself?
Absolutely. One of our major goals when designing the MKIV Ocean was to make assembly super easy. In most cases, the foils slip over the standard marine eye and headstay wire without cutting the wire. Once assembled, simply cut the top foil to fit. The bottom foil adjusts to fine-tune unit length.

Is it easier to install the furler on the mast when the mast is down or up?
If the mast is down for storage or for other work, the assembled furler can be attached and go up with the mast when it is stepped. Removing the stay and raising the assembled furler on a standing mast is best left to experts and professional riggers.

Can I reuse my existing headstay?
Yes. However, when installing a furler, we recommend replacing a headstay wire used in a salt water environment if it is over three years old. Replace every five years if you sail in fresh water.

I see you offer a Harken Halyard Deflector as an option. What is a halyard deflector?
The Harken Halyard Deflector prevents the jib halyard and other halyards (such as a spinnaker or additional jib halyards) from wrapping around the foil. The deflector is easy to install.

What's the difference between the Harken Halyard Deflector and the Harken Halyard Restrainer?
The Harken Halyard Deflector installs on the stay above the foil system and prevents the jib halyard and other halyards from wrapping around the foil.

The Harken Halyard Restrainer installs on the mast near the top of the foils and keeps the line against the mast. This provides a better angle to the halyard swivel and prevents it from wrapping around the foil. Stainless steel brackets feature hardcoat-anodized aluminum sheaves that accommodate both wire and rope.

You offer three different lower attachment options. Which one is right for me?
If your furler has a turnbuckle, measure its length to determine whether you need a Long or Medium Harken Leg Kit. Long and medium legs raise the drum to clear the turnbuckle and anchor, reduce sail chafe, and increase visibility. If your furler attaches directly to a marine eye at the bottom of the stay, choose the Short Leg Kit. Short legs allow the sail to be closer to the deck.

Is the turnbuckle easy to adjust?
Yes. Removable clamp screws allow legs to pivot out of the way so you can easily adjust the turnbuckle.

My boat doesn't have a turnbuckle. Which kit should I order?
If you want a low sail tack, order a Short Leg Kit for direct attachment to the marine eye mounted on the end of the stay. If you want to raise the furling drum to clear the anchor, the Long or Medium Leg Kits also work without a turnbuckle.

What other components do I need for installation?
1. The 7404 Lead Block Kit
 has everything you need to lead line aft to the cockpit. The kit features outboard leads to keep the side deck clear and also includes a ratchet block to maintain furling tension for clean spooling and easier furling.

2. Furling Line: Harken supplied polyester double-braid furling line can also be ordered. If you don't order line from Harken, here's a simple method to determine the length of line you will need. Take the length of your boat and multiply that distance by two. If your boat is 10 m (32 ft), you would order 20 m (64 ft) of line.

What information do you need when I place the order?
Start with your boat length and refer to our typical boat lengths listed for each unit. Next find your wire/rod headstay and clevis pin diameter. Finally check your stay length to see if you need an extra foil and connector.

Questions for your sailmaker

What does it cost to add luff tape to my sail?
Costs vary, but most sailmakers base prices on luff and leech lengths.

What brand of sails should I buy?
Select a sailmaker who offers answers that show an understanding of reefing and furling systems.

What size genoa should I use as my primary reefing sail?
This depends on your boat and your normal sailing conditions. Most boats find a 135-percent genoa ideal. Light air 150 and heavier air 100-percent genoas are also common in certain regions. Discuss sail size with your sailmaker.

Can I use my old sails with my new jib reefing and furling system?
Yes. Ask your sailmaker to modify the sails you use regularly, including at least one genoa and one heavy-air sail. If you sail in an area that requires specialty sails like drifters, convert these as well. Sails should be in good condition.

How are sails modified for jib reefing and furling systems?
Your sailmaker will remove the hanks and add a luff tape so the sails slide into the foils. Larger sails may need to be shortened to make room for the halyard swivel. Adding a sun cover to the sails you store furled will protect them from ultraviolet damage.

What should I look for when I purchase a new sail?
Look for a sail designed for a range of wind conditions. The sail should be powerful enough to move the boat in light air and chop, but flat enough to sail reefed in severe conditions. Modern sail shaping devices allow sailmakers to build sails that work in a range of conditions from 5 to 40 knots. Most sailmakers use foam or rope luff pads. Ask your sailmaker which shaping device is best for your boat. Adding a sun cover to the sails you store furled will protect them from ultraviolet damage.

What's the best way to protect my sail from the sun?
Prolonged exposure to ultraviolet rays deteriorates most sailcloth, so any sail left rolled on the headstay needs protection. Your sailmaker can add UV-resistant material to the foot and leech panels-this can usually be done without adding a lot of extra weight. Most sailmakers prefer acrylic-type material like Acrilan® fabric (the same material used for mainsail covers).

Alternatively, some sailors use a long sock-like bag to cover their furled sail. This design won't add weight to your genoa, but you'll need a spare halyard to hoist it. Be aware these covers can flog in a breeze.

Acrilan® is a registered trademark of Solutia Inc. Corporation

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MKIV Ocean Jib Reefing and Furling

Fewer components make this affordable furler quick to assemble and easy to use, while providing the same styling, durability, and low maintenance bearing system of our performance line.

Install a MKIV Ocean and trim safely from the cockpit when it blows and unfurl instead of motoring when it's light for a great day of sailing.
Harken MKIV Ocean furlers don’t require professional installation.

Tech Tips

Harken Link Plate Leg Extension Kits
Choose long or medium legs with standard turnbuckles using swage, Norseman, or Sta-Lok® terminals; short legs when attaching directly to the marine eye at the lower end of the stay.


The 7404 Jib Reefing and Furling lead block kit reroutes lines outside the stanchions for a cleaner deck. A ratchet block is included in the lead block kit to keep tension on the furling lines. This will prevent the line from overriding in the drum.

The 7402 Ratchet block offers total control over your furling line. The ratchet provides the extra holding power you need for reefing or furling the sail in heavy winds. The static sheave supplies the correct tension to help the line spool smoothly on the drum when unfurling, making it easier to furl the sail again.