Harken furlers split into five families — MKIV, MKIV Ocean, MKIV Underdeck, Reflex (a top-down furler for Code Zero and asymmetric sails), and the discontinued-but-still-supported ESP line — each broken into numbered Units (0 through 4) sized to your boat, and MAURIPRO stocks genuine spares for every unit. Match the family and unit number stamped on your furler, or measure it directly, and you're at the right parts collection without guessing.
This is written for the cruiser at the wheel of a ~30-45 ft boat, standing at the bow trying to work out exactly which Harken furler is on the headstay before ordering a replacement part. Harken has sold jib furling systems since the 1980s, across several generations and mounting styles, and the company reuses the same unit numbers (0 through 4, roughly) across different families — so "Unit 1" alone isn't enough to order the right drum flange, foil connector, or swivel. You need the family too.
The good news: Harken designs its own identification path around exactly this problem, and MAURIPRO's own catalog is organized the same way — by family, then by unit. Here's how to use both.
Harken furler families at a glance
| Family | Boat size range (by unit) | What identifies it | Example spare part |
|---|---|---|---|
| MKIV | Units 0-4: 22-80 ft (6.5-24.4 m) | Above-deck drum; twin-groove aerodynamic foil; drum splits and removes for racing | Unit 0 head swivel (HARH-39923) |
| MKIV Ocean | Units 0-3: max headstay 38.6-88.7 ft (11.7-27.0 m) | Above-deck drum; single-groove round foil for easy rolling; one-piece fixed drum, spool, and guard | Unit 1/2 intermediate extrusion (HAR75113) |
| MKIV Underdeck | Units 0-3: 22-60 ft (6.5-18.3 m) | Same drive train as MKIV, but the drum is recessed below deck for a clean bow — no visible drum at the tack | Shop Underdeck Unit 1 spares |
| Reflex | Units 1-3: roughly 35-60 ft (10.6-18.3 m) | Top-down furler — a continuous torsion cable, no permanent foil on the headstay; flies a Code Zero or asymmetric/gennaker, not the working headsail | Unit 1 snap shackle (HAR735120) |
| ESP (legacy) | Units 0-3, varies by boat | Harken's earlier cruising furler; no new orders since June 2021, but Harken still provides tech support and a limited spares run | Shop Harken furler spares |
Boat-size and headstay figures per MAURIPRO's own current Harken listings, checked live against each unit's product page.
Shop all Harken furler spares →
How do you tell which Harken furler family you have?
Start with the drum, not the unit number. Per Harken's own furler service guide, step one is identifying the family — the unit number only matters once you know which family you're looking at. Look at three things: is the drum above deck or hidden below it (Underdeck), is it a split drum that comes apart (MKIV, built for racing) or a one-piece fixed drum (MKIV Ocean, built for cruising), and is there a permanent foil running the full length of the headstay at all? If there's no foil — just a drum with a continuous line and a torsion cable running up the luff of the sail itself — you're looking at a Reflex top-down unit for a Code Zero or asymmetric sail, not a headsail furler.
How do you find the unit number once you know the family?
Per Harken's own tech support guidance: MKIV and cruising furlers have the unit size printed on a label, and "MKIV" stamped on the feeder. On older units without a legible label, Harken's own instructions are to measure the drum diameter across the top of the drum, the clevis pin diameter, and the torque tube length. Clevis pin diameter is the fastest of the three to check with calipers and climbs steadily with unit size — on MKIV Ocean units, for example, it runs 1/2 in (11 mm) on Unit 0, 5/8 in (16 mm) on Unit 1, 3/4 in (19.1 mm) on Unit 2, and 1 1/8 in (29 mm) on Unit 3, per MAURIPRO's own listed specifications for each unit. A part ordered against the wrong clevis pin diameter simply won't fit the toggle, so this measurement is worth taking even if a label looks legible.
What's the real difference between MKIV and MKIV Ocean?
Both are above-deck, permanent headstay furlers sized the same way (by unit number), but Harken builds them for different jobs. MKIV uses an aerodynamic, double-grooved foil for faster hoists, douses, and sail changes, independent halyard and tack swivels for better sail shape, and a split drum that removes entirely so racers can sail without the furler engaged. MKIV Ocean uses a single-groove, round-profile foil built for easy rolling, a fixed halyard/tack swivel, and a one-piece drum, spool, and guard that isn't meant to come apart — the cruising trade-off of fewer parts to service in exchange for giving up the removable-drum feature. If your furler's drum comes apart in two halves, it's MKIV; if it's one continuous piece, it's MKIV Ocean.
What about the Reflex and legacy ESP lines?
Reflex isn't a headsail furler at all — it's a top-down system built to furl a Code Zero or an asymmetric spinnaker/gennaker from the head down, using a continuous furling line that spins a torsion cable running up the sail's own luff, with a drive unit, head swivel, and tack terminal rather than a foil bolted to the headstay. ESP, by contrast, was Harken's earlier cruising jib furler: Harken stopped taking new ESP orders in June 2021, but continues to provide technical support and inventories a limited run of spare parts and manuals for owners who already have one on the boat — a discontinued unit is not the same as an unsupported one.
Which Harken furler unit do you need if you're replacing the whole system?
If servicing isn't enough and you're sizing a full replacement rather than a spare part, start from the family your headstay setup calls for — a permanent headsail furler on a coastal or blue-water cruiser generally means MKIV Ocean, most mid-size cruisers in the 30-45 ft range landing on a Unit 0 or Unit 1 depending on headstay wire diameter, not boat length alone. Racers and cruiser/racers who want the option to disengage the furler and sail on a bare twin-groove foil look at the equivalent MKIV unit instead. A Code Zero or asymmetric sail that isn't flown every day is sized separately, by sail luff length and boat size together, against the Reflex range.
Expert notes
From our rigging bench: the single most common mix-up isn't between two unit numbers on the same family — it's assuming a fixed, one-piece drum is "the wrong part" because it doesn't split like a friend's racing boat's furler. That's simply MKIV Ocean's design, not a defect.
On boats old enough to carry an ESP unit, we've found it faster to photograph the drum housing and link plate and match it against Harken's own family identification chart than to guess from boat length — ESP shares some hardware naming with early MKIV parts, and the two are not interchangeable.
Common mistakes
- Ordering by boat length alone. A 36-footer with a tall rig or a reinforced forestay can call for a larger unit than its length alone suggests — Harken's own guidance is to confirm with a direct measurement, not LOA.
- Assuming the same unit number means the same part across families. A Unit 1 drum flange for MKIV, MKIV Ocean, and MKIV Underdeck are three different parts — the family has to match, not just the number.
- Treating "discontinued" as "unsupported." Harken stopped selling new ESP units in 2021 but still stocks spares and offers tech support — don't assume an ESP furler is a dead end.
Frequently asked questions
How do I find the unit number on my Harken MKIV furler?
Check the label on the drum and the feeder, which is stamped "MKIV" along with the unit size on current units. On older, unmarked furlers, Harken's own instructions are to measure the drum diameter across the top, the clevis pin diameter, and the torque tube length to match against a known unit.
What's the difference between Harken MKIV and MKIV Ocean furlers?
MKIV uses a removable split drum and an aerodynamic double-groove foil built for racing and fast sail changes. MKIV Ocean uses a fixed one-piece drum and a single-groove round foil built for easy, low-maintenance rolling on a cruiser.
Is Harken's ESP furler line still supported?
Harken stopped taking new orders for ESP furlers in June 2021, but it continues to provide technical support and stocks a limited run of spare parts and manuals for existing owners, per Harken's own published guidance.
What's the difference between a Harken Reflex furler and a headsail furler like the MKIV?
Reflex is a top-down furler for a Code Zero or asymmetric spinnaker/gennaker — it has no permanent foil on the headstay and furls via a continuous line and torsion cable. MKIV and MKIV Ocean are permanent headsail furlers with a foil bolted the length of the headstay.
Where can I buy genuine Harken furler replacement parts?
MAURIPRO carries Harken furler spares across the MKIV, MKIV Ocean, MKIV Underdeck, Reflex, and legacy ESP lines, organized by unit — see the collection links above and below to shop by family and unit number.
Recommended gear
Harken Head Swivel w/o Shackles, MKIV Unit 0 — the top swivel assembly for the smallest MKIV unit, a common identification point when there's no legible label.
Harken Intermediate Extrusion (2.13 m), MKIV Ocean Unit 1/Unit 2 — a standard foil section for extending or replacing a damaged length of headstay extrusion.
Harken Drum Bottom Flange Assembly, MKIV Unit 2 — a unit-specific drum component, worth checking against your measured clevis pin diameter before ordering.
Harken Snap Shackle for Head & Tack Swivels, MKIV Unit 1 — a wear item at the head and tack connection points, sized to the Unit 1 swivel.
Shop all Harken furler spares →
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Last updated: September 4, 2026.