Installing a Harken MKIV Ocean genoa furler is a five-stage job: replace the headstay, assemble the furler unit onto it, rig and tension the stay, commission the system, then make final adjustments and safety checks. Done in that order, with the mast securely supported throughout, a competent rigger can fit a Harken MKIV or MKIV Ocean unit reliably on a boat from roughly 22 to 80 feet.
Harken MKIV Ocean installation at a glance
| Stage | What you do | Key check |
|---|---|---|
| 1. Headstay removal & replacement | Remove the old headstay with the mast safely secured; fit the new stay to the correct length and termination. | Mast supported; stay length correct. |
| 2. Furler assembly | Assemble the unit per the manual: foils, halyard swivel, drum assembly and hardware. | Foils connected and free of twist. |
| 3. Rigging | Fit the turnbuckle and toggle, attach the furling line and feeder, run the halyard. | Headstay "straight as an arrow." |
| 4. Commissioning | Feed the sail, connect the tack, wind up the drum and test furling. | Smooth furl and unfurl. |
| 5. Final checks | Fine-tune turnbuckle, line tension and halyard; inspect the whole system. | All connections secure. |
What preparation do I need before starting?
Before touching the rig, gather your tools and materials, review safety precautions, and pre-assemble the furler components where the manual allows. Working through the parts on the bench first means fewer surprises once the headstay is down and the clock is running. The short video below walks through the sequence.
How do I remove and replace the headstay?
Remove the existing headstay only after the mast is safely secured, then install the new headstay cut to the appropriate length with the correct termination. This is the foundation of the whole install: the MKIV Ocean unit is built up over the stay, so an incorrectly sized or terminated stay will compromise every stage that follows.
How do I assemble and rig the furler?
Assemble the furler unit following the manual step by step: attach the foils, halyard swivel, drum assembly and remaining components. Then rig it by fitting the turnbuckle and toggle to connect the headstay to the furler, adjusting headstay tension until the stay is straight as an arrow, and attaching the furling line and feeder. Finally install the halyard, checking its routing and tension so it will not wrap or foul in service.
Which Harken MKIV unit should I choose?
Harken MKIV furlers are sized by unit number to match headstay diameter and boat length, from Unit 0 for boats around 22-30 ft up to Unit 4 for 65-80 ft yachts. The MKIV Ocean units are rated by maximum stay length for bluewater and larger cruising boats, while underdeck versions relocate the drum below deck for a cleaner foredeck. Match the unit to your stay wire size and pin diameter, not just boat length.
How do I commission and finish the installation?
Commission the system by following the manual's guidance on furler adjustments and initial operation checks: feed the sail through the foils, connect the tack to the tack swivel, and wind up the drum to prepare the system. Test the furling to confirm smooth operation and clean furling and unfurling. Then make final adjustments to the turnbuckle, furling-line tension and halyard, and thoroughly inspect the entire system for proper installation and secure connections before sailing.
Frequently asked questions
How long does a Harken MKIV Ocean install take?
It varies with boat size and rig access, but budgeting a full working session is realistic once the headstay is measured and prepared. Pre-assembling components beforehand saves the most time.
Do I have to replace the headstay when fitting a MKIV furler?
Yes. The furler is built over a new headstay cut to the correct length with the correct termination, so a fresh, properly sized stay is part of every MKIV installation.
How tight should the headstay be?
The headstay should be tensioned until it is straight as an arrow. A sagging stay causes poor furling and uneven sail shape, so this adjustment is critical before commissioning.
What is the difference between a standard MKIV and a MKIV Ocean unit?
MKIV Ocean units are rated by maximum stay length and built for bluewater and larger cruising boats, while standard MKIV units are sized by boat length. Underdeck versions move the drum below deck for a tidier foredeck.
Can I install a Harken MKIV Ocean furler myself?
A competent, well-prepared owner can, provided the mast is safely secured throughout and the manual is followed exactly. If you are unsure about headstay sizing or rig safety, have a professional rigger do the install.
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