Clean/inspect 34
Replace Line 34
Storage/Transporting/Remove 34
Troubleshooting 35
Parts List 36–37
Drilling Template 38
Please read these instructions carefully before installing, servicing, or operating the equipment.
This manual may be modified without notice. See: www.harken.com/manuals for updated versions.
PLEASE SAVE THESE INSTRUCTIONS
Safety Precautions/Parts Description
Introduction
This manual gives technical information on installation and service. This information is destined exclusively for
specialized personnel or expert users. Installation, disassembling, and reassembling by personnel who are not
experts may cause serious damage to property or injury to users and those in the vicinity of the product. If you
do not understand an instruction contact Harken.
The user must have appropriate training in order to use this product.
Harken accepts no responsibility for damage or harm caused by not observing the safety requirements and
instructions in this manual. See limited warranty, general warnings, and instructions in www.harken.com/manuals.
Purpose
®
Harken
Jib Reefing and Furling is designed for rolling sails on sailboats to reduce sail size or to completely roll
so wind has little effect on the sail. Use of this product for other than normal sailboat applications is not covered
by the limited warranty.
Safety Precautions
WARNING! This symbol alerts you to potential hazards that may kill or hurt you and others
if you don't follow instructions. The message will tell you how to reduce the
chance of injury.
CAUTION! This symbol alerts you to potential hazards that may hurt you and others if
you do not follow instructions. The message will tell you how to reduce the
chance of injury.
WARNING! Strictly follow all instructions to avoid potential
hazards that may kill or hurt you and others. See www.harken.com/
g
h
manuals for general warnings and instructions.
f
b
c
a
e
d
1
2
Size Check
1. Check headstay in chart below.
Part No.SizeWire SizeRod Size
7410.11Unit 0
Parts Descriptions
Hub Assembly
a) Bridge Fairlead Assembly
b) Ball Spool Guard Assembly
Note: See dimensions above. Unit requires a connection to underdeck chainplate for stay loads.
See page 38 for deck plate dimensions.
Furler Requires Drained Compartment
Harken’s Underdeck Furler is designed to keep much of the water from entering the bow compartment. Water
will drip through the furler when it rains or when sailing in heavy weather. The furling compartment must drain.
Upper Unit
1) Bottom Foil
2) Feeder
07/14/10 MKIV Underdeck Unit 0 3
3) Connector Bushing
4) Bottom Connector
5) 7' (2.13 m) Foil
6) Connector Wedge
7) Connector Screws
8) Connector
9) Halyard Swivel
10) Trim Cap Screws
11) Trim Cap
Preassembly Parts
Foil Screws
Hub Assembly
Bottom
Connector
Connectors
Halyard Swivel
Feeder
2.5, 3, 5 mm
Hex Keys
7' (2.13 m)
Foils
2' (610 mm)
Bottom Foil
Plastic Connector
Wedges
Connector Bushings
Trim Cap Screws
Bow Shackles
Prefeeder
Trim Cap
Line (Not included with Furler)
Note: Line is not included with furler. Drum of
unit is smaller to allow it to fit into narrow bow
sections. If overlapping sails are used, standard
diameter line will fill up drum and jam furler. To
prevent this, use small diameter, high strength
line at forward end and have a rigger add a
cover at aft end where line is handled.
5200
Adhesive
Injector
Red Loctite
®
Main Components
Part No.QuantityDescription
HFG9511
H-399231
Hub assembly with foil clamp
Halyard swivel
Foils (Standard Package)
Part No.QuantityDescription
7410.305
7410.331
7'(2.13 m) foil
2'(610 mm) Botton foil
Tools
QuantityDescription
1 Each
4 MKIV Underdeck Unit 0
2.5, 3, 5 mm Hex keys
Line Specifications
Forward ØMin Break StrengthAft Ø
3
/16" (5 mm)1300 lb (590 kg)
Other Components
Part No.QuantityDescription
7410.314
7410.321
HFG2941
HFG2981
HFG3411
HFG6791
HFG6291
9471
H-397131
21103
HFG7251
HFG7392
6.5" (165 mm) Connector
10" (254 mm) Bottom Connector
Connector bushing set (10-H-42067/10-H-42068)
Plastic connector wedge set (12-H-39625)
Foil screw set (26-HFS1105)
Trim cap set (H-37335/H-37336)
Trim cap screw set (3-HFS1126)
Prefeeder
Feeder with screw and tab
6 mm Bow shackles
Injector, 1 oz. 5200 Adhesive (HFG722)
®
Red Loctite
(for foil screws)
1
/4" (6 mm)
Preassembly Rigging Parts Check/Tools
1. Turnbuckle components are not included and
must be purchased separately.
2. Rod rigging requires Harken rod adapter stud.
3. Order Harken Lead Blocks and one additional
7403 if necessary. Fits 1" (25 mm) stanchions.
3
4. Furling Line - Use
/16 to 1/4" (5 to 6 mm). To figure
line length, measure the distance from the furler to
the furling cleat. Add 15' (4.5 m).
7404 Lead Block Kit
(Sold Separately)
131
349
Recommended Furling
Compartment Lead Blocks
UnitTurningThru-Deck
0349131
Tools You Will Need
ROD RIGGING
Harken Rod Adapter
Stud Required
(Sold Separately)
7420 -4
7421 -6
Rod Adapter Stud
Adhesive Alert
MKIV Furlers are shipped with 3M 5200
adhesive. Use adhesives on dry connectors
and foils using the special injection system
described in the assembly section. Parts
may immediately be exposed to rain. Cure
is best at 70F (22C) with 50% humidity.
Do not apply at temperatures below 40F
(5C) and above 100F (38C).
Although adhesive has not cured it will
remain in place on foil joints whether
they are left on the ground or raised up
on boat. Foils can be raised immediately
after assembly and sails fitted.
Note: A small amount of adhesive may
bulge out of injection ports. If possible
let system sit for a couple days before
sailing. If adhesive gets on sails remove
using acetone. For faster-curing adhesive,
purchase 4200 Fast Cure.
Note: Damaged foils can be repaired.
Use a hand-held propane torch to heat
joints until foils can be pulled apart.
5
3
UnitDrill Ø
0
1
2
7
4
8
12
1
/8"
(3 mm)
15
16
18
19
Use 6 mm bolts and washers to
mount deck flange. To figure bolt
length, add 3/8" (10 mm) to deck
6
9
1. Long tape measure 6. Side cutters11. Center punch16. Hole saw 41/4" (110 mm)*
2. Short tape measure 7. Rat-tail file12. Rigging or black tape17. Deck sealant
3. Power drill 8. Hex keys (provided)13. Scissors18. Box end wrench
1
4. Drill bits
5. Hacksaw10. Needle-nose pliers15. Hammer
*Requires some beveling of bottom edge of deck hole to provide a good fit. Alternatively a smaller hole may be used to fashion a socket in deck to conform
to ball shape. This may improve appearance and reduce amount of water that enters. A 4
09/17/10 MKIV Underdeck Unit 0 5
/8" (3 mm)9. Slotted/Phillips screwdrivers14. Metal straight edge19. 6 mm bolts, nuts, and washers
10
11
13
14
1
/2" (115 mm) hole saw may also be used if no beveling is desired.
thickness. Minimum thread
engagement must be 9 mm.
17
Preassembly Dimensions/Sailmaker's Instructions
Luff Length
Note offsets above and below sail.
A shorter luff may be required if a halyard restrainer is necessary
(page 30).
If luff of sail is not long enough to put halyard swivel near top of
headstay foil, a pendant must be added. See page 29.
Tack Setback
Note setback for tack shackle and cut the sail accordingly.
B
A
Luff Tape Size
6
All units require #6 (
/32" or 5 mm) luff tape.
Luff Tape Length
Cut off top of luff tape so it is 18–24" (450–600 mm) below head
of sail. This allows head to lag behind rest of sail to help flatten
sail. It will also help head to roll more smoothly.
Note feeder height and extend bottom of luff tape downward so
it is below feeder. This will prevent luff tape from catching in
feeder as sail is lowered.
Tack and Head Shackles
Make sure tack and head shackles fit sail
A
rings. The minimum inside dimensions
of standard head and tack shackles are:
E
UnitAB
1
0
1
/16" (27 mm)1/2" (13 mm)
B
Suncover
7410.11 Furls in one direction only.
IMPORTANT! Suncover must be installed on starboard side of sail.
C
D
F
UnitPart No.ABCDEF
07410.11
3
/4"
3
96 mm
61/4"
158 mm
119/64"
33 mm
15
/64"
6 mm
345/16"
817 mm
319/32"
91.5 mm
6 MKIV Underdeck Unit 0
Preassembly Rigging Options — Turnbuckle
The stay runs up the center of the MKIV Unit
0 Underdeck furler. It does not attach to the
furler in any way. Choose one of the following three turnbuckle locations based upon
diameter of turnbuckle body and access to
the turnbuckle below deck. The interior of
the furler components are shown below.
A
B
UnitABCDEFGH
7
/16"
1
0
36.4 mm
101/8"
258 mm
1"
25.4 mm
71/2"
190.5 mm
51/2"
140.5 mm
17/8"
47.6 mm
25/16"
58.6 mm
11/2"
38.1 mm
C
D
E
F
G
H
Turnbuckle Options
Turnbuckle Below Furler
Make sure that the upper stud wrench
flats are accessible. If necessary, the bridge
fairlead assembly can be lowered below the
turnbuckle to allow access to wrench flats.
07/14/10 MKIV Underdeck Unit 0 7
Preassembly Turnbuckle Options
Turnbuckle inside torque tube
Set up a pendant below making sure
to have a turnbuckle toggle.
Use a swage to swage turnbuckle
located just above the lower unit.
Check turnbuckle fit inside torque
tube. Requires a “third hand” to adjust.
Turnbuckle above swage
On smaller size wires 3/16" (4 mm)
a small turnbuckle should fit. Check
dimensions above for clearance.
Options for Snaking Stay into Foils
1. Swage stud at end of wire.
2. Open end of wire and install Norseman or Sta-Lok
®
stud after
foil is assembled.
3. Rod adapter nosepiece for Harken rod adapter stud: Threaded
nosepiece must have a positive lock as well as adhesive.
Use Harken stud with cotter pins. See page 22.
WARNING! Using a threaded nosepiece with only
adhesive at the upper rod eye terminal may result
in headstay system failure. Make sure there is a
mechanical lock.
8 MKIV Underdeck Unit 0
Assembly Deck Plate
71°
–
73°
Note: Deck plate angle
matches a stay angle of
72° when compared to
deck. Angles can vary
between 71° and 73°. If
deck does not fall within
these angles, shims must
be made using structural
adhesive to avoid excessive pressure on deck
and deck bearings.
Tip: Run line through fairlead
and dead end line into spool
before mounting lower unit.
Carefully locate center point in deck to locate deck plate. Line from mast to underdeck
chainplate must intersect this center point. Mark center fore/aft and athwartships line.
Use template to mark four outer holes and center pilot hole. Make sure closer pair of
holes is forward. Mark center hole for drilling large hole.
Once you are certain hole is located in line with
chainplate and any required shimming is done,
drill hole 90° to deck.
Make sure hole is just large enough so deck
plate bears against deck. It is better to make
hole slightly smaller and file opening larger
to fit. Use template to mark large hole and
bolt holes. Use hole saw to drill deck.
Tip: After pilot drill bit clears deck, drill final
hole from bottom using pilot hole to line up
hole drilled from top. This will prevent glass
from chipping.
Use 6 mm screws, washers, locknuts and deck sealant to fasten lower unit to deck.
3
Note: There must be a minimum of
/8" (9 mm) thread engagement into deck flange.
MKIV Underdeck Unit 0 9
Assembly Under-Deck Lead Block
Mount lead block so furling line is 90° to
hub assembly.
90°
Mount thru-deck block. Be sure to angle
it toward stanchion lead block.
10 MKIV Underdeck Unit 0
UNIT 0
Preassembly Unit 0—Top Foil Length
Measure A and add to this chart
and length chart below
Inchesmm
A
B.4*10*
E24610
F14359
G
Total A+B+E+F+G
*Add 1" (25 mm) if using a Halyard
Deflector.
Make sure upper
measurement points
of A and pin-to-pin
Alternate
Measurement
Point
A
are the same.
TOP FOIL LENGTH WORKSHEET
1
2
3
4
To find “D” pick number from chart below that is closest to, but not greater than total from step 3.
5
Result (Pin-to-Pin – ABEF)
Inchesmm
3 X 84 = 252
4 X 84 = 336
5 x 84 = 420
6 x 84 = 504
Example–If result from Step 3 is:
Result (C) Top Foil Length
Pin-to-Pin Length
Subtract ABEF
Subtract D
3 x 2133.6 = 6400.8
4 x 2133.6 = 8534.4
5 x 2133.6 = 10668
6 x 2133.6 = 12801.6
500 inches “D” = 420 inches
12,000 mm “D” = 10,668 mm
–
–
Pin
to
Pin
A
B
C
D
Pin
to
Pin
Length Check
After completing worksheet above fill in A, C and D below. Add “A”
through “F” to confirm total equals your pin-to-pin measurement.
A Center of Pin to Bottom of Terminal
B Bottom of Terminal to Top of Foil
C Top Foil Length
D Number of Foils ________ x 84" (2133.6 mm)
E Bottom Foil24610
F Bottom of Foil to underside of deck14359
Length Chart
DimensionsInchesmm
.40*
Pin-to-Pin Length
10*
E
F
*Add 1" (25 mm) if using a Halyard Deflector.
MKIV Underdeck Unit 0 11
Preassembly Short Top Foil
If top foil is shorter than 7" (177.8 mm), use one of the following special techniques to ensure sufficient bearing
surface for the foil in the area of the halyard swivel.
/8" (162 mm)
3
63/8" (162 mm) No special treatment required.
/8" (159–117 mm)
5
/4"–4
1
6
1
/4"–45/8" (159–117 mm) Do not use plastic bushing
6
Cut-Offs
Do Not Use
above top connector.
/2 (63 mm)
/2" (38 mm)
1
2" (51 mm)
2
/2" (13 mm)
1
1" (25 mm)
1
1
Cut-Offs
Do Not Use
21/2"–1/2" (63–13 mm) Shorten top foil and adjoining
full length foil so two screws are used to assemble joint
instead of four. Do not use plastic bushings above top
connector.
Top Foil
Length from
Worksheet
1
2
/2"
(63 mm)
2"
(51 mm)
1
/2"
1
(38 mm)
1"
(25 mm)
1
/2"
(13 mm)
1. Initial
top foil
cut length
(143 mm)
(130 mm)
(117 mm)
(105 mm)
(92 mm)
55/8"
1
/8"
5
45/8"
1
/8"
4
35/8"
2. Cut through
middle hole in
top foil.*
Resulting Top
Foil LengthLength
41/16"
(103 mm)
39/16"
(90 mm)
31/16"
(78 mm)
29/16"
(65 mm)
21/16"
(52 mm)
3. Shorten
full length
adjoining
foil by
cutting
through
middle
hole.*
4. Shorten
connector
(83 mm)
(83 mm)
(83 mm)
(76 mm)
(70 mm)
31/4"
31/4"
31/4"
3"
23/4"
5. Shorten
trim cap
No
No
No
Yes
Yes
/2" (114–89 mm)6
1
Cut-Offs
/2"–3
1
4
Do Not Use
41/2"–31/2" (114–89mm) Do not use plastic bushing
above top connector. Shorten top of connector and if
necessary shorten trim cap.
/8" (86–67 mm)
5
/8"–2
3
3
3
/8"–25/8" (86–67 mm) Do not use plastic bushing
3
Cut-Offs – Do Not Use
above top connector. Cut connector right at cross formed
by glue dispersion channels. Use single foil screw in top
foil only.
12 MKIV Underdeck Unit 0
Cut-Off
Do Not Use
*To allow for saw cut, position blade so upper half of
middle hole is preserved.
/2" (13 mm)
1
Under
Under 1/2" (13 mm) Eliminate top foil and run foil higher
in drum assembly.
Preassembly Foil Length Check
Confirm foil length by laying foils alongside
stay with turnbuckle components and torque
tube. Pull stay out straight.
Line up bottom foil so foil clamp is just
above or below center of notches in
bottom foil.
Note: Position top foil so that with top
cap the foil will ride below terminal. If wire
fitting at top of stay is swage, foil must ride
just below shoulder of swage. Mark cut line
on foil. Wrap tape around foil as a guide so
cut is straight.
14" (359 mm)
to underside of deck
If 7301 Halyard Deflector is used, add 1" (25 mm)
MKIV Underdeck Unit 0 13
Assembly Top Foil
Cut foil to length using hacksaw.
Deburr inside edge using rat-tail file.
Prepare top foil for drilling.
Tip: Mark top foil to distinguish
from cutoff piece.
Scribe line on top of foil to mark drill
holes. Lay top foil alongside cutoff
piece and use a flat metal object
(i.e. metal ruler) to scribe top
line of foil.
14 MKIV Underdeck Unit 0
Assembly Top Foil
Cut out template at right. Line up template
with top of foil and scribed line. Tape in
place. Use a center punch to mark holes.
Check center punch marks to confirm
they are 3/16" (5 mm) and .8" or 13/16"
(20 mm) from top of foil.
Drill two (2) 1/8" (3.2 mm) holes for
trim cap.
!
Foil
3
/16" (5 mm)
Top
.8" or 13/16"
(20 mm)
Lay top foil in line with others. Slide stay
into top foil and down line of foils or slide
each foil up stay.
MKIV Underdeck Unit 0 15
Assembly Top Foil
Install trim cap. Place each side over wire.
Halyard Deflector
Red Loctite
®
Push trim cap into foil to start, then tap
in using hammer.
Install trim cap screws.
Place halves of plastic bushings on stay so
hooked part of longer section faces out.
Tip: With foil screw holes up as shown
below, place longer half of bushing
with hook on upper half.
16 MKIV Underdeck Unit 0
Assembly Top Foil/Connectors
Slip connector on wire, mating hook of
plastic bushing with connector.
Put a drop of red Loctite® into screw holes.
MKIV Underdeck Unit 0 17
Assembly Foils/Connectors
Hold plastic wedge in place with thumb
as you insert into foil. Line foil holes with
connector screw holes.
Loading Injector with Adhesive
Tip: In cooler weather, keep sealed
adhesive in pocket to keep warm. Use
instructions below to fill injector less
than half way; you will only use a small
amount of adhesive. Refill if needed
but do not keep open sealant for long
periods. Use adhesive within 3 hours.
Use cap of adhesive to break seal. Remove
injector tip cap and plunger. Hold injector
at an angle with applicator tip facing down.
Squeeze adhesive into tube so lower half
of injector is full as shown. Keep tip free
of sealant to let air inside.
Adhesive in
lower half
Start plunger into injector and immediately
hold upright so plunger is down and
applicator tip is up.
As sealant runs down towards plunger an
air pocket will form near tip. Push plunger
to evacuate air. You are now ready to begin
injecting adhesive.
18 MKIV Underdeck Unit 0
Assembly Foils/Connectors
Inject only a small amount of adhesive
into middle hole. Unit 0 will only take
1/4 to 1/3 of a graduation mark. Do not
press tip of injector into hole. Back off
slightly while injecting.
Tip: When you see a small
amount of adhesive enter
one of the screw holes,
Use “ml”
marks to
estimate
adhesive
stop. You have applied
enough adhesive.
Stop when you see a small
amount of adhesive enter
one of the screw holes.
Tighten screws into connector holes. Make
®
sure a drop of red Loctite
entered each
screw hole. If not, apply to screw.
Red Loctite
®
Use bushings, connector, wedge, and
adhesive in other screw hole and insert
into other foil. Use 1/4 to 1/2 ml. of
adhesive.
MKIV Underdeck Unit 0 19
Assembly Bottom Foil/Connectors/Halyard Swivel
Continue installing connectors and wedges.
Make sure to use adhesive in screw holes.
Red Loctite
®
Continue assembly. Use bottom connector
to assemble bottom foil.
Slide halyard swivel onto foil above feeder
window. Make sure taller “half” is up as
shown.
20 MKIV Underdeck Unit 0
Assembly Torque Tube Assembly
Loosen foil clamp screws at top of
drum assembly.
Slide drum assembly onto foils.
Tip: Face clamp downward so it clears
foil notches during installation.
Temporarily clamp torque tube to top of
bottom foil, leaving feeder gap partially
exposed as shown at right. Gap will be
used to rig a foil system lifting line.
MKIV Underdeck Unit 0 21
Assembly Rod Rigging: Rod Adapter Stud
Apply a few drops of red
®
Loctite
nosepiece.
Screw main threaded stud
portion onto bronze nosepiece
until flats align with two cotter
pin holes in terminal body.
Tip: Turn nosepiece completely
into threaded stud portion.
Flats will be close and may
only require a small half turn
to align with cotter pin holes.
to threads of
Insert two cotter pins and
®
spread. Clean excess Loctite
from terminal body using
special care to ensure that
there is no red Loctite
threaded stud.
®
on
ROD RIGGING
22 MKIV Underdeck Unit 0
Assembly Attach Turnbuckle/Foil System to Boat
Thread turnbuckle to stud protruding from
foil. Assemble turnbuckle.
®
Note: If using Sta-Lok
or Norseman®
stud, you must use a washer above
stud as shown below.
Tip: Rig a large round plastic wash basin
below furler to catch any parts that may
be lost overboard.
Carefully raise foil and stay up onto boat.
Raise foils using line attached to feeder gap
as shown.
Adjust turnbuckle. Secure with cotter pin.
When stay length is set, use side cutters
or needlenose pliers to bend cotter pin
to secure turnbuckle.
MKIV Underdeck Unit 0 23
Assembly Attach Turnbuckle/Foil System to Boat
Assemble torque tube using the three screws at the
base.
Loosen foil clamp while holding torque tube and
carefully lower into place.
Note: Do not remove screws, just loosen them.
Check foil height at top, set and secure
using hex key. Top of trim cap should
be about 7/16" (11 mm) to
bottom shoulder of terminal.
24 MKIV Underdeck Unit 0
Assembly Feeder/Final
Tip: Do not remove foil clamp screws to adjust foil.
Loosen screws, hold foils and bring clamp away
from foils. Adjust and reclamp.
Slide halyard swivel above feeder. Place feeder in foil
recess. Push screw down so tab catches under foil.
Tighten screw.
Note: Screw will turn with some difficulty. It is plastic
coated to prevent loosening due to vibration.
Important: When removing screw, loosen no more
than one full turn. Slide screw up and remove feeder.
MKIV Underdeck Unit 0 25
Commissioning Turnbuckle on Boat
Have extra cotter pins on hand to replace used ones
at base of unit and for turnbuckle. Determine if the
turnbuckle is located below deck or inside torque
tube. If it is located inside, follow these steps:
Rig a screw catcher.
Hold foils and loosen torque tube screws until you
can pull clamp part way out in order to lower foils.
Lower foils.
Loosen, but do
not remove
Remove the three screws at the base of the torque
tube.
26 MKIV Underdeck Unit 0
Commissioning Turnbuckle on Boat
Check location of turnbuckle. It may be below deck
under the hub assembly. If it is inside the torque tube,
follow this procedure:
Slide torque tube onto foil and clamp just below top of
feeder gap as shown. Use halyard to lift foil assembly.
CAUTION! To avoid injury, make sure drum
assembly and foils are securely lifted using
a halyard before adjusting turnbuckle.
Reassemble Torque Tube to lower unit. Lift foils so top
is 7/16" (11 mm ) below upper terminal.
Slide foil clamp into foil notches and tighten screws
to secure.
Adjust turnbuckle
MKIV Underdeck Unit 0 27
Commissioning Lead Line to Cockpit
Feed the line through bullseye and into spool. Run down into deadend hole located on the lower flange of
the spool and add a stop knot. Tie an overhand or figure-8 knot in the end. Set up lead block so line runs
perpendicular to drum when it leaves bullseye.
The bullseye can correct small differences in line angle. Lead line aft using ball bearing blocks where line
makes a turn more than 30 degrees. Install cleat.
2
1. Run line out of hole in bottom of spool
1
and tie a single overhand knot.
2. Pull knot back up to seat at hole.
Deadend Hole
Rotate the drum clockwise to charge the spool. Wind 10–15 ft (3–4.5 m) of line on spool.
IMPORTANT! Make sure that the suncover, if used, is installed on the starboard side of the sail.
28 MKIV Underdeck Unit 0
Commissioning Halyard: Swivel Height/Lead Angle
Halyard Wrap
The most serious problem with furling systems occurs when the jib
halyard wraps around the headstay foil. Halyard wraps will keep you
from furling or unfurling and may cause serious damage to the unit
and the halyard.
WARNING! In severe cases, a halyard wrap can cause loss
of control of boat and/or headstay can break suddenly.
Make sure halyard is clear of top foil before using system.
To prevent wraps, the halyard must exert a slight pull to the rear. This
allows the foils to turn while halyard remains stationary.
Prevent Halyard Wraps
WARNING! Sail must be fitted to foil length before using
to prevent halyard wraps and possible headstay loss.
1. Halyard swivel should be within top 4" (100 mm) of foil unless a
halyard restrainer is used.
2. Halyard must pull slightly to rear (8–10°).
3. Halyard must be snug, but not too tight.
If halyard wraps, do not force unit to turn. Attempt to open sail by
carefully furling in and out a little at a time. If sail will unfurl, lower
it by releasing jib halyard. Severe halyard wraps can only be cleared
by going aloft and freeing halyard.
If sail will not furl or unfurl, try to remove jib sheets and manually
wrap sail around headstay.
Testing at dock does not indicate halyard angle is correct. In wave
action, halyard may wrap if lead angle is not correct. The 8–10°
diverging angle shown at right is critical.
Pendants
If your sail luff is not long enough to position halyard swivel properly,
you must add a pendant. Pendants should be made of plastic-coated
wire and be permanently attached so sail height will be correct.
Adjustable-length pendants are not acceptable, as they might not be
adjusted correctly during a sail change.
1. Raise sail, but do not attach tack shackle.
2. Position halyard swivel correctly near top of headstay.
3. Secure halyard.
4. Tie a piece of rope to sail tack.
5. Lead line through tack shackle on furling drum.
6. Tension sail.
7. Measure distance from tack shackle to sail tack and permanently
attach pendant of this length to head of sail.
8. Repeat procedure for every jib in your sail inventory.
To prevent wraps, jib halyard must pull slightly to rear. On most
boats, halyard lead angle is acceptable if halyard swivel is raised
to top of foil.
On some boats halyard sheaves are located too close to headstay
and a Halyard Deflector or a Halyard Restrainer must be used.
Halyard restrainers should be used only when required by masthead geometry. Restrainers tend to limit sail luff length and may
cause problems if not installed properly.
If your boat needs a Halyard Deflector, use Part No. 7301 or a
Halyard Restrainer, use Part No. 944.
The Restrainer should be mounted as high as possible on face
of mast. Position restrainer so that foils will not hit it when
under load.
The restrainer should deflect halyard as little as possible or you
Halyard Deflector
may experience difficulty in tensioning sail luff, friction when
furling, and possible damage to foils. To decrease deflection
angles, shorten sail luff.
Tip: Boats used in charter service should have a halyard restrainer,
regardless of masthead geometry.
Halyard Tension
The jib halyard should be firm, but not too tight.
Tip: The luff foil system supports sail along its length so halyard
tension is used only to shape sails, not to support them. Use
enough halyard tension to remove some wrinkles along luff of
sail. Do not tension halyard enough to cause vertical wrinkles in
luff of sail. Tension to adjust position of draft in sail to suit sailing conditions. Halyard should be firm but not tight. If in doubt,
release halyard tension. To protect sail, ease halyard when boat
is not in use.
Halyard Restrainer
30 MKIV Underdeck Unit 0
Operation Halyards/Headstay Tension
Spinnaker Halyards
Spinnaker halyards occasionally cause problems
with furling.
WARNING! In severe cases, spinnaker halyards
can jam furler causing loss of control of boat.
Make sure halyards are clear of top of foils
and halyard swivel.
On many boats it will not be possible to attach spinnaker
halyard to bow pulpit or it may be "sucked" into jib when
furling.
On some boats the spinnaker halyard lays across
headstay and will catch on halyard swivel, foils, or
jib halyard. To prevent problems it may be necessary
to install a masthead bail to move spinnaker halyard
block forward and to one side.
Boats with external halyards may find it necessary to
flip both ends of spinnaker halyard behind spreaders
to prevent fouling with furling system.
Headstay Tension
A furling system will work best if headstay is tight.
A loose headstay is difficult to rotate and can cause
unusual wear on foil joints.
To adjust headstay tension, first check to see if turnbuckle
is below deck. If so, make adjustments up under the bow.
If it is not below deck remove sail and follow instructions
on page 26.
Tip: Before adjusting headstay tension, slack mainsheet
and vang.
Backstay Adjusters
Backstay adjusters allow headstay tension to be varied to change sail shape to
match conditions. They permit a very tight headstay to be eased when boat is not
in use. For best performance, consider adding a backstay adjuster; either a block and
tackle, a mechanical adjuster like those offered by Harken, or a hydraulic adjuster.
Remember to keep headstay tight for best performance when furling or reefing.
If your boat is fitted with an adjuster be sure that it is tensioned before the
halyard is tensioned. If not, backstay adjuster may increase halyard tension and
could damage the sail or furling system.
Racing boats often slack the headstay completely when sailing downwind. Check
to be sure that foil does not jam against upper headstay terminal when backstay
is released. To prevent this, it may be necessary to shorten foil slightly.
MKIV Underdeck Unit 0 31
Operation Raise Sail/Storm Sail/Reef
Raise Sails
1) Install prefeeder by securely tying end of line to a deck fitting or to
toggle below furler so it is 2' (610 mm) below feeder.
2) Shackle tack of sail to tack shackle. Install shackle so screw pin head
is on same side as sun cover.
3) Secure genoa sheets to clew of sail.
4) Attach genoa halyard to halyard swivel.
5) Pass luff tape through prefeeder and feeder into foil groove.
6) Attach head of sail or pendant at head of sail to halyard swivel.
7) Hoist sail.
Tip: New sails are often stiff and may hang up on prefeeder during
raising. Do not force sail when it hangs up—lower and remove
twist. Sails "break in" with use and will become easier to raise.
Storm Sails
Most people will use one multipurpose genoa for all their sailing, but it is not good seamanship to go offshore
without storm sails.
Heavy-air working jibs and storm sails may be used with your unit. These sails need to have luff tape added to
allow them to be raised in headstay foils.
These sails will generally require pendants to ensure that halyard swivel is properly positioned at top of headstay.
See page 29.
Remember that heavy-air working jibs and storm jibs may be reefed and furled like any other sail.
Furl and Reef
To furl or reef, ease the jib sheets and pull
furling line.
In very light air, it may be necessary to place
some tension on jib sheet to insure a tight furl.
In a breeze, you must completely luff sail by
totally slacking jib sheets before furling.
The furling line should pull readily. The amount
of force required is related to amount of wind,
but unit should never require use of a winch
to furl. If the sail will not furl, or if furling
requires a great deal of effort, there is a problem with system. Consult the Troubleshooting Guide on page 35.
Do not use a winch to force a system to turn. If you are certain that the system is operating properly, you may
use a winch to make furling easier.
32 MKIV Underdeck Unit 0
Operation Reef/Secure Sail
Reef
A sail may be partially furled before you resume sailing. This is
known as reefing.
Many sailors find it helpful to place marks on foot of sail so that
they can reef to a variety of predetermined jib sizes. This allows
marks to be placed on jib lead tracks or toe rail so that lead
block position can be changed to correspond to reefed jib.
Sails are generally reefed to balance boat and to reduce heeling
moment. Sails may also be reefed to improve visibility or to slow
2–3 wraps
of line
boat while sailing in congested areas or entering or leaving harbor.
Secure Sail
When furling prior to leaving your boat in slip or on mooring, be sure that you get a tight furl
and continue furling system until sheets wrap around rolled sail two or three times. Some
people secure sail with shock cord or sail ties. Be sure to securely cleat furling line to a
standard horn cleat.
Be sure that mooring lines are not placed across furling line where they may cause chafe.
Operation Race Conversion
Race conversion allows use of both
grooves for sail changes and tacking
genoas on deck for use of maximum
luff length genoas.
Halyard Swivel Below Feeder
Use halyard to lift halyard swivel up, away
from feeder. Loosen screw one revolution only. Slide screw up and hold. Remove
feeder carefully—bottom end first. Don’t lose the feeder overboard! Lower swivel
onto torque tube. Replace feeder.
Halyard Swivel Off Furler
Serious racers may want to remove the
halyard swivel.
1. Rig a secure, temporary headstay.
2. Determine location of turnbuckle.
3. Refer to pages 23 to 25 for procedure
for loosening and disassembling
turnbuckle so that the halyard swivel
can slide off foils and stay.
Note: It is not possible to remove halyard
swivel on a unit with a Norseman/Sta-Lok
®
or rod adapter stud unless you disassemble
terminal stud. Make sure you use a new
®
Norseman/Sta-Lok
Norseman/Sta-Lok
wedge to reassemble
®
fitting.
Remove Feeder
Loosen screw one revolution only. Slide screw up and hold.
To Remove
Feeder For
Racing
1.
2.
1. Loosen screw
one revolution only.
2. Slide screw up.
Remove feeder.
3. Lower halyard
swivel.
Carefully remove feeder–bottom
end first. Don't drop the feeder
overboard!
MKIV Underdeck Unit 0 33
Maintenance Clean/Inspect/Remove Furler
Clean and Lubricate
Keep unit clean. When you wash boat,
flush unit with soap and fresh water.
Occasionally lower sail and flush halyard
swivel with soap and fresh water.
1) To clean drum bearings, squirt a mild
detergent and water solution into the small
gap between the plastic ball and the spool
extension as shown at right. Spin drum
Clean Halyard Swivel bearings
Clean drum bearings
and let soak. Follow with one minute
flushing with hose.
2) If a more thorough cleaning is
required: Taking all precautions to keep
mast secure, disconnect stay. Remove
bridge assembly. Remove ball/spool
assembly. Flip upside down and flush
bearings as above but through the line
opening in the ball/guard.
Clean foils by washing with soap and
water. A scrap of luff tape may be run up
foil to scrub inside the grooves. Spray
®
foils with McLube
during sail changes.
to reduce friction
Remove Bridge AssemblyRemove Ball/Spool Assembly
WARNING! Periodically inspect items listed below and any others as necessary. Failure to inspect
can cause an accident.
Inspect
1) Unit for signs of chafe, wear, or damage.
2) Turnbuckle below drum or inside torque tube for signs of loosening. Check headstay tension for signs of loosening.
3) Rigging components for signs of stress corrosion.
®
4) Norseman or Sta-Lok
terminal or rod terminal for signs of loosening.
5) All screws on unit to be sure they have not loosened.
6) Foil to make sure that it has not dropped into torque tube. Periodically inspect wire for signs of wear or unraveling.
Replace Line
Use small-diameter, high-strength line at forward end and have a rigger add a cover at the aft end where the line is
3
handled. Forward diameter
/16" (5 mm). Aft diameter 1/4" (6 mm).
Storage – Mast Down
In areas where it freezes, do not store system where water can accumulate in foils. When water freezes it will
rupture aluminum. Store foils under cover, with grooves facing down or on an angle so water will run out.
Storage/Transporting
Do not store or transport system with large extensions beyond mast. Remove masthead clevis pin and shift furler
up so drum assembly can be strapped securely to mast. Some people remove drum assembly and halyard swivel
for storage and transport.
After Storage or Transport
After storing or transporting unit, clean thoroughly including ball bearings. See instructions above.
Remove Furler From Boat
In order to prevent foils from locking against upper stay terminal when backstay is released, loosen torque tube screws
and lower foil before loosening backstay.
34 MKIV Underdeck Unit 0
Troubleshoot
ProblemProbable CauseSolution
Sail will not furl or
is difficult to furl.
Sail will not unfurl
or will not unfurl
completely.
Sail will not furl
completely.
Headstay rotates in
jerks or elliptically.
Sail does not stay
furled.
Sail will not go up.
Sail will not raise
completely or luff
will not tension.
Sail will not
come down.
Ultravoilet cover rolls
up inside of sail.
Delrin® is a registered trademark of E. I. du Pont de Nemours and Company or its affiliates.
Loctite® is a trademark of Henkel AG & Company KGaA
McLube™ is a registered trademark of McGee Industries, Inc.
Jib halyard is wrapping around headstay because
angle between mast and halyard is too shallow
Jib halyard is wrapping around the headstay
because halyard swivel is too low.
Jib halyard is too tight.Ease jib halyard.
Foils riding on turnbuckle.Raise foils. See adjusting turnbuckle on page 23.
Foils too high, binding on swage eye.Lower foils until clear. See adjusting turnbuckle on page 23.
Spare halyard is wrapping in sail as it furls.Secure spare halyards away from furling headstay by flipping them behind spreaders
Salt or dirt in bearings.Flush bearings frequently with fresh water and a detergent solution.
Furling line tangled in drum.Overrides are best prevented by using a 7402 ratchet block as the last furling line lead to
Stop knot catching.Make sure knot is a single overhand and is pushed up inside drum.
Sail full of wind.Luff completely before furling or reefing.
Sail flogging too much.Release a short length of sheet, pull some furling line and repeat.
Jib sheets are not free.Free jib sheets.
Foil out of torque tube.Reinstall foil in torque tube and tighten clamp screws.
No wraps of furling line on drum.Remove sheets. Rotate stay wrapping as much furling line on drum as possible.
Furling line is charged in the wrong direction.Make sure line is charged clockwise so that furling direction is counter-clockwise.
Jib halyard is wrapping around headstay because
angle between mast and halyard is too shallow.
Jib halyard is wrapping around the headstay
because the halyard swivel is too low.
Foils riding on turnbuckle.Raise foils. See adjusting turnbuckle on page 23.
Foils too high, binding on swage eye.Lower foils. See adjusting turnbuckle on page 23.
Jib halyard is too tight.Ease jib halyard.
Spare halyard is wrapping in sail as it furls.Secure spare halyards away from furling headstay by flipping them behind spreaders
Salt or dirt in bearings.Flush bearings with freshwater and detergent.
Furling line is not free.Free furling line.
Insufficient furling line on drum.Remove sheets. Rotate stay, wrapping as much furling line on drum as possible.
Too much line on drum.Adjust amount of line on drum or change position of forward lead block to allow line
Spare halyard catching in sail as it furls.Move halyards away from furling headsail as above.
Insufficient tension on headstay.Tighten headstay and/or backstay to eliminate sag in headstay.
Sail not furled tightly on stay.Maintain drag on sheets while furling.
Furling line not secure.Secure furling line.
Luff tape will not go into groove.Check luff tape for fraying.
Sail catching at prefeeder.Flake sail more loosely on deck.
Dirt in groove.Clean groove.
Halyard swivel is hitting end stop.Luff of sail is too long and must be recut.
Angle between halyard and mast is too sharp
and halyard is pulling too much to the rear.
Halyard is wrapping on headstay.Angle between headstay and halyard is too shallow and must be optimized per installation
Halyard swivel off foil.Sail luff too long or foil is too short or low and must be lengthened or raised.
Furling line is wrapped on drum in wrong direction.Remove sail and sheets. Pull line to remove all furling line from drum. Turn stay to rewind
See installation instructions regarding optimal halyard angle. It may be necessary
to mount a halyard restrainer on front of your mast to hold halyard to rear.
See installation instructions regarding optimal halyard swivel height. A wire pendant
may be needed at head of sail to raise halyard swivel to proper height.
maintain proper drag on line while unfurling.
See installation instructions regarding optimal halyard angle. It may be necessary to
mount a halyard restrainer on front of your mast to hold halyard to rear.
See installation instructions regarding optimal halyard angle.
to roll evenly on drum.
Check luff tape size.
Halyard must be routed from a point higher on mast. This may require that any halyard
turning blocks aloft be replaced or sail shortened.
instructions.
line on drum in a clockwise direction. Suncover must be on the starboard side of sail.
Make sure line is charged clockwise so that furling direction is counter-clockwise.
®
is a registered trademark of Sta-Lok Terminals, Ltd.
Sta-Lok
®
Torlon
is a registered trademark of Solvay Advanced Polymers
Online Product Registration
www.harken.com/FurlingWarranty
MKIV Underdeck Unit 0 35
Warranty: www.harken.com/manuals
or call, write, email or fax Harken, Inc.,
Pewaukee, WI USA
MKIV Underdeck Unit 0 Parts List
No.DescriptionOrderPart No.
Foil Clamp1H-42959
Socket Head Cap Screw (M4 X 12MM) 4HFS1102
Torque Tube 1H-52148
Socket Head Cap Screw (M5 X 8MM) 3HFS331
Bow Shackle 6MM 12110
Deck Plate1H-52081
Clevis Pin (
Cotter Pin (.094" X .750") 2HFS181
Keeper1H-52131
Socket Head Cap Screw (M6 X 16MM) 2HFS747
Smalley Retaining Ring (VS-150-SO2) 1HCP821
Ball/Guard 1H-52061
Torlon
Spool1H-52141
Bridge1H-52720
Bullseye Fairlead1237
Slotted Roundhead Screw (10-32 X 1.500") 2HFS106
Flatwasher 10 (.032" X .203" X .438") 2HFS111
Hex Nut 10-32 2HFS110
5
/16" X 2.219") 2HCP637
®
Ball (3/8”)17MP-127
HFG951
HCP637
HFS181
1
H-42959
HFS1102
H-52148
1
2110
HFS331
H-52081
HCP637
HFS181
H-52131
HFS747
HCP821
HFS747
H-52061
MP-127
H-52141
H-52720
HFS106
HFS110
HFS111
237
36 MKIV Underdeck Unit 0
MKIV Underdeck Unit 0 Parts List
This manual may be modified without notice. See: www.harken.com/manuals for updated versions.
Hole Saw Size Recommendations
Read before drilling.
41/4" (110 mm)—Requires some
beveling of bottom edge of deck hole
33/8" (86 mm)
!
to provide a good fit. Alternatively, a
smaller hole may be used to fashion
a socket in deck to conform to ball
shape. This may improve appearance
and reduce amount of water that
enters.
41/2" (115 mm)—Use if no beveling
to underside of deck is desired.
83/16"
208 mm
529/32"
(150 mm)
23/4" (70 mm)
Hole Saw Size
See Above
41/4" (110 mm)
Hole Saw Size
See Above
41/2" (115 mm)
IMPORTANT: If you print this template from a computer file,
measure to confirm that template is the correct size.