Stearns Twinstay One / Dynafurl One

Introduction

The Stearns Twinstay One was the first double groove luff support system.
The Stearns Dynafurl One was the first double groove furling system.
The Stearns Dynafurl One is made by adding a halyard swivel and a drum and drum cover assembly to a Stearns Twinstay One.

*** The Stearns Twinstay/Dynafurl Three (TS3) is a later version with 2 grooves aft and is anodized Black. Some parts are as Dynafurl One #12, others are available, please call.

Designed by Tim Stearn as an improvement on his original Hyde System design, and introduced in 1973, the Twinstay One immediately came to dominate the U.S. and international racing circuits. For the first time boats could hoist a new headsail before taking down the old one! This was a revolution in racing circles. Although we take it for granted today, before the Stearns system all sail changes were bald-headed.

Other improvements on the earlier system were performance-oriented as well. The narrowing of the rod profile increased its aerodynamic performance by reducing windage, rod and terminal ends were optimized to reduce weight even further, and terminal end design was simplified. Another improvement was an ingenious 'wedge' method for fitting the rod to the terminal ends. This allowed the system to be assembled to its final length on the dock or elsewhere quickly and without the use of special tools.

Popular with race boat owners and boat builders alike was the fact that the Twinstay racing foil was designed to be quickly and easily converted to the Dynafurl furling system, with the use of a few additional components. See: Dynafurl One Components. Racers liked the fact that after a regatta, in just a few minutes, their racing foil could be converted to furling for the trip home. Boat builders liked the fact that they could equip their racer/cruisers with the same efficient, Circuit level racing foil and offer an easy furling option.

Though 45 years have passed since the introduction of the Dynafurl system, many of its features have not been surpassed by any of the more recently introduced furling systems. All of the modern crop of furling systems are designed around UPS shipping restrictions which limit their maximum section length to about six feet. This basic design constraint creates many problems in addition to increased weight and windage, most of which are due to the necessity of connecting all those short sections back together. Fastening the joints, keeping them from bending or kinking, and keeping the fasteners in place have been problems for many newer systems. The tendency of these systems to chafe the wire forestay, as they spin around it, at the joints and at the end of the extrusion can cause damage leading to snagging and unlaying of the stay. This has caused the loss of many a rig over the years. All of these problems are eliminated by the use of a one-piece solid rod.

Stearns systems are still in use on thousands of yachts worldwide, and although new systems are still being made, we frequently get calls from people who bought a used one or who found a system abandoned in a boatyard. Usually all these systems need is a bearing replacement kit or a shortening kit to put them back in use on a new yacht – which they will probably outlast as well. Twinstay systems can easily be converted to furling systems with the addition of a Dynafurl conversion kit.

Occasional bearing replacement (on average about 8 years), and periodic inspection are all that is necessary to keep this system in top form indefinitely.

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Features

Solid Rod Design -- means less stretch, less windage and greater strength.
- Forestay rod of 6061-T6 aluminum stretches far less than a wire headstay – less even than stainless steel rod rigging. Less stretch means less headstay sag and greater sail efficiency.
- Aerodynamic rod profile is more efficient than any other furling system available – resulting in less windage and more efficient sail performance.
- Solid rod is much stronger and more impact resistant than hollow systems. An impact from a spinnaker pole that would deform the luff grooves of a sectional system –making it impossible to raise or lower a sail- will not affect the rod. Even the travel-lift can't hurt it.
Stainless Steel Terminal Ends: Type 316 Stainless Steel rod end components are machined from solid bar for strength, reliability and a virtually permanent life span. End fittings are permanently attached to the rod, but are reusable in the event that a system needs to be shortened, or the rod replaced.
Drum, Drum Cover, & Halyard Swivel: Cast from high-strength, lightweight, Almag 35, these fittings are machined and hardcote anodized for long term corrosion resistance.
Low System Weight: This maximization of innovative design engineering and careful selection of materials results in a furling system that, 45-years after its introduction, still weighs less than any system available today. Less weight -- especially in the ends of the boat and aloft -- translates directly to increased boat performance.
Easy Maintenance: Occasional bearing replacement (on average about 8 years), and periodic inspection are all that is necessary to keep this system in top form indefinitely.
Easily Convertible: Quickly and easily converts back and forth from maximum-hoist racing configuration to furling system.
Proven Reliability: For 45 years the Stearns Twinstay/Dynafurl One has been in production, virtually unchanged from its original design. Boats all over the world are still sailing with their original system, many are entering their 4th or 5th decade of continuous service.

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System Specifications

The Stearns Twinstay One is a rotating twin-luff support system with an elliptical, aluminum, one-piece, solid rod luff extrusion, with two luff grooves on opposite sides. The solid rod replaces the conventional wire forestay.

The Stearns Dynafurl One is a furling system made by adding a halyard swivel and a drum and drum cover assembly to a Stearns Twinstay One, see: Dynafurl One Components.

System Sizes are identified by Rod Width. To determine your system size, measure the narrow dimension of the forestay rod. Measure the width carefully – sizes vary as little as 1/16". We recommend using calipers or a micrometer.

Stearns SYSTEM SIZES
Stearns	#6*	#8	#9	#10	#12	#14**
Rod Width "W" (inches)	3/8"(.400)	1/2" (.500)	9/16" (.580)	5/8" (.650)	3/4" (.740)	13/16" (.820)
Equivalent Wire Size	3/16"	1/4"	9/32"	5/16"	3/8"	7/16"
Luff Tape Size	#4	#6	#7	#7	#8	#10
Rod Breaking Strength (lbs.)	*	8,200	10,300	12,500	17,600	23,500
Rod Weight per foot (lbs.)	*	.236	.330	.398	.546	.830
Terminal End Diameter "E"	1 1/16"	1 1/4"	1 5/8"	1 5/8"	2 1/8"	2 1/8"
Weight of Terminal End (lbs.)	0.6	0.9	1.5	1.5	3.6	3.6
Maximum System length (pin to pin)	*	41'	51'	63'	65'	65'
Drum Diameter (Maximum OD)	5"	5"	6"	6"	7 1/4"	7 1/4"

* #6 Rod is out of production. All other parts are available.
** Larger Size #16 (.930" Wide), and #32 (1.45" Wide) Rods are out of production, all other parts are available.

Stearns

#6 / #8

#9 / #10

#12 / #14

A (eye width)

3/8"

1/2"

5/8"

B (pin hole)

3/8"

1/2"

5/8"

C (pin ctr. to end)

5/8"

3/4"

E (terminal body dia.)

1 1/16" / 1 1/4"

1 5/8"

2 1/8"

F (pin ctr. to rod end)

2 5/8"

2 3/4"

4 3/8"

G (drum dia.)

7 1/4"

H (pin ctr. to pin ctr.)

I (cover plate dia.)

2 1/2"

2 3/4"

3 3/4"

J (tack pin dia.)

3/16"

3/8"

1/2"

K (aft of rod to pin ctr.)

L (clevis gap)

3/8"

7/8"

M (eye hole)

7/8"

1 1/4"

N (aft of rod to pin ctr.)

P (pin dia.)

3/16"

1/4"

5/16"

Q (bearing housing OD)

3 1/4"

3 3/4"

4 1/2"

R (delrin insert OD)

1 1/4"

1 1/2"

S (LOA)

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Twinstay One Components

For complete Part Numbers, additional Data, and Pricing, See Stearns System Pricing, below.
* Substitute System Size for *.

Twinstay One Components**		Part #
	Upper Deck Eye	Stearn # * -16
	Upper Terminal Body	Stearn # * -15
	Feeder Assembly	Stearn # * -14
	Prefeeders (feed rings)	Stearn # *-13
	Twinstay Rod	Stearn # * -12
	Terminal Cap set screw	Stearn # * -11
	Lower Terminal Body	Stearn # * -10
	Locking Pin	Stearn # * -9
	Dowel Pin - 2 each end	Stearn # * -8
	OD Wedge - 2 each end	Stearn # * -7
	ID Wedge	Stearn # * -6
	Torque Nut (2 sizes for #12/14)	Stearn # * -5
	Bearings	Stearn # * -4
	O-Ring	Stearn # * -3
	Terminal Cap	Stearn # * -2
	Lower Deck Eye	Stearn # * -1

** Note: Terminal End interior components are identical in Upper and Lower ends.

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Dynafurl One Components

For complete Part Numbers, additional Data, and Pricing, See Stearns System Pricing, below.
* Substitute System Size for *.

Dynafurl Halyard Swivel Assembly		Part #
	Halyard Swivel Complete	Stearn # * -30
	Delrin Insert Pair, with screws	Stearn # * -31
	Delrin insert screws (2)	Stearn # * -32
	Split Sailhead (pair)	Stearn # * -33
	External Snap Ring (2 required)	Stearn # * -34
	Bearing Top Cover	Stearn # * -35
	Bearing Housing	Stearn # * -36
	Internal Snap Ring	Stearn # * -37
	Halyard Swivel Bearing	Stearn # * -38
	Shackle	Stearn # * -39

Dynafurl One Drum and Cover Assembly		Part #
	Drum & Cover Assembly Complete	Stearn # * -40
	Drum Only, with bolt	Stearn # * -41
	Drum Bolt	Stearn # * -42
	SS Fastpin (2 required) or,	Stearn # * -43
	Shackle (2 required)	Stearn # * -44
	Drum Cover Only, with screws	Stearn # * -45
	Drum Cover Plate, with screws	Stearn # * -46

Dynafurl One Halyard Swivel Complete Stearn # * -30
Complete Halyard Swivel for Stearns Dynafurl One.

Dynafurl One Drum & Drum Cover Set Complete Stearn # * -40
Complete Drum and Drum Cover Assemblies with fasteners for Stearns Dynafurl One.

Dynafurl One Fittings Complete Stearn # * -50
This package includes all the parts to convert your Twinstay racing foil to a Dynafurl furling system, includes Halyard Swivel and Drum & Cover Assemblies with all fasteners.

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Bearing Replacement Kits

With a little easy maintenance and occasional bearing replacement, your Stearns System should last several lifetimes. Bearings are easily replaced by any individual who is mechanically inclined and has the ability to follow instructions. The system must be down in order to do a complete bearing replacement. To purchase bearings and components that go inside the ends of the system, you will need to know your system size, and, for System sizes #8 - #14, additional data listed below. Then, See Stearns System Pricing.

Stearns Systems size #8 has been produced with 2 different End Bearing Arrangements. Earlier systems used 3 bearings per end, newer systems used 1 stronger bearing per end. The only way to tell which type you have is to disassemble them (See: Terminal End Bearing Removal, below. You will need a 1/16" Allen wrench). The two Bearing types are not interchangeable, nor are any other of the Terminal End components.

Stearns Systems sizes #9 - #14 have been produced with 2 different Terminal Body Types, Tapered & Cylindrical. Earlier systems used the Tapered Terminal Ends. The two Bearing types are not interchangeable, nor are any other of the Terminal End components.
Tapered Terminal Ends taper down in diameter as they approach the rod. They are cast Stainless Steel, and have the Stearns logo cast right into them. On the Lower end, the logo will be covered by the Furling Drum.
Cylindrical Terminal Ends are machined from Stainless Steel bar stock and are a consistent diameter their entire length. They have no markings.

Tapered (Old-Style) Terminal Ends Bearing Replacement Kit Stearn # * -51
This kit has all materials needed to replace bearings in both ends, including screws, Allen wrenches, special high-torque locknuts, bearings, ultra high-pressure bearing grease, loctite, O-rings, and instructions. No special tools are required.

Cylindrical (New-Style) Terminal Ends Bearing Replacement Kit Stearn # * -52
This kit has all materials needed to replace bearings in both ends, including screws, Allen wrenches, special high-torque locknuts, bearings, ultra high-pressure bearing grease, loctite, O-rings, and instructions. No special tools are required.

High-Torque Locknuts Stearn # * -5
These special all metal high-torque locknuts are used, one per end, to retain the bearings on the deck eye, and are the only ones able to withstand the loads of the system. They are designed for one-time use only and lose their holding ability after removal.
Stearns System Locknuts must not be reused!!!

Halyard Swivel Bearing Stearn # * -38
You will need a large pair of snap ring pliers to complete this replacement.

Halyard Swivel Delrin Inserts Stearn # * -31
Full-length Delrin Insert bushings provide a low-friction surface and allows the Halyard Swivel to slide easily up or down the Rod. You will need a large pair of snap ring pliers to complete this replacement.

Terminal End Bearing Removal - Applies to Both ends of all Twinstay One/Dynafurl One Systems.
To remove the Terminal End Bearings:
1. Locate and remove the set screw(s) in the Terminal Body using an Allen wrench. They are close to the Deck Eye end of the Terminal Body. These set screws lock the threaded Terminal Cap into the Terminal Body.

2. Locate the vertical holes (2) in the Deck Eye. Insert (2) Pins into the Deck Eye holes and rotate the Deck Eye to engage corresponding holes in the Terminal Cap beneath it. When Pins are engaged, rotate the Deck Eye to unthread the Terminal Cap from the Terminal Body.

3. You have now removed the Deck Eye with Terminal Cap, Bearing stack and Lock Nut from the Terminal Body. Put the Deck Eye in a vise and remove Lock Nut to access Bearings.

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Accessories

Heavy Duty Jaw/Jaw Toggle
Heavy Duty Eye/Jaw Toggle
Heavy Duty Link Plates
Halyard Pullback Devices

Wire/Rope Furling Line
To maximize luff length and minimize weight and drum sizes, the Stearns Dynafurl One is optimized for use with wire/rope furling lines. Tail-spliced, like a halyard, these furling lines come with stop & oval sleeves for attachment to the drum with a nicopress tool.
Trim the wire length to the distance from the cockpit to the furling drum, making sure the wire is short enough that it doesn't come into your hands in your normal furling position. Overall length, after trimming, should be approximately twice the boat length for large genoas in average installations.

Stearns Size Wire/rope sizes Stearns Part # Std. Lengths wire/rope

#8 1/8"/ 3/8" fl 46-3030
fl 46-3040 30' / 30'
30' / 40'

#9 / #10 5/32"/ 3/8" fl 56-3040
fl 56-4050 30' / 40'
40' / 50'

#12 3/16"/ 3/8"
3/16"/ 7/16" fl 66-4050
fl 67-5050 40' / 50'
50' / 50'

#16 7/32"/ 7/16" fl 77-5570 55' / 70'

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Troubleshooting

The standard considerations in all furling system installations are:

Halyard angle -- angle should be aft of parallel to the luff when the sail is fully hoisted. On many masthead arrangements this will require a halyard pullback device installed on the mast. (See Accessories)

Halyard Swivel Height -- halyard swivel should be within 12" of the halyard sheave when the sail is fully hoisted. On shorter sails, this will require a wire pennant attached to the sail at the top (for performance), or at the bottom (for visibility). To check Halyard Swivel height, or to measure for a pennant, carefully hoist the Halyard Swivel with the sail attached to it, but not attached at the tack. When sail is fully hoisted measure from the tack of the sail to the tack pin, or shackle, on the furling drum. Pennant should be 6–12" shorter than this measurement and preferably, attached directly to the sail.

Furling line Angle -- furling line should enter the drum at 90 degrees to the luff. This is achieved by adjusting the position of the furling line block or fairlead closest to the furling drum.

Furling line Tension -- Furling line should always be under tension when the sail is being unfurled. Leading the line through a ratchet block mounted aft of the operator is usually a big help.

Furling line Jam -- there should not be so much line on the drum that it binds against the drum cover when fully wound for any particular sail. Start with the sail rolled up. There should not be more than 3 wraps on the drum when the sail is tightly furled with the sheets wrapped around it twice. If you cannot get enough line on the drum to completely unfurl the sail, then the line you are using is too large. Reduce line size or, remove the core in the forward third of a braided line. "Coring" the line will reduce the amount of space it takes up and cause it to lie flatter on the drum. This should be done in all furling installations using standard braided line, as it reduces fouling and overrides while still giving you a full diameter line in the cockpit. Some systems, notably Hyde and Stearns, are best suited for wire/rope furling lines in many applications. (See Accessories)

If you are experiencing trouble with your Stearns system that is not related to any of those items above, it is usually one of the following problems:

System doesn't rotate smoothly – With reduced backstay tension and no tension on the furling line, grab the drum and rotate the system by hand. If it feels rough or bumpy it is time to replace the Terminal End bearings, torque nuts, and O-rings. (See Bearing Replacement Kits)

Hard to furl – If you've already checked the Terminal Ends (System doesn't rotate smoothly, above) then it's time to check the halyard swivel. Lower the sail and rotate the top of the Halyard Swivel while holding the bottom. It should rotate smoothly and easily. If not, you need to replace the Halyard Swivel bearing. (See Bearing Replacement) Also be sure to check the white Delrin Inserts between the halyard swivel and the rod. Make sure that they are firmly in place and that they fit snugly against the rod. If they are sufficiently worn they can allow the Halyard Swivel to cock to one side. This will increase the effort needed to furl and they should be replaced.

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Ordering/Pricing

Parts - To order parts, you must know your System Size. System Sizes are identified by Rod Width. To determine your system size, measure the forestay rod the narrow way. Measure rod width carefully - sizes vary by as little as 1/16". Then, see Stearns System Sizes to determine your System Size.

Parts Pricing - To get exact Part Numbers and Pricing for them, Click on your System Size, below. Currently all Twinstay/Dynafurl One parts are in stock.

Pricing: Stearns Twinstay/Dynafurl One

#10

#12

#14

To place an Order, See Ordering, you will need Part Numbers.

Complete Systems Pricing – Specify size, system length, pin diameters, and shipping destination and contact us for a quote. As these systems must be shipped full length, and shipping options are limited, please allow extra time for shipping arrangements and delivery.

Introduction	Stearns Twinstay One
Features
System Specifications
Parts Breakdown
Accessories
Bearing Replacement Kits
Shortening Kits
Troubleshooting
Ordering/Pricing

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