This blog is devoted to my John Welsford designed 15' Navigator yawl Ellie. I built her in my garage over a period of 18 months and launched her in 2011. She sports a sliding gunter main, roller furled jib and sprit-boomed mizzen. Her construction is glued-lapstrake over permanent bulkheads and stringers. This blog is a record of her construction and her voyages here in the Puget Sound area and (hopefully) a useful resource for fellow Navigator builders.

Thursday, December 9, 2010

How to build a roller furler for under $40

Ellie's home-made sub-$40 roller furler

There are many different types of roller furling systems. This furler is a "Wykeham Martin" or "wire luff" type.  This popular design has been in continuous use worldwide for well over 100 years.  It requires a jib that has a stainless steel wire sewn into the luff, or has a "jib set flying" (a jib that does not attach to a stay).  If your jib hanks onto a fixed forestay or needs to wind around a forestay this furler won't work for you. The furler you need would be more like this one.

This furler, as illustrated below, is sized for my 15' Welsford Navigator, or any similar sized small sailboat. It is comparable to a Ronstan RF76 or a Harken 434 dinghy furler.  It can be scaled up in size and strength for larger boats by substituting a stronger eye-bolt, stronger u-bolt, upper swivel, and ball bearing thrust bearing.

Here is a test run of the furler


In issue #58 of Small Craft Advisor magazine, Kirk Gresham wrote an excellent article on how he designed and built two roller furlers for his 17' cutter Eider for a mere $40 each using bits of scrap and a few bits and pieces of hardware from a local hardware store. This saved Kirk a whopping $670 off the $750 price tag he was quoted for two furler units from a local Port Townsend chandlery. I knew from the moment I read Kirk's article that I wanted to build one of his furlers too. I love building things. I'd much rather build something than buy it, even if it ends up costing me more. But in this case building it saved me a bundle too. That's a two-fer for me!

I had some questions after reading the article, but I knew Kirk attends the Port Townsend Wooden Boat Festival every year, so I met Captain Kirk at the festival. He answered all of my questions and allowed me to take some close up photos of his furlers.

Being a mechanical designer by trade, naturally I couldn't resist making some improvements to the design.  I used bronze thrust washers in place of the steel radial bearings Kirk used, and I made the spool with a core of solid hardwood instead of using a section of PVC pipe.  These two changes significantly increase the strength of the furler, make it operate more smoothly and increase corrosion resistance. I also used an ABS end cap instead of the bent aluminum strap used to contain the furling line. It looks better and does a much better job of containing the line.

So, here I present my improved version of Kirk's $40 roller furler.
Click to enlarge

Making the Drum Assembly

The drum is made from an inexpensive 3" ABS drain pipe end cap available at any home center that sells indoor plumbing supplies, like Home Depot, Lowes, Grainger, etc.  The cap I used is a Mueller 2979H.  (Note: a 3" cap is actually 4" in diameter.  It caps a 3" inside diameter drain pipe).  Caps are available in a variety of sizes if you want a larger or smaller furler. You will also need a stainless steel eye-bolt. I used a 1/4" x 4" Stanley V2161 from Lowes, but this metric SD-080708 welded eye bolt from Duckworks is a better choice as it is much stronger. To make the drum assembly, drill a 1/4" hole in the center of the end cap for the eye-bolt. Drill 7/8" diameter holes every 45 degrees around the outside for access to the furling line. Locate these holes so they are 1/4" below the open end of the cap.
I also drilled a series of small drain holes in the bottom of the drum.
Use locktite to secure the two nuts on the eyebolt.

Making the Spool Assembly

To make the spool assembly, first I cut two plywood disks from 1/4" plywood. The outer diameter of the disks should be just slightly less than the inner diameter of the ABS cap. We don't want the furling line to slip through the gap and jam the furler. Sandwiched between the disks is a piece of oak (or any other hard wood) that is 2" in diameter and 7/8" thick. Glue these three pieces together taking care to align them accurately. Drill a 1/4" hole through the center for the eye-bolt. Drill two more holes to match the stainless steel U-bolt legs. The U-bolt I used is a 1/4" x 1-1/8" x 3-1/2" Stanley V2193. Drill one extra hole in the upper disk for the stop knot of the furling line. Paint the spool with several coats of enamel paint. Cut and file the legs of the U-bolt flush with the nuts. Use locktite to secure all four nuts.

Assembling the unit

To assemble the unit, place the spool onto the eyebolt of the drum assembly. Then add a 1/4" stainless steel washer, your thrust bearing, and a securely locked nut. It is crucial that this nut be secured so that it cannot turn in either direction, or worse yet, come off in service causing the furler to come apart.  A locknut alone is insufficient - it will eventually loosen.  There are many ways to safely secure this nut.  Using locktite is adequate. Using two ordinary nuts tightened against each other, either with or without locktite, is excellent.  Or, if you want the ability to disassemble the furler  easily, you could use a castle nut, drill a tiny hole through the eyebolt and secure it with a cotter pin or split ring.
The thrust bearing is simply one or two 1/4" I.D. sintered bronze thrust washers. These strong, inexpensive, corrosion resistant self-lubricating washers should be available at any good hardware store, or you can order them here. Once in a great while, apply a drop of motor oil to the thrust washers. It will soak into the porous metal and lubricate them for a long time.

A ball bearing can be used instead of the thrust washers if you prefer. They are more expensive but may operate more smoothly under high tension.  The exact size you need will depend on the diameter of your eyebolt and the space available inside your u-bolt. The style of bearing you would want is shown below, and a source for stainless steel thrust bearings in many sizes is here.  I've tested both the thrust washers and the ball bearings on my boat and there was no noticeable difference.

Tie a stop knot in the end of your furling line, feed it through the hole in the upper disk and out through one of the holes in the drum. Spin the spool to wind up the line.

Upper Swivel

A swivel is required at the head of your jib to allow the wire luff to spin and roll up the jib.  With this type of furler you want a swivel that spins easily. I have tested three different swivels on my boat that have worked well for me.

This anchor swivel, is a good choice provided your luff tension is not too tight.  If your jib uses a jib halyard, this swivel will work for you. It is extremely strong, very inexpensive, and spins well under moderate tension.  However, since it's not a ball bearing swivel, it can stick when tensioned too much.

Ball bearing swivels are a better choice.  The Ronstan RF75 swivel is considerably more expensive, but is an excellent choice for larger sailboats with higher luff tensions.  Amazon has a number of swivels that look promising, but I haven't tested them.  And this jumbo sized (size 10) fishing swivel is an excellent choice for smaller sailboats and sailing dinghys.  It is the largest ball bearing fishing swivel I've been able to find and works very well on my Navigator. It is rated to support up to 810 lbs.  Do not rely on this fishing swivel to hold up a mast on anything larger than a sailing dinghy.

A word about strength

Make sure you select components that are strong enough for your application. An easy and conservative way to do this is to look at the diameter of the stainless steel cable used to make your jib's luff wire.  My jib uses 1/8" cable, which has a Safe Working Load (SWL) of 352 lbs.  3/16" cable has a SWL of 740 lbs, and so on.  The SWL of each one of your components (eye-bolt, u-bolt, swivel, thrust bearing, shackles, etc) should be at least as high as that of your cable's.  You'll be able to find the SWLs on the product's packaging, at the manufacturer's website, or with a bit of Googling. That way you'll know your furler is stronger than your luff wire.


This furler has performed flawlessly on my Navigator Ellie for over 12 years now, and I couldn't be more pleased with it.  If you have any feedback or if you build one of these furlers for yourself, I'd love to hear about it.  Please leave a comment below.