Junk Sails

"I can't wait for the oil wells to run dry, for the last gob of black, sticky muck to come oozing out of some remote well. Then the glory of sail will return." -Triston Jones

We did not fall in love with sailing or a particular type of sailboat. Instead we wanted to explorer, work, dive, salvage, charter, operated an ROV, and build things.  We did not want to cruise from one bar to the next.  So we sized the boat to fit the job, then we needed sails that one person could manage. After sailing on a bermuda rigged boat, and watching a big gaff rig go up, we got on a junk rigged boat and saw for ourselves how incredibly easy these sails are to raise, lower and especially reef.  So now we love junk sails. Seeker will have about 2,200 square feet of sail. She will need more than 5 knots of wind before will sail, but she'll be able to make about 9 knots in a good wind.

Mast

A 1251 sq ft sail in a 35 knot (40 mph) gust from a passing squall will sustain a 8,626 pounds of load.  At  61 knots (70 mph) that goes to just over 20,000 pounds. With a center of effort about 20ft up the mast from the partners that spread the loads to the hull.  A light weight boat would simply be healed over or knocked down so that the force of the wind is spilled from the sail.  But Seeker is more elephant than gazelle.  Fully loaded she is 40 tons, with 15 tons of lead ballast and a 16 foot beam. She will not heal easily so the rig must be stouter than most so that something horrible does not happen.

Mast Criteria

#1 Strength - We have 3 mast and what we expect to be a very stiff boat when loaded so I don't see quick healing spilling load from the sails. Hence I have used strongest recommendations I could find, which were in "Design and Build Your Own Junk Rig".

Seekers' Sail Plan

#2 Cost - We are a work boat, and not a charter cruise boat so it does not have to be pretty.

#3 Speed of Construction - Laminating a mast from strips of wood is right out. Tapering a steel pipe does not look that bad,  but an off-the-truck galvanized and ready to install mast would be great.

#4 Weight - I know there are some good arguments for heavy mast and longer roll intervals, especially when it's a junk rig anyway. But I'm having problems getting past how counter intuitive that sounds. :)   Jay Jeffries who is studying to become a naval architect contributed to following: "It is an inertia issue, you don’t need a lot of weight for this as it is a long distance from your center of rotation. Here is my submitted answer for the issue: A dismasted sailboat is more vulnerable to capsize as compared to a vessel with an intact mask due to the large inherent roll inertia (i.e. resistance to rolling motion) of the mast and rigging. It is estimated that the mast and rigging contribute 60% of the total roll inertia when compared to the other two major weight contributors to a boat: hull and ballast. While the mast’s and rigging’s combined weight is much less than the other two, it’s gyradius (k, also known as radius of gyration) as measured from the vessel’s CG is much greater. The moment of inertia (Ir) is defined by the calculation:

Note that the distance of the center of mass of the mast and rigging from vessel’s CG as defined by k is squared which greatly increases the resistance to roll.

A longer natural period of roll (Tn) for a boat is desirable to avoid resonant magnification between the wave trains and the hull. As found in the following equation, a larger Ir will contribute to a larger natural period of roll for the boat.

where:
Tn = the vessel’s natural period of roll
Ir = vessel’s moment of inertia
GM = vessel’s metacentric height
∆ = vessel’s mass displacement" 

You can download this here:  Mast_and_roll_inertia.pdf

#5 Hollow Mast - We want the mast hollow and open for wiring, possibly the engine exhaust and ventilation so having it hot dipped galvanized seems like the best way to protect the inside surface.
 

Steel Mast

Following the formula in "Design and Build Your Own Junk Rig" we get the following:

A = sq ft of sail area
H = height of mast above the partners (supports) in inches.
S = safety multiplier (2 for small ballasted, 3 for large, 3.5 for beamy  boats or boats over 35 ft.

Diameter in Inches = Cube Root of (16 x A x H x S / 15700). Our numbers for the main mast are: A = 1252, H = 542, S = 3.5 Or the cube root of 38000704 / 15700, or the cube root of  2420.4270063694267515923566878981 which comes out to: 13.426536495548100264179437252339.  Did it all in my head. ;)

So we need a main mast that is about 14 inches at the partners; it's total length is 56.25 ft the mast above the partners is 45 ft and 11.25 ft extends down to the keel.  The mast is tapered so that the top of the mast is  7 inches or 1/2 of the diameter that it is at the partners. The thickness of the steel is 3/8 inch for 50 ft or more, 1/4 inch for 30 to 40 ft, and 3/16 to 1/4 for 20 feet, so our main mast will be 3/8 inch.

Eight Sided Steel Mast

Just a mile down the street from us in a Valmont manufacturing site that make 8 and 12 sided steel galvanized utility poles to order.  Kay and I put on nicer cloths to look more respectable and walked in there front door with our mast specs.  After a few "your stupid looks" we got Tom, the utility department manager convinced we were for real.  Unfortunately the press are only able to form 8 sided poles when the top is less than 10 inches, however the price is better than I expected. Below is the quote from Tom Lovegrove.

Round Tapered Galvanized Steel Mast

There is another Valmont plant in El Dorado, Kansas that does produce round tapered steel utility poles. They have standard poles that would work for the fore and mizzen mast, but their longer poles have a wall thickness that is too thin so that would have to be custom built.
Fore #H00J500-P4; Length 50 ft, Base 13 in, Top 6 in, Wall 3 gauge, .2391 in, 1335 lbs (including base)
Mizzen #950A350-P2; Length 35 ft, Base 9.5 in, Top 4.6 in, Wall 11 gauge .1196 in, 370 lbs (including base)

We got another quote from Mike Skeen, skeen@unionmetal.com with Union Metal Corporation in Nebraska.

Quotation   To: Jackson Boat Building   Proj.     ATTN: Doug Jackson   Proj. #           Date: May 29, 2009         QTY:   Description Unit Pr.     Extd.           1 ea. Galvanized steel pole 5/16" x 17" x 56 ft $4,470 $4,470.00 1 ea. Galvanized steel pole 1/4" x 12" x 43.5 ft $1,920 1,920.00 1 ea. Galvanized steel pole 1/4" x 7" x 32.33 ft $950 950.00               Total $7,340.00

DIY Steel Mast

The local steel yards are about 38 cents a pound. (May 2009)  The fore mast would be about $520.  So we could cut the price in half, but would require tapering the pipe by cutting darts, pressing the seems together and welding it back up. None of that is actually necessary except to make it look right and save perhaps four hundred pounds overall. But it will add on considerable time and will never look as good or be as strong as a machined tapered steel pipe.

Steel Mast Example from "La Chica"

Main Mast
LAP: 10,460mm       (34' 4")
Bury: 2,240mm         (7' 4")
Dia Partners: 235mm (9 1/4")
Dia Top: 96mm         (3 3/4")
Dia Base 117mm       (4 5/8")
Wall is 3mm  (.118" < 1/8") thick except for first section which is 4mm (.158" < 3/16")
Sail Area: 37.35M Sq.                (402 Sq.Ft)
Weight of Mast - LAP = 136kg   (300 lb)
Bury = 30kg                                  (66 lb)
Total = 166kg                              (366 lb)

Just for comparison the "Practical Junk Rig" (PJR) book states that a solid wood mast with 402 sq ft and 34' 4" LAP would be 10" 3/8 diameter main.  La Chica's mast is 9 1/4" diameter.  Some have the opinion the PJR specifies mast that are too heavy. 

Fore Mast
LAP: 8,745mm                            (28' 7")
Bury: 1,165mm                              (3' 9")
Length of mast: 9,910mm             (32' 6")
Dia Partners: 195mm                    (7 5/8")
Dia Top: 80mm                            (3 1/8")
Dia Base 95mm                            (3 3/4")
Wall is 3mm  (.118" < 1/8") thick except for first section which is 4mm (.158" < 3/16")
Sail Area: 24.81M Sq.                  (267 Sq.Ft )
Weight of Mast - LAP = 94kg      (207 lbs)
Bury = 13.5kg                               (30 lbs)
Total = 107.5kg                            (237 lbs)

PJR recommends a solid wood mast at 9 3/4" compared to La Chica's 7 5/8" steel mast.

"The mast are 16 sided and made up of 3.6M (0.142" < 3/16") sections which were bent up in a brake for me by local company (New Zealand) called CSP. The sections were computer welded up one side. Where the sections join, a sleeve has been inserted. The sleeve was first puddle welded to each section and the the seam fully welded up by hand."

"I made the first section for each mast from 4mm stock. This was no so much for strength as for toughness as 3mm steel is actually quite thin and if a hollow section is dented, it looses quite a bit of strength. After being made up the whole mast was hot dipped galvanised. They will be epoxy coated as well and finished with two part polyurethane before I step them on La Chica. Hopefully that will be this year." --Regards, Paul Thompson  -- www.sailingwithoutasound.com

Solid Wood Mast

Wood vs Steel;  U.S. - Douglas Fir's strength is 7,000 psi. Locally available pines may be as little as 5,000 psi. A steel main mast will need to be 14 inches in diameter and 1/8 or possibly 3/16 inch wall.

Douglas Fir don't grow in Oklahoma, or anywhere near for that matter.  But an fir pole for the main mast can be purchased for about $3,500 including shipping from www.americanpoleandtimber.com. A galvanized steel 12 sided mast is about $2,500. Salvage yard steel will be about $1600 plus a lot of work.  Steel is also more that 40% lighter than a solid wood mast. A 1,465 pound savings on the main mast.  Other sources for wood poles can be found on www.sticktrade.com.

Fiberglass Mast

Armed with the specifications for a steel mast, I sent those to Rob at Architectural Lighting, an Oklahoma distributor for Shakespeare Composite Structures to have them find an equivalent wound fiberglass.   Rob: 918 584-5554 rob@okals.com

I got this reply back from Rob: "The regional sales manager just emailed me stating that Shakespeare does not
manufacture poles for this application. Sorry."

I just love it when some douche bag decides I can not buy their product for my application.

Our Mast

Foremast

We found the foremast via Craigslist, outside of East St. Louis, Illinois.  Only problem is it was actually 47 feet long and not the advertised 40 feet.  The drive back was done at less than 50 mph making for a 23 hour long day.  The up side is that the Suburban gets much better mileage at 50 mph.

Battens

Batten Details

One idea is to use PVC pipe and glue laminate strips of wood to the outside of it and fully encapsulate that in epoxy.  A mast could be done in similar fashion but its a lot of work compared to raw pipe and tapering a steel pipe.

Jack recommended 2" aluminum pipe, my guess is Sch40.  That 2" Sch40 is 1.264 lbs/ft with a 2.375" OD.  I like go with 2 1/2" Sch 10 which is relatively the same weight at 1.221 lb/ft, but it has a 2.875" OD which should make it significantly stiffer.

100 ft - 2 1/2" Sch40 5086 - 2.004 lb/ft, 2.875" od, .203" wall - Top 2 battens of foresail and mainsail.
360 ft - 2 1/2" Sch10 5086 - 1.221 lb/ft, 2.875" od, .120" wall - All other battens of foresail and mainsail.
80 ft - 1" Sch40 5086 - .581 lb/ft, 1.315" od, .133" wall - Mizzen battens.

The mainsails boom and bottom 4 battens are 185 feet of 2 1/2" Sch10. At 1.221 lb/ft that comes to 226 pounds.  The top two battens are 65 ft of 2 1/2" Sch40 at 2.004 lb/ft adding another 130 pounds, and the yard at the top will be built from 3/16" sheet and will likely weight in at an average of 3.5 lb/ft or another 90 pounds.  The brings the mainsail total batten weight to 446 pounds. Add on another 100 pounds for 11 ounce sailcloth and sheets and the total is about 550 pounds.

Just a little thinking about forces. The yard pulls the most weight and it focuses it's 25+ ft span into a single attachment point.  The battens just stiffen the sail and transfer wind loads to the mast and sheets.  Except for the first two battens below the yard, those also have a compression force because they are pushing the leach (back edge) towards the aft.  The batten with the most wind load is the first batten above the boom as it caries load from each of the two largest panels. Together those panels are just under 360 square feet, but 60 sq ft is forward of the mast, leaving the largest unsupported load at 300 sq ft. That batten between those panels caries 1/2 that load or about 150 sq feet.  The formula for sail wind load is Sail Wind Load = SA * ( WS ) 2 * 0.0043, which for 150 sq ft in 35 knot (40 mph) the load is 800 pounds. For the 30 feet of unsupported span that is about 27 pounds per foot.  Interestingly if you double the wind to 80 mph or Hurricane speed the load more that tipples to over 100 lbs per foot.  So can 2 1/2" Sch10 support 800 pounds distributed evenly over 30 feet?  It's suppose to but I think that is asking a lot. 

I'm more confident when Annie Hill, an experienced Junk Rig sailor and she had this to say: "From personal experience a rig built to PJR standards will stand up to 35 mph winds - we were caught out sailing close-hauled under full sail by a gust that was a full F7 (50 – 61 mph). We watched carefully - nothing happened, so carried on under those conditions for about another 5 minutes before the wind dropped back to around F4 (13 – 17 mph)."  You can read more of Annie's travels here: www.anniehill.blogspot.com

The small is 235 square feet mizzen mast is 33 feet tall. The 5 battens ranging from 11 to 14 feet.  These will likely be 1 inch x 1/8 inch wall. (25mm x 3mm) aluminum pipe. The sheets for the mizzen will attach to the davits that will raise and lower the tender. The yard at the top of the mizzen is 8 3/4 ft  and the pipe will be 1 1/2 or 2 inches with an internal stiffener.

Batten hinge in place. Batten pulled apart at the hinge. Gerry O'Brien's China Girl II Hinges with sail pulled forward.

Cambered Panels and
Hinged Battens

Most believe that there is some windward performance gain proved by cambered panels or hinged battens. Cambering the panels would cause the sailcloth to press more against the dual sheets and lazy jacks and defeat one of the purposes for our using backing strips to attached the battens as described below so cambering does not seem like a good choice.  It also moves the load from the top and bottom edges of the panel to the smaller area at the ends of the panel and that is something else that does not seem like a good idea for a big rig. 

However hinging the battens in order to make the sail cambered is an option. Gerry O'Brien's China Girl II's was refitted with hinged battens.  The details are here: http://wincit.co.uk  As seen in the photos of  China Girl, the battens are reinforced for the hinge which in reality is just a dual tapered cone.  We will not plan on hinging our battens when we set sail, but  we will likely add it latter.

Attaching the Battens to the Sailcloth

Hot glue?  Most battens are simply lashed to the sailcloth through grommets.  Only one grommet every 15 inches or so is needed. The lashing runs around the batten, through the grommet, and around a rope that runs down the opposite side of the sail, and back through the same grommet.   Another method is to use a backing strip on the opposite side of the sail from the batten and lash the batten through the sailcloth and around the backing strip.  Having a strip of material opposite of the batten helps stiffen the batten and reduces chafe from the lazy jack lines that extend from the top of the mast to the boom on both sides of the sail as well as the dual sheet system that has a set of sheets to each batten on both sides of the sail.

One of our requirements is to have the separate panels between each set of battens.  Separate panels will be easier to make and repair.  It also gives us the ability to use lighter and less expensive material for the lower panels if we chose. 

Aluminum Batten Attachment Optional Batten Attachment

Separate panels can be done by simply adding a pair of grommets on the edge of each panel and  then lash them to the batten by passing the lashing through both pair of grommets. 

Our plan is to combine the backing strip idea and the separate panel idea.  If the top and bottom of each panel is doubled over to form a loop, then 1/4 inch bolt ropes can be added.  Then a pipe smaller than the batten is ripped into thirds to form a backing strip.  The backing strip is attached loosely at first to the batten with stainless steel pan head bolts thought holes tapped into the batten.  The panel's bolt ropes are then slid down the length of the battens, under the edges of the backing strip.  Once in place the bolts thought the backing strip are tightened down.

Another idea from is to pinch the panel bolt ropes between two batten halves that are then bolted together.  The example given is using wood, but rectangular aluminum tubing would work as well.

Rivnuts are rivets that has treads inside for a bolt.

Instead of threading the pipe for bolts we could also go with a more exotic fastener like Rivnuts. These are rivets are rivets that has treads inside for a bolt.

Another product recommended to will save on maintained is Tef-Gel which bonds stainless steel to aluminum so that the dissimilar metals do not corrode.

Or we can just use good old aluminum pop rivets. They would make changing a panel more time consuming; but how often would we need to do that anyway? They'd be stronger than bolts threaded into Sch10 aluminum pipe, they would eliminate the corrosion issue, and they are cheep, like me.

The potential down side to this design is the addition of holes in the batten as these will slightly weaken the batten and add starting points for cracks due to fatigue.

We could also use lashings on no more that 15 inches centers to retain the backing strip against the batten. This would require adding grommets that allow the lashings to past through the sail.

Preventing CLANG, Clang, CLANG...

Put a dozen aluminum battens hanging from the top of steel mast in light wind on a rolling sea, and you have a very big wind chime.  I hate wind chimes almost as much as undisciplined children, both are annoying after about 60 seconds.  Chafing is also a problem.

Annie Hill; the guru of the Yahoo JunkRig group had these recommendations; "When the boat is underway, the battens tend to rotate a little. The best anti-chafe either goes completely around the batten or covers top and bottom, as well as the part that normally lies against the mast. I don't know if they still do so, but Sunbird used to use clear polythene tubing for their anti-chafe. Plastic-covered fire hose also works quite well as does wrapping the relevant part with (cheap) rope, secured with a screw or glue at each end."
 

Sailcloth

Poly tarp will do in a pinch, but we really would like something more durable. Sunbrella at 9.5 ounces per yard was in the running for a while.  It is commonly used for covers and awnings, but experience has shown that it has too much stretch and not great ability to resist chafing.  And chafing is a common problem on junk rigs due to the battens pressing the sail against the mast.  The experienced recommendation is for Top Gun at 11 ounces or Odyssey III at 6.5 ounces per yard.  11 ounces a yard does not sound like much, but a 1250 sq ft sail has over 150 yards by the time you make all of the seams and that comes out to about 100 pounds.  Comparatively  Dacron comes in 4 to 9 ounces but the yard measurement for material intended for sails is 36 by 28.5 inches.  I'm going to blame that on the French.  If your in or near the UK, then look for Richard Hayward brand sailcloth called Clipper Canvas.  They make a cloth much like Top Gun.