Skin-on-Frame Dory Sailing Rig

Documenting the addition of a sailing rig to our SOF Dory


After having rowed our Dave Gentry - designed Skin-on-Frame Dory for a few years I decided to add a simple sailing rig to the boat.

Concept image

My original plan related to the sailing conversion was to also add a small aft cabin. I have chosen to get the boat sailing well first, before deciding whether a cabin is appropriate for the boat and our use of the boat. My wife Sue likes to paddle her SOF kayak and so far has shown little interest in sailing so I expect that most sailing will be done solo. We launch together, each going our own way but keeping in contact via hand-held radios.

So here we go with the individual components in about the order they were built.

The first step was to design a skeg on which to mount the rudder. A little research turned up that the the maximum angle for the aft edge of the skeg should be about 15 degrees from vertical. Less of an angle would be better but 15 degrees looks good to me so that's what I went with. The forward edge of the skeg is attached to the aft stem by snuggly fitting over the existing cherry rub strip. In the photo below you can see the edge profile of the skeg.

Skeg edge profile      Click any image to enlarge

Cutting opening in skin for support bars      Cutting holes in the skin with hot knife

Skeg with rudder mounted     Skeg fastening detail

The body of the skeg is made up from 2 layers of 1/2" fir marine plywood. All but the underwater surface has 1/4"  Baltic birch plywood glued to it on each side. This layer has three jobs to do; (1) backs up the 'flange' that goes on either side of the rub strip, (2) provides a lot of reinforcement for the support bars and (3) gives the skeg enough thickness to accept the rudder hardware. I used Racelite's Weekender Vertical Gudgeons with Racelite Medium Duty Pintles, both from Duckworks.

Skeg-Stem connection 

The support bars are 1-1/2" x 1/4" fiberglass boat cover support bows. Very strong and easy to work with. Below you can see how they are fastened with two 3/16" SS machine screws with nylon insert lock nuts.

Skeg support bars - inside

Once the skeg was coated in epoxy and varnished I attached it with PL Premium construction adhesive along the entire joint and with two 2" SS screws up through forward end of the skeg into the keel. The small openings in the skin around the support bars were sealed with thickened WEST G-Flex epoxy.

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The rudder assembly is pretty heavy duty. The blade is made from two 1/2" layers of marine fir plywood bonded with thickened epoxy and shaped to a foil shape provided by Michael Storer in his OZ Racer plans. The odd shape is my own design. It seems to be very effective. For example when rowing with the rudder down you can maintain a pretty straight track using just one oar. You definitely need to swing the rudder to make a turn when rowing with it down.

Rudder blade

The rudder head body is also made from 1/2" plywood with ...

Rudder head body

cheeks from 1/4" Baltic birch plywood. By the way, I love this stuff. It is the only thin plywood I can get locally that is actually flat, has no voids and is made with waterproof glue. I have soak and boil tested this material with no ill effects at all. A little heavy maybe but it works and finishes well.

Rudder head cheeks

The blade pivots on a 1/2" SS bolt and is equipped with fastening locations for both pull up and hold down lines. I'm not crazy about my current rudder management system so may go with Jim Michalak's suggestion and add some lead to the lower aft edge of the blade to help keep it down.  Jim's formulas say I'd need about 6 lb. of lead added to the lower aft area of the blade. I'm still thinking on this because I'd rather not make the rudder any heavier.

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The rudder has a 22" cross beam attached to an 8' 1"x1" pine shaft. The two are joined by a 5/16" SS Heim joint and that part of the unit is working fine. At  this point I have only been out sailing a few times but I have to say that this tiller does not seem as intuitive as a conventional tiller - yet. Time will tell if I continue with it or possibly switch to a yoke with ropes.

Tiller - starboard side  <  You can see my hold-down

Tiller - port side  Tiller - Heim Joint

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The leeboard is 48" x 13" x 1" thick (two layers of 1/2" plywood). The bottom 30" or so are immersed. Like the rudder it was shaped with a power plane, belt sander and long-board using a version of Michael Storer's foil template. The design is completely from Jim Michalak's book Boatbuilding for Beginners (and Beyond). The only deviation from Jim's plan is that he would have the board mounted at the widest part of the boat but the position on my boat was driven by the mast (and therefore, sail) location.

I decided that I wanted the mast just aft of the front thwart with a rake aligned to be perpendicular to the gunwale at that point. The center of effort of my sail is about 28" aft of the center of the mast. I positioned the leeboard so that the Center of effort is lined up with a point 1/3 of the way back from the front edge of the leeboard. The leeboard pivot is 15" (~7%) forward of the center of the sheer. From a practical point, positioning the leeboard where it is leaves all three row-locks in their original, correct position and completely functional. Also, the board is centered on a bulkhead, a pretty strong location. One reason I thought I might get away with this is that because of the rounded hull shape the board enters the water quite a way from the hull. Yes, a bunch of research and messing around to come up with that position but so far it seems to have worked OK.


I coated both the leading and trailing edges as well as the tip with two additional coats of epoxy heavily laced with graphite powder. So far it has held up very well.


The upper leeboard bracket is fastened through the openings in the starboard gunwale by seven 1/4" carriage bolts. I fashioned backer plates for through and under the gunwale to spread the leeboard load out as much as possible on either side of one of the central frames.

Lower leeboard Bracket

The lower bracket is fastened through the skin into two filler blocks epoxied between the two stringers. They are also epoxied, with large gussets, to that central frame. Six long deck screws go through the blocks, through the skin and into the lower leeboard bracket.


There is a 1/2" SS bolt epoxied in place through the lower bracket. I mounted an 8" diameter x 1/8" thick HDPE disk between the lower bracket and the leeboard and wood disk and a couple of large SS washers on the outside. The pivot tension can be adjusted with a nylon-filled locknut. I currently have the board tensioned so it will pretty much stay where you put it. When it swings up from hitting bottom I either leave it alone or if the water is getting deeper will pull it back down with a line that runs  from the top of the board to a cleat along the starboard gunwale. Although it isn't easily seen in the photos there is a 1/4" plywood reinforcement plate that connects the outer edge of the lower bracket to the gunwale just under the rub rail and adds a lot of stability to the unit.


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The 11' tall square 'hollow' mast is made from 5/8" clear New Zeeland pine. The lower 32" is 2-3/4" square and from there upward it tapers to about 1-3/4". I filled the lower end (northern white cedar) and inserted several filler blocks and filled the top 12" or so. The filler pieces are shaped to avoid any hard points along the length of the mast. That funny shape is easily made by cutting two 'V' shapes on the band saw.


I rounded the corners with 3/8" and 1/2" radius round-over router bits then coated the end grain with a couple of coats of epoxy before varnishing. There is a 7/16" ID Ronstan fairlead bolted through at the top of the mast. I'm finding there is a lot of friction there making raising the sail, especially on the water, quite a chore so will add a single block up there in the near future. The mast weighs 11 lbs with its center of gravity about 55" (40%) from its base.

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The mast partner was made from a 5/4" x 8" piece of clear NZ pine. I shaped it a bit for esthetics and to lighten it a little. A piece of 3/4" cherry runs across the under side for reinforcement at each end and there is a 3/8" brass threaded insert in each reinforcement piece.


I made up a couple of 4" cherry cleats bored for 3/8" x 3" carriage bolts which were slightly counter-bored then epoxied in place. The bolt heads were pretty ugly so I ground them off flush with the tops of the cleats - they look better and now don't interfere with the lines on the cleats.

cleats-in-use     Partner securing system

The whole point of these things is to easily, with no tools, fasten the partner securely to the gunwales. I made up a couple of bearing plates to spread out the load and topped them off with a couple of tapered cherry disks so the bottoms of the cleats don't bind when tightening them down. I use the port cleat to guide the downhaul line back to another cherry cleat bolted to the inside of the gunwale.


I used a 1-1/4" x 1/4" thick steel bar to hold the mast to the partner. The starboard end is bored and pivots on a 3/8" embedded bolt; the other end is notched so it can swing down and be held in place by a turned cherry knob fitted with a brass threaded insert. Very snug and secure.


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The base of the mast step is a pine 1 x 12 shaped to fit up against the forward frame. There are cleats underneath that hold it securely in position and it is screwed to the keel and floor stringers. The upper part of the step was made from a 2-1/2" thick cherry block cut down and shaped to lighten it up a little and make it somewhat less of a stumbling hazard.



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The sail was made from one of Dave Gray's PolySail kits; 'Medium PolySail Essentials Only Kit' that included a 12' x 16' white tarp, double-faced tape and rope for around the edges of the sail and a brass grommet setting kit with 24 grommets ($100 delivered). The 76 sq. ft. balanced lug sail design is by Jim Michalak as modified slightly by Andrew Linn.

sail shape & seam     Sail shape & tarp seam

I liked his step-by-step presentation on how and why the sail is shaped the way it is. We followed those instructions very closely. We moved a little furniture in the living room and laid out the shape of the sail, cut to the lines and taped it up then Sue went to work sewing it together. The process took longer than expected but the sail looks OK and seems to work well. I'm not crazy about that seam in the tarp but the sail seems to smooth out once filled in a good wind.

The boom and yard are both 11' long and laminated from 3/4" clear NZ pine. They started out at 1-1/2" square. In his OZ Racer plans Michael Storer has very detailed diagrams on how the spars should be tapered for proper bending while under sail. I spent a couple of hours converting his measurements from metric and then scaling them to my spar lengths then when out in the shop decided that in real life I'd be just as well off getting somewhat close to his spar shapes. The boom is pretty stiff with just a little taper (in the vertical plane) at the forward end and a bit more at the aft end. The yard has significant tapering with the thickest area about 1/3 of the way back from the forward end. Both spars were rounded with a 3/8" router bit and there is a 1/2" hole in each end. I wrapped nylon cord around the ends to ensure that the ends don't split and then epoxied over the cord and up about a foot. A few coats of varnish and they were ready to go. The whole package of spars and sail weighs about 14 lbs. 

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As this is written, August 10, 2018, I have only had the boat out sailing a few times so I'm still refining a few things but unless there is some major structural failure I don't expect the components shown above to be changed much though I am certainly open to suggestions for improvements! It has been quite a while since my admittedly limited sailing experience (owning a Hobie 16 forty-five years ago does not make one a sailor) so I'm really relearning to sail as well as testing out the sailing rig.

The most recent outing was in a brisk breeze, 5 - 10 mph with higher gusts according to NOAA. Finally got to get a feel of the boat moving through the water. My overall impressions from this recent trip was that the boat is more stable as a sailing boat than while rowing and that it is quite forgiving of my learning mode experiments. I found out that: Tacks slowly with rudder still pulled up (pilot error), better with rudder lowered but I still need to refine my technique. When sailing towards the beach in increasingly shallower water the leeboard pivots up smoothly and the boat still sails pretty well - better than I thought it would.

More sailing reports later. Here in the Upper Peninsula of Michigan sane sailing weather usually extends into the first few weeks of October. Sometimes. I'm looking forward to many more trips out on the water!

Update - Fall of 2018:

We did manage a few more sailing adventures before the cold weather and fall chores forced an end to the season. Overall I am happy with the boat just as it is, that is, I'll probably not pursue adding a cabin to the boat right now. The one modification still on my to do list is to add a smaller rudder for use when rowing. My experience with the sailing rudder was that it was very effective at keeping the boat on a track but I'm pretty sure I can make a smaller, thinner rudder that will create less drag and still work. I'll probably use rope steering to keep it simple.

Update - 3/1/2019:

I have made a sliding seat unit that can easily fit in the dory and I'm looking forward to seeing how well it works with my existing 8' oars with Gaco locks. The unit is designed to fit right over the thwarts and clip in place with a couple of simple swivel latches. It was actually designed to be used in my new rowboat but can be easily be moved from one boat to the other - I still seem to be limited to rowing one boat at a time, but I'm working on it.

Steve Schmeck

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