Jim Michalak's Boat Designs

1024 Merrill St, Lebanon, IL 62254

A page of boat designs and essays.

(15 April 2017) This issue will look into ways of measuring leeway. The 1 May issue will discuss scarfing lumber.



is out now, written by me and edited by Garth Battista of Breakaway Books. You might find it at your bookstore. If not check it out at the....


...which can now be found at Duckworks Magazine. You order with a shopping cart set up and pay with credit cards or by Paypal. Then Duckworks sends me an email about the order and then I send the plans right from me to you.


Richard Spelling rigged up his own computer controlled cutter and here it whittles out the beginnings of a Toto. Stay tuned.



Contact info:


Jim Michalak
1024 Merrill St,
Lebanon, IL 62254

Send $1 for info on 20 boats.



Measuring Leeway


...The best way for us poor folk to measure leeway is to tow something and measure the angle the line makes with the boat's centerline. Like this...

I pointed out in past issues about how the underwater leeboard shape and size is supposed to affect leeway. Leeway is usually thought of as slippage of the hull downwind although I was treating it more as the "angle of attack" the underwater boards uses to produce a side force equal to the side force produced by the sail, which can be considerable. And leeway can be considerable too, say 20 or 30 degrees or more at times. Now, all that was sort of paper theory but based on testing of ideal sections and such. I have never seen anyone actually try to measure leeway.

For most of us puddle sailors it doesn't matter too much. But a beginning sailor like me will usually notice when he starts out that when sailing to windward, which is when the leeway situation is most difficult, he never gets to where he wants to go. Here is why....

He starts his long windward leg by pointing his bow at his goal a few miles away, say that nude beach he has heard so much about. All seems fine at first as the boat settles in. If he is holding his heading by a compass (probably not) or just aiming the bow, maybe half way across he has to make an adjustment to windward. Then another. Then another. Sailing this way he will never get to the beach, at least not without a bunch of last minute tacking. Leeway produced by the sail's side force in sailing to windward has made him slide off to leeward. At first it won't be noticed but after a while it will be clear he ain't gonna make it without changing course. To get there on one tack he needs to steer his boat to windward to counteract the effect of leeway. Done properly when he hits the beach it really will never be directly ahead, always a bit downwind of "straight ahead". He will hit the beach in a "crab". How much of a correction does he need? I dunno. It varies with boats and conditions. But if you measure your leeway at the start of the leg you could get a good idea of how much correction is needed.


...I have never seen this done for the purpose of measuring leeway but there is a standard gadget called a Knotstick that measures boat speed by towing a small special thingy with a line hooked to a spring loaded scale. Here is a photo of one...

Pretty simple and accurate I think. Back in olden times, before gps, it was all you could really use to measure speed quickly (OK, you could install a speedometer dial hooked to a little prop under the water). Now, if you could tow a knotstick and also measure the angle the tow makes to the boat's centerline you would be a very well informed guy knowing both speed and leeway at a glance. I would picture a large protractor attached to the transom with the tow line coming out of the hub of the protractor. Get sailing and settled down and read the angle. No need for electronics at all. And the answer it gives will be instantaneous so you won't have to sail long stretches to get a measurement. I suppose you could use it to fine tune your sailing on the spot.


There is another way. When I googled "measuring leeway" I quickly found the "tow something, stupid" method mentioned above. And then next was the approved method. You have a special "flux" compass to hold your heading carefully hooked to your autopilot so it holds your magnetic heading with an iron will. Then a plotting gps to give your direction of motion. The difference should be your leeway as long as you have conquered issues with magnetic variation. Wait, maybe the gps is hooked to the autopilot and the flux compass is the reference. I have forgotten. (By the way, Charles Lindburgh used a flux compass on his Spirit of St Louis as he flew the Atlantic. If you have the old Microsoft 2004 flight simulator you can give it a whirl!) Seriously, people like to spend money on their boats. But my whole effort for these decades is to convince folks that being clever and not spending lots of money on your hobby is way more fun.


You need a good compass and a good map and fine steady weather and some good landmarks to navigate to and from. Lay out a course on your map that will be obvious to you with landmarks, the course being to windward. Leave landmark A and head directly to B and make note of the compass heading. Steer the compass heading solid to the other side of the lake, that is, once you are going don't look at landmark B anymore, just use the compass. You will end up downwind of the landmark B by the amount of leeway. Make note of the landfall position on your map and measure the leeway. Sounds easy but it might test your abiltily to steer a steady course with a compass since you are trying to measure a fairly small angle of leeway. I suppose the longer the course the more accurate the results and I myself would shoot for maybe a couple of miles from A to B. In some ways I think this method would be the truest measure of leeway although it clearly takes a lot of time and good steady weather.


You might say, "Hey! I've got a good gps to tell me the direction of motion made good. I will compare that with my compass heading. It could be done but the compass is pointing to magnetic north and the gps thinks in true north. The difference is magnetic variation and you can look that up on the internet for your area.


Let us say you have the good compass and good gps but don't have the magnetic variation, or don't trust it, or maybe you aren't sure if your stuff is measuring magnetic or true direction. I think you can figure the leeway this way by tacking into the wind with fairly long legs. Let's say the wind is from 090 and you start a tack at 040 for maybe a mile, maybe 20 minutes, holding the compass heading very very carefully. You note the diection of motion the gps tells you. Then you tack over through the wind to 140, sail carefully for another mile and note the new direction the gps is recording on that tack. So you have tacked by your compass through a total of 100 degrees. But your gps should be telling you have tacked through a larger angle because leeway will have move you downwind a bit on both tacks. If the gps says you really tacked through 110 degrees then your boat has 5 degrees of leeway under those conditions. Since you are only using the difference in the angles, I don't think the compass has to be calibrated and the magnetic variation does not come into play.

All this is going to take a while and might be way less accurate than the "tow something, stupid" method. Then again, I haven't really tried any of these things myself.


Not to change the subjest or anything, but if you have a boat with traditional dual leeboards or bilgeboards, that is you have a board on each side of the boat where you lower just the leeward board while sailing to windward, raising the other board, you can play a little game by mounting the boards so they "toe in" the amount of leeway you expect. Let's say you expect 5 degrees leeway and you angle the board to windward by that amount. Now as the boat's centerline points toward your landmark or desired compass heading, the leeboard is flying through the water at 5 degrees angle of incidence, correcting for the leeway, and your boat is actually going where it is pointing!

Sounds too good to be true but Phil Bolger, who designed and sailed lots of tradional dual leeboard boats, warned against trying it in one of his books. He said you would usually overdo it and get unsettling results. Not totally sure why except that maybe your 5 degree estimate is really based on just one sailing condition, to windward, and the rest of the time it will likely be too much.





Mayfly16 is large enough to swallow up three men or maybe a family with two kids. She has two benches that are 7' long and there should be plenty of room for all. I would say that her fully loaded maximum weight might be 900 pounds and her empty weight about 350 pounds, leaving 550 pounds for the captain and crew and gear.

At the same time the Mayfly16 can easily be handled solo, although with just the weight of her skipper she will not be as stable as when heavily loaded. The boat also has two large chambers for buoyancy/storage and I can see her used as a solo beach cruiser because the floor space is large enough for a sleep spot. I've made her deep with lots of freeboard.

Mary and George Fulk built the prototype and passed by here with the prototype on their annual migration north for the summer and I had a chance to see and sail in Mayfly16 for a short bit. Weather was hot and the wind light and steady, perfect for testing. She sailed quite well I thought and everything worked as planned. It certainly was roomy and easy to rig and use.

The balanced lug rig sets on short spars and sails very well reefed, in fact can be set up with jiffy reefing. The spars are all easily made and stowed, the mast being but 14' long setting 91 square feet of sail. In addition there are oar ports for those with lots of time and little money and a motor well for those with lots of money and no time. Two horsepower is all that a boat like this can absorb without going crazy.

The motor well is an open self draining well that uses the full width and depth of the stern. It will come in handy for storing wet muddy things you don't want inside the boat, like boots and anchors. I've suggested in the plans that the rudder can be offset to one side a bit to give more room for the motor. We did not use George's little Evinrude since the boat sailed easily in all directions, but George says the sidebyside sharing on the stern of the motor and rudder works fine. There was no interference with the rudder. (As with any outboard on any sailboat, the motor has a desire to grab the sheet with each tack so you usually have to tend the sheet a bit.)

Mayfly16 uses conventional nail and glue construction needing six sheets of 1/4" plywood and two sheets of 1/2" ply.

Plans for Mayfly16 are $35.


Prototype News

Some of you may know that in addition to the one buck catalog which now contains 20 "done" boats, I offer another catalog of 20 unbuilt prototypes. The buck catalog has on its last page a list and brief description of the boats currently in the Catalog of Prototypes. That catalog also contains some articles that I wrote for Messing About In Boats and Boatbuilder magazines. The Catalog of Prototypes costs $3. The both together amount to 50 pages for $4, an offer you may have seen in Woodenboat ads. Payment must be in US funds. The banks here won't accept anything else. (I've got a little stash of foreign currency that I can admire but not spend.) I'm way too small for credit cards.

We have a Picara finished by Ken Giles, past Mayfly16 master, and into its trials. The hull was built by Vincent Lavender in Massachusetts. There have been other Picaras finished in the past but I never got a sailing report for them...

And the Vole in New York is Garth Battista's of www.breakawaybooks.com, printer of my book and Max's old outboard book and many other fine sports books. Beautiful job! Garth is using a small lug rig for sail, not the sharpie sprit sail shown on the plans, so I will continue to carry the design as a prototype boat. But he has used it extensively on his Bahamas trip towed behind his Cormorant. Sort of like having a compact car towed behind an RV.

And a Deansbox seen in Texas:

Another prototype Twister is well along:

The first Jukebox3 is on the (cold) water. The mast is a bit too short - always make your mast too long. A bit more testing will be nice...

A brave soul has started a Robbsboat. He has a builder's blog at http://tomsrobbsboat.blogspot.com. (OOPS! He found a mistake in the side bevels of bulkhead5, says 20 degrees but should be 10 degrees.) This boat has been sailed and is being tested. He has found the sail area a bit much for his area and is putting in serious reef points.






1may16, Scarfing Wood, Blobster

15may16, Prismatic Coefficient, Roar2

1jun16, Figuring Displacement, Mayfly14

15jun16, Rend Lake 2016, Mixer

1jul16, Ballast Calculations 1, Dorado

15jul16, Ballast Calculations 2, Robbsboat

1aug16, Ballast Calculations 3, AF4

15aug16, Taped Seams, Cormorant

1sep16, Butt Joints, Vireo

15sep16, Old Outboards, Philsboat

1oct16, D'Arcy Ballast, Larsboat

15oct16, D'Arcy Ballast 2, Jonsboat

1nov16, D'Arcy Ballast 3, Piccup Pram

1dec16, Sail Area Math, Ladybug

15dec16, D'Arcy Thoughts, Sportdory

1jan17, AF3 Capsize, Normsboat

15jan17, The Weather, Robote

1feb17, Aspect Ratio, Jewelbox Jr

15feb17, Aspect Ratio 2, IMB

1mar17, Normsboat Capsize, AF4Breve

15mar17, Underwater Board Shape, Harmonica

1apr17, Capsize Lesson, RiverRunner


Mother of All Boat Links

Cheap Pages

Duckworks Magazine

The Boatbuilding Community

Kilburn's Power Skiff

Bruce Builds Roar

Dave Carnell

Rich builds AF2

JB Builds AF4

JB Builds Sportdory

Hullform Download

Puddle Duck Website

Brian builds Roar2

Herb builds AF3

Herb builds RB42

Barry Builds Toto

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