Jim Michalak's Boat Designs

1024 Merrill St, Lebanon, IL 62254

A page of boat designs and essays.

(15 September 2023) We look at leeboard issues. The 1 October issue will review a hull coefficient.




... 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.

ALSO...In addition to the Duckworks downloads I also now have access to a large format inkjet printer which is making very nice full sized prints on paper. So I can return to what I started 30 years ago, you order direct from me by snail mail using the address above only with cash or check in US funds with the prices shown on this website, and I mail you full sized 2'x 3' paper prints. The price includes first class mail to US and Canada.


Jamie Sauder (Ottawa, Canada) writes of his new Mayfly14, " Not me at the helm. My friend (small woman in her 60s) capsized in a surprise jibe while sailing downwind in 7 knots and was able to right it by herself and board using the toe slot in the rudder. After my first boat I started putting the toe slots at the very bottom of the rudder under the sink weight because I found that the slot was too high to use easily otherwise. Anyway, my friend is rowing to warm up after the capsize as she is soaking wet and it is none too warm as you can see by the clouds. She is rightly proud of herself for recovering unaided (though she lost her phone). Simple boat but I find it functions extremely well. "



Contact info:


Jim Michalak
1024 Merrill St,
Lebanon, IL 62254

Send $1 for info on 20 boats.



Leeboard Issues


I've covered sizing and placing of leeboards in previous issues that you can find down in the Way Back Issues link. But to recap, the things you might remember are that the immersed area of the board should be about 4% of the sail area, and that the leeboard must be mounted at the hull's widest beam in order to be in flow parallel to the boat's motion. The suggestion on area would apply to any board such as a centerboard or a daggerboard (but those boards need not be limited to mounting at the boat's widest beam). Lastly, the sail area has to be aligned with its sail area center right above the center of the board's area, more or less.

Here is an example of a leeboard on Slam Dink.


Notice that it pivots around a bolt which is placed to allow the board to retract fully above the bottom of the hull. You can't tell from the drawing but the pivot bolt runs through a lower hull guard and the top of the leeboard runs in a slot in an upper hull guard. The board is thus braced to take loads in both directions, unlike a tradional loose leeboard. As a result only one of these pivoting leeboards is needed on the boat, it works on both tacks, where the tradional loose leeboard only works on the lee tack so two are required. In truth these pivoting leeboards aren't really leeboards but are more like centerboards mounted outside the hull. While sailing you handle it just like a centerboard - just leave it down almost all the time except maybe while running and broad reaching. But I'm still going to call it a leeboard.

The pivoting leeboard has several advantages. They are easily built and altered. There are no holes required through the hull except for the pivot hole. Best of all the leeboard takes up no room on the boat's interior. On the Slam Dink that same board mounted as a centerboard would take up the whole interior. You could see the same situation below on Richard Spelling's AF2 (shown with an experimental mizzen sail).



I've found that no ballast is required for these boards, they are laminated from layers of plywood with the edges streamlined. If they are loosely pivoted they have a natural tendency to drop down a bit so that they might drop about 20 or 30 degrees until the buoyancy of the immersed segment balances the weight of the board. If you are trailering your boat it is often prudent to secure the board in the full up position so it doesn't catch on things while launching. That happened to me once while launching my Birdwatcher which has a conventional centerboard. I bashed away at it perplexed until the tiny voice of a six year old watching said, "Mister, that board thing on your boat is catching your trailer."

So in that AF2 photo Richard is releasing a line that secures the leeboard in the up position.

How to get the board down? Easy. There is an ear attached to the upper aft edge of the leeboard that sticks up through the upper guard and there is a lanyard attached to it. Grab the lanyard and pull back on it and the leeboard rotates down until it goes kerplunk against the aft end of the slot in the upper guard. Here is Richard hauling the board down.


Once the board is down it prefers to stay down, especially if there is a bit of friction between board and guards applied by tightening the pivot bolt. There are two things that can make it pop up. First if it strikes something like a stump or the bottom. Second is drag on the board when there is no side load on the board such as when running downwind or sometimes when tacking through the eye of the wind.

Once that happens the board will pop up to its comfortable 20 or 30 degree position and stay there until you yank it back down. In the partially down postition the board will still provide skeg effect when running downwind. But some boats will steer better downwind if the board is pulled down again and you might experiment with that. In the situation where the board pops up while tacking through the eye of the wind, you must pull it back down again to sail on the new tack. As always, if the boat suddenly feels funny while tacking through the wind, always check the leeboard first and make sure it is down.

It is possible to cleat off the lanyard to make sure the board stays down but you must remember to release it before running into shallows. I don't do that myself. Instead I prefer to run the lanyard back around an oarlock and into the cockpit. The oarlock acts as a turning block. Here is a photo of Herb McLeod's AF3 and you can clearly see the leeboard, upper leeboard guide, pivot bolt, and the lanyard running aft to a cleat which is handy at the back edge of the cockpit.


Again, usually on a boat like AF3 I would run the lanyard through the oarport and around the oarlock (Maggie the Dog would not appreciate that) and not cleat it off. But I do use a cleat on the forward end of the upper leeboard guard. I can secure the board in the up postition by leading the lanyard forward to that cleat. But in normal use the board is cleated up only while trailering.

Birdwatcher type boats have a problem with a leeboard like this in that there is no convenient access to the outside of the hull to handle that lanyard. My suggestion would be to run the lanyard through a small hole in the side of the hull which is kept radiused to act like a bearing. Pull the board down at any time that way without leaving the inside of the boat. No need to ever pull it up except to trailer.

No one has done that but some of those boats have lanyards running fore and aft to be captured by cleats on the fore and aft decks. So you can pull the board around like a puppet in any direction. Here is a photo of Karl James' Jewelbox chuckling along. You can see here the leeboard, the upper and lower guard, pivot bolt, and a loose lanyard running outside the hull to a cleat on the aft deck. (There is also a line running forward but it's not really visible.) You can see there is no tension required in that lanyard to keep the board in the down postion.



This one applies to any foil running through the water such as leeboards, daggerboards, centerboards and rudders. It is expecially true for deep narrow foils of the type preferred for low drag.

If the leading and aft edges of these boards aren't properly streamlined they will vibrate. That happened to me in the original Piccup Pram which had a really long narrow board. I wrote to Bolger about the problem and his answer was something like this:

"Streamline the edges more. If it still vibrates, streamline it some more."

So I streamlined the edges and the vibration went away. Bolger has seen everything.

We recently learned an intersesting spin on this. Richard Spelling was having problems with his leeboard vibrating and was getting tired of streamlining the edges. About the third time he wrote me about the problem, I had just received an issue of Small Craft Advisor and there it was - a discussion about foil vibration by the racing boat designer Stephen Baker.

Here is what Baker said:

"...A thin trailing edge, if faired into the shape properly, is a must. Do NOT round the trailing edge, rather cut it square and thin, and then bevel it about 30 degrees (doesn't matter which side) to stop it from vibrating at speed..."

A few days later Richard wrote me back, "Thinning and beveling worked pretty well. All leeboard vibration gone. Thanks guys."




Philsboat is essentially an IMB with the nose extended to a pointy bow. The width and multichine configuration are the same as IMB's. The cabin is 3" deeper because Phil is at least 3" taller than most of us. In a boat with a Birdwatcher cabin like this one added depth to the cabin makes it safer in that the righting forces in a knockdown are greater. That would be true of any boat if the center of gravity did not move with the cabin roof but with the normal cruiser adding depth to the cabin also means raising the crew deck up so the folks can see over the raised cabin. And that means the CG is elevated too, and then all bets are off concerning self righting. But with a boat like Philsboat eveyone rides down low inside looking out through the windows.

Here is a photo of Bob Williams' IMB:

In addition to the pointy bow and added headroom I added what I hope is a serious motor mount. Probably 3hp will drive it as fast as it will ever go and that at part throttle. But the motor well gets to looking pretty large even for such a small motor. For one thing it must be deep to put a short shaft motor on a deep stern like this so I ran it straight down to the boat's bottom. Working on the motor down it its well will be about impossible and you might need to keep an eye on your knuckles when you pull the starting rope. And the well must be surprisingly wide to allow the motor to swivel in steering although the usual case here will be to keep the motor locked straight ahead and steer with the tiller. The wide well pushed the rudder off center and you need a crooked tiller or rudder linkage to make it all work. I opted for a simple but crooked tiller.

I also added low seats like those I saw added to the two IMB's that came to the Lake Conroe Messabout. Pretty much the same as what I have in Scram Pram where the seats do double duty as water ballast tanks. Philsboat seats could easily be converted into water ballast tanks also but the IMB capsize tests imply the ballast isn't needed.

The sail rig uses a balanced lug, 113 square feet and the same as that of a Bolger Windsprint.

Philsboat uses taped seam construction. Five sheets of 1/4" plywood, five sheets of 3/8" and three sheets of 1/2" plywood.

Actually the size and material list for Philsboat are about the same as that of Scram Pram. So which boat would be better? Take Philsboat if you are a pointy bow guy. It should be better in really rough water. On the other hand Scram is wider and roomier. It has a flat step through bow that will splash and spit in rough water but makes beaching a very nice experience.

Update, 2007. Chris Feller completed his Philsboat, probably the first prototype completed, and brought it to the 2007 Rend Lake Messabout. Very well made and to plans except he used the 91 sq ft lugsail he had on hand for his AF3, with some mast rake changes he calculated with his "sail area math". Sailed correctly rigtht off the drawing board, so to speak. We had a chance to use it for a few really nice days. In a good sailing breeze, say 10 to 15 knots with occasional whitecaps, our gps bobbed between 5.5 and 6mph for two hours of reaching as we crossed back and forth on the big lake. When I used the Philsboat I thought it was probably just as easy to enter from a beach as the blunt bowed Scram. The front deck is about 2' high so you can sit on it and swing you legs around onto the deck and then into the cabin.

Chris is a big boy but there was plenty of room inside for the two of us and more. Rumor has it that at the campsite the night before Chris slept in the Philsboat on the trailer with an airconditioner in the front hatch plugged into the campsite power. So the boat is plenty big in the way most people would use it.

The stern layout has the motor in a small well to one side and the rudder offset to the other side to give the motor room to swing. There is no linkage to the tiller, the tiller is simply "unstraight" so that is falls on centerline at the skipper's hand. Seems to work well and is quite simple. Chris uses a 2hp Honda which has a fairly large cowling for its size and must be rotated 180 degrees to grab reverse. He said the motor well size is a bit too small for that. Karl James had the same problem with his Jewelbox a long time ago and simply cut away the side of the hull in top of the motor well region - after all it is just there for looks. Chris said he tried the boat under power and found it went 6 mph max, just like under sail. No surprize to me. My Birdwatcher also maxes out at 6mph under 3hp and under 5.5 hp. This sort of hull will only go so fast. Add more power and you just dig a deeper hole and make a bigger wake - you won't go faster. But sometimes more power is nice on a windy day.

(As an update, Chris has brought his Philsboat to several more Rend Lake meets. In 2008 the meet was very windy and Philsboat got a full windows wet knockdown with Chris and Tom Hamernik on board. She self righted with no issues and they kept right on sailing, but Chris confessed he has 100 pounds of lead shot under the seats. Also he is using a 3hp vintage Johnson which he says is quieter and smoother than the Honda.)

You might recall from the Prototypes section recently that there was another Philsboat being built in California. That one last I heard was about to be launched. Has more changes from blueprint than Chris's boat but still is pretty true to form. Seems to be known as Bumble and made by Rex Meach.

And in New Zealand Rob Kellock has been sailing his with a junk rig. He has been knocked down a couple of times and self righted as planned:

Plans for Philsboat are $45.


Prototype News

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:

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.






1oct22, Prismatic Coefficient, Larsboat

15oct22, Figuring Displacement, Jonsboat

1nov22, Lugsail Jiffy Reef, Mayfly14

15nov22, Sharpie Reefing, Piccup Pram

1dec22, Making Oars, Batto

15dec22, Taped Seams, Sportdory

1jan23, Rowboat Setup, Normsboat

15jan23, Sail Area Math, Robote

1feb23, Bulkhead Bevels, Toto

15feb23, Trailering Boats, IMB

1mar23, Small Boat Rudders, AF4B

15mar23, Making Sink Weights, Scram Pram

1apr23, Sailrig Spars, RiverRunner

15apr23, Water Ballast, Mayfly16

1may23, AF3 Capsize, Blobster

15may23, Mast Tabernacles, Laguna

1jun23, Underwater Boards, QT Skiff

15jun23, Capsize Lessons, Mixer

1jul23, Rend Lake 2023, Vireo14

15jul23, Rigging Lugsails, Frolic2

1aug23, Horsepower, Oracle

15aug23, Sharpie Sprit Sails, Cormorant

1sep23, Prop Thrust, OliveOyl


Mother of All Boat Links

Cheap Pages

Duckworks Magazine

The Boatbuilding Community

Kilburn's Power Skiff

JB Builds AF4

JB Builds Sportdory

Hullform Download

Puddle Duck Website

Brian builds Roar2

Barry Builds Toto

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