Tidmarsh Major's prototype Skat goes for a sail.
Contents:
Contact info:
Jim Michalak
118 E Randall,
Lebanon, IL 62254Send $1 for info on 20 boats.
Jim Michalak's Boat Designs
118 E Randall, Lebanon, IL 62254
A page of boat designs and essays.
(15Jul04) This issue will rerun a really old issue about leeboard issues. The 1 August issue will take a look at hull shapes.
THE BOOK IS OUT!
BOATBUILDING FOR BEGINNERS (AND BEYOND)
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....ON LINE CATALOG OF MY PLANS...
...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.
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Tidmarsh Major's prototype Skat goes for a sail.
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Leeboard Issues
THE VERY BASICS...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).
HANDLING THE LEEBOARD...
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.
WHAT'S THAT VIBRATION???...
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."
NEXT TIME...
...We'll look at hull shaping.
Ladybug
LADYBUG, SAILBOAT, 14' X 5,5', 250 POUNDS EMPTY
Ladybug is a lot like Woobo which was one of my first designs. There was a Woobo near here for a while. I never got to sail it but was told it would really fly. (That boat was made of Lauan plywood from Home Depot which fell to pieces after rainwater filled the boat over the winter.) Ladybug is a bit shorter and wider and deeper and has bench seating, much more suited for older legs. Both boats have a small motor well. The best motor for something like this is the 2hp Johnson/Evinrude which weighs 25 pounds. Even that is overkill since 1hp will push this hull at top speed, anything more just makes bigger waves. Here Sandra Leinweber pushes into a stiff breeze with a 2hp Honda.
This shape of hull with multichines and a plumb bow seems to be a good all around thing with rough water abilities. I think if there is a problem it is that it has almost no lateral drag and unless the boat has a big skeg or keelson or something like a leeboard or daggerboard or centerboard it would just as soon go sideways as straight. I've given Ladybug a keelson and when using power you should keep the leeboard down just enough so its tip drags the water.
Ladybug's hull has the layout I like the best - a 6-1/2' cockpit between two storage/buoyancy boxes. It would be a great solo camping boat. The buoyant wooden spars prevent it from turning turtle. You bring it upright with weight on the lowered leeboard. Then you must climb back on board and a slot in the rudder seems to be the best boarding ladder around, bringing your weight back on board where it least affects the boat. You will have to bail some water.
I've kept the same sail as with Woobo, a 75 square foot balanced lugsail. It hoists on a 13' mast with 11' yand and boom. All very low tech built with common materials.
Chuck Leinweber of Duckworksmagazine.com built the prototype and brought it to our Rend Lake messabout so I had a chance to go for a long ride in it. One thing that impressed me was how large it was for a 14' boat. In the opening photo you see it sail with three men on board, all comfortably sitting to windward on the bench seat, and I'm told it has sailed with four men with no effort. I do think it would be quite suitable for a family of four say with lots of room for all and storage space for all their junk. Here Sandra Leinweber sets things up at a recent campout on the Texas coast:
Here is the same campout from a distance with the mast folded to support a tent. I'm told the tent is not done yet. Chuck has modified the bench seats so that his expand towards the center and meet in the center thus making a 6' x 5' sleeping platform. Turns out a small commercial camping tent can be set up on that platform and that is what they are using for now.
Ladybug uses taped seam construction. Six sheets of 1/4" plywood, on sheet of 3/8" plywood and two sheets of 1/2' plywood.
Plans for Ladybug are $40.
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.
Out West the Picara gets its fiberglass coat:
The Deep South Skat is done! Hopefully a full story in a few weeks:
Another Picara, this one with a 1' stretch in the middle, going together in Arkansas. Sailmaking done and its on to glassing the hull.
The AF4G is upright on its trailer now:
AN INDEX OF PAST ISSUES
Hullforms Download (archived copy)
Plyboats Demo Download (archived copy)
Brokeboats (archived copy)
Brian builds Roar2 (archived copy)
Herb builds AF3 (archived copy)
Herb builds RB42 (archived copy)