Jim Michalak's Boat Designs
118 E Randall, Lebanon, IL 62254
A page of boat designs and essays.
(15JUN98) This issue will show how I lay out the design of the pivoting leeboards that I use. In the 1July issue I hope hope to start a discussion about sails that will last a few issues, ending with how I have been making polytarp lugsails of late.
NEAT WEB SITE ALERT1...Click on over to Dave Carnell and sit down for a good read. It seems like I've known Dave forever. I recall reading his stuff in Boatbuilder, Small Boat Journal, and The Instant Boatbuilder way back when I first got started making boats. Dave is the keeper of the Simmons Sea Skiff plans and has developed the "$200 Sailboat". Also on his page are essays on buying and using epoxy (he's a retired chemical engineer) and treating wood rot with chemicals. Dave also sells Matsushita thin kerf carbide saw blades, the blade that made my AF4.
HERB McLEOD'S AF3
This is a pretty easy writing assignment for me. I put a pivoting leeboard on my Bolger Jinni back in 1982. At the time I thought I had invented the thing until I saw Jim Huxford's Bolger Otter which apparently had been built in the mid '70's. That boat had TWO pivoting leeboards just like I had used. But these boards are braced to take loads in all directions (so in fact they aren't really "lee" boards) and there is no need to have two, one will do it all. For me the germ of the idea came from Bolger's pivoting leeboards that appeared on his Cynthia J and again on his original Dovekie. Those boards bolted directly to the side of the boat. All I did was to stand the board off the side a bit with a stick at the pivot point and contain the top of the board in a slotted guard. Those two guards provide the reaction points that allow the single board to be braced to take forces in all directions and operate on all tacks. In most ways these are pivoting leeboards are just like the usual centerboard mounted outside of the hull. I quickly learned that an "eye" mounted on the top edge of the board was important in that it provided a lug for attaching a lanyard and, just as important, gives you a visual clue to the position of the board. (My first attempt just had a radiused top edge. It looked the same from the cockpit at all board positions and I never knew the actual position without peeking over the side at the board, very difficult to do on a small boat.) Anyway, here are the basics:
Leeboard size was discussed two issues ago. If you make the immersed area of the board about 5% of the sail area you will be in the right ballpark.
Shape was discussed in the last issue. If you make the immersed board about twice as long as wide you will have an aspect ratio of 4 and that is pretty good for overall performance.
Here is where the leeboard differs greatly from a centerboard or daggerboard. A LEEBOARD MUST BE MOUNTED AT THE WIDEST POINT OF THE HULL TO BE IN FLOW PARALLEL TO THE HULL'S MOTION. If you are using one on a slab sided scow you might have some options in this regard, but for a normal pointy ended boat, it can only go in one spot.
Most folks won't mind placing the board at the hull's widest point. But remember: THE SAIL AREA MUST BE BALANCED AROUND THE LEEBOARD AREA. So you can't go around moving the mast or changing sail layouts without taking this into account. There isn't much room for variation here, especially with a narrow leeboard. Moving the sail forward a few inches will make for lee helm (release the tiller and the boat heads downwind on its own). Moving the sail aft a few inches will make for more weather helm (release the tiller and the boat heads into the wind). SO THE SAIL AREA MUST BE CENTERED OVER THE WIDEST POINT OF THE HULL. You can't treat them separately.
Knowing the size shape and position of the leeboard you can draw it on the side view of your hull. Check to see that isn't wider than the hull is deep. If it is, you won't be able to pivot it up so that the grounded boat will rest on the hull bottom and not on the leeboard.
The leeboard supports, which I call the guards, need to be spaced apart a fair amount to handle the loads introduced by the board. The farther apart they are spaced, the more effective they are at sharing the loads of the leeboard. If the guards get quite close together, they probably won't always be strong enough and having the leeboard break loose will ruin your day. Here's is a figure that demonstrates the effect:
The numbers used in the example might be pretty typical of a small sailer. With one exception: consider a situation where a 200 pound skipper is trying to right a capsized boat by stepping on the tip of the leeboard. Then the loads will be much higher than shown. To put it all into perspective, a typical cheap 1/4" bolt might handle 2000 pounds of tension and a 1/2" bolt maybe 9000 pounds.
About all that's left to do now is to find a pivot point that will allow the leeboard to retract fully under the upper guard. Here is a way that works well for the type of board I like to use which extends straight up and down when lowered. Draw a line as shown in the figure below starting where the trailing edge of the lowered leeboard meets the bottom surface of the top guard, extend down at a 45 degree angle. Where that line crosses the center of the lower guard is where the pivot bolt needs to be mounted. I try to arrange things such that the bolt falls about 1/3 to 1/2 of the way aft from the leading edge.
I've found that if the board has just the right amount of friction in the guards (by adjusting the pivot bolt) it will stay down until it hits something. If it hits something it will usually float up about 75% of the way and stay, still providing some lateral area. Then if you yank it down again, you are back in business until you hit the next thing. If it is a shallow shore you are approaching you just let it continue to come up until the boat is beached. I attach a lanyard to the eye on the aft top edge of the board for yanking it down. I don't cleat off the lanyard. I've never ballasted the board to sink although some have tried that. I've never used a shock cord to hold it down although some have tried that. I've never used a second lanyard to hoist the board up although some have tried that.
So the operation of the leeboard is quite simple as you see. It's mostly like using a regular centerboard. When sailing anywhere but downwind the board stays all the way down. When sailing downwind, I usually leave the board down (usually the boat will steer better) although at times it will swing up because it will have a fair amount of drag and no side force to produce friction to hold it down. If so, I'll leave it up but one must remember to yank it down again prior to turning from the downwind run. If it ever hits something it will pop up. Yank it back down. That's it!
I'd like to start the topic of sails. This will most likely take a fair amount of time. I might have to split it up with other topics to make it more palatable and to give me time to figure out what to say.
SAILING SHARPIE, 22' X 7'', 2200 POUNDS EMPTY
Someday I may get to put my full catalog on the net. For now I'll put one design in each issue.
Viola22 is a cabin sharpie: a handy cruiser suitable for a solo sailor out maybe a week, or for duet out for a couple of days (I almost said a weekend but mid-week boating is usually a lot more satisfying). Compare Viola22 to a Catalina 22 which is something like the standard in trailer-cruisers. They can be bought for about $3000 which about what the Viola would cost to build if you watched your costs. Many older Catalinas aren't really worn out at except for sun chalk. They are much harder to rig than the Viola and draw a lot more water, even with their keels swung up. They will sail better in rough conditions, but they could never be dry-shoe beached as the Viola could. I'd say for solo boating from a trailer the Viola would be a much beter choice. Compare to a San Juan 21, which might sell used for $2000 on the trailer. The San Juan will beach and trailer and launch similar to the Viola but won't have the living quarters..
The living quarters of Viola are very good for her size. The main sleep room is 6-1/2' long and almost 6' wide, plenty for two. There's a hatch in its front for ventilation and setting the main in security. AFt of the sleep room is a 3' long by 6' wide utility room. Use it as a bathroom and kitchen and you can see that the sleep room needn't get too cluttered with those necessities. Another advantage to this set up is that the bedding shouldn't get wet everytime the main hatch is opened or when someone strips off some wet clothing. Aft of the cabin is a large flat cockpit with great storage underneath which is accessible from both the cockpit and from the cabin. One trip on a Micro will show you what a wonderful setup this is. Best of all, this type of deck is very quick and easy to build. Aft of the cockpit is a slop well meant to store the motor gear. There's another slop well in the bow which is great for muddy anchors.
Construction is of straight forward nail-and-glue jigless plywood needing no lofting or jigs. The plywood bill looks like twelve sheets of 3/8", ten sheets of 1/2" (mostly for the double planked bottom) and one sheet of 3/4" for the leeboard. Ballast is 600 pounds of steel bars bolted to the bulkheads inside.
Blueprints for Viola22 are $25 until one is built and tested.
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. (If you order a catalog from an internet page you might state that in your letter so I can get an idea of how effective this medium is.) Payment must be in US funds. The banks here won't accept anything else. (I've got a little stash of foreign currancy that I can admire but not spend.) I'm way too small for credit cards.
Anyway..... Anytime a design from the Catalog of Prototypes starts getting built I pull it and replace it with another prototype. So that boat goes into limbo until the builder finishes and sends a test report and a photo. Here are some boats in that catagory (although I been leaving most in the prototypes catalog).
Sportdory: Dave Burdecki has his boat structually complete. He needs to sand and paint and whittle out a set of oars. I think he may be also finishing a Bolger Pirogue at the saime time. I know that sounds like a lot of boats but it's all relative. We had a fellow show up at our September messabout in Bloomington, In. a few years ago who claimed to have owned 51 boats "not counting canoes"! You can check out John Bell's Sportdory progress by clicking here .
Skat - the prototype Skat builder is Roger Palaski. Up until now he was a mystery man know to me only as "Roger", his Skat plans bought for him by someone else. Then I find out he has his own web page with the Skat construction photos on it! Skat is a small somewhat traditional 12' cat boat with a gaff rig. Even has a centerboard, the only boat I've ever designed with one! See Roger's progress by clicking here.
The Way Up North AF3 project by Herb McLeod is shown completed up in lead photo. It's not in the prototypes catalog anymore. Here's another view:
Get updates on Herb's progress by clicking here (archived copy).
Concerning the Texas IMB that is under construction. Click here (archived copy) to visit Tim Webber's page and see some photos of the IMB as of a few weeks ago. Then poke around Tim's web page a bit.
Harmonica (ex Fusebox) is still being fitted out and painted. Hoping it will be at the Midwest Messabout by the time you read this and I can get some good photos and it don't sink.
BACK ISSUES LISTED BY DATE
Mother of All Boat Links
Messing About In Boats
Shantyboats (archived copy)
The Boatbuilding Community
Kilburn's Sturdee Dory
Bruce Builds Roar
Table of Contents