Jim Michalak's Boat Designs
118 E Randall, Lebanon, IL 62254
A page of boat designs and essays.
(1May2011)This issue is about small boat rudders. The 15 may issue will start a short series on how I take a stab at determining sail area.
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.
MESSABOUT NOTICE:THE REND LAKE MESSABOUT WILL TAKE PLACE ON JUNE 10 and 11 AT THE PINTAIL LOOP OF THE NORTH SANDUSKY CAMP GROUND AT REND LAKE IN SOUTHERN ILLINOIS. USUALLY THE SANDUSKY CAMP GROUNDS MIGHT BE FULL FOR THAT WEEKEND. BUT SOME OF OUR BOATERS HAVE RESERVED SOME OF THE SITES THEIR SO YOU (AND I) MIGHT PASS THAT WAY FIRST SINCE SEVERAL TENTERS CAN SHARE A CAMPSITE. IF NOT, THEN I WOULD TRY THE WAYNE FITZGERRELL STATE CAMPGROUND WHICH IS ON THE MAIN CAUSEWAY LEADING TO SANDUSKY. THEIR WEBSITE SAYS IT IS STRICTLY FIRST COME FIRST SERVE, NO RESERVATIONS ALLOWED. IT IS A VERY QUICK DRIVE FROM THERE TO SANDUSKY. HOPE TO SEE YOU THERE!
Tristan Gosnell learns to sail with his dad's new Toon2. This picture is clipped from a great U Tube video he put together which you can view at http://www.youtube.com/watch?v=oCIyyH3nutQ
SMALL BOAT RUDDERS
I have no rule that I use to size a rudder. I just draw something that looks like the proper size for the boat. I always make it shorter than the leeboard with the idea that the leeboard will bump the bottom first, you will notice that and prepare for shallow water or underwater objects with unlashing the main sheet and having a firm hand on the tiller. But the question arises, "How much rudder do you need?"
I think the worst condition the rudder will usually see is when running downwind with the sail boomed way out like this:
There might be conditions of imbalance during close wind sailing when the rudder will be overpowered but not if you have done your "sail area math". So what have we in the above picture? The sail is boomed out all the way and its force is pulling straight ahead but many feet off to the side. The hull has a drag equal to the sail's force and the boat has reached its terminal velocity so to speak. The distance between the sail force and the drag creates a torque that the rudder and leeboard must balance. I suppose on an old square rigged boat the sails would still be on centerline and this condition hardly occurs and you might hardly need a rudder running downwind. Perhaps the worst case would be the old catboats with huge booms, short hulls and very shallow rudders.
In the sailing I have done with my own boats the only case of ever running out of rudder came under this downwind condition with the original WeeVee. It had a gaff sail, was only 7' long, and I was trying a shallow end plated rudder. In a brisk downwind no amount of rudder deflection would hold it on course, it would swing around and round up into the wind. I found I could "tack" it downwind by sailing a broad reach instead of running straight downwind. I tried various sizes of endplates but finally went to a deeper conventional swing rudder as shown in this article. That cured it! I gave up on shallow rudders.
I think Chris Feller has suggested the rudder on Mixer (and later his Philsboat, too) was too small. Maybe so but the clear answer on how to fix such a situation is simply to make the rudder bigger, deeper in particular since deeper is in general more effective than wider. Almost any rudder I've ever designed was something that hung on the stern transom so changing it is pretty easy, unlike say a rudder that is mounted to a shaft that runs through the hull. Anyway I wanted to point these things out before getting into the meat of this older article.
Here is an article I wrote a while back that appeared in the great paper magazine BOATBUILDER. I've included copies of it in my prototypes catalog since then. The article shows how I've made rudders for my own small boats.
Where I sail only a kick-up rudder works well. It's not because once a year you might strike a ledge and break off a fixed rudder. It's because our waters are generally shallow and a fixed rudder would require endless fussing on every trip. With the weighted kick-up rudder shown here you just blast along without giving the kick-up blade a second thought.
I have also tried kick-up rudders that weren't weighted, but were held down by lanyards. Nearing a shore or shallow I had to play the thing like a puppet and quickly ran out of hands because the tiller, sheet, and board all needed handling at the same time. The weighted rudder blade is much better. In this article I'll show you how I build a kick-up rudder from the ground up from plywood. This sort of rudder can be suitable for boats up to about 22 feet length.
The best way to make the blade is to laminate it from thinner plywood. I've seen warped blades made from a single piece of 1/2" plywood, but I've never had a problem with a blade built up from two layers of 1/4" plywood.
Cut out the plywood blanks and butter one up with glue. I prefer plastic resin glue. It comes as a dry powder and is mixed with water to the consistency of regular white wood glue. It's best to spread the glue with a notched trowel like you use to paste down floor tiles. Place the glued-up blanks together on a flat surface protected with plastic or paper, and tap a couple of light nails through them so they can't slide around on each other. Apply clamping pressure with weights like concrete blocks placed atop the blanks. Now stay away until the glue has set good and hard.
Now give the blade a final trimming and streamline the edges where required. (If your rudder, daggerboard, leeboard or centerboard vibrates in use, streamline the edges some more. That almost always cures the ailment.)
I called this the "counterweight" in the drawing but "sink weight" is a better term.
The sink weight should be slightly heavier than the buoyancy of the immersed blade. Wood is about half as dense as water, and lead is about 11 times denser than water. It works out that the area of the lead weight should be about 1/16th the area of the immersed blade, or maybe 7 percent of the area to give a slight negative buoyancy. For example, a blade that is 10 inches by 15 inches immersed is 150 square inches. The lead weight could be 150 x .07 = 10.5 square inches, which would be a square 3.24 inches per side. Cut a hole in the blade for the lead to the proper size, preferably toward the tip and toward the trailing edge. Bevel the hole's edges so the lead will lock in place by forming flanges around the blade. Also place some rustproof nails or screws around the interior of the hole to further lock the lead in place. Clamp the blade to a flat metal plate and place it level on the floor.
To figure the weight of the lead required, multiply the area in inches by the thickness in inches and again by .4. In the example, if the example blade is 3/4" thick, the weight of the lead required is 10.5 x .7 x .4 = 3.15 pounds.
To melt the lead, I use a propane camp stove. I place it right next to the job so I woun't have to tote molten lead around the shop. For a crucible I use a coffee can with a 1/2" pour hole drilled about 3" above the bottom of the can, with a long metal handle bolted to the side of the can. The crucible goes on the stove with enough lead wheel weights inside sufficient for the pour.
Begin the pour as soon as the lead is molten. (The steel clamps on the wheel weights will float to the top and not pass through the pour hole.) Take your time and be very careful with the pour, but it must be done all at once. Overfill the hole in the rudder blade somewhat to allow for shrinkage on cooling. Shut off the stove and walk away from the job for a few hours. Lead stays very hot long after it has solidified.
If the weight gets loose in the blade due to shrinkage, you can tighten it by placing the weight over an anvil and hitting the lead with a hammer. That squeezes the center and expands the perimeter.
Now contemplate what it's like to pour a thousand pound keel!
Laminate this exactly as you did the rudder blade. You need to add the downstop and it's amazing to me how sturdy this part needs to be. A block of hard rubber or phenolic plastic bolted in place might be best.
Don't make the tiller too short! Make it too long and shorten it later if needed. The tiller should fold neatly along the back edge of the rudder for storage.
Use light braided line, about 3/16" for the lanyard. Tie it to a small hole in the rudder's trailing edge. The hole needs to be located about where the raised rudder meets the aft end of the tiller. Then pass the lanyard through a hole in the back corner of the tiller, then forward to a small cleat on the top of the tiller. Pass the lanyard through a small hole in the base of the cleat and tie and loop for your fingers. To raise the rudder, yank on the lanyard and belay it around the little cleat. To lower the rudder, uncleat the lanyard and let the blade drop kerplunk against the stop.
This works very well on smaller sails that don't require multipart main sheets. Screw a fairlead solidly to the tiller's top face. Place the fairlead right above the rudder hinges so the sheet loads won't affect steering. Run the sail's sheet through the fairlead and forward along the tiller. You can secure the sheet merely by wrapping it a couple of times around the tiller's grip under your steering hand. Then you can steer and hold the sheet with the same hand. To release the sheet in a puff you need only slacken your grip without letting go of the tiller. You can also belay the sheet around the rudder lanyard cleat if you are feeling lucky.
I haven't figured out hinges yet. I think the best ones are welded up from stainless steel, but I'm working towards building boats totally from lumberyard stuff. Stevenson Projects used barrel bolt locks for hinges. Payson used eyebolts and rods. Dick Scobbie used door hinges with big cotter pins for pivots. Seeing those, I tried some door hinges on a dink rudder and was quite satisfied, especially since they came from the scrap bin. Most door hinges won't mount as simply as real boat fittings - check out the angles they swing through and do some head scratching.
One thing I'm sure of: Don't rely on gravity to keep your rudder on your transom. In a knockdown the rudder may unship and leave you with a very wet boat and no rudder. Also, with the sheet fairlead on the tiller as I've shown it, the sheet can produce a large upward force on the assembly in strong winds and lift the whole thing out of conventional fittings. Both of these things have happened to me. Now I secure conventional fittings against knockdowns and sheet loads by drilling as small hole in one pintle below the gudgeon and putting a cotter pin through the hole.
THE CARY HINGE...
I wrote the above a few years ago. But very recently I got letter from Ted Cary in Florida. He has a way of making effective rudder hinges from scrap seatbelts.
Here is his description:
"Thought you might be interested in my solution to the rudder pintle problem. My first experience trying to hit two gudgeons with the pintles in a big chop, while hanging over the transom, disqualified that system for me. I came up with a simple track and slide system, then epoxied up the slide and rudder stock around pieces of connecting webbing strap. The stap flexes when you steer. You can bend a seat belt a lot of times before it breaks, and nylon doesn't corrode in salt water. I found that you must align the strap longitudinally across the direction of the flex, and you must not allow the epoxy to harden on the strap where it has to flex. But the ends of the strap have to be well saturated to hold the slide and the rudderstock halves together. The most successful way I've used to avoid glue where I don't want it is to get the parts all glued up and assembled with clamps, keeping the glue off the flex line as much as possible. Then use a syringe or squirt bottle to saturate the flex line with vinegar, working it through the fibers, before the glue starts to set. The acetic acid neutralizes the amines in the epoxy hardener, so it won't polymerize. The clamped parts won't allow the vinegar to reach the glue on the strapping between them, so it goes off where you want it to."
"Dropping the triangular section slide down the transom track installs the rudder in a fraction of a second.This hinge rig has been working great on several dinks for over 4 years now."
Well, I must try Ted's system sometime. I think model airplane guys have been using flexing plastic hinges for a long time. My only comment might be that I would also lock the slide it to prevent it from unshipping in a knockdown.
BLOBSTER, SAILBOAT, 16' X 6.5', 750 POUNDS EMPTY
Blobster has a lot of features I like in a boat. Lots of volume for its size, sort of like Micro or Scram Pram. The multichine shape is almost exactly like Scram's but this one does not have a Birdwatcher cabin. It has the more traditional cabin with a raised watertight deck behind. Also it has one feature I would love to have in my personal boats - a step-through bow so that when you beach you can go forward through the cabin and out the front without going into the water or climbing over the bow. The cabin also has a slot top roof.
This shape of boat with multichines has proven good in rough water and with fair speed in spite of its blobular proportions. Blobster has about 600 pounds of water ballast in its belly and should be OK to 90 degrees heel although such depends mostly on weight distribution of the crew, something the designer has little control over. On the other hand, if the crew jumps overboard the boat will be almost assured of righting without their help. Then the problem becomes reboarding. Be prepared!
Sail rig is a large but simple 139 square foot balanced lug on an 18' mast. Mast is stepped off center to allow you to walk upright down the slot top and out the front. Should be rigged in an instant with no one going on deck ever. All very low tech built with common materials but effective.
The prototype Blobster was built by Miles Bore in Australia. He had built several boats prior, including a Micro, and did a great job of it using very nice materials.
Outside and on its trailer for the first time, the likeness to Micro is clear. But you can see it was meant to be much easier to trailer and launch.
Then he used it for a while as a low power motor cruiser while he finished the sail rig. You can see how easy the boat was meant to use from the beach with its step through bow transom.
Then for the rig and off for a sail, shown here with ballast tanks full. Miles reports it sails with no vices so far. No, he hasn't capsized it yet.
Miles got this photo of the inside. The living platform you see is 7' long and 6' wide max and about 42" at its deepest from platform to slot top. With the slot top cabin and step through transom it is a pretty airy home. Maybe not the little cruiser that Micro is but clearly much easier to use in general and a good choice for a daysail when you have but a couple of hours at the lake.
Great job, Miles!
Blobster uses taped seam construction. Five sheets of 1/4" plywood, eleven sheets of 3/8" plywood and one sheet of 1/2" plywood.
Plans for Blobster are $45.
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.
I think David Hahn's Out West Picara is the winner of the Picara race. Shown here on its first sail except there was no wind. Hopefully more later. (Not sure if a polytarp sail is suitable for a boat this heavy.
Here is a Musicbox2 out West.
This is Ted Arkey's Jukebox2 down in Sydney. Shown with the "ketchooner" rig, featuring his own polytarp sails, that is shown on the plans. Should have a sailing report soon.
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:
The prototype Twister gets a test sail with three grown men, a big dog and and big motor with its lower unit down. Hmmmmm.....
Jackie and Mike Monies of Sail Oklahoma have two Catboxes underway....
AN INDEX OF PAST ISSUES
THE WAY BACK ISSUE ARCHIVES
15may10, AF4 rebottom1, Catbox
1jun10, AF4 rebottom2, Ozarkian
15jun10, Rend Lake 2010, Vector
1jul10, AF4 rebottom3, Wooboto
1aug10,Texas200b, Family Skiff
15oct10,Sail Area Math, Jonsboat
1nov10,Sail Oklahoma a, Piccup
15nov10,Sail Oklahoma b, Caprice
1dec10,Taped Seams, Trilars
15dec10, Bulkhead Bevels, Raider
1jan11, Mast Tabernacles, OliveOyl
15jan11, Knockdown Recovery, DarcyBryn
1feb11, Knockdown Recovery 2, Caroline
15feb11, Windsurfer Mod, IMB
1mar11, Rowboat Setup, Paddleplank
15mar11, Rigging A Lugsail, Hapscut
1apr11, Displacement, Marksbark
15apr11, Sharpie Sprit Sails, Toon2
Mother of All Boat Links
The Boatbuilding Community
Kilburn's Power Skiff
Bruce Builds Roar
Rich builds AF2
JB Builds AF4
JB Builds Sportdory
Plyboats Demo Download
Brian builds Roar2
Herb builds AF3
Herb builds RB42
Barry Builds Toto
Table of Contents