Jim Michalak's Boat Designs

118 E Randall, Lebanon, IL 62254


A page of boat designs and essays.

(15August 2015) This issue is the plywood butt joint essay rerun. The 15August issue will try another look at box boat stablilty.

TIME FOR THE INDIANA MESSABOUT!

Fellow Messers,

July 4th is behind us and mid-September is closing fast. We just wanted to send a short reminder that the 24th occurrence of the Lake Monroe Midwest Messabout will be September 18, 19, & 20 -- mark your calendars.

Go to https://sites.google.com/site/lakemonroemidwestmessabout/home for additional information and feel free to drop us a line if you have any questions. If you're planning to attend, and want us to add your name/boat/homeport to the website's "Who's Coming" list just send us an email.

Hope to see all of you in just a few weeks. We have the ice cream maker standing by!! Pass the word to all your boating friends. Regards, John & Susan McDaniel

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.

Left:

Ken Giles takes his new Picara for a spin in northern waters.


Contents:

 

Contact info:

jim@jimsboats.com

Jim Michalak
118 E Randall,
Lebanon, IL 62254

Send $1 for info on 20 boats.

 

 



Butt Joints In Plywood

BACKGROUND...

Almost any boat you build from plywood will require panels longer than the 8' lengths you will find at the lumberyard. For an "instant boat" the usual manner of joining the panels together to get one long panel is with a butt strap or butt plate. I've tried lots of different ways to make the joint in the 15 or so boats I've built over the years. All the methods worked. I have a feeling that the butt joints on the usual instant boat hull are not highly loaded and not too critical to overall boat strength. Since I've tried several ways and they all worked I've gotten to be pretty nebulous about the subject on my drawings. Lately I've been specifiying a butt plate as something like "Butt plate from 3/4" x 3-1/2" lumber, or equal" which doesn't tell you much. Most builders get by pretty well with just that but recently one builder asked what in the world I meant, and rightly so. So let's start the discussion with one joint I've never tried in plywood.

TRADITIONAL PLYWOOD SCARF JOINT...

scarf joint

Figure 1 shows the traditional plywood scarf joint. I''ve never done this in plywood although I've made a lot of scarf joints in plain lumber. The two overlapping faces are tapered and glued together such that both joined faces remain smooth. If you are building a traditional lapstrake boat from plywood you have to make the joints this way.

What's good about it? The faces are smooth both sides. Essentially you have a single piece of wood to work with after making the joint. It's quite strong, as strong as the base wood provided the taper is long enough. I've seen the taper range from 6:1 to 12:1. The shorter tapers are easier to make and probably just as good given modern glues.

What's bad about it? The tapers can be hard to make properly although thickened epoxy has made experts of most of us. Some experts have special saw rigs to cut the taper. Most use power hand planes or belt sanders, I think. When gluing the joint you must press it up against a firm surface while the glue cures, making sure nothing glues to that surface, and making sure the two pieces are secured lengthwise so the tapers don't push them apart as you apply clamping pressure.

There is one more warning for instant boat builders. Almost all instant boat designs have panels layouts which assume you will not be using a scarf joint. If you join two 8' panels with a scarf joint you will NOT end up with a 16' panel. It will be shorter by the overlap amount. That might be just enought to negate the ply panel layout.

THE PAYSON TEAL BUTT STRAP...

Payson butt strap

I think this type of joint was described in Payson's great book INSTANT BOATS. I used it on my Teal which was my first homemade boat. The side panels were 1/4" thick on my boat, the bottom 3/8". The butt straps were 3/8" plywood, 6" wide. So the effect of the joint was similar to a 12;1 scarf on the 1/4" ply sides and about 8:1 scarf on the bottom. The nails were supposed to be copper, but I think Harold might have also suggested copper rivets or short bolts for fasteners.

What's good about it? It's pretty simple to visualize and make. If the fastening is good you can make the joint and go right on building without waiting for the glue to set. You might do that with the sides, for example. Another neat thing about this plain butt strap joint is that, with a typical flat iron skiff type of assembly, the bottom panels need not be joined before assembly onto the hull. In that case you will have the hull inverted on sawhorses ready for the bottom. Then you put the first bottom piece on attaching it to the sides. Then you install the first butt strap at the end of that piece. Then you install the next bottom panel to that butt strap and the sides. And so forth until the entire bottom is planked, like laying bricks.

I might mention now that I think butt straps and plates should be well rounded at the ends to avoid trapping dirt and moisture. In boats that have taped seams I advise stopping the butt strap short of the edge of the panel so you will have room to run the tapes undisturbed. This is especially true of butt straps on the bottom. You must have a clear limber channel around the perimenter of the bottom. In that case I stop the strap about 1/2" short of the side, fill the little gap with epoxy to keep the water out, and tape over the bottom of the joint with glass tape and epoxy. Usually I don't put glass tape over the outside of the side panel joints. But butt joints in any deck should be well sealed with glass and epoxy. Here is an end view of the treatment:

joint end view

What's bad about the plywood strap? I think in Maine you aren't a man until you've made a boat with clenched copper nails or rivets. Not so where I live, can't buy them any place I know of. I got by with bronze boat nails but they really aren't flexible enough for the job. They didn't look too cool. And the edges of the plywood butt straps don't look too cool either, wanting to have gaps and splinters showing. It takes a while to finish them. And, of course, you have a lump at each joint and folks will ask, "What's that?"

By the way, when I built my Toto I used the simple plywood strap method with no fasteners. Just carefully lay the ply panels over the straps which were well buttered with glue, weighed it all down with concrete blocks to provide pressure, and stayed away for a few days until I was sure the glue was totally set.

THE BIRDWATCHER BUTT STRAP... Birdwatcher joint

When I built my Birdwatcer in 1988 I think I piled on more layers of plywood straps such that I wouldn't have to bend over the nails. And by that time I was more expert at finishing the edges of plywood. It worked but it was very obvious that I could have done the same thing with regular lumber and saved a bit of work.

THE LUMBER BUTT PLATE...

lumber butt plate

This is what I like to advise now. Not much to it. Very quick and easy to make. Some say it looks too clunky for their tastes.

If there has been any structural problem with the above butt plate it is at the ends of a plate that joins bottom panels, ending short of the sides to allow a limber path. If the ends of the plate are not solidly glued and fastened to the bottom panels the butt plate will eventually loosen at the ends. I think that is due to the rapid change in flexibility in the system where the plate suddenly ends. A better solution might be to taper the end of the bottom butt plates starting maybe 3" in from the end of the plate and tapering down to maybe 3/8" thick at the ends. That will allow a gradual change in the flexibility and prevent a stress riser at the end of the butt plate. By the way, for any bulky butt joint care must be taken in design to see that the joints don't fail in places where the butt plate will be in the way.

LIGHT FIBERGLASS BUTT JOINTS..

light glass joint

Both Harold Payson and Dave Carnell presented this one to U.S. readers in the '80's but I'll bet the English inventors of taped seam boats did it earlier. Simple as can be in theory. Just a layer of fiberglass on each side of the plywood.

Dave Carnell presents lots of details at his web site. He has done scientific load tests of these joints and says the joint will be as strong as the base wood if you use one layer of fiberglass cloth in epoxy on each side of 1/4" plywood, two layers on 3/8" plywood, three layers on 1/2" plywood, and four layers on 3/4" plywood.

I used the glass butt joint on my Roar rowboat but went back to wooden butt joints later. At first it would appear that the joint is easily made by laying the ply pieces on the floor, taping one side with fiberglass, waiting to cure, flipping the panel and repeating on the other side. But I found that plywood on its own often does not want to lay flat enough to get a smooth fit, so I had to place the joint over a board and screw the pieces down flat. Next the idea of flipping the panel with only one side taped doesn't work well because that one layer of glass has little strength by itself. But it can be done carefully. Better yet is what both Payson and Carnell advise: glass both sides at once. Lay the first side of fiberglass layers wet with epoxy on a protected flat surface, lay the plywood to be joined upon it, lay the second side of fiberglass over the top of the joint, cover with plastic sheet and weigh down with concrete blocks. The plastic sheeting not only protects everything from gooey epoxy, but it should provide a smooth final finish and if you are lucky no filling or sanding required afterward.

THE PAYSON HEAVY GLASS JOINT...

heavy glass joint

Harold Payson did a little more work on the glass butt joint. I'm doing this from memory and hope I'm getting it right. To hide the build up of glass on a thicker sheet of plywood he recessed the surfaces roughly with a sanding disk in a drill. Then he added a layer of light fiberglass matt to the wood before pasting in the glass. Fiberglass matt is generally thought to provide better adhesion to wood than glass cloth although by itself it has little strength. Harold is big on using polyester resin on his boats instead of epoxy so perhaps the matt is more important for the polyester users. But you can see the advantage of the system: the final joint can be more or less invisible as the multiple layers of glass are recessed.


Paulsboat

PAULSBOAT, SAILING CANOE, 15' X 3', 120 POUNDS EMPTY

I had a request from Paul Moffitt, of the famous sailing Moffitts, for a sailing canoe. Now, a "sailing canoe" can mean a lot of different things. But to me the sailing canoes that you read about from the late 1800's were what we both had in mind. I had always put off designing one because I had the idea the usual sailing canoe design is too wide to be good with a paddle, and too narrow to be good with a sail. Many of the old classic sailing canoe designs were actually small decked over rowing boats that were wide enough to sail with some stability. I guess there were still called canoes because of their double ended shape and perhaps because they had recently evolved from true canoes which were rigged with small sails.

Anyway, it was going to be a compromise. Paul also wanted some capacity to carry some camping gear. So I drew Paulsboat. It was really based on my Larsboat which in turn was based on my Toto which in turn was based on the Bolger/Payson multichine canoe, etc. To get more sailing stability and more capacity Larsboat was widened from 30" to 36" and the bottom plank also widened 6". I gave the cockpit a 7' long open space with the idea that the skipper could camp inside the boat, which by my experience is quite superior to sleeping outside. For one thing setting up a shore tent will usually quickly bring down the law almost anywhere and sleeping inside discretely will not. I slept in the smaller Toto many times. Anyway, the cockpit is large enough to float two adults and is between buoyancy/storage chamber fore and aft. Access to these chambers might be difficult. I've shown them with large deck plates in the bulkheads but you likely won't be able to reach way down in them. I've noticed many folks put several smaller deck plates in the decks, as Paul did, to allow access. The deck plates also allow for airing of the chambers and if you ever build in a closed box and don't allow for airing you can expect rot very quickly.

The sail rig was pretty well copied from the old sailing canoes which often used something similar. I stuck with my usual leeboard for lateral area and placed it such that the boat should handle well under main sail alone. The rudder was something to think over. Many of the traditional canoes had a tiller with complications used to get the tiller to clear the mizzen mast. I wanted to avoid all that since it usually means some metal forming and welding and that will turn off many builders quickly. What Paul wanted was to be able to steer with pedals and had aquired from Duckworks some plastic kayak pedals where the pedal did not pivot but could slide in a groove a total of 14". Well, let me back up a bit. The rudder drawn simply has a tiller horn on each side, each 12" long. That might sound long but in reality it would be like steering with a 12" long tiller and then it seems way short. The idea was to tie a line to the horns that looped around the cockpit through pulleys forward such that you could steer with your hands by pulling on the line. Not an uncommon idea. The downside I thought would be that at times you would hardly have enough hands to steer and work the sails. So Paul got those pedals and installed them connected to that steering loop. He says it all works fine and he was able to reduce the length of the rudder steering horns. But don't give up on the idea of the continuous loop around the cockpit. With the loop you could let your passenger steer as you take a nap.

We pondered a bit about what would happen in a capsize. With the decks and flotation chambers it should float high with little water inside but getting back in could be a challenge. I am pretty sure you should prepare, and test, a stabilizing system which uses a float attached to your paddle which is somehow secured across the cockpit to steady the boat enough to allow you to enter over the side. Nothing new about that idea. You probably need to be somewhat strong and nimble.

Paul has been paddling with a single paddle and reports no troubles. Having the pedal operated rudder would be a big plus especially with the single paddle. I have a feeling we did a good job compromising on the width of the boat.

Construction is the usual taped seam requiring six sheets of 1/4" plywood. It is going to weigh a bit, no getting around that, but Paul has been cartopping without trouble.

Plans for Paulsboat are $35 when purchased direct.

Contents


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:

And the first D'arcy Bryn is to the point the builder can sit and relax in it and imagine boating. You can follow the builder's progress at http://moffitt1.wordpress.com/ ....

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.) Double layer bottom on and glassed, hull returned to upright. On to the interior and superstructure...

Contents


AN INDEX OF PAST ISSUES

THE WAY BACK ISSUES RETURN!

MANY THANKS TO CANADIAN READER GAETAN JETTE WHO NOT ONLY SAVED THEM FROM THE 1997 BEGINNING BUT ALSO PUT TOGETHER AN EXCELLENT INDEX PAGE TO SORT THEM OUT....

THE WAY BACK ISSUES

1sep14, Rowing 1, Vireo

15sep14, Rowing 2, Philsboat

1oct14, Guessing Weight, Larsboat

15oct14, SailOK2014, Jonsboat

1nov14, Chine Runners, Piccup Pram

15nov14, Lugsail Rigging, Caprice

1dec14, Sail Area Math, Ladybug

15dec14, Poly Laminates, Sportdory

1jan15, Sharpie Spritsail, OliveOyl

15jan15, Knockdown Recovery, Dockbox

1feb15, Mike Monies, Laguna

15feb15, Cartopping, IMB

1mar15, WeeVee Lessons, Vole

15mar15, Bulkhead Bevels, Frolic2

1apr15, Capsize Lessons, Riverrunner

15apr15, Hollow Spars, Slam Dink

1may15, Boat Costs, Blobster

15may15, Small Boat Rudders, Roar2

1jun15, Emergency Flotation, RB42

15jun15, Thailand Mixer Cruise, Mixer

1jul15, Rend Lake 2015, Musicbox3

15jul15, Box Boat Stability, Mikesboat

1aug15, Taped Joints, Cormorant

SOME LINKS

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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