Jim Michalak's Boat Designs
118 E Randall, Lebanon, IL 62254
A page of boat designs and essays.
(15may06) This issue will rerun the important bevel essay. The 1 June issue will discuss "headroom".
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.
THE 17TH MIDWEST HOMEBUILT BOAT MESSABOUT will take place at Rend Lake in Southern Illinois on the weekend of June 10 and 11. Remember that lots of folks come on Friday and leave early Sunday. Take I-57 to exit 77W and then follow the signs to the Gun Creek Recreation Area. There is no schedule of events except a pot luck dinner in the campground on Saturday evening - we wing it. Some of us have reserved the campsites on the water of the two middle camping loops so look for us there if we aren't at the boat ramp.
Sandra and Chuck Leinweber of duckworksmagazine.com tune up their new RiverRunner for a long Out West float trip next month.
I don't know if there are many topics that cause more confusion to boatbuilders than bevels at bulkheads and transoms. Some slant in and some slant out. Sometimes you can measure them right off the lines drawing but often you can't. To a certain extent the subject has become less important with taped seam construction, but many glue and nail boats are still being built and as you will see, I like to use nail and glue construction in the very early stages of building a taped seam boat because it allows a quick and solid alignment when that is most appreciated, as shown in this photo of Dale Dagger in Nicaragua with a Toto project. At this stage the hull has used conventional construction which required cutting bevels on some of the elements. Dale asked for clarification on one of them.
I did update the Toto drawing to include the full sized bevel drawings shown below. One is for the side edges of bulkhead 10 and the other is for the side edges of the transom.
When I figure out the dimensions of the plywood piece that forms the shape of the bulkhead or transom, I take its dimensions off my lines drawing as if the piece had no thickness.
But the real panels do have thickness. So I rig it such that one face of the panel lies on the plane where I took the panel dimensions and mark that face "Dimensions to Here". Now if the side or bottom panels are sweeping in or out from the dimensioned face, then the other face of the bulkhead or transom will need to be smaller or larger than the dimensioned face.
Let's take the case where the adjacent panels are sweeping outward from the dimensioned face. We'll call this one an "outy". The transom bevel on Toto is as outy. The dimensioned face of the Toto transom is on the plane of the end of the boat and the transom's forward face needs to be slightly larger than the dimensioned face to allow for the outward sweep of the side panels, which measures 10 degrees at that point. How much larger? The Toto transom is supposed to be 1/4" plywood with a 3/4" thick framing stick, for a total of 1" thick. So to allow for the 10 degree bevel each side needs to have 1" X tan10 = .176" extra material which is 3/16" to most of us. But when I build one of these outy's myself, I pay no attention to that extra thickness. See the figure below to see how I do it on my own boats.
I've found the best tool to cut straight bevels is a table saw. First I cut the side sticks on the table saw to the correct bevel. Then I cut the transom (or bulkhead) panel out of plywood to the dimensions with no bevel, just a square cut. Then I glue and nail the beveled sticks to the plywood piece such that a straight edge along the beveled stick will just kiss the "Dimensions to Here" edge. That's it. I haven't fussed with that "extra material needed" measurement at all. This gives a nice straight edge to the right dimensions and it doesn't really get involved with thicknesses - if you use thicker or thinner wood than specified it will still fit.
"But," you say,"there's a little triangular area on the edge of the plywood that isn't right." True. I fill that with glue when the panel is glued and nailed to the side. That triangle isn't very big. On this 10 degree bevel it would max at .045". No problem. To me the glue there is really a hope of sealing the grain on the edge of the plywood, not a strength issue since a lot of that ply edge will be end grain anyway and about useless for glue strenght.
Now let's talk about the inny. Bulkhead 10 on Toto is an inny. (I suspect the trouble Dale had was that he made this one an outy the first try.) The basic dimensions of bulkhead 10 were taken 10' aft of the bow tip of the boat. That is the actual front face of the bulkhead, the face marked "Dimensions to Here". At that point the sides are sweepin inward 7 degrees as they go aft. This bulkhead is also 1/4" plywood with 3/4" sticks for a total of 1" thick. So the aft face of the bulkhead needs to be 1 X tan7=.12" smaller on each side edge than the front side edges.
Innys are a little easier to picture. You could make all the edges square to the basic dimensions and then run them through a saw set to the proper bevel to shave off the extra material. I used to do them that way and still do on occasion. The problem I have is that I use a bandsaw for this which doesn't care to cut straight. And a large bulkhead is a beast to run through the saw all at once. You could try a saber saw or circular saw set to the proper bevel if you think you are good enough at it to keep the blade just kissing the edge marked "Dimensions to Here". I' not.
So I've gone to making the inny bulkhead the same way as I make an outy. First I prebevel the framing sticks with a table saw. Then I cut the plywood panel to shape with no bevel, just a square cut. Then I glue and nail the sticks to the sides of the panel. If the bevel is severe I do try to line up the face of the bevel stick with the "Dimensions to Here" edge of the plywood. Then I will have a small triangle of plywood protruding from the beveled face. I can trim that off later. In the case of a small bevel, I don't do that. I just line up the stick with the back edge of the panel. When I assemble it to the sides there will be a little triangle to fill with glue again. And the panel will be slightly wider than what the lines call for. In the case of Toto's bulkhead 10 the error would be .25" X tan7 = .03". Nothing to worry about.
NEXT TIME: We will take a look at "headroom".
PICARA, CABIN SAILBOAT, 18' X 7", 1300 POUNDS EMPTY
A while back I presented a design called Fatcat2 which was a 15' x 6' unballasted sailing cuddy catboat. It is still in the prototype catalog, although one was built a few years ago but never used to my knowledge. A problem with any unballasted boat is that if it capsizes it will usually lie on its side and the skipper will need to go for a swim to right the boat and then he has the problem of getting back into the righted boat.
The usual fix for that problem is to deck the boat over very well so that nothing will flood when the boat gets knocked down by the wind. (I'm reminded of Reed Smith's Rule that any boat that gets sailed a lot will eventually get knocked down.) Then ballast is added down low such that the boat's center of gravity will be "below" the boat's center of buoyancy when it is on its side. The lower the ballast, as on the end of a deep fin or keel, the less ballast is needed but of course the draft of the boat goes way up. Buoyancy up high, such as a high raised deck, also helps but there are limits to that too since the boat's CG will also be raised with it, both because of more structure up high and also because the crew weight, which often is a major contributor to a high CG, must be lifted higher so that the skipper can still see ahead over the new raised deck.
So Picara is in a lot of ways a Fatcat2 that has gone through the above changes to make it self righting, that is to say if knocked over it will right itself when the wind force is eased, with the crew staying on the deck, shedding water like a duck and being ready to go again once the crew feels up to it. (Even here the idea of "self righting" means different things to different sailors. Howard Chapelle wrote somewhere that a sharpie is selfrighting if it can return from 45 degrees of heel. I'm quite certain that is not enough for most of us. Blue water sailors try to self right from 140 degrees of heel. No, the wind won't blow you over that far but a big wave can roll you that far. On my ballasted boats, like Picara, I try to get the boat to self right from 90 degrees, a compromise I suppose, but I don't design blue water boats.)
To get Picara to right from 90 degrees with two adults sitting on the aft deck requires 500 pounds of steel ballast spread flat on the deepest part of the boat's bottom in addition to using a 1" thick plywood bottom which also has about 100 pounds of ballast effect. Sound like a lot? Maybe so but the numbers kept coming up the same using Hullforms6 to figure the hydro work. I believe it. I tried it with water ballast but gave up. Steel is over eight times as dense as water so the 1-1/2" steel plate I show as ballast would be equal to a water tank over 12" deep to match the weight, but with internal ballast the water would end up centered about 6" above the bottom where the steel sits centered .75" above the bottom so the water ballast was no where near as effective here as steel. It won't work here.
Picara is 18' long where Fatcat2 was 15' in order to get a cabin that two people might really sleep in. There is a small anchor well ahead of the cabin, a raised deck aft of it, and a motor well in the stern. I used multichines to get a hull that can handle rough water better than a flattie. That makes it a taped seam project. She needs nine sheets of 1/4" plywood, six sheets of 3/8" plywood, and seven sheets of 1/2" plywood. The resulting pile of plywood would weigh about 800 pounds and I would expect the empty hull to weigh about that. Add 500 pounds of ballast and you have about 1300 pounds on the trailer. The wide deep hull can handle that and it takes a total weight of 2500 pounds to set it down 10" deep so its chines touch the water.
As for the sail rig, I used a gaff sail to get good area from a short 17' mast which pivots on a tabernacle and stows within the length of the trailered boat. I added a small mizzen for balance and provide steadying at anchor or during sail changes.
Prototype Picara plans are $30.
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.
The out West Picara is I am told done to the point of using it as a powerboat:
The down South Picara is more or less complete now. Should have an updated photo soon.
This long and lean project is a 19' version of Toon2. Shown here on its first sail in very light winds. We will wait a bit longer to get a sailing report in stronger winds.
A Vector builder is keeping a website of the project at http://firstname.lastname@example.org/ and here is a photo of his boat on its first sail, just before the storm hit. I also have photos of a Vector completed by Pete Mohylsky in Florida. Hopefully a report soon:
Here is a Musicbox2 I heard about through the grapevine.
We have a Philsboat going together in California:
And here is another Philsboat in northern Illinois:
AN INDEX OF PAST ISSUES
BACK ISSUES LISTED BY DATE
Mother of All Boat Links
The Boatbuilding Community
Kilburn's Power Skiff
Bruce Builds Roar
Rich builds AF2
JB Builds AF4
JB Builds Sportdory
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)
Barry Builds Toto
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