Jim Michalak's Boat Designs
118 E Randall, Lebanon, IL 62254
A page of boat designs and essays.
(30DEC)This issue presents some scans of the finished AF4 drawings. And we'll go over the major features and talk a bit about fuel economy. Next time, about January 15, 1998, we change gears a bit and fly a few ideas about setting up a trailer for a plywood boat.
I finished the drawings of the AF4, traced them, shrank them by a factor of 4, scanned them and converted the scans. I thought the boat came out quite well. Of course, there are always some "ifs" to think about.
(You might wonder how long it takes a fellow to draw up a boat like this. For me the answer with a typical small boat is about three working days from starting the drawings until finishing the tracings ready for the blueprinter. It works a lot better if the thoughts are in process for a month or so before I start drawing and AF4 has been in my head a lot longer than that. Luckily the very very best way to think up a boat is to go boating! So in good weather I'm out boating and no matter how well things go I make a point of thinking to myself, "How could this boat be better?" It's usually a good sign when the drafting goes quickly and my most successful plan, the Toto canoe, was probably a two hour effort to actually define the boat. Phil Bolger once told me I should take more time at it. I'm not so sure about that. For me it's like rifle practice back in the service. When the sights are on the target, why "take your time?" Phil said he would draw every boat over at least twice, and I can see the wisdom in that.)
...DAVE CARNELL'S INPUT...
Before digging into the AF4 I'll mention some details Dave Carnell sent after he read the last two issues. Dave is the keeper of the plans for the Simmons Sea Skiff, a boat not too different from the AF4. He said the 18' Simmons weighs 300 pounds if built of 3/8" plywood. Dave said his Simmons probably weighs 1100 pounds complete with crew and goes 36 mph (31 knots) with a new 50 horse motor. Looking at the chart presented last issue, Dave's boat is going a bit faster than the "average" chart predicts although it's not that far off. A change of 10% in the assumed pounds per horse will put it back on the curve. Thanks, Dave, for the numbers.
Dave has also surveyed the Simmons in prep to make the working drawings and found a "hook" in the stern bottom just like Kilburn's Sturdee! It's subtle, less than 1", just like Kilburn's.
The scan shows the layout of the AF4. The first two feet of the bow are open with drains through the bottom. The idea is to place messy anchors and junk there, out of sight. I'm suggesting cutting a step into the side of that bay to ease boarding. I can tell you that difficulty boarding is one of the first reasons your wife/girlfriend will mention for not liking boating and in most ways she is correct. This bay ends with a watertight bulkhead at station 2.
Next comes the "main salon". It's a lot bigger than the one on my Jinni. It's 8 feet long, about 3-1/2 feet tall and 4-1/2 feet wide at the aft end but only 14" wide at the bow end. There will be room to sit up and maybe you might be able to use a cot in there instead of an air mattress. You could "sleep two" but there won't be room to do much besides sleep. I think of it more as a spot to sleep one with your junk off to the side and handy. The top is slotted open for 7 feet. Normally you leave the slot uncovered to allow walking access as with an open boat. In good weather you can lay a bug net over the slot and sleep with a view of the stars. Very nice. In worse weather you can cover the slot with a simple tarp. Lots of us have tried hard segmented covers. Then the usual thing is to travel with the hard covers in place and leave them with the tow vehicle as you boat with a softcover. On Jinni I made up a folding PVC pipe frame to make a spot with "standing headroom" under the cover. There are lots of options. The bulkhead at station 10 should be water tight to prevent rain water from running into the salon from the cockpit.
Aft of the salon is the cockpit. It's just a big open area, 6 feet long and over 4 feet wide with about 30" of freeboard. You could put benches in there but my own choice would be to try it without, sitting on folding chairs or one of those cheap folding chaise lounges you buy at Wal Mart for $10. They double as a sleep cots and triple as row benches.
As for rowing, I've shown oar ports and 7' oars. This boat won't row worth a hoot but it might come in handy especially in water too shallow for the motor. I'll bet the oars get used more for poling than for rowing.
I've also shown a bimini top which is really quite important almost anywhere. It doesn't have to be expensive or fancy to be effective. John McDaniel had rigged on his Micro a simple flat cover raised at each corner by a plug-in pole. The trouble with a cover with no center crown is that water will pool big time in the middle, but John had fastened a small drain hose there. So the hose could be lead overboard or to jugs for collecting water to wash with.
Behind the cockpit is the draining motor well. Under the well's bottom is some volume for flotation foam and a spot I hope will be large enough for the required fire extinguisher and maybe tools and parts, for PFD's and cushions. The bulkhead on the front of the well has an access hole to the storage and limber holes to encourage free drainage. The well is larger than it needs to be. It will easily take the standard 6 gallon tank my friend has donated.
Nothing fancy here. I've not used the "hook" in the bottom although perhaps time will show it might be needed. If so, the first boat might get by with small wedges on the stern to simulate the hook. Karl James told me he had a power dory with a stern that swept up a little bit. To keep the boat from squatting (70hp) he added wedges but they were quite small, 1/2" thick as I recall. It doesn't take much.
So the bottom is dead flat from station 10 aft. But I've pinched the sides in a bit at the stern for looks. The old Carolina Dory Skiffs were pinched that way, too. In genral I've heard this sort of boat is best with the sides and bottom running straight back from the middle for best performance. We'll see.
Contruction is totally typical of an old fashioned instant boat. Sides are cut to prefab shapes shown on the plywood panel layout sheet. There are two butts required per side and I prefer to use plain 3/4" x 3-3/4" lumber as butt plates. Many other butt methods will work. The plain lumber butt is the easiest to finish, allows regular glue and screws, and provides about the only thing that might be called a "rib" on this boat. There is no need to tape the outside of the butt. If you've got good mechanical fasteners in the butt joint there is no need to wait for the glue to cure before putting your boat together. I'm suggesting 1/4" ply for the sides in my case to keep the boat light enough to tow behind my little car.
The bottom is another story. I can tell you that a 1/4" bottom will "breath" up and down with each wave unless it is otherwise well stiffened. The flexing seems to do no harm but it will bother you. So I'm suggesting 3/8" minimum ply for the bottom with three skid/stiffeners on the outer bottom. (I should mention that, engineering wise, the stiffness of a panel in flexing is proportional to the cube of the thickness. So a 3/8" panel is 1.50 times as thick as a 1/4" panel. And it's stiffness in flexing is 1.5 x 1.5 x 1.5 = 3.4 times as stiff as 1/4" ply.)
The bottom is fastened to the sides with external chine logs. A lot of folks don't like the looks of these but I think they are superior to inside chine logs in every practical way. There is no need to notch any bulkhead or frame. They are by far the easiest to spring into position. They provide a bit of a bash stake for the sides. But you can go with an internal chine log if you want, or a taped seam joint. I can't see how the external log will slow this boat in any appreciable way.
Speaking of taped seams, I would tape only the chines on this boat if it were mine, in the manner of Payson's INSTANT BOATS. That would save a lot of weight, mess, cost and work over glassing the whole boat. I would try to invest in epoxy for taping the chines and not use polyester. These chines can see a lot of abuse.
The hull is pretty routine and has very few pieces. When this boat is being set up I've shown a couple of extra temporary forms to try to keep the shape under close control.
...THE PLYWOOD PANEL LAYOUT...
You can tell a lot about a design by looking at one of these layouts. In fact I often do the layout as soon as I define the shape of the boat, before the construction drawing is down.
It looks like a minimum version of the AF4 requires four sheets of 3/8" plywood and five sheets of 1/4" plywood. What can we tell from that?
For one thing we can get a wag at the weight. That much ply would amount to a block of plywood about 2.75" thick. That would amount to 7.3 cubic feet of wood. If the wood weighed 35 pounds per cubic foot, we'd have over 250 pounds of plywood. But it has been my observation that conventional boats like this end up weighing about 35 pounds for each sheet of 1/4" plywood used, and 50 pounds for each sheet of 3/8" plywood. That would imply a hull weight of 375 pounds. That's more than I want. Perhaps my efforts to keep the structure spare will keep it down. And I'm encouraged that the Simmons weighs 300 pounds.
Also I can visit my local lumberyard and find that last week they priced 1/4" ACX fir at $20 a sheet and 3/8" ACX at $22 a sheet. I think I can get it cheaper but these guys will let me get picky. So for $200 I can get the ply to build her. Not sure how much plain lumber is in AF4 but it isn't much. It would be nice to find 20' lumber although I'll probably end up scarfing shorter lengths to make up the wales and chines. As for glue, that might be another $100 including Weldwood, epoxy and glass tape. Paint will be exterior latex, say a gallon of primer and a gallon of dark green for the hull and a gallon of buff for interior and top, and maybe a quart of spar varnish for bright work. Maybe $75 there. Fasteners will be galvanized nails and maybe zip screws from the lumberyard.
I think there's about $500 in the hull.
...A NOTE ABOUT FUEL CONSUMPTION...
Here is how I make a wag at the fuel problem. Go into the charts hp/lb vs speed charts presented in the last few issues and figure your boat speed at different powers. Then assume a certain fuel consumption per horse per hour. Gerr suggested diesel engines burn .05 gallons of fuel per horse per hour and that gasoline engines burn about .10 gallons per horse per hour. Then you can convert from horsepower vs speed to gallons per hour vs speed.
The only engine I've had experience with is the Clinton which seems to burn well above the .10 figure. It's old and crude technology compared to new stuff, especially new four strokes. So the above chart is optimistic at suggesting a specific fuel consumption of .20 gallons per horse per hour as far as the Clinton goes. Some of the newer outboard motors I've heard of approach the .10 figure. I'll be running at the very low horse part of the curve where the better fuel economy is.
But look at what happens when the horsepower and speed begin to increase! Once the boat starts to plane the fuel economy seems to becomes almost a constant. It's quite poor, of course. (If you see a large motor yacht, say a 40 footer that is two or three stories high, he probably has two big V8 motors going. He's very lucky to get 2 mpg and 1 mpg or less quite possible. I met a man who had a boat like that on the north edge of St. Louis. He said his standard 70 gallon tank was not enough to reliably reach the next fuel stop in south St. Louis! Most of the big ones rarely make long trips. ) When I figured out the above chart what was really interesting was that, in the "transition" region that I guessed at between displacement and planing, the fuel economy acutally reverses. That is to say for a while the boat gets cheaper to run as you speed up!
...AF4 PLANS FOR SALE...
The drawings are done and ready for a prototype builder. Three 2' by 3' blueprints with keyed instructions for $20 until one gets built and tested. The boat will appear in the Prototypes Catalog by the time you read this.
Someday I may get to put my full catalog on the net. For now I'll put one design in each issue. The text will be for the most part the same as what appears in the paper catalog.
An AF4 builder might face the difficult choice of maybe building a boat like Twister instead. It's quite a different boat from AF4 but comes out of about the same pile of wood and labor. Twister is a bit smaller and won't go as fast but it can sail! It will sail quite well in the right conditions. Don't we know by now that when you go to the water with a staight power boat the wind is always perfect for sailing? And when you go to the lake with a straight sailboat, the wind is too light to get anywhere and conditions are perfect for motoring?? So in between boats like Twister can have their place.
TWISTER, POWER/SAIL CUDDY CAMPER, 16' X 6', 350 POUNDS EMPTY
Twister is one of those 'mixture' boats that borrows a lot of ideas from other boats that worked out well. In particular I did some camping in an AF3 look-alike and had time to contemplate some changes. Camping in the little cuddy cabin is actually a lot more civilized than in an open boat, although the open boat can be as good in uncivilized areas. The difficulty with the open boat is privacy. Men go fishing at all hours of the day and night around here. Even with the cuddy boat I've had them casting about the boat during normal sleeping hours. But they don't bother you otherwise and in general are very sympathetic to your simple camping idea. (In fact I believe that if it weren't for the the sportsmen, who often have very good organizations, many of our boating facilities wouldn't exist.) So Twister has a cabin to sleep one, or hide two. The cockpit is too small to sleep in and I put some low benches there. I must be getting old.
The hull shape is borrowed from my Twixt, a jonboat with a V entry bow that twists to a flat bottom for the main part of the hull and sweeps up to the waterline at the wide stern. The big stern allows a serious motor well. Twixt has always done fine under oars, sail, or small motor. I doubt that Twister will row well in the normal sense, but she would be useful under oars during launching or covering glassy water. Most people will eventually put a motor on a boat like this and this hull should take 5 hp or so. In fact one idea behind the boat is to use it under power alone, leave the sail rig at home and go camping on rivers where oars and sails are not useful.
The sail rig shown has been tested in polytarp on my Jinni. It seemed a bit much for the Jinni but Twister is wider and heavier and should be a lot more stable.
Jigless construction with taped seams. She needs four sheets of 1/4" plywood and five sheets of 1/2" plywood. Plans are $20 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. There are three boats in that catagory right now.
Scram Pram, a 16' multichine Birdwatcher type, is being built near Savannah. Here's a photo of the Mrs contemplating it.
And Skat, a 12' cat boat daysailer, is being built near Phoenix.
The Kansas Boat Psychologist keeps plugging away at his Fusebox. The bulkheads and transoms done. I'm leaving Fusebox in the Prototypes Catalog for now because it has appeared on at least three web pages.
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