Jim Michalak's Boat Designs
118 E Randall, Lebanon, IL 62254
A page of boat designs and essays.
(1Dec09)This issue will rerun an essay about the ballast problem. With luck I'll be able to close out the new design ballast essay in the 15 December update.
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.
Cary Berger in Texas built this nice QT rowing skiff, did his sail area math, and designed this nice sail rig. 67 square feet all set on 10 foot spars. Also note his perfect hull trim gained by sitting well forward. Nice job!
WEIGHT HAS A BIG EFFECT....
...on how your boat will go. Here is an example with will use my AF2 design from a few years back. Here is a photo of Richard Spelling's AF2 (the only one I know of to get built):
And here is a line drawing:
AF2 is a rather typical sharpie, 20' long and 5' wide on the bottom with a single gaff sail. The cuddy cabin is roomy enough for a solo bed room and it has a slot top that could be left open for sailing on nicer days.
One of my design guesses was that it would have an empty weight of 600 pounds and I'll tell you how I stab at that. AF2 requires, no guesses here, six sheets of 1/4" plywood, seven sheets of 3/8" ply, and one sheet of 1/2" ply by the blueprint. The usual plywood weighs about 25 pounds for a 1/4" sheet, about 38 pounds for a 3/8" sheet, and about 50 pounds for a 1/2" sheet. The resulting pile of plywood should weigh about 470 pounds and I have found that to be a good guess at the weight of such a hull bare with no extras. Add maybe 50 pounds for the sail rig. Then round up and there I am at 600 pounds.
Now that is a minimum weight boat in the water. Add a skipper and some of his junk and let's say the boat is sailing at 1000 pounds most of the time. Using our old friend Hullform we would expect a waterline like this:
It looks quite good to me and I have been taught to look at it with Phil Bolger's eyes. He said sharpies need to sail over the water and not through it. The bow is swept well above the water to meet the waves with the bottom and not pushing through them with the sides. The stern is also well out. She would have a short waterline bolt upright as in light winds, minimum wetted surface area so they say. But a sailing breeze would heel her over to get a longer waterline when there is power in the wind. And heeled she would meet the waves with the edge of her chine like a V bottomed boat. It all works great provided the conditions are right. The best case is a strong wind with smooth water. The worst case is rough water and little wind. So sharpies have split personalitites much moreso than V bottomed or round bottomed boats.
I might add that the short upright waterline helps a lot for quick maneuvering.
Now let's add a couple of big passengers and we are up to 1500 pounds and she looks like this:
Still looks OK but I might suggest this would be the limit for brisk sailing.
Now let's add a couple more passengers, a full house but AF2's benches have room for four adults. Then we have this at 2000 pounds total:
The transom is pretty much in the water and will drag when the boat is heeled. The bow is ready to plow through the water. I'd say this is a maximum but most likely it would be a once a year sort of outing, not serious sailing.
HERE COMES TROUBLE...
Home Depot has some great looking 1/2" plywood on sale and you can't resist. You buy fourteen sheets of it and make the whole AF2 from it. She's bulletproof now but she's probably going to weigh about 800 pounds empty. Perhaps the best way to look at it is that you gave up one adult's capacity. If you are a loner there would be no problem.
...AND HERE COMES REAL TROUBLE...
Let's say you are going to use AF2 as the basis for a small cruiser ballasted to be self righting. I tried this a number of years ago. The ballast will be something like metal inside on the bottom although it might be water ballast too as low down as possible but still inside the hull. But just adding ballast is seldom enough. The top of the boat must be make watertight like a bottle with a sealed raised deck aft that would resist swamping in a knockdown and shed any water like a duck. The trouble is raising the deck also raises the crew and they are a major portion of the weight.
OK, next step is to figure the ballast needed to make it self righting and if you want to start a big argument just try to define "self righting". To me with a boat to be sailed close to shore where huge waves won't lurk and where rescue is possible I think it might mean it would return upright from a 90 degree tilt. To Howard Chapelle self righting for a sharpie was to return from just a 45 degree tilt. To an ocean sailor, who could get rolled by a big wave, it can mean righting from way past horizontal, say to 140 degrees. I don't know if any boat with inside ballast could do that.
Here is the picture I draw for a first cut at a problem like this:
What we have here is a front view of the boat knocked over 90 degrees with the weight of three adults on the raised cockpit deck. I've taken the weight of the hull to be 550 pounds distributed evenly thoughout, and the weight of the rig at 50 pounds. The main effort of the buoyancy of the tilted hull is taken to be halfway up the side. Now solve for the ballast weight needed to put it all in balance. If you take the torque about the point of buoyancy you see the torque twising down to the right is the passengers (= 12x500=6000 inch pounds) plus the sailrig (= 102x50=5100 inch pounds) for a total of 11,000 inch pounds. Counteracting that is a torque in the other direction provided by the ballast at 18" so the ballast must weigh 11000/18=611 pounds for this crude first look. I am not surprised at all. All of Bolger's small sharpies seem to have 500 pounds of it.
Here I've assumed the weight of the bare hull is right above the point of buoyancy and I think that is pretty safe to start with. So the hull weight hardly figures into it. The real killers are the crew and sailrig weights and distributions. You can see how outside ballast placed way down on a keel has a real advantage. And you can see that the crew weight, if placed on the bottom as with a Birdwatcher type hull suddenly becomes its own ballast to help the hull right instead of trying to pull the hull over.
And you can note that buoyancy down low in the boat, as say beneath that raised aft deck, actually tries to turn her turtle. But whatareyougonnado? You need to seal that area so the boat doesn't swamp and become helpless at far less heel than 90 degrees (water usually comes over the side at about 45 degrees of heel, I think). And you can note that the higher the cabin is to the rest of the boat as in a raised deck cabin, the more buoyancy you will have up high provided that cabin does indeed go into the water (with its windows closed) and is not a trunk cabin with a low walkway around it.
But the upshot of it all is that we would start with an empty weight of about 1200 pounds and then we go from there. When I tried this on a design more along than this one I actually had to give up on it since I saw I needed to redraw everything to give more hull rocker.
HEY, HERE'S AN INTERESTING QUESTION...
Noting that the crew weight has a huge effect on the equation, the boat is more self righteous if the crew abandons ship, right? Yes it is. As the crew slips into the water it relieves the boat of that up high weight and it will self right. But the crew is in the drink and has to get back on board some how. So keep that in mind. (Karl James in Texas once told me his sharpie, bigger than AF2 but with 500 pounds of internal water ballast, did indeed get knocked over with a party of passengers on board. And it did indeed self right as soon as they fell into the water!)
POWERBOAT, 18' X 6', 350 POUNDS EMPTY
This was supposed to be a cut down AF4, without cabin, but with a large open cockpit for sightseeing, and maybe a canopy over all of those seats. Chuck Leinweber called it a "picnic boat" which is a pretty good idea.
It is the same overall size as AF4, should be about the same weight. In general the bow has a 6' long recessed deck, storage under if you want, followed by a 10' long cockpit with bench seating on both sides, followed by a 2' long motor well segment just like AF4's.
But I did simplify the construction a bit from the original AF4. I made the sides a constant 2' width so you make them by ripping plywood panels straight down the middle with no curves to the edges. Then when you bend them around the bulkheads the bow will pop upward in a nice swoop. The stern aft of 10' is constant width and depth, unlike the original AF4 that had its sides pinched inward a bit strictly for looks. But I like the looks of this new one too.
This sort of shape has some advantages beyond the simple setup. Because the hull is constant aft of the middle a fellow could lengthen, shorten very easily. You can't make it wider or narrower easily. In addition, the bench seats are I think pretty much nonstructural. You could omit them leaving the center open except for the center frame. Sit on a folding chair like I do with my AF4. Unfortunately I do think the center frame is needed to keep flexing of the bottom under control. But there are other ways around that, for example using a deeper center shoe. The bottom, as shown, is a copy of what I use on my AF4 now with satisfaction. 1/2" plywood with a 2x4 center shoe full length. Max Wawrzyniak showed me the way on this after my first AF4 bottom proved flexible beyond enjoyment. It is a very simple build indeed.
I can picture fishermen making this one stripped down but maybe with the bow deck left to stand on.
The canopy is somewhat bothersome but it is very important if you are to spend all day on the water. A fellow might do just as well to buy a premade job from someone like Taylor Made. Here are the problems I see with a homemade top. For one is weight. The boat can certainly float the weight but weight up high can be dangerous, so I would suggest a polytarp lashed to a simple wooden frame. Best would be a simple frame of aluminum tubing but most of us can't weld it and if you start buying factory fittings and tubing you might find the Taylo Made solution is actually cheaper. OK, next problem is probably that you will want to fold it down for towing and probably will have to fold it down to get it into a garage. I designed this one to fold aft but on second thought reversing the hinges so it can fold forward might be better and hope it will stow nicely on the bow deck. Anyway, the boat will be fine without the top so you could start it out that way and ponder a top solution as you wait for the fish to bite.
Let's say 25 hp max. (AF4 likes 15 to 20 hp.)
Construction is simple nail and glue requiring three sheets of 1/4" plywood, two sheets of 3/8" plywood, and four sheets of 1/2" plywood.
Blueprints for AF4Casa are $30 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. 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 I heard about through the grapevine.
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 Batista's of www.breakawaybooks.com, printer of my book and Max's book and many other fine sports books. Boat is done, shown here off Cape Cod with mothership Cormorant in background, Garth's girls are one year older. Beautiful job! I think 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.
And a new Down Under Blobster is off cruising under outboard power as it waits for its sailrig.
A view of the Caroline prototype showing a lot of the inside, crew on fore deck. Beautiful color:
And here is another making I think its maider voyage in the Texas 200. (I'm told the Chinese rig will be replaced by the blueprint rig.)
I gotta tell you that on the Caroline bilge panels I made an error in layout and they are about 1" too narrow in places on the prototype plans. I have them corrected but it always pays, even with a proven design, to cut those oversized and check for fit before final cutting.
And a Deansbox seen in Texas:
And in Texas Gordo Barcom has completed the first Laguna and I hope to give a full report soon. Here he blasts along on his first flight:
The Leinwebers have ganged up on me to rename the Sandrasboat to RioGrande. And here is a photo of Sandra in her RioGrande on the Rio Grande. We have to sort out some fit problems Chuck reported he had in building but then it will go public. It is essentially a decked Toto.
A Twister goes together in good shape:
AN INDEX OF PAST ISSUES
THE WAY BACK ISSUE ARCHIVES
1nov09, Ballast Again, Piccup Pram
15dec08, Knockdown Recovery, Raider
1jan09, Knockdown Recovery 2, Caroline
15jan09, Knockdown Aspect Ratio 1, JB Jr
1feb09, Aspect Ratio 2, Mayfly16
15feb09, IMB Capsize, IMB
1mar09, Mizzens, Blobster
15mar09, Lugsail Rigging, Imresboat
1apr09, Laguna, Frolic2
15apr09, Rigging Sharpie Sprits, Sportdory
1may09, Small Boat Rudders, Robbsboat
15may09, Rowing Gear, Roar2
1jun09, A Bimini Boot, Ozarkian
15jun09, Phil Bolger, Vector
1jul09, Rend Lake 2009, Fatcat2
15jul09, Rowboat Setup, Mikesboat
1aug09, Sail Area Math, Family Skiff
15aug09, Beach Designs, Cormorant
1sep09, Taped Seams, Trilars
15sep09, Birdwatcher Cabins, Philsboat
1oct09, Bevels, Larsboat
15oct09, Transom Height, Jonsboat
1nov09, Ballast Again, Piccup Pram
15nov09, Ballast Again2, Caprice
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