Jim Michalak's Boat Designs
118 E Randall, Lebanon, IL 62254
A page of boat designs and essays.
(15February2013) This issue will continue the old "drawing a boat" essays that first ran in 2005. The 1 March issue will continue the topic.
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.
Chuck Pierce's Mayfly14 poses with all the gear it swallowed for the five day TX200 a while back. Not sure where Chuck put himself.
Drawing Boats 3
In the last "drawing boats" issue I talked about the importance of the end view of the design. This issue will start the layout of the lines of the Bobsboat design.
THE END VIEW...
I'm going to start by putting hard dimensions on the drawing of the end view. A lot of this is arbitrary but based on experiences with past similar boats. The size of the boat is based on what it's mission is: lets' say take four adults in relative comfort at slow power speeds, say with a new 5hp four stroke motor that will be quiet and fuel efficient. Four adults will total maybe 700 pounds and that motor another 100. The hull of something like this will weigh maybe 400 pounds so the total I would like to float with good lines (ie the ends and chines of the boat, all the sharp corners, will be out of the water) will be about 1200 pounds. The next web page issue will show how to check this.
Another goal will be that the planks will not be twisted. This will mean that section lines of a plank in the end view will be parallel. But I'm going to break this rule in the bow of the bilge panels and allow some twist. I'll explain why later.
And finally as discussed the last time I'm going to show all the lines in the end view as straight lines. Like this (this drawing and others will not be to scale but the dimensions shown were figured on the paper drawing):
Just some general notes about the layout. The top width and depth is to give comfort and spread out room for the adults with some wide bench seating. The bottom width is at 4' to fit on a sheet of plywood, it could be narrower but I see no need for that and the wider the less tippy. The transom width is at 4' to fit on plywood also, it could be narrower but this boat is supposed to have its motor mounted in a wide slot so width might be important here. The stern is swept up higher than I expect will ever be needed to keep the transom from "dragging" through the water at this boat's slower cruising speeds. Same with the height of the bilge panels. But in the bow bottom I swept it up less with the idea that it will push through the water a bit and stay quiet. Bows like this work quite well if they are not swept up at all, by my experience. And by my experience a boat shaped like this can take quite an overload and still go well, unlike a plumb bow boat.
The sweep of the "sheer" on the bow and stern are also quite arbitrary in a boat like this. It is mostly for looks and I suppose the boat would go just as well if the sheer were dead straight but most folks would think that ugly. You could also sweep it too much and make it ugly, I think. This is one area where only a model can tell you how it's gonna look, although some of the new boat modling software will take a good stab at a pictorial representation.
NEXT, THE TOP VIEW...
You might be tempted now to draw the side view but I can assure you that your work will be a lot less if you go straight to drawing a top view. In this hull with plumb sides the sheer line and the top bilge line will appear as one and the same.
Here is how I would do that: First determine where the widest point of the boat will be. Hint: If you put the widest beam at 55% of the length you will end up with a normal looking boat. That is where I am going to put it on this 20' long hull - at 11' from the bow. (I'm reminded here of Phil Bolger's argument that the bow of your boat should be a little faster than the stern - otherwise the stern will on occasion try to pass the bow and that ain't good.)
So now I have three points of the top view of the sheer determined, the bow tip, the widest point and the stern flat. On the drawing board I lay out those three points and spring a batten through them using just three spline weights, like those shown in black. After those points were established I found I had to add other weights as shown because the natural curve of the batten wanted to spring outward beyond my 55% point and I used two more weights to spring it back into position. Like this:
That done I take dimensions of the sheer's width say every two feet to sort of "digitize" the curve of the line. Like this:
The shape of the hull aft of the widest beam is now totally esablished. We need only figure it out. The shape of the hull forward of the widest beam is about 70% established because we are allowing some twist in the bilge panels. If we were not allowing the bilge panels to twist then the hull shape there would now be totally established. That would be true of plumb bow multichine hulls I've done like Ladybug. But for a hull like this where the upper chine sweeps way up at the bow, to not allow twisted bilge planks would doom the boat to having an extreme rake to the lower bow which would shorten the waterline, and reduce capacity. In the case of Bobsboat the point of the V of the bow bottom would be about 5' aft of the bow at the sheer line if the bilge planks were not twisted to extend that point to 2' aft of the bow sheer.
Let's go back to the stern and find all the points needed to draw the side view. First use the top view to take note of the width of the hull at various stations. Then draw those stations in on the aft end view, like this:
Now at each station you can measure up from the base line and determine the height of the sheer and upper bilge panel in the side view. You can spot them onto the beginning of a side view in that area.
But since there is no twist in the panels in the stern we can also draw the lines that represent the bilge panel in the end view, like this:
Connect those bilge lines across at the bottom panel and you will get the width of the bottom panel at each section.
At this point you can go to the top view again and draw in the bottom plank, at least in the stern. In the region of the bow I will extend the bottom plank smoothly to a point 2' from the bow as shown in the original Bobsboat sketch. Like this:
Now we also can measure the widths of the stations along the bottom plank in the bow region and transfer those to the bow end view, like this:
Then we can fill in the remaining section lines in the region of the twisted bow bilge planks, like this:
All the thinking is done. With the top view complete and the end view complete, the side view dimensions are all there. Just drawing it remains. The "lines" of this boat are done.
There are other ways of doing this but I have found the above to be the most efficient both in labor and in getting a good looking boat. It's quick once you get the hang of it. I suppose it might take an hour to get the lines completely done like this. If you decide to change something remember that changing something in one view usually results in changes in the other views.
At this point the best plan of action is usually to scope it out with a good program like Hullforms. In fact one of the very first things to do is to get a handle on the displacement of your new design, so next time I'll show how that is done with a rerun of an old essay on the subject. If it proves OK we'll move on to the details.
We'll continue this topic next issue...
IMB, SAIL BEACHBOAT, 13.5' X 5.5', 350 POUNDS EMPTY
IMB features a "Birdwatcher" cabin, full length with panoramic windows and a center walkway slot in the roof. Everyone rides inside. This style of boat was invented by Phil Bolger in the early 1980's.
These boats can be self righting with minimal, or no, ballast because crew weight works as ballast. They sit low looking out through the windows (although standing in normal winds is quite acceptable). The cabin sides provide lots of buoyancy up high to ensure a good range of stability. IMB, which is small with a light bottom, should reliably self right from 60 or 70 degrees and in the test described above self righted from a full 90 degrees of roll.
These boats are operated from within the cabin, like an automobile. No one need ever go on deck. For boating with children I can see no equal.
These are usually cool inside. The tinted windows cut the sun's power. The crew can sit in the shade of the deck. Downdraft from the sail cascades through the walkway. (By the way, at the Conroe messabout two boaters with Lexan windows noted that mosquito spray will ruin Lexan with one application and they noted belatedly that the back of the spray can says so.)
IMB has an 8' long cabin on a multichine pram hull. The prototype was built to perfection by Gerry Scott of Cleveland, Texas. At the Conroe (Houston) messabout I got a chance to look over his boat plus the only other IMB I know of built by Bob Williams. Both boats were quite true to the plans. Both had added low inside seats which made them more pleasant to use to the point that I will show some seats on the plans. I was worried when I drew IMB that the headroom would be minimal so drew no seats thinking the crew would sit on the floor, as with the original Birdwatcher.
While I was sailing with Gerry, Bob's boat came out on the lake with four adult males and no sign of bogging down, showing that these fat pram shapes, very much like my Piccup Pram, can handle a lot of weight in the 13.5' length.
(Later they rescued a mermaid and returned to the dock with five total.)
I don't know if either boat had ever been weighed and the 350 pounds I quote as the empty weight is just a guess. One of the ideas behind the boat was that it might be towed behind a compact car and I was glad to see that Gerry tows his behind a 1500cc mini SUV.
Both men adjusted well to the lug sail/leeboard rig. Gerry's has the blueprint 104 square foot sail and Bob's uses the 114 square foot Bolger Windsprint sail available from Payson. I used to worry a bit about running a leeboard on a full cabin boat like this since handling must be done by remote control, so to speak. No problem. Both boats have the leeboard lanyard running to a cleat on the aft deck. The leeboard position is plainly in view at all times through the cabin window. In use these leeboards need only lanyards to pull them down. Once down they will usually stay down until they strike something. Then they pop up and you will need to pull them down again. I've never seen a need for a lanyard to pull the board up although I've seen several rigged that way. The Dovekie design had elaborate cam operated levers in the cabin that operated the leeboards and I thought that all very clever. But in talking to some Dovekie owners I found the internal levers are not universally loved since they can often be in the way. Anyway, my idea was not to run the down lanyard to the aft deck but rather through a small hole in the side of the boat, say 1/2" for a 1/4" lanyard, so it could be operated totally from inside the cabin.
Both Gerry's and Bob's boats used electric trolling motors. The plans show rowing ports and no provisions for a motor. A boat like this won't be a fast row boat but it might be useful in a calm. Even the 24' Birdwatcher would row about 2.5mph in a calm. But I'll admit that adding a motor to Birdwatcher makes it a much more useful thing.
IMB takes two sheets of 1/2" plywood, eight sheets of 1/4" plywood and one sheet of 3/16" Plexiglass. Taped seam construction using no jigs or lofting.
IMB 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.
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:
Another prototype Twister is well along:
And the first D'arcy Bryn is taped and bottom painted. You can follow the builder's progress at http://moffitt1.wordpress.com/ ....
AN INDEX OF PAST ISSUES
A NOTE ABOUT THE OLD WAY BACK ISSUES (BACK TO 1997!). SOMEONE MORE CAREFUL THAN I HAS SAVED THEM. TRY CLICKING ON...
which should give you a saving of the original Chuck Leinweber archives from 1997 through 2004. They seem to be about 90 percent complete.
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)
Puddle Duck Website
Brian builds Roar2 (archived copy)
Herb builds AF3 (archived copy)
Herb builds RB42 (archived copy)
Barry Builds Toto
Table of Contents