Jim Michalak's Boat Designs
118 E Randall, Lebanon, IL 62254
A page of boat designs and essays.
(2DEC97)This issue includes some observations about a boat put together by Kilburn Adams. I thought his boat was of particular interest because it is a very useful sort that operates efficiently in a performance range that is seldom used.This particular essay is to be one in a series that will lead to a new design. A design done live on the net, so to speak. Look for the next issue about the fifteenth of December. It should have the number crunching start of a new plywood design similar in spirit to Kilburn's boat.
I first met Kilburn Adams back in the early 80's, shortly after I started boating. Small Boat Journal magazine was in its glory then teaching us all how to mess about in the latest sail/rowing boats and beach cruisers. At that time I had just finished my Jinni, with sharpie yawl rig and a pivoting leeboard, and Kilburn had a new Sea Pearl with lug sails and leeboards. He chased me down on Carlyle Lake one day, his first words being "That's a Bolger boat, isn't it."
He introduced me to a lot of new ideas. Some took years to settle in, but now when I see Kilburn arrive with a new boat or a mod to an old boat I pay attention.
Three years ago Kilburn came to our June Messabout at Rend Lake with a powered model of a small power boat he was brainstorming. (Kilburn's model making has put him on the cover of some national model magazines.) I don't remember the exact details of the model but I think it was more or less of a lapstrake flat bottomed power skiff perhaps similar to a Simmons Seaskiff, about 20' long. It had a minimal cuddy cabin with a step through slot top similar in principal to Birdwatcher. It was long and narrow. Kilburn said it was a model of a real boat he intended to build. But the years and other projects slid by (including a very interesting mod to his Sea Pearl that I'll try to cover in a future issue) and the full sized cuddy power skiff stayed on the back burner. Even so, at that messabout Kilburn said he had already gotten a deal on an outboard that would fill the bill.
...THE NEW BOAT...
As I understand it, Kilburn was thinking about retiring this year and wanted to get an efficient cruising boat on the water . He's a perfectionist at building and realistic in knowing perfect boats don't get built in a short time. He cast about for a production hull that might jump start his project.
He got in touch with the Stur-Dee boat company in Rhode Island (probably found it in those old Small Boat Journals or maybe Messing About In Boats) and bought what I might call a 16' Amesbury power dory skiff. We had already seen the construction quality of Stur-Dee boats at our messabouts because Tony Woodruff had been bringing his Stur-Dee 14' sailing catboat for a couple of years. That boat was a beautiful traditional design, very well built, all details well thought out and executed. No gimmicks and nothing kinky. A beautiful solid boat.
And so it was with Kilburn's new dory. As you see in my fuzzy scan (you don't need to remind me that my scans are lousy. The same with my spelling) the dory has lapstrake sides even though it is fiberglass. The length is 15.5'. The bottom plank is 39" wide with the sides rounding up and out to a max beam of 6'. The stern is wide for a good power installation and this is no rowing dory.
The bottom is of particular interest. The bottom plank looks at first to be dead flat but on closer look it appears to have a reversed "hook" to it Just when you think it might be starting to sweep up at the stern it sweeps down a little, no more than 1". There is a partial skeg on centerline that stops well short of the stern. There are two side skegs that go all the way to the stern. If the boat is placed on flat pavement it would rest on the skegs in a three point stance.
As delivered the boat is all white fiberglass with three (I think) stout wooden thwarts. It has oar lock sockets but this is not a rowing dory.
The spec weight on the empty hull is 450 pounds although Kilburn thought out loud that it might be a bit lighter.
The hull was pretty much standard when Kilburn brought it to the Rend Lake messabout in June. The only mod at that time was an added wooden strake near the sheer line for cosmetics. But Kilburn showed us a drawing of the boat with a cuddy cabin he was planning.
At the messabout near Bloomington, Indiana in September he brought the dory with the boat rigged as shown in the photo. She was more or less complete although he planned to yet add some simple bunks.
The cabin you see is basically open to the back. The "bulkhead" you might think is there is really some partial framing. There is no framing across the bottom anywhere in the boat - it's flat and open. The cabin top is open on top with a slot about 2' wide, to be closed with a fabric cover. The bulkhead on the front of the cabin has a removable drop board. And there is an open well in the very bow for the anchor gear and fenders. With the top open you can stand securely in the cabin slot with the edges about waist high.
The factory thwarts remain in place. The passenger area behind the cabin is covered by the Bimini top and there is a swing up lexan windshield attached to it.
The driver sits on the center thwart with the engine and steering controls at hand. The steering is by wheel and a push-pull cable with rack and pinion to the wheel. So the crew weight is centered in the boat.
Kilburn felt the mods he added might amount to 100 pounds.
This gets interesting, too. The motor Kilburn bought a few years ago was a 4 cycle Yamaha rated at 10 horse power. kilburn had done a lot of homework on the motor. He pointed out that by the specs he had seen the 10 horse 4 cycle had the same prop, gearing, and rated power head speed as the Yamaha 2 cycle 15 horse.
The motor is said to weigh 100 pounds.
A guess at the typical operating weight of the whole assembly might include 450 pounds for the empty hull, 100 pounds for Kilburn's mods, 100 pounds for the Yamaha, and maybe 350 pounds for Kilburn, a not-too-big passenger, gas and gear. The total looks like a round 1000 pounds.
The chart below plots speed vs lbs/hp.
The segment with more than 100 lbs/hp is the same as the chart presented last issue although I did not include data beyond 200 lbs/hp on this chart. As before it plots the data for waterlines from 10' to 25'.
The segment with lbs/hp less than 50, that is higher powered boats, is a "planing" line based on Dave Gerr's info for "average" hulls. (Dave also included a line for "racing" hulls that went to 70 knots.)
(I don't really know if there is an official definition of 'planing". There probably is and if a reader knows of it I'd like to hear from them. I suspect it will be an erudite thing that we don't really need to know to crank out our numbers. )
In between those two segments is a "transition" line I had the computer draw in.
Remember that these charts are to get you into the right ball park.
If the boat weighs 1000 pounds and the motor puts out 10 horsepower you'd think the boat would have 100 pounds per horsepower and that, with a 15' waterline, the chart predicts a speed of 9 knots.
At full throttle Kilburn has measured his speed with GPS at 13 knots. Point "A" on the chart marks the place where 100 pounds per hp meets a speed of 13 knots. It really doesn't fit well into the scheme of things. If you think the Yamaha might really put out 15 hp you would enter the chart at 1000/15=67 pounds per hp and wind up at point "B" which is right on the line.
But there are other combinations that might work. For example if Kilburn made his GPS run solo and his hull were lighter than spec, the total rig might weigh in at 800 pounds. Then if the motor peaked at 12 hp you still end up at point B. Then again it could happen that the motor really is 10 horse and the chart is simply off by 20% , the Stur-Dee dory being much more efficient than "average". The chart can put you in a pretty big ballpark with lots of ways to explain it.
Kilburn used his boat quite a bit during the summer of 1997. On the pool above the dam on the Mississippi at Alton, Il., he said he'd covered 50 miles (always statute miles here) burning four gallons of fuel. I don't recall if he said he had an average cruising speed of some sort. There is usually little current in that part of the river but there will be a lot of distractions on a 50 mile river trip. He has said he thought the rig was capable of maybe 20 mpg with a lot of tweaking.
I took a ride with Kilburn at the Bloomington meet and the boat clearly was planing, comfortable, quiet and well controlled. There seemed to be no "hump" in its actions, no changes in pitch as it got up to speed. (Perhaps the forward weight placement of the crew helps here.) Kilburn said my weight (160 pounds) made a noticable difference in performance. And that the boat is noticably faster in a light chop than on glassy smooth water. He added that a third passenger slows the boat to the point where it may be dropping off plane. Crew placement is important.
Well, I was impressed. I had always seen power boats with large motors. No one seemed to advise operating in the power range that Kilburn is running. The usual idea is that you need at least a horse for each 50 pounds (you would need 3 or 4 extra horses per extra passenger). So then Kilburn would need at least 20 hp. I saw in Dave Getchel's book that the engine makers advise a horse for every 25 pounds. So they would say Kilburn needs at least 40 hp. But he's doing great with (what Yamaha calls) 10 hp.
Two last points of interest. First,on the chart it's apparent that once a boat starts to "plane", it becomes more efficient from the standpoint that more horsepower makes for more speed, as compared to the "displacement" region where more power mostly makes for more waves. Indeed, a big bass boat with 200 hp at full throttle will go by you with hardly a ripple. Of course, it takes a lot of power to get on plane. Second, if you accept that the motors burn about .1 gallons of fuel per horse per hour, a funny thing happens to your mpg as you go fast. It almost levels off and becomes constant as you speed up. We might look at that more closely next time.
We'll start laying out a plywood design in the spirit of Kilburn's boat. It's true that Bolger has explored this area a bit with long light boat like Sneakeasy. But the new one will have a cuddy cabin with something like traditional looks.
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.
This issue's design is from the Catalog of Prototypes and is called "AF3". It's the third iteration of a cuddy sharpie design from a few years ago called "Alison's Fiddle." The first two were larger but all were supposed to be simple with traditional looks. I'm showing this one now because next issue I'll start laying out the design of a power sharpie patterned after the Fiddle designs.
(So who is Alison? Back in the early '80's an acquaitance of mine stuck me with the job of helping judge his annual fiddle contest. I protested a bit pointing out that I couldn't begin to play one. "No problem." he said, adding modestly, "You've heard me play. If they play like me be sure they win!" I don't remember much about the event except that the winner of the Junior division was a scared-looking ten year old from Champaign named Alison Krauss. She's gone on to become quite famous.)
AF3, CUDDY SHARPIE, 15-1/2' X 5', 250 POUNDS EMPTY
AF3 is one in a series of simple cuddy sharpies that started with Alison's Fiddle a while back. The first two were larger than this one - more like family daysailers with bench seating. This smaller one is half the work and cost of those, but it will still take three adults. This will be a handsome boat, too.
There is very little risk in this design. The sail rig was lifted from the proven Pencilbox, which in turn was lifted from my old Jinni, which, after years of modifications, is almost identical in size, shape and style as AF3. I align the sail area above the trailing edge of the narrow leeboard on sharpies. If weather helm becomes a problem (hardly ever happens) you can dial it out by sweeping the leeboard aft. Traditional teaching would have the sail much farther forward but that guarentees undesirable lee helm in this type of hull. I'll bet the old rule about "lead" in sail layout applies well to the sharp deep cutwater designs of traditional planked boats.
Also, I've shown external chine logs on AF3 and all my sharpies. They are an easy, quick, and strong bottom attachment. But many can't accept their looks. Use traditional interior chine logs if you wish. Better yet, use epoxy/fiberglass tape chine joints with a healthy interior radius. That makes for a really clean looking layout and the worst rot area in wooden boats, that chine log, is totally eliminated.
AF3 uses six sheets of 1/4" plywood and two sheets of 1/2" plywood. Plans are $15 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. The first Scram was completed two years ago in Houston but I think the builder went straight to building another boat and I didn't get a real test report or suitable photo of the completed Scram. And Skat, a 12' cat boat daysailer, is being built near Phoenix. And a Fusebox has been started by a Boat Psychologist in Kansas.
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