Jim Michalak's Boat Designs
118 E Randall, Lebanon, IL 62254
A page of boat designs and essays.
(15jan08) this issue will rerun another knockdown article. The 1 February issue will take another look at power boat power.
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.
Robb Rhode-Szudy has revamped this AF4b (originally built by ??).
JEWELBOX JR KNOCKDOWN
I got a nice letter the other day from Rick Bedard in California. He had just finished a Jewelbox Jr and took it out to sail. There was no wind to speak of! He had read the knockdown episodes that were recently presented on this site and decided to take a bit of time and see what the JB Jr would do in a knockdown.
Two things to mention here before getting into his story. One is that JB Jr has a Birdwatcher type cabin where everyone rides inside looking out through the windows. It is supposed to be self righting without ballast but some boats of this this type have proven to need ballast and paper analysis of JB Jr using programs not available when I designed it had shown it would be stable on its side if heeled over about 60 degrees. So I was really interested in a test of the real thing. Second is that if you are to do a test like this it is usually best done with a brand new boat, one that has not gained much gear and junk that will need to be removed for the test or else the stuff with slide and tumble all over the place during the test, as it all will do in a real knockdown.
Rick's JB Jr looks right to the blueprints to my eye. He said the bottom was doubled to 1" thick from the blueprint's 1/2" for stiffness although the extra weight there, probably about 70 pounds, will help the stability too. Also the mast is a hollow round "birdsmouth" mast instead of the blueprint mast which is square in section and solid.
First he put the boat in waist deep water with bow and stern tied to the shore to prevent the boat from moving sideways when the halyard is used to pull the boat over. The sail and boom were stowed.
With no one in the cabin the boatwas pulled out using the halyard like this:
At this point which looks to be about 45 degrees of heel the boat will still self right as indicated by tension on the halyard.
Here it is at about 60 degrees still with tension in the halyard so still with positive stability.
He pulled it over a bit more and the halyard tension went to zero, the boat falling over on its side. Like this:
Looks to me to be at 70 or 75 degrees of heel. Rick had these comments at this point:
"Here's what happened. When pulling the empty boat over, the pull on the halyard to heel her was at first light, then it took more and more force to heel further, until the gunnel was immersed and the windows began to touch water. Then the load on the halyard quickly diminished, until it was gone. At this point the outer corner of the center of the cabintop was less than two inches from the water. Then the weight of the mast alone caused the boat to heel by herself that two inches, and she plopped over till the windows hit the water, then maybe one inch (of the cabintop) immersed as the buoyancy of the cabintop stopped any further heeling. The boat came to rest at that point, -(that's what I meant by stable). However the slightest push up on the mast and she popped upright. Thinking back, I bet (but didn't think to try) that a lowered leeboard would have been more than enough to keep her from "falling" that last couple inches."
"I then tried to heel the boat further. Pulling down on the halyard from that heeled position took significant effort. One time while holding the masthead in the water while waiting for my kid to snap a photo, my hand slipped releasing the mast and the boat popped upright. My feeling is it was the buoyancy of the cabintop that built enough momentum to get the hull past the "stable" zone as I called it."
"Then when floating in that heeled mode, I waded to the hull and pressed down on the mast next to the cabintop and had to put most of my weight there to get the mast to touch, and all of my weight only put the top two feet of the masthead under an inch or so."
"Climbing inside, I could only keep the boat heeled down by keeping my weight (feet) in the chine or on the hull side and leaning on the cabintop rail. Any shift of my weight towards the sole and she rolled under me upright. When I tried to sit centered in the chine she rolled herself upright."
"I did this three times while trying to put the cabintop under. Again, getting the hull to right was nearly effortless, it was a balancing act to keep it tipped over."
"When inside the hull, starting upright, my one hundred pound assistant could not pull the boat over using the halyard until I leaned hard out the cabintop while he was pulling. (I did this fearing a snapped mast, he was aggressively tugging away). The boat would stop heeling just before the cabintop corner would get to the water and go no more. By leaning out, and carefully staying to the heeled side of the chine I could keep her heeled. Any shift back and upright she went."
"Apparently I put little thought into what it took to right the boat, as empty it only took a small tug, and with me inside it was all a balancing act to keep her from righting."
WHAT I THINK IT MEANS...
Well, the JB Jr seems to behave just like Bolger intended a Birdwatcher to behave. Although the boat is stable on its side with no one inside, the weight of the crew is sufficient for the boat to self right. I think Rick's test is pretty convincing. It might be added that Birdwatcher designs have never been popular, probably because sailors don't care to be inside. But if you compare the knockdown results we've seen for IMB and now JB Jr to a knockdown of a conventional open boat, you might think the Birdwatcher boat is safer. If you compare the IMB or JB Jr to a conventional ballasted cabin boat you might think the Birdwatcher boat is a lot lighter and simpler.
Jewelbox Jr. plans are $35.
SAILBOAT, 15' X 5', 400 POUNDS EMPTY
This is Jewelbox Junior, a 15' version of the original 19' Jewelbox built a while back by Karl James in Texas. That Jewelbox went all over the US and parts of Canada and I understand was sold a few years ago to someone in Florida and replaced by a larger sharpie that Karl had designed. Here is a photo of the original Jewelbox.
JB Jr is also narrower than the original boat, the bottom now planked with just two sheets of 1/2" plywood. Perhaps a good comparison of the two boats would be that Jewelbox needs 16 sheets of plywood and JB Jr needs 9. In particular I hope that JB Jr could be towed behind a small car. Two protoypes of JB Jr were completed last fall. One by Vern Stevens in Idaho and the other by Erwin Roux in Pennsylvania. Vern had a chance to take this photo before winter hit:
And Erwin sent quite a few great photos taken on a beautiful autumn day.
Here you see that JB Jr has that Birdwatcher cabin. The idea behind the Birdwatcher cabin, invented by Phil Bolger in his Birdwatcher design, is that the crew sits low inside the cabin looking out through watertight windows.
The crew weight thus acts like ballast. The boat becomes more stable with extra crew where a normal raised deck boat becomes less stable. I did some paper studies of the self-righting abilities of Junior. With it lighter bottom planking, Junior is bound to be less in that department than Jewelbox, which Karl says has righted from having its windows submerged. By my studies Junior should self right from up to 65 degrees of roll. Beyond that and she would roll another 15 degrees and become stable on her side. She won't flood due to her Birdwatcher cabin. If you couldn't rock the boat back upright you would have to exit, right the boat from the water by stepping on the leeboard, and climb back in. And you would need a reliable step to do that in any high sided boat. These are just paper studies. I would expect my IMB design to behave the same way. Larger heavier designs, like Jewelbox and Scram, should self-right from a full knockdown. More weight on the bottom, especially another layer of plywood there, would be a good investment if you could tow the extra weight.
I've shown Junior with a sharpie sprit rig, although you could substitute a lug sail as Stevens did.
JB Jr plans are $35. Simple nail and glue construction with no jigs or lofting.
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. Has a temporary rig and he is working on the blueprint rig.
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 the Leinweber's make another prototype! This one by Sandra, an Imresboat shown here on its first outing. They are taking it on a "cruise" so more about it later.
HMMM....Just connect the dots and you will have a new Mikesboat...
And a new Down Under Blobster, as seen looking aft....
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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