Jim Michalak's Boat Designs
118 E Randall, Lebanon, IL 62254
A page of boat designs and essays.
(1January 2011)This will take a look at mast tabernacles. The 15 January issue will be about knockdown recovery.
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.
Tim Chock takes his new Mixer2 out for a sail in the New England autumn.
A fellow who keeps his sailboat on a trailer has to rig it everytime he motors to the lake. Rigging a sailboat quickly is of the greatest importance for a trailer sailer because if the rigging/derigging operations take more than about 15 minutes the skipper will begin to think twice about hitching up the boat for a quick sail. He'll likely end up using the boat two or three times a year after the first season by that point. Not a good situation and not a successful design, no matter how the boat performs otherwise. Smaller boats like my AF3 or Piccup Pram can be rigged in perhaps 5 minutes with minimal practice. One simple trick to designing a boat that will rig quickly is to keep the rig to a minimal number of parts - that's why I always use free standing masts with no wires, and why I don't care for multisail rigs for daysailers. Even the 24' Birdwatcher could be rigged in less than 10 minutes.
When a sailboat's mast gets to be more than about 20' long and 30 pounds a fellow starts to think seriously about mounting it on a tabernacle. The Birdwatcher, with its 24' mast that weighed maybe 35 pounds complete with sail, was right at the borderline. Raising that mast required a bit of planning and care. The heel of the mast was tied loosely near the step with the mast laying lengthwise in the boat. You grab the top end of the mast and start walking forward, raising the mast over your head as you go. Once you have walked forward of the mast's center of gravity, the mast will try to tip backwards but can't because you have the heel tied down. You keep walking forward raising the mast until it is standing on end. Then you have to lift it straight up a few inches and guide the heel into the mast step. Then you push the mast into the partner and secure the latch there. It is quickly done once you have worked out the system, but I would never do it willingly with the boat afloat. Even if the water is calm a boat wake that passes and rolls your boat when you have the mast up but not secured can make you lose control. Nor is stepping the mast with passengers aboard a very safe idea - they have to hide in a safe place.
After using my Birdwatcher I got to rig a Micro which has essentially the same main mast. But in the case of the Micro you have to do the above while balanced on top of a cabin deck. Not a job for the old or weak! In the stretched Micro Bolger went to a tabernacle.
I wouldn't put a tabernacle on Birdwatcher but the experience taught me to always at least design one on larger boats. As I'm writing this none of my tabernacles have been built and tested under sail that I know of.
TABERNACLES ARE A BIT FRIGHTENING...
...because all the loads of the mast must pass throught them. They are really a hinged splice in an unstayed freestanding mast. A stayed mast can have a fairly simple hinge since usually the sailing loads are taken by the guy wires, the mast step taking no bending, only compression and side loads. The unstayed mast has to transfer everything, including the bending of the mast, to the hull. To me that means the tabernacle has to have some depth to it to keep the reactions small, in the same way that old time sharpie builders worried about the "bury", the distance between the mast step and the mast partner, on their unstayed masts.
ONE OF THE VERY BEST TABERNACLES I'VE EVER SEEN...
...was on this sharpie, "Endeavor", built by Karl James.
You might recall that Karl had built the prototype of my Jewelbox design a while back and his brother Pete had built the Petesboat design that was based on Jewelbox. But even back then Karl had told me that he was thinking about a trailerable version of Bolger's Black Skimmer. As his thoughts advanced Karl had blended in ideas from Bolger's Martha Jane, in particular the yawl rig with a balanced lug main, and water ballast.
You can see from the photos that his rig folds very neatly on its tabernacle down onto a gallows on the aft end of the cabin. All of the rigging is kept in place ready to go. The main sail is bundled up there too to port of the stowed mast. The sail is wrapped in a velcroed cover full length to keep road dirt off. (There is also a small mizzen sail stowed on the roof of the cabin.) Anyway, to rig the main Karl has only to raise that mast by walking it up, secure the mast heel in a clever way we will talk about later, remove the sailcover, and hoist the main. I don't recall how the tack and sheet lines are attached but they could be left attached to the yard ready to go, or snapped into position just before hoisting.
Let's look at the the aft side of the tabernacle.
Karl said the mast here is the same one he used on Jewelbox, which means it is 3-1/2" square and solid. But you can see that in the region of the pivot bolt he has laminated another layer, probably 1-1/2" thick, onto the aft face of the mast such that the pivot bolt does not go through the main meat of the mast, very important I think since the pivot bolt area is probably the most highly stressed part of the system. (Karl added the beautiful laced leather to keep the boom from chafing the mast.)
That would mean the mast is 3-1/2" x 5" in the region of the pivot bolt. So the tabernacle verticals are probably 1-1/2" x 5". In the region of the pivot bolt the verticals are plated with I would guess to be 1/2" plywood. A good idea to prevent splitting of the lumber. The pivot bolt itself appears to be maybe 1/2" in diameter. The pivot bolt takes the compression load in the mast in this system. And it resists the tendency for the mast to spread the verticals apart with side loads. So the entire unit works together. Also below the mast is a cross bar that extends out one side to support the stowed bundle of boom, sail and yard.
Here is a photo of the front side of the tabernacle:
I see no bolt heads passing through the verticals in the region of the cross bar that supports the stowed sail, so I guess that cross bar is attached with screws.
Here is a view of the lower part of the tabernacle, looking down into the bow well:
You can make out the mounting bolts, they look like about 1/2" diameter, going through blocks in the bulkhead. I'll let you drill those holes through those edgewise planks. There is also a healthy dose of thickened epoxy fillets. Also note that the vertical planks are mounted clear of the bulkhead by those blocks mounted to the bulkhead and I would guess the verticals are about 2" clear of the bulkhead plywood.
Now, if you look back at the overall boat photo you will see that the mast heel extends about three feet past the pivot, and swings down into the slot formed by the two verticals. Look closely and you will also see a rope going through the heel of the mast and going down into the bow well. Look again in the bow well photo and you can see that same rope running through a hole in a wood plate towards the bottom of the tabernacle. When the mast is walked up to vertical, that rope is held in hand and tightened when the mast is upright. To lock the mast in position, that same rope is belayed many times around and around the mast and the bitt you see running across the back of the tabernacle. That's it!
When I drew Caprice last year I had seen Karl's rig and tried to copy it. Here is my interpretation of it:
I think Karl's system is the simplest and best I've seen. The locking of the mast in the vertical position is often the trickiest part and Karl solved that with a simple rope. (Karl sails his boats very hard and I'm told this tabernacle has passed all the tests.) On some of my other tabernacle designs I used no pivot bolt, but had capture plated fore and aft at the top of the verticals like this:
This is closer to the Birdwatcher system in that you walk the mast upright and then lift it up a bit to drop it into a step. On other designs I've used the pivot bolt but also showed a pin at the mast heel to secure the mast - easy to draw but reaching down to fit that pin into position might he hard in real life. I think on Bolger's Long Micro the heel of the mast is locked into position with a long wooden plate that hinges just below the heel. So that plate is layed flat while the mast is raised, then pulled with a rope up into position and that rope safely belayed.
OLIVEOYL, Cabin Sailboat, 15' X 6', 500 pounds empty
OliveOyl was designed for someone who liked AF3 but wanted more cabin room and comfort, but not more length. So I actually had some AF4breve drawings handy when I drew the lines for the new boat. Although Olive is the same length as AF3 the cabin is deeper and the bottom a foot wider. One thing the owner did not want, which made the larger cabin possible, was a large cockpit. So I've drawn a bridge deck which extends into the cockpit, reducing foot space there, and also just borrowed length from the cockpit and put it in the cabin. So the floor length in the cabin is over 8'long but you will probably sleep with your feet stuck under the bridge deck. I suppose the downside is that the cockpit is less than 5' long so two adults would fill it. I am guessing an empty weight of 500 pounds but it will take 2000 pounds to put its stem in the water so she should take a fair load.
I suppose I've learned a bit since I drew AF3 a while back. One thing I've learned is that when beached a boat like this is much easier to board if the bow is not too high, thus on this boat I've cut down the bow enough so you can sit on it anD swing your legs around right into the cabin entry in the bulkhead, I hope. The owner did not care about that and I don't think she beaches much in her area.
Now, the owner wanted a conventional cabin with sliding hatches so I drew that. And with it went a mast mounted on a tabernacle. I drew the mast off center as I normally do, attaching it to one of the main cabin deck beams. That moves it out of the center of the boat where you will be sleeping. But this boat could be simpler if it had my usual open slot top with a one piece mast. Such a layout would be a lot better I think for a boat which would be sailed off a beach too since it would allow the skipper to hop on the bow after pushing off, and then run upright back to the cockpit. As is he would have to creep down and tHrough the cabin or go over the cabin but I should warn you that, with AF3 at least, standing on the cabin top is an invitation for capsize. After all, these are not large boats.
The rig shown is pretty much right out of the AF3 experience, in particular with AF3's balanced lug rig. The spars are short and cheap and the mast short enough that the tabernacle won't be required if the open slot top is used.
But I doubt if OliveOyl would stay with an AF3 in a race. She has the same rig but she is wider, deeper and heavier and bound to be slower. On the other hand she is a much better overnighter since the AF3 has a minimal cabin suited for a backpacker.
In a lot of ways I think OliveOyl is more of a shortened Normsboat and if you don't mind the extra length and the weight and cost that go with the extra length, Normsboat would be I think a lot more boat for the buck.
Conventional nail and glue construction. She needs seven sheets of 1/4" plywood, two sheets of 3/8" ply, and four sheets of 1/2" ply.
Prototype plans for OliveOyl are $35.
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 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:
The prototype Twister gets a test sail with three grown men, a big dog and and big motor with its lower unit down. Hmmmmm.....
Jackie and Mike Monies of Sail Oklahoma have two Catboxes underway....
Tom Wolf has completed the first Toon2 that I know of and was waiting for some good testing weather...
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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