Jim Michalak's Boat Designs
1024 Merrill St, Lebanon, IL 62254
A page of boat designs and essays.
(15 May 2020) We discuss mast tabernacles. The 1 June issue will be about underwater boards,
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.
REND LAKE 2020...CANCELLED!!
..I see no way that any gathering will be safe by mid June, at least not in southern Illinois where the virus is still gathering steam. Campgrounds are still closed, no word on reopening, and some launch ramps also. First miss in over 30 years, but we will be back next year.
 | Left:
Paul Breeding takes his customized AF4 out West. Paul had a Skiff America a while back and it shows in his mods to the AF4. I don't know if Paul knows it but way back when Kilburn Adams, who designed Skiff America, had a large powered model with all the features of what became AF4. I know that because I saw it and it cemented my approach to AF4. But Kilburn went on to do the more complex Skiff America. |
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Mast Tabernacles
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 heeled 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 an unstayed mast (that is one free standing with no support wires or rods) must pass throught them. They are really a hinged splice in an unstayed freestanding mast. 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.
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. In the bending case here the tabernacle only needs enough strength to support the mast itself, after you have raised it but before you have hooked up the support wires or stays. But beware - the compression loads in a stayed mast can be huge.
ONE OF THE VERY BEST TABERNACLES I'VE EVER SEEN...
...was on this sharpie 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. So this sharpie is Karl's design, not mine. I have no idea if he has plans for sale. Karl is retired now and I've lost touch with him but he stopped by last year on his drive from Canada to Texas.
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. Another detail worth noting is that the added doubler is well tapered on each end which avoids sudden stress concentrations which would happen if the mast cross section were to change abruptly. (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 moves 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.
Laguna
Laguna, Sailboat, 23' X 5.5', 450 POUNDS EMPTY
This boat was designed for Duckworks to run the Texas200, 200 miles of brisk downwind running they say in the somewhat protected waters of the Texas intercoastal waterway. The boat was supposed to be cheap and quick and hold two crew with floorspace for them to sleep on board. The basic idea I had was to stretch the Mayfly16 with an 8' plug in the middle. In the end I kept the basic cross section and stretched it out with a simple flat iron skiff shape. The bottom is the width of a sheet of plywood which simplifies things even more. The first doodle looked like this:
I drew it up in detail getting this:
And a card model from the detailed drawings looked like this:
My cross seats are supposed to be big and comfortable and removable to give sleeping room on the floor. Each crewman has his own stateroom.
The sail rig was to be a split rig with identical lugsails fore and aft with the option to sail with just one of the sails mounted in the center, like this:
I think the single sail option would be preferred if sailing solo since that fore mast is way up yonder and one may not be able to handle it and the tiller at one time.
The prototype was quickly built by Gordo Barcom in Texas and here he is blasting along with family and polytarp sails straining. It was clearly a fast roomy boat:
Then another, the Blue Laguna, was built and run in the 2010 Everglades Challange, 300 miles from Tampa to Key Largo, by Andrew Linn and Michael Monies. This boat had very little testing time as far as I know before the race. But they finished in 5 days and a bit but I think they slept in motels for two of the nights while the "press on regardless" guys were daring the night waters. Here they are launching off the beach (a requirement for this race):
And then pushing off in shallow water (there is a Sea Pearl behind them for comparison):
Finally a really nice photo of them approaching one of the three checkpoints in the race:
I think both Gordo's boat and the Blue Laguna have been modified in details from the blueprint but the rigs and basic hull features all look correct. I've noticed that no one takes sleeping floor space as seriously as I do but that is OK.
Well, I was thrilled. My main caution would be that this probably is not a good solo boat due to its size and split rig. I think it might be a good family boat in that there is plenty of room for everyone and a rope for all idle hands to play with. The other caution might be that, even though the boat has big buoyance boxes, it also has large cockpits to swamp in a knockdown and it will roll upright with a lot of water to bail. So you note on Gordo's boat he has inflated fender tied to the mast head, an idea to reduce the carnage of a knockdown.
Plans for Laguna are $45. It is all simple nail and glue construction needing six sheets of 1/4" plywood and five sheets of 1/2" plywood.
Prototype News
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.
We have a Picara finished by Ken Giles, past Mayfly16 master, and into its trials. The hull was built by Vincent Lavender in Massachusetts. There have been other Picaras finished in the past but I never got a sailing report for them...
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:
A brave soul has started a Robbsboat. He has a builder's blog at http://tomsrobbsboat.blogspot.com. (OOPS! He found a mistake in the side bevels of bulkhead5, says 20 degrees but should be 10 degrees.) This boat has been sailed and is being tested. He has found the sail area a bit much for his area and is putting in serious reef points.
AN INDEX OF PAST ISSUES
THE WAY BACK ISSUES RETURN!
MANY THANKS TO CANADIAN READER GAETAN JETTE WHO NOT ONLY SAVED THEM FROM THE 1997 BEGINNING BUT ALSO PUT TOGETHER AN EXCELLENT INDEX PAGE TO SORT THEM OUT....
THE WAY BACK ISSUES
1jun19, Capsize Lessons, QT Skiff
15jun19, Rend Lake 2019, Mixer
1jul19, Scarfing Lumber, Vireo14
15jul19, Rigging Lugsails, Vamp
1aug19, Rigging Sharpie Spritsails, Oracle
15aug19, Rowing1, Cormorant
1sep19, Rowing2, OliveOyl
15sep19, BC Scram Pram, Philsboat
1oct19, Herb's OliveOyl, Larsboat
15oct19, Herb's OliveOyl 2, Jonsboat
1nov19, Herb's OliveOyl 3, Shanteuse
15nov19, Herb's OliveOyl 4, Piccup
1dec19, Taped Seams, Ladybug
15dec19, Plywood Butt Joints, Sportdory
1jan20, Sail Area Math, Normsboat
15jan20, Trailering, Robote
1feb20, Bulkhead Bevels, Toto
15feb20, Cartopping, IMB
1mar20, Small Boat Rudders, AF4Breve
15mar20, Rudder Sink Weights, Scram Pram
1apr20, Two Totos, River Runner
Table of Contents
