Jim Michalak's Boat Designs
118 E Randall, Lebanon, IL 62254
A page of boat designs and essays.
(15jan01) This issue will discuss mast tabernacles. Next issue will review some rowing thoughts.
Joe Millard in his lug rigged Tween, again.
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.
Will present some thoughts about rowing.
MUSICBOX3, CABIN SAILBOAT, 15' X 6-1/2', 800 POUNDS EMPTY
Musicbox3 is about the same size as the Bolger Micro and is clearly derived from it. I've sailed on a couple of Micros. Amazing boat in a lot of ways, especially in the amount of room inside a 15' boat. The volume is the result of a 6' wide beam and flat bottom.
I thought that in most ways Micro's strength and weakness was in its keel - about 450 pounds of lead casting permanently fixed for a draft of about 18". The strength is that Micro is very stable and selfrighteous. The weakness is in the difficulties in launching and using a boat with that much draft, and in making the casting. For all the griping about making the casting, I never heard of anyone trying one with internal ballast, or using a leeboard on Micro, both mods would be quite possible. So I tried both on Musicbox3. The ballast shown on the plans is in the form of a water box which holds about 500 pounds of water. That could be replaced with lead or steel bolted to the bottom of the bulkheads if you didn't mind trailering the ballast - it would give more room inside, too. So Musicbox3 should float off the trailer in just 5" of water, and float in 7.5" with the ballast tank flooded, and about 9" with two full sized adults with their junk.
The pivoting leeboard and rudder allow the boat to be driven full tilt over shallows or onto a beach, something you would never do with Micro. But keep in mind that the ballasted Musicbox3 weighs about 1300 pounds and you will have to lift and push that back into the water. I suppose in a tough situation you could pump out the ballast water to float her, as they used to throw cannons overboard in Columbus's day to refloat a grounded boat.
I used a gaff rig on a tabernacle on Musicbox3 to improve on Micro's set up time, and I think Musicbox3 would befar and away the better of the two if you had but an afternoon for sailing. I didn't show a gallows but you could add one such that you can fold the sail rig with the yard, boom, sail, and mast all in a neat package, with all the rigging ropes left installed. Micro's yawl rig is superior for cruising, especially for anchoring in open water. I think Musicbox3 could be tinkered with to add the mizzen mast. To me the best cruising rig might be this gaff with a shortened boom, a small mizzen sail, and a very good outboard motor. Musicbox3 has a small well in the stern for the motor, and a small well in the bow for anchors.
The capacity of these boats comes at the expense of weight and materials - after all, they are 20' boats compressed to 15'. Musicbox3 requires 5 sheets of 1/4" plywood, eleven sheets of 3/8" plywood, and one sheet of 1/2" plywood. She is more robustly built than Bolger's drawings show Micro, but I suspect most Micros are built heavier than the drawings show.
Plans forMusixbox3 are $25 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. 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.
Here are the prototypes abuilding that I know of:
Caprice: A brave and experienced builder in Texas is making the 25' Caprice water ballasted sailboat. A big project that looks bigger with each new photo.
Jon Jr has been completed by Joe Leinweber and Dan Ellis and tested to a certain degree. Click here to read about the test and the surprize ending! ("The waters are only safe until next time!")
Skat: I'm told the prototype Skat project is underway again and very close to being done.
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Messing About In Boats
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Kilburn's Power Skiff
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