madam tirza - WoodenBoat Store
MADAM TIRZA A 20' catboat/sloop
Particulars LOD 20'0" LWL 19'3" Beam 9'6" Draft (cb up) 2' 0" (cb down) 5'3" (keel version) 3'0" Displacement 4,940 lbs Sail area (gaff-cat) 338 sq ft (marconi-cat) 315 sq ft (sloop) 406 sq ft Power (inboard) 21 hp
H
ere we have an easy-to-build 20' catboat (or sloop) from Charlie Wittholz, who drew many good cats in his time. Regular readers of these pages will know of my honest prejudice in favor of catboats. For those recently come aboard, let’s begin with a definition: “Catboat” most often describes a very wide, shoaldraft craft; driven by a large single sail (usually gaff-headed); and with its mast located way far forward. The type, and its name, seem to have originated with the Crosby family on Cape Cod in the 19th century. For a concise history of catboats, and a good read, see Carol 12
Crosby’s story about her family’s “eight generations of boatbuilders” in WoodenBoat No. 153. As the piece opens, she passes along this family legend from the early 1800s: “Andrew [Crosby] envisioned a boat that would sail well in both light and heavy air and could hold more fish than the narrow double-ended pinkys that were then being used on the Cape. He began to design her but died [in 1837] before completing his dream. His teenage sons, Horace and C. Worthington, struggled with the design….” Their mother, Tirza Crosby, then “spoke” with her late
Boat Design Quarterly No. 43
husband through a medium, Mrs. Manley, and “relayed the final design” to her sons. The resulting boat sailed fast and, according to one observer, came about “as quick as a cat!” More than a century later, in a letter dated January 13, 1986, designer Wittholz referred to the latest of his catboats as “Madam Tirza” in “overdue credit” to this long-ago Mrs. Crosby. Catboats have attracted legions of followers through the years, but there are nonbelievers among us. These folks, given to terrible fits of reason, take pleasure in pointing out a cat’s restless nature and heavy weather helm. That
We can rig this easily built 20’ sheet-plywood hull as a gaff-sloop, marconi-cat, or gaff-cat.
is, when we hoist her sail, our cat will want to sail away at once. She’ll not lie politely to her mooring, as do yawls or schooners with far-aft sails set to keep their heads to the wind. Once underway, we can indeed expect our catboat to show some weather helm, and she might wish to round up when a gust hits her. That long boom causes the sail’s center of effort to move far outboard when reaching and running. In addition when a hull that carries great breadth relative to its length heels down, the waterlines become wildly asymmetrical…strongly convex on the lee side and straighter
on the weather bottom. This geometry makes any boat want to turn toward its high side. Madam Tirza’s sheet-plywood hull, with low chines up forward, will exaggerate this behavior. There seems more than one way around this problem. We could replace Tirza’s specified wheel steering with a tiller, a long tiller, which will allow us quick response to keep her from rounding up every time she’s hit by a gust. In addition, we might consider raising the chines forward or building a round-bilged hull. Either of these last two modifications should result in a hull that’s less “hard
Boat Design Quarterly No. 43
mouthed,” but we’ll not be able to build all of it from sheet plywood. Charlie Wittholz took yet another path: He kept the hard-chined plywood hull, but moved Tirza’s mast several inches aft, reduced the size of the gaffheaded sail, and tacked a self-tending jib to a new bowsprit. He referred to the result as a Noank Sloop. In a letter to boatbuilder Dale Johnson, dated November 10, 1988, the designer spoke highly of the modifications: “I am delighted that you are going to use the sloop rig on your boat. I think that it adds character…and that it will balance better [than the cat] especially broad 13
Sheet plywood naturally bends to the subtle convex curves in Madam Tirza’s body plan.
Designer Wittholz drew this revised maststep arrangement for the sloop-rigged variant.
14
Boat Design Quarterly No. 43
reaching in a breeze.” Builder Johnson expressed concern about potential structural problems that might come along with the changes, and Wittholz responded: “Originally, I had thought there would be no trouble with simply moving the mast step aft on the gripe. Therefore I concentrated on the above-deck rigging arrangement. However, after reviewing the construction in more detail, I agree that a separate drawing for the mast step is in order. I’m going to make a new drawing and hope to send it within the next week.” True to his word, the designer followed up a few days later with modified
A traditional layout on deck and below: simple, roomy, and comfortable.
drawings and specifications. The accompanying letter explained: “You will note that there are two important changes from the basic catboat construction; namely, the extension of the gripe to form a mast step, and a heavy floor timber on the forward side of Frame No. 7 [page 14]. The deck reinforcement blocks at the bit and the mast partner have been revised to suit the new mast location…. I have simplified the actual mast step to show a mortise and tenon at the heel of the mast; though, of course, there are other ways you may do this if you wish.” In addition to the sloop and the original gaff-cat, Wittholz drew a
marconi-cat rig for Madam Tirza. The sloop offers good balance and easy handling. The gaff-cat offers tradition and simplicity; that is, there’s no bowsprit or bobstay, and we’ll have “only one string to pull.” The marconi-cat rig offers… well, I’ll confess to seeing no real advantage to it for this boat. Although most of us will value the shallow draft and easy trailering allowed by Tirza’s centerboard, the plans come with a full-keel option. The centerboard trunk does take up space in the cabin, but this is a large cabin and that intrusion might be welcome. A nice dropleaf table
Boat Design Quarterly No. 43
hangs from the trunk’s forward portion, and I’ll wager the cook often will perch on the cap at the after end. On occasion, the trunk could brace us against falling. Proponents of the full keel might point to its simplicity, to its allowing greater freedom of layout below, and to the increased righting moment provided by 900 lbs of outside ballast. The keel variant draws only 12" more than the centerboard boat (3' vs. 2'), but old thin-water sailors will tell you that a single foot can make all the difference. For auxiliary propulsion, the designer specifies that we fit Madam Tirza with a 21-hp inboard diesel engine. She is 15
The “old-fashioned” plywood construction (with chine logs and other good things) allows us to use a variety of goops, glues, and fastenings.
16
Boat Design Quarterly No. 43
Charlie Wittholz liked working the specifications into his drawings, rather than listing them separately.
a big 20-footer, no doubt about that (9'6" breadth, and almost 5,000-lbs displacement). Still, outboard motors have come a long way since she was drawn in 1986. We could devise a tooclever means of hiding an outboard in a well. An inboard engine, almost any inboard, adds exponentially to the cost and complexity of construction and maintenance, but it certainly offers
comfort and smooth running when well cared for. Perhaps we should make our engine decision based upon how much we intend to cruise under power. If our Madam T will serve as a motorsailer (and she would make a nice one), we might go with the inboard. Even if we choose to rig her as a sloop, Madam Tirza seems a cat at heart. I like that, as some of my best days, and
nights, were spent aboard our old catboat (see BDQ No. 13). No matter what the technical ratios tell us, there’s just something about catboats. — M.O’B. Plans from The WoodenBoat Store, P.O. Box 78, Brooklin, ME 04616; 800–273–7447; www.woodenboatstore.com.
Some builders might prefer the simplicity and added righting moment of this keel variant.
Boat Design Quarterly No. 43
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Particulars LOD 20'0" LWL 19'3" Beam 9'6" Draft (cb up) 2' 0" (cb down) 5'3" (keel version) 3'0" Displacement 4,940 lbs Sail area (gaff-cat) 338 sq ft (marconi-cat) 315 sq ft (sloop) 406 sq ft Power (inboard) 21 hp
H
ere we have an easy-to-build 20' catboat (or sloop) from Charlie Wittholz, who drew many good cats in his time. Regular readers of these pages will know of my honest prejudice in favor of catboats. For those recently come aboard, let’s begin with a definition: “Catboat” most often describes a very wide, shoaldraft craft; driven by a large single sail (usually gaff-headed); and with its mast located way far forward. The type, and its name, seem to have originated with the Crosby family on Cape Cod in the 19th century. For a concise history of catboats, and a good read, see Carol 12
Crosby’s story about her family’s “eight generations of boatbuilders” in WoodenBoat No. 153. As the piece opens, she passes along this family legend from the early 1800s: “Andrew [Crosby] envisioned a boat that would sail well in both light and heavy air and could hold more fish than the narrow double-ended pinkys that were then being used on the Cape. He began to design her but died [in 1837] before completing his dream. His teenage sons, Horace and C. Worthington, struggled with the design….” Their mother, Tirza Crosby, then “spoke” with her late
Boat Design Quarterly No. 43
husband through a medium, Mrs. Manley, and “relayed the final design” to her sons. The resulting boat sailed fast and, according to one observer, came about “as quick as a cat!” More than a century later, in a letter dated January 13, 1986, designer Wittholz referred to the latest of his catboats as “Madam Tirza” in “overdue credit” to this long-ago Mrs. Crosby. Catboats have attracted legions of followers through the years, but there are nonbelievers among us. These folks, given to terrible fits of reason, take pleasure in pointing out a cat’s restless nature and heavy weather helm. That
We can rig this easily built 20’ sheet-plywood hull as a gaff-sloop, marconi-cat, or gaff-cat.
is, when we hoist her sail, our cat will want to sail away at once. She’ll not lie politely to her mooring, as do yawls or schooners with far-aft sails set to keep their heads to the wind. Once underway, we can indeed expect our catboat to show some weather helm, and she might wish to round up when a gust hits her. That long boom causes the sail’s center of effort to move far outboard when reaching and running. In addition when a hull that carries great breadth relative to its length heels down, the waterlines become wildly asymmetrical…strongly convex on the lee side and straighter
on the weather bottom. This geometry makes any boat want to turn toward its high side. Madam Tirza’s sheet-plywood hull, with low chines up forward, will exaggerate this behavior. There seems more than one way around this problem. We could replace Tirza’s specified wheel steering with a tiller, a long tiller, which will allow us quick response to keep her from rounding up every time she’s hit by a gust. In addition, we might consider raising the chines forward or building a round-bilged hull. Either of these last two modifications should result in a hull that’s less “hard
Boat Design Quarterly No. 43
mouthed,” but we’ll not be able to build all of it from sheet plywood. Charlie Wittholz took yet another path: He kept the hard-chined plywood hull, but moved Tirza’s mast several inches aft, reduced the size of the gaffheaded sail, and tacked a self-tending jib to a new bowsprit. He referred to the result as a Noank Sloop. In a letter to boatbuilder Dale Johnson, dated November 10, 1988, the designer spoke highly of the modifications: “I am delighted that you are going to use the sloop rig on your boat. I think that it adds character…and that it will balance better [than the cat] especially broad 13
Sheet plywood naturally bends to the subtle convex curves in Madam Tirza’s body plan.
Designer Wittholz drew this revised maststep arrangement for the sloop-rigged variant.
14
Boat Design Quarterly No. 43
reaching in a breeze.” Builder Johnson expressed concern about potential structural problems that might come along with the changes, and Wittholz responded: “Originally, I had thought there would be no trouble with simply moving the mast step aft on the gripe. Therefore I concentrated on the above-deck rigging arrangement. However, after reviewing the construction in more detail, I agree that a separate drawing for the mast step is in order. I’m going to make a new drawing and hope to send it within the next week.” True to his word, the designer followed up a few days later with modified
A traditional layout on deck and below: simple, roomy, and comfortable.
drawings and specifications. The accompanying letter explained: “You will note that there are two important changes from the basic catboat construction; namely, the extension of the gripe to form a mast step, and a heavy floor timber on the forward side of Frame No. 7 [page 14]. The deck reinforcement blocks at the bit and the mast partner have been revised to suit the new mast location…. I have simplified the actual mast step to show a mortise and tenon at the heel of the mast; though, of course, there are other ways you may do this if you wish.” In addition to the sloop and the original gaff-cat, Wittholz drew a
marconi-cat rig for Madam Tirza. The sloop offers good balance and easy handling. The gaff-cat offers tradition and simplicity; that is, there’s no bowsprit or bobstay, and we’ll have “only one string to pull.” The marconi-cat rig offers… well, I’ll confess to seeing no real advantage to it for this boat. Although most of us will value the shallow draft and easy trailering allowed by Tirza’s centerboard, the plans come with a full-keel option. The centerboard trunk does take up space in the cabin, but this is a large cabin and that intrusion might be welcome. A nice dropleaf table
Boat Design Quarterly No. 43
hangs from the trunk’s forward portion, and I’ll wager the cook often will perch on the cap at the after end. On occasion, the trunk could brace us against falling. Proponents of the full keel might point to its simplicity, to its allowing greater freedom of layout below, and to the increased righting moment provided by 900 lbs of outside ballast. The keel variant draws only 12" more than the centerboard boat (3' vs. 2'), but old thin-water sailors will tell you that a single foot can make all the difference. For auxiliary propulsion, the designer specifies that we fit Madam Tirza with a 21-hp inboard diesel engine. She is 15
The “old-fashioned” plywood construction (with chine logs and other good things) allows us to use a variety of goops, glues, and fastenings.
16
Boat Design Quarterly No. 43
Charlie Wittholz liked working the specifications into his drawings, rather than listing them separately.
a big 20-footer, no doubt about that (9'6" breadth, and almost 5,000-lbs displacement). Still, outboard motors have come a long way since she was drawn in 1986. We could devise a tooclever means of hiding an outboard in a well. An inboard engine, almost any inboard, adds exponentially to the cost and complexity of construction and maintenance, but it certainly offers
comfort and smooth running when well cared for. Perhaps we should make our engine decision based upon how much we intend to cruise under power. If our Madam T will serve as a motorsailer (and she would make a nice one), we might go with the inboard. Even if we choose to rig her as a sloop, Madam Tirza seems a cat at heart. I like that, as some of my best days, and
nights, were spent aboard our old catboat (see BDQ No. 13). No matter what the technical ratios tell us, there’s just something about catboats. — M.O’B. Plans from The WoodenBoat Store, P.O. Box 78, Brooklin, ME 04616; 800–273–7447; www.woodenboatstore.com.
Some builders might prefer the simplicity and added righting moment of this keel variant.
Boat Design Quarterly No. 43
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