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July 1, 2000 Issue


July 15, 2000 Issue




July 1, 2000

Bolger on Design Day-Cabin Diesel Launch

Design #528: 30'0" x 7'7" x 2'0" -- Bridge Clearance 5'6" -- Displacement 5,700 lbs.

This boat was designed to replace an open fantail launch, and the primary object was to make a private space to change clothes and for a toilet. More room for a large party to spread out was desired, and a little more speed and rough-water comfort were acceptable. The 27hp diesel was expected to cruise her at seven knots without a very heavy wake, or 5-1/2 knots with no wake; appreciably faster than the fantail (which was also our design and quite nice). The very sharp lines forward plus moderate flare make a dry boat and a smooth-riding boat even, much of the time, for people sitting in the forward cockpit.

Her usual use would have been to run from her home mooring to one of several beaches, none more than ten miles or so away, to lie at anchor as a base for swimming and sunbathing for a few hours. She is a "picnic boat" (small letters and no registered trade-mark!), a phrase sometimes used before her time (designed about 1986).

Construction was conventional (now old-fashioned) with carvel planking on steam-bent frames; at the time an economical method that allows a complex hull shape. The "built-down" concave hull lines abaft amid-ships make a good pump well, and allow the stuffing box to be placed well back on the shaft where it acts as an intermediate bearing. Its location would allow installing a thrust bearing and universal joints for a very soft-mounted engine. Nowadays we would give her a dry exhaust and radiator cooling to eliminate all underwater openings except the one for the prop shaft.

The style was derived from a series of boats designed in the late 1920s by Walter McInnis that were certainly among the handsomest motorboats ever built. This one would have been in their class for looks, though the McInnis boats were fast commuter types and could look more spectacular. At congested-waters speeds the cleaner wake of a low-speed stem like this one looks well.



July 15, 2000

Bolger on Design Design #589 Plywood Catboat (Optional Revision)

15'1-1/2" LOD -- 6'6" Beam -- 10" Draft in normal sailing trim with centerboard raised -- 2'6" draft with centerboard down for windward sailing

In 1985 I was challenged to design a plywood version of a Beetle Cat. The primary objective was to make a boat of that type that would stand trailer sailing without drying out; a secondary point, to reduce the time and skill needed to build one. The result was the ITY x 6'0" Bobcat (Design #470), which turned out to be an exceptionally nice-handling craft. We still haven't heard of any trials against Beetle Cats, but Bobcat feels at least as good and we suspect that she's better, mainly because of the end plate on the rudder which produces very sharp and positive steering by comparison with a traditional shallow rudder without one.

Bobcat's rudder is only 8" deep in average sailing trim, yet there is never any feeling that it's losing its bite. Every now and then we suggest that somebody racing in the Beetle Cats should quietly add an end plate to the rudder of their boat and see how she does against the standard boats. We would put down a moderate bet that the boat with the end plate would show superior form, especially on windy days.

Some years later we were asked to de-sign a cuddy-cabin daysailer, and we used a similar hull shape to Bobcat for the 19'8" x 7'5" x 1'0" Chebacco 20. This design is one of the most popular we've done, with an international association. We gave it a cat-yawl rig because many people don't like a very long boom projecting over the stem, and if you chop the boom shorter they don't sail as well or look as perky as a cat should. The Chebacco 20 would be faster with a real cat rig, but she would be trickier to handle and would lose the steady riding at anchor and ability to heave to that are part of the attraction of the boats.

Beach Cat was designed to fit between these two well-liked boats. She was small enough for a real cat rig to be within most people's idea of controllable. We had the idea of making her into a camping cruiser, with high sides and enough deck to make her cockpit float well clear of the water even in a beam ends knockdown. She could go off by herself in squally weather without much tension at the helm. We gave her a keel (but no ballast) to clear out the inside to make a 52" wide sleeping flat, and made space for a portable toilet forward. The keel only needed VY of water, which didn't seem prohibitive even for trailer-hauling; she actually needed less water to sail close-hauled than a centerboarder The photo shows a boat built to this design, by John Turna, a California professional boatbuilder for his own use.

This boat performed quite well, but the ergonomics weren't nearly as good as they should have been. I tried to make it look like a classical catboat, with the result that the broad side decks were too low to sit under and too high to sit on top of at all comfortably, an overall configuration that gave many potential builders material for endless interpretations as to how it should work. In fact, it was possible to slouch under the deck in a very good position for shelter and for helping the boat stand up to her sail, but not very comfortably and with no view except some sky or sea (depending on angle of heel) to leeward.

The sides ought to have been much higher and full of picture windows, Birdwatcher-fashion, to sit inside in comfort, or else the decks should have been much narrower. John Tuma put seats inboard of the coamings at a height to bring heads above deck level. This was comfortable but brought the weight too far inboard to do much toward helping the boat stand up to strong wind, and more or less wasted the space under the deck.

At any rate, we figured that an otherwise good hull and rig were not helped by the unusual interior geometries, and that it was time for a "normal" catboat layout. Now the narrow decks are high enough, and the hull sides are buoyant enough, to make it very hard to ship any water over the coarning in day-sailing weather. And the seating is very comfortable. She could still be organized as a camping overnighter without much trouble, boom tent and all.

The centerboard is a further option, to make her still more like a traditional catboat. We guess that performance and handling are close to the same. The keel boat's deeper rudder may just about compensate for her less-efficient lateral plane shape, We carried over the keel boat's inboard rudder into the centerboarder, to retain the very convenient and neat-looking motor mount that has been appreciated in the Chebacco 20.

Some day we'll probably get around to redrawing her once more, to cater to those with the widespread no-lead-melting impulse who desire a "garageable" light cruiser with hard shelter for 1+1 crew, this time with a Birdwatcher-type house.

Plans of Bobcat, including the new optional layout on four 22" x 34" and three 17" x 22" sheets of plans with a keyed specification, are available for $100 to build one boat from Phil Bolger & Friends, 66 Atlantic St., Gloucester, MA 01930-1627. Fax (978) 282-1349. For those who already own their set of Bobcat plans, the three upgrade sheets are $50 to build one boat.


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