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The 28' Fantail "CHINA CAT"

Copyright 2013 Michael Kasten
 

The 28' Junk - CHINA CAT - Kasten Marine Design, Inc.
Perspective Aft | Perspective Side | Perspective Side Close-up | Perspective Forward Sailing
 

Hull Form

This prototype / concept design was modeled in response to a request for a small steel sailing vessel having a hull form similar to Boojum.  Actually this is very workable, and a number of my designs make use of the same general hull form, both power and sail.
 

The Layout

I favor the type of "flush deck" cabin arrangement shown here, and for all the reasons articulated at the Bedouin and 38’ China Cat web pages.  As with those examples, the China Cat 28 has a secure well-deck forward, a small self bailing cockpit, a "bridge deck" between the cockpit and the companionway, an inboard diesel engine, and a rig that can be easily handled, even by a solo sailor.

For an approximation of what’s possible with the layout, please see the Bedouin design.
 

The Rig...

The request in this case was for a two-mast Junk Rig... 

A junk rig poses two fundamental challenges… One, if it is to be free standing, then the mast must be very stout, and the hull structure must be equal to the task of holding the cantilevered mast in place. The other challenge is that the junk rig is relatively heavy for its sail area, therefore stability must be adequate to carry the rig.  Especially this is so with two masts.

A junk rig arrangement that I favor is that of my Jasmine 48 design, where both sails are equal and can therefore exchange parts as needed, and no Western sails are present to complicate the rig.

If you were to combine the Boojum hull (in this case, refined for sailing) with a full sailing keel to counter the relatively heavy rig, with the Bedouin cabin arrangement, and the Jasmine 48 Junk Schooner Rig, you’d have the China Cat 28 concept design shown here.

The China Cat 28 has the following particulars:

At 28' LOD and under 13k lb displacement, the China Cat 28 will be best if built in aluminum. 
 

28' Junk - China Cat - Kasten Marine Design, Inc.
Click for Larger Image
 

Suitable For Steel Construction...?

Could the China Cat 28 also be built in steel...?   Yes, actually.  In steel, in order to save weight and reduce the height of the CG there would be a 1” cold moulded monocoque wooden cabin top.  That, combined with a few other tricks would indeed allow construction in steel.  Here are a few considerations...

As a general rule, actual length on deck is less a criterion for what can be built in steel than the eventual displacement. In terms of its displacement then, it will be quite a challenge to build a steel sailing boat under around 10k to 12k lbs due to the weight of the steel.

If building small in steel, plate thickness must be reduced to the minimum. One eighth inch steel plate is roughly the practical minimum for ease of weldability, although 14 gauge is certainly possible, however controlling distortion in mild steel having a thickness under 10 gauge is really quite a challenge.

To address the distortion during weld-up, it is very favorable to make use of Corten steel, which has roughly 1.5 times the yield strength of mild steel, and is thus able to resist distortion approximately to the same extent as a mild steel plate having roughly 1.5 times the thickness of the Corten plate. Please see my article on Metal Boats for Blue Water for clarification of the alloys to which I refer.

With Corten (or an equal strength HSLA steel), I would have no qualms about welding up a 14 gauge hull, although a well-planned and strictly adhered-to Weld-up Strategy will be very important in order to achieve success. MIG welding is very definitely recommended, as it imparts considerably less heat to the surrounding metal than stick welding, and therefore inherently produces far less distortion. Welding Corten is no different than welding mild steel, only a different wire is used for the MIG gun in order to match the strength properties of the base metal.
 

Four Trailerable Sister Ships...

A group of four 'sister' vessels each of which share the same hull form and general configuration have been preliminarily detailed as concept designs, one of which is shown here.   Check out each of the four sisters at the following links:

38' China Cat   |   28' China Cat   |   28' Bedouin   |   23' Sarah Cat
 

28' Junk - China Cat - Kasten Marine Design, Inc.
Click for Larger Image
 

The China Cat 28 shown here is a minimalist cruiser that is intended for easy construction in steel or aluminum, although plywood - epoxy construction is also possible.  If further development of this concept is of interest, please inquire.