Messing about in boats since 1975.  Online Since 1997.

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The 64'Tern Schooner "AMETHYST"

56' Ketch SHIRAZ - Kasten Marine Design, Inc.

Perspective Aft Sailing | Perspective Forward Sailing | Perspective Forward | Perspective Aft | Perspective Side

Copyright 2015 Michael Kasten

General Concept

Larger sister to the 56' motor sailing ketch SHIRAZ, the 64' AMETHYST is designed as a 100% capable sailing vessel that is also an efficient motor sailor.  Construction is intended to be steel, but aluminum is equally viable.  Intended for ocean passages and coastwise cruising AMETHYST will carry her passengers in comfort and in style. With a sheltered 'midships hard dodger one need not be offended by the elements, be they too warm or too cool.  With Herreshoff-like classic lines, AMETHYST will turn heads wherever she goes.

Hull Shape

The AMETHYST has been given a graceful single chine hull shape for ease of construction and in order to achieve the most performance per dollar.  How so? With a simply built economical and easily driven hull form, one can afford to make the vessel a bit longer and realize some very real performance gains. In other words, a rounded hull of this size could not be built for the same cost, so for the same cost it would necessarily be smaller and therefore inherently slower.  Just as with any aspect of a vessel's aesthetics, the question of chine vs. radius vs. rounded hull finally comes down to one's personal choice which, once made, cannot be argued. In this case, I believe the choice is an excellent one.

Particulars are:

Given the refined hull form of the AMETHYST, the theoretical hull speed to length ratio of 1.34 will be exceeded fairly easily. True hull speed is expected to be around 11.5 knots, for a speed to length ratio of 1.53.

The Motor Sailing Advantage...

The engine selected is a John Deere 6068-SFM75 diesel.  With a fuel capacity of 1,321 USG (5,000 Liters) AMETHYST will function as a true motor vessel.  Per the Beebe algorithm, with a 20% reserve for generator usage, range under power alone will be on the order of around 2,400 NM.  However being a thoroughbred sailing vessel as well, AMETHYST' range is virtually unlimited. 

Making good use of the synergy of motor sailing, range will be greatly extended, and speed will be dramatically enhanced. Rather than having a motor vessel on which the roll stabilization will ordinarily rob the boat of speed and efficiency, the sail rig will provide a very welcome improvement to both.

The Rig

The simple Tern Schooner rig given to AMETHYST has much to offer. Simplicity of materials, ruggedness, reasonableness of cost to build and maintain, those are elemental virtues. The materials used for traditional rigging of this type are extremely basic: aluminum pipe for all spars, with galvanized wire, anhydrous lanolin, friction tape, tarred nylon seine twine, latigo leather and waxed thread to sew it up. Using this approach, the longevity of the rig is outstanding, and will outlast stainless rigging several times over.

 In "The Aero - Hydrodynamics of Sailing" Marchaj has shown ample evidence that the loose footed sail is more efficient than one which is laced to a boom. I prefer loose footed sails for a more basic reason: If the sheet is located at the end of the boom where the sail is attached, the sail does not then impose a side load on the boom, therefore the boom is permitted to act purely as a strut. With that, the boom can be less heavy and will be more easily handled.

As for the rake of the masts, this is a choice based on practicality. The rake of the masts causes the booms to lift as they are let out, which serves to keep the boom ends out of the water. Less obvious benefits are that the sails will be more easily lowered, and that the halyards may be used to lift a dinghy onto the cabin top more easily.

64' Tern Schooner AMETHYST - Kasten Marine Design, Inc.
Click for Larger Image

The Interior

The interior is similar to that of the 56' Shiraz, but with much more room given to the aft stateroom, as well as having an equally large stateroom forward.  A walk-through of the interior is as follows:

A roomy owner's stateroom is located in the aft cabin along with a private head and shower.  The engine room is located below the cockpit, and extends to port.  To starb'd of the engine room is a passage that leads forward below the cockpit seating.  The passage contains a laundry and a large freezer.  Forward of the passage is a large galley to port with a nav station opposite to starb'd.  The saloon settee seating just forward of that will easily seat six at the table.  Above and outboard of the settees are a pair of pilot berths.  Forward of the saloon is a head to port, and an enclosed tub / shower to starb'd. The forward cabin provides a second large stateroom for guests complete with island sytle double berth. In the fo'c's'l is a true bosun's locker. 

On deck, the cockpit area can sleep two. Below, the vessel can sleep six, counting the pilot berths, or eight if also using the settees. Of course that is too many for more than just an occasional party...! The arrangement is quite open amidships for the sake of entertaining and also very private with regard to the staterooms which are located at opposite ends.  As such, AMETHYST will accommodate two couples in excellent comfort for long term cruising. 

64' Tern Schooner AMETHYST - Kasten Marine Design, Inc.
 Click for Larger Image