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48' Cutter

"AWAHNEE III"

48' Cutter - AWAHNEE II - Kasten Marine Design, Inc.
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Starb'd Aft Perspective | Starb'd Forward Perspective | Side Perspective | Aft Perspective
 

Copyright 2013 Michael Kasten

The following is an outline of how the concept design of the 48' Cutter "Awahnee III" was developed. "Ahwahnee" is the name the California Miwok Indians originally used for the Yosemite Valley.

Famed yachtsman Robert Griffith, with his wife Nancy and son Reid, sailed the original Uffa Fox designed 53' wooden cutter named Awahnee I on many voyages, completing a circumnavigation upon return to French Polynesia. Wrecked on a reef near the Tuamotu Islands, Griffith and family moved to New Zealand where they built a new vessel, the Awahnee II, more or less to the same dimensions as the original Uffa Fox design, but this time building it in ferro-cement. When finished the Awahnee II was reportedly some ten percent lighter than the original wooden hull..!

In the Awahnee II, the Griffiths proceeded to circumnavigate twice again, eventually sailing well over 200,000 nautical miles between both vessels, a feat for which Bob Griffith was awarded the prestigious Blue Water Medal in 1972. Among the various impressive sailing records achieved by the Griffith family was that the Awahnee II was the first ferro-cement boat to circumnavigate. This is an extraordinary accomplishment, as well as an outstanding recommendation for the hull form.

The request in this case has been to create a new design, similar to the Awahnee II, but slightly smaller in overall length, and optimized for construction in steel. Among the changes made have been to deepen the forward knuckle of the keel and to increase the freeboard throughout, especially aft.

The 48' Awahnee III has a hull form similar to our 48' Hiawatha and 120' Chief Seattle designs both of which have been based on the Grand Banks fishing schooners of the early 20th century. However the 48' Awahnee III differs in that, per the original Uffa Fox design, a canoe stern has been specified, a small pilot house has been added, and a flush fore deck is used. It is a good combination, which combines the excellent seakeeping and inherent balance of a canoe stern, with the superior large angle stability and large interior volume offered by the flush foredeck.

As with Bob Griffith's original yachts, the 48' Awahnee III has been specified with a Bermuda rigged cutter sail plan for the sake of extreme simplicity and superior sailing performance to windward. 
 

HULL FORM

The model shown here is heavily based on the original Awahnee, but is smaller and has been proportioned accordingly in order to take advantage of steel as a structural material.

The Awahnee had very well balanced waterlines fore and aft. In other words, canoe stern successfully avoids having a wedge shaped underbody when heeled. This prevents the stern from being lifted when heeled, thus avoiding the steering anomalies present in wedge shaped hull forms.

The Awahnee had very easy and slightly convex waterlines forward, thereby avoiding any possible added drag induced by the tendency of hollow forward waterlines to create a second bow-wave. The Awahnee diagonals were very fair without any tendency to form a hook astern. The buttock lines on Awahnee were very easy and fair forward, with a long straight run aft extending into a graceful canoe stern.

The refined canoe stern, combined with the long bow overhang support the vessel well at speed when bow and stern wave rise, providing a heeled waterline that is much longer than the static waterline. The combination of these factors is indicative of a fast sailing machine.

The keel on the Awahnee was relatively short, with a knuckle roughly one third of the WL aft, and having moderate drag to the keel bottom - thereby having reduced wetted surface as compared to vessels of the day, yet providing an underwater profile conducive to excellent directional stability at sea. The long easy entry profile forward offers excellent handling down-wind, with no tendency to "gripe" when reaching the trough of a wave, as often is the case with a deep forefoot. As has been reported, handling under sail is excellent with this hull form.

All of these features have been retained in the 48' Awahnee III prototype shown here.

48' AWAHNEE III
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CHINE VERSION...!

When building a metal boat it is natural to entertain the concept of building a single chine hull. This is for the sake of vastly simpler and much faster construction time, especially if cost savings are paramount... To address this possibility, I have modeled the same design as a single chine hull.  As we have pointed out in our article on Aluminum for Boats, a single chine hull form offers few if any disadvantages.  A properly designed single chine hull not only offers excellent sailing ability... if one considers that a single chine boat can afford to be built larger, a very real performance advantage is possible...!  A bigger boat for the same money...  what's not to like..?

48' Awahnee III - Kasten Marine Design
Also see these links... Above Forward | Above Aft | Forward Low
 

STEEL CONSTRUCTION...

Wooden craft require that the rabbet along the lower edge of the garboard plank be more or less parallel to and not too distant from the keel bottom. This is for several reasons, not the least of which is to structurally reinforce the "blade" of the keel, especially aft where it is deep. This was also beneficial in that the rabbet did not have to cross the deadwood timbers in the keel, which would have invited leaks and would therefore have required numerous stop-waters along the rabbet. This meant that there had to be a strong "reverse" curvature at the turn of the garboard, so that the planking could extend downward to the rabbet line, approximately parallel to the keel bottom.

Since the 48' Awahnee III has been planned for construction in in steel, there is no need structurally for there to be a "reverse" curvature to the garboard in order to support the keel, nor to carry the garboard / rabbet down onto the keel aft in order to prevent leaks. Thus on the prototype presented here, the rabbet at the keel is able to follow the simple projection of the deadrise onto the upright face of the keel. This allows vastly simpler construction in metal and increases the effective "lateral plane" of the keel. Further, we are able to provide a NACA foil shape for the sake of increased lift and greatly reduced drag.

The classic cutaway cruising keel has been used here primarily for the sake of having excellent directional stability, the strength to take the ground with impunity, and for good performance on all points of sail. Inevitably, one might argue in favor of a split keel / skeg arrangement to reduce wetted surface. Although unseen above the WL, and therefore un-noticed, that could be considered a natural step in the evolution of the type. Whether a full keel or combined keel & skeg are used, there is no doubt this would be a fast and weatherly vessel - and one with an unquestioned pedigree among classic yachts.

Displacement of our prototype as-modeled is quite adequate to carry the structure, equipment, outfit, fuel, and rig. Particulars are as follows:

SAIL RIG

The rig I've proposed is that of a Bermuda cutter. A short bowsprit will take the outer jib stay, and will provide convenient stowage for the ground tackle. A short boomkin aft will allow a permanent backstay without forcing the rig to be too tall. The rig is as simple as it can be made for the sake of sailing short-handed. The main sail and the stays'l are loose footed, with booms. Coming about, the only sail to handle is the jib. In light airs, a larger jib / genoa can be added.

48' AWAHNEE III
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INTERIOR LAYOUT

At 48 feet on deck a comfortable layout for two is possible, with four others able to be accommodated if needed.

Bulkheads have been placed in order to achieve a large forepeak, an owner's stateroom forward, head and shower just aft of that, and a 7 foot long saloon just aft of the head / shower. There is enough beam to allow a pair of pilot berths outboard of the settees, or alternately plenty of space for a large coffee table or dining table on center with ample storage outboard.

Aft of the saloon a large galley is located on both sides, or alternately a chart table could occupy part of one side. The Pilot House is 7 feet in length so that it can contain two pilot berths, one on each side. An engine room / mechanical space is located below the pilot house sole. Aft is a small cockpit, tiller and robust stern pulpit. Below the aft deck is a generous lazarette.
 

SUMMARY

The 48' Awahnee III shown here carries forth the pedigree of the original Awahnee I and Awahnee II which have been proven to be an all-ocean capable sailing vessels, in this case redesigned to take advantage of the ruggedness of steel for structure and aluminum for masts and spars.

48' AWAHNEE III
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