Globetrotter 66

PARTICULARS

Loa:                            66’ 0”                                       20.116 M
Lwl:                             60' 6”                                       18.490 M
B:                               16’ 6”                                       5.029 M
Design Draft:              6’11”                                         2.108 M
Displ:                       70,000 lbs. at Dwl                     31,752 Kgs at Dwl
Ballast:                     32,000 lbs.                                 14,515 Kgs.
Sail Area:               2,212.8 sq.Ft. (incl. masts)   205.48 sq. M
Displ/(.01Lwl)³          140.0

SA/Vol^2/3 20.83

FEATURES:

In the summer of 2009, I was approached by David Brooks of California to design a new boat for himself and his family—wife Tamara and four children. They liked my Globetrotter 45 , but wanted something longer, say 64' to 68', with room for their family of six for offshore voyaging. Plus, David wanted to build the boat himself in aluminum. Was I interested in doing the design? Could I say no? Of course not.

The next three weeks resulted in a constant flow of emails back and forth on what was to be included in the design. Inspiration came from the Dashew Deerfoot boats and a number of other one-off designs. Unique features to the G66 would be water ballast for extra stability, using fresh water and not sea water, and an additional inside aluminum skin to effectively make the yacht a double-hull design. The space between the inside and outside plating is to be filled with foam for extra flotation and insulation. There would also be watertight bulkheads to subdivide the boat against catastrophic flooding. This design is going places, and one of those place is not supposed to be Davey Jones' locker, so safety is paramount.

Fig. 2. Globetrotter 66 sail plan, rendered in color

The rig was conceived as a cat ketch, although in the end it came out a cat schooner. Both masts and sails are absolutely identical, and the schooner look comes as a result of the mizzen mast passing through the deck house, thereby being raised up a few feet taller than its forward mate. The masts will be free-standing carbon fiber rotating wingmasts and will utilize the half-wishbone booms as are typical of my Globetrotters.

Fig. 3. Globetrotter 66 deck plan

Other requirements are that the yacht be a raised pilot house design with midship cockpit all above deck so that engine room aft has full headroom. Behind the cockpit is storage on deck for a hard-bottom inflatable dinghy. The master stateroom with ensuite head is forward, separated from the main saloon and galley by a laundry and storage area. The main saloon has two U-shaped settees, one each port and starboard. Aft on starboard is the inside helm station and navigation area. Opposite to port is a large galley that is sunk down 8”, yet is still completely open above to the rest of this space. The galley person has ample room for appliances and still has view directly out the deck house windows. Aft of the main saloon and galley are two guest cabins port and starboard. Between these cabins is a head with watertight door into the engine room. This head serves as a vestibule of sorts to keep dirt and grease from being tracked into the cabins, and to provide a noise and vibration buffer to dampen the sounds and shakes, such as they may be, from the engine room.

Fig. 4. Globetrotter 66 general arrangement

The hullform is to be narrower rather than wider, so we limited the length-to-beam ratio to 4.0. The keel draft is just 7' so that access to shallow harbors is possible. Narrow hull and shallow draft can limit stability and sail carrying power, so water ballast is a pleasant feature to have. There are four water ballast tanks, two each side and outboard of the main saloon/galley area. There is plenty of capacity for water, and rather than haul the sea around, these are actually the fresh water storage tanks. Most of the time these tanks will be about half full and more or less balanced port and starboard. But should conditions arise that require extra weight outboard, all the water can be pumped to the high side. There will be a watermaker on board, although the brand and capacity are not yet determined.

The hull proportions impact overall performance, and we want assurance that this yacht is going to be a good performer yet carry the load a voyaging family requires. Before establishing a design contract, I reviewed the design parameters by analyzing sail area/displacement ratios (SA/D) and displacement/length ratios (D/L) of the various exemplar boats and some proposed design ideas. I charted these in a spreadsheet and came up with the following plot.

Fig. 5. G66 Sail Area/Displ ratio vs. Displ./Length ratio, with S# categories

This is a chart of SA/D ratio plotted against D/L ratio, overlaid with contours of S Number (S#). S# is a relatively new concept that I have been instrumental bringing to light recently over the internet from its inventor who was a past client of mine. S# is a performance factor that rates all sailboats on a scale of 1 to 10. To see a complete description of S#, you can go to post #198 on the thread at BoatDesign.net (click here). Chart #1 above shows S#s from 1 to 10 with data points representing the SA/D vs. D/L ratio of the exemplar boats.

Grouped in the middle of Chart #1 are three sample G66 designs. The SA/D ratio is held constant at 20 which is a respectable amount for a cruising yacht, and the lengths are the same at 66' Loa and 62' Lwl. The displacements vary from light at 65,000 lbs, mid-weight at 70,000 lbs., and to heavy at 80,000 lbs. This places the G66 in the middle of the “Racer-Cruiser” category (or “Cruiser-Racer,” if you prefer.) This means that the proposed yacht will have good performance, particularly in relation to its inspirational sisters. Note where the Dashew designs are—the Deerfoot 61 is close by to the G66s, with slightly lighter displacement by comparison and notably less in sail area. The Sundeer 64 and Beowulf , an aluminum 80'er, are just over the line in the “Racing Machine” category. They are not racing machines, actually, it is just that their S#s place them at the higher end of this chart. Sail areas are a touch higher, but their lighter displacements push them to the left side of the chart.

Another concern is general motion and comfort. We can calculate Brewer's Motion Comfort Ratio (MCR) which is an indicator of comfort in relation to rolling accelerations. MCR is kind of like a D/L ratio, but there is a beam factor added in the denominator, so it is actually a D/LB ratio. Basically, it says that with higher MCR, there is more displacement be greater in relation to length and beam, so the motion will be better (slower rolling accelerations), thereby leading to greater comfort. If displacement is lower, and/or if beam is greater, the MCR goes down and motion becomes more uncomfortable.

Fig. 6. G66 S# vs. Motion Comfort Ratio

Brewer divides comfort zones into three parts [ Commoditas est omnis divisa in partes tres— “All comfort is divided into three parts.”—to coin a phrase, with apologies to Julius Ceasar. I can't help it; my sister is a Latin teacher. ] These are Lesser, Average, and Greater Comfort—not original or clever terms, but they get the point across. Chart #2 is a plot of S# against MCR. Note that the proposed G66s fall squarely in the middle of the Average Comfort zone. The Deerfoot 61 is close by, and the Sundeer 64 and Beowulf are up in the Lesser Comfort region.

The Sundeer 64 and Deerfoot 61 are composite boats; Beowulf is aluminum yet is deep in the ultralight category having a D/L ratio of about 61. Another boat in this list that matches closely with the G66s is the Kanter 65 , built in aluminum and with many similar design features that provided design inspiration. The Kanter 65 is heavier, and along with the Deerfoot 61 , to my mind, both are undercanvassed with SA/D ratios only in the mid-teens. So what we decided on is the mid-weight G66, displacement of 70,000 lbs and a sail area of 2,212 sq. ft. SA/D ratio is 20.84. The length on the waterline came out a bit shorter on the Dwl, so D/L ratio is 140.0. I think this is a good place to be for an ocean voyaging boat of this length—very respectable performance with descent capacity for provisions and comfort.

Shortly after this analysis, David Brooks signed a design contract and we proceeded with the preliminary design for the Globetrotter 66 . Over the next few months we exchanged a lot of emails and sketches as the design details were fleshed out. Practical issues tended to take precedence over style issues, and that's OK, so long as the boat was still nice to look at. No sense in having an ugly girlfriend (ladies, the same applies to you, no sense in having an ugly boyfriend), and certainly, a boat can be an interloper in an otherwise committed relationship. To this end, David's wife Tamara also gave her input into the design which she communicated through David to me. It is always healthy to work with both sides of the client's team.

At this first stage in the design, I work out all the basic structural parts for the aluminum structure. This includes all the hull and deck house plating and the layout of the seam and butt welds. This is a radiused bilge hull form, meaning that the turn of the bilge is close to a constant radius at about 36” to 38”. Small plates are cut and rolled in a single degree of curvature so that it is easier to make a compound curved hull. The deck house and cockpit plating are basically flat panels or single degree of curvature. The top of the deck house is compound curved, so it will have to be made up in smaller plates.

I have the hull and keel modeled in 3D at this time. David Brooks is adept at his own rendering, so what I would draw in AutoCad in 2D, he would return to me in 3D. Below is an example of two of his renderings.

I am publishing this at the end of the preliminary design stage. After some review and cost estimating and construction planning, we should be able to continue with the detailed design. Stay tuned for more design and construction information.

Fig. 7. Globetrotter 66 in an earlier rendition of the hull and deck house profile. The current model has a shorter deck house with a different shape to the windows, which can be seen in the plans above.

If any of you would like to have a Globetrotter 66 for yourself, give me a call and we can discuss it. Other models may be created from this design.

THE GLOBETROTTER 66