The theoretical maximum speed that a displacement hull can move efficiently through the water is determined by it's waterline length and displacement. It may be unable to reach this speed if the boat is underpowered or heavily loaded, though it may exceed this speed given enough power. Read more.
Classic hull speed formula:
Hull Speed = 1.34 x √LWLA more accurate formula devised by Dave Gerr in The Propeller Handbook replaces the Speed/Length ratio constant of 1.34 with a calculation based on the Displacement/Length ratio.
Max Speed/Length ratio = 8.26 ÷ Displacement/Length ratio.311
Hull Speed = Max Speed/Length ratio x √LWL
A measure of the power of the sails relative to the weight of the boat. The higher the number, the higher the performance, but the harder the boat will be to handle. This ratio is a "non-dimensional" value that facilitates comparisons between boats of different types and sizes. Read more.
SA/D = SA ÷ (D ÷ 64)2/3
A measure of the stability of a boat's hull that suggests how well a monohull will stand up to its sails. The ballast displacement ratio indicates how much of the weight of a boat is placed for maximum stability against capsizing and is an indicator of stiffness and resistance to capsize.
Ballast / Displacement * 100
A measure of the weight of the boat relative to it's length at the waterline. The higher a boat’s D/L ratio, the more easily it will carry a load and the more comfortable its motion will be. The lower a boat's ratio is, the less power it takes to drive the boat to its nominal hull speed or beyond. Read more.
D/L = (D ÷ 2240) ÷ (0.01 x LWL)³
This ratio assess how quickly and abruptly a boat’s hull reacts to waves in a significant seaway, these being the elements of a boat’s motion most likely to cause seasickness. Read more.
Comfort ratio = D ÷ (.65 x (.7 LWL + .3 LOA) x Beam1.33)
This formula attempts to indicate whether a given boat might be too wide and light to readily right itself after being overturned in extreme conditions. Read more.
CSV = Beam ÷ ³√(D / 64)
One look the Coast 34 with her distinctive canoe stern takes us back to the mid 1970s and the work of Bob Perry who made the style outrageously popular. The Coast 34 started life as a home-build design called the Roberts 341. She was penned in 1978 by Grahame Shannon and already by 1980 a project was initiated to take her into production as the Coast 34. Over the years she’s been well regarded as a liveaboard offshore cruiser with loads of storage that’s proven seaworthy with competent sailing abilities in a wide range of sea conditions. In total, it’s been estimated over 100 of these boats have been built, of which around half were from the production mold and finished in semi-custom format by various boatbuilders.
The story of the Coast 34 started in 1978 inside the offices of Bruce Roberts Design Group when Shannon sketched up his ideas in his own time and pitched it to his boss. Roberts liked it and gave the go-ahead for the design that became the Roberts 341. It also gave birth to a smaller boat based on the same hull shape, the 28 foot Roberts 281.
By 1980 Shannon was approached by a boat builder from Canada with the idea to take the Roberts 341 into production. A per boat royalty deal was struck and a few tweaks were made to the design. Probably most notable was a tee-shaped cockpit better suited to wheel steering (at the time tillers were more common on boats this size). This new production boat was dubbed the Coast 34.
Shannon promoted the Coast 34 with full page ads in Cruising World Magazine and orders were taken for 30 boats before the construction of the mold was kicked off. The project was not without its hiccups. Along the way, the original builder ran out of money, abandoning the project, requiring new parties to step before the project continued.
The Coast 34 went on to be built by a variety of boat builders in British Columbia, Canada, including Clearwater Marine, Cape Marine, Marquis Marine, and Randle Yachts with other yards employed to finish the interiors. Today the molds lie with Spencer Yachts on Vancouver Island who have yet to produce any hulls.
Rumours exist regarding the production Coast 34 being a unauthorized copy of the Roberts 341. In truth this resulted from a lack of royalties being paid. Shannon recalls receiving a couple of royalties, but nowhere close to the amount agreed for the numbers that were being built. Other sets of molds are around also. There was a “pirate” set of molds built in San Francisco taken from an existing production Coast 34, however only one hull was built.
With her high freeboard and generous 11′ 6″ beam, owners comment the Coast 34 has a big boat feel. There’s ample stowage throughout, including a huge cockpit seat locker. Down below, the layout is predictable for a boat this size, up front is a very useable v-berth, followed by an opposite facing head and locker area. Further aft is the saloon with twin settees either side of the table. The galley is to port with diagonal twin sinks near the centerline which makes for a secure C-shaped area for bracing while underway. Finally to starboard is the navigation table and seagoing double quarter-berth. It’s an ideal size and arrangement for couples looking to do some extended voyaging.
Construction is solid fiberglass below the waterline and coring in Klegecell foam on the topsides and deck. Reports are that the fiberglass work is of good quality, uniform and free from blisters. Ballast is lead encapsulated in the keel cavity. The mast is deck-stepped with a rig that features a double-spreader high aspect ratio setup, more commonly seen in high performance yachts. Most rigs are setup as cutters, though a sloop rig was an option. Side decks are expansive for a boat this size, and are bordered with a substantial bulwark.
As you’d expect from half the boats being home-built and the other half being semi-custom finished by various boat builders, the quality will vary wildly between individual boats. You’ll find them in all manner of configurations as well; the original Roberts 341 plans had options for both fin and full length keels, and even a few are built with pilothouse cabin layouts.
Underway she’s well balanced on all points of sail maintaining a light helm in a most sea conditions. She’s a good all-rounder, she doesn’t lag too much in light airs where her high aspect rig keeps her moving along at 5 knots even in only 10 knots of breeze. In a stronger conditions she proves quite powerful, able to carry her working sails (115% foresail, yankee, and main) up to 20 knots. Windward ability is sensitive to sea conditions, though able to tack through 90 degrees in smoother conditions, this will drop to 120 degrees when the sea state gets really rough.
The Coast 34 was originally specified with a 30hp engine which has proven to be underpowered, especially given most boats were built much heavier than specified. Some have uprated to larger engines with the comment that it’s quite a squeeze in the engine bay. One particular owner reported vibration issues with their uprated engine installation.
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