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)
Launched in 1978, the Shannon 28 is regarded as one of the highest quality production 28 footers to come from America. The boat was conceived to serve well for family cruising right through to serious offshore sailing with liveaboard capability for two. Notable accomplishments include the two single-handed passages across the Atlantic by Rudder Magazine’s editor, Monk Farnham, at age 72 and again at age 76 which earn him a spot in the Guinness Book of World Records.
The design came from Walter Schulz, a boatbuilder described as one of the last of a wonderful breed, the complete boatbuilder – one who designs boats, invents rigs, iterates on hull shapes not only computer but also crafts the half models for testing and finally builds the real boat with his own hands. He founded Shannon Yachts in Rhode Island in 1975 with the launch of the sweet sailing Shannon 38 offshore cruiser. The Shannon 28 followed just 3 years later as the second yacht to join the stable.
Schulz’ design goals for the Shannon 28 was typical of a good cruiser – seaworthiness, comfort, and stable handling across all wind and seas condition, but he also wanted the boat to be exciting to sail. Her heavy displacement and full keel configuration fulfils the former, but interestingly, by positioning the rudder further aft and cutting away the aft portion of the keel, the Shannon 28 is also quite responsive. Rig selection also reinforces the design theme with the choice of a true cutter configuration, a favourite for offshore passage-making for its ability to maintain balance over a wide range of wind conditions. At 470 square feet of canvas, her sail area to displacement ratio is high enough to give her respectable light air performance and overall performance is good.
“I’d like to have every boat I build outlive me” – Walter Schulz
No article about Shannon boats should go without a mention of build quality – it’s exemplary. Right from the early days, Shannons have certainly earned their reputation for quality, not only in build quality but also in their seaworthy designs, even winning a nod of approval of Ferenc Mate by the inclusion of Shannon Yachts in his book The World’s Best Sailboats Vol. 2.
The Shannon 28 was available in three interior layouts, including an offshore configuration that had an aft quarter berth. There were thoughtful details to ease maintenance like breaking her tankage down into three smaller water tanks plus a fuel tank, any of which can be removed without cutting away any part of the boat or joiner work. Choice of a outboard rudder and keel sections which allow her to stand on her bottom also simplify maintenance.
The hull was built as a one piece fiberglass molding – hand laid mat and woven roving with additional reinforcements in potential stress areas such as the bow, keel and transom intended to provide the hull with added strength in the case of grounding situations.
The decks were constructed in fiberglass and cored in balsa with well thought out deck hardware attachment points. Delamination and deck leaks are rare. The hull-to-deck joint was an internal flange bonded with adhesive bedding compound and bolted on 8-inch centers. Structural bulkheads were attached with fiberglass straps through the bulkhead and then further secured with continuous fiberglass tabbing along the entire joint. These belt and suspenders methods were typical of the entire construction.
In total around fifty-five boats were produced between 1978 – 1986, after which they continued to be available from Shannon on a semi-custom basis right up to 1999, by which time the price had risen from $55k to $175k. The Shannon 28 remains one of the classic models of the Shannon line, and continues to be sought after in the used boat market with their prices holding up very well.
» The official Shannon Yachts website
» The World’s Best Sailboats Vol. 2 by Ferenc Mate
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