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)
Penned as Sparkman and Stephens design #1899 by Olin Stephens, the SHE 31 introduced in 1969 has enjoyed popularity in the UK and Europe. Though originally intended as a half ton IOR racing thoroughbred, this boat often nicknamed a “baby Swan”, has gone on to be adapted for cruising in a myriad of derivative models. Known for her speed, close winded performance, and absolutely beautiful lines this racer/cruiser is often compared the Contessa 32.
The unusual SHE name comes from the initials of South Hants Engineering, a UK light engineering firm founded in 1947 that branched out with a marine division. Headed up by two brothers, Derek and Simon Fitzgerald armed with an enthusiasm for sailing, the SHE line of yachts flourished from the late sixties to the mid seventies producing solely Sparkman and Stephens designs from the cramped SHE 27, the SHE 31 which was the most popular, the SHE 32, and the SHE 36 which was without a doubt the best boat in the line up.
The division ultimately succumbed to the financial climate of the late seventies and competition from cheaper, faster and roomier French imports. The company continues today as SH Enterprises but no longer produces boats.
The SHE 31 moulds were bought by Laird Adams Engineering who developed the design with increased headroom and a new, more practical interior. These boats sold under the name Delta 94. Also there were a few examples that were home-built by enthusiastic amateurs.
The design, optimised for racing, was the beneficiary of Olin’s latest thinking in the same era of the legendary S&S 34 and Swan 36 both introduced 2 years earlier in 1967. He was a master of designing yachts to take maximum advantage of IOR rules for ocean racing.
Typical of these designs the SHE 31 has pinched bow and tail sections and a tumblehome amidships, reminiscent of much larger yachts. Her sharp bow profile gives her a good bite on tacks, and a swept back fin keel carefully faired into the hull with 3400 lbs of lead in results in a balanced feeling and stability in nearly all sea conditions. Notable is the skeg rudder pushed far aft and the propellor on a P bracket forward allowing better reversing.
There is accommodation for five but belowdecks it’s reasonably cramped with very little headroom, especially in the forecabin. The interior finish was restrained, modern and perhaps a little austere and betraying the use of ply.
Many variants were produced, we’ll summarise these below.
SHE 9.5 Traveller
South Hants Engineering responded to public demand for a cruising model by producing the 9.5 Traveller, a version with more lavish accommodations;. It had a new deck, coachroof providing better cruising accommodations, higher topsides and increased headroom. Most owners will refer to their Traveller simply as a SHE. They are relatively rare.
Performance was still good and many examples will have been raced hard and spent long lives on exposed moorings rather than snug in marinas. Despite this, most have stood up well to the action, reflecting the high quality of build.
This particular boat caused quite a stir when she was unveiled to the yachting world at Southampton Boat Show in 1977. Produced by Laird Adams Engineering in the late senventies, the Delta 94 (also called the Delta 95) is a later version with the same hull, but with slightly more freeboard to produce more interior headroom, and a revised interior layout. Only 17 of them were produced.
Simultaneously with the South Hamp Engineering yachts, Swedish builder I.W. Varvet on the island of Orust, an island which traces its roots back to the time of Viking ships, produced a large number of yachts. Over 350 boats were produced starting around 1968 in three revisions.
MK I (1968 – 1972): Small stern, ‘dinette’ layout.
MK II (1972 – 1980): Larger stern, new deck, revised wood trim.
MK III (1980 – 1985): Aluminium toe rail (instead of Teak), glass hatch, revised hardware.
Please note the SHE 31B produced by South Hants Engineering from 1970 onwards was an altogether different design – being Sparkman and Stephens design #2042 which was also designated for 1/2 ton IOR racing. It was further developed into the SHE 32 – a more luxurious and roomier yacht intended for cruising.
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