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)
Now forty five years on from its first introduction, the Bristol 27 can be considered as well proven as a blue water boat can get. Although the boat was intended more for coastal sailing, the design is inherently seaworthy; well prepped boats are easily capable of offshore work.
Brothers Clint and Everett Pearson made their mark founding Pearson Yachts and when they sold up in the mid-1960s they formed Bristol Yachts. The first boat out of the gates was the Bristol 27, some say it’s very much a copy of their earlier successful Pearson Triton 28. The Bristol 27 launched in 1966 and sold in large numbers, particularly in the first two years (more than 170). It’s been estimated that 337 were built before production ceased in 1978.
The design was from Carl Alberg and reflects the Scandinavian Folkboat influence of the day. These boats were narrow with long overhangs, graceful low-slung sheerlines, and sweeping full keels that are cutaway in the forefoot. The narrow beam adds to seaworthiness but doesn’t do much for form stability, so they are quite tender initially. That’s not all bad as they were designed to lengthen their waterline when heeled.
The boats carried a masthead sloop rig, originally with roller-reefing in the mainsail boom. These days most have reverted back to simple slab reefed mainsails which hold a better shape and do not suffer from jamming.
Bristol 27s came in three flavors, a day sailing model with a large cockpit and small interior, a standard model which had a larger cabin and twin settees, and a dinette model which substituted a settee for a table. Power options included an outboard engine mounted inside a cockpit well or an inboard engine in either petrol or diesel. The inboard engines are preferred for any offshore work, especially the diesel.
Boats of this era were not designed for interior space and the Bristol 27’s interior is cramped by modern standards. Even in the cruising model with the larger cabin there’s a relatively large cockpit which takes space from the cabin. One of the practical decisions made in the design was for a raised portion of in the cabin house to allow 5′ 10″ of standing room in the main cabin or more if below the companionway with the hatch slid open! The V-berths accommodate 6′ 6″ while the settees 6′ 4″.
All Bristol boats were strong and the Bristol 27, being one of the first generation of fiberglass boats, was no exception. They had solid GRP hulls with deck, cabin, and cockpit as an integral molding and connected to the hull via deck clamp and through bolting. The mast was deck stepped, but in this case supported by a substantial bulkhead that’s well tabbed into the hull. Lead was used as ballast and encapsulated in fiberglass.
Underway the Bristol is nimble and easy to sail, exhibiting a slight weather helm. They are middle of the road as far as performance. Some have found them to be a bit tender, but that is inherent in their design and they do stiffen up after 15-20 degrees of heel and have good ultimate stability. Owners have been known to throw an extra 300 lbs. of ballast in the bilges which they claim helps.
Overall the boat’s design is classically seaworthy and in rough seas these designs are well suited to heaving-to or laying ahull.
You can usually find a Bristol 27 in the $5k-10k USD range, sometimes even cheaper, so it’s definitely priced to be a good first boat. They had good construction and now well over forty years, some boats are showing their age.
The hull to deck join has become prone to leaks, not that surprising for its age, and sometimes this can be a hard problem to fix properly. Also age related, are superficial non-structural gelcoat cracks and crazes. Try and get a model with an inboard engine.
» Bristol Owners Association
» Twenty Small Sailboats to Take You Anywhere by John Vigor, (Ch4, p19-25) an in depth look at the Flicka 20. ISBN:978-0939837328
» Bristol 27 Review by John Kretschmer (Sailing Magazine) and also The Best Used Boat Notebook, by John Kretschmer (p27-30)
John Vigor turns the spotlight on twenty seaworthy sailboats that are at home on the ocean in all weather. These are old fiberglass boats...
This collection of capable blue water boats features time-tested sailboats with rich histories.
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