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 of designer Joe Adams’ most popular, the Adams 13 is well known in Australia. It was introduced in 1978, which is surprising as the boat seems modern even by todays standards. Adams took quite an innovative approach with the Metre series of boats, with the Adams 13 it’s essentially a 36 foot yacht stretched to 43 feet to produce a narrow hull that’s roomier below deck and more slippery through the water. Best of all, the Adams 13 retains much of the affordability of a 36 footer.
The boat is versatile; she’s nimble enough for racing around the buoys, has had a long successful career as an offshore racer, and has also proven to be a competent, seakindly blue water cruising vessel. Most have centerboards, which when pulled up aids down wind performance and usefully draws barely over one metre for cruising into those shallow bays. Not surprisingly owners report the boat is easily handled and fun to sail.
The Adams 13 was penned around 1977-78 shortly after the introduction of her smaller sibling, the Adams 10 Metre. Designer Graham Radford, who was a partner in Adams Yacht Design for a decade during those years, tells us the Adams 10 was the first boat produced in the “Adams Metre” range. These were light displacement, narrow beamed performance cruising yachts.
When we asked about the design goals of the Adams 13 Radford commented:
“It was really just a small but long cruising boat. Not a big volume boat, it’s narrow, it’s long, it’s got the accommodation volume of a 36 footer but in 43 feet of length … The centerboard was to give it very shallow draft for cruising. That style of centerboard we used on quite a few designs from little boats right through to 56 footers. It’s proved very popular and has done a lot of sea miles.”
Interestingly the Adams 13 was a boat Joe Adams initially designed for himself, he invested a lot of time dialing in this particular design. The moulds were funded by a syndicate of five owners including Adams himself. Each put in one fifth of the cost and after the five boats were built the moulds were sold off and since then they have changed hands multiple times.
The very first boat was called Fanny Adams which was built for an owner in Sydney who did some offshore racing with her. Since then an estimated 80 boats have been built by various builders and we hear the last hull to have popped off the moulds was in 2002. The moulds are presently owned by Peter Rigby of Adams Yacht Sales, who are open for new orders.
No history on the Adams 13 would be complete without a mention that although designed as a cruising yacht, the boat has had a successful career as an offshore racer including many entries in the Sydney-Hobart race. She remains competitive to this day.
One look at the Adams 13 and you can tell this is not your average blue water cruiser. Narrow and sleek to an extreme with a nearly straight sheerline, it flies in the face of conventional cruising yacht design circa late-1970s. Her displacement and beam measurements reads that of a regular 36 foot cruising yacht, yet her length is 43 feet overall with a long waterline of nearly 41 feet.
The boat was expressly designed for a couple to sail and see the world, the way Adams went about this goal was to stretch the boat to provide extra room below deck, while retaining the lighter displacement and associated rigging thereby keeping costs closer to that of the smaller boat. The payoff is obvious; speed.
Along the performance theme, the boat employs a fractional cutter rig boasting a healthy 1075 square feet of sail area. The rudder is transom-hung with tiller steering for simplicity and reliability. Below the waterline is a keel/centerboard arrangement which when pulled up enhances downwind performance by reducing wetted area and draws a shallow 1.04m of depth allowing close-in anchoring.
Of note is the mainsheet/traveller system which is located right in the middle of the cockpit and can get in the way of cruising activities; on some boats owners have relocated the sheeting control further forward to open up the cockpit area.
There is an Adams 13E variation of the boat better suited to the needs of offshore racing, the “E” representing “extended cockpit” with an open transom. The centerboard is gone in favour of a fixed keel and the rudder relocated under the hull behind a sturdy skeg with wheel steering.
Interiors vary a lot between boats, this is the case with most Adams boats. Many boats were bought as hull and decks and finished professionally by various boatbuilders or fitted out by their owners. The standard accommodation layout provides for four to six people with 5′ 11″ of headroom. The saloon is forward of the centerboard case and provides a cosy area removed from the working part of the accommodation. There are two large quarter berths aft which may be singles or doubles. The saloon can accommodate two extra in single berths if required and in the V-berth are two single berths or a double. A large toilet/shower compartment is enclosed alongside the centerboard case.
The hull is of fiberglass sandwich construction using an Airex foam core. The decks are in fiberglass using end-grain balsa coring, though some decks used Airex foam. The stub keel is made from solid GRP skins with moulded lead ballast, the structure is encapsulated in fiberglass and the structural floors are then fitted.
The Adams 13 is easily handled, rather nimble and owners report it as being fun to sail. The boat’s motion is comfortable and seakindly, and it is said crossing oceans in her can often be less effort than a 36 foot yacht. Not surprisingly with such a narrow hull and light displacement, the boat is easily driven. You’ll often find these boats fitted with incredibly small engines, some having 2 cylinder 20hp diesels or even smaller.
They are particularly fast off the breeze with their centerboard up, a useful strength given a decent amount of miles covered when offshore cruising is done off the wind. The tradeoff is the high center of gravity of the ballast in the stub keel, which makes the boat relatively tender which detracts from windward performance. The boat needs to be reefed early despite the large amount of sail area the boat can carry.
Though setup as a cutter rig, the favourite for long distance passage-making, when sailing inshore she is commonly sailed as a sloop with headsails of modest size. Her best point of sail is in a broad reach when most of the sail area can be used in to good effect without reefing.
As of 2010, the asking price of the Adams 13M in the used market is in the range of: $110k-$140k AUD.
New hull and deck kits are available from Adams Yacht Sales for $58k AUD.
» A History of Graham Radford’s time at Adams Yacht Design on Radford’s official site.
Thanks goes out to Graham Radford of Radford Yacht Design and Michele Pippen for their assistance in the research of this article.
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