Publications, 2006-1997
7 articles, published between 2006-1997
“Sailing Cruiser Design”, Part 1 and 2
PDF, “Sailing Cruiser Design” Part 2
“ Sailing Cruiser Design, Part 2: History, Hydrostatics, and Art ”
Wooden BoatNumber 176, January/February 2004
Summary: Part 2 evaluates the last four of eight cruising sailboats designed for the article
32ft centreboard barge Tilikum
34ft 6in. fin-keeled sloop Flash
39ft fin-keeled ocean cruiser Wizard
42ft double-ended schooner Wild Cat
Extract: Drawing Wild Cat's lines, with their wonderful symmetry, was a pure pleasure, and it's easy to see how these boats came to captivate people. If I retained Colin Archer's beam/length proportions for Wild Cat, he would come out about 14ft 3in. wide. This would create a nice, roomy interior, but the waterlines would be too full forward, meaning he would be too blunt for good windward performance. Looking at half-angles of entry is an easy way to measure how blunt or fine the bow of a boat is. Measuring the angle between the centreline and waterline at the stem of a Colin Archer rescue vessel gives a result close to 30 degrees. Modern ctruisers run somewhere between 18 degrees and 22 degrees; racers are much finer. Wild Cat came out at 22 degrees.
PDF, “Sailing Cruiser Design” Part 1
“Sailing Cruiser Design, Part 1: History, Hydrostatics, and Art ”
Wooden BoatNumber 175, November/December 2003
Summary: Part 1 evaluates the first four of eight cruising sailboats designed for the article
17ft cat-schooner Capt. Flint
20ft cat-ketch Ratty
28ft coastwise cruising ketch Teazer
29ft 6in. offshore cutter Hero
Extract: When looking at the drawing, the first clue to [Teazer's] intended use is the huge cockpit with a short trunk cabin forward. I have taken her strongest elements from traditional cruising designs: classic sheer, the low, rounded house, elliptical transom, and ketch rig. Modern touches are the short overhangs, fin keel and spade rudder, and tight bilge radius with flattish sections amidships. The wild card in this mix is the slight reversal in the stem profile. I think the slight clipper bow balances the short stern nicely and gives Teazer a distinctive look. She is no longer trying to look like a Herreshoff but has developed her own character.
Copyright notice: Verbatim copying and redistribution of the articles “Sailing Cruiser Design: History, Hydrostatics, and Art, Part 1 and 2”, copyrighted by Tad Roberts, is permitted provided the origin www.tadroberts.ca, the author attribute Tad Roberts, and this notice are preserved.
“Passagemaker Lite”
PDF, “Passagemaker Lite” (Passagemaker)
“Passagemaker Lite: A Modern Lightweight Restatement of the Lean Long-range Power Cruiser”
Passagemaker2003
Summary: The article evaluates three Passagemaker Lite designs
PL 46
PL 56
PL 80
PDF, “Passagemaker Lite” (Professional Boatbuilder)
“Passagemaker Lite: A Modern Lightweight Restatement of the Lean Long-range Power Cruiser ”
Professional BoatbuilderNumber 81, Feb/March 2003
Extract: Passagemaker Lite, the design series presented here, is a high-speed displacement hullform, a shape closer to a naval frigate than a fishing vessel. It has a long waterline, relatively narrow beam, and fine entry. In the manner of a frigate, there is some rise to the sections aft, but there is still deep immersion of the hull at the transom. The prismatic coefficient is fairly high (.678), and displacement is spread out along the hull to counter trimming tendencies. The difference between high-speed displacement and semi-displacement (or semi-planing) is intent: a high-speed displacement hull will slip through the water with minimum resistance, while a semi-displacement form, such as a lobsterboat with its wide flat after-sections, has dynamic lift and stability.
Copyright notice: Verbatim copying and redistribution of the article “Passagemaker Lite”, copyrighted by Tad Roberts, is permitted provided the origin www.tadroberts.ca, the author attribute Tad Roberts, and this notice are preserved.
“A Brief History of Lightweight Motor Yachts”
PDF, “ A Brief History of Lightweight Motor Yachts ” (Passagemaker)
“A Brief History of Lightweight Motor Yachts ”
Passagemaker2003
Summary: Supporting article that appeared in the same issue with "Passagemaker Lite".
Extract: The history of lighter weight, fast boats with serious cruising range goes back almost 100 years. In the early part of the last century, motoryachts such as the 75' x 14' (22.9m x 4.3m) Nokomis, built in 1903, began as refinements of fashionable and elegant sailing yachts. These became the rumrunners and fast commuters of the Roaring Twenties. Engines of the day were of fairly limited power, so efficiency was achieved with long lean hullforms. Marlin, built in 1930 for Edsel Ford to a design by Walter MacInnis, is a fine example of this type. Measuring 51'6" x 12'6" (15.7m x 3.8m) with 3' (1m) draft, the boat was powered by twin 245-hp Sterling gas engines producing a top speed of 24.5 knots at 1,500 rpm. The design was an interesting combination of commuter and sportfisherman. Marlin was capable of 20-knot sprints up Long Island Sound, but most of its cruising would have been at 14 to 15 knots. It is at this speed that the vessel would have headed offshore in search of swordfish.
Copyright notice: Verbatim copying and redistribution of the article “A Brief History of Lightweight Motor Yachts”, copyrighted by Tad Roberts, is permitted provided the origin www.tadroberts.ca, the author attribute Tad Roberts, and this notice are preserved.
“Power Boat Design: Form and Fuction ”
PDF, “Power Boat Design: Form and Fuction ”
“Power Boat Design: Form and Fuction and Their Effect on Performance”
WoodenBoatNumber 137, August 1997
Summary: Analyses the effects of form and function on the performance of 10 power boats, 18ft to 38ft, designed for the article
38ft. lobsteryacht White Pine
38ft. classic motor yacht Yellow Cedar
38ft. express Teak
18ft. flat-bottomed displacement boat Alder
18ft. inshore fisherman Oak
18ft. deep-v Sitka Spruce
28ft traditional displacement boat Ironbark
28ft. displacement boat Douglas Fir
28ft. family coastla cruiser Red Cedar
28ft. 5.5in. planing hull Mahogany
Extract: With a deep rounded forefoot evolving into hardchined shallow vee sections aft, [Douglas Fir] is a real hybrid. The fastest in this group of semi-displacement hulls, the vee sections will semi-plane the stern, provide dynamic lift, and improve trim. Some are of the opinion that a boat this wide is no good running in a big sea, but I think rudder size may have as much to do with it as anything. Many fast boats are equipped with tiny rudders to reduce drag, but they also reduce turning moments. Douglas Fir has two oversize rudders. It's a balancing act getting a hull that's optimum in many conditions at high speed, trading weight and section shape against LCB location.
Copyright notice: Verbatim copying and redistribution of the article “Power Boat Design: Form and Fuction and Their Effect on Performance”, copyrighted by Tad Roberts, is permitted provided the origin www.tadroberts.ca, the author attribute Tad Roberts, and this notice are preserved.
“Performance Hulls ”
“Performance Hulls ”
“Performance Hulls”
Southern Boating 1998
last updated July 26, 2007
Featured Article
“Passagemaker Lite: A modern lightweight restatement of the lean long-range power cruiser”
Passagemaker Lite, the design series presented here, is a high-speed displacement hullform, a shape closer to a naval frigate than a fishing vessel. It has a long waterline, relatively narrow beam, and fine entry. In the manner of a frigate, there is some rise to the sections aft, but there is still deep immersion of the hull at the transom. The prismatic coefficient is fairly high (.678), and displacement is spread out along the hull to counter trimming tendencies. The difference between high-speed displacement and semi-displacement (or semi-planing) is intent: a high-speed displacement hull will slip through the water with minimum resistance, while a semi-displacement form, such as a lobsterboat with its wide flat after-sections, has dynamic lift and stability.