Rovings June/July Issue 143

from Professional BoatBuilder magazine No. 143
Compiled by Dan Spurr

Classic Runabouts From Switzerland

Boesch MotorboatsHenri Thibault

Boesch Motorboats, founded in 1920 by Jakob Bösch, built many sailboats before and during World War II. In 1928 his son Walter presented his apprentice masterpiece; he is the grandfather of Markus, who runs the company today. In the 1960s, the German electrical equipment manufacturer Bosch opposed the boatbuilder’s use of its trademark name; thanks to the subtlety of German, “oe” replaced “ö” without changing the pronunciation.

Located in Kilchberg, a quiet village a few kilometers from the center of Zürich, Switzerland, Boesch Motorboats is the last in the world to produce serial mahogany runabouts. On the road that closely runs along Lake Zürich, at the water’s edge stand a few wooden buildings from a bygone age. The white Boesch signature across one facade contrasts with the bright red of the building’s wood siding. In the 1970s Klaus Boesch, an engineer and naval architect, succeeded Walter Boesch, who had succeeded Jakob, who founded the company in 1920. Now, Klaus’s son Markus is the fourth generation to head the business. Even in this country, where stability is a national treasure, it is rare to find examples of such continuity. Each generation has contributed to technical progress and innovation, assuring that every Boesch is a boat of its time.

The company’s various activities form a small, independent group spread over several sites. The well-preserved original buildings—once owned by Treichler & Co. boatyard—house the administrative center, the engineering and design offices, the restoration and mechanical workshops, a showroom, a marina, and boat storage. In 1973 the series production was installed in large, modern workshops in Sihlbrugg, less than an hour’s drive toward the mountains.

Production has remained stable over recent years. Of the 25 to 35 units built a year, half are sold to the domestic Swiss market and the other half for export to predominantly German-speaking markets. Since the 1970s, Boesch has created a network of dealers and boat services associated with the parent company. One is on the other side of Lake Zürich, where the concentration of Boesch boats is impressive (480, of which 250 are stored by the builder for the winter season), as well as in Rolle on Lake Geneva, on Lake Lucerne, and farther south on the Swiss part of Lake Maggiore at Tenero in the Ticino canton. Abroad, there is a distributor for each of the European countries and representatives in other major countries of the world.

Boesch bulge rudders

In the ’80s Urs Boesch, a mechanical engineer, designed the unusual “bulge” rudders after studying water flow along the hull bottom through a Plexiglas panel installed for viewing.

Klaus Boesch

Urs’s brother Klaus Boesch, an engineer and naval architect, continues to design all the models by hand with splines and “whale” weights.

Boesch structure aids in hull construction

This large metal and wood structure pivots on a central axis to aid hull construction. The yard builds about 30 boats a year. A 710 (7.5m/24.6′) model requires roughly 1,000 man-hours, and a 970 (10m/32.8′), twice that.

Boesch laminated hull

The laminated hulls of Boesch boats are cut from mahogany plywood manufactured specifically to the company’s standards (up to 11 layers) by its supplier of more than 50 years.

10 passenger 970 model

Klaus’s brother Urs Boesch, who is responsible for all mechanical systems, adapted a diesel engine for this special 10-passenger 970 model for an Austrian hotel. Custom orders are not unusual.

Markus Boesch test drives

Henri Thibault (ALL) Markus Boesch test-drives a 750 (7.8m/25.6′) Portofino Deluxe powered by a V8 gas engine; an electric-power version of the model is also available.

Several hotels and resorts maintain fleets of Boesch boats for waterskiing and excursions. Some establishments employ their Boeschs for promotion, offering champagne cruises. These hotels sometimes order special models, such as the 10-seater 970 powered by a Yanmar diesel, an exception in an exclusively V8 gasoline-fueled range. The latter includes four models with various finishes and equipment, namely the 620 (6.5m/21.3′), the 710 (7.5m/24.6′), the 750 (7.8m/25.6′), and the 970 (10m/32.8′).

In recent years, the shipyard has expanded its model lines with three electric-powered versions of the 620, 710, and 750. One of its loyal customers owns three boats, two of which are electric. Klaus Boesch says, “Not so long ago it was unthinkable for most of our customers not to have a big V8 engine. Now, they are more and more interested in zero emissions propulsion and its silence.” In fact, one third of sales are now the electric versions that cost almost double the V8 models.

But the gas engines are also notable for their quietness, appreciated especially on the Swiss waters. As Klaus’s brother Urs says, “A Boesch V8 doesn’t bark or growl. It is characterized by a rather reassuring murmur.” This is the result of a “cascade” system of exhaust silencers, an invention by which standard mufflers are extended with a second that optimizes the flow of exhaust gases with the cooling water and propels the mixture into a soundproof chamber located on the transom. There the gases are mixed with water sprayed by a special blade below the waterline. As the boat goes faster, the water spray increases to reduce the noise.

Also contributing to quietness is the “bulge” rudder. Urs, a mechanical engineer, developed the rudder profile during routine testing in a boat with a Plexiglas panel allowing him to observe the turbulence generated by the propeller. The rudder’s special shape enables the boat to run straight ahead with minimal steering.

Markus says, “We have a niche market, but it obviously poses some problems. We have a very good reputation and a strong brand, but our production is limited. We must therefore adopt a marketing plan adapted to our size. We could try to reach out beyond Europe, to Asia for example; however, our structure is not suited to global distribution. In the 1990s we could have sold a lot of boats in the United States, but there, dealers must have a lot of stock, as customers want the product immediately. We could not provide these quantities with our quality requirements. We much prefer relationships that are pursued over time. We know personally most of the families who have a Boesch and we remain in contact with them.”

Boesch Motorboats AG,
 Seestrasse 197, Postfach 529, 8802 Kilchberg/Zürich, Switzerland, tel. +41 44 711 75 75, fax +41 44 711 75 76, website

—Gerald Guetat


Making Molds With Built-in Post-Cure

Parabeam fabricParabeam

Parabeam drapable fabric is made of E-glass and engineered with warp, weft, and pile fibers that maintain some airspace between the two skins. In tooling built from the material, that space can be filled with warm water to post-cure the laminates.

We’ve written a number of times about Parabeam, the 3D drapable fabric made up of two skins of E-glass connected with vertical strands that resist compression. When wetted out on both sides, the skins collapse but only temporarily, as they spring back to the original profile, between 3mm and 12mm (0.12″ and 0.47″) thick. Thicker versions are available by special order.

Most recently, in “Process Control Refined” (Professional BoatBuilder No. 125), we wrote about Andre Cocquyt’s employment of Parabeam in making water-jacketed tooling. In that article, PBB editor Aaron Porter described how in 1997 Cocquyt painted a Parabeam panel black, plumbed it for water flow, and set it in the sun to be heated. It worked. He followed this experiment with a demonstration at IBEX 2000, where he infused a dinghy in a temperature-controlled mold made with Parabeam. Seemed like a great idea, but alas, Cocquyt said, “It went absolutely nowhere.”

That has changed. At Princess Yachts (Plymouth, United Kingdom), Julian Spooner confirms they are employing Parabeam in making heat-controlled tooling, and Larson Boats (Little Falls, Minnesota) evaluated Parabeam in its VEC tooling program. In 2006, Larson and Glastron brands of small powerboats were part of Irwin Jacobs’s Genmar marine conglomerate. Jacobs also had bought Greenville, Pennsylvania–based VEC Technology, a proprietary manufacturing process employing lightweight composite mold skins supported by water in a heavy steel chamber. As I wrote in “VEC” (PBB No. 101): “A VEC ‘cell’ can be operated by one person, from laying in reinforcements to initiating the resin injection to removing the part.” It has brought considerable innovation and efficiencies to production boatbuilding, the likes of which have not been seen elsewhere in the industry. Parabeam was experi­mented with in place of conventional reinforcements, first with an 18mm (3⁄4″) product, then a 12mm (1⁄2″) product, and then with multiple layers of 5mm (3⁄16″).

Following my visit to Little Falls, Larson apparently experienced some deterioration in its Parabeam-made vinylester resin molds. Consultants suggested epoxy but the resin change was not implemented, and application in the water environment was discontinued. However, out of this application evaluation came recognition of the benefits of tooling made with Parabeam, and Larson adopted an ongoing application for its open-mold tooling and has been employing Parabeam in its mold manufacturing for the last six years.

Advantages are said to be faster mold build time; better impact resistance and less repair time; weight savings up to 30% over conventional tools; temperature control option; and less time to bring the mold up to working temperature after it has been stored outside in the cold.

Here’s Parabeam’s suggested mold lamination schedule with vinylester resin:

  • Tooling gelcoat 0.010″ (0.25mm).
  • Lamination one is 0.05″ (1.26mm) chop or mat with neat resin.
  • Lamination two is 0.05″ chop or mat with mold-making (filled) resin (Cook, Nord, or RCI filled mold-making resins).
  • Lamination three is 0.06″ (1.5mm) chop or mat with neat resin.
  • Lamination four is ParaGlass/ 5 with neat resin.
  • Lamination five is ParaGlass/ 5 with neat resin applied at right angle to first PG 5 lamination.
  • Option of third and fourth ParaGlass/ 5 lamination.
  • Lamination six is 0.02″ (0.5mm) chop or mat with neat resin.
  • A framework may be applied after full cure to provide further structure and aid.

To take advantage of Parabeam’s unique spatial qualities, over time several other companies have incorporated it in their manufacturing: Kenway (Augusta, Maine) for the hollow jacket in TCM (temperature controlled molds) processing; and Parabeam’s parent company, ZCL Composites (Edmonton, Alberta, Canada), in its proprietary underground storage tanks and tank liners in order to detect leaks before they get into the ground water. Parabeam has also been working in France with Stuart Ford, owner of Marine Technique Mediterranean, in the development of his patented Cameleon composite fence system, made of Parabeam panels, through which swimming pool water is circulated and heated by solar energy.

“Way back in the mid-1980s,” Cocquyt writes, “I even made a keel cooler out of it for one of the fishing boats I built. I used four 4″ [102mm] strips in between core panels; that way there was no external piping or connections. It worked great, not as efficient heat transfer as metal piping, but I made them long enough and close to the keel, manifolded at both ends. For all I know, that boat is still in use. That was what made me think first of using it for TCM. I plan on using it in my lobsterboat hull if I ever get around to finishing it.”

In addition to the applications outlined above, Parabeam has been most active in supplying companies in aerospace/military (Boeing, Airbus, Metal Cladding, and Oshkosh-Fiberdome), rapid transit (Bombardier, CAF, and BFG), and architecture (Kunovar & Kamni, and Disney theme parks and movie sets) with advanced composite solutions through its customer networks in North America, Europe, and Asia.

Parabeam, P.O. Box 134, 5700 AC Helmond, The Netherlands, tel. +31 492 591 222, fax +31 492 591 220, website

Expedition Powercat From Du Toit

Du Toit Yacht Design

Du Toit Yacht Design of Durbanville, South Africa, recently celebrated the launching of a 75′ (23m) expedition power catamaran with a range of more than 3,400 nm at 8 knots.

Sport fishermanDu Toit Yacht Design (BOTH)

Provisions were made for the owner, an avid deepsea sport fisherman, to occasionally tow his 48′ (14.6m) sportfisherman, Big Bob.

At the risk of stereotyping South African yacht design preferences, I must say the country certainly has estab­lished itself as a font of catamaran inventiveness, in sail and power. The dominance of Robertson & Caine (Capetown) comes to mind (see “After Apartheid,” PBB No. 83; and “A Couple of Impressive Cats,” No. 119). Anton du Toit—who grew up circumnavigating with his parents for 13 years; apprenticed with Angelo Lavranos & Associates (then in South Africa, now in Auckland, New Zealand), a distinguished design firm specializing in cruising catamarans; and worked at Southern Wind Shipyard (Cape Town)—continues the tradition. In business on his own since 2001, du Toit and his team have produced a varied and noteworthy portfolio that includes a whale-watching RIB, a steam launch, a day charter cat, a high-performance powerboat, a research vessel conversion to luxury yacht, a sportfish cat, trailer-sailers, and numerous sailing catamarans.

The latest is a 75′ (23m) expedition powercat. Displacing 52,900 lbs (24,000 kg), it’s powered by twin 305-hp (228-kW) Cummins diesels. For cruising range, two scenarios were figured: passage from Cape Town to Natal, Brazil, of 3,500 nm at 8 knots, and a cruise from Durban to Mauritius of 1,600 nm at 10 knots. Du Toit: “Total fuel capacity on the vessel is 8,120 liters [2,145 gal] and considering that the fuel consumption, for both motors, at 8 knots is around 2 liters/nm [0.5 gal/nm] and at 10 knots is 3.4 liters/nm [0.9 gal/nm], these cruising ranges are well within the vessel capabilities.”

Interestingly, the client is an avid sport fisherman, and wishes to tow his 48′ (14.6m) Two Oceans Sport Fisher on “lengthy game fishing expeditions.” Du Toit says the mother ship, Quo Vadis, “has been robustly designed and built for transatlantic voyages. Hull and deck are con­structed from Saertex stitched E-glass fabrics and Ampreg 20 epoxy over Corecell M foam core; the hull outside skin is an ELT and EQX [E-glass longitudinal and transverse multi-directional fabric, and E-glass quad multi-directional fabric, respectively] over a 25mm 80 density core and EQX on the inside skin. The bridge deck is a double panel arrangement separated by shallow transverse top hats chosen for being able to allow for utilities to pass across the vessel easily. These panels are constructed from EQX skins over a 20mm core. Bulkhead panels are from EBX skins over 25mm core with cutouts capped with unidirectional carbon tape. The primary transverse beams/bulkheads have added carbon planks for additional strength and stiffness requirements. All hull, deck, and bridge deck parts are built on female plugs and then faired and painted.”

Other current projects are a 75′ sailing catamaran, another 750E expedition cat to be built by Two Oceans Marine (Cape Town) and launched midyear, a Bongers 47 (14.3m) sailing cat, a 29′ (8.8m) racing catamaran for GW Marine (Durban, South Africa), and a Carkeek 60 for Premier Composite Technologies (Dubai, United Arab Emerites).

Du Toit’s in-house team includes Sean Youldon, who is working on a Westlawn degree; interior designer Lucille Barry; and Charmaine du Toit, who helps with interior and detail design, and bookkeeping.

Du Toit Yacht Design, P.O. Box 2524, Durbanville 7551, Cape Town, South Africa, tel. (021) 975 2580, fax (021) 975 4039, website

TruDesign Nonmetallic Seacocks

Glass-reinforced nylon seacocks

Perhaps hard to believe, but TruDesign’s glass-reinforced nylon seacocks have passed flame-resistance tests.

Seacock monitorSteve D’Antonio (BOTH)

The company’s Seacock Monitor indicates whether a given valve is open or closed.

When it comes to raw-water plumbing, there are essentially two reliable material choices, bronze and internally reinforced plastics. Bronze is tried and true, rugged, long-lived, abrasion and fire resistant. It has proved itself over many years and thousands of installations, from seacocks to raw-water strainers and distribution manifolds. It has, however, one fatal weakness: it is susceptible to stray-current corrosion and in some cases galvanic corrosion as well. It’s also incompatible with aluminum and to some extent steel, and as such is typically not used on vessels whose hulls are made from those alloys.

Nonmetallic plumbing components, while not failure-free, are very attractive in that they are completely immune to corrosion and are well suited to alloy vessels as well as to harsh applications such as sanitation systems. As I walked the aisles at the Marine Equipment Trade Show in Amsterdam last November, I encountered TruDesign, a New Zealand manufacturer founded in 1974 that offers a variety of glass-reinforced nylon raw-water plumbing components, including conventional valves, sanitation system Y-valves, Y-fittings, remotely actuated electronic valves, antisiphon loops, and valve position monitors, among other items. Valve seals are Teflon and require no maintenance other than periodic cycling. Components resist fuel and most other shipboard chemicals, and they meet BV, ISO, and IMCI standards (the valves have passed flame-resistance tests), and have been independently tested for compliance.

TruDesign Plastics, 243 Ti Rakau Dr., East Tamaki, 2013 Auckland, New Zealand, tel. 0064 9 274–5792, fax 0064 9 274–6722, website

—Steve D’Antonio

Membrane Hull Skins

Low profile framingStructural Composites

The low-profile framing of this 28′ (8.5m) RIB incorporates Prisma preforms; the boat was infused at Brunswick Commercial Products in Edgewater, Florida. One result of the thin-skin low-section framing is a 40% reduction in hull and deck weight.

Scott Lewit’s Structural Composites company in Melbourne, Florida, engineers supporting structures for boats. In fact, it set up a separate sister company called COMPSYS Inc. to market Prisma preformed grid systems. But that’s not all it does: SC offers design, engineering, and prototyping capabilities for military and commercial clients (the latter includes automotive and amusement parks as well as marine). R&D is a big part of what the company does, and over the past few years it has been involved in several interesting research projects for the U.S. Navy, includ­ing development of composites to reduce noise in under­water structures, and a study of fire performance in composite materials for naval applications. We’ll briefly describe a third here: the development of a new composite construction method for certain combatant craft, such as rigid hull inflatable boats (RHIBs).

In its 2007 issuance of a Small Business Innovation Research (SBIR) award, the Navy sought two solutions: increase payload by reducing weight, and minimize the effects of wave impacts on crew, for whom, according to the Problem Statement, “Speed, acceleration, and maneuverability [are] critical to survivability and mission success.”

Zodiac Boats (Stephensville, Maryland) and SC collaborated on a solution, were funded, and completed Phase I in December 2009. Phase II, to design, test, and deliver two 7m (23′) RHIBs, was awarded in November 2010. Using COSMOS finite element analysis software, SC proposed abandoning conventional rigid hull skin and framing in favor of a shock-absorbing suspended cockpit design and hull structure that uses co-infused low-section preform framing and a single-skin composite laminate that reduces weight by more than 20%. In Phase III a 28′ (8.5m) RIB, built in collaboration with Brunswick Commercial Products, had a 40% reduction in hull and deck weight; and a 36’ (11m) RIB, built with Zodiac, had a 37% reduction in hull and deck weight by applying the same design concepts.

Lewit: “The thin-skin low-section framing arrangement allows us to reduce weight and allows the hull laminate to transition into membrane tension. We are taking advantage of the hull laminate’s in-plane properties as opposed to its out-of-plane properties. The hull laminate’s job is to transfer the load to the framing, keep the water out, and increase damping.”

In the advanced design a three-layer laminate membrane consists of 0°/90° carbon fiber to absorb most of the in-plane loads, sandwiched between two layers of Innegra HMPP that Vectorply Corp. converts to a ±45° fabric. The low-profile framing incorporates Prisma preforms from Lewit’s COMPSYS company. Because conventional gelcoat isn’t suitable for the more flexible membrane in the advanced design, a Sharkskin coating was employed. Sharkskin is an emerging technology under development at SC as a gelcoat-and-resin system; it utilizes elements of urethane chemistry to allow coatings and laminates to have much more elongation than conventional resin provides.

These shock-mitigation efforts address the same issues discussed in recent articles in PBB: “Practical Impact-Exposure Testing” in No. 142, and “Analyzing Accelera­tions,” Parts 1 and 2 in Nos. 140 and 141. SC’s range of solutions incorporates other measures beyond the skin and frame. The company proposes decoupling the RHIB cockpit from the hull framing by suspending it, and is researching how air pressure inside the cockpit structure and under the floor can mitigate shock loads.

Lewit says “We are looking into pressuring the hull-to-deck cavity to further mitigate shock loads. The hull is pressurized using an industrial blower; the concept is to have the hull pressurized prior to impact and have the pressure release during the impact event. In essence, we want to create a breathing boat that gets the wind knocked out during wave impacts, thus reducing impact load on the crew.”

The inspiration for this latter study? Lewit was collecting data aboard a test boat when it came off a wave and every drink holder popped like a cork from a champagne bottle.

Structural Composites, 7705 Technology Dr., West Melbourne, FL 32904 USA, tel. 321–951–9464, fax 321–728–9071, website The end.