Foam vertical strip planking... the very latest procedure, and the next major step.

Ian Farrier has kindly allowed us to publish an extract from his study site methods page. The F-boat study book has been on my bedside table for quite some time and contains a wealth of information for any amateur builder considering building in foam. At $15 the downloadable PDF version is a real bargain whether you are considering building one of Ian's plans or not. The study site has larger versions and more photos than published here.
Tony

It came about from using foam fore and aft strips, which gets very tiresome, there being so many strips to cut, edge glue and fit. It was suddenly realized that much wider and shorter strips could be used simply by turning them around and running them vertically. The more ductile foam core makes such a vertical orientation possible, and the strips can be held in place and very fair by temporary fore and aft battens. The vertical foam strips (or panels in some areas) are considerably easier to handle and fit, and the female form frame mold system also makes it very simple to hold them in place, as access is easy from both sides. Not only were the hulls lighter, but they were fairer, with significantly fewer joins, easier to laminate, and much quicker to build.

But better still, one also does not have to buy thicker foam in order to allow for the extensive fairing required with fore and aft strips to take out all the little flats, as is recommended by some promoters of fore and aft stripping methods.


Henny van Oortmarssen's F-39 float being vertically foam stripped. The small pieces of wood are used to screw/hold strips against battens, until screws can be fitted from behind - makes it easy to plank hulls single-handed


The battens do take a little longer to setup, but no longer than say the first 10 to 15% of the numerous strips required for the more traditional fore and aft wood stripping. Fewer more widely spaced form frames can also be used. The relatively few battens are then just quickly laid in wherever they want to go, or as needed, and from then on the much fewer/wider vertical strips are considerably quicker and easier to apply.


An F-9A hull half having the vertical foam strips applied. In this case the foam is being held in place by screws through the stringers from the outside. This eliminates the need to crawl inside a hull framework and working blind as with the male molds traditionally used for 'one off' foam core construction.

Hull strips can vary in width from around 8 to 12" (200 - 300mm) by around 6 - 7' (1.8 - 2.2m) long. Fore and aft strips will be 32' (10m) long by around 1 1/2 - 2" (40 - 50mm ) wide and will require over 800' of join line! Over four times as much edge fitting and gluing required in fact.


An F-41 outer hull half being built with vertical foam strips. The large foam deck and cabin side panels are also being initially held in place by temporary screws and ply pieces from inner side until join glue sets. Quick and easy. Screws are then added from back for laminating, the original screws being removed. There are more screws this way but overall it can work out faster and easier than just using screws from behind

There is actually around 3000 less lineal feet (915m) of glue join line required with a foam vertical stripped 41 footer, and every foot of these joins has to be carefully fitted and glued. It doesn't take much math to work out the considerable extra work and weight with over 1/2 mile (1 km) more of glue line to be done.


F-9A foamed hull, with the screws on the outside to hold foam in place being visible


An F-33 main hull, fully foamed, laminated, and with bulkheads starting to be fitted.

Once all foam is in place, the inside of the hull is laminated, using either epoxy or polyester/vinylester resins as desired (epoxy only with wood). Bulkheads are then made from full size patterns and fitted, which is very easy to do at this stage, eliminating difficult fitting later. Hull is then removed for exterior glassing once resin has cured. Form frames are then simply reversed, and battens re-positioned to build the other hull half.

Advantages over the old male mold method of foam core construction include all the holding screws being on the outside for access (no awkward crawling inside a mold) and stiffening bulkheads are already there when hull is removed from the form frames. This makes the partly finished hull rigid and easier to handle, a major problem with the traditional foam system being the hard to handle ‘floppy’ hulls that are produced.

The vertical foam stripping system has now been used on many F-Series designs with excellent results, and has become the recommended, and designer's preferred method.

The final word has to be from a builder, and probably the best qualified is Australia's Dean Snow, from Geelong, Victoria, who has built three Farrier designs (F-9A, F-82R and F-9R), and is one of the few to have practical experience with both types of stripping. He used fore and aft wood stripping for the F-9A and then vertical foam stripping for the F-82R and F-9R. Dean considers vertical foam stripping to be much faster and says "A float half in wood stripping used to take days with all the fiddly strips, lots of messy glue, and edge pins. With foam it's a fast moving, no mess, low stress job (on both form frames and builder) - a foam float half ready to glass takes less than a day."

Ian Farrier
www.f-boat.com
Christchurch, New Zealand, June 2006

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