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BOAT BUILDING NEWS
Hi fellow boatbuilder, this is the start of our on-line FIBERGLASS BOAT BUILDING NEWS that is updated on a regular basis. We can only share with you a fraction of the information included in our BOAT BUILDING STUDY PLANS & Complete BOAT PLANS & PATTERN packages. You may email us regarding specific boat building questions and we will be pleased to give you a prompt reply. In the meantime ...good boat building ....from us all at Bruce Roberts. Please email me your comments on our site....criticisms as well as other comments please.
There are many & varied methods of fiberglass boat building, we will try and explain each method in sufficient detail to enable you to make a decision as to which boat building method is best suited to your requirements. In general round bilge hulls such as sail boats are best built over a batten mold & power boats are usually but not always built in a female mold. We have developed a 'cheap one-off mold' fiberglass boat building system that is ideal for building larger powerboats.
BUILDING THE EZI-BUILD FEMALE MOULD
First we will look at the female mould method. Back in the early 1960’s, we were designing fishing trawlers that could be built of fibreglass using inexpensive one-off or limited production moulds. With the current rise in the number of people interested in power boats and the acceptance of chine hulls in general, we decided to simplify and streamline our original methods to make them suitable for one-off production by amateur and professional builders.
When looking at these techniques, we were developing a new range of power boat designs using the latest CAD software so that these designs did not involve difficult curves but instead were easily assembled in simple one-off moulds. These new designs all reflected the ability of the computer to produce absolutely fair, developable hull surfaces suitable for turning flat sheets of fiberglass into attractive hulls. Most of the original designs were directed towards steel or aluminium but the demand for similar fiberglass methods led us to develop computer lofted hulls with full developable surfaces and the result is the Ezi-Build technique.
MAKING THE FRAMES “EZI-BUILD”
Build the hull frames in a way that provides an outer framework to support the whole mould structure details of which should be in your plan. In designs under 32 feet [10 metres], the bottom of the support structure can be canted 45 degrees which will enable the whole structure to be tilted, side to side, for easy lamination. On larger hulls, it is advisable to hang scaffolding inside the hull structure to support planks for working from.
|INSTALLING THE BATTENS
This is how your mold will look in profile. Not all battens are shown for sake of clarity,
|FINISHING THE MOULD
Here we see the mold set up ready to receive the laminates. Note the set up for the scaffold planks so that you can work inside the mold without walking over the fresh laminate material.
The plans have much more detail than can be included here.
Ideally, you should use a clear isothalic NPG gelcoat and back it up with a layer of surface tissue and vinyl ester resin. This is important so see your resin supplier about getting the right materials if you want to be sure of increased resistance to water permeation and avoid any possibility of osmosis, at a later date. You will need two or three helpers as you start to lay up the hull and it is advisable, for temperature control, to be at the same stage of lamination each day with each successive layer. If the laminate overheats from applying too much material at one time, it may cause distortion and pre-release from the mould.
Once the gelcoat and first layer of mat are in place you will have passed the most critical stage of your laminating process. Providing you follow some form of temperature control, you should go on to complete the laminate without any problems. As mentioned earlier, always finish your laminating at the same part of your hull each day. Three willing workers can lay up a fifty foot [15 metres] hull in a few days. Two layers of fibreglass per day, one mat and one roving, is a reasonable amount to install at one go without causing the laminate to overheat. New resins are being formulated all the time so you must have the latest technical data and support from your materials supplier.
The number of layers of mat and roving required will be shown in your plans. After the layers that cover the whole hull surfaces are completed, you will most likely be required to install extra layers in the areas of the keel and below the hull waterline. Most laminate schedules call for overlapping and or interleaving the various layers in the areas such as the chine and keel, thus building up extra strength where it is required.
Again, we remind you to trim the sheerline of your hull each day. This will usually be done as work progresses and about an hour after the final layer for the day has been installed. Once you have installed the basic laminate and any extra layers called for in your plan laminate schedule, you should add any stringers, sole shelf, deck shelf etc and any other reinforcing members called for in your plans.
You should then install all the ribs, stringers, bulkheads and web floors before you remove the hull from the mould. After you have completed the installing of the stringers and ribs etc and if you do not plan to use the mould again, you may prefer to remove only the mould above the chine or water line, leaving the bottom section to act as a cradle.
Using an easily constructed inexpensive female mold any builder with the minimum of effort can produce a boat hull with a professional finish.
For panel construction, the system of building the female frames and setting them up on a set of bedlogs, is similar to the methods used when building an Ezi-build mould. Only a few battens are required to hold the frames square and vertical. The technique of setting up the basic framework to hold the fibreglass panels is similar to the first stages of building the Ezi-build mould. The fewer battens required and the absence of a mould lining material, are the main differences between the Ezi-build and the Panel methods.
Additional bracing is used on the outside of the frame assembly and once the frames and the few battens are installed, the mould is ready for the fibreglass panels. The success of the Panel method depends upon the builder obtaining accurate information such as computer generated full size patterns for the frames and either patterns or computer lofted offsets for the panels. We have successfully used this method when designing power catamarans and out builders report excellent results using the technique.
|SETTING UP FOR PANEL
See the way that frames are erected to receive the pre-laminated panels. These drawings are from our Power Cat plans. The plans have considerable detail on setting up the building frames etc.
You will need two laminating surfaces for panel construction - one will be the flat table as described above the other will be a convex table shown on left which is used to laminate decks and cabin tops.
Once the panels are laminated they are laid inside the framework and joined together. The method of making each panel is quite simple, providing you have accurate patterns or offsets for each panel. Using masking tape, mark out the shape of each panel on the laminating table and lay up the required laminate to form one panel. If you are using a core material, it should be installed while the laminate is on the table. Consider which way the panel will need to bend, if any, when it is laid in the mould, before installing the core on your laminate. Depending which brand you are using, cores often take a bend better in one direction than another. Usually only outer laminate and the core are installed while the panel is on the table.
Some deck parts, cabin sides, cabin tops and other areas of your boat can have both sides the sandwich laminated while the panel is still on the table. This is only recommended in areas where there is a minimum bend required to place the panel in its final location. Installing the interior laminate, stiffeners, if required, and bulkheads etc., follow similar methods to those used in other fibreglass hulls.
THERE IS LOTS MORE AND IT IS IN ALL THE PLANS THAT ARE DESIGNED TO BE BUILT USING THE TECHNIQUES OUTLINED ABOVE.
FOAM and BALSA
The most common one-off boat building technique is the Foam or Balsa Sandwich building method which involves the use of a frame and batten mold over which is laid either semi-rigid PVC foam core or balsa sheets that are sewn into the mold. The outer skin is laid up over this. The foam core comes in varying thickness, usually 4 ft x 2 ft x 3/4" / 1.2 m x .6 m and the 3/4" / 15 mm is used for boats up to say 45ft / 13.7 m LOA. The foam is now more widely used for boat hulls and we have found it easier to use and provided you choose the correct grades it will provide the basis for a long lasting hull.
The balsa comes in approximately 2" square blocks which are glued onto a scrim to make up 1’6" x 3’ panels. The balsa is quite flexible and lays around most compound curves without giving too unfair a surface. In general balsa is limited to use above the water line although we do extend the balsa down to the cabin sole & cheaper urethane foam is used below the waterline during the laying up stage. The urethane foam is later removed from the inside to give a single skin area below the cabin sole and down into the keel where the web floors will be bonded in after the hull is externally complete.
Balsa sandwich is more widely used in powerboats ( flat surfaces make it easier to install in those areas ) and for sailboat hulls we do prefer the foam sandwich. Balsa is widely used for sandwich deck construction.
Balsa sandwich generally is made up in 3/8", ½" or ¾" thickness. It can also be two layers of 3/8" with a layer of chopped strand mat between the layers of balsa. This double balsa technique provides an extremely strong and stiff hull, however, the technique is a little more expensive than using the single layer of balsa. The inner skin on a balsa sandwich vessel usually is one third of the thickness of the outer skin. Balanced laminates can be used but we feel that the extra laminate on the outside is required to provide the necessary impact strength. Although a balanced laminate of 50% of the weight of the inner and outer skins would give a better structural result, one has to think of the impact strength as this is quite an important matter with a cruising vessel.
The first step is building the batten mold. How to is described step by step in the plans. The materials for the mold are quite inexpensive and second hand timbers are ideal for this purpose. If your lucky someone nearby will be inspired by your efforts and purchase the mold of you when you're finished to build his own boat allowing you to recover some of your costs. When the mold is finished the foam or balsa is attached via stitching , toggling or nailing. The outer laminations of fiberglass and resin, as per the specification in your plan, are then applied. The hull, with the mold inside, is then rolled over and set up in a suitable cradle after which the mold is then lifted out of the hull and once again recycled as internal fittest material or sold to another builder.
After the hull shell has been trued up and the sheer line faired with battens the next stage is to cut channels through the core in certain stress areas. These areas are shown clearly in the plans. Reinforcing strips of extra fiberglass are laid in these areas attaching to the outer skin. The whole of the interior is now laminated with the inner layers of fiberglass. Bulkheads and solid floors are now installed as per the plans. You can how proceed to start on the interior fit-out.
For FOAM CORE supplies (similar to AIREX)
|Here we see the
construction of the hull male mold which consists of frames cut using the
full size patterns supplied with the plans plus the addition of timber
battens, C-flex fiberglass and shows the first layers of fiberglass
|This illustration shows the male hull mold covered with either thin pre-laminated fiberglass strips or inexpensive plywood or hard-board followed by the inner fiberglass laminate, next either foam or balsa core and finally the outer layers of fiberglass. Note the area of the keel is not cored but has additional fiberglass laminate to provide maximum strength in this area.|
On the left we see the C-Flex
Fiberglass being installed on a hull mold as described above. Similar
methods are used to install core material such as Corecell or Airex foam.
On the left we see hull rolled over to the upright position and then the mold is lifted out of the hull shell. The mold is sometimes removed in one piece as shown here or in parts depending on the shape of the hull and the method used to laminate the hull.
|Here we see the construction of the deck and cabin male mold which consists of deck and cabin top frames and battens covered with either with either thin pre-laminated fiberglass strips or thin inexpensive plywood or hard-board followed by the inner fiberglass laminate, either foam or balsa core is then installed and finally the outer layers of fiberglass are laminated in place.|
SINGLE SKIN over a BATTEN MOLD
This technique entails the use of a batten mold for which the full size patterns for each frame are supplied with the construction drawing. Upon building the frame of the mold 1 ½"x 5/8" battens fairly closely spaced are laid up over them. To this a cheap rigid polyurethane foam, pre-laminated fiberglass strips, Masonite or melamine covered plywood is lain on and the complete outer laminate of the Fiberglass is laid over this former. It is possible that with the battens placed closer together than normal, plastic sheeting can then be stapled over the mold and the fiberglass laminates laid directly onto this. The hull is then turned up the right way and, if foam is used, it is now removed .In some of the smaller boats it is possible to put channels in the cheap foam and use a modified type of sandwich construction. This only applies in vessels up to 24’. In other cases it may be possible to have enough thickness in the outer skin so that stringers or reinforcements will be unnecessary. Bulkheads, furniture and the floors, will give adequate framing without the addition of ribs or stringers. This construction is generally limited to vessels up to 40’ in length. With the addition of stringers and ribs a vessel of up to 100 feet may be built using this technique. The deck and superstructure can be built using Bruce Roberts 'Panel technique' ( see Bruce's book 'BOATBUILDING') or other fiberglass construction methods
C-Flex fiberglass planking has been developed to make it possible to build a fiberglass boat without a traditional mold. All that is needed is a lightweight framework. In some the bulkheads and other frames which are usually fitted in the boat later can be used as part of the framework that you build the boat over.
This combination of rigid rods held together loosely, with pliable areas in between, is what makes C-Flex unique in construction materials. In our knowledge, it is the only self-supporting material available today which will conform to compound curves without having to be stretched or deformed in some way. Furthermore, C-Flex will bend sideways, a property which virtually eliminates the problem of having to fit or spile the ‘planks’. Most boats can be built by starting the first ‘plank’ parallel to the sheer line then butting the next ‘plank’ right alongside all the way to the keel.
Aside from the obvious advantage of being able to build an all fiberglass boat without a mold, C-Flex also affords the designer and builder the opportunity to save weight over a conventional fiberglass laminate without sacrificing strength.
This is because C-Flex is an unidirectional reinforced material and is considerably stronger in the direction of its fiber orientation (lengthwise) than an ordinary fiberglass mat or woven roving laminate. This property is used to save weight in the hull shell by running the C-Flex along the lines of anticipated greatest stress (usually fore and aft).
The weight savings also translate into a cost savings. Even though the C-Flex itself costs more per pound than mat or woven roving, the completed hull shell will cost about the same as a hull built with just mat and woven roving. The advantages of being able to build without a mold and the weight savings are a bonus. Contact: firstname.lastname@example.org
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