Fiberglass Boat Construction: Techniques And Challenges

Every modern boat builder has their own unique approach and process to manufacturing vessels. Some boat builders use a fiberglass chopper gun to help build a hull while others just say no. Perhaps the biggest dividing line in the boat-building world centers around the chopper gun, which feeds strands of fiberglass, Kevlar or carbon fiber roving through a device, chops it into manageable pieces, mixes it with resin and catalysts and allows the operator to spray it into a mold to build up what will become the boat’s hull.

Many builders swear by it, while others eschew its use and instead, hand-lay layers of carefully cut sheets of woven roving fiberglass cloth down and wet it with resin. In both processes, workers use small rollers to make the material lay flat and eliminate any bubbles that might form. Those using a vacuum process to deliver the resin skip this step since the vacuum squeezes any bubbles out.

The Human Error Factor

Operating a chopper gun is not a job a builder would give to a new-hire. Typically, its operator is one of the most skilled workers in the factory for a good reason. If the chopped mix is applied too thin, the hull is weaker and subsequent layers of woven roving can “print-through” or show up under the gelcoat, which is usually one of the first things sprayed into the hull mold as boat hulls are build from the outside in. If the chop mixture is sprayed on too thick, the hull will weigh too much and can adversely affect handling and performance.

Who Uses Chop in the Layup?

Manufacturers who produce large numbers of boats love the chopper gun because it’s a fast way to apply fiberglass and resin in one step. This isn’t just done on entry-level boats either. High-end builders like Sea Ray, Everglades, Malibu and Ranger, to name a few, all use chop in varying degrees.

Everglades Boats, founded by the late Bob Daugherty, an industry-innovator best known for his decades-long work at Boston Whaler, pioneered a unique boat-building process called RAMCAP. Instead of the usual method of pumping liquid foam into voids after the deck is in place for flotation and acoustical dampening, Everglades creates precision foam components in their own molds and places them on top of a wet bed of fiberglass chop that is sprayed evenly into the mold.

The foam they use weights a hefty 6 pounds per cubic foot instead of the more common 2-pound material typically used and becomes an integral part of the hull’s structure. The chopper gun is then used to seal it and bond fiberglass to the foam. The deck cap is then put on and is put under vacuum for 24 hours, creating a one-piece hull that is incredibly strong.
Builders like Sea-Ray, Ranger and Malibu use the chopper gun to lay down the first layer of fiberglass to avoid the pattern of woven roving from showing under the layer of gelcoat.

Resin And Hardening Agents

Subsequent layers of woven roving cloth are laid into place and impregnated with resin and hardening agents to build up the hull to its desired thickness. Additional layers of chop can be added in addition to coring material to build up the desired thickness of a hull. Chop is easier to apply in areas like corners and intricate contours in the mold. Hand-laid cloth is typically cut by an automated CNC machine to exacting standards and in the aforementioned hard-to-cover spots, workers can sometimes have too much overlap, wrinkled fabric or not enough coverage, which necessitates a patch.

To make sure the proper amount of chop is being delivered, manufacturers like Sea Ray have a digital display that shows the weight of the chop that is being dispensed to allow the operator to meter it to the correct specifications for that particular hull.

Vacuum Infusion Technology In Boat Building

Some companies handle the issue of woven roving print-through differently. At Bonadeo Boatworks, a custom manufacturer of outboard-powered fishing boats like its flagship 45, the entire hull is hand-laid with woven roving but for the skin coat, they use chopped mat that comes in a wide roll and is laid out by hand. It’s produced and sold by the weight per square foot for use in different applications.

According to Tony Bonadeo, “We love it because the material goes on nice and even.” Bonadeo uses the resin-infusion technique for his hulls and larger parts where all the laminates are laid out dry, bagged and put under vacuum. The resin is then pulled through the fiberglass and other laminates like Kevlar and carbon fiber. “This process gives the laminate a better resin-to-cloth ratio,” said Bonadeo. “This makes it lighter and stronger. It does require more forethought and is more expensive but the results are worth it.”

Ken Clinton at Intrepid Powerboats explains their fiberglass boat building process.

Above: Ken Clinton at Intrepid Powerboats explains their fiberglass boat building process. Photo:, Factory Fridays.

The Intrepid Way: High-End Custom Boat Building

Another high-end builder of custom boats that uses the hand-laid, vacuum-infused resin technique is Intrepid Powerboats, known for its no-compromise approach to boatbuilding. “We started doing it more than 20 years ago,” said Intrepid president Ken Clinton, “and it offers many benefits over the traditional hand-laying process. The problem with the way we used to do it is when you would apply the resin, any excess had nowhere to go; a boat hull is like a bowl and it just sits there. Now, we lightly glue each piece of cloth — that’s cut and labeled by our Eastman machine — and put it in place. Then, we bag it, put it under vacuum and the resin is pulled through. With this process, if there’s any excess, it gets removed by the vacuum.”

Hand-Laid Fiberglass Issues

Hand-laid hulls aren’t without their potential issues either, according to Clinton. “It is important that you train your teams to be consistent when it comes to the technique of laying all the material. You must not use too much glue between the layers, watch your overlaps, and be careful with how you wrap your cloth around some of the tougher shapes in your tooling.”

Another concern with the vacuum-infusion technique, according to Clinton, is the results are hard to inspect properly afterward. “Once the infusion is complete, you only have a visual inspection possible for anything above the core that is facing you. Anything under the core has no way of being seen because of the gel-coated surface on the other side. That is what caused me to go the way of an infrared inspection. By heating the part and viewing it with the infrared camera, it allows you to see the different densities cooling at different rates. If there is dry cloth that did not get wet under the core you will be able to see it with the camera because it is less dense and cools at a different rate, therefore, allowing you to know that there is an issue.”

The one takeaway is that to build a quality fiberglass boat you need great employees and companies that pay their staff well. Creating a good work environment and instilling a culture of excellence gives builders a huge leg-up on the competition, no matter which techniques they employ.

Written by: Alan Jones

Alan Jones is a marine journalist who has tested more than a thousand boats and written more than 500 boat reviews and video walkthroughs online, including fishing boats, cruisers, PWC, pontoons and ski boats. If it floats, he's tested it. One of his passions is testing new products that make boating easier and safer. Currently the president of Boating Writers International, Alan is a gearhead who's tested almost every engine that's come out in the last 20 years. He also loves fishing of all kinds.


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