Mar 19

Mar 19 Material Innovation: Composites

In the boat world there has been a slow but steady adoption of new technology when it comes to building boats. Wood, once the go to structural material in many different applications has been replaced by different types of composite materials. In general, there has been a quest, particularly in performance and race boats, to build things lighter and stronger. Over time, materials once reserved for race boats or high end custom boats made their way to more mainstream builders. In this article, we are were fortunate enough to ask Jean Pierre Mouligne, from Gurit, a global leader in composite materials, some questions about some of their marine products. We talk about a new breakthrough technology that is very exciting for builders, some features and benefits of modern core materials as well as their application.

Gurit was founded in Switzerland in 1835, and over the course of time has continuously been involved in designing and producing advanced materials for a host of industries, including marine, aerospace, automotive medical and other advanced manufacturing; as well as offering engineering services, design, tooling and components. It was about 30 years ago Gurit made an impact in the marine industry with advanced core materials for race boats, and now is one of the leaders in materials for many marine manufacturers of all types of boats. Jean Pierre is a senior account manager with a wealth of experience in this area. We really appreciate his time and expertise here.

What is the biggest change in fiberglass materials, resins, laminating techniques or core material that has made an impact on how boats are built now compared to maybe 20 years ago?

The biggest impact in the last 20 years has been the introduction of the infusion process. In the infusion process the resin is drawn under vacuum into the laminate as opposed to being laminated by hand. The main advantage of the infusion process from a manufacturer stand point is that it reduces styrene emission considerably. From a customer stand point, an infused laminate will have better fiber compaction and no voids so no potential for water to penetrate into the gaps often left over in the coring process.
Today almost all boat production manufacturers use the infusion process in some parts of their process and the technology is still growing

How closely does Gurit work with marine manufacturers on structural testing and the lamination process in general?

We offer structural testing of laminates in our lab in Canada and the UK. It is sometime required by builders which need to meet certain specifications or to make sure that they get best properties out of laminates. Gurit produces a wide range of composite products and we offer technical support as part of our service.

Did the concept of coring, sandwich structures come from airplane construction?

Yes, according to Bob Lacovera from Convergent composites, the first composite sandwich application was the WWII British lightweight bomber “Mosquito” which use wood skins over a balsa core. Quickly after the war, boat builders adopted the sandwich construction in applications where weight was at a premium.

Although Balsa is still used as a light core, what is the advantage of going to full synthetic closed cell composites, like Corecell™ or a PVC core material?

Balsa is technically not a composite but a natural honeycomb. If you look at balsa under a microscope you will notice long tiny cells that run all the way through the core. These cells carry the nutrients from the roots to the leaves. The big breakthrough in balsa came in the sixties when Baltek corp came up with the idea of cutting balsa across the grain so that the cells would be vertical. This increased compressive strength and prevented water from migrating across.
The problem with balsa is that even if water cannot travel across its grain (otherwise “trees would leak” as the old saying goes) it still relies on having a perfectly sealed laminate with no voids which is virtually impossible. Additionally, In order to make balsa conformable, manufacturers most often offer balsa wood in a format called “countourscrim” This is a combination where small blocks of balsa are held with a polyester scrim which leaves path for water migration if the laminate is punctured or not sealed properly like around through hull fittings or deck hardware.

So the plus of balsa wood are:
Low cost
High compressive and shear strength
The minuses are:
Heavy compared to foam core (10 pounds per cubic foot versus 5 pounds per cubic foot typically)
Will absorb water and rot over time if laminate is breached even in very small ways

In general, If you were advising a small performance boat company on materials, what kind of lay up, and materials would you recommend that balance strength, weight and cost?

This is a difficult question but the general consensus for a production performance boat would be:
Infusion process (better than hand layup)
Knitted fabrics (better than woven roving and mat)
Vinyl ester resin (better than Polyester)
PVC core or Corecell™ core (better than balsa but more expensive)

For structural areas, particularly the transom, shear strength and compression strength are often brought up. Wood is often thought to have good compression strength, and quite good shear strength. With outboard engines being heavier than they used to be and big boats running multiple engines on brackets levering the weight far aft of the transom, how do you contend with those strength requirements and how do modern materials compare to marine plywood here?

It is true that shear and compressive strength are the most important core properties to consider in a transom application. That said, plywood is excellent in both categories. The problem with plywood is that it is heavy at about 600 kgs per m3 versus 300 kgs for typical high density foam and the bigger problem is that it absorbs water when exposed to it and it will rot quite quickly.
If you are replacing plywood with foam in a transom, especially one that has large OB engines, careful consideration must be given to the load path and it is sometime best to invest in a composite engineer to review the design and advise on the type of core and reinforcements needed to meet the requirements.

For restorations, that seem to be getting more popular especially for classic performance boats, where do some of the composite products fit in as far as replacing wood, and re-coring?

It all depends on what kind of restoration you are doing. One of the most common composite repair on old sailboats is to replace rotten balsa in the deck. This is best done using foam core such as PVC (usually 80 kgs per cubic meter density is adequate.) Most important is to use epoxy resin to do the repair and not the cheaper polyester resin. Epoxy has much better adhesive properties especially in areas that are not totally dry.

Gurit Corecell™ comes in different densities and properties for different applications.

Transoms and stringers are often wood and need replacing, how would you address the transom and stringers with new materials on a quality restoration?

We recommend using high density core to replace wood in transoms and stringers. It will not absorb water and provide good compressive and shear properties.

A new core on the market is called PET foam (Polyethelene Teraphalate). This is a thermoplastic based material with good properties and low cost. This material is quickly being adopted and is replacing balsa in many marine applications. Gurit is one of only two companies in the world to offer a 100% recycled PET core called Kerdyn™. It takes 200 small plastic bottles to make one sheet of 1’’ thick 4ft x 8ft Kerdyn™! We think that the idea of using plastic bottles in the deck of a boat is a lot nicer concept than seeing the bottles floating around the bay.

Afterword

As a follow up, Jean Pierre and I talked about how smaller manufacturers can now benefit from new products like PET and Kerdyn™ by utilizing a composite that is inline with the price of marine woods, while being easier to laminate, better for the environment and outperforming wood materials over time. The biggest challenges for some small builders is the man hours and labor of laying up the boat using the infusion process and or vacuum bagging the hull. The key part of the process is the bonding of the core material to the skin layer. It is critical to get that bond perfect. The infusion process is ideal for the ultimate strength to weight, and eliminating voids; while a hand laid vacuum bagged hull is more common for small builders, it is also labor intensive as bonding is best accomplished with a wet layer bonding the core, as opposed to a dry layer.

For DIY repairs and or projects, you always want to consult or have a professional do the structural work if you are unfamiliar with it, but the good news is that the costs now make these materials accessible to small projects. Using high density composite boards instead of plywood and following some basic principles, a restoration can be lighter and stronger than new. You can use clamps and other means of applying pressure to the materials instead of the vacuum process and get great results.

Again, this is intended to provide an overview of some new and exciting products, as well as some processes used in modern boat building. Gurit works with many of the top builders in the industry, all over the world. If you’re not familiar with fiberglass, resins and laminates, find a professional to help you on your project. If you’re a builder, contact Gurit to talk about their products and engineering services to help you deliver the best product possible.