About the repair of fiberglass yacht hulls
Denis Korablev
  • 15.07.2020
  • 153

About the repair of fiberglass yacht hulls

Repairing the hull or deck of a fiberglass yacht built in the 70s or 80s of the last century is not a difficult task for experienced owners. However, when it comes to relatively new ships released in the 90s of the last century and later, you have to face difficulties when you repair yourself. In the 90s of the last century, laws concerning restrictions on the content of carcinogenic volatile chemicals (VOCs) in the composition of resins, the negative influence of which were exposed to workers of yacht yards, were tightened. As a result, in order to reduce the emission of harmful VOCs, the chemical composition of resins and gelcoats was changed, which led to an improvement in the working conditions of shipbuilders and made a significant contribution to the environment. However, the use of new resins in shipbuilding and repair hid the difficulties associated with their higher technical requirements.

Polyester resins used in the construction of yachts harden and obtain the required strength only as a result of a chemical reaction that occurs after the application of the hardener. The monomer curing agent binds the long molecular chains of the resin-polymer and must be in the correct proportions to cure. Under normal conditions, undiluted resin looks like a liquid with a viscosity similar to that of honey - reliably impregnate fiberglass while it cannot, and to reduce the viscosity, a thinner was added to polyester resins of the past decades (up to the 90s) - styrene. The styrene released in the process created the “fiberglass smell” to which ship modelers and yacht workers are accustomed.

To reduce the content of styrene, which is recognized as a slightly toxic substance, dicyclopentadiene, which has a reduced viscosity, and to which only a small amount of styrene must be added to obtain a substance with an acceptable viscosity, began to be included in the resin composition. Since the 2000s, virtually all American yacht factories have been using resins with some dicyclopentadiene. And if your yacht was released in the late 90s of the last century, it is almost certain that this ingredient was included in the resin and is contained in the glass fabric of the vessel, as a result of which certain difficulties arise during its repair.


Resin with a high styrene content was widely used in the 70-80s of the last century, and if styrene did not fully react with the polymer in the production of fiberglass at the initial stage of resin curing, then later it is also included in the material ... The yachtsmen of that time are well aware of the smell of a new vessel, which was emitted by the not fully "stuck" resin in the composition of the vessel's elements. Over the long years of use of the boat, styrene should evaporate completely from the fiberglass, but this may take too long.

The presence of incompletely "embedded" resin often indicates the presence of not only structural, related to the strength of the material, but also purely external problems. Partially cured resin becomes soft when exposed to high temperature (heat from the sun), reducing the strength of the gelcoat, and in the bulk of the hull it expands more than glass fiber, forming a precipitate when cooled. As a result, a relief structure is formed on the surface, including bulges and depressions. Hulls of dark shades, which are more strongly heated by solar radiation, suffer greatly in this respect.

As the specialists 2yachts note, on high-quality yachts of recent times, you can rarely notice the bleed-through of the structure of fiberglass on the surface of the gelcoat, since during their construction there were used polymers with dicyclopentadiene and other modern components, contributing to the complete hardening of the resin over several days. These properties are ideal for achieving a visual effect, but if a secondary gluing is required on an already hardened surface, this creates additional difficulties.

Secondary lamination of “new” fiberglass plastics is provided only by the adhesion of the resin to a chemically inert surface and the creation of a single polymer block does not occur, but only bonding to the depth of a layer of several molecules. But when performing this operation with fiberglass of the old type (smelling of styrene), there will be no difficulties, since the new laminate forms a single polymer compound (many times stronger) with not fully "stuck" plastic, capable of continuing chemical reactions.

For this reason, modern shipbuilders must consider this property of resins containing dicyclopentadiene. When building new yachts, they have only a few days in stock, during which the resin has not "stood up" and it is possible to obtain a monolithic composite material by attaching glass elements to each other or laminating overlay layers. During such a short period, the elements of the internal and power set of the body must be installed in their places and attached. At the same time, even an insignificant level of natural UV radiation on a sunny day can be enough to shorten this time "window" from 3-4 days to several hours.

Problem detection

You can independently identify problems with secondary lamination of the yacht - for this, it is enough to inspect along the attachment lines by gluing and laminating with a "wet" corner of frames, stringers, flora and equipment foundations. You can find out the location of damage and poor-quality connection by tapping the places you are interested in with a hammer and listening to the sound - the usual is a booming and dense knock, if an unusual, muffled or “empty” knock occurs, these areas should be noted as problematic.

Examine carefully the areas of delaminated glass material, the surfaces of the dispersed adhesive joints - if they are rough, with protruding fiberglass hairs, then you should not worry too much about the quality of the joints. However, if the surfaces are smooth and shiny, this indicates serious problems with secondary lamination at the yacht yard and a possible unreliable connection to the hull of all elements of the power set. Please note that testing to determine the content of dicyclopentadiene in hull materials will require contacting a specialized laboratory and may be costly.

Material selection

The selection of glass material for secondary lamination is carried out most carefully - taking into account the weight, type and orientation of fiberglass threads during laying. It will be good if you can get your yacht's original laminate coating scheme from the shipbuilder. Many modern (especially high-speed) yachts have sophisticated fiberglass laying schemes, and then the materials must be selected adequately to the factory specification. It will not be difficult to pick up glass mats and fiberglass, difficulties arise with identifying the density of materials. But what to do if there is no certainty in the direction in which the layers of material were laid during the construction of the ship? In this case, a "burnout test" will be required, which will give a value for the density of the material and its orientation in the sample. However, retrieving the sample for testing will incur additional costs - they will be required to seal the hole left after cutting it, and also to send the sample to the laboratory and wait for a response.

A prerequisite for the successful repair of a fiberglass yacht is also the correct choice (in accordance with the factory requirements) of resin and hardener, as well as a much smaller amount of gelcoat. It will require the use of protective equipment - disposable painting overalls, respirators with reliable filters against glass dust, goggles for working with power grinding tools and dust gloves to protect the hands. Preparations for repairs should also include the purchase of a thermometer to control the air temperature, beakers or laboratory scales for dosing resin components and tight skirts for organizing the supply of warm air using a heating hair dryer when the temperature drops or there is a danger of increasing humidity above normal ... Only after the above preparations can you safely proceed to repair work.

If you are interested in yacht charter in your chosen area of the world - you can always contact the managers of the 2yachts company, specialists will select acceptable offers at the most affordable prices in accordance with your preferences.