Epoxycraft
Menu
  • Home
  • About
  • Epoxy Basics
  • How To
    • DIY
    • Artists
    • Board Sports
    • Woodworking
    • Boat Building
  • Trade Secrets
  • Projects
    • DIY
    • Artists
    • Board Sports
    • Woodworking
    • Boat Building
    • Motorsport
    • Aviation
    • Architecture
  • Meet The Maker
  • News
  • Contribute
  • Contact

Projects: Building an 18th century gajeta – Part 2
18th December 2018

Building an 18th century gajeta – Part 2

Part 2: Applying the skin

In a remarkable project that combines traditional boatbuilding skills with modern techniques, a Croatian Gajetareceives its primary wooden framework, cut by computer and bonded with WEST SYSTEM® epoxy.

With the plywood formers for the 7m (21ft) fishing boat assembled at the Betina Shipyard in Croatia (see part 1) the task of attaching the timber frames could begin. The process of creating the structure to ‘form’ the hull is usually known as ‘lofting.’

“As the whole boat was modeled in a 3D programme, this data could be sent to a CNC (computer numerical control) cutter for creating precision components,” said the project’s naval architect, Srdan Dokovic. “Some parts, like the frames, were first bonded together using thickened WEST SYSTEM epoxy to make a strong, shaped piece of timber. This was then trimmed into the required dimensions by CNC.”

At the Betina Shipyard team, the whole project was assembled like ‘a giant Lego set’ as Srdan puts it.

“Every part of the structure was a perfect fit with the next one,” he explained. “Everything on the boat was bonded with epoxy to reduce the amount of metal fasteners required and we laminated several interior components this way as well. With computer modelling, we were able to minimise the amount of mistakes and the CNC machine also gives a big reduction in assembly time. The result is a much lighter, stronger and faster gajeta with minimal waste in man-hours and materials.”

Assembling the frames:

The plywood formers outline the shape the hull will take. Note the spacers between them that will prevent the uprights from leaning out of shape.

Laminating the inner keel with WEST SYSTEM epoxy. In days of old, joiners had to find the bough of a tree where the grain ran into a curve that suited the shape of the keel. Now bending several thin layers of timber against metal formers and bonding the layers together with thickened epoxy can achieve an even better effect. Note the clever design of the metal frame that allows for an infinite variety of curves.

As the keel and frames will be on display, wooden wedges between the clamps and the timber prevent circular indentations being formed but care has to be taken to ensure the wedges are not accidentally bonded into the project! Note the electronic sensor, which is showing the time, temperature and humidity. The higher the temperature, the quicker the bond will cure. Beyond around 20°C, it is better to use a slower hardener to lengthen assembly time.

Building a boat with epoxy resin - images of mix

The project used WEST SYSTEM 105 Resinwith 205 Fast Hardenerin the colder months and 206 Slow Hardenerin the warmer months. (Boat builders in the Tropics often use 209 Extra Slow Hardenerto deal with excessive heat and humidity.) Accuracy when mixing the resin and hardener in its 5:1 resin to hardener ratio guarantees a highly dependable bond. Here the components are being measured by volume…

:..but they can also be measured – or double-checked – by weight. The weight ratio is close, at 5: 1 (5 parts resin to 1 part 205 hardener). Some builders prefer to use digital scales throughout the project for a more precise calibration, especially if mixing very small quantities.

The inner keel was made from two laminates, port and starboard, which were then laid over each other and cut as one. The CNC machine has introduced a camber into both sides at the stem so the planks will butt up against a flat surface when they are fitted.

At the same time, smaller supports are assembled as opposing pieces, with the final CNC trim ensuring that they are perfectly symmetrical. Traditional boat builders can achieve near accuracy but rarely match the perfection available from a machine that can cut to tolerances of 1/100th of an inch.

The cut and shaped halves are bonded together with thickened WEST SYSTEM epoxy and then the complete unit is dropped into its precut notches in the plywood formers. Note the perfect fit, especially where the prow is cut horizontally.

Building a boat with epoxy resin

A close up of the forefoot profile. Note the number of laminations involved, which allows a thick piece of keel to be made that has incredible strength without excessive weight. The epoxy also serves to protect the laminates against water ingress, achieving a very long lasting structure.

The next job is to make the two inner stringers, one for each side. These will create the curved ‘wishbone – shaped’ longitudinal support against which the floorboards will rest. We’ve jumped ahead in this image to show you how it sits inside the hull. It is an important part of the structure, so has to be strong and accurately made.

From the computer drawings, the exact position of the stringer is known, so notches are measured and cut into the formers. These are lined with duct tape to aid release of the subsequent epoxy work. Strips of cedar are then bonded to each other and attached by screws through stainless steel washers to backing batons. (Although it looks like a series of silver-rimmed holes in the wood, close inspection reveals that the screws are black!) The screws and washers have all been waxed to aid removal.

A second layer of planks is overlaid on the first and held in place by reusing the waxed screws and washers that held the first layer. The second and third layers are laid onto the partially cured “green” epoxy. Wet onto wet bonding achieves a strong chemical bond.

After the third layer has been attached, the thickened epoxy is allowed to fully cure and is then sanded in situ. This will flat back any runs or raised patches. Note how the shape has been achieved by progressively re-clamping the stringer to batons screwed into the plywood formers. No need for protectors here – any indentations will be hidden in the final build.

Here is the port stringer, ready for final sanding and finishing. Note the permanent twist achieved by the lamination process and the number of strips used – three across and five down. This has made a very strong structure that will not warp and lose its shape, thanks to the rigidity achieved by the thickened epoxy.

Note: The adhesive is a mix of WEST SYSTEM 105 Resinwith 205 Hardenerand 403 Microfibres Adhesive Filler. This filler is added at a ratio of between 4% to 16% by weight, depending on the thickness required. Alternatively, adding 406 Colloidal Silicainto a 105/205epoxy mix makes an equally powerful adhesive. The ratio required of the 406 Filleris between 3% to 8% by weight.

Next time: Adding the planks, and making some more frames.

Primary bonding relies on chemical linking of adhesive layers such as the wet lay-up of fibreglass laminate in a mould. All the layers of adhesive cure together in a single fused layer. Epoxy applied over partially cured epoxy will chemically link with it to form a primary bond. The ability to chemically link diminishes as the previous layer of epoxy cures and the bond becomes a secondary bond.


Share on


Back to projects

Subscribe to our newsletter
Our unique epoxy knowledge and experience, delivered straight to you

Events

Southampton Boat Show 16th -25th September 2022
METSTRADE 15th - 17th November 2022

What is epoxy?

Epoxy Projects

Hydroplane Part 2

  • 20th July 2022
Read More

Working With Epoxy In Warm Weather

  • 15th July 2022
Read More

Multi-Mission M-Class by Ultimate Boats

  • 15th June 2022
Read More
1234567
1234567
  • Home
  • Epoxy Basics
  • Projects
    • DIY
    • Artists
    • Board Sports
    • Woodworking
    • Boat Building
    • Motorsport
    • Architecture
    • Aviation
  • Trade Secrets
  • How To
    • DIY
    • Artists
    • Board Sports
    • Boat Building
    • Woodworking
  • News
  • Privacy Policy
  • Contribute
  • Contact
West System
Pro-Set
Entropy Resins
Subscribe to our newsletter
Copyright © 2022 Epoxycraft | Website by MAA
We use cookies on our website to give you the most relevant experience by remembering your preferences and repeat visits. By clicking “Accept All”, you consent to the use of ALL the cookies. However, you may visit "Cookie Settings" to provide a controlled consent.
Cookie SettingsAccept All
Manage consent

Privacy Overview

This website uses cookies to improve your experience while you navigate through the website. Out of these, the cookies that are categorized as necessary are stored on your browser as they are essential for the working of basic functionalities of the website. We also use third-party cookies that help us analyze and understand how you use this website. These cookies will be stored in your browser only with your consent. You also have the option to opt-out of these cookies. But opting out of some of these cookies may affect your browsing experience.
Necessary
Always Enabled
Necessary cookies are absolutely essential for the website to function properly. This category only includes cookies that ensures basic functionalities and security features of the website. These cookies do not store any personal information.
Functional
Functional cookies help to perform certain functionalities like sharing the content of the website on social media platforms, collect feedbacks, and other third-party features.
CookieDurationDescription
bcookie2 yearsLinkedIn sets this cookie from LinkedIn share buttons and ad tags to recognize browser ID.
langsessionThis cookie is used to store the language preferences of a user to serve up content in that stored language the next time user visit the website.
lidc1 dayLinkedIn sets the lidc cookie to facilitate data center selection.
Performance
Performance cookies are used to understand and analyze the key performance indexes of the website which helps in delivering a better user experience for the visitors.
Analytics
Analytical cookies are used to understand how visitors interact with the website. These cookies help provide information on metrics the number of visitors, bounce rate, traffic source, etc.
CookieDurationDescription
_ga2 yearsThe _ga cookie, installed by Google Analytics, calculates visitor, session and campaign data and also keeps track of site usage for the site's analytics report. The cookie stores information anonymously and assigns a randomly generated number to recognize unique visitors.
_ga_91ZH5F88XM2 yearsThis cookie is installed by Google Analytics.
_gat_gtag_UA_103456315_31 minuteThis cookie is set by Google and is used to distinguish users.
_gid1 dayInstalled by Google Analytics, _gid cookie stores information on how visitors use a website, while also creating an analytics report of the website's performance. Some of the data that are collected include the number of visitors, their source, and the pages they visit anonymously.
CONSENT16 years 3 months 20 days 13 hours 3 minutesThese cookies are set via embedded youtube-videos. They register anonymous statistical data on for example how many times the video is displayed and what settings are used for playback.No sensitive data is collected unless you log in to your google account, in that case your choices are linked with your account, for example if you click “like” on a video.
Advertisement
Advertisement cookies are used to provide visitors with relevant ads and marketing campaigns. These cookies track visitors across websites and collect information to provide customized ads.
CookieDurationDescription
_fbp3 monthsThis cookie is set by Facebook to display advertisements when either on Facebook or on a digital platform powered by Facebook advertising, after visiting the website.
bscookie2 yearsThis cookie is a browser ID cookie set by Linked share Buttons and ad tags.
fr3 monthsFacebook sets this cookie to show relevant advertisements to users by tracking user behaviour across the web, on sites that have Facebook pixel or Facebook social plugin.
IDE1 year 24 daysGoogle DoubleClick IDE cookies are used to store information about how the user uses the website to present them with relevant ads and according to the user profile.
test_cookie15 minutesThe test_cookie is set by doubleclick.net and is used to determine if the user's browser supports cookies.
VISITOR_INFO1_LIVE5 months 27 daysA cookie set by YouTube to measure bandwidth that determines whether the user gets the new or old player interface.
YSCsessionYSC cookie is set by Youtube and is used to track the views of embedded videos on Youtube pages.
yt-remote-connected-devicesneverYouTube sets this cookie to store the video preferences of the user using embedded YouTube video.
yt-remote-device-idneverYouTube sets this cookie to store the video preferences of the user using embedded YouTube video.
Others
Other uncategorized cookies are those that are being analyzed and have not been classified into a category as yet.
CookieDurationDescription
AnalyticsSyncHistory1 monthNo description
cookielawinfo-checkbox-functional1 yearThe cookie is set by GDPR cookie consent to record the user consent for the cookies in the category "Functional".
li_gc2 yearsNo description
pvc_visits_11[0]1 dayNo description
UserMatchHistory1 monthLinkedin - Used to track visitors on multiple websites, in order to present relevant advertisement based on the visitor's preferences.
SAVE & ACCEPT
Powered by CookieYes Logo