Why Bonded Acrylic Boat Windows Leak — The Engineering Explanation #boatwindows

In this video I explain why saloon window leaks on the Bavaria 37 Cruiser (Farr design) are not simply a sealing failure, but a predictable result of thermal expansion mismatch and constrained movement. Large smoke-grey acrylic windows absorb far more solar energy than the surrounding white GRP coachroof. Under normal day–night conditions this produces several millimetres of differential movement across a 2.3 m window span. Traditional mastic or polyurethane bonding systems are too rigid to accommodate this repeated shear and peel loading and will inevitably fatigue and fail. Drawing on façade engineering principles, I break down: • how thermal expansion and solar loading actually affect acrylic and GRP • why mastic-only bonding has a limited service life • how compliant bonding using 3M VHB structural tape accommodates movement • why a low-modulus silicone edge seal is better suited for weatherproofing • and how external solar shading can significantly reduce thermal stress This approach aligns the glazing detail with the real mechanical and thermal behaviour of the materials, resulting in a far more durable solution. If you’re dealing with recurring window leaks, surveying one of these boats, or planning a long-term fix, this explanation is based on engineering fundamentals — not trial and error. 00:00 Introduction 02:40 “I Can’t Stand the Rain Against My Windows” 05:30 Thermal expansion explained Sail Safe Guys, Ant & Cid XX 🇬🇧 ⛵️⛵️⛵️⛵️⛵️⛵️⛵️⛵️ Perspex supplier: https://wholesalepos.com/search/results,1-24?keyword=Cast+Acrylic+&x=13&y=15&limitstart=0&option=com_virtuemart&view=category&virtuemart_category_id=0&Itemid=346 =================================================== 👋 We’re Ant & Cid aboard SV Impavidus – two adventurers sailing full-time since 2018. From stormy crossings to quiet anchorages (and plenty of dad jokes), we share family-friendly stories of life at sea 🌊 🎥 New episodes every Sunday – honest & safe for all ages. 📌 Links 🛒 Shop https://www.svimpavidus.com/general-5 💻 Website https://www.svimpavidus.com/ 👌 Patreon https://www.patreon.com/SVImpavidus 🍻 Buy us a beer https://www.paypal.com/paypalme/svimpavidus 😎 Facebook https://www.facebook.com/impavidus.ontheboat.5 ▶️ Playlists https://www.youtube.com/@SVImpavidus/playlists 🌱 Our Philosophy We live by a “Pay It Forward” ethos – where those taught become teachers, and goodwill multiplies. 🙏 📣 Sponsors & Contact We’re currently looking for sponsors to support our video production 🎥 📩 Email impavidussailing@gmail.com 📺 Our Second Channel 🎶 Stunning drone footage + eclectic music YOUR DRONE TV https://www.youtube.com/channel/UCqYQUohmJ3yLq1zeRd9s3wg