AME Unit 5 Q3

Osmosis is the spontaneous net movement of solvent molecules through a selectively permeable membrane from a region of high water potential (region of lower solute concentration) to a region of low water potential (region of higher solute concentration).  

1. www.slideshare.net

2. Osmosis – Wikipedia

3. en.wikipedia.org

In simpler terms, it’s the movement of water from an area of low solute concentration to an area of high solute concentration through a barrier that allows water to pass through but not the solute.  

1. what is osmosis? (video) – Khan Academy

Example: If you separate pure water from salt water with a semi-permeable membrane, water molecules will move from the pure water side to the salt water side to try to dilute the salt concentration.

Osmosis in the context of GRP (Glass Reinforced Plastic) hulls refers to the process where water molecules penetrate the laminate and accumulate within the material, causing blistering and delamination.

The Process

1. Water Absorption: Water molecules, smaller than the resin molecules, can penetrate the GRP laminate, especially if there are voids or imperfections.
2. Salt Concentration: Seawater contains salts that act as solutes. The higher concentration of salts inside the hull compared to seawater creates a concentration gradient.
3. Water Migration: To equalize the concentration, water molecules move from the seawater into the GRP laminate.
4. Blister Formation: The trapped water forms blisters as it accumulates, causing the laminate to delaminate.

Opens in a new windowmoisturemeters.com.au

Factors Affecting Osmosis:

• Resin Quality: Low-quality resins with higher porosity are more susceptible to water ingress.
• Laminate Quality: The presence of voids, delaminations, or other defects can accelerate osmosis.
• Environmental Conditions: High humidity and temperature can increase the rate of water absorption.
• Hull Design: Inadequate ventilation can trap moisture within the hull.

To prevent osmosis, modern GRP hulls use high-quality resins with added barriers, proper laminate design, and ventilation systems.

Disclaimer: While it’s possible to treat a single blister, it’s essential to remember that a single blister might be an indicator of a larger underlying issue. A thorough inspection of the hull is recommended.

Here’s a basic approach to treating a single blister:

1. Preparation:
   • Clean the area around the blister with a mild detergent to remove dirt and grime.
   • Dry the area completely.   1. How To: Fiberglass Blister Repair | Bilbo’s Marine bilbosmarine.com
2. Opening the Blister:
   • Carefully open the blister using a sharp blade or a Dremel tool.
   • Remove any loose debris or delaminated material.
3. Drying:
   • Allow the area to dry completely. Moisture trapped inside can hinder the repair.   1. How To: Fiberglass Blister Repair | Bilbo’s Marine bilbosmarine.com
4. Filling:
   • Use a marine-grade epoxy resin to fill the cavity. Ensure the epoxy is mixed according to the manufacturer’s instructions.   1. How To: Fiberglass Blister Repair | Bilbo’s Marine bilbosmarine.com
   • Apply the epoxy in layers, allowing each layer to cure before adding the next.
   • Fair the repaired area to match the surrounding hull shape.   1. How To: Fiberglass Blister Repair | Bilbo’s Marine bilbosmarine.com
5. Finishing:
   • Once the epoxy is fully cured, sand the repaired area smooth and apply a primer and topcoat to match the existing hull finish.

Important Considerations:

Safety Equipment: Wear appropriate protective gear, including gloves, mask, and eye protection.

Underlying Cause: Treating a single blister might mask a more significant osmosis problem. Consider having a professional marine surveyor inspect the hull.

Material Selection: Use high-quality marine-grade epoxy resin specifically designed for hull repairs.

Ventilation: Ensure proper ventilation when working with resins.   1. Is Epoxy Safe? The Ultimate Guide to Resin Safety! promiseepoxy.com