In this episode of the Bayliner Bowrider 175 restoration, we are tackling a critical but often overlooked safety component: the expanding foam. If you are doing a floor-up restoration like “Big Dreams, Part 1,” you can’t just slap wood down and call it a day.
Here is the breakdown of why we use this stuff and how to apply it without creating a structural mess.
The Problem: Structural Integrity and Buoyancy
When we ripped the old floor out, we found the original foam was waterlogged and heavy.
- Waterlogged Foam: Over time, water gets into the hull and turns the factory foam into a heavy, moldy sponge. This adds hundreds of pounds of “dead weight” to the boat and rots your stringers from the inside out.
- Structural Support: The foam isn’t just for flotation; it supports the floorboards. Without it, your new marine plywood will flex and eventually crack under your feet.
The Solution: 2-Part Expanding Urethane Foam
We are using a 2-part expanding foam system. This stuff is a chemical reaction—you mix equal parts of Side A and Side B, and within seconds, it expands to 30 times its liquid volume.
The Chris Does What Technique:
- Clean the “Channels”: Before pouring, ensure the hull sections are bone dry and free of debris. Any moisture trapped under the new foam will just start the rot cycle all over again.
- The Pour: We pour the mixture into the cavities between the stringers. You have to work fast because once it starts to kick, it moves like lava.
- Trimming for the Floor: Once the foam cures (it becomes rock hard), you have to use a saw or a large rasp to level it off perfectly with the top of the stringers. This ensures your new floor sits flat and is fully supported across its entire surface area.
Why Not Leave it Empty?
Some people ask why we don’t just leave the cavities empty for extra storage. While we are leaving a few central sections open for skis and life jackets, filling the outer “pockets” is non-negotiable for safety. If you ever take a wave over the bow or spring a leak, this foam provides the positive buoyancy that keeps the boat from heading to the bottom of the lake.
The Result
The hull is now rock solid. There’s no “echo” when you tap on the sides, and the structural base is ready to receive the new marine plywood floor. We are one step closer to getting this Bayliner back on the water!
Watch the foam expansion in action here: Installing Expanding Foam in the Hull EP #15