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All hulls need to be built with rigidity and support. However, this can be achieved by using a method that leads to hull corrosion, or by using a method that PREVENTS hull corrosion.
Method #1: Creates Hull Corrosion
The least expensive method of providing the needed rigidity and support is by installing only the longitudinals and then spraying the hull with polyurethane foam that then hardens. The only problem with this method (and trust me, it can be a huge problem) is that polyurethane absorbs water rather than allowing it to drain out.
When water is absorbed by polyurethane, the two components react together to cause corrosion inside the hull which can then lead to HUGE repair bills. As well, since the foam absorbs water, it becomes heavier over time. This causes the deck to sit lower, and will then require a bigger engine to drive the boat, thus consuming more fuel.
By now you're probably thinking that there shouldn't be any water inside the hull. Ideally, there shouldn't be; however, we live in the real world where water always manages to find a way into areas it shouldn't. A couple of ways it does this is through condensation, and seepage through mounting holes.
Method #2: Prevents Hull Corrosion
The proper and best way of outfitting a hull is with both longitudinals and ribs (see diagram 1). This provides the hull with the rigidity and support it requires, and then polystyrene is added to comply with Transport Canada Regulations. Since the polystyrene is cut and fit into the hull rather than sprayed in, any water that may get into the hull is free to drain down to the water tight inspection hatch.
In this way, the hull is kept safe from corrosion so it can be used for many years without worry.
At Ironwood Boats, we believe in quality craftsmanship WITHOUT compromise. Thus, you'll only see longitudinals and ribs in our boats, and no sign of polyurethane! As well, for safety reasons, all Ironwood Boats are outfitted with polystyrene, even those greater than 20 feet in length.
If you have any question about the above, please feel free to contact us at (604) 520-0014.