If you own a rotomolded polyethylene plastic kayak, you may very well have some dents in the bottom of your kayak hull. The hull area under the cockpit is generally the broadest and flattest part of the kayak and therefore, the most prone to these kinds of deformities. Luckily, most of these dents really have very little effect on the performance of your kayak (in spite of what you may have heard). Unless your kayak has a hull deformity that causes the keel line to curve left or right, your boat will paddle more or less like it is supposed to. Any increase in drag will be minimal and most likely not noticeable. The scratches in your hull will probably create more noticeable drag.
However, if you just don’t like the way your kayak looks with that big dent in the bottom, you can generally remove it pretty easily. You will need a hair dryer, and possibly some heavy rocks or something else that can be used as weights.
I could kick myself for not taking a “before” photo of the dent in the hull of the used 2003 Perception Eclipse that I just bought. It was a rental boat at a local store and had been stored improperly on racks made of 2×4’s for about 7 years. The bottom of the hull under the forward part of the cockpit looked like someone had been trying to fold the boat in half from front to back. Between the rather severe looking hull deformity and a missing rudder rest on the back, I got a really good deal on the price of the boat.
I first set the boat on a couple of foam saddles with the saddles positioned directly below the bulkheads. The dents usually do not form under the bulkheads because the foam inside the boat helps the kayak to hold its shape in those areas. I used a hand-held hair dryer to apply warmth to the area of the dent in order to soften the plastic. Do not be tempted to use a heat gun to do this step. The high temperatures of a heat gun can quickly melt and damage the plastic of the kayak. If you don’t have a hair dryer, you can also try pouring hot water onto the plastic to warm it.
After a few minutes of blowing hot air onto the area of the dent, I was able to start pushing the dent out with my hand. I put my hand inside the cockpit and pushed down on the center of the dent. The warm plastic allowed me to push the hull back into its original shape. If you have a dent that has only been in the boat for a short time, this may be all you have to do. Just keep pushing the dent out while the plastic cools, and your kayak will be good as new. In my case, the deformity had been there for many years, so to make sure that it retained its new shape instead of reverting to the indentation, I placed a large stone inside the cockpit and left it there for a few days. I occasionally returned with the hair dryer to warm the plastic again and make sure that I was pushing the dent out as far as I could. Finally, I removed the stone and the dent is pretty much gone.
There is still a slight deformity to the hull, but it is so small that it really doesn’t affect the performance of the kayak at all. I used the kayak today in a physical education class that I was teaching at a local high school. I put the empty kayak in the water and gave it a shove to float it across the pool. The tracking was arrow straight and there was enough glide to get it from the shallow end of the pool all the way across to the deep end with very little effort.
If you are looking for a used kayak to save some money, don’t be afraid to buy a boat just because it has some indentations on the hull. Washboarding on the bottom of the hull will be harder to remove, but it has very little effect on the performance of the kayak, so I wouldn’t worry about it. And if you see one or two large indentations, you can easily remove those with the technique I have just described. I actually prefer to buy older plastic kayaks because much of the hardware on those boats is more substantial than that found on newer boats. If you are comfortable with the minor repairs needed, you can get some terrific deals on these older kayaks and end up with a great boat!