This is a question that a lot of people ask when they go into a kayak/canoe shop and are looking at different boats made out of different materials. The most common answer I hear is that the toughest boats are made out of plastic. Most questions like these can't be answered quickly and definitively. The problem with the question is the word "tough". I think we need a follow up question:
What kind of Abuse?
One of my rep buddies, Kurt Renner, taught me that there are really several types of Abuse that can happen to our boat. After 30 years of repping I'd think he would have seen every way a boat could break. Come to think of it just a couple of years ago he had a semi-truck drive through a Kevlar canoe on the trailer. 4 Types of Abuse from most common to least.
1. UV Abuse--Sun kills everything...but it is oh so nice!
2. Abrasion--My papa always taught me to get my ankles wet when landing a boat but abrasion is pretty hard to avoid over the life of your boat. I like to just choose my scratches instead of scratching everything I come across. Hard to avoid abrasion if you are running rivers or surfing.
3. Glancing Impact--This is the type of abuse that most commonly happens while moving your boat on and off the car. There is not a ton of force behind this but certain materials can react poorly to a "glancing impact".
4. Loaded Impact--Force and Impact mean Ouch! This is the type of shot that is more common in river running and rough water. Your gear, weight, and momentum combine to cause loaded impact and this might not be as common but it can cause a lot of damage.
So, which materials hold up best to each type of abuse (listed from best to least)?
1. UV--Composite boats, made of glass or kevlar and resin, should have the longest life span in regard to UV abuse. We all know of sailboats and motor boats that are several decades old and still on the water. Thermal Formed boats, made of acrylic capped ABS, will not deform in the sun and should last 10-15 years. Thermal formed boats will not reform unless the surface temperature reaches 185 F or above. This doesn't happen on our planet so a Thermal Formed boat should keep its shape over time. RotoMolded Poly boats can deform at 130 F surface temp. Put some weight on the boat (ie racking or suspending) and this molding temp decreases even more. The term is "oil canning" and it is common. Over the long haul a rotomolded boat will lose it shape. One thing to note is that all materials will lose their ability to flex over time with exposure to UV. A hit that would be just a bounce in the early life of a boat can eventually could cause more damage as UV degrages the flexular modulus of the material.
The best thing you can do is cover and protect your boat using 303 UV protectant and/or Danuu Canoe and Kayak Covers.
2. Abrasion--Thermal Formed boats which have an acrylic cap seem to have the hardest outer skin. Gel coat on composite boats come in second. Finally, Rotomolded Poly is the softest and most likely to lose material when scratched. When eddyline had both composite boats and thermal formed boats I can remember several times that I had composite boats strapped against thermal formed boats. The gel coat from the composites would scratch off onto the Carbonlite boats. The good news on abrasion with composite and thermal formed boats is that is can easily be tended too. It is much more difficult, if not impossible, to fill in Poly boats but there is a new repair material out there that might help. http://www.crgindustries.com/recrepair.htm
3. Glancing Impact--Rotomolded Plastic bounces, Thermal Formed can bounce pretty well too but if hit on very sharp surfaces they can fracture. Composite boats can bounce but you may have gel coat repairs and fractures with sharp objects.
4. Loaded Impact--Rotomolded Plastic, Tie for second place Thermo Form and Composite. Poly really wins the battle and this is why it is preferred for WW and Surf Zone. Thermal formed and composite boats can fracture but the good news is that these are both repairable too. But if you are going to spend a lot of time slamming into objects with momentum you might want to think plastic or get ready to do repairs.