smoothing up plastic?

I have an old Walden Scout - roto-molded polyethylene - with a very scratched up bottom. What is the best way to smooth it up? I’m just trying to see how fast I can get it to go.

Just paddle it and forget the scratches

– Last Updated: Mar-10-13 10:00 AM EST –

Seriously, trying to make a scratched plastic boat look better is a waste of time, as it's only going to get scratched up again when you use it. It's just the nature of the material; it's soft and scratches easily. If there are lots of "whiskers" on the hull, you can take them off with a sharp scraper so they don't catch on anything.

Yes, it's possible to use heat to smooth the surface, but with polyethylene, there's a fine line between "Ah,that looks better" and "I JUST MELTED A HOLE IN MY BOAT!" I respectfully suggest that you don't go there. It's a significant risk with little reward. Poly' boats are meant to be used an abused, so go have some fun with it. You don't see the hull when you're paddling, anyway.

Short, wide boats with large cockpits like the Scout are not designed for speed, they're meant for meandering and exploring quiet waters at a moderate pace (hence the name "Scout"). The design is what limits the top speed (look up "wavemaking resistance"), not the scratches on the hull. Even a world-class kayak racer is not going to be able to exceed its design limitations.

Not trying to make it look better (well maybe, but that’s a different issue), just go faster.

We cross-posted
I added something about speed in my original post.

Smoother & Faster
How fast do you think you can make it og, what is your baseline ?

I doubt seriously you could even get a 10% performance increase, and then you reach a to smoothe variable where it actually slows down.

Speed is in the paddler
Get a better forward stroke, it’ll do far more to get speed than trying to smooth up a boat like that. But as bnystrom said, you can’t do a lot about a boat’s design speed, and the Scout is slow compared to boats with thinner profiles to the water.

Run it up on a sandy beach a few times
every now and then.

That is what I do with my old poly Eclipse.

Jack L

Here is what I was told.
A couple of years ago a fellow stopped by the launch area and chatted for awhile about kayaks. He said he worked at a factory that builds polyethylene kayaks. Then he told me how they fix little surface flaws that often happen in the process. He said they pour lighter fluid on the flaw and light it. I guess when it smooths out they quickly extinguish the flame–he didn’t say how, but I assume maybe they just blow it out. I’m not sure I believe the guy and I’ve never been tempted to try it.

One of my poly boats came with a couple of minor scuffs on the bottom and one day as I was doing some finishing on a wood project, I noticed that the water-based urethane I got on my fingers was quite durable and not that easy to get off. I decided to see how well it would stick to polyethylene. First I used a wax remover on the boat’s hull and then gave it a coat of urethane. The scuffed spots disappeared and the hull shined like a new penny. Over time, the urethane has peeled off in a couple of areas, but it only takes a few minutes to fix it.

He can stretch it to go faster. Trimmit
and it will go slower. };-)>

I used a Teflon coated tacking iron to
smooth rough and deeply scratched areas on a kayak. But I did it more out of curiosity than any expectation of increased speed.

Attainable Speed

– Last Updated: Mar-11-13 9:24 AM EST –

There are two ways to look at speed. One is maximum attainable speed, and the other has more to do with effort needed to make the boat go at "normal" speed. Charlie Wilson has posted numerous times citing research by some famous canoe designer (I can't remember the name) that quantifies to what degree a badly scratched hull contributes to drag, and I seem to recall it's like 15 percent of the total. If that's the case, or something similar, a smooth hull would be noticeably easier to propel. I've noticed that every time the "scratched plastic kayak" topic comes up, everyone says scratches don't affect speed. Who's right? I'm betting on Charlie Wilson.

With that in mind, I don't doubt that a really scratched-up hull will have noticeably more resistance at typical cruising speed than a non-scratched hull, BUT, with a boat that's only 12 feet long, you'll be able to get it up to hull speed with just moderate effort unless it's a really bad hull to begin with. Once you reach hull speed, the boat is "trapped" within its own wake and the resistance to pushing the boat farther into its bow wave and making the stern "squat" deeply into the water eats up far more of your effort than hull scratches ever could. No matter what you do, you will NOT make it go more faster than hull speed unless you exponentially increase your paddling power. Even then, you'll probably only gain another couple tenths of a MPH and the effort will not be sustainable.

What's your goal, to cruise comfortably with a tad less effort or to increase your maximum speed? If you want a faster top speed, you need a longer boat.

Thanks for all the input
I appreciate all the advice. I am working on the paddle stroke - getting out whenever I can (yesterday I did 4.39 miles in 1:05) and I realize that’s a big part. I also recognize that the boat is going to be limited by design, but I’m interested in seeing what it can do (trying to bloom where I’m planted). After years of canoeing, this is my first kayak, so I didn’t really know what I was getting when I bought it. I did discover that shaving the worst plastic hairs, and then hand-sanding the scratches with 150# did make the worst areas feel a lot smoother to my hands. The ends were so bad, it looked like the previous owner dragged it through gravel parking lots on a regular basis. I’m trying to learn what I want in the next boat, but in the meantime, I’ll make the most of this one.

Mostly a waste of time

Put your effort into your technique and strengthening your core. If the scratches and such add resistance, that just adds a little resistance for you (not much).

If you can video yourself on a smooth lake, look to minimize the extraneous motions that aren’t propelling you forward (such as exaggerating rocking side to side). Watch your posture and compare your strokes to competitive racers. Upgrade gear, rinse and repeat.