I think I recall reading somewhere that going from poly to composite, fiberglass in same model kayak that the gain would only be about 1% to 2% in speed with the same effort. I was thinking of replacing my 17’ Tempest with a fiberglass or composite kayak but if the gain is only 2% it isn’t worth it as weight isn’t an issue. Any thoughts about the validity of 1% to 2% gain in speed/ efficiency (less effort to maintain same speed as poly)?
scratches and such degrade performance much more… The material is ergo not important. What is an issue is the mold… Is the same mold used for both fiberglass and poly hulls? There is sometimes a difference
Composite hulls can be molded to have much finer lines and a sharper water entry. They are also typically stiffer so they flex less which can result in an improvement in efficiency. How much you will benefit from these advantages will vary from one model to another and will depend on how hard you push the boat.
Stroke mechanics will make a bigger difference in speed than materials used to make the boat, IMO. So in that respect, a couple of lessons to fine tune your stroke would potentially make a bigger difference, and cost a lot less. If you like the boat you have, and aren’t interested in a different design even if you replace it, then I’d say it’s not worth it. But as kayamedic said, there can often be differences in the overall shape of the hull for the same design, due to the fact that poly cannot be molded to match a lot of designs that composites can be shaped to…
The best way to know what you think is to try one of each material, and decide for yourself.
If you’re really interested in switching boats, why not look around at different designs while you are at it. Not to say there is anything wrong with the Tempest, but there are plenty of other boats to consider.
Here’s some to look at: NC Expedition, NC Quest, Valley Nordkapp, Valley Etain, Current Designs Prada, Stellar Intrepid, Current Designs Caribou, P&H Cetus and Tiderace Excape.
I have had all types of kayaks. In a nutshell: Poly if you’re planning on hitting things, fiberglass if you want a better design with more speed, carbon fiber and kevlar if speed and light carry is what you want. Professional inflatable if you want to do a lot of traveling with your kayak.
Lighter, stiffer boats will move faster. They will transfer power more efficiently and ramp up to max cruising speed faster from a dead stop.
Not sure about what incremental difference it makes, but when your top cruising speed is 5.7 mph, 1-2 % actually is significant, especially if you are touring over long distances.
A few other things will come with it:
They will be a touch less stable.
Will also be a bit easier to roll and maneuver.
Now, I’ll insert my opinion: If you’re not racing or planning to paddle across Antarctica, dragging your boat behind you, and also don’t have money to burn, I’d stick with a good poly boat.
Cheaper, less to worry about and tough. They get the job done for a 1/3 of the price.
Thanks for all the responses. Perhaps I wasn’t all that clear about poly vs fiberglass re speed/efficiency.
My 1st kayak is a Perception Expression which is 15’ X 24" which I average a little over 4mph at 58 to 60 strokes/minute. Based on reviews and reputation I purchased a Tempest (17’ X22") off craigslist. I thought the Tempest would be quite a bit faster considering WL length, streamline hull etc. I was wrong. I average the same mph with the Tempest as the Expression. My conclusion based on info from this forum is that the hull speed of the Tempest is indeed faster than the Expression but this 79 year old engine is down more than a couple of cylinders. Also maybe loaded weight 200 lbs (me and gear) is too light to take advantage of the Tempest potential.
There are quite a few used high quality fiberglass kayaks for sale on craigslist that would meet my objective but since I cannot try them out before purchase I’ll probably stick with the Expression
Again thanks for the feedback.
I’m envious of anyone who is 79 and still getting it done whether on all cylinders, or not. More power to ya.
Is the waterline length of the Tempest actually longer than the expression?
Is the waterline width of the Expression actually wider than the Tempest at your load weight?
Often the waterline measurements aren’t as different as the overall measurements might lead one to believe.
If you compare two completely different hull designs, factors such as cross-section contour, prismatic coefficient, and waterline dimensions are going to have much greater impact than the material composition.
Both the Tempest and the Expression have bow and stern stems that are quite “proud” sticking well out past the waterline length. But the Tempest more-so. The waterline length of the Tempest is probably substantially less than 2’ greater than that of the Expression.
The so-called “maximum theoretical speed” of a hull is dependent only on waterline length. But few paddlers apart from racers routinely paddle their canoes or kayaks up to “maximum hull speed”, let alone above it. Maximum theoretical hull speed is not some absolute speed limit, but as this speed is approached and exceeded, drag increases dramatically and much greater effort is required to achieve very little additional speed. Longer boats always have greater theoretical maximum hull speed, but they usually also have more skin friction, so a shorter boat may actually have less drag and be easier to paddle at the “cruising” speed that most paddlers go at, which is usually well below maximum theoretical hull speed.
Maximum theoretical hull speed in knots is the square root of the waterline length (in feet) x 1.34. Assuming the waterline length of your Expression is 15", maximum hull speed is 5.19 knots, or just under 6 mph. If the waterline length of your Tempest is 15.5’, its maximum hull speed would be 5.28 knots, or just under 6.1 mph. So if you are averaging 4 mph, you are going at a respectable flat water pace, but well under theoretical maximum hull speed in either case.
@pblanc said:
Longer boats always have greater theoretical maximum hull speed, but they usually also have more skin friction, so a shorter boat may actually have less drag and be easier to paddle at the “cruising” speed that most paddlers go at, which is usually well below maximum theoretical hull speed.
My understanding was that all things otherwise equal, the shorter boat will sprint up to speed faster than the longer boat from a stop, but the longer boat will hold it’s cruising speed better. Skin friction initially holds the speed back and and then begins to work for the paddler.
Frictional resistance is always working against the paddler and gets worse with increasing velocity. For those who are interested in the finer points of hull design, John Winters is worthwhile reading. Take a look especially at the three part “The Shape of the Canoe” on this page (the same factors hold true for kayaks, obviously):
@Mountainpaddler said:
My understanding was that all things otherwise equal, the shorter boat will sprint up to speed faster than the longer boat from a stop, but the longer boat will hold it’s cruising speed better. Skin friction initially holds the speed back and and then begins to work for the paddler.
Skin friction never “works for the paddler”. Skin friction is always a detriment and it is always at work resisting your forward progress. But what limits speed even more than skin friction, once you are moving fast enough for it to matter, is the exponential increase in resistance due to wave-making that occurs with increasing speed. With longer boats, that drastic increase in wave resistance with increasing speed occurs at a higher speed than it does with shorter boats, just as Pete summarized.
Also, to say that a longer boat “holds its cruising speed better” misses those two main points related in Pete’s earlier post. For one thing, if cruising speed is based on paddling effort, a shorter boat will hold its cruising speed just as well, since both boats are simply moving at whatever speed a certain amount of propulsive effort will make them go, and at their respective speeds, the propulsive force is exactly counterbalanced by resistance in the opposite direction. Beyond that direct comparison in terms of effort, things likely get too complicated to explain with any kind of oversimplification based only on length in the way you tried to do. What you might be considering in this case, based on observation, is that if you put forth the extra effort needed to make a long boat cruise faster than the practical cruising speed of a shorter boat, the boat will glide farther once you stop paddling simply because it is going faster to start with, not because it glides more easily at speeds well below that where wave-making resistance is dominant. It’s simply a case of the longer boat gliding for a time before it slows to the speed the shorter boat would have been going, so that adds time and distance to the overall glide. Just keep in mind that for similar boats, the skin friction of the longer boat is always greater when compared at identical speeds. One way to think of it is that the rate of deceleration when coasting (which unfortunately is not constant across all speeds, but let’s generalize) is a completely independent aspect of glide compared to initial speed. Both affect glide, but in entirely different ways, which confuses the issue of cause and effect when comparing boats of different length.
I think in essence we are saying the same thing.
You’re right, I think I used the term skin friction in the wrong form.; and by cruising speed I mean a generally fast speed. Not a sprint, but a pretty good clip which will require effort–say 7 mph or so on flat water. Maybe this is where we are defining it differently.
So when you mention the longer “glide” of the longer boat, doesn’t that in effect mean that the boat is holding speed? It seems like when we paddle we are basically repetitively pushing or lifting the boat forward with each stroke, allowing it to glide while we reset our stroke and then repeat.
I generally paddle two boats and use Motionize tracking analytics for efficiency.
I have a K1 sprint boat that is 17 X 15.3/4
and surfski that is 21.2 X 17.0
Between the two, getting the K1 off the line faster than the ski is easier due to the overall increased wetted surface of the ski. But letting the boat run when up at speed goes to the ski. My stroke rate is a bit lower on the ski at the same speed as the K1.
21.2 x 17? Sounds like the Think Uno Max.
@Mountainpaddler said:
I think in essence we are saying the same thing.
You’re right, I think I used the term skin friction in the wrong form.; and by cruising speed I mean a generally fast speed. Not a sprint, but a pretty good clip which will require effort–say 7 mph or so on flat water. Maybe this is where we are defining it differently.
Yes, that clears that up. No disagreement there.
So when you mention the longer “glide” of the longer boat, doesn’t that in effect mean that the boat is holding speed? It seems like when we paddle we are basically repetitively pushing or lifting the boat forward with each stroke, allowing it to glide while we reset our stroke and then repeat.
Not necessarily. It’s very possible that with greater skin friction going on, the deceleration between strokes would be more abrupt with the longer boat than with the shorter one (in fact, nothing else even makes sense), but you don’t really perceive that to be the case since even at the end of the glide between strokes, the speed is still faster than that of the shorter boat. Just making up numbers to illustrate what I’m getting at, maybe the long boat loses 0.5 mph of speed between strokes but the shorter one only loses 0.2, but if the longer boat is going 6 mph and the shorter boat is going 5 mph, the longer boat still “seems” to have better glide since it’s faster at all times, even though in reality the glide efficiency is worse. As another example, a car with lightly dragging brakes that’s going 50 mph will coast farther and faster while you take your foot off the gas for ten seconds than is the case for another car going 40 mph even if there’s no brake friction going on at all. In this case, the slower car definitely coasts more efficiently since there obviously is less drag, but because of the speed difference, there’s no way the driver would ever be able to tell.
Of course, you bring up the subject of surf skis, which of course, do glide better than standard boats, so the comparison between long boats and short ones normally isn’t even valid in that case. The comparison ought to be between boats of very similar design.
I embrace any opportunity to learn. I would like to understand more about what you’re saying.
So when you mention the longer “glide” of the longer boat, doesn’t that in effect mean that the boat is holding speed? It seems like when we paddle we are basically repetitively pushing or lifting the boat forward with each stroke, allowing it to glide while we reset our stroke and then repeat.
Not necessarily. It’s very possible that with greater skin friction going on, the deceleration between strokes would be more abrupt with the longer boat than with the shorter one (in fact, nothing else even makes sense), but you don’t really perceive that to be the case since even at the end of the glide between strokes, the speed is still faster than that of the shorter boat. Just making up numbers to illustrate what I’m getting at, maybe the long boat loses 0.5 mph of speed between strokes but the shorter one only loses 0.2, but if the longer boat is going 6 mph and the shorter boat is going 5 mph, the longer boat still “seems” to have better glide since it’s faster at all times, even though in reality the glide efficiency is worse.
Okay, so if the speed is the same (7 mph), which would you say would hold it’s glide better: a boat that is 21 X 17 or a boat that is 17 X 17–assuming for the sake of argument that the hulls are shaped identically?
Of course, you bring up the subject of surf skis, which of course, do glide better than standard boats, so the comparison between long boats and short ones normally isn’t even valid in that case. The comparison ought to be between boats of very similar design.
I agree, it’s relevant if it’s apples to apples, so let’s use the measurements above as a reference.
Although the author is referring to rowing, the description below is the assumption I’ve been under–and I don’t declare myself an engineer by any stretch, so I’m going off of a general understanding at best.
" The classic built-for-speed vessel is the racing shell because its human cargo is also its engine. Even though it has only an 8- human-power engine, compared with the thousands of horsepower driving the tug, the crew shell really flies across the water. Now what about that shell’s design? Not only is it needle-like from stem to stern, but it has an awful lot of length both in front and back of where the crew sits.
In the 1830s and 1840s, there was a fever among clipper ship owners to break the speed record for various ocean crossings. Because they had only sail power to rely on and couldn’t simply install a bigger engine, the the only way to gain speed was to change boat design. A naval architect named W. Froude tested various vessel shapes in a water tank to figure out what ratios of length, width and draft would produce the fastest boat.
Froude’s critical discovery was that, all other things being equal, the best way to reduce drag was to design the boat to be longer at the water line. To this day, “Froude numbers” are used in boat design, and if you look at any boat-built-to-go-fast, from the racing shell to an America’s Cup yacht, they all have the same long, sleek shape."
@Mountainpaddler said:
Okay, so if the speed is the same (7 mph), which would you say would hold it’s glide better: a boat that is 21 X 17 or a boat that is 17 X 17–assuming for the sake of argument that the hulls are shaped identically?
I’m going to have to read between the lines here since you didn’t provide any units of dimension. Assume that in this case you are trying to compare two boats of the same length? Both being 17 feet but one being 21 inches wide and the other being 17 inches wide? In that case, I’d expect the narrower boat to have better glide at high speed. Off the top of my head, I’m not sure which boat would have more wetted surface area and thus more skin friction, but at high speed, wave-making is far and away the biggest source of resistance, and I’d expect that to control which boat has better glide. With a narrower boat, approaching hull speed is less like “hitting a wall” and more like “pushing against the side of a balloon”. Both of these boats would be more like the second case, with the narrower boat being more so. The speed you list is well over hull speed for this length of hull, so the boat with a more-forgiving entry into speeds of that range will glide better. To put it in a way that explains why, the narrower boat requires less propulsive force to achieve the given speed, which means that there must be less resisting force pushing the other way, which in turn means that once “the power is turned off”, there’s less force present slowing the narrower boat down.
In the 1830s and 1840s, there was a fever among clipper ship owners to break the speed record for various ocean crossings. Because they had only sail power to rely on and couldn’t simply install a bigger engine, the the only way to gain speed was to change boat design. A naval architect named W. Froude tested various vessel shapes in a water tank to figure out what ratios of length, width and draft would produce the fastest boat.
Froude’s critical discovery was that, all other things being equal, the best way to reduce drag was to design the boat to be longer at the water line. To this day, “Froude numbers” are used in boat design, and if you look at any boat-built-to-go-fast, from the racing shell to an America’s Cup yacht, they all have the same long, sleek shape."
This illustrates what factors become important when applying high amounts of power and needing all the speed you can get in return, so it’s very different from the comparisons that were pointed out earlier in this thread regarding long boats versus short boats and how they perform at relaxed paddling speeds. The example here is more applicable to the comparisons that you yourself are more interested in, though.