I’ve been doing some interval training in a Romany and I find that once we really get going, a noticeable bow wave starts to form maybe 1/3 of the way down from the tip of the boat.
The 17 foot Valley paddling alongside me doesn’t have a similar phenomenon even if the two of us are traveling at around the speed and I was curious about what the science is on this.
Is it the bow wave just signaling that the hull has exceeded its top or most efficient speed? Is it because the generous rocker on the Romany causes the water to peel off the bow differently? Is it my weight in the boat that has pulled it into the water a bit (I’m at the higher end for a regular Romany)? I’m sure people on here have much better answers than I do!
Curious, because anything, even swimmers and ducks, that go faster than the ambient water speed create a bow wave.
Displacement boats create a deeper wave than planing boats, but both make bow waves. Rocker has nothing to do with it.
If you create enough bow wave you will create resistance, but that usually only happens with blunt nosed craft; faster kayak hulls are designed to manipulate the frequency of the wave. That is why some boats lose efficiency in shallow water.
Most boats rise up on the bow wave and reduce the wetted surface, that reduces drag, and makes them slightly more efficient.
My go to boat for bigger water these days is my husband’s old Romany. His first composite sea kayak was a Valley Aquanaut. The Aquanaut had higher hull speed and when he got it going well he could see and feel the diff between his Aquanaut and the rather dense array of NDK Explorers in that older paddling group. And easily the diff between that and the Romany, though only part of it was hull speed because they were also two very different design goals. The choice of the Romany was often made because it was a paddling day where higher maneuverability was going to be an asset.
My faster boat off the start is an old P&H Vela. Which is truly a spritely boat up to a certain point, when she gets to hull speed. Then there is a noticeable bow wake and boats that may be harder to come up to speed are having an easier time. My first sea kayak, a plastic CD Squall, rarely ever had a bow wake with me paddling. Fairly good hull speed for a plastic boat, like most of the Solstice line.
I am not clear on how designers assess or measure hull speed. But across a variety of other design factors - rocker, stiffness, tracking - in my experience boats that have lower hull speeds set up bow wakes sooner than ones with higher hull speeds. And in the case of my Vela can be faster at the initial sprint up to that point.
The bow wake being back from the bow is a matter of the rocker in the Romany, in my Vela with a deep bow it is right at the front. But the effect on speed is the same wherever it sets itself up.
If you are finding this to be an issue, I suggest you look for an older Valley Aquanaut. Should be cheaper since it is an older design, behaves well in all the stuff any Explorer can handle and has better hull speed. You will have to put it on edge to turn, something you can hint at in the Romany to get a turn. But you will find it to be an easier paddle once you have it to speed than the Romany.
hull speed iirc, is 1.34x square root of the waterline length. Anything faster, you’re pushing water in a displacement hull (the latter day “high speed” trawlers come to mind, and are part of the reason I don’t miss sailing) or you’re planing, if your hull is so designed. Oversimplified, somewhat inaccurate assessment I’m sure, and I also have no idea how a tub of a design has the same formula as an 8 man shell or a sleek sea kayak or slalom boat…
It’s the hull planing off from the speed. Every hull design has a speed that it starts to max out at, and create a bow wake, and then if you keep accelerating, the bow will start to climb onto it. Like watching a fast power boat when they accelerate.
I put a GPS on my boats one time to see what their respective top speeds that I could make them go were. My Valley Anas Acuta made it to 7.5 mph when the bow started to climb, and it wasn’t worth the effort to go any faster. My Current Designs Caribou made it to around 9 mph, and my Betsie Bay Recluse made it to 13 mph, when I couldn’t paddle any harder. Probably could have gotten a little more out of her, but I wasn’t capable of doing it.
If you look at the hull designs of the 3, the Anas looks like banana. The Caribou is a lot less rockered, but still has a banana shape, and the Recluse was almost straight. The amount of rocker has a significant effect on top speed (And maneuverability). There are other factors as well, but rocker is a big one.
Any boat in displacement mode has to push water out of the way and the bow wave is the most visible evidence of that.
One reason I got a new boat was I was always “climbing the bow wave” on my old 14 footer. Climbing the bow wave is what happens when you reach hull speed. The bow wave oscillates the water and at slow speed you see numerous parallel waves behind the bow wave. At hull speed the next wave back from the bow is right at your stern and your cockpit is in the trough. When you speed up the second wave moves farther back from your stern, causing you to paddle more and more uphill on the back face of the bow wave, hence the wall.
Hull shape has a big effect. When I got my 18 footer I noticed that the bow wave is hardly there. The new boat has a much rounder hull in cross section and an almost vertical bow, while the 14 is more flat bottomed and the bow angles down. Both have zero rocker. Also your bow wave is more pronounced in shallow water than in deep. In deep water the hull can push some of the the water down and away; in shallow it has to squeeze it off to the side, and it really slows you down.
Depending on how much science you want you might enjoy this site.
They say the bow wave is caused by the fact that water needs to slow down when it hits your bow and that creates forces and energy that need to go somewhere so based on conservation of energy it turns into potential energy (it takes energy to raise water above surface level). So in principle you want to minimize slowing down the water so a longer, narrower, straighter boat will have a smaller cross-section (and “push less water”) and a sharper, more pointy bow will help. I’m no expert; there are other factors affecting resistance and wave-making as others have mentioned (boat length, water depth, ?).
This is a subject that comes up from time to time. I don’t know if you’ve already seen this guy’s writing, but if you want to get pretty “deep into the weeds” with this, his writing is probably well worth looking into. He was a professional nautical engineer and later designed hulls for Swift, and perhaps others as well.
John Winters The Shape of the Canoe and its available on CD. Some of it can bee seem from links at John Winters Page. Makes me wish I’d taken integral calculus to better calculate wetted surface areas of variably curved surfaces…
As a more practical matter, years ago there was a fellow, a racer, here on the board who advised that hull speed was reached when the trough of the wave made by the bow (which is three dimensional - also why you lose speed then this wave interacts with a shallow “suck water” bottom, BTW)) reaches the center of buoyancy (on a symmetrical boat, the middle or widest point when trimmed evenly). So a longer hull can go faster before that half-way point is reached, but a longer hull also has more wetted area (= friction), so it takes more “horse power” from you to keep it at speed. As the hull is pushed faster yet, this wave trough moves continuously aft beyond the center of buoyancy, the stern settles into it, and you find yourself paddling against gravity - up hill. The further back the trough moves the steeper the hill you’re climbing. At least that’s the idea…
He further claimed that as the trough moves past the midpoint of the hull the water flow under the boat begins to grow turbulent. And a gurgling sound can be heard. I suspect this is something of an oversimplification - a kind of “rule of thumb” - but I do know from experience that it is quite exhausting to try to paddle any of my canoes faster and longer after I hear continuous hull gurgling. If I’m just trying to paddle efficiently through the day, I paddle at a pace so that there’s just a touch of hull gurgle at the start of each stroke. This might not be true of all hull shapes and sizes, but as a “rule of thumb” it has worked pretty well for me. But I’m not a racer, just a guy who likes to paddle.
All I know is that they were top speed in a sprint per the GPS. Not sure how far the distance for those readings were. But all 3 sprints nearly gave me a stroke
For the 200m sprint event, world class boats exceed 13 mph which is twice the 6.35 mph theoretical hull speed of an approximately 18 foot sprint kayak . Both sprint kayaks and canoes have grown increasingly narrow over the years to reduce hull friction.
Not happening. My CD Expedition is 7.5 for a burst, Nomad 7.25, Solstice 6.5 or 6.75 I forgot. That’s in a short burst. I do slack tides near zero wind in both directions. World champion racers couldn’t get my boats to 13 mph ever.
My Westside wave exceed has a top speed I will never get to. I have broken 9 mph in it when racing marathons. It can go faster, I have seen it paddled by a Czech Olympian and I will never get there.
Back to bow waves. When I first built a CLC Pax 20 it could only get past 6 mph. The cockpit was in a recreational position of 56% of the total length measured from the bow.
When I re-built it I moved the cockpit up a foot. It could then reach close to 7 mph because it rode the bow wave and didn’t climb it. The bow wave started further back on the boat.
There are a lot of variables about getting past the optimum bow wave, most is in the hull design.
