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.
I had the BB when we paddled out to Eastern Egg Rock one time. I sold it about 3 years ago because I couldn’t get the cockpit comfortable anymore, no matter what I tried. Only got $500 for it, because they’re not “Chic” anymore, at least around here. Very happy with just the 'Bou and the Anas. Judith’s Silhouette was a temptation every so often, but it’s outfitted for her and I’m a bit bigger than I used to be. But if she ever decides she doesn’t want to paddle it anymore…
Silhouette is still a very nice boat. Speaking of Eastern Egg, got out there with puffins still in the water last July. First time in a few years. Well worth the dogged long paddle back, Ma Nature decided to skip the afternoon wind part and go dead flat.
OK, here’s my point - those speeds were “Top Speeds” recorded by the GPS, which means they could have been for 5 feet. You are talking about average racing speeds, which is a huge difference. I also use a GPS cycling, and on a long steep hill it can accurately record 45 mph as a top speed, which would only be for a few seconds going down a hill. No real effect on the 14 MPH average speed over the 30 miles I rode. GPS records both. In a distance racing situation, 14 is the only number that matters. I was talking about top speeds recorded by a GPS in a short all-out sprint. Nothing more than to show that different hulls have different points where they climb their own bow wakes.
I’m talking about a two hundred yard sprint with professional racers. The hull is not capable of 13 MPH even for a nano second without super currents and or wind.
My GPS says high numbers at times too. They are not real.
