Mike wrote: >>> If you speed up, the bow wave goes faster. If you slow down, the bow wave slows down. How do you climb a wave that you are making? <<< You are partly right: The bow wave will have the same speed as the boat. However, there is a relation between wave speed and wave length. I don't have the exact formula handy, but a certain wave speed (the speed of the boat in this case) dictates a certain wave length. If your speed is low, the wavelength is shorter then your boat, so your boat will be resting on a couple of short waves, keeping the boat horizontal. When your speed increases, the wave will become longer, so your boat ends up completely on the edge of your bow wave. Indeed, you will be paddling UP all the time. *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
Niels Blaauw wrote; > > You are partly right: The bow wave will have the same speed as the boat. > However, there is a relation between wave speed and wave length. I don't > have the exact formula handy, > A wave's speed (in knots) equals 2.5 times the square root of the wave length in metres. A boat's waves are the result of pressure differences in the water created by its forward movement. Above very low speeds, one wave crest is created at the bow, and one at the stern. Although the wash travels outwards, this wave profile travels along with the boat. The length of the wave is thus approximately equal to the waterline length of the boat, and because of the relationship between wave length and speed, the boat cannot theoretically exceed a speed of 2.5 times the square root of waterline length without something drastic happening to the wave. This speed is considered as the boat's maximum displacement speed (all other things being equal, <G>). If the boat attempts to exceed this speed, the wave travelling with the boat must increase its length, which is achieved by the second crest at the stern falling back further behind the boat, with the boat's stern settling into the wave trough while the bow remains on the crest of the bow wave. A further increase in power only makes the bow wave larger and the wave length longer. This puts the stern deeper into the trough giving an even larger hill to climb. A planing hull is designed so that it will lift and overtake its bow wave (given sufficient power), and then has only a small proportion of its hull in contact with the water. So hull speed isn't wave climbing, but attempting to exceed it with a displacement hull is. Allan Singleton *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
From: "Allan and Joyce Singleton" <alsjfs_at_voyager.co.nz> > So hull speed isn't wave climbing, but attempting to exceed it with a > displacement hull is. All of what you say makes perfect sense, except this. It still remains that the force increase is not consistent with grade resistance. So I would argue that you're not climbing the wave, you're pushing it at a bad angle - your cutwater now includes the whole bottom of your hull! Mike *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
>From Michael Daly: > > So I would argue > that you're not climbing the wave, you're pushing it at a bad > angle - your cutwater now includes the whole bottom of your hull! > Which is what a power boat does on the way towards planing. If you take a 5.2m (17ft) kayak, say waterline 5m, then hull speed is 5.6 knots. According to the figures Matt gave, it takes a top recreational racer in a long narrow kayak to achieve this kind of speed, so most of us do not exceed theoretical hull speed anyway and don't have to worry about the bow wave. The kayak I use for exercise is 5.2m, as above, and I average just over 4 knots for the hour I am on the water. As the all up weight is 200lb, not 300, this would put me in Matt's category 3, a fit and efficient paddler (if I could keep it up for several hours!). Allan Singleton *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
> So hull speed isn't wave climbing, but attempting to exceed it with a > displacement hull is. All of what you say makes perfect sense, except this. It still remains that the force increase is not consistent with grade resistance. So I would argue that you're not climbing the wave, you're pushing it at a bad angle - your cutwater now includes the whole bottom of your hull! If you had enough horsepower you could climb out of the hole in the water you made (and reach a higher plane) just like a powerboat does. The increase in drag from a regime that increases a little less than the second power to one that increases (during the climbing phase) at near the 4th power is due to your trying to climb out of the hole you are making in the water against the force of gravity which is added on top of the drag due to skin friction. You could adjust the trim drastically to keep your bow down and cutting the water but this might actually result in even more drag from trying to push through the water rather than climb over it. I have read that extremely narrow hulls like those on a narrow catamaran overcome hull speed by slicing through the wave rather than climbing out of the hole but I don't know if that is true. The narrow hulls on kayaks and their lightweight do allow them to go a little faster than the wave speed formula predicts. A wave in deep water moves at a speed (in knots) that is 1.34 times the sq. root of the wavelength (in feet). Matt Broze http://www.marinerkayaks.com *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
Where so ever do you guys find the time to come up with this stuff? I have difficulty in just finding the time to paddle, much less figure out the physics. Being new to paddlewise, I must say it is fascinating reading. Let me know if you can figure out how to make these things fly... James Matt Broze wrote: > > So hull speed isn't wave climbing, but attempting to exceed it with a > > displacement hull is. > > All of what you say makes perfect sense, except this. It still remains that > the > force increase is not consistent with grade resistance. So I would argue > that you're not climbing the wave, you're pushing it at a bad angle - your > cutwater now includes the whole bottom of your hull! > > If you had enough horsepower you could climb out of the hole in the water > you made (and reach a higher plane) just like a powerboat does. The increase > in drag from a regime that increases a little less than the second power to > one that increases (during the climbing phase) at near the 4th power is due > to your trying to climb out of the hole you are making in the water against > the force of gravity which is added on top of the drag due to skin friction. > You could adjust the trim drastically to keep your bow down and cutting the > water but this might actually result in even more drag from trying to push > through the water rather than climb over it. I have read that extremely > narrow hulls like those on a narrow catamaran overcome hull speed by slicing > through the wave rather than climbing out of the hole but I don't know if > that is true. The narrow hulls on kayaks and their lightweight do allow them > to go a little faster than the wave speed formula predicts. A wave in deep > water moves at a speed (in knots) that is 1.34 times the sq. root of the > wavelength (in feet). > > Matt Broze > http://www.marinerkayaks.com > > *************************************************************************** > PaddleWise Paddling Mailing List - Any opinions or suggestions expressed > here are solely those of the writer(s). You must assume the entire > responsibility for reliance upon them. All postings copyright the author. > Submissions: PaddleWise_at_PaddleWise.net > Subscriptions: PaddleWise-request_at_PaddleWise.net > Website: http://www.paddlewise.net/ > *************************************************************************** [demime 0.92b removed an attachment of type text/x-vcard which had a name of jssmith.vcf] *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
The wave speed is always the same as the boat speed. The wave is made by the boat and sticks with the boat so it can't really go any faster or slower. At "hull speed" the wave length and the boat length are the same, and the wave speed and boat speed are also the same. It is hard to make the boat go faster because it doesn't like creating waves longer than itself. Since the wave length and wave speed are related, it can't make the wave move faster unless it makes it longer than the boat. Since the boat is making the wave, it can't go faster without making the wavelength longer, but it can't. And the wavelength can't get any longer because the boat isn't going any faster. And the boat can't go any faster because the wave isn't getting any longer. So you are stuck in a catch-22. When you get to hull speed, paddling harder just makes a higher wave because it can't make it longer. The harder you paddle, the steeper the wave so it feels like you are paddling up hill. And making the wave steeper makes it even harder to make it longer.... Narrow enough boats make such a small wake that you can avoid the catch-22. At 4:46 AM -0400 5/15/01, Blaauw, Niels wrote: >Mike wrote: >>>> >If you speed up, the bow wave goes faster. If you slow down, the bow >wave slows down. How do you climb a wave that you are making? ><<< > >You are partly right: The bow wave will have the same speed as the boat. >However, there is a relation between wave speed and wave length. I don't >have the exact formula handy, but a certain wave speed (the speed of the >boat in this case) dictates a certain wave length. If your speed is low, the >wavelength is shorter then your boat, so your boat will be resting on a >couple of short waves, keeping the boat horizontal. When your speed >increases, the wave will become longer, so your boat ends up completely on >the edge of your bow wave. Indeed, you will be paddling UP all the time. > > >*************************************************************************** >PaddleWise Paddling Mailing List - Any opinions or suggestions expressed >here are solely those of the writer(s). You must assume the entire >responsibility for reliance upon them. All postings copyright the author. >Submissions: PaddleWise_at_PaddleWise.net >Subscriptions: PaddleWise-request_at_PaddleWise.net >Website: http://www.paddlewise.net/ >*************************************************************************** -- Nick Schade Guillemot Kayaks 824 Thompson St Glastonbury, CT 06033 (860) 659-8847 *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
This archive was generated by hypermail 2.4.0 : Thu Aug 21 2025 - 16:33:22 PDT