I've often heard (and intuitively accept) that all other factors being equal, a longer kayak will be faster than a shorter one. I've got a friend who disagrees with this, but I've had a hard time explaining why this would be true. I would speculate (fancy word for "guess") the following possible reasons: 1. Paddling on the ocean, there are generally little (or big, for that matter) waves and chop that push against the kayak from different angles. The longer the kayak, the more these "local" disturbances would tend to cancel out and thus interfere less with the boat's movement through the water. If this is true, then would this advantage disappear when paddling in very smooth, flat water? Or would the longer kayak continue to be faster? 2. A longer kayak has more floatation than a shorter boat (again assuming other factors are equal), so it would float a little higher in the water, thus reducing drag. I assume that most of the friction comes from the movement of the bow cutting through the water and that the additional length contributes very little additional drag. (I expect I'm going out on a limb on this one, having once gazed at Matt's speadsheet on this subject (phew!)) I know enough to know it's ultimately more complicated than that). My friend countered my comments by saying if that were true, then paddling a boat a mile long would be faster than a 17 footer. Obviously a REALLY long boat like that would weigh a lot and thus have a lot of inertia to overcome getting it moving, but once up to speed -- would it be faster than the 17 footer? Or perhaps another way to ask it: would it require less paddle effort to maintain a given speed than a 17 footer?? What if it were so loaded with weight that it floated the same height in the water as the shorter kayak -- would it still be faster? Lastly, is there a simplified formula for estimating the speed, given a certain beam and length (holding other factors constant)? Evan Dallas Woodinville, WA. *************************************************************************** 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 ability for longer boats to go faster has to do with the interaction of the waves generated by the moving boat and the hull shape. As boat speed increases, the length of the wave created also increases. When the length of the wave equals the length of the boat, it is hard to make the boat go faster because the wave starts getting bigger without getting any longer and the force required to make the boat go faster increases dramatically. This interaction is called "hull-speed" but it is not a real speed limit. It is a theoretical idea based on the increase in drag as the wavelength and boat length become the same. Hull speed is proportional to the square root of the boat length. However shorter boats can have less drag at a given speed because most of the time the primary source of drag is the skin friction of water molecules moving against the hull of the boat. This drag is related to the wetted surface area of the boat. More wet surface, more drag. Shorter boats typically have less wetted surface and are thus more efficient at speeds below their hull speed. It is just hard to push them beyond their hull speed. Since a longer boat has a higher hull speed it can be more easily pushed to go faster, even if it has more drag at lower speeds. It is kind of silly to say one boat could be "slower" at slow speeds, but since a long boat may have more drag at low speeds, it may be harder to move than a shorter boat. At 12:53 PM -0700 5/12/01, Evan Dallas wrote: >I've often heard (and intuitively accept) that all other factors >being equal, a >longer kayak will be faster than a shorter one. I've got a friend >who disagrees >with this, but I've had a hard time explaining why this would be >true. I would >speculate (fancy word for "guess") the following possible reasons: > >1. Paddling on the ocean, there are generally little (or big, for >that matter) >waves and chop that push against the kayak from different angles. The longer >the kayak, the more these "local" disturbances would tend to cancel >out and thus >interfere less with the boat's movement through the water. If this is true, >then would this advantage disappear when paddling in very smooth, flat water? >Or would the longer kayak continue to be faster? > >2. A longer kayak has more floatation than a shorter boat (again >assuming other >factors are equal), so it would float a little higher in the water, thus >reducing drag. I assume that most of the friction comes from the movement of >the bow cutting through the water and that the additional length contributes >very little additional drag. (I expect I'm going out on a limb on this one, >having once gazed at Matt's speadsheet on this subject (phew!)) I >know enough to >know it's ultimately more complicated than that). > >My friend countered my comments by saying if that were true, then paddling a >boat a mile long would be faster than a 17 footer. Obviously a >REALLY long boat >like that would weigh a lot and thus have a lot of inertia to overcome getting >it moving, but once up to speed -- would it be faster than the 17 footer? Or >perhaps another way to ask it: would it require less paddle effort >to maintain >a given speed than a 17 footer?? What if it were so loaded with >weight that it >floated the same height in the water as the shorter kayak -- would it still be >faster? > >Lastly, is there a simplified formula for estimating the speed, >given a certain >beam and length (holding other factors constant)? > >Evan Dallas >Woodinville, WA. -- 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/ ***************************************************************************
In a message dated 5/14/2001 9:59:53 AM Eastern Daylight Time, schade_at_guillemot-kayaks.com writes: > However shorter boats can have less drag at a given speed because > most of the time the primary source of drag is the skin friction of > water molecules moving against the hull of the boat. This drag is > related to the wetted surface area of the boat. More wet surface, > more drag. Shorter boats typically have less wetted surface and are > I really do try to follow these discussions on boat and paddle physics, even though a lot of it is clearly over my head. I always though the wetted area of a boat was the result of the weight of the boat and how much water it displaced -- not the length. Is that not correct? Just wondering, Scott So.Cal. *************************************************************************** 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/ ***************************************************************************
Wetted surface area is determined solely by how much surface is wet. While there is a some relationship between how much weight the boat carries and wetted surface, it is not a direct correlation. Weight determines how much water is "displaced" and this is a volume. Some shapes enclose more volume with less surface area than others. The lowest wetted surface are for a given volume would be a hemisphere, in other words - a short, fat kayak. Long narrow shapes generally have more surface area for a given volume than short wide shapes. So longer boat will often have more wetted surface area than short ones. At 4:10 PM -0400 5/14/01, KiAyker_at_aol.com wrote: >In a message dated 5/14/2001 9:59:53 AM Eastern Daylight Time, >schade_at_guillemot-kayaks.com writes: > > >> However shorter boats can have less drag at a given speed because >> most of the time the primary source of drag is the skin friction of >> water molecules moving against the hull of the boat. This drag is >> related to the wetted surface area of the boat. More wet surface, >> more drag. Shorter boats typically have less wetted surface and are >> > > I really do try to follow these discussions on boat and paddle physics, >even though a lot of it is clearly over my head. I always though the wetted >area of a boat was the result of the weight of the boat and how much water it >displaced -- not the length. Is that not correct? > >Just wondering, > >Scott >So.Cal. > >*************************************************************************** >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/ ***************************************************************************
For those interested there is a short discussion of hull speed and length and how it relates to paddlers in the FAQ section of our website. Somebody who wants to get into this in more detail should go to the DOWNLOADS section where they can download a spreadsheet I did based on a method John Winter's came up with to estimate drag. You can change many of the characteristics of a kayak important to drag on this spreadsheet and see how they effect the total drag and the breakdown of drag due to friction and that due mostly to wavemaking (and graphed curves as well). Also many of the sea kayaks that Sea Kayaker Mag has tested have their parameters included in the spreadsheet (all in one place for comparison). I once calculated how fast a strong paddler could paddle a very narrow lightweight 100' long kayak. If I recall correctly it was 1.5 knots. The same paddler could push an 18' kayak about 6 knots. The theoretical hull speed (using 1.34 times the sq. root of the waterline length commonly used--but 1.4 to 1.5 is probably more accurate for a narrow kayak)of a 100' kayak would be 13.4 knots. The FAQ's quickly explains why the facts don't always support the longer is faster "common knowledge". Here is what I wrote for Sea Kayaker back in 1998. They may have edited it some, I don't recall. It has come to my attention that some paddlers are comparing kayaks using the drag calculations all the way out to six knots (6.9 miles per hour). When I originally proposed taking the results out to six knots it was so a comparison could be made between kayaks in an all out short sprint. I still think it valuable to include the drag calculations from 4.5 to 6 knots even though these speeds are rarely achieved in a loaded sea kayak. However, from this issue on we will include a caveat with the drag calculations that states “Note: Three pounds of drag is common for a fit paddler at cruising speed. Only a few can work against five pounds for long distances, see Vol. 15, #2?, p? for more details”. If you think the speeds are a little slower than you travel remember that the calculations are for a 150 pound paddler with 100 pounds of added “gear” weight and we are using knots (not miles per hour--1 knot = 1.1516 mph). If we were to remove 100 pounds of “gear” weight the kayaks speed would increase about 3/10 or 4/10 of a knot for any given drag. What follows is a description of what each pound of drag means to a paddler with 250 pounds plus the kayaks weight (for a total weight usually over 300 pounds). Note: Horsepower is resistance times speed. HP=.003069 x Drag (pounds) x Speed (knots) Pounds of drag. What it means to a paddler Horsepower required at typical speeds 1. Easy paddling for almost anybody .006 HP _at_ 2 knots 2. Most paddlers can overcome this much drag for long distances .019 HP _at_ 3 knots 3. A fit and efficient paddler can overcome this drag for several hours .0325 HP _at_ 3.5 knots 4. A strong expert working hard can withstand this drag for many hours .05 HP _at_ 4 knots (Note: doubling the speed to 4 knots increases the drag about 4 times but requires 8 times the horsepower) 5. A recreational racer can move a narrow sea kayak for several hours .07 HP _at_ 4.5 knots 6. A good recreational racer can move an average sea kayak for an hour .08 HP _at_ 4.5 knots or a good rec. racer in a long narrow kayak at 5 knots for an hour .09 HP _at_ 5 knots 7. Good recreational racer moves a slow kayak 4.6 knots or a fast one 5 .1 HP _at_4.6-.11 _at_ 5 knots 8. Good recreational racer pushing a long narrow kayak for up to a mile .13 HP _at_ 5.2 knots 9. Top recreational racer in a very long and narrow kayak for up to a mile .15 HP _at_ 5.5 knots 10. Top rec. racer in a kayak designed mostly for racing for up to a mile .175 HP _at_ 5.7 knots (Sea Kayaker’s very strong expert (DM) appears to generate about .166 HP for one mile going all out) 11. Olympic kayaker in Olympic kayak (198 lb. total--not 300+) for 3 hrs. .22 HP _at_ 6.5 knots 16. Top Olympic competitor in Olympic kayak for 1000 meters (198 lb.) .40 HP _at_ 8.1 knots 17.6 Top Olympic competitors for 500 meters (198 lb. total wt.--not 300+) .525 HP _at_ 9.7 knots 19. Greg Barton in a 19’ fast sea kayak (~260 lb) for a few hundred meters .46 HP _at_ 7.9 knots 25. Olympic champ in an Olympic kayak for less than 10 seconds flat out .90 HP _at_ 11.7 knots (Note: Olympic kayak drag from tank tests done in 1970’s and reported by Andy Toro in Canoeing: An Olympic Sport, thanks to Greg Barton for finding the Olympic kayak results) 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/ ***************************************************************************
Nick Schade wrote: > // The lowest wetted surface are for a given volume would be a hemisphere, // I hate to start a major debate, but the lowest wetted surface for a given volume would be a sphere. A major bad design for a kayak. But, would turn easy. -- Wayne Smith (ò¿ó) http://www.waynesmith.net/ Humour: http://www.yahoogroups.com/subscribe/Bandido_Jokesters October 7, 1999 - 315 lb. - BMI: 44 - Dr Rumbaut - Monterrey, Mexico Reached goal of 185# July 2000 - Have been +/- 4# ever since. *************************************************************************** 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/ ***************************************************************************
----- Original Message ----- From: "Wayne Smith" <wsmith_at_cts.com> > > > // The lowest wetted surface are for a given volume would be a hemisphere, // > > I hate to start a major debate, but the lowest wetted surface for a given volume > would be a sphere. A major bad design for a kayak. But, would turn easy. Actually, in the wacky world of whitewater rodeo kayaking, a sphere is a excellent kayak design. Just put points on the ends, and you've got instant cartwheeling potential! If you check out the latest designs, you'll see the puffy midsections and pointy ends. This page has pictures of all the rodeo kayak designs... http://www.freestylekayaker.com/fklo.html Cheers, Kevin ps. in case you were wondering, noseplugs are indeed mandatory when using these boats ;) *************************************************************************** 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/ ***************************************************************************
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