Boat length - interesting analysis

1 month 4 hours ago #36936 by mrcharly
Very interesting analysis of the effects of boat width and length on speed.
Is longer faster?
The following user(s) said Thank You: ErikE, leolinha

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3 weeks 5 days ago #36950 by waverider
supports the theory that "faster" boats are only really faster at high speeds, hence no real need for recreation boats to be long for the sake of speed, but more for their ability to manage the peaks and troughs in rough conditions. On flatwater differences are not huge, until doing race pace, and sustaining it. The differences have diminishing returns as they get longer. but that difference is critical in a race boat but not so much for recreational purposes.

The shorter boats also waste more energy "yawing" from side to side with each paddle stroke, its one reason those short pedal kayaks cope better than the short paddle equivalents as all propulsion is directed down the centre line of the craft forward eliminating any lateral energy spill.

skinny boats also tend to be longer in order to maintain the required bouyancy to enable larger paddlers to actually use them. K1's can be short compared to skis as they simply do not require the bouyancy levels and most have a lower paddler weight capacity 

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3 weeks 5 days ago #36951 by mrcharly
I absolutely agree about K1 and bouyancy. Over 80kg is considered 'heavy', and finding a boat for someone weighing 90kg+ can be challenging.

One thing I found interesting from the analysis is that for lowish speeds (8kph/5mph), a shorter boat might well require less energy. Shorter-wider = less surface area. 

At lower speeds, skin friction becomes a more dominant force in the total drag equation. 

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3 weeks 5 days ago #36953 by waverider
once you get to less than 13 foot the wasted energy of side swing becomes quite pronounced, and obviously paddler technique and efficiency goes out the window as boats get wider, . so there is more to it than just straight line theoretical hull mathematics. You simply cant paddle a dumpy little boat with the efficiency of a skinny race boat, so the ability of a paddler to actually put power down is handicapped.

One of the joys of paddling a K1 once you have mastered it is the simple efficient graceful way you can zip along with total economy of technique, with the slightest change in technique having a huge difference. You hit a wall with the little boats and no matter how much you tweak your technique or pile on the power it seems to make little difference. Not to mention you have bugger all glide so there is no respite. Still amazes me just how well you can keep your speed up even with pronounced pause paddling drills in a race boat

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3 weeks 4 days ago - 3 weeks 4 days ago #36963 by mcnye1
Yes, that is an exceptional article.  For those not familiar with the author, Nick Schade is one of the best and most prolific designers for the home built market.  He was a US Navy engineer before moving into building/designing kayaks full time so unlike most, he has a very technical approach.  One of the things that I like about Nick's work is that he provides detailed drag and stability curves for all of his designs, which allows for an objective comparison of boats.  This is something that I wish that the commercial surfski/kayak companies would do.  I have built two of Nick's designs and they are quite competitive in their respective classes.  The boat in front is a Yukon (18'x20.5") and the back boat is a Mystery (20'x20").  The Yukon races in the USCA SK Class and is faster than a V8.  The Mystery races in the Touring Class under USCA and is faster than a V8Pro and equal to the V10 Sport.  
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3 weeks 4 days ago - 3 weeks 4 days ago #36968 by Arcturus
The other thing is that a 17’ kayak with lots of rocker does not mean 17’ waterline, especially with a lightweight paddler in it. My own 17’ sea kayak probably has only 14’ waterline while my “short ski” actually has 17’ in the water. The sea kayak also has a narrower beam, but it doesn’t have as much glide as the ski does. Their hulls are very, very different in shape, viewed either in side profile or in cross section.

Nick’s brother, Eric, also designed kayaks. I bought the kit to make the original Shearwater Merganser (4-panel S&G), before he changed the design to widen it.

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