18.5" x 20' vs 17" x21" : Cruising speed diff?

If I can maintain 6 mph on a 18.5" x 20' Huki S1-R, what sort of speed increase should I expect on a 17" x 21" ski?

Flat water, assume no capsizes.

Not sprint speed, just max aerobic cruising speed.

I'm not looking for great detail - just ballpark: a few tenths of an mph? .5 mph, more?

Here's the chart that Greg Barton of Epic put out: www.surfskinews.com/blog-2016-decjan-201...son-with-greg-barton

So if the 20' x 18.5" ski is most similar to the Epic V10 sport, then the 21' x 17" ski would be similar to the EPIC V12, so you would save between 10 seconds and a minute over 10K depending on whether you are closer to an intermediate paddler or closer to Greg Barton.

It is always surprising how little additional speed a faster hull actually provides. Also surprising is how little speed a lighter boat provides. According to this exhaustive tome, lightening the boat by 1 kg will save seven seconds in an hour of racing. So going from a fiberglass to a carbon boat will speed things up by about 35 seconds an hour.

www.lcrk.org.au/pmwiki/uploads/Main/WeightEffect.pdf

Sounds to me like the diff would be in the neighborhood of .1 mph.

Which is bad news for Yours Truly because now he cannot ascribe the paddlers walking away from him to having faster boats .. -)

The thinner the ski the less people will ask to borrow it because they can't fit. It's a win win for me.

agooding2 wrote: Here's the chart that Greg Barton of Epic put out: www.surfskinews.com/blog-2016-decjan-201...son-with-greg-barton

Just remember although helpful this is an "Estimate", not real world figures.

I've done real world testing over 1km at set HR and the results are really surprising for various boats in the same conditions.

I'd say as long as the weight, construction, rocker and hull shape is the same.a .2km/hr difference would be the minimum I'd expect to gain from moving down from 18.5 to 17in.

Last week at a local race meet-up I paddled an Epic V8 Ultra just for giggles.

The course is roughly 3.5 miles, and I paddled without much draft benefit to a 26:45 (7.8mph).

My typical time in my V12 Ultra is usually 24:45 in similar conditions (8.4mph) and I don't usually get a draft benefit from other racers.

My typical V14 time over that distance is 24:30.

When I switched from a V14 Ultra to a V14 GT, I paddled roughly :20 seconds faster per mile (GPS verified).

My K1 (Epic Legacy XXL) time is considerably faster still, and I've been hovering around 24:00 flat, and my PR is a 23:55.

I chewed on this a lot because neither number matches the theoretical's I run into out in the world wide interwebs. But I attribute it to the following 1) boat acceleration is affected every stroke I take 2) boat glide is dramatically better in a narrow waterline, long ski. A heavy, short and wide ski doesn't like to accelerate or glide. A narrow, long and lightweight ski likes to glide very much.

Paddling a V8 Ultra, I could get it up to mid-8's in the first 1k, but it was very, very expensive from an energy perspective and I had to back off.

I asked Greg B about it, and he thinks that the V14 and K1 rewards speeds above 8mph in dramatic fashion, but much less so in the sub 7mph range.

Hope that helps.

Cryder

Don't underestimate the difference 0.1 or 0.2 kmh makes during a paddle. We are talking 100 to 200 metres over an hour of paddling.

For 12 odd years I have paddled with the same group for an hour 4 or 5 times a week. I get annoyed when I'm 20 metres behind. 200 metres would be buy a new boat territory....and I have on more than 1 occasion.

Small numbers do add up over a longer paddle or race. Try and imagine how far 200 metres is after a relatively short paddle. The distance will probably increase as the distance increases.

My experience is that is is about 1.0-1,5 kph difference between Fenn XT to a ElitesS /V12 on reasonably flat water in the 11.5-13 kph range.

At a level of aerobic power that produces an average of 6.0 mph, I don't think you'll see any difference in speed between the two skis that you mentioned. At that speed, and with skis that long, and assuming a similar rocker, most all your resistance is wetted surface area. With one ski shorter and wider and the other longer and narrower, their wetted surface area might be similar - or the shorter one might be lower in overall resistance. Once you get into the high 7's and 8's, wave resistance comes into play big time, and that's when strange things happen and narrower really helps.

When I've compared my cruising speed on flat water between different boats I typically find about .1 to .2 mph difference going up a level. You'll really notice the improved glide and lower resistance, even if the speed gain seems small.