When is an unlimited slower than a 14'?

[FloridaWindSUP]

I got to try a 17'6x23 Starboard Sprint today in the lazy Imperial River near my house in Bonita Springs, FL. The unlimited was fast, but not clearly faster than my 14x23 Riviera... at least not in that venue. I.e to make it go 9 or 10 kph on my gps seemed to require at least as much effort as it takes to go that speed on my 14. Also, the guy who was racing the board finished a little slower than he did a few weeks ago when he raced his 14x21.

One factor may have been that the tide was super low and much of the river was less than waist deep. Maybe the benefit of extra length is negated when speed is limited by water depth anyway? Or maybe the extra effort to turn the board around the many bends of the river wasn't made up for in straightaway speed.

Have any of you who have more experience with unlimited length boards noticed that the unlimiteds are actually slower, or at least not faster, in certain conditions? Conversely, when would an unlimited have the biggest advantage?

[digger71]

Others with a more in depth understanding of fluid dynamics will likely chime in, but the shallow water drag you were experiencing pretty much make your experience/results meaningless.  Anytime the water depth drops to 1/2 boat length this occurs and the resulting drag can be significant.

[covesurfer]

I've ridden a wide variety of 14's but only a few unlimiteds, SIC F16's, Bullet V1's and a V2. With the F16 and the Bullets, especially the V1, the shape is not good for flat conditions. The rockered nose tends to push water and there is a lot of board to paddle through the water. Even though the V2 is a less rockered shape, the design of the nose still slows the board considerably in flat conditions.

14' boards with race shapes are definitely faster in my experience, if conditions aren't full downwind. I also have a hollow SIC F14, that is 28" wide, vs. the 26" of the Bullet 17's. That F14 is slower in ALL conditions. 

Never ridden the Starby but 23" wide is pretty darn narrow. I'd think that board could be a real knife in the water in the conditions it's designed to excel in. 23" would be a handful for me to deal with in open ocean, too much going on to balance a narrow board for this old man.

[PonoBill]

Cove is talking about a different thing--any unlimited downwind board is 17 feet of pain when the wind isn't blowing. But the thread is about flatwater, and there are two answers.

First, an unlimited board has more skin friction than a shorter board, but less wave drag. Wave drag increases rapidly as you approach the froude "limit", but you need a paddler that has enough muscle and form to get close to the limit. For smaller paddlers a shorter board will go faster. Unlimiteds benefit the Rob Rojas, Chuck Pattersons,  and Thomas "Maximus" Shanahans of the the world. Big guys with big muscle.

Put those guys on a 14 and all the skinny little dudes blow right by them. Put them on an unlimited and they fly.

The other factor is shallow water drag, and it's a killer. When the water is shallow enough, the wave generated by the bow--which spreads from the bow not just across the surface of the water, but in a 180 degree cone from the tip, can hit the bottom and refract back to the board, creating big time wave drag. If the water is deep enough and the board is short enough, the wave misses the board. Unlimiteds experience shallow water drag sooner than 14's because the wave hits the board in deeper water. 6 man outrigger canoes are really effected by shallow water drag. When we run the Hood river Canoe Club OC6 over a sandbar it feels like we ran aground, even if the water is six feet deep. 40 feet of OC6 needs 20 feet of water under the hull to be unaffected.

[Off-Shore]

I think the greater weight of the unlimited board vs a 14' also has and effect on speed in flat conditions. I've paddled the Bullet 17-4 and the Bullet 14 on consecutive days in flat ocean conditions and just the shear weight difference of the 17-4 tires you out much quicker than the 14.

[PonoBill]

Weight of a board is pretty trivial compared to total system weight (board and paddler). This is one of my favorite pages on the entire internet. It's all here:
http://eodg.atm.ox.ac.uk/user/dudhia/rowing/physics/weight.html#section7

[Luc Benac]

Cove is talking about a different thing--any unlimited downwind board is 17 feet of pain when the wind isn't blowing. But the thread is about flatwater, and there are two answers.

First, an unlimited board has more skin friction than a shorter board, but less wave drag. Wave drag increases rapidly as you approach the froude "limit", but you need a paddler that has enough muscle and form to get close to the limit. For smaller paddlers a shorter board will go faster. Unlimiteds benefit the Rob Rojas, Chuck Pattersons,  and Thomas "Maximus" Shanahans of the the world. Big guys with big muscle.

Put those guys on a 14 and all the skinny little dudes blow right by them. Put them on an unlimited and they fly.

The other factor is shallow water drag, and it's a killer. When the water is shallow enough, the wave generated by the bow--which spreads from the bow not just across the surface of the water, but in a 180 degree cone from the tip, can hit the bottom and refract back to the board, creating big time wave drag. If the water is deep enough and the board is short enough, the wave misses the board. Unlimiteds experience shallow water drag sooner than 14's because the wave hits the board in deeper water. 6 man outrigger canoes are really effected by shallow water drag. When we run the Hood river Canoe Club OC6 over a sandbar it feels like we ran aground, even if the water is six feet deep. 40 feet of OC6 needs 20 feet of water under the hull to be unaffected.

Now I understand while I am so slow on the nearby shallow lake even if the water is super flat.

[Pierre]

Others with a more in depth understanding of fluid dynamics will likely chime in, but the shallow water drag you were experiencing pretty much make your experience/results meaningless.  Anytime the water depth drops to 1/2 boat length this occurs and the resulting drag can be significant.

this is absolutely true, especially if water depth is less than waist high ( 1/6 of board length) i still experienced it yesterday on my UL, when depth  got restricted I was feeling as dragging a sea anchor behind... it happens also in narrow channels, this effect is called "squat" on ships, it results in drag increase and hull sinkage.
Another factor is that the paddling technique on a flatter UL should be different than on a 14 footer.
regarding weight, this is trivial, and the sprint 17'x 23" is quite light.
In deep flat water with no wind ( or light DW), ULs allow you a much higher speed provided wetted surface is reduced and rocker as flat as possible, the sprint shape is quite OK in that matter. it may be improved with a little rounder sections( but loosing stability).. 
In upwind conditions definitely better go shorter.

[ukgm]

Weight of a board is pretty trivial compared to total system weight (board and paddler). This is one of my favorite pages on the entire internet. It's all here:
http://eodg.atm.ox.ac.uk/user/dudhia/rowing/physics/weight.html#section7

If that's true it really highlights why its not worth paying the extra for a full carbon board over a hybrid that is a grand less......

[Ichabod Spoonbill]

The only race I ever did was a 19 mile Shelter Island circle. I was one of two people on a 12'6". Let's just say I didn't do so well. I was going back and forth with a guy on an unlimited. I could tell he was standing about a foot aft of center, which was putting a foot or more of his nose out of the water. He trounced me in a long downwind section, but I ended up crossing the line ahead of him because of his stance!

[PonoBill]

Weight of a board is pretty trivial compared to total system weight (board and paddler). This is one of my favorite pages on the entire internet. It's all here:
http://eodg.atm.ox.ac.uk/user/dudhia/rowing/physics/weight.html#section7

If that's true it really highlights why its not worth paying the extra for a full carbon board over a hybrid that is a grand less......

Like almost everyone else, I prefer light boards over heavy, but for most of the boards we buy, the performance difference in flateater racing is minimal. For most of the Starboard race range, the difference between all carbon and hybrid is 15 percent--about four pounds for the 14'. The total weight with a 150 pound rider is around 180, so the difference is about two percent. That yields about a one percent increase in wetted area, and given that for a typical hull with everything else being equal the loss of speed is 1/6 the difference in total mass it's a .3 percent difference. If you can do 6mph with the heavier hull you'll do 5.982 with the lighter. Unless you believe the hull is giving you an advantage, in which case you might go a lot faster.

Of course you don't actually get all of that .018 mph advantage, because there are favorable momentum effects from a heavier hull, but I'll leave that as an exercise for the reader.

If you want to crank through some real world examples of weight and it's significance, look at the Tahitian teams vs. most of the folks they come up against. The Tahitians almost always have a 30 to 50 pound advantage in total weight of boat and crew. For a 1000 pound boat and crew that's about a 1 percent advantage in speed even given a minor difference in available power from the heavier crew (given similar training). Trivial in a sprint, a big deal in a long race. Multiply that advantage by 50 miles and you won't be able to see them from the heavier boat.

Total weight is a killer in SUP racing--it's very difficult to overcome a 20-30 pound system difference by superior training. That's why you won't see Thomas Maximus winning races on a 14'. But a board weight difference of two to five pounds won't win races by itself.

[warmuth]

 Well this sure does help explain an issue I just ran into the other day. I could not figure out why maintaining speed in a certain stretch was so hard. I chalked it up to some weird current effect but the water there was quite shallow compared to the rest of my route.

[SUPflorida]

A lot of my flatwater paddling is in 2' to 5' of water. I been out on my 25.5" x 16'-2-1/2" board now 11 hrs over 6 sessions. Out on my 26" x 14' hundreds of hours. It's next to impossible to get consistent times where I paddle. There is always wind & tide effects that are constantly changing from one run to the next...so I can't definitively say the 16 is "this much slower" than the 14.

But I have to say I'm a bit disappointed with the sixteen. I refined a lot of things from my fourteen...flatened the rocker (sits beautifully in the water), 1/2" narrower overall sharper entry and exit. The only time it feels better on the sixteen is up wind in chop (carries momentum better).

Both are plenty stable, 16 tracks straighter.
Overall although it seems faster on the 16, the average time seems higher than the 14' by a minute or two per mile in certain conditions.

So how much does this sholllow water drag account for? Always though my per/mile time sucked big time compared to what I read here. Is that part of the problem?

Moving it around is much more of a pain on land even though the 16 is only one pound heavier than the 14.
I haven't given up on it yet...wondering if the potential is much higher but I just don't want to kill myself to achieve it. I was shooting for more speed with same effort not less speed. At this point (191 lbs and going back down) the next board build will be 14 not 16+. Or maybe a lighter 12'-6"

No doubt big boards work for big guys...but for the rest of us maybe not so much...at least that's my impression so far... right now I wished I had built a 24" X 14 instead. Opinion to change without notice

[Area 10]

Yes, a longer board is by no means always faster, even when the water depth issue isn't a factor. Except for pure downwind (and even sometimes then), in very choppy windy conditions a shorter board can be faster for sure. You can even see this sometimes with a shorter surf SUP paddling against a longer surf SUP in really awful conditions - you don't need race boards to see the effect. Unless you have the possibility of glide and approaching hull speed etc. then having a longer board doesn't really add much, and can in fact just add a lot of surface area to get battered by wind , current, and waves and that needs controlling. Sometimes the advantage of an UL board comes more from increased stability for a given width, and better tracking, than it does from the length per se. Also, as already noted, (unless wind/bump assisted) bigger boards tend to need bigger power. Anyone who thinks that in general paddling conditions they are always going to be faster once they buy an UL is likely to be disappointed. Some people are actually slower consistently on UL boards (and yes, I know that everyone here will tell me that this is not true and that I am crazy, but sorry, I've GPSed several friends and it is true for some people no matter what you think). I really enjoy my UL boards, but I paddle a wide variety of conditions and very often I'm no faster on them than I'd be on a 14, and sometimes I am a little slower.

BUT when they are in the right conditions, ULs are an absolute joy - and quite a lot faster. And they give a different feel too.

[warmuth]

A lot of my flatwater paddling is in 2' to 5' of water. I been out on my 25.5" x 16'-2-1/2" board now 11 hrs over 6 sessions. Out on my 26" x 14' hundreds of hours. It's next to impossible to get consistent times where I paddle. There is always wind & tide effects that are constantly changing from one run to the next...so I can't definitively say the 16 is "this much slower" than the 14.

But I have to say I'm a bit disappointed with the sixteen. I refined a lot of things from my fourteen...flatened the rocker (sits beautifully in the water), 1/2" narrower overall sharper entry and exit. The only time it feels better on the sixteen is up wind in chop (carries momentum better).

Both are plenty stable, 16 tracks straighter.
Overall although it seems faster on the 16, the average time seems higher than the 14' by a minute or two per mile in certain conditions.

So how much does this sholllow water drag account for? Always though my per/mile time sucked big time compared to what I read here. Is that part of the problem?

Moving it around is much more of a pain on land even though the 16 is only one pound heavier than the 14.
I haven't given up on it yet...wondering if the potential is much higher but I just don't want to kill myself to achieve it. I was shooting for more speed with same effort not less speed. At this point (191 lbs and going back down) the next board build will be 14 not 16+. Or maybe a lighter 12'-6"

No doubt big boards work for big guys...but for the rest of us maybe not so much...at least that's my impression so far... right now I wished I had built a 24" X 14 instead. Opinion to change without notice

  It doesn't help that conditions in Florida have been awful for several months now. It's hard to get good comparable data on much of anything these days. I caught one or two very nice mornings but other than that every day brings wind ,wind and more wind.