Is longer always faster for Unlimited boards?

[Newcastle]

Had a chance yesterday to ride 16' foot  and a 19 foot unlimited boards side by side. Did about 7 miles overall and swapped boards a couple of times.  The 16 did have a sort of "natural" fast speed of about 6.2 mphs. Higher speeds pretty easy for short bursts. Up to 7.4 mphs. About what i hoped for. The 19 though was quite a bit faster. 6.5 mphs without paddling that hard not full effort. Also, i know its not glide, but it also took a while to fall below 6 mphs. As much as two to three strokes before falling beneath the 6 mphs mark. Pretty surprising. I can only imagine what an an advantage that would be in a long race. These were the two fastest boards i've ridden. Longer was better yesterday, but there was only a short section of heavy chop. The unlimited paddler i was with said the big board became more of a handful with side chop and roll.

[Area 10]

Newcastle - very interesting. But if what you are suggesting is that the average speed difference between the 16fter and the 19fter was about 5% (the % increase from 6.2 and 6.5 mph), then this demonstrates the points being made here quite well.

This is because a 19ft board is an increase in length of approx 19% over a 16ft board. Yet that 19% extra length has only resulted in a 5% increase in average speed.

This is about the same percentage speed increase that many people get when moving from a 12-6 to a 14ft board. But there the increase in relative board length is 12% (and of course in real terms is only 18 inches rather than 3ft, or 50% less).

So in other words, there are diminishing returns for extra length, which is principally presumably because you are having to move a bigger vessel through the water.

So, yes, of course a 19ft board of similar width and design will, in perfectly flat and windless conditions and with a good paddler on board, be faster than a 16fter. But you pay increasingly heavily for your speed increase until such point as, probably, any further length increase (all other things equal) would actually just make you slower.

The point at which that is reached will vary greatly from paddler to paddler, and board to board.

The "Hull Speed" of a 19ft board is a little under 6mph I think. So even though we are learning that these calculations don't always seem to fit terribly well with the observed speeds by professional athletes in races, nevertheless average speeds much faster than that over considerable distances won't easily be attained by many paddlers even on a board that long.

[PonoBill]

The hull speed curve isn't a vertical line, but climbs to one pretty quickly. A person that trains to push hull speed will record an average speed a little higher than hull speed--they're up on the curve somewhere. Takes a lot of motor, it's much easier to go a little slower than hull speed.

But remember that we're paddling very light craft, even if we're personally a bit on the portly side. The total weight of my "boat" is about 250 pounds. You can view the wave system that a hull creates as a hole that it has to climb out of. You won't see a tugboat exceeding hull speed at all--they make a deep hole that they can't climb out of. we make a much smaller hole and we can get part way out. We can't stay out, and so the nose of the board drops. there's lots of drag slowing the hull, and then Danny Ching takes another stroke. And pulls himself partway out of another hole. It's just as hard as it sounds, and most of us won't do that. Though I see 6.0 on my Bark 14 pretty often, and that's hull speed for a 20 foot hull.