Shallow water performance?

Any ideas what affects shallow water performance in surfskis? Had a race a month ago and we noticed that the boat with more rocker, an Stellar S18S, was slower than an Epic V8.

Also heard that the Van Dusen Mohican is faster in shallow water than other boats.

Any way of determining which is faster without time trialing boats side by side?

-- Andrew

Shallow water slows you due to your wake interacting with the bottom. 

I think that the change in drag from one boat to another will be minute. 

More significant will be the effect of the shallow water on the wave shape - each boat shape is more or less suited to a particular wave profile.

See  Physics Stack Exchange .

The above doesn't directly address your question Agooding2, nor can I answer it, however there may be something in the generation of the bow wave relevant to your query. Could greater rocker on one of two boats of same length, width and displacement create a larger bow wave at same speed due to wider point of contact at waterline as a result of rocker? 

I know in marathon canoe racing some boats are better in shallow water than others. Part of the issue with shallow water is the bow wave, the other is stern squat, so possibly boats with less volume in the front and a wider back end might be better.

A friend time trialed his Stellar S18S (G2) Epic V8 (G3) and Epic V8 Pro and found that these were in order slow to fast, though the Stellar S18S was generally comparable to the V8 on deeper water.

I've got a Nelo 550 (G1) and contemplating putting a kick up rudder on it for shallow water races, or alternately getting a Kape Master 46 or Nelo Viper 44 or 46 for both shallow water and sprints.

-- Andrew

I have a New Zealand built 5.9m x 45cm wide multisport kayak with flip up rudder in flexible river lay up and it is obviously faster over shallow river banks than my v10 g3, though on deeper water the v10 is clearly faster, similar weights. Main obvious differences is the multisport has a flat bottom and practically zero rocker, So maybe this induce more of a "planing" action with less depth displacement. This is the very situation they are designed for. Shooting shallow rivers with shoals and riffles. In really shallow water biggest issue is depth for good blade purchase, and fear of ripping underslung rudders off
 

TBH better to avoid using regular composite skis in shallow water rivers etc as the risk of scraping a rock and putting an expensive gouge or rudder damage is too high and expensive. River layup boats dont have foam core and are more flexible so they absorb impacts better and easier to fix/patch as there is no core to absorb water. Marathon k1s have flimsy rudders that will break before punching a hole in the hull. Afterall they do get dropped when they run through portages with them
 

Yes, my Nelo 550 is WWR so no foam core, though it would be harder to fix than a K1 due to lack of access to the inside. Yes, It is good to avoid foam o rather honeycomb core boats in shallow water.

-- Andrew

If you want a good tutorial on the physics of shallow water paddling, read this:   Science of Paddling Part 4 .

I also notice that boats with more rocker are impacted more.

Regarding rudders, one of the reasons that I am a fan of Stellar is that most of their boats come equipped with the ability to use either the regular under-hull rudder or a stern mounted pop-up.  It takes about 15 minutes to switch from one type to the other.  I live in Florida and many of our races are inland with many obstructions in the water, so having a pop-up is a huge advantage.

   

 

Great info in that article, sounds like if shallow water is 1/2 the length of the boat, a shorter boat will be less affected by shallow water than a longer one. So having a longer boat could be a disadvantage.

Yes, putting an overstern on my Nelo for that very reason.

-- Andrew