New twist to me, rudders.
Most of the time I paddle/race and teach in skeg kayak. I just got a Valley Rapier 20 with a SmartTrack rudder with race housing and when I use the rudder I feel the drag from the solo kayak length rudder blade and my gps bears it ou as well. Now before anyone chimes in “Don’t use it!” it’s 20’ of straight skinny kayak so when Murphy’s Molecules pile up on one side vs. the other it can be compensated for but not easily. Beyond which I’m thinking of adding a P&H/FEKS sail to it for WT races.
So before I go all MacGyver on the blade with a Dremmel cutting wheel, is there a calculation for optimal rudder length and surface area for a give length/width hull? I’ve found some power boat calculations but they don’t seem to apply to human power plants all that well.
Personal experienced opinions please, not google search links.
See you on the water,
Marshall
The River Connection, Inc.
Hyde Park, NY
www.the-river-connection.com
hudsonriverpaddler.org
rudder sizes
for surfskis vary depending on conditions. The rudders we use are all carbon NACA foil profiles, with a stainless shaft. Even so, the bigger the rudder the more the drag so we tend to use the smallest rudder possible.
Basically the flatter the conditions, the shorter the rudder.
A big rudder gives more turning power and adds to stability. Check out epic kayaks and huki kayaks for rudder pictures.
The usual range is something like the following. In the NW we are lucky enough to have a guy who makes really nice custom carbon rudders so most of us end up with a quiver of rudders.
3" tall for dead flat conditions
6" weedless 45 degree leading edge to shed weeds
6-7" tall more upright general rudders
9-10" elliptical for downwind conditions,
9-10" shark fin for downwind but more forgiving.
For light chop less than 2’ I use a 6" weedless on lakes, for open ocean I use a longer 8". For winds over 20 kts, I use a 9 or 10" elliptical for maximum steerage.
Rudder length
I don’t know of any formulas for determining rudder length but I do notice the stock rudder on my Ruahine Firebolt (19’3") is longer than the rudder on my 17’6" Ruahine Swallow and I’d be glad to measure them both and send the dimensions on to you if you thought it would be helpful.
Obviously the conditions you will be paddling in (wind, current, waves) will be factors in choosing how much rudder is enough.
Good food for thought
Nick, thanks for the description of the various shapes and sizes of surfski rudders. It gives me some ideas for customization.
WW, I found a picture of a Firebolt. How deep is your draft? Depth of the rudder blade below the hull? Rectangular blade?
Thanks again for the info.
See you on the water,
Marshall
The River Connection, Inc.
Hyde Park, NY
www.the-river-connection.com
hudsonriverpaddler.org
I can’t hep with the calcs, but
I have one that is cut and shaved almost in half given to me by a fellow racer and it definitely is worth it.
I keep the normal one on for touring and switch it out for the baby one when I race.
It only takes a minute to change it out.
Jack L
Was thinking the same
Hi Jack
Giving the existing rudder an incremental shave till it feels right was going to be the first step. In case I botch it I ordered a new blade. Once the length is good I was thinking of thinning the blade by replacing the wetted portion w/ 18ga stainless or titanium slat in the same profile shape.
Once I’m done experimenting I’ll post the pics on my blog.
See you on the water,
Marshall
The River Connection, Inc.
Hyde Park, NY
www.the-river-connection.com
hudsonriverpaddler.org
Another place it helps
Is in a race where there is a lot of floating sea weed or sea grass.
I do a race every year up in the North River in Mass that is a tidal river, and has a lot of floating sea grass.
About five years ago I started using my “baby” rudder, and it doesn’t catch nearly as much of it.
Still winning the “over the hill class” so I’ll stick with it.
Jack L
rudder
The kickup rudder on the Firebolt extends 4.5" below the bottom of the hull. The width is 4"
Rectangular shape. That’s one beefy rudder. I’ve felt like that amount of rudder has been needed in most of the conditions I’ve been paddling in.