Designing a fast hull -- Vespoli?

-- Last Updated: May-13-05 2:06 PM EST --

My son seems to be doing a lot more paddling (rowing) then I do these days as he is now in his thrid year of crew. Last weekend his team made it to the Eastern Nationals where their dream ended early, but it was a good ride (row) till then.

If you want to go fast on water the winning boats were covering 3000 meters in the upper 5 minute bracket.

I did stop in the Vespoli tent (they manufacture shells) and asked them how they can justify their Ad that claims their boat reduces drag 5% on the catch and 3% on the release. It was a fun and interesting conversation on how they design their hulls. The first thing they did is hire designer Manolo Ruiz de Elvira whose designs swept the 2003 America's Cup. He incorporated his America Cup ideas and technology into their latest hull designs and some of the things they are doing go against what we typically think of as a fast hull. First they shortened their hull, use a fish form shape, carry a little more volume in the wider section of the hull, removed the long slow tapered bow for a shorter more plumb bow with a sharp "V" entry to slice the water. For technology to test a hull they don't use water tanks any more, but rather have a device that looks like a mouse from a computer that they just slide back and forth over the hull of and somehow it reads all of the actual specs (depth, width, length, contours etc.)of that actual hull. The data from that device goes to a computer that crunches all of the info and can determine the actual potential speed, drag, most or least efficient part of that hull and even calculate where and how they might reshape that particular hull to increase its' speed if they were to rebuild it. This might also explain the 30+k price tag for the hull that the bigger schools and clubs use.

What would be interesting is if a kayak company interested in building a boat for speed teamed up with one of these companies. These companies have also mastered making very light and strong layups.

I once remebered watching on the Discovery Channel the "Myth Busters" and the myth was that a long time ago an "8" rowing shell pulled a water skier. After retrofitting an "8" they recruited the Stanford team who did succesfully pull a skier. Kind of a hoot watching a skier being towed behind a row boat.

Goethe said…
“everything has been thought of, the trick is to think of it again.”

Along with Vespoli, one of the more innovative shell builders is Resolute. They also employed designers of succesful racing yachts, and came up with something similar, especially the cross section, shortend length, and near plumb bow.

Funny, they are starting to look like Olympic K-1 racing kayaks! I say that because one of the major influences on K-1 design was Struer, over 20years ago, started designing boats using more computor testing pre-prototype, and tank testing the prototypes. An example is the hallowed Cleaver and Cleaver-X boats. Soon to follow was Composite Engineering, makers of elite single rowing shells, who came up with the Eagle K-1.

Seems the kayak tech world was ahead of the rowers!

karl (a reformed rower, who discovered the joy of seeing where you are going. Sold my single shell for a Cleaver-X)

They didn’t have a rep or tent at this event, but their boats were there. First thing I noticed on them is how their stern isn’t pointed at all ,but looked a little like a cross between the racing yatchs and a Baidarka. Had no idea how it plays into creating hull speed, but on none of these boats does a detail exist without a purpose.

Speaking of Struer. The April edition of the Danish Canoe and Kayak Association’s members’ magazine brings the obituary for Jørgen Samson(1918-2005).

He’s noted as the designer of Zephyr, Attack, Slender, Makker, Triton and Glider. The Danish National Art collection likewise marks him as the designer of the Cleaver-X.

An article of Samson on the design of kayaks kan be found here:

The text is in danish but there are som drawings.

Best regards Peter

K-4 with waterskier
I have seen a K-4 pulling a water skier for about 150 meters.

Despite the horsepower in a heavyweight 8man shell, there is a critical difference between how an 8 moves through the water, compared to a K-4 (BTW, I have raced both).

The problem with all rowing shells is that the body mass moves. This leads to a lot of deceleration and accelerating every stroke; when not carefully reduced by good technique, it is called “check”, or “checking the boat”. This makes pulling a waterskier difficult, not becuase of lack of speed (faster than a K-4), but becuase of the uneveness of speed.

In comparison, a flatwater kayak racer appears closer to even in speed, with very little decelleration between strokes.

This is also why a flatwater kayak can get “off the line” much quicker.

Even though I am out of shape, as the local crews ramp up for the upcoming races, I line up next to them in practice starts in my K-1. No matter what the boat class (single, double, 8) I can always get a lot of open water on them at the start.

But then they walk past me as I gasp for breath!


In designing a shell
the Vespoli guy said that you have to take into consideration that the weight in the boat is moving back and forth about 6’+ creating a whole new set of parameters for them to solve as to what shape will be most efficient. I wonder what would happen if they attatched hydrafoils on one. My quess is the up and down lift of the hull from stroke to recovery would make it difficult to judge where to drop the oar in. If that could be solved it would sure be fun to watch one go.

Maybe then they would retime the power
phase of all those oars.

I remember reading…
that the most aerodynamic shape possible is basically a teardrop shape with the point end cut off, then face this shape into the wind blunt end first(just like fishform). This would translate (I would guess) almost directly into water dynamics.

Teardrop is an underwater shape
Just look at fast attack submarines! Similar in the air - look at a jetliner’s nose (or any thing fully immersed in a something that behaves as a liquid).

Things are quite different at the surface. Only part of the body is immersed, and that introduces variables that do not favor the teardrop. Like wave making, power application, etc…

Fishform may seem to be a teardrop shape - but that’s only looking at it in two dimensions.

Racing kayaks and fast surface ships tend to be Swedeform, and that’s not an oversight or accident.

With sea/touring kayaks the difference between fish/symmetrical/swede tends to be over a fairly narrow range. More info from


“The %LCB is the longitudinal location of the LCB [Longitudinal Center of Buoyancy] with respect to the waterline. %LCB is what often distinguishes whether a kayak is ‘Fish’ or ‘Swede’ form. Fish form kayaks have LCB less than 50% of LWL while Swede hull forms are more than 50%. Swede hullforms displace water more efficiently, reducing the effect of wave resistance and are therefore faster, especially at higher cruising and racing speeds. Smaller pitching motion in waves, good handling in following seas (waves coming from the back) and drier ride are few other benefits of Swede hull forms…”

“…LCB in sea kayaks ranges from 49% for ‘Fish forms’ up to 55% for ‘Swede forms’. Designs beyond these limits result in poor directional stability as in the Swede forms or lack of maneuverability as in the Fish forms.”

Yes, Ted van Dusen
told me that this causes rowing shells to be longer than they ideally would be given the increase in skin friction with increasing length. But if too short, the movement from rowing would make the hull pitch.