Stevep wrote:unfortunately the answer is in the physics
for a displacement hull ( i can't paddle fast enough to get a kayak on plane) the speed is limited by the length
the formula being hull speed = 1.34x square root of the length in feet
so for my old prowler 13 (4.1 M) the hull speed is ~4.9 knots maximum
the shorter the hull the slower the hull speed
a 5.5m stealth kayak has a hull speed of ~5.7 knots
hope that helps
laneends wrote:
Waterline width also has something to do with it.
My surf ski at 6.1m(20feet) I can just touch 14kmh(7.6knots) in it. Elite paddlers can do well over this. K1 sprint paddlers go over 17kmh(9.18knots) in 5.2m(18ft) boats and sustain 14kmh over 2 hour marathons. Of course these are skinny as compared to fishing kayaks.
Due to the lack of paddle bracing pedal kayaks have to be on the wider side as they rely heavily on primary stability. Skinniest is revo 16 at 70cm, compared to stealths at 60cm, Skis down to 43cm and flatwater K1s 40cm.
Pedals are better for hauling heavy loads compared to paddle in the same hull. Pedalling long distances quickly takes strength and endurance training, no skill, other than handling stability in rough conditions etc. Paddling fast over long distances , especially in faster boats, takes increasing levels of skill as well as fitness. .
Seasherpa wrote:
Moreso the wetted surface area but the waterline width and hull shape are factors of this
What both keith and Eoin are pointing out is drag - water line length is one thing that all displacement hulls deal with drag however is what the paddler/pedaller has to deal with
first problem is wetted surface a longer kayak normally has a greater area of the boat effected by the friction of the water this adds drag
of cause a longer kayak is also narrower for the same stability as there is a longer surface in the water to hold you up
a narrower kayak along with the hull shape can reduce Residual drag
both fictional and residual drag is what the paddler has to over come to create speed
on most fishing kayaks we have poorly designed scuppers - good for draining water but not good for reducing drag
many have tranducers for there sounders in the water even using tranducer scupper that are not a drag free as a smooth hull
although this doesn't effect a pedal kayak the narrower hull for a paddle kayak being narrower around the feet area helps if you are using a good paddle stroke
as more power and of cause speed can be created from a catch closer to the centreline of the kayak
something that hasn't been mentioned is materials that a kayak is made from as most wont look this far
most plastics are quite soft and dont hold there shape that well so even if a good hull shape can have more drag than the design
harder plastics do this job better but are probably more costly to build
Fibreglass is normally lighter and stiffer than plastic and for the most part will hold its shape better and to no ones surprise that are normally quicker
carbon fibre ( the holy grail ) Carbon is quite stiff and strong so a kayak built from this material is normally lighter again than fibreglass and stiffer
and again normally quicker even as the same shape
of cause there are trade offs - plastic hulls are cheap to produce in high numbers with there moulding process and are fairly tough - fibreglass not as easy to make as plastic adding to the cost
and while tough probably hole easier if hitting rocks or other hard objects ( still fairly easy to repair ) - carbon more expensive than glass also needs to be handled nicer than plastic hulls and still repairable but harder to repair
Another material that can produce a light stiff hull and is not used that much in fishing kayaks is wood normally only used by DIYers - there are plenty of sea kayaks built with both marine ply or strip built using quite light wood species and glass covered
