Hi there Merijn,
First let me congratulate you on what looks like a very well executed design. If this is your first kayak or boat design you have reason to be proud… As others have commented – don’t be afraid to build. You can’t have enough boats…

Since I have been working on a design with similar goals off and on for about 2 years, I have a bunch of comments, ideas, suggestions and experiences to offer. Feel free to use any or all as you see fit. Apologies to others for the long response. Merijn just happens to be designing a boat like I’ve been designing with for quite a while – and I just love this topic : )

Length
You may want to consider scaling the boat down to 17 feet (5.18M).
I own several kayaks and race both my hard chine CLC LT17 and my Epic 18X. The waterlines are approximately 16 feet and 18 feet respectively. While the 18X is definitely faster under all conditions than the LT17, I wonder if I am really strong enough and in good enough physical shape to make use of the 18 foot length.

I have designed versions in both 17 ft and 18 foot length – and cannot quite make that final decision on which way to go. I can tell you that I have test paddled a 17 ft. performance oriented kayak: the Fit from Think Kayaks (http://thinkkayaks.com/think-fit.html) with my hand held GPS – and the Fit feels comparable – if not a little faster. (Keep in mind the Fit has a beam of 20 inches where the 18X is 22 inches wide… Serious racing kayak enthusiasts I know tell me a thin 17 footer will beat beamier 18 footer any day.)

My point is – 17 feet feels as fast as 18 feet to paddler like myself. Your requirement for rough water maneuverability also suggests going shorter as well. If you have an Epic representative near you I’d strongly suggest you try out both their 16X and 18X. These would tell you a lot about what length to settle on and how your paddling style and conditioning will make use of the longer waterlines.

( I’d love to hear Nicks opinion on this: Is there a meaningful difference between 17 LWL and 18 LWL on a design with all other things equal, paddled by a fit amateur, the goal being speed in waves less than 1 foot?)

Final word on speed: if you really want to go fast, get a wing paddle. I was astounded at the speed increase when i started paddling with a wing. I still use my greenland paddle for fun and winter pool rolling but for covering grounf quickly, a wing is the only way to go. Hey Nick how, about a wooden wing paddle kit? That would be so cool - if a little heavy...

Hull parameters
To my eye it looks like you’re on pretty solid ground for things like prismatic and block coefficient. The cross section looks pretty close to the 18X – as you intended. I’ve made molds from my 18X hull and found the hull is fairly “U-shaped” with lots of flair – especially in the after sections. The aft sections are also fairly flat – which contributes to the hull surfing pretty easily in following seas.

One change you might want to consider is going with an even simpler 4 panel, hard chine design. I know hydrodynamic theory suggest more chines and a rounder cross section but I am personally convinced this will make little difference in overall speed potential given the average paddler. This is based on many miles with my two boats and lots of test paddles with all types of kayaks.

Hull profile
Your hull profile does look pretty much like the 18X and many other performance sea kayaks. So I’d guess you’re in pretty good shape here and can’t really go wrong.

However, if you’re going for optimum speed, you might want to consider a hull shape with an aft run that has the stern just kissing the waterline by time it reaches the stern. Study the fastest kayak designs, you will note they ALL have this shape.

Look at SurfSki sterns (although they are faster many other reasons too). Also look at European designed club racers like the Nelo Razor, Viper and Coastrunner: http://www.kayakdesign.org/coastrunner/coastrunner.html
http://www.fastkayak.com/neloviper51.html
http://www.kayakdesign.org/coastrunner/coastrunner.html

Here’s even a performance oriented 18 foot SOF design that looks beautifully executed. Note the comments on stern design: http://www.capefalconkayak.com/tyak.html

There are challenges with this type of shape and plywood construction though. I am finding it difficult to design a shape that is deep enough to allow strong construction at the stern. My quarter scale models just won’t come our right with this type of stern… Still fiddling... Also, this type of hull will not track straight and will weathercock without a rudder or skeg.

(Again Nick: We’d love your comments on the need or value of a high speed profile with these smooth, upward sloping buttocks like those on surfskis. All these K1 club racers seem to go pretty fast.)

Some similar designs you might want to look at…
Some years ago John Winters, noted naval architect and small boat designer , designed a kayak for a client to meet the fast sea kayak rules and is hence almost identical to the 18X in dimensions. Several of the designs were built by the client and enjoyed local racing success:
http://www.kayakforum.com/cgi-bin/Design/index.cgi/noframes/read/3734
http://www.nspn.org/forum/index.php?s=a05fdbc44f406850f857d1f9b45e951d&showtopic=487
http://www.nspn.org/forum/index.php?s=a05fdbc44f406850f857d1f9b45e951d&showtopic=487

Summary
This response has gone on longer than I had intended. For my boat, I have also researched skeg vs. rudder, new rudder designs, self bailing cockpit fittings, and a host of other things that may be of some help to you. Should you or anyone on the board be interested in details, shoot me an email or board post and I’d be happy to share the results of this delightful part-time obsession.

Enjoy the new boat whatever you settle on...

Greg Jones
Columbia, MD
gjones1960@gmail.com

: Hi all,

: I am new on this forum. Usually I build bicycles and model
: aircraft, but now I am contemplating a seakayak.
: My current boat is a Wilderness systems Tempest Pro 170, A nice
: manouverable able rough water boat . On my flat water training
: paddle I run into the limitations of the hull speed, it just
: will not go much over 5.5 knot, whatever I do for it. That
: started me thinking about a S&G boat. Strip planking is to
: much work.
: Some requirements:
: -Fast
: -Not extremely tippy
: -Good secondary stability
: -easily rolled
: -Footroom for size 12 and up
: -Suitable for rough water and surfing on larger waves

: Using the lines of the Epic 18 I did some work on a design in
: Delftship. The design will need a rudder, but that is not drawn.

: Some specs:
: Design length 5.500 m
: Beam over all 0.547 m
: Displaced volume 0.135 m3
: Beam on waterline 0.499 m
: Total length of submerged body 5.442 m
: Waterplane area 1.699 m^2
: Total beam of submerged body 0.499 m
: Waterplane area 1.699 m^2
: Block coefficient 0.4604�
: Waterplane coefficient 0.6264�
: Prismatic coefficient 0.5910�
: Waterplane center of floatation 2.653

: Here a first picture.

: Knowing little about kayak design I would like to have some
: comments. What information do you need to judge the design?

: Greetings,

: Merijn