Kayak design

[cthippo]

Went out to the WAKE demo day yesterday and tried on a few boats. I didn't find anything I like better overall than my current Emotion Edge, but I did paddle a neat little boat that really turned my crank. It's a Sterling Grand Illusion 17'3" x 23.5" and the model I paddled can be had for a mere $5000.

It wasn't perfect, I felt that the cockpit was a little cramped for my size extra-fat ass, though a lot more comfortable than some of the boats I paddled. As you can see it's a fairly narrow design with a lot of rocker and apparently optimized for surf and open water. This design has been very popular with competition surf kayakers and folks who like playing in heavy waves.

Using that as a start I worked up a design that incorporates the features I liked about the Grand Illusion, but is more in keeping with my own preferences in design and construction and a little bigger. Elements of the design I liked included the high bow for seakeeping and the amount of rocker which meant that it turned in something less than a mile, which is usually my complaint with boats of this size. I also converted the measurements to Metric because Freeship loses a lot of features if you use imperial units.

Dimensions are 5.3 Meters LOA (17' 4"), .66 Meters beam (26") and .152 M draft (6") and a displacement of 156 kg or about 344 lbs.

Due to the concave shapes of the hull at the ends I'm looking at cedar strip construction for the hull with solid doorskin panels for the deck.



So, am I missing anything important here? Feedback welcome.

[rwatson]

Why the 'back pinching' aft cockpit end ?

For that matter, why the rope snagging, ball catching groove in the front of the cockpit ?

[cthippo]

Because I don't know how to convince Freeship to make cockpits.

Or transoms for that matter. Still learning to use this tool.

[Petros]

two things come to mind for me; 1) it seems a bit wide for my tastes. I do not like a kayak any wider than about 22 inches, even for my 200 lb plus current weight. If you actually need it that wide because of your anatomy, than there is not much you can do about it. I do not spend much time in waves, I try to avoid them, my intended use for a sea kayak is long distance traveling. A wide kayak feels like you are pushing a shoe box through the water after the first hour or two of paddling. Factory kayaks are always wide because they are selling to mostly inexperienced paddles, only their best models are in the 22-23 inch wide range, and they do not sell many of those.

The other issue is I suspect this will want to weather cock rather badly. Is there a reason the Stearn has to sweep up so much? I would eliminate this in the rear and reduce the forward up swept bow to keep the wind from blowing you around.

Otherwise the hull lines all look nice.

[rwatson]

Originally Posted by cthippo

Because I don't know how to convince Freeship to make cockpits.

Or transoms for that matter. Still learning to use this tool.

Thats a very valid reason - I can only import chine lines - doing anything with the mouse makes big problems for me. No wonder its (virtually) free !

PS - Pointy ends may look nice, but in surf they can be lethal. Try even retrieving an empy hull being pushed towards you by a small wave - danger !!

[cthippo]

Originally Posted by Petros

two things come to mind for me; 1) it seems a bit wide for my tastes. I do not like a kayak any wider than about 22 inches, even for my 200 lb plus current weight. If you actually need it that wide because of your anatomy, than there is not much you can do about it. I do not spend much time in waves, I try to avoid them, my intended use for a sea kayak is long distance traveling. A wide kayak feels like you are pushing a shoe box through the water after the first hour or two of paddling. Factory kayaks are always wide because they are selling to mostly inexperienced paddles, only their best models are in the 22-23 inch wide range, and they do not sell many of those.

That's exactly the issue, I'm afraid. I'm 6'1" and 260 lbs with a pelvis that is 19" across and I have the devil's own time finding boats I can even fit into. My current boat is 30" beam, but I find that just a bit wide, but the 23.5" one I paddled yesterday was pretty tight, so 26" seems like a good compromise.

Originally Posted by Petros

The other issue is I suspect this will want to weather cock rather badly. Is there a reason the Stearn has to sweep up so much? I would eliminate this in the rear and reduce the forward up swept bow to keep the wind from blowing you around.

The only reason for the high stern is that the original had it. I have seen some designs with high bows and low sterns. My guess is that the high stern is to help you deal with following seas. Perhaps someone else can shed some light on that subject.

Originally Posted by Petros

Otherwise the hull lines all look nice.

Thanks

I'm looking at the KAPER resistance calculations Freeship spit out and I'm trying to figure out what they mean. The "point" of the speed / resistance curve appears to be about 16 Newtons at 4 knots. Is this good? Bad? Indifferent? Unfortunately, I don't have anything to compare it against.

Also, what are the factors that go into residual resistance?

[Easy Rider]

cthippo,

You may like my kayak. Necky Pinta. 17.5' x 27.5". It's a double chine hull and the first chine has a beam of 19". Mine is in Kevlar and it's a very straight tracking boat and because of that you may not like it. But it is excellent for your weight and size. You could come up here and paddle it home!

High bow and low stern is best for a balanced boat in the wind. As one sits in a kayak one's torso is up in the wind and aft of the CG of the sitting paddler so beam winds tend to blow the stern downwind so a low stern and high bow gives the boat balance.

[NoEyeDeer]

Originally Posted by cthippo

Because I don't know how to convince Freeship to make cockpits.

Or transoms for that matter. Still learning to use this tool.

You have to set the borders of the cockpit as crease edges. If you do that it will come in without the funny points.

[cthippo]

A couple of videos of similar kayaks by the same builder doing things I'm not brave enough to try...

[LP]

Originally Posted by cthippo

I also converted the measurements to Metric because Freeship loses a lot of features if you use imperial units.

Hey CT,

I'm curious, now. What features do you lose with Imperial? I've been using Imperial forever.

[cthippo]

Originally Posted by LP

Hey CT,

I'm curious, now. What features do you lose with Imperial? I've been using Imperial forever.

A lot of the drag analysis calculations won't work with Imperial units for some reason.