As a backyard builder I have enjoyed making three boats, but have relied more on my eye (art school background) then any knowledge on nautical design to create the kayaks I have designed/built so I thought it would be fun to see how the P-net crowd would design the mythical (near) perfect boat. To do this I have done my best to dissect the boat into its’ 3D parts for others to reassemble as they see fit.
1. Hull shape
a. symmetrical
b. swede form
c. fish form
2. Hull cross section profile
a. hard chine
b. multi chine
c. soft chine rounded bottom
d. soft chine v-bottom
e soft chine flat bottom
3. Bow entry (looking head on)
a. flared
b. straight sided
c. rounded
d. narrow below waterline and full above
4. Stern exit (looking rear on)
a. flared
b. straight sided
c. rounded
d. narrow below waterline and full above
5. Bow profile (side view)
a. plumb bow
b. sloped up (Greenland style)
c. long steady slope up (Baidarka style)
6. Stern profile (side view)
a. plumb
b. sloped (Greenland style)
c. vertical and quickly tapered to a low volume (Baidarka style)
7. Bow rocker
a. none to very little
b. first fifth of the boat
c. first fourth of the boat
d. first third of the boat
8. Stern rocker
a. none to very little
b. last fifth of the boat
c. last fourth of the boat
d. last third of the boat
9. Width
a. 21" or less
b. 22"
c. 23" or more
10. Length
a. 16.5’ or less
b. 17’
c. 17.5’
d. 18’ or more
Directions: For each of the numbers (1-10) assign it a letter or just redesign the parameters and directions (which is fine by me)and Computer assistance is allowed.
Wow, interesting post.
Can you define bow entry and stern exit a little more? I’m not familiar with those terms. I’m sure it’s easier to draw on paper than describe in words.
Bow entry/stern exit
This would be the shape that the water would see as a bow approaches it and the shape of the stern as it exits the back of the boat (if it could turn around and look back at it)
There Is No “Perfect”
Boat. There always compromises in coming up with a design. The design lends itself to near "ideal" performance for the load, conditions and types of paddling the designer have in mind but my be less than ideal for some other paddler.
So in doing this exercise, it's just as important for the paddler to state his/her size, what usage and conditions the boat is be designed for. Without these, there is no way to judge whether the design will come even close to what was intended.
So, for example, if I wanted to build a "long boat" optimized for surf for my size of 5'3", 140 lbs, I would answer in the following way:
1. Hull shape - A. Swedeform because I want my balance further back towards the stern to avoid pearling in deeper waves, and two initiate turns from back there with leans/edging.
2. Hull cross section profile - A. Hard Chine because these will carve better on the wave face rather than slide like the softer chines or multichines.
3. Bow entry (looking head on) - D. narrow below waterline and full above. I want the bow not to dig into the wave trough rather to have volume above to float over rather than to cut in.
4. Stern exit (looking rear on) D. narrow below waterline and full above. For the same reason above but further amplified by the characteristics below.
5. Bow profile (side view) b. sloped up (Greenland style)
6. Stern profile (side view) a. plumb
7. Bow rocker- d. first third of the boat, and combined with long slope of the bow will ride over rather than through waves.
8. Stern rocker a. none to very little to combine with the swedeform and hard chines. This hopefully will result in leans/edging that carves into from the last third of the boat while the front 2/3 of the boat will go in the direction designed and float/plane over the water.
9. Width b. 22" just because it's a "longer boat" so I don't want too wide of a beam, creating too much volume along with length, that will make the boat harder to control.
10. Length a. 16.5' or less. Specifically around 13-14'. Just because under that we won't be in the "long boat" category anymore. Over 14' I would have too much volume with a 22" beam. But if I narrow the beam in favor of length, then the narrow boat will end digging in more, even with a rocker. Plus, it would not have as much curve along the chines to effect faster turning when edged/leaned.
You forgot to mention "deadrise" the angle from the middle of the hull bottom to chines. In a surf oriented boat I want a flatter bottom underneath and just in front and back of where the paddler sits. This flatter bottom will plane better and when leaned/edged will dig the chines into the wave better for turning. I wouldn't want the deadrise more than ten degrees. At the same time, I wouldn't want 0 degrees either because that would create a very unforgiving edge which can catch and result in maytagging if I am not careful of my leans and edgeing.
Depth of boat was also missing. I would want maybe about 5" at the aft deck by the rear of the coaming. This allows me to do sweep rolls easier. My front deck would be no higher than 8" - just enough to squeeze my size 6 feet in. I think any higher depth with the length and rocker will create more volume (and more too control) than I would need to surf with.
sing
one rocker combo not listed
which interests me would be a keel profile with the front 1/3 straight but sloping down to a curved center 1/3 and a straight but sloping up stern section. this profile in theory would produce a fast (straight entry and exit lines) manuverable (ends lifted to not inhibit turning) shape, yet i dont know any yaks with this profile.
That Would Also Depend
of the rocker aft and forward. If the rocker is greater than 2", it’s going to turn more. If less than 2", it begins to track more and more over turning.
From what I under stand of Flatpick’s description of how designed the Tempest with a “loose bow” than means more rocker towards the bow and minimal rocker at the stern. So, when you paddling sitting straight, the keel will keep you tracking. But as soon as you lean, the front keel line, especially towards the bow, will begin to clear out of the water, and allow for easier turning.
sing
What the hull?
I started this posting for two reasons. First curiosity. Second I know that I do not know or understand how the shape,size and volume of a hull works yet anybody who has tried different boats quickly realize how they can drastically vary in their behavior. I realized this the hard way when one boat I owned had behaved so fantastically till I got my first chance to paddle it in rougher water (storm off shore) and quickly realized what little skill I had would be needed to keep it up right and pointed in the right direction. My hope is to see people discuss what they like or would like in a hull shape/design and why (thought Sing did an excellent job with his posting) and this might lead to people who are looking to build or purchase be more knowledgeable. For instance we often see postings over the virtues/downfall of the NDK boats, but what is it in their hull shape that still has a strong following even though their quality control is more then suspect at times. Being an “informed consumer” should extend beyond brand name recognition or terms like initial stability, secondary stability, speed etc. etc. Bottom line is that we will never know in advance or firmly be able to predict how the “Waters” will behave so it might be positive to understand how a hull will. Thanks
Lots of missing data
Like someone posted earlier…how far towards the midship is the rocker carried. Two inches of rocker that is carried gradually to the full 1/3 of the boat is much different than two inches carried only 6" back. How flat is the midship hull area? That will help determine how quickly it turns and the initial stability. Is the flatness of the hull carried forward or aft? This will help determine whether or not stern strokes or bow strokes will help turn the boat. How far back is the flare on the ends carried? This will affect where the bow wave comes onto the deck & how wet the ride is. The use of CAD programs has greatly impoved design methodologies.
Data?
What I would like to see is people offer their data on their mythical boat and if possible explain/defend what characteristics/behavior their boat will have.
my current s&g project
is derived from the pygmy queen charlotte, john lockwood’s first kayak plan… so far i have the bottom panels cut, i took a half inch out of each panel down the middle to yield a narrower boat. i also added 5" to the length of the bottom. then i lowered the sheer on the side panels by an inch in the middle and more on the ends to reduce volume and windage, and reduce the length back to 17’. basically this is classic greenland style, raking ends, shallow v bottom swedeform hull modified to meet my desire for a relatively manuverable, pretty fast and stable enough to sit still and fish dayboat/camp cruiser. compromises, compromises! i expect the finished product to come out at 17’x22 1/2" at 45 lbs.
Data Shmata…
I’ll bet you’re building better boats with that art background than with data. You’ve put together a great post but you’re not going to get the response that you were hoping for. There are a lot of irrelevant data pushers around here (not that they’re wrong though, there is a good knowledge base here).
Here’s mine:
- Hull shape
a. symmetrical
- Hull cross section profile
a. hard chine
- Bow entry (looking head on)
d. narrow below waterline and full above
- Stern exit (looking rear on)
d. narrow below waterline and full above
- Bow profile (side view)
b. sloped up (Greenland style)
- Stern profile (side view)
b. sloped (Greenland style)
- Bow rocker
a. none to very little
- Stern rocker
c. last fourth of the boat
- Width
a. 21" or less
- Length
d. 18’ or more
Rocker Question
Curiosity has me wondering–what would the on water charecteristcs of this design be with little to non rocker in the bow, but rocker in the back (stern) fourth of the boat? Thanks
That’s just how I built my SOF
Don't really know what effects it has but it still handles very well. But between volume distribution and center of buoyancy, the bow comes up a bit when sitting in the water with me in it or not. I have another boat with a lot of rocker in the bow and the only thing it does well is turn. The Bernoulli effect (if you're unfamiliar with it:http://members.iinet.net.au/~bluep/wavedrag.html ) is extremely evident in shallow water with that design.
think about it
bow would track and stern would be loose.
When moving forward, the bow already tracks as the bow wake pins 'em and sterns are already loose cuz they’re in an ‘eddy’ so designing a boat that amplifies this ‘out of balance’ characteristic will…pin the bow and loosen the stern…and what 'bout if you paddle in reverse???
oooohhhhmmmm… balance, grasshopper.
steve
Baidarka?
It appears to me that the Aleution Baidarka's work with the rocker emphasis in the reverse of little in the bow and a lot in the stern. I notice that their rocker starts way back on the hull and continues up all the way to the tip of their bow, while their stern seems to have much less rocker and is quite plumb. Since it was a design that plied the seas (and rough one at that) for century's, what are the pros and cons of their approach compared to the ideas posted above? Speed doesn't seem to be an issue as I once read in Scientific America that Greg Barton paddled one of Dysons' Baidarkas in a controlled timed setting at a speed that was just slightly less then what he achieved in his hi tech Olympic boat.
An Aussie version
This guy’s take on the “ultimate” is kind of interesting:
http://www.nswseakayaker.asn.au/mag/52/TheDevelopmentOfTheUltimateSeaKayak-TimDillenbeck.htm
very interesting
thanks for the link.
seems a bit ‘battleshipish’ for my tastes, but heck looks like he done hims homework!
steve
No specs?
Or did I miss them? Like to know L/W, deck heights, LWL/BWL, etc. Overall it looks somewhat familiar…
It did look sort of familiar
I’m thinking it might have been pictured in SK sometime in the last few months with other home-built yaks. Wouldn’t swear to it, though.
I don’t know whether it’s a good design or not, but it’s kind of fun to see what people come up with when they try re-thinking stuff.
fine ends = pitching?
my skeptical self did a double take when i saw that. in my little mind a full ended boat would pitch more, depending on wavelength, or what?