Hard Chine purpose & differences

so what exactly is your point
I’m not sure I follow you?

So…
…if design doesn’t matter, a boat with a cylindrical hull will be more stable than my shallow-arch kayak as long as it has more volume?



Sketch the force vectors – where does the restoring force come from?

The center of gravity
and how much it rises as the boat is heeled over. If it’s located close to the bottom of the semicircle and the semicircle is of large diameter, it’ll rise quite a bit. Very stable.



Mike

Yes,
I’d like to see the point to these comments.



I certainly know that chine shape has a significant impact on stability. Sometimes it’s subtle, and sometimes not so subtle.



Two boats I’ve paddled a reasonable amount: romany and legend. Two very different boats with very different stability (Legend is sqirrely, the Romany is very stable) with similar ‘volumes’. So what determines the stability? Not the ‘volume’ in this case, maybe rocker, but what on earth do those chines do???



Considering the guillemot web page on stability, the theory ties in quite nicely with practice (suprisingly enough): a ‘flared’ hull vs. a rounded hull (Legend Vs. Romany).

chine’s impact on stabilty…
has more to do with location relative to the keel the the shape. Even on “hard” chine hulls, positioning the chines closer to the keel approximates a rounder cross section. Placing them farther out from center results in a more boxlike cross section.



This oversimplifies, but square has more primary - angled/rounded less primary.



As Sing already noted - deadrise is often more critical.

True, but
It’d have to be a diameter significantly larger than the beam of most touring kayaks. A 22-24" cylinder would probably put the paddler’s CG at or above the centerline axis.



Thought experiment: take a cylinder of the same beam as Jim’s QCC700, mount the seat the same distance below the centerline, and make it long enough to have more volume. Which will be more stable?

Well, if you want to make the
volume bigger by extending the length…the cylinder gets very unstable, since the beam at the waterline gets narrow, and the COG ever higher above the water.



Mike

Seat would not fit…
… at the same distance from center in a 21" diameter cylinder as it will in a 21" wide QCC 700!!!



The bottom of the fairly flat 16" wide seat pan is almost on the floor of the kayak - and the butt depression’s curve gets the center of that pan right down into the keel of the shallow V hull. A cylinder that would fit this pan that close to the bottom would be very large in diameter.



A cross section through the kayak at the low point of the seat would give people some idea of how this relatively fast 21" beam kayak can feel so solid both flat and heeled over.

which is where hard chines

– Last Updated: Jul-14-05 4:22 PM EST –

come into play, i.e. wetted surface - it does add stability (water is sticky)

Today hard chines go on planing hulls and some are mistakenly used with wide touring kayaks. The original designers would've never built a three-chined (keel being one) hull on a 22"+ beam, it's just unbalanced.

hull shape
has to do with turning, tracking and other performance factors but nothing to do with stability. All other factors being equal, it’s supposed to be volume that determines stability.

I am just parroting what I have read. I am not an engineer.

Go paddling guys!!!
Boats are what people convince themselves they are. It’s not about what’s technically sound science for most people, it’s about market jargon, and a lot of emotion. Bad paddlers in any hull are still bad paddlers. Need more emphasis on the paddler, technique, skill, fitness.

more on deadrise please
haven’t heard the term but get the concept. “increased deadrise results in decreased primary but increased secondary” is that so? how does that work? i think i can see how it decreases primary but not sure how it increases secondary. my gut tells me that secondary will be as much affected by the whole cross section of the boat therefore including deck shape in the freeboard area, no?

Primary Vs. Secondary And Deadrise

– Last Updated: Jul-14-05 4:56 PM EST –

A flat bottom sitting on flat water is very stable and this what I consider primary stability. Secondary stability is the ability to for the boat to give support as you begin to lean the boat. If you consider tilting a boat with "v" shape over more on its side, it will have more surface still resting near horizontal and providing support. In a lean, the the far side (away from the lean/pivot point)of the hull of a flat bottom boat will begin loose contact with the surface. The flat bottom hull will then quickly go completely over. A boat with more secondary stability will not feel as stable just sitting in flat water, but the secondary stability gets used more in rough water conditions, especially if waves are coming from the beam.

My skin on frame orginally have very little deadrise. It felt very stable on flat water when I first made it. However, it did not feel as stable in rougher seas. I actually went over on beam seas with 3-4' waves. When I repaired the broken ribs in the boat, I also took the opportunity to add on a 7' strip to the keel. The strip was 3/8" at the center and than tapered off to the ends. Adding this piece to the keel stringer, I effectively increased the rocker and the deadrise in the SOF. I believe the boat handles in rougher seas much better as a result of this change. 3/8" may not seem much, but in a boat with an 18" beam, and the width from chine to chine about 14", that little additional piece had a noticeable effect on the boat's performance.

sing


The Shtuff They Told Me…
when I was shopping was that hard chines act somewhat like a V hull; that hard chines actually make a boat track better.


emphasis
Great - so go start threads on those things instead of bitching about this one. I agree they’re more important, but some us us are interested in design too. Room for all.



Personally, as Product Designer and paddler, I find it’s a natural interest! Next kayak for me will likely be of my own design. Then I’ll get to paddle AND evaluate whether my limited understanding of these things translates to the performance I want.

The way i understand this
and i know absolutely nothing except what i’ve read and was told (Pygmy) that the hard chine on an Arctic Tern when edged over onto the chine acts as a keel. This chine/keel is curved lengthwise(rockered) and this is why the boat turns much easier because the boat want to follow that chine/keel. Am i understanding that correctly?

yes

NOt only turned lengthwise

– Last Updated: Jul-16-05 11:46 AM EST –

but assymetrical The assymetry on most boats helps the boat turn as much as the added rocker does.

that's is one of the reasons why the foster shadow out turns the legend. The extra width means extra rocker when it's on a hard lean.

makes sense

what you say makes sense, but…

– Last Updated: Jul-15-05 8:34 AM EST –

are you saying that different hull shapes will affect the VOLUME of the boat above the water line on a lean?
I believe that the hull shape only affects the shape of the water carving abilities under the water line and so a hard chined boat with equal dead rise to a soft chined boat, will turn more sharply. But I am not sure that the above-waterline volume is changed between a soft chined and hard chined boat of equal volume on an equal lean. Both would remain EQUALLY stable at equal angles with equal volumes above AND BELOW THE WATERLINE. Do you feel that you can lean a hard chined kayak further than a soft chined one?