Not useful space
Look at the addition from a top view. You’d be extending a fine entry of a plumb bow forward. A small wedge at best.
Gains drag x 2
You already add drag as displacement increases (increasing both skin friction and wave making drag). If the kayak also get longer as it sinks you only add to this drag. This addition is NOT in your favor.
Doing this in waves is even worse - as you give up more energy to the waves the more you have to bury in them. Cutting deeper costs forward progress. Some designs use this for stability reasons - dampening the ride (Explorer) so it’s easier to manage. Can make them more forgiving, but being slower - they need to be. Just more trade-offs.
Note the common preferences for short kayaks to play/hang out in the rough - and more plumb designs with longer waterlines for powering through upwind and grabbing rides down.
As already noted -typical paddling uses are so middle of the specs that all this stuff hardly matters - paddle what you like - just don’t mistake preference for advantage.
While LWL are selected for performance, customer expectations play a large role in driving overall lengths -with most “sea kayaks” being from 17’ - 19’ long, and the majority now between 17’ 8" and 18’ For designers to get a range of handling/feel in such a narrow length range they need to adjust waterlines from there. Want more playful? Shorten the LWL (leaving more overhang. What better speed and/or loaded efficiency? Keep more LWL.
Rocker can take either end of this range and make it behave more like the other (ex: QCCs have more rocker than it might appear - and more than several of the pointier ended designs). Tradeoffs…
Performance of more plumb designs like the EPIC 18, QCC 700 and CD Stratus should be compared to longer kayaks like the Seda Glider and CD Extreme that have similar waterlines - and not to other +/-18’ kayaks with overhangs and much shorter waterlines. Few of the “faster” British sea kayak even have the waterline of a QCC 600/500, and some less than a 400.
The interesting thing about the more plumb 18 footers is how good they are all around. The speed potential’s a bonus - not the only point of these designs.
this
would have some aplication if the boat or boats in question didn’t flare or become wider, the further into the water they settle. in otherwords this is only truly apliciable to a pointy ended box with flat sides. If a given boat increases in width the farther into the water, then it would be more desireable to arest the depth by adding to the length. As a plumb bow equipt boat settles deeper into the water, if it has a hull that gets wider by the gunwales then in effect it will become wider because it is not held higher in the water by the length change adding to the floatation of the hull.
Best Wishes
Roy
I might::
http://www.playthesea.com/
Never paddled it, but I hear Malcolm from Mega had a hand in designing it, so it may truly be a wunderkind in surfing sea kayaks. Agreed, the Coaster is a rippin’ little boat.
Dogmaticus
Superb post Grekay!
kindasorta
– Last Updated: Oct-08-06 11:43 PM EST –
You simplify a premise by saying length at waterline increases drag. If so, a boat with plumb bow and stern would have more drag than a traditional brit boat of the same length at waterline. There's a proportion component there. That's why you see race drivers draft, and why you see "long tail" versions of race cars at Le Mans and other fast tracks.
Having said that I don't find anything wrong with the notion that upswept ends are a historical projection and for aesthetics. There are claims that the upswept stern was engineered by the original designers to keep the boat facing upwind during hunting.
Helps climb over waves
Whenever in doubt about an engineering theorm, exagerate the example and you wil have your answer.
Imagine a kayak with a 90 degree angle at the bow and one with a long overhang. If you run a line from the under water bend of the 90 degree boat up to the deck, it will have no gain in boat width. On the one with overhang, the area under water up to the deck gets wider or fatter allowing it to climb up overwaves whereas the 90 degree entry has to plow through them. Same with a following sea. The overhang stern rises over the following sea and the 90 degree one gets shoved by the sea or is forced to slice through it.
All things being equal (rocker etc.) that’s it.
The overhung bow basically has it’s entry in to waves on an angle helping it climb and slice with less resistance. Some race kayaks with a more vertical entry get by because of the long length and extremely gradual taper of the boat and generally are meant for smoother waters. (no rocker to gain speed)
Volume? Buoyancy?
Aren’t these what really create the effects you’re describing.
“Imagine a kayak with a 90 degree angle at the bow and one with a long overhang. If you run a line from the under water bend of the 90 degree boat up to the deck, it will have no gain in boat width. On the one with overhang, the area under water up to the deck gets wider or fatter allowing it to climb up over waves whereas the 90 degree entry has to plow through them.”
To do a fair comparison you’d need to measure from the tip down - and back, not up and forward. Compare what the wave sees, not what your eyes see. Flare will be similar and the more plumb will have more volume and give more lift.
“Same with a following sea. The overhang stern rises over the following sea and the 90 degree one gets shoved by the sea or is forced to slice through it.”
No again. Plumb stern a has more volume and so more lift.
“The overhung bow basically has it’s entry in to waves on an angle helping it climb and slice with less resistance.”
Sliding and slicing = drag.
The slicing can be OK in certain conditions to temper the ride (already mentioned in other posts) but comes at a price.
The mechanical lift as you describe is minimal compared to the lift from buoyancy - unless you have big bow vanes like a spec ski or something grafted on AND you are charging down-wave fast enough for them to work.
Even if angle and flare were the main elements - the more plumb bows are also flared ad lift. As far as wave piercing goes a plumb bow acts the same PLUS has more volume/buoyancy below the tip! Again, you have to consider this from the top down, and from the tip aft - not forward of the knuckle.
“Some race kayaks with a more vertical entry get by because of the long length and extremely gradual taper of the boat and generally are meant for smoother waters. (no rocker to gain speed)”
Tell that to surf ski designers - as well as those designing all manner of fast displacement vessels. All sea kayaks are relatively long and have gradual taper.
Borrow a QCC 700 and compare the way it rises over waves and compare to an OI or any other of the many excellent pointy ended designs of similar dimension. Differences are not extreme - minimal in most situations - but are there and will change your assertions above.
The real differences people feel are much more from differences in volume distribution, LWL, rocker, etc.
If a design benefits in any way from grafted on wave dampening overhangs fore and aft - and the performance/trade-off is acceptable - by all means add them on or shorten waterlines to get them. If the net is a loss, don’t.
This is why we have different designs (beyond history/marketing) and why I have 2 of each type (though neither my SOF nor the Sparrow Hawk are extremely raked). Currently the raked bows are our favorites, but that has nothing to do with the angles of their bows and sterns.
Flare
– Last Updated: Oct-09-06 5:12 PM EST –
The upward flare is not similar. That was my problem with those pictures you did further up. Though they were fun in side view to make the point you were trying to make, they overlooked that you'd have to pinch in the above-water volume considerably, or be left with funny transom-like ends fore and aft.
After having done that pinching, you'd no longer be left with a Force 3 equivalent in anything but flat water.
As to whether that pinched-away volume is significant, as well as the overhanging bow that was lopped off, I think it could be, could imagine it getting close to a gallon of displacement, right out at the end where there's a lot of leverage. As to whether better or worse, I'm not even going to guess. But it is different.
Mike
don’t mistake preference for advantage.
– Last Updated: Oct-10-06 1:09 PM EST –
Great aphorism!
Plumb stern and a smooth ride
Greyak wrote:
"No again. Plumb stern a has more volume and so more lift.
“The overhung bow basically has it’s entry in to waves on an angle helping it climb and slice with less resistance.”
This, in itself, may be a reason to design a boat with a plumb stern. If you want to reduce the lifting action of the bow when paddling into waves, one way to do it may to put more volume in the stern (you could also reduce rocker). By this principle, a boat with an upswept bow, a plumb stern, and little rocker might have the smoothest ride. Whatdayathink?
Wavelength variations
– Last Updated: Oct-10-06 6:42 AM EST –
You could probably optimize a boat for a particular wavelength, but you then have to imagine the opposite, or the out-of-phase case. What happens to your bouyant-butt boat when the stern's rising on the crest as the nose heads for the bottom of the trough? What happens when the waves are twice as long, or half as long?
It's fairly straightforward to optimize a design for a particular environment. Making a design that works well in a wide variety of conditions is much more difficult.
An extra foot or so…
To shove tent poles, fishing rods, sleeping pads, chairs. Making room for other stuff farther back…
Overhang ends
Greyak
Maybe you misunderstood my point. Or my example is not clear.
check your illustration
http://www.appliedeccentrics.com/kayak/forces.jpg
Compare the top one to the bottom.
Pretend rocker and length are equal.
See where the water meets the bow on the top kayak.
The deck above that point has width or… boyancy… or (V) shape.
See where the water meets the bow on the bottom kayak.
The deck above has no boyancy or (V) shape.
That’s it. With all the various paremeters, you can blame this on that etc. but the fact remains that the overhang allows the kayak to have width over the point where the water meets the boat. The fact that it occurs means something physical and not just esthetics. You can derive anything you want from it, but it is not the same as the boat on the bottom.
“Extra”? How do you figure?
You pointy ender defenders do some funny math!
Are you comparing something like a Caribou or Brit sea kayak against a QCC300 or EPIC GP?
Most plumb bow kayaks discussed/compared (QCC 700/EPIC 18) are nearly 18’. As long or longer that similar pointy enders. Exceptions being kayaks like the old school “fast” hulls like the CD Extreme and SEDA Glider.
Using your Impex illustration.
At the same waterline there is more storage available on the pointy enders, at least a foot more room to store long narrow items.
And they are pretty.
More illustrations
I get what you’re saying about width above the waterline. I just doubt the significance.
“Compare the top one to the bottom.
Pretend rocker and length are equal.”
LWL or LOA? Image shows equal LWL so let’s start there…
“See where the water meets the bow on the top kayak.
The deck above that point has width or… buoyancy… or (V) shape.
See where the water meets the bow on the bottom kayak.
The deck above has no boyancy or (V) shape.”
http://www.appliedeccentrics.com/kayak/forces2.jpg
From the side view it appears so (see image above), but head on as it presents itself to the wave that upper wedge is relatively insignificant. It’s not a ramp, but a knife edge. This extra piece cut may cut in more, but really has no significant V or volume to provide lift. The lift comes from the V in cross section as you’re saying - but aft of this small piece - where both types have more flare.
The only wat yo really illustrate this woud be a cutaway view above that point. I’d suspect more similarity than difference.
If we now switch to equal overall length kayaks - more like what’s on the market - the more plumb one gets more volume into/onto the wave sooner. The finer bow buries sooner and deeper then lifts as the wave moves back along the hull. Compare the Force vs. a more plumb bow version of same overall length (more like a QCC or EPIC):
http://www.appliedeccentrics.com/kayak/forces3.jpg
This is more of a real world situation given available models. Now your argument essentially disappears, as the plumb bow has fuller ends from top or side - and more volume under the nose.
“With all the various paremeters, you can blame this on that etc. but the fact remains that the overhang allows the kayak to have width over the point where the water meets the boat.”
A rather on dimensional way of looking at it. Finer ended kayaks tend to also have more pinched gunwales. This makes the tip very narrow - and minimizes the already minimal difference you’re talking about. It’s usually a blade more than a wedge.
Plum bowed designs tend to have no pinch and carry their volume to the ends. More lift, more of the time.
I have noticed a trend in the more recent designs (of the past 5-10 years) to reduce this pinch, and steepen the entries a bit. Rather small differences, but there (compare Force and OI to Nordkapp in next image).
I would contend that there is little real difference in most cases. Both slice and both lift. What difference there is in feels has more to do with the degree to which the volume is concentrated amidships or carried more to the ends (again, not drastic differences in the types of kayaks being discussed).
Let’s take another look at the width of the shape above water you’re talking about - again above the point the water intersects the hull at the waterline - and from there lets also go a couple feet back. What’s that shape like? How do various kayaks compare? Have a look at this image:
http://www.appliedeccentrics.com/kayak/forces5.jpg
Interestingly (to me anyway) this secton is nearly identical in area and shape on a Nordkapp, an Outer Island, a Force 4, and a QCC 700 (all of similar overall dimensions). Look at the the most different two - the Nordkapp and QCC. The Nordkapp’s pinch is balanced out by it also being more fishform. The unpinched QCC balanced by being more swede (not also that the QCC does have some width at the point you identified). Result - very similar overall areas in the nose. Adding in the rest of the tips to the areas makes little difference and evens things out even more.
Your using an example for a kayak…
… that doesn’t exist.
Look at these that do exist:
http://www.appliedeccentrics.com/kayak/forces5.jpg
No fair
Greyak, you’re the one who started this latest thought exercise chopping the ends off a Force 4, which was actually a way of looking at the subject that might have removed some of the variables this discussion always devolves into.
And now you’re trying to muddy the waters tossing those longer waterline boats back into it. Doesn’t help.
Mike
Doesn’t help?
– Last Updated: Oct-11-06 1:38 PM EST –
Discussing different aspects, different ways. Comes full circle taken all together.
Whether the overhang is seen as extra volume above or less volume below (or vice versa for more plumb) colors peoples' impressions. LWLs need to be shown both ways to get past that.
The top view stuff is more telling, but still rather limited. Cross sections and buttocks lines would be more useful to show where the flare is and how the volume's distributed.
Longer overhangs are like hard chines. Not good or bad - just highly overrated as far as their impact on performance.