Start with a flatish canoe or kayak hull and cut a “tunnel” down the middle of it, so you end up with a shape something like two pontoons running down the sides of the boat.
What are the likely effects on stability, speed, and maneuverability?
boat:
http://www.nativewatercraft.com/ult_12_elite_lg.cfm
guy standing:
http://www.chesapeake-angler.com/storyoct06-Ultimate12kayak.htm
This boat was mentioned in a nearby thread called “canoe/kayak hybrids”. I don’t really see how it is a hybrid of those forms, but it is interesting. They claim much greater stability from the hull shape and show a picture of a guy standing and casting a fishing lure in a 12-foot long, 31-inch wide boat.
Of course, I can stand in a canoe like the Old Town Pack long enough to get a picture taken, but it’s not something you want to do all day. If this boat really is stable enough to do that, what are you giving up? Speed? Maneuverability?
Memphis I have a Riot Polarity with the
same shaped hull. It is a tandem 16’6" long 26" beam. It tracks very well, has decent speed but as far a stability is concerned I am not convinced it is any better than a normal shaped hull. Just my opinion.
my two cents
The hull should exhibit high initial stability, low secondary stability, poor manueverability, and a lower speed than a hull without the pontoon shaped hull. Might have its purposes, but I would say the cons outweigh the pros.
least it cant deform if stored upright
but neither can y pamlico 140, which has a regullar u-hull
uh oh
I just came across this marketing verbiage elsewere on the Ultimate site. It’s so horrible that it kind of sabotages everything else they say:
The Ultimate has a split hull (tunnel hull)… kind of like a catamaran, but better. The Split hull reduces the wetted surface and displaces less water than traditional kayaks. Less water displaced from the hull makes the boat faster and more efficient. Boats that have more displacement, have more drag…Thus requiring more energy to move the boat. The Ultimate’s split hull results in a much lighter boat in the water,when compared to traditional displacement hulls. Its no surprise that the hull shape is just faster and more efficient than traditional kayak hulls."
“Reduces the wetted surface”? Wouldn’t it increase it, due to the more complicated nature of the outline thanks to the dent or tunnel in the middle?
“Displaces less water than traditional kayaks”? Isn’t displacement volume a given for a known weight? Isn’t this statement like saying “weighs 58 pounds but weighs less than other 58-pound boats”?
Good catch!
Wow, that’s pretty horrendous, and your interpretation of that write-up’s “meaning” is spot on. It DOES give me an idea though. It would be fun to put together a collection of over-the-top advertising statements by all the different boat makers. I wonder if there is any company out there that would be immune?
Perception America has this kind of hull
I had 2 of them. They were okay for beginner boats but no manuverability. Boaring.
might be partly correct
You’re right about displacement. To float a given mass of boat(and contents), you need to displace an equal mass of water. The “hole in the water” can be any shape, but it’s got to be the same volume for the same mass.
As for surface area, the hull shape with the least surface area per unit volume is a cylinder. Two semicylindrical pontoons might have less surface area then a rectangular hull shape. I did a quick calculation for two 10" x 12’ semicylinders vs. a 12’ x 30’ rectangle with the same volume, and the "pontoons’ did have slightly less area.
what about the flat part between?
I think you're forgetting to add the flat part of the hull between the two half-cylinders. There's no way a W shape has less area than a U. Minimum wetted surface for a boat means a smoothly rounded bottom, side to side and front to back. The farther you get from that shape, but greater the wetted surface. Unless that boat floats with the center of the hull out of the water, then it has more wetted surface than a typical canoe.
re: nativecraft
hi…i test paddled a 12’ nativecraft this past fall… Pros/very stable… i could turn the boat with a sweep stroke within it’s own length easily, lots of storage for gear …Con’s/ a tad heavy for it’s size …i would not qualify it as fast or even quick,an aluminum canoe in the same length would paddle faster and easier, certainly not a WW boat …a tad 2 wide, banged my knuckles a couple of times. probably best for quiet waters, big people, photo shoots,fishing, slow,easy paddling. also noticed i was getting a lot of water runoff from paddle into boat , even with drip guards on paddle, this may have been due to high angle paddling due to 220? paddle i was given during test
All said and done …despite some flaws …i will probably be buying one next spring for fishing purposes, and adding spray skirts and other acc. in due time. As the caveat here in pnet goes …test paddle one 1st if at all possible.
PS; also tested the “pedal” model …quite fast fer little effort but i don’t think i could pedal it for hrs on end, and no forward space for anything with drive unit installed.
pretty old science
Nothing new about “multi-hull” designs - they’ve been around in various forms for many decades. Experience shows that they can be a more stable platform at rest than other designs. By design, the two hulls must sit lower in the water, for a given displacement, than a flat or nearly flat hull. This can help with primary and directional stability. What you give up is some of everything that you might want when the boat is moving or on moving water.
Seems like if you would spend most of your time fishing while at rest, in locations that don’t involve long distances or moving water, they might be a great choice. Personally - I prefer a conventional hull with a wider beam for that use, since it would give up some, but not all, of the same - and would sit higher in the water (an advantage I’m not willing to give up). Although the Native design would probably do better on a windy lake, for obvious reasons.
I have to agree that the ad copy seems to be way out of sync with reality.
Details?
EVERY boat can be "turned within its own length with a single sweep". What varies from one boat to the next is HOW MUCH it turns in that situation. Since the only "design feature" of this boat that would aid turning is its short length, I'd be surprised if when compared to many other general-purpose designs it would deserve to be judged as "maneuverable". Those twin hull bulges would make this boat sit pretty deep in the water and provide a lot of lateral surface area to resist pivoting.
burden and surface area
at rest, any displacement hull will displace enough water to equal the weight of the hull and paddler and any other stuff carried.
Excluding end shaping, the cross sectional shape that will do this with the least surface area is round. Think Olympic boats and a year of swimming.
The more one flutes a hull, the more surface area touches the water. Surface area and skin condition are the two main factors in canoe/kayak drag up to ~60% of max hull speed.
Roto-molded hulls have terrible skin condition after moderate use, and need flutes to keep the hull ~rigid, so mostly perform poorly anyway.
With magic/Ultimate, stability standing has been the design goal, so efficient paddling performance has never been a priority.
If you want to stand to cast, they work, but get the Tegris model, it's way lighter at ~35 lb.
And never plan on knocking down 30 miles in a day.