asymmetrical are swede form

[tx river rat]

There is so much knowledge on here and Jacks boat science, :lol: that I have another question I sure would like you to kick around.
Pros
Asymmetrical swede form
First I just like the looks of it
It seems this is the shape that is chosen in cars rockets arrow heads airplanes any thing that wind resistance is a factor.

In yaks I think it is more stable, sitting 18 to twenty inches behind the center of the boat puts your weight in the wider part and your upper body
which affects rolling the most in the widest part of the boat

You float shallower because weight is in the widest part

I think it is a faster better handling shape

more room in the cockpit

Cons
More trouble to build because you cant mirror image the front and back panels

Boat is wider so paddle interference is greater

Come on guys tell me where I am wrong or need to adjust my thinking

Ron
You know the Laker is a great boat wonder what a 13 ft laker asymmetrical swede form would be like hummmmmmmm Matt?

 

[oldsparkey]

Looks to me like the Pro out weighs the Con part of your argument , especially the part you said .........."First I just like the looks of it". To me that is the major concern when building a boat.

If you like it then the boat is going to be what you want , if you don't like it then the boat has one strike already against it. No matter how great it is.

Chuck.

 

[JEM]

you're about right on the swede form. Keep in mind it's generalities. It gets more complicated when you try to make everything interact.

 

[nobucks]

Pros

First I just like the looks of it

I like the way it looks too, that's one reason why the kayaks we design tend to be Swede form.

I think it is a faster better handling shape

Agreed. Swede form tends to have a finer entry and, with the fuller stern, it's easier to get up to top speed and maintain the speed.

Also, IMO, a finer entry is preferable in punching out through surf and riding swells, as the kayak tends to punch through the wave, rather than ride over the top, shooting for the sky, which is what a fish form kayak with a fuller bow tends to do. The Swede form, fine entry kayak tends to be a wetter ride, but I prefer it.

Cons

More trouble to build because you cant mirror image the front and back panels

Not a problem in a skinboat. Although there are no duplicate frames inside our Swede form kayaks, whereas, with our symmetrical, fish form kayaks, the three frames in the front have a mirror image frame aft.

Boat is wider so paddle interference is greater

That's not really a problem that I've noticed. I think that a kayak is narrow enough that, unless you get into bigger rec boat sizes, it's not a problem, at least, for me.

 

[Tor]

First I just like the looks of it

I like the way it looks too, that's one reason why the kayaks we design tend to be Swede form.

Well those two quotes put pay to a post I made earlier suggesting that a particular design wasn't popular because of the asymmetric design (but that was a canoe).

maybe it's at it's widest where you sit but much skinnier elsewhere, it wouldn't be any wider than a symmetrical design so there is no increased interference with paddling.

Tor

 

[hairymick]

G'day Ron,

I am sort of divided into two camps on this one.

I like the assymetrical hull shape for it performance and pleasing looks as stated here in other replies - but there is a trade off (for me anyway)

I am mainly a recreational paddler now and have little, if any need for this added performance. I think in a rec or even a touring boat, the performance gained is, at best, marginal. Is this little percieved added performance worth all the extra effort in marking and cutting all the extra panels - for me I don't think it is.

Case in point, I have built two fairly simple Jem pirogues, both of similar length and beam. One is symmetrical (P5) and the other is assymetrical. (Touring Pirogue) Both are superb pirogues and I am very hard pressed to tell the difference in paddle speed between them.

I have also built two big canoes. Southwind is assymetrical and Sasquatch is symmetrical. (very different boats I know) but my point is this, All other things being equal, no wind etc, There is practally no difference between them in paddle speed or glide for the same effort expended to make them go forward.

Take a big complex built canoe or kayak for example, with a lot of panels. Assymetric, there will be twice as many panels to mark and cut as in its equivalent symmetrical sister. Not an issue if you are happy to spend twice as long in the mark out stage. is the extra effort worth it - for me - not really - unless I really like a particular design.

Another example, is the new Sasquatch (14) Matt is working on. symmetrical hull - lots of panels and a truly beautiful hull. The symmetry of it is part of hits appeal to me. Five panels per side with the back half identical to the front. This mean that there are only five panels to mark out and trim and then use them as templates to mark out the other 15!. Likewise there will be mirrored temp hull stations.

http://www.jemwatercraft.com/forum/view ... hp?p=10666

Compare this to Matt's fine Issaquah 14 - another beautiful canoe of similar size and capacity but with an assymetrical hull and only 4 panels per side. This boat has eight panels to mark and cut. = more panels to mark in a hull that actually has less panels in it.

http://www.jemwatercraft.com/StudyPlans ... yPlans.htm

 

[tx river rat]

Mick
I agree with everything you say on here ,and to me I can lay out the other panels in a hour are so Matts plans make it easy,but it does take longer.
We talk about performance gained and sometimes I think I give the wrong impression. I like performance not to race I like to look and play ,
but if the extra speed is there and I am bucking a 30mile an hour wind, going up the river against the current are have a storm blow up that I need off the water the faster the better. That is where the performance shows.
My T-V is a good mile an hour faster than any boat I own and this lets me paddle less to cover the same amount of miles so It is my favorite.
I very seldom go all out in any of my yaks unless I am just playing.
Ron

 

[nolafolk]

Asymetric stripper

This is my first post to the forum. As my first project I'm building a 16' canoe, plans from Compumarine. I'm interested in any experience or comments about this very asymetric design. If there's no experience out there I'll post my impressions when I'm done, probably in the fall sometime.

So far the build isn't bad. You do have to lay out more forms (10 in all) but that went pretty well. Two days for all the forms, working relaxed and not full time.

My paddling experience is entirely in regular canoes. I went the asymetric route because of (hopefully) better paddling efficiency.

 

[Kayak Jack]

Without hard data from a water tunnel (as opposed to a wind tunnel) I would not say a lot about how much more streamlined an asymmetrical hull is than symmetrical. If a person had two designs of the same boat, one symmetrical and one asymmetrical, then he could attach a spring, run water through at various speeds, and see how much resistance was presented.

I think that a long, narrow entry versus a shorter entry may be such a small difference in resistance that without the suggested water tunnel with speed controlled water current and a spring attached to the hulls, a paddler couldn't actually tell the difference. And, if you took a Swede form, turned it bassackwards to make it a fish form, what would the differences be in resistance?

We have to remember the type of resistance in the medium through which a hull is going. An arrowhead is pointed because it penetrates meat - MUCH more resistance within a solid than in a fluid such as water or air. Also, an arrow is going through air much faster than a boat goes through water. But, of course, water is thicker than air.

A Swede form is more hydrodynamically clean in the front, but not as clean in the aft end. The more blunt rear end will tend to produce drag, partially or wholly making up for the advantages gained by a fine entry.

The MOST stream lined would be a long, fine entry followed by a long, fine exit. Take the water apart over a long distance (fine entry) and put it back together again with a fine exit (mirror image of the front.) That will provide the cleanest, most efficient hull for going straight and level straightforward.

BUT, in use, we don't go only straight forward; we tend to wobble around, stop, lunge, turn, rotate, ferry, eddy out, etc. THAT is where the asymmetrical form begins to show its worth.

All that being said - hell, Ronnie, if you want it, BUILD it. I don't see you apologizing much for choices you make. (Me neither, for that matter.) Go for it, and enjoy it to the hilt.

 

[nolafolk]

There's the solution

Kayak Jack, that's exactly what's needed. A GPS (for accurate speed), a boat with a trolling motor (for consistent speed), a good fishing scale and a couple of different canoes. I'm a long ways from wetting my project, but when it's done I think I'll do some experimenting.

 

[Kayak Jack]

Nolafolk,

Sea Kayaker Magazine has formulae which they will provide and can be used for estimating drag of a hull at various speeds and loads.

I was on a forum for skin on stick kayaks a few yeas ago. they began to wax all enthusiastic and hydrodynamic engineering like over the bifurcated bow. (An open vee in the bow with a point sticking out in front, underwater.) They go talking about ocean going liners etc.

What happens at 3 knots does NOT happen at 30 knots. A displacement hull futzing along at a slow speed is not a really good platform to start blossoming forth with high falutin theory. Make it pointy fore and aft and kinda smooth and bulgy in the middle and you pretty well have it.

Yes, we can alter handling a lot with design, we can make it a lot easier to perform various tasks with changes in design, some changes just look better than others, etc. And top end speed or drag at any given speed will vary - but not all that much. Those variations are more evident in a race where most times the difference between #1 and #2 is less than 1%. But when paddling down the stream with camp gear aboard, or when paddling out to go fishing, much of those differences simply evaporate and become individual choice.

 

[jdupre']

Jack, I've read a few drag tests for different designs, lengths, materials,etc. and you are right-- right around the 3 knot level, there is not much difference at all between a sleek sea kayak and a chubby 12" plastic play kayak. Actually, some short boats score better at about the 2.5 mph level than the 17' high-dollar jobbies.

 

[tx river rat]

I am a lucky guy, I have a lot of friends here in this area that have yaks from wooden ones built to race ( marothon boats 20 feet long ) My fellow builder here Gerald with his excellent boats to SOT.
I have paddled them and with them , my hot air perow, is asymetrical 15 ft 6 in and 28 at the bottom It will stay with most of the plastic sot with out any problem and stability is great, My TV is 24 inches at the bottom asymetrical tracks like it is on rails and even with over 400 lbs in here did very well staying with Jacks boat which is two inches narrower , stability is great on this boat I think the asymetrical part has a lot to do with the straight tracking of both these boats The Laker is symmetrical and performed above what she should do, but she is 2 inches narrower than the TV and sets in the water several inches deeper at my weight I think that is a big part of the tracking of this boat.To me this boat takes a low seating position for a couple reasons 22 inches wide, and your weight is not in the widest part of the boat. The Tv even at the wider width is faster.
In archery you put on vanes on the back of a arrow for stability basically asymetrical, and I have played with chronograph enough to realize
that a straight arrow flight means speed I think asymetrical in a boat design helps the tracking and that means speed in a Yak to.
AND BESIDES THAT THEY LOOK PRETTY
rON

 

[Kayak Jack]

Ron, I have no argument with your observations on which boat performs how. You are, however, leading yourself astray on at least one point. Where you sit in a boat.

A hull shape, for discussion purposes lets use a Swede form with a long front end, has a center of lift, just like it will have a center of gravity. The center of lift is that point along the keel line, at which if you apply weight, the boat will neither tip nose up or nose down, but will remain flat and settle deeper into the water.

So, if the center of gravity (CG) of a seated paddle, let's say his belly button, is directly above the boat's center of lift, the boat will have neutral trim - neither nose up or nose down.

Ron, that center of lift may - or may not - be at the widest part of the hull. For lateral stability, it makes no difference where the roll torque is applied, the entire hull rotates at eh same time. Let's set up an experiment.

If we had 10 boats, all exactly like your boat. If they all had the same weight of load in them, Ron (at 225 pounds) plus 100 pounds of lead bars placed in various locations. All 10 have the CG of the load in the same location, say 8" above the center of lift (or any other point in the boat for that matter). No load is arranged like the load in any other boat, but its CG is identical in all 10 boats. Boats#1 through 9 has Ron sitting in them, with additional weight to balance trim. Boat# 10 has the same weight (all lead) and an identical location of the CG

Now, if all 10 boats had an identical rolling moment applied to them, all of the Ron's brace themselves rigidly in the boat, and they all would roll identically. (If a paddle moves, it changes the CG of the load and will give different roll characteristics.

I may have done a poor job of explaining this, but it is true, nonetheless.

 

[tx river rat]

Jack
I agree with most of what you posted, except I do not sit in the center
my butt where I sit is behind center about 19 inches, this trims you a little nose high, and puts me in the widest part of the boat,asymetrical, this changes some of the geometry of the boat. and also the depth of the boat in the water changes that, nose heavy tail heavy can increase or decrease how much force it takes to roll the hull, dang If had a drawing it would help,
ok lets go at this a different way if my weight was on the center line of the boat I would agree a 100 percent, sitting behind center in the widest part of the boat which has moore surface area (wider) front end trimmed up a little there is more stability, if I was sitting backwards in the boat
in the narrow part and started to roll the wide part would be slower affecting the stability because it is sitting shallower in the water (less contact
the amount of pressure to get the roll you are talking about varies when you apply different forces from the weight and trim.
Ron

 

[Kayak Jack]

OK, lets set some ground rules which we need to define, modify if need be, and then agree upon.

1. When the hull rolls, it all rolls at one time. Nothing leads and nothing lags.
2. Attitude of the hull (nose low, level, nose high) for any given cargo load, can affect how much roll has to be induced before the widest part of the boat contacts water.
3. A paddler sitting rigidly will affect roll the same as if lead weight were installed replicating his position and CG.
4. A paddler who moves can overcome #2 & 3 above.
5. A paddler who moves AND braces can CURE most or all of #2 & 3 above.
6. A boat with sides that are not straight up and down, but sloping outwards, will resist rolling as the wider parts of the side contact water further and further out away from the center of the boat.
7. Paddler technique is more important in a rolling situation than boat design, up to some point. (Obviously, a boat only 10" wide will tip with any paddler. But, boats with beams of, say, 24-30 inches become much more reliable and predictable.)

 

[tx river rat]

Jack
Found a good example take Chucks canoe sit in the middle try to turn it over , then sit in the back with nose high try the same thing it is a lot easier to do if you are sitting in the back of the hull.
Ron
Then run like hell because here comes Chuck and we done stole his canoe

 

[tx river rat]

bye dang i think you got it jack

 

[oldsparkey]

Jack
Found a good example take Chucks canoe sit in the middle try to turn it over , then sit in the back with nose high try the same thing it is a lot easier to do if you are sitting in the back of the hull.
Ron
Then run like hell because here comes Chuck and we done stole his canoe

Ron... If you want to paddle it ... I will furnish the paddles and camping gear , just leave me my Vienna's and Beanie Wieners or you ...WILL... be used for target practice and you do not want to see what I can do to a target.

Don't know about you but it is just common horse sense to sit a fraction back of the center to balance out a boat , sure ain't rocket science. Heck anyone in the third grade knows that , or should.

The seat in this one I'm building will be like all the rest of the solos I have made , the leading edge of the seat is right at the center line , not past it and not way back from it , right at the center line just kissing it with the front of the bar going across for the leading edge of the seat.

One Pirogue I made , John Deppa picked it up , all 32 pounds and 15 1/2 feet of it and it was so well balanced he walked across Floyd's Island in the Okefenokee Swamp and did not have to hang onto it for the whole portage. It sat on his shoulders like it wanted to be there and in fact he even drank a beer while doing that. That is a fact cause I picked up the empty beer can. ( That was before he quite drinking alcoholic beverages and stopped smoking. )

Unlike Jack who gets ... WAY ... to involved with the higher stuff and thoughts , the best thing is the K.I.S.S Idea....... Keep It Simple Stupid.

We will get together ... one day for a trip and if you want to use my canoe , you are more then welcome to , as long as you have something for me to paddle. If you are like someone else and want to hit ever rock while paddling .... Then I'm going to have some serious thoughts about your paddling abilities. :lol:

Chuck.

 

[bearridge]

If you are like someone else and want to hit ever rock while paddling ....

If I tole ya once, I tole ya twice more.....it aint like pinball. Ya try NOT ta hit them rocks. :wink: When yer goin' downriver, keep yer eyes off the fancy women. It always ends the same way, like that time Marc Antony went after Miz Cleopatra. Same az Sonny when he went after Miz Cher. In my younger days I made that mistake a few times myownself. :mrgreen:

regards
bearridge
bodine nautikle society

You can observe a lot just by watching. Yogi Berra