Fast or slow
- Thread starter tx river rat
- Start date
TRR
Displacement hull speed is limited by waterline length. The longer the length is the faster it will go. That is very simplistic. Maby one of our more edumacated wordsmiths can expound on this more eloquently than I. If'n they don't say anything about it Google up displacement hull speed and see what you get?
By the way. Are you going to get to make your Colo. hunting trip>
Bob
Displacement hull speed is limited by waterline length. The longer the length is the faster it will go. That is very simplistic. Maby one of our more edumacated wordsmiths can expound on this more eloquently than I. If'n they don't say anything about it Google up displacement hull speed and see what you get?
By the way. Are you going to get to make your Colo. hunting trip>
Bob
Wait for Matt to come on board with the mathematical formulae.
In the meantime, fast requires a hydrodynamically clean configuration. IE, a'' easy curves and no sharp corners. Long and lean (that's called "aspect ratio" - ratio of length to width). A tactical jet fighter will be aerodynamically as clean as it can get (A-10 Warthog notwithstanding). A javelin is an example of the most clean object I can think of right off hand.
Smooth, fair lines, pointy fore and aft ends, length. The bow of a boat separates the water, the stern puts it back together. A square ended boat creates a lot of drag, as evidenced by swirls and eddy currents. Fine entry and exit is what you want on a paddle craft.
Less wetted surface. A sphere is the solid with the lowest surface area to volume. To get a boat, you want length. For this application, a cylinder is the usefully shaped solid with the lowest surface area to volume. The closer to a perfect circle the cross-section of boat bottom is, the less wetted surface it will have. (Go back and take a look at old dugout canoes.) Flat bottom will have the most wetted surface, and the highest drag factor.
Sea Kayaker Magazine does a nice job of showing pounds of resistance at various speeds. (They also have pretty high integrity on product evaluations.)
Another thing that makes a hull fast is a 175 hp outboard. Most hulls will just go like hell with one.
In the meantime, fast requires a hydrodynamically clean configuration. IE, a'' easy curves and no sharp corners. Long and lean (that's called "aspect ratio" - ratio of length to width). A tactical jet fighter will be aerodynamically as clean as it can get (A-10 Warthog notwithstanding). A javelin is an example of the most clean object I can think of right off hand.
Smooth, fair lines, pointy fore and aft ends, length. The bow of a boat separates the water, the stern puts it back together. A square ended boat creates a lot of drag, as evidenced by swirls and eddy currents. Fine entry and exit is what you want on a paddle craft.
Less wetted surface. A sphere is the solid with the lowest surface area to volume. To get a boat, you want length. For this application, a cylinder is the usefully shaped solid with the lowest surface area to volume. The closer to a perfect circle the cross-section of boat bottom is, the less wetted surface it will have. (Go back and take a look at old dugout canoes.) Flat bottom will have the most wetted surface, and the highest drag factor.
Sea Kayaker Magazine does a nice job of showing pounds of resistance at various speeds. (They also have pretty high integrity on product evaluations.)
Another thing that makes a hull fast is a 175 hp outboard. Most hulls will just go like hell with one.
What was said above pretty much sums it up. Hull length, width, hull shape, displacement, weight on board, rocker, hull surface smoothness, wetted surface area, water conditions, wind conditions....all factor in.
Here's another way of looking at it.
First, think of Cathy Bates in a swimming suit. This equals a slow hull.
Then, think of a Nicole Kidman in a swimming suit. This equals a fast hull.
The difference is in cross-section and weight of the hull.
First, think of Cathy Bates in a swimming suit. This equals a slow hull.
Then, think of a Nicole Kidman in a swimming suit. This equals a fast hull.
The difference is in cross-section and weight of the hull.
These responses make sense, however I noticed that for e.g. Mick said his touring pirogue with a flat bottom was quick. Is that relative to the effort required to push a sea kayak or canoe? hmmm. Ok let's say if the same person could race himself in a pirogue a canoe or a kayak. Apart from being tired, what kind of result would he expect?
Much has to do with seating position but also wetted surface area.
Sitting higher up will allow a more powerful stroke than sitting low to the water.
It also could be a case that hull displaces an ideal amout of water to keep surface resistence low allowing Mick to go scooting along.
But also consider this: Take the 2 hulls out in sloppy, ugly surf. Which one would go faster? The kayak because to pirogue would be swamped a few times! :lol:
Sitting higher up will allow a more powerful stroke than sitting low to the water.
It also could be a case that hull displaces an ideal amout of water to keep surface resistence low allowing Mick to go scooting along.
But also consider this: Take the 2 hulls out in sloppy, ugly surf. Which one would go faster? The kayak because to pirogue would be swamped a few times! :lol:
I noticed my Freedom goes up river(into current a lot better. On flat water the perow is just a quick but I do have a long water line on that boat also.
Ron
Ron
"Quick" is something achieved with "effort". Put a boat in the water with a spring scale attached tot he pull rope. Tow it at various speeds and record the pounds of resistance. Do that with various hull shapes and you will soon discover that a flat bottomed boat will have more resistance to forward motion (meaning it is harder to paddle at any given speed) than a rounded bottomed boat.
Yes, length will make a difference, so will beam. Compare any two boats of equal length and beam, and the round bottom boat will be more hydrodynamically clean every time. Flat bottomed boats are fro different applications than speed. They perform well in their envelope. Fast speed isn't in it. Satisfactory speed is.
Yes, length will make a difference, so will beam. Compare any two boats of equal length and beam, and the round bottom boat will be more hydrodynamically clean every time. Flat bottomed boats are fro different applications than speed. They perform well in their envelope. Fast speed isn't in it. Satisfactory speed is.
I hope Chuck reads this Jack finaly admitted flat bottoms had there place and were satisfactory on speed
LORD LORDY
Ron
LORD LORDY
Ron
Well, TRR, the speed is satisfactory only to folks who choose flat bottomed boats. Lower expectations are well met.
Should they ever treat themselves to a round bottomed hull, they'd never go back. :roll:
Should they ever treat themselves to a round bottomed hull, they'd never go back. :roll:
Ok just to make sure my spanner stays in the works a little longer. 'Cos I know this is an unanswerable question on account of different requirements/shapes available.
Has anyone thought of rounding, or actually rounded out the bottom of a basic pirogue shape slightly ( I know it wouldn't technically be a pirogue still but I guess I'm asking if I'm on the right track for what I think I want to build) and rounded off the sharp corner twixt side and bottom using a third party curve, maybe even throw in a few strips to make the curve?
I'm trying to make you guys think for me on account of your knowledge and my lack thereof. Then I'll know if I'm headed in the right direction. To summarise: A pirogue, slightly curved keel and where the sides would normally meet the bottom a half a dozen or probly less strips following the curved outside corner of the ribs. I think something like this could provide the best of both worlds. Its easy for me to ask questions on account of I"m not ready yet to start building. :lol:
Has anyone thought of rounding, or actually rounded out the bottom of a basic pirogue shape slightly ( I know it wouldn't technically be a pirogue still but I guess I'm asking if I'm on the right track for what I think I want to build) and rounded off the sharp corner twixt side and bottom using a third party curve, maybe even throw in a few strips to make the curve?
I'm trying to make you guys think for me on account of your knowledge and my lack thereof. Then I'll know if I'm headed in the right direction. To summarise: A pirogue, slightly curved keel and where the sides would normally meet the bottom a half a dozen or probly less strips following the curved outside corner of the ribs. I think something like this could provide the best of both worlds. Its easy for me to ask questions on account of I"m not ready yet to start building. :lol:
The blue pirogue has a slightly rounded bottom. It is a style built by Chitimachi Indians on the coast of LA. They're not looking for speed, the shape of the bottom allows the pirogue to break the vacuum should it get stuck in the mud. This pirogue is for traveling in wet areas where some folks would say there is no water. Unfortunately I don't have a picture of the bottom.
john the pom said:
It certainly could be done on the bottom. You add up to 1" camber with little trouble. I'd say the strips could even be plywood about 1.5" - 2.0" [4-5 cm] wide. You'd probably need to set up a simple strongback with temp frames about 24" apart to ensure you maintain the shape with the strips.
you be doing the bottom pretty much by eye. Lay the center keel strip. Staple it to the temp frames. Lay one on either side. Might need a little trimming and sanding to fit each one to fit the center strip. Then just join the seams with the strich and glue method.
It's a blend of old-style boat building with modern materials. I thought about doing an entire simple canoe like this.
My understanding of where pirogues originally came from is the original dugouts. Is that somewhat correct? Dugouts had rounded bottoms by default, coming from a log. Maybe the flat bottomed ones are a more recent (2-300 years recent) for ease of construction?
I like the concept of "breaking the vacuum" should it get stuck in the mud. Maybe that's why we geezers have round bottoms? Cause we get "stuck in the mud" often.
I like the concept of "breaking the vacuum" should it get stuck in the mud. Maybe that's why we geezers have round bottoms? Cause we get "stuck in the mud" often.
Jack on my perow I took a piece of 2+4 about 8 ft long flipped the boat upside down blocked it up annd put tie downs on the sides pulling down putting about a inch crown in the bottom before I glassed it so I guess Its not a flatbottom.
Ron
Ron
ha jack, by default, the dugout tree was round and solid. just thinking outside the stump. and that round bottom in sitting in the water deeper than my row and when you get stuck in the mud, i'm still going strong. but it will come down to who has the longest arms. later keith
G'day guys,
Been away for a few days.
Here are some of my addled thoughts on what would make a fast paddle craft.
I agree with allmost everything Jack said, Consider a well designed expedition sea kayak - long, very fine entry and long very fine stern, and generally, a shallow "V" hull in about the middle.
To my mind, this type of hull is the most efficient for a paddler to propel through the water.
Agreed, a round hull form provides the least wetted surface area, but this is more than compromised by the total loss of initial and secondary stability. A shallow V with soft or rounded chines, overall is more efficient to paddle. The same boat, with harder chines, whle a little less efficient through the water provides very goos secondary stability.
The pot of gold is to achieve the perfect compromise between minimum wetted surface area with adequate stability.
Racing kayaks and surf skis are very long, and very slim and are notoriously unstable, but they are close to the optimum of hull speed. Remember, just about all touring paddlecraft are displacement hulls. They cut though the water like a spear. This also allowes a paddler to cover more distance with less effort.
Flat bottom boats will never achieve this type of hull speed for any significant distance and they will require much greater effort. My Touring pirogue and Robins P5 are fast for flat bottom boats but could never be compared to a true kayak or the Southwind for achievable hull speed that could be maintained for any distance.
They more than make up for this, however with their immense initial stability, ease of build, and simple elegance. There is much more to a very good paddlecraft than shear hull speed.
Been away for a few days.
Here are some of my addled thoughts on what would make a fast paddle craft.
I agree with allmost everything Jack said, Consider a well designed expedition sea kayak - long, very fine entry and long very fine stern, and generally, a shallow "V" hull in about the middle.
To my mind, this type of hull is the most efficient for a paddler to propel through the water.
Agreed, a round hull form provides the least wetted surface area, but this is more than compromised by the total loss of initial and secondary stability. A shallow V with soft or rounded chines, overall is more efficient to paddle. The same boat, with harder chines, whle a little less efficient through the water provides very goos secondary stability.
The pot of gold is to achieve the perfect compromise between minimum wetted surface area with adequate stability.
Racing kayaks and surf skis are very long, and very slim and are notoriously unstable, but they are close to the optimum of hull speed. Remember, just about all touring paddlecraft are displacement hulls. They cut though the water like a spear. This also allowes a paddler to cover more distance with less effort.
Flat bottom boats will never achieve this type of hull speed for any significant distance and they will require much greater effort. My Touring pirogue and Robins P5 are fast for flat bottom boats but could never be compared to a true kayak or the Southwind for achievable hull speed that could be maintained for any distance.
They more than make up for this, however with their immense initial stability, ease of build, and simple elegance. There is much more to a very good paddlecraft than shear hull speed.
well done on ya mick. you did a nice job on the matter. and sometimes it depends on where the race track is. later keith
Our forebears designed boats for pretty much specific jobs, it seems. And hunting was one of those tasks, in various environments. So, our paddle craft today follow their original paths - except maybe the white water boats.
Different designs perform well in different places.
Different designs perform well in different places.