Canoe length, efficiency and speed

Manfred that looks like a fun boat. Do you have any videos of it in action? I would probably opt for a sit on top hull for easier re-entry. Also, can you explain how you handle the sail trim?

 

Ok, that's clarify the initial question. Here are the rules for the dimensions, which are actually in the FAQ of the web site / Question : How do I measure etc... / Tandem canoe (C2) : http://www.yukon1000.org/faq/

 

Nice catch there Comfisherman.
Any other good websites or videos you know of for such events?

0.14375 @ 4" is right out of the OP... and the rule book.
Well, we couldn't have a more clearly defined SOR now could we?
Let the games begin.

 

I don't have much knowledge about the races, but the op likely does. If the world is as small as my hunch leads me to believe, this could be an interesting build thread.

 

Well Gentlemem, I certainly appreciate all the input. I didn’t give too many extraneous details because I didn’t want to muddy the waters. Perhaps a more consice question would be: Which canoe has less drag at (Let’s simplify it a little more) 5 mph? A 17’ x 29.3”? Or a 18’6” x 32”? Of course, all other aspects are equal.

I just can’t see how the larger boat could produce less drag Than the smaller boat at those speeds. Of course if we were talking about speeds over the hull speed of either boat, the answer would be odviouse. But to my understanding those hydraulic forces are not in play at the slower speeds.

 

It's a question of the sum of two different drag elements. The larger boat will have greater skin friction drag due to larger surface area, but will be operating at a lower speed/length ratio. This 2nd factor will (probably) result in lower wave making drag.

Given that 5mph is not far off "hull speed" for these lengths it would be reasonable to assume that wave making drag contributes a large proportion of the total, and so increased length is likely to at least offset the increased area.

 

At those speeds, the longer boat will be marginally faster.
That was easy.

 

Simple answer: Given the conditions, the longer boat will produce less drag because it sits higher in the water, which reduces the face of water against which the hull will push.

 

Example is to take a milk carton with a half kilogram loaded into it. Measure the water line on the floating horizontal milk carton. Now take 2 milk cartons taped base to base and load a quarter kilogram into each. Measure the water line on the floating horizontal milk cartons. Now you have something like half the frontal water resistance as well as less rear pull(suction) on stern.

 

My opinion is there is no significant difference between the two, compared to at least some of the many other factors which you are keeping constant. Such small differences in length and width should not make a great difference, unless you are asking only about the theoretical aspect?

 

For this comparison, which payload you consider : 2 adults + all the stuff for this 10 days endurance race >>> 200 kg ?, or more ?

 

For a 10 day race I would prefer the larger hull. You have to factor in things like stability and comfort. Plus you will have a slightly shallower draft.

 

I didn't take into account the difference in beam.
I believe the longer boat would still be less drag but by a smaller margin still.
So, the difference is really nothing compared to the value of other variables.
It's the design-spiral or the jigsaw-puzzle-effect where one change affects all the other pieces and how they fit together.
For example, if you choose the longer boat you may have more stuff which makes you heavier, and slower.
But, because you have more stuff you may have improved endurance which lends itself to longer and slower.
I could go on all day, but what I am trying to show is what you choose is up to the racer and what they think is a good call.
What works for one team may not work for another...

If it was me, I'd be inclined to go with the longer boat and make every effort to keep it as light as possible.

 

Build both, test each. The slower one gets a camo paint job and goes hunting. Faster one gets duplicated in space age composites and a Harley Davidson flame paint job.

 

bang on the money. I'd only add that the drag due to surface area increases in a gentle linear way as speed or surface area increase. wave resistance increases exponentially with speed. Hitting hull speed is when the wave resistance very quickly goes near vertical. When you have very limited human power available, You really are hitting a wall.
My experience with a dart18 (skinny hulls, heavy boat conversion) converted to pretty efficient pedal drives so in the same ballpark as paddling, is that 2 people could pedal all day at 4.3 knot ish, but 50 yards total Max out flat out.
was only 5.3 knots. We'd hit the hull speed wall where the wave resistance had kicked in.

I'd go skinny as possible and upto 23-24 feet maybe.