Quick, Easy 3-Man Canoe Plans

Good luck for you. Manfred

 

Thanks Manfred.

 

So, I discovered another option at the supplier today.

1/8 " (3mm) door skin! It's one layer (not plywood) and the grain runs in the 8' direction.

It's cheaper too! Plus, I can make a round shear (cross section) out of it, so less wetted area AND less material.

Thing is, I can't figure out how to taper the ends...

I tried it with a sheet of cardboard...

I figured with a 1/4" ply frame under each paddler (simply a half round) the load would be distributed sufficiently including the 1/4" sit-on top deck.

I have to go up to 16" beam and 8" draft...

I've looked through the Gougeon brothers book but I still can't taper the ends...

 

Is it worth the 33% gain in beam for a 7% reduction in wetted area and material?

16" half-round vs 12" square. (Edit: 12" X 8" draft)

I'm starting to wonder...

 

Taper

"I've looked through the Gougeon brothers book but I still can't taper the ends..."

Try to cut out long wedges as with KSS Design from Derek Kelsall. Make a model with aircraft birch ply - not under five feet with 1/16 " or thinner - 1mm ply or with the original doorskin.

 

You seem to be under a bit of a misapprehension about length/beam ratio.

For wavemaking, what's mostly important is how much water you shove out of the way. That's what makes the waves. You can shove it sideways (beam) or you can shove it down (draft), but either way it's still getting shoved.

In other words, it's the cross sectional area of the midship section that really matters. When talking more or less informally, people often talk about length/beam ratios because all else being equal a longer thinner hull will have less wave drag at a given speed.

If you make the hull half the width but twice as deep, all else aint equal. It's twice as deep, and it's still shoving the same cross sectional area through the water. This means you are probably not going to get a massive reduction in wave drag, and you probably are going to get a significant increase in wetted surface.

Check out racing cats and tris. The immersed hull sections are usually pretty close to semi-circular. Ditto for racing shells and kayaks.

 

That should have read 12" rectangular not square.

I get more like an 11% difference in wetted area not 7% that you claimed earlier.

I see your point very clearly.

We may both be getting a little distracted here as I think it's really more about length to displacement ratio.

I'll mull it over some more, it'll likely hinge on ease of construction.

Thanks

 

Thanks Manfred.

I'll give it a go.

The problem then becomes how to seal the seams with the few materials and time at hand due to the budget constraints...

 

NED,

The "hole" size is the same. I still need 0.7 square feet of cross section to achieve the buoyancy.

So the only thing I'd be gaining is a reduction in wetted area.

I'd be further ahead to make the hull fuller, i.e. not as streamlined, in order to reduce the cross sectional area.

 

You can do that too, which is why high speed hulls have a higher prismatic. There are practical limits to that though.

You might be further ahead, and you might not. It depends on what prismatic you have now, how long the boat is, what speed you are travelling at, and how much wetted surface you can get rid of. It's a balancing act. However, for any given prismatic, minimising wetted surface will still keep total resistance down. This is why multihulls, sculls, and K1's all do it.

Yes, which is a reduction in resistance, which is what you seem to be chasing.

If you can build the round one, it would be an advantage. If the construction is too much of a PITA for this event, then stick with rectangular.

 

I have a design challenge I'd like to present for your consideration.

As the displacement monohull approaches hull speed (~8 knots), it's small, lightly loaded outriggers could begin to plane.

For this they would need a low l/b ratio.

But at low speed, they can be more heavily loaded and forced into displacement mode where a high l/b ratio is favoured.

How to design these outriggers for both scenerios?

One idea I had was to put a small step in the bottom of the flat, displacement hull as in post #55.

 

I wouldn't bother worrying about any of that.

 

Why not?

 

Couldn't find that reference Manfred, although my edition is from 1985!

 

with your time constraints I would build the shape of hull that is fastest to build, which is likely the retangular cross section. Say is true with outriggers, best is fastest to build. I doubt you will ever get outriggers on plane, just make them as low drag as possible, which usually means long and narrow.