# Hull Design; Rock& Roll

I am currently designing a canoe. 13’ long, 34" wide.

My question is about how much rocker should it have along the keel, and I don’t want a totally flat bottom, but rounded a little for better speed.

Just how much rocker and hull “roundness” would be right for general use on quiet rivers and lakes where wind is experienced producing 1’-2’ waves. Don’t want it to be too tippy either.

The construction is in cedar strip so I can make about any curvature necessary.

34 inches?

– Last Updated: Jan-09-10 11:18 AM EST –

thirty four inches seems overly wide for a 13 ft boat. It seems to be a solo, as 13'X34" will not work for most as a tandem. The very widest solo canoes are 31-32 inches wide, most are 29-30. You'll have a time trying to apply a vertical paddleshaft. What is the intended burden, how tall is the paddler, what kind of paddle?

I'd suggest something like 1.5-1.75 inches bow rocker, .75 to 1 in the stern.

Bottom roundness and how it's carried stemward is one of the designers dilemma. I'd want an elliptical bottom shape with ~ three inch rise to your ~32 inch waterline. You may want a little more V aft than into the bow, and how the rocker will carry out will affect turning/tracking.

With a Length/Width ration of 13X12=156/32 = 4.9 the hull will not track well. What is the intended usage?

My
My intention for a wider boat is for stability. Thought I could make up for the “slowness” by rounding the bottom a little.

Length = Speed

– Last Updated: Jan-09-10 1:40 PM EST –

Speed is pretty much determined by length, Sq root of the length in feet multiplied by a constant that includes the Froude number. The constant changes for different shapes, but not much with canoes, so for your 13 footer sq rt of 13 = 3.6 X 1.55 = 5.6 mph.

This simple formula arrives at theoretical hull sped; the two transverse wave wash, with bow and stern cutting down through those waves. Hulls can be driven past the theoretical speed by skilled athletes. Race boats tend to be a little fuller in the stems than recreational cruisers to eek out a little more speed.

Your width will be a severe limiting factor in achieving that speed due to the inefficient horizontal paddle angle to get the blade in the water and the yaw that would cause, particularly in a hull that will not track well due to very low L/W ratio.

A rounded bottom will not overcome the limitations of relatively short length and extreme width. The very slight reduction in wetted surface will not be apparent.

CE … That was one of your all time
best posts IMHO.

I
I don’t want to flip over.

I built a canoe last year, 11’ X 27" and it is so tippy that I have to sit on the floor. But it is very fast and tracks very well.

I want one that I can send my kids on out on the lake and not fear too much.

The canoe will have two seats for two people but perhaps be paddled solo using the canoe in reverse (I mean sitting on the front seat and paddle facing the stern).

Also
I once owned a small canoe 12’ X 34" that was very practical for two with a light load. Sure it wasn’t very fast but was stable enough for duck hunting, etc. The bottom was flat. The manufacturer was American Fiberlite. Not a well built boat but a functional design.

I’ve also noticed looking over some old literature from Bart Hauthaway that many of his small canoes were 32" or 33" in width. He was also an avid hunter/fisherman which may explain the need for a little more width.

Go to 14 feet, with a 32 inch beam or
less, and you will be delighted with the result.

As for stability, extra length does contribute more stability, beam being about equal.

Do you plan to kneel? Or sit on a seat right on the bottom and used a kayak paddle? Either of these solutions will make for good stability in a short hull. But if you plan to sit on a seat 6 or more inches off the bottom, you’re throwing away much of your chance for stability. Sitting on a raised seat in a short boat is for quiet ponds.

Iowa
I live in Iowa, a land where our lawmakers are scarecrows (no brains). It is also a DNR Nazi state. Maximum canoe length in Iowa is 13 ft or else you get “fined” registration fees every three years. Isn’t so bad if you only have one canoe but when you have a whole bunch it gets expensive!

This is really a shame since the more desirable canoe lengths are more than 13 ft. And Iowa probably has more miles of paddleable streams than any other state! Tourism could be huge and they miss the chance for increased revenue from income taxes and sales tax!

how bout 13 feet
and 29 inches. Inches DO matter in width. The 27 was too narrow and the 29 may be just right.

The Mohawk Solo 13 is about that width and its a terrifically stable boat for sitters and kneelers. Look at its hull shape.

That said you must give yourself more than five minutes in a boat to feel comfortable. We put beginners in “tippy” canoes and after about 30 minutes they are very happy. They are apprehensive and not breathing properly (which leads to muscle shakiness) in the first five minutes. In two hours we have to wrestle the boats back.

I have seen some really unstable strippers but usually its the hull shape that is the culprit.

Software?
Are you using any software to design it? If so most will calculate the stability/righting moment and give you something to work with rather than just guessing. There are several free software packages out there. You can also see the resistance figures and just how slow your boat is going to be.

I like to use Steve Killens Stabilty factor, it gives me a hard number to compare from one of my designs to another. It’s not perfect but it give me an idea of what to expect before I commit the design to wood.

design
29 inches might be alright if the hull lays out flat enough.

Where do you get software for hull design? I’m just not sure about how useful it would be since I’m doing a balancing act between stability and speed.

One thing about strippers is that you like the hull to have a large radius of curvature for the strips to fit easier. And that does make for a tippy boat but a fast boat. They are fun to paddle as they are quite fast!

KF
"Where do you get software for hull design? I’m just not sure about how useful it would be since I’m doing a balancing act between stability and speed."

The balancing act is the perfect reason to use software. Are you calculating anything or just taking a wild guess? Software gives you hard numbers to work with instead of just hoping it works. I am always comparing resistance and stability numbers.

There is several free programs out there on the internet.

Not
Not a wild guess but a more seasoned one. I consider shapes of the other boats I have had and try to estimate well.

Obviously the reason I made this post was to get experienced input from a few others.

Kayak Foundry 1.6.2 and later
Have stability curves estimation. There is a newer version that than, but in 1.6.2 the curves are there.

You can play with it if you have not to see how shaving off several inches width and playing with the hull profile can let you optimize the stability vs. speed to your liking.

On their forum you might even be able to find a design already that can be your starting point…

Thanks
Thanks for the info. I’ll study it out!

Being a hunter & fisherman kind of…

– Last Updated: Jan-11-10 11:18 AM EST –

explains why their "type" of stability are "Barges" or often lack some secondary stability. Ditto on taking a look at the Solo_13 dims...for ideas.
\$.01

Length = HULL speed
If I understand Mr. Winters correctly…

It is possible to achieve a higher hull speed with a longer hull due to wave making.

Below hull speed, where many of us paddle, skin fricton is more of a factor.

IIRC in “The Shape of the Canoe” he states that adding rocker can reduce wetted surface area and thereby reduce skin friction.

A 27" beam should be stable enough…
…for youngsters.

Depends on the child’s build… but please don’t just assume a canoe that is “challenging” for an adult is going to be equally so for a youngster.

Back in early the 1980s I was one of a handful of youngsters at a local canoe club. We EVENTUALLY got to mess around in our club’s new sprint / marathon racing kayak. This is after the senior instructors (mostly adult males, mostly 180lbs+) had almost all struggled and fallen out (in many cases repeatedly). We got REALLY fed up with being patronised by adults telling us we wouldn’t be able to cope.

When we DID get to paddle the racing boat… we had NO PROBLEMS. Stationary, with no paddle? No big deal. Healed over in a following sea? Fun: really rewarding, in a way that paddling the less performance oriented craft could never match.

Not sure the same folk could cope now they’ve (in some cases) doubled in size, but I’ve never topped 140lbs and seem to have far fewer stability issues than those who carry 40lbs of excess around their middle…

On a slightly different note, what sort of message does it send out to a youngster to put him/her in a poorly-performing tub that is so wide that those little knees can’t reach the chines and those little arms can’t reach far enough for a vertical paddle stroke? They can read the books and listen to the instructors to find out what they SHOULD be doing… can’t practice because the canoe is inappropriate.

More generally, do we want children thinking that the answer to finding something difficult (say: staying upright) is to go find an easier option (a more stable canoe)… or do we want them to think the answer is to become more accomplished (say: learn to paddle properly)? It ain’t difficult: anyone can do it. Just needs a bit of determination… which any self-respecting kid should surely learn anyway!

I’d rather see children (inparticular, though also adults) learn by soloing in an unstable craft with a lot of rocker: I doubt most would get much wetter… and at least they’d be challenged to become proficient.

Yes
Length will improve speed. As many of us know when you start pushing those waves the paddling gets tough. A longer hull makes that wave push speed higher and therefore easier to paddle.