Unstable cedar strip canoe

I am in need of some advice from experinced canoe builders.  I have built a 15' cedar strip ribless canoe.  I fiberglassed the body inside and out.  The top of the seats are 10" from the floor of the boat.  The gunnels are made of ash.  The gunnells are about 2" wide and 2.25" high.  \The boat turned out beautifully.  However, it is very unstable.  It is fine with a single paddler (without much wind) but once you get a second person on board it gets very tippy.  I am assuming that means the center of gravity is to high.  I am wondering if the weight of the ash gunnells are the problem.  I don't think I can lower the seats much without having to paddle with my knees in my chest.  Additionally, the camber of the hull at the location of the seats is such that I would have to cut the width of the seats to keep them in the same position or move them in toward the middle where the boat is at its widest.  Because the boat is finished (and wooden) I am not too exited about experimenting with changes to the boat without having a pretty good idea that the change I am about to make will result in a more stable boat.  Can someone out there give me some advice on what to do?

19 replies:

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RE: Unstable cedar strip canoe

Could you give us some more information, such as the canoe design, the width of the hull etc. Without this information, I could suggest trying a temporary seat such as a box which is at a lower height to see what difference that makes.

Robert

RE: Unstable cedar strip canoe

I think that, compared to the weight and height of the occupants, the gunnels are much too low and much too light to be a significant factor.  You need to look elsewhere for the cause.

It may be a tippy hull shape.  This is why Robert asked about the design.

Also, from the fact that the boat is fine with one person aboard, it seems possible that your second paddler may be adding dynamic unstability.  The latter problem is easily cured by the two of you spending time in the boat.  Over a period of a few trips, the balancing reflexes of both paddlers--which are initially out of phase with each other and with the boat's constantly reversing "righting moment"-- will become tuned to the boat and to each other, and what seemed to be a tippy boat will seem perfectly stable.  At that point, it may also feel more nimble and "better" than another, more inherently stable boat would.

With kayaks, this "training effect" is reported here frequently.  In fact, surprisingly enough, buyers who are looking for a long term relationship with a kayak have been advised here to ALWAYS buy a kayak that feels a little tippy at first.

 

RE: Unstable cedar strip canoe

I agree with the above. I canoe regularly, and the most important thing by far is how the two (or more) occupants work together.

Nothing you have described suggests that the canoe is the problem. Sure, some designs are more 'tippy' than others. Usually with one or more distinct, outweighing, advantages in fact. However, the closer you get to a 'proper' canoe, the more you (and your co-pilot)  will need to know what you are doing.

 I ride a motorbike too and I have one simple rule: The rider rides, and the passenger is freight.  Enjoy the view, but don't try to 'help'. A similar thing applies to canoes, except the "captain" sits in the rear. S/he steers, balances and plans. S/he is in charge, and in control. The person in the front sits still, pulls-like-a-mule, keeps a lookout for rocks, and enjoys the view.

Another thing which really helps both occupants: Don't sit, kneel. Knees on the floor, a comfortable distance (maybe 12-15 inches) apart, butt resting on the front edge of the seat. Really stabilises things. Locks you into the boat, almost like a 'yaker.  Feels weird-as-heck at first, but much more comfortable in the long run, and much more efficient. 

As a last resort, lowering your seat hight by even an inch or less does help but, frankly, it's a work-around, not a solution.

 

RE: Unstable cedar strip canoe

I built the Sasifras 14 and ran into the same problem.  It's probably why CLC discontinued the offering.  I ended up accepting the fact that it's a one person canoe.  I lowered the seat as much as possible using 6" carriage bolts and installed foot braces.  I use a long double  kayak paddle.  The seat could be a little more forward. but the stability problem is solved.  Makes a comfortable fishing platform.

RE: Unstable cedar strip canoe

Thank you all for your responses.  I do not have much experience as a canoeist though I did some in my younger years so your tips are all great.  I will try to get some better dimensional information posted soon.  Unfortunately the canoe is about an hour away from my house at the moment so it may be a few days before I can get to you the requested information.  To further enumerate on the problem, I built it without plans or instruction.  In retrospect, probably not the best approach.  However, I have a fair amount of experience as a woodworker and have built a CLC kayak which I use often.  I had always wanted to build a strip canoe and found a platform that had been used and abandoned by someone who had built a canoe on it.  I was told that the canoe built on it turned out fine.  Those who refuse to ask for directions usually stay lost.  I will post the dimensions soon.  Thanks to all of you again for your time.

RE: Unstable cedar strip canoe

This is totally off-topic, but a true-but-amusing tale was brought to mind by David's motorcycle analogy above (I'm also a motorbiker).  

A mature-aged lady we know had been a pillion-rider for many years and had thoroughly learned the lesson "sit there but don't do anything", as enumerated by David.

Came the time she decided she wanted to ride her own bike.   Truly indoctrinated, it happened that more than once, coming to a stop at traffic lights, she just sat there as the bike gently toppled over to one side or the other!

No harm done - other than a red face - but it took a while!

Enjoy.

Wordsmith

RE: Unstable cedar strip canoe

15' sounds borderline for 2 people. With 2 aboard the hull shape is probably inherently unstable, I'm sure I've read some technical explanation around here about initial/secondary stability when a hull is loaded beyond design.

You could do what I did with the secondhand 16' kayak I bought cheap. Similar scenario: OK with 1, tippy with 2. I went 'to the dark side' / 'native' / 'troppo' and added an outrigger ! Initially a small 4' 'float' on a couple of closet poles. Great improvement - instant increase in fun factor, paddled beautifully with double or single paddles.

Then I found the fascinating world of outrigger sailing canoes (see links below). I now have 8' outrigger (ama), 64' polytarp crab claw sail on hollow wooden mast, bamboo boom, 3' leeboard and 3' stern mounted kick up rudder: all retro-fitted with no change to the original hull. I'm having an absolute BLAST, and planning to build a 'real' one from scratch.

So theres another option to consider...

   ka kite (thats native for 'later'), Dave
 

 

Gary Dierking is 'the man', designs and blog here:

http://homepages.paradise.net.nz/garyd/

http://outriggersailingcanoes.blogspot.com/ 

 

This forum is a great outrigger hang out:

http://groups.yahoo.com/group/proa_file/ 

 

The folks here often put floats  on their more conventional canoes (they have yet to fully embrace the dark side:-)

http://groups.yahoo.com/group/sailing_canoes/ 

RE: Unstable cedar strip canoe

I stand corrected.  I had not heard of the loss of initial stability with second person aboard before.  But I now realize that this is more likely the problem than the second person adding jitteriness.

RE: Unstable cedar strip canoe

Don't go away. Salvation may be at hand. And at little cost to you in dollars or in effort.

If the boat was set up properly adding more weight should make it more stabile. You problem is, therefore, not the weight of the second paddler but the fact that the second paddler adds weight to the certer of gravity which is too high. You need to lower the seats. You can check your setup out by having both paddlers kneel. If the boat firms up when kneeling then the CG is too high when sitting. 

RE: Unstable cedar strip canoe

 I have gotten around to taking some measurements.    I have also received a lot of feedback to my dilemma and so I put it back on the water to try some of the suggestions I had been given.  Paddling from ones knees did help but didn’t completely stabilize the ride.  It was a bit uncomfortable as well.  I want to be able to fish from it primarily so fitting it with an outrigger doesn’t seem practical.  I have come to the conclusion that the problem is twofold.  The hull shape is such that there is very little flat area and the COG is too high.  I am going to move the seats in toward the middle about a foot and lower each a little more than they already are.   They were installed below the gunwales to start with.  If that doesn’t work I will either turn it in to a one person boat or try to find someone or some restaurant that wants to put it up on their wall as decoration and start over with an actual plan.  Meantime if you see something in the measurements that may lead to a solution please let me know.  Thank you for your time.  C

Length – 15’5”

Gunwales -1.625” x 1.5”

Beam – 31”

Seat location:     Front seat –  51.5” from tip to front of the seat

                                                 63.5” from tip to back of seat

                           Rear seat             39” from tip to back of seat

                                                       51“             to front of  seat

Seat heights       Front seat – 10.75” from floor to top of seat

                                Rear seat – 11.5”                  

RE: Unstable cedar strip canoe

The traditional way to install seats in canoes was to hang them from the inwales. There are special extra-long bronze carriage bolts sold that enable a paddler to adjust seat heights up or down. At each corner of the seat there has to be a wood spacer with a hole drilled up thru' the middle for the screw. You have to make the correct length spacers for any particular installation.

I paddle a plywood pirogue. It was designed to have the paddlers sit on the bottom. You can install seats or pads but if they are more than 4" from the bottom you are asking for trouble. I neve bothered making a seat because they have to be so low they would require a backrest, too.  Yes, kneeling takes getting use to but, when things get narley. kneeling gives you as much control as can be had.  

RE: Unstable cedar strip canoe

Thanks, Charlie.  I have been using 6" carriage bolts and will need to find longer ones.  I think by moving the seats in toward the middle I am making more knee room which should make paddling from the kneeling position a little more comfortable.  The challenge of tinkering to make it better shouldn't be too bad.

RE: Unstable cedar strip canoe

31" beam? Well there's yer problem. Your conclusion that there's very little flat area is right on. Just think about how much there would be if the beam was more like 35-36". If the canoe was 20' long you would have a lot more surface area in contact with the water. The design sounds like one made for looking at, not floating.

RE: Unstable cedar strip canoe

Redbird-17 ½ xz 33½

Peterborough-15' 10" x 32

Chestnut  Prospector-16 x 35 

Hiawatha-15 x33

Sunnyside Cruiser 16 x 32

Arkansas Traveler 13½ x 30

The above are all popular stripper designs and only one is 35" wide. If any of them was inclined to roll they would have been forgotten long ago.

RE: Unstable cedar strip canoe

Charlie, you wrote, "If the boat was set up properly adding more weight should make it more stable."

I thought the same thing, but I think that folks are trying to educate us that 'taint necessarily so.

I think that the theory goes like this.  A boat with a certain load has plenty of initial stability because a small tip causes a lot of righting moment.  (A lot of bouyancy is added far from the centerline, as more of the nearly horizontal bottom plunges below the water.

Brunhilde comes aboard.  Now a small tip doesn't add much righting moment at all. Yes, the vertical sides go deeper underwater, which adds buoyancy.  But being as the sides are vertical, the moment increase is small, because the added buoyancy is no longer being added at a progressively higher distance from the centerline.

 

RE: Unstable cedar strip canoe

"The above are all popular stripper designs and only one is 35" wide."

Yes, Charlie..and only one is less than 32". Which one is more stable? I'll bet on the wider beam. Think about it. Go to Old Town Canoe, click on the product list, see how many canoes are less than 32".

RE: Unstable cedar strip canoe

If you all will indulge me, I'll throw in a quick lesson on stability.

 First, beam.  All else being equal, stability increases linearly with length (on the waterline) and as the cube of the beam.  So, a little beam does a lot.

Stability is also directly proportional to the moment of inertia of the waterplane, divided by the underwater volume.  So, if you think about a shoe box, the heavier it is the deeper it goes in the water and the greater the immersed volume.  However, the waterplane, and its moment of inertia never changes.  So, the heaveyer it gets the less stability it has.  On the other hand, a hull with extreme side flare will pick up a lot of waterplane inertia with a small weight addition.  This is typical for car ferry designs which often have a "V" shaped cross section.

Now, going back to the canoe.  Even if the shape is such that inertia over volume gets better with load, if that load is a person then the vertical center of gravity of the loaded boat is going up and stability is being reduced.  Add the same weight in the form of rocks in the bilges and things will probably get better.

If you are glassy eyed by now I appologize.  Been working tugboat stability all day and the canoe problem was a nice divergence.

Paul G 

RE: Unstable cedar strip canoe

Experience years back with Cajun pirogues, made from single sheet of 12X4 ft marine 1/4" plywood gives a 34 inch beam, a 25 inch bottom, and a length just over 11 feet. Any seat heighth more than 4 inches off the floor was unstable with a single, experienced paddler. The 4 inch seat, if made from something flexible like heavy canvas or a piece of oyster sack (heavy burlap), reduced the amount of 'squirm' energy that was transmitted to the boat.

It was not remarkable to spend an entire 11-12 hour daylight period in such a boat, without leaving it.

 If it draws 4 inches of water, a seat four inches is positioned at the waterline, and is inherently very stable. If you want comfort AND stability, get a rowboat.

 Denny Hugg

Gulfport, MS

 

 

RE: Unstable cedar strip canoe

Paul,

I think your shoebox example left out the vertical position of the center of gravity, as well as some dynamic effects, such as the inertia of the underwater mass. I believe that if you factor those in, the heavier shoebox will be more stable than the lighter one.

Laszlo

 

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