Pilotwingz question?

Pilotwingz, I am considering the purchase of a OT Expedition 169 and I noted several of your comments on how to check if it is twisted before you purchase the canoe with a string. Would you be so kind and share that tip with me? If needed my cell # is 859-750-5800 Bart

OK , I’ll explain , it’s easy to do …

– Last Updated: Jul-21-11 9:42 AM EST –

...... have the canoe setting on it's bottom on a flat floor .

Tape a string line from bow tip to stern tip (in the center) keeping it rather tight . I like to let the string run over the edge and tape it on the edge (vertical) as oppossd to the top of deck , cause that helps it hold a little tighter . It really doesn't matter if the string has a slight downward bow to it cause of it's weight , it doesn't have to be tightrope walking tight . The idea is to just have a straight line (in a one demension plane) to measure from that runs down the center line of the canoe . You know , as if you were floating above the canoe looking down , the line has to be straight that way only .

Once the string is in place , mark the string with a Sharpie marker every couple feet or so .

Then just measure from string to gunnel on each side of the marks . I like to start measuring at the center most mark and progress towards each end . The measurement on either side of an individual mark should be very close to same , perhaps an 1/8" differnce now and then is acceptable . Oh , when measuring try to measure at a 90 degree angle to the string (eye ball close to 90 is sufficient) .

If for instance as you measure from center towards bow along the marks , the measurements on the left side begin to become less than the right side measurements (or vice versa) ... what you are seeing is a twist over the length of the canoe . If you measure from the center towards the stern now , you will probably notice the same thing happening but on the opposite side the measurements will be less than on the front half . This is a twist on the hull .

If the measurements on either side of the string remain reasonably equal at each Sharpie mark then you have a straight non-twisted canoe .

The proceedure is really simple to set up (do) , it's fast and accurate enough .

The idea is the same as measuring between 3 parallel lines evenly spaced apart . Where the measurement from center to either outer line would be exactly the same "always" , but the difference being you are measuring an arc on either side of a center line , so the measurements at each Sharpie mark will change instead of being exactly the same (but the measurements on each side of an "individual" mark should be equal)... they will become shorter from center towards each end as the arc gets closer to the center line . You are still checking (measuring for) symetry .

If your measurements indicate a twisting to the hull , it's almost guaranteed that if you sight the canoe down the string line from the end now , with your eye at deck height , you will see the twist just as the measurements showed it was there .

Hope I was able to word this well enough that's it's easily understandable for you now .

A twisted hull wants to constantly track in an arc as opposed to a straight line ... also a twisted hull will make you feel as if you need to set off center and even lean towards one side to ballance it while paddling . That can get annoying and even uncomfortable after awhile .

Sorry , didn't realize I wrote a book length post ... usually only do that when telling stories and spinning yarns , lol .

Thanks Pilotwingz!
Your advise on how to test for a twisted canoe is much appreciated. You must have an engineering background!

My best, Bart

thanks , you’re much welcome …
… no engineering degree , but it sounded good when you said it .

I do have a good architectual foundation that helps me understand and see things well in variuos dimensional planes though .

bartman and pilotwingz
thanks for posting that for everyone to see. Great info. Seems especially useful for used canoe purchases, where you can’t always try before you buy and sales are final.

If only this message board had stickies…

As I understand this test, you are measuring from the center string to the gunwales.

If this measurement reveals some twist or asymmetry, why would you assume that this same pattern is repeated at the waterline? A gunwale line or sheer line may or may not affect the water line or keel line, and the effect may be different depending on what material the canoe is made of. A wooden canoe hull with components under tension and compression, for example, may transmit stresses across the hull differently from a molded canoe.

Perhaps I’m not picturing the test accurately.

For example
Look at the following picture of the deliberately wavy gunwales of the PBW Ohneka, which has nothing to do with whats going on at the water line and keel line of the canoe:


not sure what you’re getting at Glenn

– Last Updated: Jul-25-11 9:38 PM EST –

...... you mentioned wooden canoes , stress transfers (tensions/ compressions) , wavy gunnel designs ?? I understand that a canoe no matter what material it is made from , can and probably should flex when out on the water , but this same canoe should return to it's original non-twisted shape when at rest or being less stressed on the water . Think of jello (extremely flexy) , it wiggles all about but returns to it's original shape when calm again .

In the wavy gunnel boat from your pic. , I would expect to be able to perform the string test the same way to determine if the hull is twisted .

A hull design would not "have to be" a perfectly symmetric type such as a double ender (ie., OT Disco , Grumman , etc.) where the front 1/2 is a mirror image of the rear 1/2 . But one would expect at the least , a mirror image on each side of the center line (ie., the string) .

As well , one would expect that the right 1/2 as if cut down the center of length (like a cake) , would be identical to the left 1/2 ... only that the left and right halves are exact opposite forms in a 3 dimensional perspective .

In a non-twisted hull the front and rear stems will be parallel . Imagine a visually clear canoe where you can see right through it . Imagine the stems have been marked with a black line . If you look at the front stem "black" line and position yourself in such a way that the rear stem line is directly behind the front one , the rear stem line will disapear or be hidden . You could also position your sight view to place the two stem lines directly above or below each other , which would appear as a single straight continous line . In doing so you will see they are parallel lines . The stem lines would not do this in a twisted hull because they will not be parallel to each other .

I believe the twisted plasic hulls happen because the cool down process and proceedure was not performed correctly , rushed , rate of cooling was too fast , or removed from the mould too soon while still to warm . My estimations from the above described test showed that 3 out of 5 hulls had twist in varying degrees , and 2 out of 5 were not twisted .

If the string line gunnel test suggest a twist , this same twist will be transfered to the hull at the water line and the bottom of the hull .

Imagine a hull setting flat on the ground . Now tilt it up a bit on one side . A twisted hull will be as if you tilted the front 1/2 up on one side and the rear 1/2 up on the other side at the same time ... ie., a twist .