ash ribs rebound

[pasteljoe]

hello all,

I'm actually building an Atkinson traveller canoë, and I use ash to make the ribs, spruce for the planking. As the ash is a hard wood, the tickness is reduced to 4mm (3/16").
After steamed it an applied all on the form, pushed all the ribs on the form by a solid piece of wood, I let it dry for several days. And the planking followed.

After I removed the canoe from the form, I checked the straight line and measures. And I realized that the ribs of the bottom at the middle was rebound of approx 2cm (13/16") . They didn't retain the shape of the form, which means that the sheer line of the canoe is altered.

I built two canoes, and the two have the same problem.. the first was the worst, I finally achieved a kind of "cree canoe", like a banana... Unusable on calm waters..

here's a little illustration of the first canoe :

Even if on my second canoe, the 13/16" move is not significant, I would like to be able to preserve the original shape of the design...

Has anyone ever encountered this problem before? is the type of wood thats poses a problem ? it is the same with the cedar ribs and you have to compensate with the shape of the form ?

Thanks you all !

ps : a littles pics of the second project :

 

[MGC]

I have no experience making ribs from anything other than cedar. I have used ash for stems, rails and snowshoe frames.
To reduce spring back I let it sit on the form far longer than what you seem to have done. I tend to leave stems on the form for a week or more and I do the same with snowshoes. Even then they do have a tendency to spring a bit.
The "cree" canoe will be great for paddling in circles.
Mike

 

[pasteljoe]

Thanks Mike
I let it on the form about a month or two. Like the stems.
So maybe it's because the thickness and the elasticity of the ash ..
In France we don't have cedar wood. We also don't have any boys who make canvas canoes....

 

[Dave Osborn]

I would think that you could pull the canoe together 13/16 without losing much original shape. Although as springy as they are it might really round out the bottom.
I once replaced ash ribs in an obscure wood canvas canoe, but did them one at a time. There was issues with the tacks splitting the ash.

 

[Dan Lindberg]

Well this partially answers the 1st question.
If you have spruce for planking, why not use it for the ribs also?

(IMO, ash is a terrible wood for canoes; heavy and discolors and rots way too fast)

In France we don't have cedar wood.

 

[pasteljoe]

I would think that you could pull the canoe together 13/16 without losing much original shape. Although as springy as they are it might really round out the bottom.
I once replaced ash ribs in an obscure wood canvas canoe, but did them one at a time. There was issues with the tacks splitting the ash.

effectively, the ash cracks with the tacks. You have to pre-drill it.

Well this partially answers the 1st question.
If you have spruce for planking, why not use it for the ribs also?

(IMO, ash is a terrible wood for canoes; heavy and discolors and rots way too fast)

oh this is a good answer
At the origin, I found a build notice on a old french book from françois Sergent, 1945. And I used the wood which it recommended. Now that you mention it, I hadn't thought about using spruce for the ribs (i'm an amateur)... maybe for the next ...

 

[pasteljoe]

I checked the waterline of the canoe, and due to the wood's rebound, I still have a bulge at the bottom... Does anyone know a way to fix this?
It will be a problem for navigation, no ?

thanks !

 

[Greg Nolan]

I don't know if there is a way to dimish the bulge -- but adding a keel may decrease the directional instability the bulge will create.

 

[pasteljoe]

thanks greg,

What thickness of keel do you think?
Perhaps I could put weight on the bottom, wet the ribs on the inside, and heat them with a heat gun...?

 

[Greg Nolan]

I suppose weighting the bottom, wetting the ribs, and using a heat gun might work -- but don't overdo it -- you don't want to hog the hull.

From some old notes I have on someone else's restoration of an Old Town Otca, keel dimension could be 7/8" thick, 1" wide at the base (the side attached to the canoe bottom), 5/8" wide at the bottom, with the sides cut with at a 20-degree angle, with appropriate tapering at the ends to meet the metal bang plates coming down and around the stems. The base of a keel is often coved or cuppped a bit, to hold a bit of bedding compound.

I'll be in Maine nest week, and can measure the keels on an OT 16' Ideal and on a 15' 50 Pound model. I expect they will not be far off the measurements above.

If you decide to mak a keel, I can send you a good article on the steps involved in making an fitting one.

 

[pasteljoe]

Thank you for your precise response Greg. Yes, I have planned to install a keel. In hope that will compensate. But I'm dubitative...
I would be pleased to have your doc !.

 

[pasteljoe]

Oh, just a question again on the sheer line.
I am not familiar with canoe architecture, but what do you think about this waterline? Is it too pronounced, or will it work well on flat water? I manipulated the colors of the image and added a virtual horizon to better visualize the bottom line.
Just to know if it is really necessary for me to embark on a somewhat risky task to restore the original line of the plans... After 6 months of work, I would still like to have a canoe that navigate well on the water )) I wouldn't like to have the same hull shape as my first one again....

The pic :

 

[MGC]

That is not what we would typically refer to as the waterline.
The waterline is considered to be the a line that approximates where water comes up to the sides of the hull when it is resting in the water. You might take into consideration some amount of loading when you estimate it.
On my sons Traveller we marked the waterline by first sitting the canoe on a flat floor. We then took a small wooden box, attached a pencil to it and used that to trace a line all the way around the hull. We had a pretty good idea how far up the sides we needed the line to be to take loading into consideration.
The image you posted of the boat floating like a cork is really not what you would expect to see if the canoe has several paddlers and some gear in it. It will only sit high in the water like that when it is empty.
What you need to consider is that a Traveller is a pretty serious tripping hull. These boats can take a large amount of load and still have a very responsive feel in the water. They are an absolute beast on big water. It eats up lakes with hard rolling waves and would be a total hoot to surf in the ocean if you didn't care about saltwater damage. Unloaded it's a heck of a lot of boat to paddle around in. That is a reason (I presume) that Rollin also designed some smaller hulls. Consider the Medford.
A keel will not correct the shape of the hull. It will conform to it. Personally, I see zero benefit in adding a keel to a Traveller. A keel will detract from the hulls handling when you use it in rivers and it will also make it much harder to angle if you do use it on big water. My sons Traveller is arguably the best handling canoe we have ever owned when we use it for tripping. It does not have keel. A keel would ruin it.

I have changed the shape of the bottom of a canoe by building a strongback that I used to pull the hull where I wanted it to go. I used a combination of wet towels and steam to "soften" the hull before I moved it towards the strongback with screws. The canoe I did this to was badly hogged out. It's now been 3 years and it is still holding its corrected shape.

Your boat is not hogged. As you note, it's a banana. Consequently, if you wanted to try and pull the bottom in you would need to put your strongback inside the hull and screw towards it. You would end up putting holes through the ribs and planking to do that. Frankly based upon my experience moving a cedar hull in the other direction, I had to pull nearly three inches to remove 3/4's of an inch of hog. I would definitely not try that on your boat. I don't think you will be able to alter its shape enough or predictably.
I think you need to call it a day and enjoy it as is.

 

[samb]

Have you tried altering the width of the boat at the gunnels by clamping thwarts in place. Is it still at designed width after removing it from the form?
I can't know if I'm right or not, but I'd first attempt to widen it a little with two thwarts, each about a third of the way along.
It might not do anything at all, or it might make it worse, but I'd certainly be trying that before adding a keel.
Sam

 

[John Sand]

Don't make yourself crazy trying to perfect the boat. Perfect is great, but good is good. I'm not sure you'll feel the difference paddling.

 

[pasteljoe]

Hello MGC, thank you for your details ! Effectively, it was not the term that I wanted to use. Not the waterline, no, I didn't know the english term for the bottom line of the canoe... the "sheer line" ? I meant to refer to the bottom line of the canoe, just above the blue line I drawn on the image. the line wich are like you says, like a banana.
I just wanted to know if this shape (the new canoe, not the first) will be great anyway for travelling, in flat waters, in solo. Because for the moment I will not use it for the sea or rapids.
However, your job with your strongback is interesting ! do you have a little image to see were the forces is applyed?

Sam, after removing from the form it is normal that the canoe opens a bit. But this did no changes anything on the bottom shape. Ash is really a hard and stubborn wood...

John, I think you're absolutely right. But after a first banana canoe (a construction problem identified too late), which are impossible to use in solo, I'm a bit worry... :/ very woory too... and obsessed by this line ...
but I think that is the good thing to do anyway. So I'm going to move at the next step.

 

[MGC]

Thanks for clarifying. There was nothing scientific about the way I straightened the hull. I made a reinforced beam. I placed it over the hull and put screws through the canoe from the inside to pull the wet steamed hull to the beam. My first try did not move the hull enough. I was being far too conservative. I removed the beam, spaced it farther from the boat and did it again, this time pulling the boat beyond where I needed the bottom to be when it dried. I left it like that for about three weeks.
The images that follow are from my first attempt where I was being too careful.
WRT paddling that canoe solo...if you built a 17 1/2 foot hull, it's a lot of canoe. You will need to add weight to the stern, assuming you will paddle from the stern. If you plan to paddle it from the center, you will end up heeling it up a bit so the shape of the bottom won't be as much of a consideration as where you are bracing on the tumblehome.

 

[Dan Lindberg]

Are my eyes bad or ??
Why are there huge gaps between the planking?

Seems like you are pouring a lot of time into a hole in the water with these canoes.

If it was me, I'd be looking for more suitable wood/s for a canoe.

Dan

 

[pasteljoe]

Are my eyes bad or ??
Why are there huge gaps between the planking?

Seems like you are pouring a lot of time into a hole in the water with these canoes.

If it was me, I'd be looking for more suitable wood/s for a canoe.

Dan

The planking are in spruce wood. And it swells with water. I'm just following the Jerry stelmok advices.

And the modified image amplify them.

I won't discard 6 months of work just because it's not the perfect wood for a canoe. I'll see it through to the end; it won't prevent it from floating. We all need to learn from our mistakes. Time is relative. And time, I have a lot

 

[Gil Cramer]

I once made a canoe with Ash ribs and basswood planking. It was long ,long ago. It was a very good learning experience. I learned why native Americans used cedar for both ribs and planking. Finish your canoe if you haven't already, and use it.There is no better teacher than experience.