Should I Add a Rib to a Nomad?

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BillR

Should I Add a Rib to a Nomad?

Post by BillR »

I remember reading on the old forum a post from a builder about problems he was having with his Nomad. I think he was generally pleased with the boat but said it sometimes "oil canned." I wish I had saved that message. Nonetheless, I am at the stage with my own Nomad where I could add one or more ribs, if that would help solve the oil canning problem. This is an appeal to Nomad owners (and others) - are ribs a good idea on a boat like a Nomad, which have large relatively flat bottoms? I plan to use two layers of 6 oz. cloth inside and out below the 4" waterline. Perhaps this is enough to stiffen the bottom sufficiently. Thanks for your help - Bill.
Jack

Post by Jack »

Hi Bill, I have a 16' Laker which has a wide, flat bottom. It does oilcan. I only used 1 layer of 6oz. cloth when I built it. I will be adding 2 more layers this summer as I have a couple of cracks in the glass at board joints. I was thinking of adding a couple of ribs to stiffen things up but have deceided to go with more glass. I think I would have been OK if I had used 2 layers of glass when I built the boat.
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Joan and Ted
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Post by Joan and Ted »

Hello - it is Joan here - Ted is teaching a class in Maine at Woodenboat School so I cannot get his comments on this question but whoa......this just does not make sense. I have just delivered our 25th sprint racing canoe to the Burloak Canoe Club yesterday and your email made me chuckle - oil canning?????
Ted and I have been building very large (30ft. long) sprint racing boats for almost 30 years. These canoes take 15 paddlers and are built using the very same materials and weight of cloth as we instruct in Canoecraft - we only use two coats of epoxy on the inside to keep it from being too slippery. The canoes themselves weigh about 180 lbs. when complete and with all those healthy athletes loaded in the displacement is about 2400 lbs. They are paddled on the national racing circuit by teams across Canada in our country's oldest organized sport.
A woodstrip epoxy hull is rigid - I am sure Ted will have some technical info from Gougeons to back this up at least as far as West System epoxy is concerned and I will pass this on to him but I really think you should just go ahead and build your hull without ribs.
Joan
Michael Freeman
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Re: Should I Add a Rib to a Nomad?

Post by Michael Freeman »

BillR wrote:... I plan to use two layers of 6 oz. cloth inside and out below the 4" waterline. Perhaps this is enough to stiffen the bottom sufficiently. Thanks for your help - Bill.
Bill,

I do not own a Nomad, but I have built a Prospector which has a similar hull shape, particularly in the mid-section where the bottom is widest (the Nomad is based on the Prospector design). It has one layer of 6oz glass inside and out and the bottom is ABSOLUTELY RIGID - it does NOT oilcan.

I don't think you need any ribs.

Happy buiding,
Mike
Jim D

Post by Jim D »

I have wittnessed this same problem, especiallywith hulls that were NOT bead and coved!.. my suggestion would be to double the layer of cloth on the outside, just up to the 2in. water line... I have started doing this on several canoes, and find this adds a little weight, and a lot of durablity!.. after all you put a lot of work into a hull, whynot protect it?.. Good Luck!... Jim
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Post by canoeblderinmt »

My 18 1/2 foot White oilcanned pretty heavily, though it didn't seem to affect the seals or the glass, which seemed to allow the flex. The Guide is flat bottomed, and wide, which may contribute to this. I had a football and full coverage layer outside and a layer inside of RAKA 5 0z (they don't sell this anymore). Now I'm making the 20 footer which is 60 inches around and FLAT in the middle. I am wondering about adding a rib or two myself. I did the football thing again, but with 6 oz instead.

I remember paddling the smaller Guide and just watching the middle pop up and down all day - VERY DISCONCERTING! :thinking

Anyone have any thoughts?

Greg
Rick
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Post by Rick »

Greg, this is one reason why I prefer shallow-arch or round-bottomed hulls - structurally more rigid and less prone to oilcanning. The advantage of a flat-bottomed hull is high initial stability and greater load-carrying capacity, so a flat-bottomed canoe isn't without benefits.

It should be possible to steam-bend ribs to shape using stations reduced by the thickness of the rib material. Ribs might be 1/2 or 3/4 inch thickness, depending on their width, and they won't have to extend all the way up to the sheerline, which should simplify their construction. The turn at the bilge is structurally stiffer than the flat area at the bottom and the ribs could end partway up the turn.

Once the ribs are bent to shape, the stations can then be used to press them into place at the right location, using thickened epoxy and some kind of set-up with duct tape, bungees, etc, to create downward pressure on the rib, to ensure close contact with the fiberglass underneath. Another layer of fiberglass will then have to be applied over the rib and bonded to the fiberglass alongside.

Good luck, this will probably be quite a bit more work, but the oilcanning should be greatly reduced, with increased structural strength in the hull.
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Post by Riverrat »

I have a Nomad. I used bead and cove strips, I used 2 layers of 6oz cloth on the bottom and one on the inside. I don't have thwarts, just the yoke. So far, I've solo'd with it and have also used it with another person in it. Together, we tip the scales at about 490 lbs. We've had about another 100 lbs of gear with us. No problems at all so far and no oil canning.
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Bryan Hansel
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Post by Bryan Hansel »

I'd build it without ribs and then if needed, which I doubt, add them later. Two layers of 6 ounce glass and one in should make your hull plenty stiff to avoid any problems.

Bryan
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no ribs needed

Post by sedges »

with the lay-up you propose. The nomad does not have a flat bottom and just the shape alone tends to makes it stiffer.

I have built a whole bunch of 16' prospectors which have the same bottom characteristics as the Nomad and all of them have been stiff. I used 4 ounce cloth inside and out over- lapped below the waterline. These have been tough boats on many wilderness trips.

I must recommend further investigation into the idea that adding glass to the outside helps stiffen the hull. Any engineer will tell you otherwise. When the hull receives a blow to the outside, the fiberglass is under compression on the outside and tension on the inside. The tension is where the strength is important and that tensile strength is what makes the hull stiff. Adding glass to the outside does add protection from abrasion and gouging, but does not add much strength to the boat.
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Bryan Hansel
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Post by Bryan Hansel »

http://www.thag-o-mizer.net/Strip.html

If I understand the info provided by this test, extra layers on the outside does help. Maybe I'm misunderstanding the results.

Bryan
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Post by canoeblderinmt »

Well Sedges, you certainly set me to thinking. Should I put a football in the inside too?

I think I was a little too stingy with the resin last time out. I used barely over a gallon of resin for an 18 1/2 foot boat. I never did get to weigh her but I could easily pick her up over my head with one hand: I don't think she weighed much over fifty pounds. So I added a fourth coat of resin filler last night. I'll have to sand a good deal of it off as it went on a little thick and runny, but I'm still worried about the oil canning. As Bryan suggested, I'll see how it comes out and add ribs if needed. This behemoth will probably be pretty heavy and I'm trying to keep the weight down, but I need her strong as she'll be pounding down rivers and scraping bottom up here where the rivers run shallow in Autum. That's why I opted for the extra resin. It took less than 20 oz. on the last coat, so that's just over a pound.

Thanks all for your input and I hope more flat-bottomed paddlers will add their two cents as we go.

Greg
jfranck

Post by jfranck »

I am building a version of the Freedom 15 and am a little concerned about "oil-canning". It is quite wide (36 inches) and flat in the center and I only have one layer of 6 oz fiberglass inside and out. I have yet to fiberglass the inside - it'll have to wait til spring.

If it has a problem, I'll probably add ribs. I read how to do it in a book on building kevlar canoes. They used 1/2 inch foam about 2 inches wide and epoxied into the bottom.
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Post by Glen Smith »

I would rather add and extra layer of glass cloth to the interior, maybe 4 ounce cloth, rather than add ribs. The ribs will make any future refinishing much more difficult to do. Some builders install a "shoe keel" to stengthen the keel-line and prevent oilcanning.
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Post by Rick »

JFranck,
I am building a version of the Freedom 15 and am a little concerned about "oil-canning". It is quite wide (36 inches) and flat in the center
The Freedpm 15 doesn't appear to be flat-bottomed in the diagrams shown on another page here on this website. The center stations appear to be shallow-arch and my guess would be the hull will be rigid if built as outlined in Canoecraft. Other shallow-arch designs with about the same waterline beam, such as the Prospector and Nomad haven't been reported to be oilcanning, so I don't see why the Freedom 15 would when those don't.

The curves in the shallow-arch hull work on the same design principle that makes an eggshell structurally strong in compression - flat-bottomed hulls don't have this, so they're much more likely to oilcan, and could benefit from keels and ribs for structural reinforcement, especially when hull bottoms are thin.

Besides arched curves, another thing that adds rigidity is the thickness of the strips - 1/4" strips used in construction will be more rigid than 3/16", so the thicker strips should be used to build a more rigid hull.

Good luck - when you say you're building a version of the Freedom 15, are you saying you've modified the design?
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