Stripbuilding and Fiberglassing Question

[Benjicohn]

Hello all,
This is my first post, as I am new to the boatbuilding hobby/professsion. I am starting with a stripbuilt adirondack guideboat, and I had a question for people with more experience than me:

I am going to be painting the hull whilst leaving the inside a bright finish. It seems, typically, that in strip building people sandwich the wood with two very thin layers of glass/epoxy, and then you can see the bright finish on the outside and the inside.

Would it be totally against the rules to run a thicker layer of fiberglass on the outside, and No glass on the inside? I understand the importance of the woodcore for structure, but is it that crucial?

Thanks for any advice you may have.
-Ben

[JimConlin]

The reason that cedar strip composite works is that there are two strong skins separated by a light core. Think I-beam. The wood is mostly along for the ride. With only a single skin, however thick, the panel would be much less stiff. The boat would be very weak.
If you're concerned about whether a glassed interior will look good if finished bright, stop worrying. 6 oz. glass will virtually disappear in epoxy if you apply it with reasonable care.
If you really are going to paint the outside, you can go up a bit on the glass weight to add a bit to rock-resistance. Going to 8 oz. glass on the outside will add about 2 lbs. to the boat.

[ 04-20-2005, 07:48 PM: Message edited by: JimConlin ]

[bainbridgeisland]

You could eliminate glass from both sides if you installed transverse frames. They could be steam-bent or laminated. Such frames would easily make up transverse stiffness and strength that would be otherwise lacking if the boat isn't glassed on both sides. A boat built this way could theoretically rival a traditional canoe in weight.

I don't know if you realize that a well made canoe of traditional canvas over cedar planking over steam-bent frames is virtually as light as the modern carbon fiber/epoxy canoes now available. This is because there is a minimum thickness needed for stiffness even for carbon fiber. Wood is lighter per cubic inch meaning it can be thicker without weight penalty. When you are only allowed ounces per square foot, wood is as stiff in bending despite the inherent superior modulus of elasticity of carbon fiber/epoxy.

The glass on the outside is good abrasion resistance on the original strip-plank scantlings. However, as long as you don't drag the boat around on its bottom you won't need it.

[Todd Bradshaw]

"I don't know if you realize that a well made canoe of traditional canvas over cedar planking over steam-bent frames is virtually as light as the modern carbon fiber/epoxy canoes now available"

Not Hardly! I love traditional wooden canoes and have an 16' Old Town Guide which I've owned since 1972, but it weighs 70 lbs. I could build the same hull, stripper-style and easily wind up in the sub 60 lb. range even with a lot of fancy trim. In carbon composite the same hull would finish off closer to 40 lbs.

Also keep in mind that the inner layers of a stripper in many ways take more of a beating and/or often do more to make it a strong boat than the outer layers. Rocks are on the outside and trying to force their way in. The outside layers need to protect the core from this and flex a little bit on impact in the process. While this is going on, the inside layer is moving farther and has to resist being literally torn apart. Skimping on the inside layers is the best way I can think of to make a weak stripper.

There have been some very nice strip guideboats built with closely-spaced laminated wooden ribs on their insides instead of inner fiberglass layers. These are guideboat-style ribs, not wood/canvas canoe-style ribs and quite different. You might do a search for John Michne who has built some really nice ones.

[bainbridgeisland]

I disagree. Some finely made traditional timber canoes are in the 43 to 46 lb range, many more are around 50 lbs. I didn't say all well built canoes could compete on weight. Certainly, 70 lb is a common weight for a traditional canoe. There are many solutions to the transverse strength issue here. Some solutions are very light. But just using one method over another doesn't assure light weight. The scantlings must be carefully refined to the service needed.

[Dan Lindberg]

BBI,

Not to pick on you but where have you seen W/C canoes (at least 16-17') that weight less then 60 lbs?

The only ones I've heard of used somthing other then canvas, as canvas and traditional filler can be easily 25-30 lbs alone.

One builder fills his canvas with epoxy and achieves a modest weight reduction, getting 16' canoes in the 60 lb range.

Dan

[Todd Bradshaw]

You can disagree all you want, but the statement that anybody's traditional wood/canvas canoes are as light as modern high-end composite layups just isn't true. For example: in touring canoes in the 16' range (not super flimsy racing layups with lawn chair webbing seats and ultra-tiny gunwales, but real canoes designed for tripping and touring) look at We-No-Nah's Kevlar versions of the 16' Chestnut Prospector design. The ultralight version weighs 40 lbs. and the somewhat heavier-duty Kevlar Flex-Core version weighs 52 lbs. The Flex-Core "Tuff-Weave" (primarily fiberglass) version is 61 lbs.

Chestnuts own original 16' wood/canvas Prospector (a model called the "Fort") was built with 3/8"x 2&3/8" ribs, spaced 2" and covered with #8 canvas. The catalog weight was 76 lbs. Other 16' Chestnuts were as follows -
16' "Pal" model - 72 lbs.
16' "Camper" model - 75 lbs.
16' "Boone" model - 75 lbs.
16' "Henry" Model - 82 lbs. (Ogilvie Series - extra heavy-duty)

In Old Towns:
16' "Guide" - 70 lbs.
16' Otca - 70 lbs.
Their lightest tandem canoes were the 15' series where the "Lightweight" model (wood/canvas) was 58 lbs., the FRP covered "Trapper" version of the same hull was 55 lbs. and the Dacron covered "Featherweight" version 46 lbs.

The top builder of wood/canvas canoes on the planet, in my opinion, is Rollin Thurlow (Northwoods Canoe Company). They are stunningly beautiful boats, but checking their weights will put them all in a similar range.

The wooden hulls of all the w/c boats I've mentioned - even before the covering fabric is applied, weigh more than the We-No-Nah Kevlar Prospectors do all-up. Other high-tech composite touring tandem canoes are similarly lightweight. The Bell "Northstar" (16.5') in their Black/Gold Kevlar/Carbon mix is 49 lbs. In their lightest layup it's 39 lbs. Mad River's Kevlar "Explorer" and "Malecite" models (both about 16.5' weigh 54 lbs. and 51 lbs.

I dearly love my wooden Old Town. It's the best rocking chair on the planet, but along with all that beauty comes a certain amount of weight. If you get up into the 18' range of bigger tripping boats you're nearly always talking about portaging something in the 80lb. range if you go wood/canvas. That's just the way it is. In wood strip construction you can trim 20 lbs. or better off of that same hull shape's weight using standard thickness strips and regular 6 oz. cloth in a reasonably heavy-duty layup. If you want to go lighter still by using more exotic cloth, thinner strips or lighter trim, it's possible. But even then, if you want to match the weight of the current high-tech Kevlar and carbon boats you had better be willing to really carefully watch the weight of the trim pieces and engineer a really high quality hull from as little stuff as possible.

[ 04-21-2005, 02:01 PM: Message edited by: Todd Bradshaw ]

[Cuyahoga Chuck]

The only taditional canoes that could compete with lightweight modern hulls were those made by J. Henry Rushton. His opertion closed in the 1920's. His boats were planked in Northern White Cedar (worth a king's ransom today) using the feather lap technique (we'd all be old and gray before we learned how to do it).
Wood canvas hulls were the economic answer to the diminishing availability of first rate NWC planks and the shortage of craftsmen to do a featherlap hull.
Wood canvas hulls require two layers of wood, a gazillion copper tacks, a whole lot of canvas, some fairly heavy canvas filler material plus the usual paint, trim wood,thwarts etc.
The WC canoe industry tried, long ago, to come up with a lightweight boat and the result was the "pack canoe". They were short (10-11 ft.) and fat and not very hydrodynamic but they were light enough for long carries.
Charlie

[bainbridgeisland]

Cuyahoga Chuck, here do those wood canoes that weigh less than 50 lb I occaisionaly see come from? They look like canvas on wood to me. They have traditional looking ribs and planking on the inside. Some of them are quite old but I have seen some newer ones too. I have seen 15' foot canoes as light as 43 lb and a 16 footer at 46 lb. Though these are not as good as the 32 lb, 15 ft carbon fiber canoe I once saw, they are pretty close to the 40 lb carbon fiber canoes out there.