I found this post on the Osprey II, and was curious about the choice of layup: Outside, 2oz. cloth with an additional layer of 4oz. on the bottom. Inside, 6oz. seam tape with 2oz. cloth on the bottom only.
Does that sound reasonable for a 15’ solo? How about glassing the whole interior and omitting the seam tape?
Using 1/8" for the sides with only 2 ounce covering that inside and out is asking for trouble.
It’ll hold for casual paddling. But if you ever have to wet enter or car-top and strap down hard for highway travel, it’ll break.
2oz is like paper
Using two layers on the outside is a lot of work (smoothing) and doesn't make sense to me. For myself, I'd use 6oz (full piece) on the outside and 6oz seam tape on the inside.
maybe an extra strip (6")of 6 oz outside on the keel line
Yeah that’s right…
I really wish I would’ve done that on my last one.
I noticed that
Pygmy uses 6 oz. cloth inside & out on their S&G tandem. Would that be overkill for a solo?
I tried using 2 Oz. on a stripper I built. It was impossible to get it to stay on the inside curves.The Osprey has alot of those curves in the tumble home and cause the 2 oz to pull away when smothing out the glass.
Plywood is actually sized in millimeters and not inches.
The term 1/8" and 3/16" gets thrown around quite a bit but the actual thicknesses are different.
4mm is generally the thinnest one should go with fiberglass coverage inside and out.
When you do the conversions:
- 1/8" is very close to 3mm. Many builders say 1/8" when they really mean 4mm.
- 4mm is closest to 5/32" while it’s often referred to as 3/16"
- 3/16" is actually closer 5mm than 4mm.
The whole mess is like talking about a 2x4 which is actually not 2" by 4".
Doesn’t sound like much difference but trust me it all matters in plywood. Dictates a lot about the layers use to construct it and its strength.
The only time I’d use 1/8"(3mm) is if were covered with 9 ounce glass on both sides. 3mm simply does not have the needed stiffness or strength.
Bottom line: to be accurate and safe, search for plywood in terms of millimeters.
1/8"=.125" 5/32"=.156" 3/16"=.188
Seems a bit thin to me
The S&G Arctic Hawk I built (Mark Rogers design/CLC kit) has a pretty elaborate glassing procedure; both inside and out...
Before any of the panels are even joined together, the inside of all the panels are glassed with 2 oz. cloth. Additional glass (in several overlapping layers) is applied to the interior of the deck panel just aft of the cockpit. After the hull is assembled, more layers of glass (4 oz.) are added to the interior cockpit area, with even more layers underneath the seat and where one's heels will be contacting the hull. The additional cockpit glass also covers the chine fillets. Glass tape over the fillets is also added to the interior keel and chines at both ends.
Then, the outside is entirely sheathed in 4 oz. cloth (with a few additional layers on the deck both fore and aft of the cockpit), and an additional layer of 4 oz. cloth is applied (first, before the full hull glassing) on the entire bottom of the hull from chine to chine (making it 8 oz. of cloth on the entire bottom of the hull). Before the glassing of the hull, there's also an epoxy/silica/wood flour "wear strip" applied to the keel at both ends (from the tips down to the keel, and for almost three feet along the bottom of the keel). Finally, there are additional layers of glass on the deck at the very tips of the boat (underneath the final 4 oz. layer).
Even with all this glassing, this 18 foot boat still only weighs about 45 pounds! (lighter than my glass CD Caribou, which is about four inches shorter). :-)
Long before I built this Arctic Hawk, I had paddled several glass Wildnerness Systems Arctic Hawks, and I always felt that the layup was a bit thin/flimsy (especially noticed on the deck). The wood/glass layup of the kit boat feels much more "solid" to me. The questionable feel of the glass WS Arctic Hawk layup was one of the reasons why I chose the CD Caribou over the AH when I made my first boat purchase 8 years ago. The Caribou is still going strong, with *lots* of heavy usage over the years.
A bit light
It’s obviously working for Loyd, but I wouldn’t be comfortable with something that light.
As far as the plywood is concerned, he did use 4mm on the bottom. it is common practice in boatbuilding (as in sail and power boats, as well as composite canoes) to reduce the thickness of the hull material above the waterline, so using 3mm there, while not typically done, is not out of line with standard commercial building practices. My concern with using the 3mm in this case is that it is only reinforced with 2oz. cloth on one side, which doesn’t add very much strength.
As for the inside, if my memory serves me correctly, the CLC kits have the inside seams taped with 9oz. tape and only the cockpit area is glassed, but it is glassed with 6oz. glass. My personal preference is to omit the seam tape and glass the entire inside. I don’t know if that is a good idea, but I’ve done it and had the boat hold up just fine. I also put an extra layer of glass in the cockpit area (or the equivalent in a canoe) because of the increased wear in that area, as well as to provide a little extra strength.
If you were going to go with something lighter than 6oz. glass (the standard) on the outside, you could consider using S-glass instead of e-glass.
It can be a hard call when you are trying to build a lightweight boat, but still retain adequate strength. I’ve seen the builder post on the CCR bulletin board, and the boat is still doing well. However, if I were building it, I’d opt for a heavier layup.
Check this site out for a good (I think) explanation of why you want glass on both sides.
4 oz plenty on bottom
And 3 MM is great for decks. Gotta apply it monocoque and laminate it with 4 oz. The stresses from curves are what give it the strength needed.
4 MM is plenty for a kayak.
4 oz glass on the bottom and realize there will be maintenance and repairs.
6 oz? Maybe. But why add the weight? It’s still going to gouge, scratch, abrase, need repairing and upkeep…
Read the report
I know MadCanoeist from another site. I have read the report. Mad wanted to build a lightweight tripping canoe, not a bombproof WW thrasher. IMO, his choice of materials were perfect for this application.
4mm bottom, 3mm for sides
2oz on entire hull, aditional 4 oz on “football”. total 6 oz.
6 oz tape on all seams. Side seams would overlap or butt equalling 6 oz coverage.
2 oz applied to bilge.
So he has 8oz coverage on the 3mm sides and 8 oz in the 4mm bilge.
His choices are further supported by several wilderness trips with no major damage and most of all, a total weight of 40 lbs.