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I'd like a side of ribs with a glass of resin
By:Paul G. Jacobson
Date: 10/12/2007, 11:05 am

: . . .Of course that would work, I wonder though if the ribs/fasteners would be
: lighter than the glass skin.

Yes, frequently, but it can be close. And, of course, you can overbuild (or underbuild) either way and introduce bias. The old wood canoes used to weigh in at about 65 to 75 pounds dry. They had a heavy canvas and oil paint covering, and thicker wood sides, as well as thicker and wider ribs. And they were seldom dry. I'd guess they soaked in another 5 pounds in water after a few weeks of use.

: Each would likely have about the same
: strength, the glass most certainly would be faster to apply.

Not necessarily. Which is going to be stronger, a blanket or an I beam? The physical size and shape of the rib acts like an I-beam in how it stiffens and strengthens. The thicker the rib, the more the effect. A layer of glass cloth is far more flexible. The surface bonding effect you obtain will keep the strips from falling apart, but it does little to stiffen or strengthen the hull itself.

Exceptions do occur. Polyester resin would be stiffer than epoxy. Laying the glass in the shape of a rib would also make it stronger. Consider using a 1/2 inch diameter piece of foam as a rib mold, spot gluing that to the inside of the boat, and then laying glass over it. You'd end up with a very stiff tunnel of fiberglass about 1/2 inch high serving as a rib. This would be much stronger than a flat layer of glass cloth, at least in certain directions. I've seen designs which in fact specify ribs be made in such a manner, with a foam, or paper core.

As for speed of application, or time involved. Not much time is needed with the ribs. Steaming them all at once you would take out onestrip of wood at a time and bend it around a mold. Working with 3 or 4 such molds at a time, you'd be pulling a cool rib out about as fast as you could get the wood out of the steam box.

Now, making all the molds for those ribs would take some time. With a symmetrical hull--or one that was fairly close to being symmetrical, you might use the same mold for 2 to 6 ribs. with 4 ribs to a foot, on a 16 foot boat, figure on 30 to 35 molds.

Bending each individual rib is fast if you have the space to work in, so figure an hour for bending all the ribs, and setting them in their slots on the mold. After that, you just nail on the strips.

With glass you need to add in a skim or seal coat, wetout coat and one fill coat. Inside a boat you don't need to completely fill the weave, but you do need two coats to be sure that cloth is well covered. You might skip the seal coat but that uses more resin. That's about 3 to 4 hours, plus any sanding time to remove lumpy drips or blobs, plus time spent waiting for the resin to get hard enough to sand. With the wait time, this could go three days or, typically, a home builder would do it over a couple of weekends.

: With my current project I was amazed at how much weight the fasteners alone
: added for just the floorboards.

Fasteners? What are you using? Would dowels work? Drill out the wood, replace the sawdust with a round piece of wood of nearly the same weight. :)

Seriously, tho, I do understand that issue. When you try to use a bolt or woodscrew with a thin wood hull, whether it is strips or plywood, the surface of the wood is not going to take a lot of force over the small area most fasteners cover. So you need to beef up the area around your fastener with more wood, additional layers of glass, or use wide and heavier fasteners which spread the loads over a bigger area. For example, embedding a "T" nut for mounting rails for adjustable foot rests adds much more weight than the "T" nut itself.

Boats with ribs on the inside were a good idea for many years, but you can't just pop them out of molds, so you won't see them made in factories. And building one at home means lots more setup time and more jigs. For a single boat it is not practical. It is barely practical unless you want to start a small factory. Just guessing here I'd say you probably wouldn't break even with time and money versus glass on wood unless you made probably 6 to 10 boats off of a mold. After that I think you'd save some shop time and about $25 on the glass and resin. I may have better numbers on this in a year or so. I am strongly considering building a mold for a 17 to 18 foot touring canoe and using it in classes. Hopefully I'll be able to offer a class where someone can build their own canoe over such a form in 4 to 5 days. That would be three to 4 days working at assembly on the mold, varnish in the evening, come back the next morning to put on gunwales, decks, and hang seats and thwarts before another coat of varnish. The next morning varnish the inside, and take the boat home in the afternoon. A classic wood canoe with no glass. Or, spend a couple more days and glass the outside. You'd have a boat in a week. Rgiht now that's the goal, but the plans are still being worked on. Talk to me in 6 months or a year.

PGJ

Messages In This Thread

S&G: S & G less durable than strip-built
john faas -- 10/3/2007, 1:58 pm
makes no sense
LeeG -- 10/9/2007, 8:20 am
Re: makes no sense
HenkA -- 10/9/2007, 10:47 pm
Yes, I'd trust a boat with NO inside glass
Paul G. Jacobson -- 10/11/2007, 1:01 pm
Re: Yes, I'd trust a boat with NO inside glass
Bryan Hansel -- 10/11/2007, 7:18 pm
Re: Yes, I'd trust a boat with NO inside glass
Bill Hamm -- 10/11/2007, 8:00 pm
Re: Yes, I'd trust a boat with NO inside glass *LINK* *Pic*
Dan Caouette (CSFW) -- 10/12/2007, 8:02 am
Re: Yes, I'd trust a boat with NO inside glass
Bill Hamm -- 10/12/2007, 8:17 am
I'd like a side of ribs with a glass of resin
Paul G. Jacobson -- 10/12/2007, 11:05 am
Re: I'd like a side of ribs with a glass of resin
Bill Hamm -- 10/12/2007, 3:52 pm
Re: I'd like a side of ribs with a glass of resin
Mike Savage -- 10/12/2007, 2:04 pm
Re: I'd like a side of ribs with a glass of resin
Dan Caouette (CSFW) -- 10/12/2007, 11:25 am
Re: I'd like a side of ribs with a glass of resin
Paul G. Jacobson -- 10/12/2007, 11:57 am
Re: I'd like a side of ribs with a glass of resin
Dan Caouette (CSFW) -- 10/12/2007, 12:18 pm
Re: Yes, I'd trust a boat with NO inside glass
Dan Caouette (CSFW) -- 10/12/2007, 10:36 am
fix up your Pal
Paul G. Jacobson -- 10/12/2007, 11:47 am
Re: fix up your Pal
Dan Caouette (CSFW) -- 10/12/2007, 12:16 pm
Re: fix up your Pal
Bill Hamm -- 10/12/2007, 3:46 pm
Re: fix up your Pal
Dan Caouette (CSFW) -- 10/14/2007, 8:19 am
Re: fix up your Pal
Paul G. Jacobson -- 10/12/2007, 1:04 pm
Re: Yes, I'd trust a boat with NO inside glass
TOM RAYMOND -- 10/11/2007, 6:00 pm
Re: Yes, I'd trust a boat with NO inside glass
Bill Hamm -- 10/11/2007, 5:02 pm
Re: Yes, I'd trust a boat with NO inside glass
John Monroe -- 10/13/2007, 6:38 am
Re: Yes, I'd trust a boat with NO inside glass
Bill Hamm -- 10/13/2007, 7:17 am
Re: Yes, I'd trust a boat with NO inside glass
Paul G. Jacobson -- 10/11/2007, 6:48 pm
Re: Yes, I'd trust a boat with NO inside glass
Bill Hamm -- 10/11/2007, 7:58 pm
Re: makes no sense
Bryan Hansel -- 10/10/2007, 12:32 pm
Re: makes no sense
Robert N Pruden -- 10/10/2007, 8:12 pm
Re: makes no sense
TOM RAYMOND -- 10/11/2007, 11:41 am
Re: makes no sense
Bill Hamm -- 10/11/2007, 2:51 am
re. ten pounds less
LeeG -- 10/10/2007, 12:55 pm
Re: makes no sense
Bill Hamm -- 10/10/2007, 1:38 am
Re: makes no sense
HenkA -- 10/10/2007, 10:39 pm
Re: makes no sense
Bill Hamm -- 10/11/2007, 2:48 am
Re: makes no sense
HenkA -- 10/11/2007, 3:46 pm
Re: makes no sense
Bill Hamm -- 10/11/2007, 2:49 am
Re: S&G: S & G less durable than strip-built
HenkA -- 10/4/2007, 8:25 pm
Re: S&G: S & G less durable than strip-built
HenkA -- 10/4/2007, 10:44 pm
Re: S&G: (Link to thread: Which gives stronger boa *LINK*
HenkA -- 10/4/2007, 10:34 pm
Re: S&G: (Link to thread: try again *LINK*
HenkA -- 10/4/2007, 10:55 pm
Two links to tests of strip & S&G
Glen Smith -- 10/4/2007, 8:54 pm
Re: Two links to tests of strip & S&G
Robert N Pruden -- 10/4/2007, 9:58 pm
Re: S&G: S & G less durable than strip-built
Bill Hamm -- 10/4/2007, 1:30 am
Re: S&G: S & G less durable than strip-built
vk1nf -- 10/3/2007, 9:44 pm
Re: S&G: S & G less durable than strip-built
Aaron -- 10/3/2007, 8:41 pm
Re: S&G: S & G less durable than strip-built
Scott Baxter -- 10/3/2007, 7:49 pm
Disagree!
Robert N Pruden -- 10/3/2007, 6:43 pm
Re: S&G: S & G less durable than strip-built
Charlie -- 10/3/2007, 5:39 pm
Re: S&G: S & G less durable than strip-built
Paul G. Jacobson -- 10/3/2007, 2:44 pm
Re: S&G: S & G less durable than strip-built
Robert N Pruden -- 10/3/2007, 6:49 pm
durability not the issue. Think "ability" instead
Paul G. Jacobson -- 10/4/2007, 9:12 am
Re: durability not the issue. Think "ability" inst
Robert N Pruden -- 10/4/2007, 6:30 pm
Only one job? You'll go mad!!! *NM*
TOM RAYMOND -- 10/4/2007, 6:47 pm
Robert is gonna start writing his books
Robert N Pruden -- 10/4/2007, 7:06 pm
Re: Robert is gonna start writing his books
Ken Sutheland -- 10/6/2007, 6:24 pm
Re: S&G: S & G less durable than strip-built
Bryan Hansel -- 10/3/2007, 2:17 pm