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Re: Material: Light weight layup
By:Paul G. Jacobson
Date: 12/6/2002, 1:08 am
In Response To: Material: Light weight layup (Larry C.)

: I'm building Nick's RBA to be used for fast touring/racing. I'm committed to
: the lightest possible layup. I am wondering what glass to buy that will
: give me the most strength and lightest weight. I have been thinking about
: 4 oz. plain weave with a few extra layers here and there but mostly one
: layer inside and out. I may use some unidirectional carbon in high stress
: areas.

: I am looking for any ideas to make this a light boat. It is being striped
: with 3/16" strips and will not have bulkheads or hatches or deck
: rigging. I may do bulkheads with hatches if I can make them super light,
: otherwise I will us float bags.

: Any lightweight ideas are appreciated.

How about some heavyweight ideas for a lightweight boat?

Here is something you can ruminate about:

A) Go with 1/8th or 1/10th inch strips over

B) 1/8th inch ribs spaced as far apart as your building forms (probably a foot apart).

C)2 ounce or 3 ounce glass on the outside.

D) Patches of 2 ounce glass on the inside.

E)Built up cockpit area.

F) Wooden sheer spline.

G) multiple, featherweight, airbags for flotation.

Now, here is the thinking behind each of these unconventional thoughts.

A) Very thin strips. The skin on a birchbark canoe is even thinner. If you want to go thinner still, you'ld be better off with a fabric. In conventional building we go with the thicker strips for a few reasons, one of them is that try to design monocoque designs where the skin of the kayak is self supporting. when you look at the ideas behind skin on frame boats, though, you see that the frame supports the loads, and the skin just needs to be strong enough to keep the water out. Thin fabrics and even 1/32nd veneer would be strong enough to resist the minor water pressure on the skin, which is mere fractions of a pound per square inch. Going with 1/8th inch wood strips you cut weight of the wood components in half when compared to 1/4 inch strips, or you cut out 33% when compared to 3/16th strips. And if you are careful, you can go thinner. From 0.125 to 0.100 (an 1/8th to a 1/10th) you are only going 0.025 (25 thousandths thinner)

B) these are very thin ribs, but they should be strong enough. You can attach your strips to the ribs with epoxy or some other glue as you strip the boat. The ribs MUST be firmly attached. In effect you want areas of the boat which ARE 1/4 inch thick, and then you surround these areas with thinner sections.

The grain of the ribs is at right angles to that of the strips. Rigidly gluing these in place contributes to stiffness.

If you cut your forms down by 1/8th inch you can make up for the removed wood by wrapping a 1/8th inch rib around the perimeter of each form, and holding it in place with a brad at each end, or a few drops of hot glue. When the boat is taken off the forms you can cut away the excess strip, or break the bonds of the hot glue. the ribs then remain firmly bonded in place.

Before the advent of fiberglass and epoxy resin canoes were constructed of ribs and slats. the ribs provided the necessary bracing for the boat. When we adopted composite technoligy, we replaced the mechanical function of the ribs with a sheet of glass fabric. Since this glass and the resin that goes with it are a major weight factor, go back to ribs for your internal bracing.

C) you only need a very lightweight glass to ensure the surface bonding of the strips, and to serve as a thickness guage for putting on a minimum amount of resin. 2 ounce cloth will need half the resin of 4 ounce cloth, so your weight is cut in half. Again, the stresses on the hull fabric are very small. you could cover a skin on frame kayak with cheesecloth and it would work -- if you could waterproof it!

D) This is something no one has brought forth before. Instead of covering the eintire inside of the boat with a single sheet of glass cloth, just use patches of cloth over the areas between the ribs. As mentioned before, the current use of internal glass replaces the older rib design -- but here I am suggesting going back to ribs -- so this may seem contradictory. Au contraire. I think of it as a belt and suspenders approach. If the ribs are on 12 inch centers, then there will be a flat space about 11 inches wide between any two of them. You could create a fillet alongside each rib, or construct your ribs with a rounded "D" shaped crossection so that you could glass over them, but why bother. A 10 inch wide piece of glass cloth covers almost the entire distance between a pair of ribs, and the amount that isn't covered is not going to affect strength very much. For that matter, you could go with a 8 inch or a 6 inch wide stripe, running from sheer to sheer, and centered between a pair of ribs. You get most of the strength of a continuous glass panel, but, the more glass you leave off, the more weight you leave off.

If you wanted to go with a unidirectional glass, or carbon fiber, or a kevlar material, then use it in wide strips on the interior, as described for glass. You are not going to sand this. Sanding would be a mess and take away little weight while adding no strength. Strength for weight for cost, though, you can stick with glass cloth. You won't be using much so the differences will be slight.

E) The only area where you have a highly concentrated weight (yours) is in the cockpit. You can build up this area with more closely spaced ribs, a layer of lengthwise strips which overlap the seams of the hull strips, or a sheet of 1/8th inch plywood for a seating area. The coamining will need to be strong enough to take your weight while you enter the boat. all of this means that your sheers ( or gunwales)will have to be strong.That implies

F) The wood sheer spline serves the same purpose as the gunwales on a canoe. It provides shape and stiffness, and transmits stresses along the length of the hull. for a light weight kayak it also provides a surface for joining the hull and deck. You won't need to use glass tape and resin on the inside if you have a sheer strip there at the seam. A few brads to keep things in alignment and you can just glass the outside.

G) a bulkhead -- even a thin one -- would provide quite a bit of internal strength. I'd suggest such a thing at the front and rear of the cockpit to support the coaming and to contribute to the strength of the cockpit area. the bulkhead can have a lareg hole cut int he center to lighten it, and this can be covered with a fabric flap held on with velcro. or it can be left open.

As far as flotation. One silly idea: Instead of filling the hull with hydrogen, you could get a lighter weight by sucking all the air our and amintaining a vacuum. Of course, any small leak would mean that atmospheric pressure would force water into the hull very rapidly, so this is not a good idea. :)

You could fill the area with plastic laundry bags filled with foam packing chips. Or, eliminate the packing chips and fill the area with heatsealed palstic bags which are simply filled with air. Make them small and make many. redundency is a virture here as then the failure of even 10 or 20 will not be catastrophic. Don't have lots of bags filled with air? Buy a bunch of balloons and fill them.

If you get water in side, a lightweight boat like this willnto be strong enough to pick up out of the water to drain. A pump is a necessary tool to carry with.

Just some ideas and thoughts. I haven't built a boat like this, and honestly, I doubt I would. If I wanted a lighter boat, I'd try to remove the surplus pounds from the paddler -- but that would mean giving up pizza :(

Hope these comemnts help/inspire/enrage/ or something. it is good to get the mental processes moving.

PGJ

Messages In This Thread

Material: Light weight layup
Larry C. -- 12/5/2002, 12:30 pm
I'm building one too
Jack Sanderson -- 12/6/2002, 2:49 pm
Re: I'm building one too
Larry C. -- 12/7/2002, 8:17 am
Thanks, everyone *NM*
Larry C. -- 12/7/2002, 8:22 am
Re: Material: Light weight layup
Paul G. Jacobson -- 12/6/2002, 1:08 am
Re: Material: Light weight layup
Jeff The Tall -- 12/6/2002, 3:18 pm
Re: Material: Light weight layup
Mike Loriz -- 12/6/2002, 1:11 pm
Re: Material: Light weight layup
Don Lucas -- 12/6/2002, 11:04 am
Re: Material: Light weight layup - Bulkheads
KenB -- 12/6/2002, 1:02 pm
Re: Material: Light weight layup - Bulkheads
Shawn Baker -- 12/6/2002, 4:44 pm
Re: Material: Light weight layup
Mark -- 12/5/2002, 6:53 pm
Re: Material: Light weight layup
Mike Loriz -- 12/6/2002, 12:57 pm
Re: Material: Light weight layup *Pic*
Chip Sandresky -- 12/5/2002, 7:25 pm
Budget, weaker pressure "vacuum bagging"
Paul G. Jacobson -- 12/6/2002, 10:42 pm
Re: vac bagging
Mark -- 12/6/2002, 10:15 am
Re: vac bagging
Jeff The Tall -- 12/6/2002, 2:48 pm
Re: vac bagging
Shawn Baker -- 12/6/2002, 6:16 pm
Re: vac bagging
Chip Sandresky -- 12/6/2002, 5:25 pm
Re: vac bagging
Mark -- 12/7/2002, 12:58 pm
Re: vac bagging *LINK*
david schneider -- 12/14/2002, 12:03 pm
Re: vac bagging
Roger Nuffer -- 12/14/2002, 12:58 pm
Re: vac bagging *LINK*
david schneider -- 12/14/2002, 4:25 pm
Re: vac bagging
Shawn Baker -- 12/6/2002, 6:20 pm
Re: vac bagging
Mark -- 12/6/2002, 4:52 pm
Re: vac bagging
Jeff The Tall -- 12/9/2002, 4:52 pm
Re: vac bagging - OK for Wiki?
Shawn Baker -- 12/6/2002, 6:19 pm
OT: thanks for the pic
Larry -- 12/5/2002, 10:50 pm
Re: Material: Light weight layup
Scott Fitzgerrell -- 12/5/2002, 3:18 pm
Re: Material: Light weight layup
Rob Macks -- 12/5/2002, 4:03 pm
Re: Material: Light weight layup
Shawn Baker -- 12/5/2002, 4:25 pm
Re: Material: Light weight layup
Mike Loriz -- 12/5/2002, 2:37 pm
Re: Material: Light weight layup
Jim Kozel -- 12/5/2002, 3:11 pm
Re: Material: Light weight layup
mike loriz -- 12/5/2002, 5:09 pm
Re: Material: Light weight layup
Jim Kozel -- 12/7/2002, 9:41 am
Re: Material: Light weight layup
Mike Loriz -- 12/10/2002, 7:33 pm
Re: Material: Light weight layup
Fred -- 12/7/2002, 10:08 am
Re: Material: Light weight layup
Jim Kozel -- 12/7/2002, 11:32 am
Re: Material: Light weight layup
KenB -- 12/5/2002, 2:29 pm
Re: Material: Light weight layup
LeeG -- 12/6/2002, 2:28 pm
Re: Material: Light weight layup
Chip Sandresky -- 12/5/2002, 3:12 pm
Re: Material: Light weight layup
Shawn Baker -- 12/5/2002, 2:24 pm
Out there.
Myrl Tanton -- 12/5/2002, 12:44 pm
Re: Out there.
Ross Sieber -- 12/5/2002, 1:49 pm
RE: Boom! - are you sure?
Myrl Tanton -- 12/5/2002, 3:50 pm
Re: RE: Boom! - are you sure?
Larry -- 12/5/2002, 10:34 pm
Re: Float bag contents
Shawn Baker -- 12/5/2002, 4:23 pm
Re: COTFLGUOAHAHA
Ross Sieber -- 12/5/2002, 5:13 pm
Re: RE: Boom! - are you sure? *LINK*
Ross Sieber -- 12/5/2002, 4:23 pm
Re: Out there.
Don Flowers -- 12/5/2002, 3:15 pm
Re: Boom!
Shawn Baker -- 12/5/2002, 2:17 pm
Re: Out there.
Bruce -- 12/5/2002, 1:18 pm