thompsondockside.com

Which is stronger, forming ribs by laminating 1/8 inch strips of oak or steam bending them?

I would guess that with using the right glue Lamination would be the stronger of the two.
But don't forget that these boats that we work on were designed to have some flexibility. I think that the laminated ribs would also be stiffer than their steambent counter parts. Not sure how that would affect other parts of the equation.
I remember riding in a CC-U22 that I helped to restore and being amazed at how much flexing there was going on while watching the gunnels on a rough lake. And the rib design on those is much stronger than the Thompsons.
What does anyone else have to say.
Karl.

Well, I am a bit biased. I work in the structural glued laminated timber industry. Laminating, if done properly with correctly selected and prepared lumber and correct adhesive will be stronger that solid wood. This is a proven fact.

Glued laminated white oak frames (ribs) and other members for US Navy 224 ft. long MineCounter Measure ship built in the 1980s.:


The Chris-Craft U22 has sawn solid wood frames. No steam bent framing in that type of boat.

Andreas

Great Pic Andreas.
Wonder if this is what it looked like when Noah built the ark ?
And as you say the Chris Craft U-22 that I was refering does have sawn frames, but not sawn on a curve. And even still, these have been known to break. All these boats whether they are Chris Craft, Thompsons or Lyman etc, all have certain aspects of their design that is prone to problems. I am sure that when they were built no one was thinking about 50 years later when some poor fool in a garage in Northen Michigan (or Minnesota) would be trying to restore one.
Karl.

I agree that laminated ribs would be stronger then a single piece of wood. The main difference is that one can assemble a boat much faster using steam bent ribs then one can build a boat using glue laminated ribs.
Glue laminated ribs require forms to assemble them on and allow the glue to set-up, where as a steam bent rib is in place and fastened on basic step.

Boats like the Chris Craft with sawn ribs had a lot more beef in their ribs or frames then what we see in Thompson's. And in most cases the ribs did not have the tight radius that Thompson used for their hulls. The Chris Craft had gentle curves and sharpe square corners in their hulls. The sharper corners were made using two peices of wood. One in each direction of the change in hull shape and backed up with knee's to reinforce them. Also the Chris Craft used a much thicker planking which needed the thicker ribs to support the steam bent planking and not deform.

As to flex, I do believe that a steam bent rib will have more flex then a laminated rib will have. Lamination tends to make the member stiffer and in most cases stronger then a sinlge piece of wood.

We could go on for a whole day talking about steam bent verses laminated and still have more to decuss about it.

Sound like a good topic to dicuss at the Thompson Rally in June. Always good to get others input on any subject.
Come to the Rally and we can get into this discussion again.

Phill

Well, I've been reading these posts for a year or so now and since I am neither a boat builder nor a restorer I've hesitated in posting. On the topic of strength and flex of laminations vs. that of solid members, however, I can tell you this, John. As a sculptor who has 30 years in laminated wood members up to 25' long from a variety of species (pine, fir, beach, mahogany, teak, oak (s), paduk etc.) that your ribs made from laminations will be FAR stronger than solid ribs. While you could build your rib laminations in place (using the hull shape as a form), you MUST keep the entire lamination under pressure as the glue sets. A most difficult aspect of lamination construction is clean-up of the edges and this alone would make for a serious negative for in-place construction of laminations. Number of laminations, kiln dried vs. air dried, clamping, form materials and spring-back are more issues. Glue is another world.

However, your boat with properly constructed laminated ribs will be vastly stronger and capable of more flexing than if you used solid ribs, in my opinion.

Now, having said this; does anyone know of a really nice '62-'64 Sea Coaster for sale?

Torchie wrote:...I am sure that when they were built no one was thinking about 50 years later when some poor fool in a garage in Northen Michigan (or Minnesota) would be trying to restore one.
Karl.

... or North Georgia, for that matter!

As an engineer and now home builder/remodeler, I will say that the laminated material is definitely stronger, size-for-size. The biggest reason for this is that you're shrinking and distributing your defects. On a piece of solid stock, a knot (or wavy grain, or split... you name it) will usually go all the way through the wood. If you take that piece and saw it into 4, 5, or 6 layers, then flip some over, flip some end-for-end, and glue it all back together, you've reduced a defect that goes all the way through to one that only goes through a single layer, and it's backed up by all the other layers that don't have that same defect in the same spot.

Even better is if you take multiple pieces of wood and saw them up, mix them up, and group them back together. Then you're even less likely to have any given defect in common between two layers.

Let's also not confuse stiffness with strength. A 1/2" steel cable will have a lot more strength than a 1/2" oak frame, but the oak will have a lot more stiffness.

* * *

I've not been too active here lately, so for those who don't know, I've been doing a complete structural rebuild on a '57 Sea Lancer over the past 3+ years. I didn't know I'd be doing all this when I got into it, but that's how these projects go, isn't it? As of this past weekend, I've laminated 58 of my 60 new frames. I pretty much have that process down to a science, so please feel free to ask away about how I've done it, or look for my other posts and photos on the subject. I'm using kiln-dried white oak and Smith's Oak & Teak epoxy.

I'm now also starting to work on rebuilding the floor framing ("sister keelsons" I think they're properly called, plus the lateral pieces that connect them). I've just spoken with my plywood supplier and will be getting material in the next week or so to start replacing all the planking below the waterline.

* * *

A final few comments on my new laminated frames: they may be stiffer than steam bent ones, but it's tough to really say. My old frames were in such bad shape, and the wood was generally so deteriorated that they would not make a fair comparison. I did try steaming my new frames at first, but the process I was using wasn't reliable enough, so I switched to laminating. I do have some frames that I steamed, and there's no really noticeable difference in flexibility between frames from the two methods. The laminated ones are still very flexible... after all, they're about 5' long and just over 1/2" thick! The math behind it would suggest that the thickness will affect stiffness a huge amount... a slight increase would probably stiffen it more than the technique of lamination. In the end, I'd rather trust a laminated frame not to break under stress than a solid one!