Construction method with prefabricated sandwich panels

Here we present a simplified construction method that directly create a hull with a perfect finish without going through the production of a mold. The method is suitable for all boats that are usually built in sheet material, such as plywood or sheet metal. It fits all sizes of boats, everything from small canoes to large yachts.

 

What about stitches between panels? They have different density and elasticity than panel itself and I'm pretty sure it will be noticeable

 

Jürgen, thanks for sharing, this is a nice building method!

Here in Lübeck, Germany, there is the Baltec Shipyard where they build catamarans using a similar approach: Standardised foam sandwich panels with a quasi-isotropic (quadraxial iirc) glass fibre layup are laminated beforehand and then the developed panels are cut using a cnc router. All panels are joined using epoxy fillets and glass tapes.

I used to have a very elaborate paper written by their structural engineer but cannot find it anymore. I remember there was a rule of thumb regarding the minimum bending radius of the sandwich panels as a function of their thickness. The minimum radius was quite large, indicating that this method would lend itself for rather slender hulls with little curvature in the panels.

What is your experience in this regard?

Thanks in advance!

 

The problem has probably rather been that the panels are too flexible. Longitudinal stringers have been required in the external templates.
In sharp curves it may be appropriate to cut grooves in the core. In this example, it is seen at the bow.
JS

 

Thanks. It appears to be a very useful method for suitable shapes. How is the thickness of outer laminate selected? Have you had a situation where the outer laminate is too stiff or cannot be bent in a tight radius without cracking or other failure?

 

The dimensioning of the laminate thickness is done as with ordinary sandwich laminates to meet the requirements of the classification societies. There have never been any problems with bending the panels.
JS

 

Am I correct in assuming you can only build developable shapes that could also be done with plywood?

 

Based on my experience, plywood has a limited ability to be bent. With this method, the panel can be bent much more as long as it is developable. This is clearly seen in the illustrations at the bow.
JS

 

Great Minds Think Alike.
I KNEW someone had to be doing this.

make homemade super-sized fiberglass/wood ply for super-sized stitch&glue? https://www.boatdesign.net/threads/make-homemade-super-sized-fiberglass-wood-ply-for-super-sized-stitch-glue.63732/

 

There are schedules available that show the bending limits of various thicknesses of ply, GRP sandwich panels I haven't seen the equivalent, but I expect the limitations are imposed by the total thickness, more than the skin thicknesses ?

 

New boat, 8,3 x 1,9, under construction.
EcoSmart, an efficient motorboat https://www.boatdesign.net/threads/ecosmart-an-efficient-motorboat.66733/
JS

 

I have made numerous dagger boards and rudders using this general idea. First laminate a skin with ordinary FRP on a flat surface. Build a frame from wood as if you were building an airplane wing. Ribs, longerons, leading and trailing edge. Like building a model airplane wing. Wrap the wing frame with the laminate and glue it together. Works great, light, sturdy, easy. I usually embed an aluminum or stainless rod in the leading edge. Make the laminate as thick or thin as you deem appropriate.

Tinkerers, can make experimental foils with this method. I once had a Hobie 3.5 that would bury the lee bow when in a blow. I built a foil to mount between the two hulls at the bow. It was mounted a few inches above the normal waterline with a few degrees of incidence. When the bow dug in, the foil would rescue the boat and avoid an unpleasant pitchpole or other disaster. It did make the boat hobby horse. Other sailors said that it looked like a moto- crosser when in going quickly in lumpy water.