Frank is building his Kombi Sail and Paddle Canoe from our plans. He has sent a video showing that it the stitch up stage that it is a very floppy canoe. He wants to know if he has to worry.
The short answer is No! Read below for the more detailed explanation.
Find out more about the Kombi Sail and Paddle Canoe Plan
Frank’s Video of his Floppy Kombi Canoe.
Dear Michael
I have purchased the Kombi boat plans and have started construction. It is generally accepted that the less weight the better in a sailing boat, and as a result decided to construct my Kombi from 4mm marine ply. All has gone well and the boat is beginning to look great (see the attached photos) . I am pleased with progress but am struggling with the general plasticity of the boat during construction. The alignment of the panels tends to reset themselves when moved or the structure lifted or turned over, with the result that I am now worrying that the lightness of the boat is possibly detrimental
to the future structural integrity of the craft? Before I proceed further, can you indicate from the present stage in the construction being Page 31 of the manual, that subsequent stages being gluing, gunwales, epoxy and addition of other structural elements etc will produce a sturdy and fairly rigid structure rather than the current floppy canoe?
Your comments on my worries will be appreciated
Frank
Photos – the boat looks fair and neat. Nothing to worry about there!
Defining the end angles with tanks or knees and other internal structure
Hi Frank, Don’t be concerned about the floppiness. When the end tanks get fitted it means the angles at bow and stern are fixed and can’t change.
And then when the gunwales and inwales are fitted the local stiffness is spread through the structure.
Finally the seats and mast partner will finish the job removing the floppy canoe syndrome.
Videos; Kombi Sail and paddle under sailing loads\
If there was a problem with hull stiffness we would see it sailing as the boat would twist under load.
Video image can take a moment to load.
How light glass is as effective as heavier glass in the real world
In terms of longevity, there have been decades of canoes built out of 4mm alone and only glass taped on the seams. We do give a glassing schedule using the light glass. This turns the somewhat floppy middle layer of the ply – which has nothing to brace to (being at the Neutral Axis) – into a significant structural member as it is now opposed to the glass layer with the intermediate outer layer of the ply acting as a structural core. In other words it becomes a sandwich structure.
This may not directly affect the floppy canoe but will add a lot of panel rigidity for where the panels are going to take foot and traffic loads.
And the small amount of light glass across the bottom, bilge panels and 25mm onto the side panels will prevent foot pressure or many impacts from making any difference at all to the structural integrity
We have found out with our Oz Geese in the Philippines something I long suspected. Some are glassed with 2oz, most with 4oz and some with 6oz on the bottom and 25mm onto the topside panel. It is not really required for most geese as they can have bottoms of 6mm ply. But here in the Philippines we have to glass because the ply is only 5mm. Anyway … over the last decade with 117 boats launched and being dragged into the water across coarse sand and numerous small volcanic rocks that the presence of glass is much more effective than the weight of the fabric used.
This is why we recommend the 2oz glass only. Main exception is with foils. I’ve tried it but it does suffer from wear and tear on the tight radii.
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