About "Stitch & Glue" Plywood utso

About "Stitch & Glue"

The vast majority of stitch and glue kayaks is built from 'Marine ' which is overall an excellent choice but marine is generally limited to only a few unimpressive looking wood species and predictably, kayaks built entirely from such material do look accordingly. After all, many S&G kayaks are painted to hide the wood. Marine is made to certain specifications so it is of predictable quality and as a result, has been adopted by and large as the only 'acceptable' and 'safe' material for stitch and glue kayaks. This is certainly understandable since confusion and mystery surrounding marine abound and 'kit biz' interests are quite happy to perpetuate this orthodoxy.

 

So, what is this stuff ?!

Marine has actually less to do with the wood itself as it has with the specifications to which it is manufactured. Let's look at the 'wood' first. The vast majority of marine in the world is made from the Okoumé (Acuomea Kleinea) tree which is harvested in the African state of Gabon in the tropical forests of the Congo Basin. This wood is also often referred to (correctly or not) as Gabon, Gaboon, Okume, Ocume, Ocoume, BS1088 etc. and the core as well as the skins are made of the same wood. Virtually all Okoume is manufactured outside of the US and Canada so it is a good bet that the in your kayak will likely come from some factory in greater Asia, Israel, France or Greece.

 

Another less common variety of marine is 'Meranti'. It is made from many subspecies of the 'Shorea' tree species which also happens to be the source of wood for the common Lauan (luan) . Both Lauan and Meranti are also referred to interchangeably as Philippine Mahogany and the wood is harvested in Indonesia and the South Pacific rim forests.

Now, there is also White Lauan made from Shorea almon, Red Lauan made from Shorea negrosensis which happens to be the Red Meranti. Other 'Meranti' is made from Shorea curtisii, S. hypochra, S. leprosula, S. multiflora, S. platiclados, S. pauciflora to name a few. Confusing enough ?

 

Marine is also made from Fir, Ash, African Mahogany (Kaya), Honduras Mahogany and/or combinations of Okoume core with Sapele, Teak as well as other wood skins but those are largely used on thicker than 4mm which is unfortunate - for kayak builders.

The look of marine is not only determined by the wood species but it can also vary according to the ply cutting methods. The most common is rotary cutting which give the surface a look of 'contours' on a topographical map (same look as common in a lumber yard). The other method of cutting is 'quarter sawn' slicing which produces nice 'ribbon' look with the tree growth rings appearing as parallel lines (like wood strip kayaks). The immediate implication of this is that building your kayak with the 'same' type of marine as your friend built a year ago may make your kayak look quite different (color and texture wise). The will have likely come from a different lot of logs and/or subspecies. Also, Meranti is less available in thickness less than 1/4" (6.2mm) and is largely heavier due to the wood density itself as well as additional glue since it comes in 5 ply. Okoume under 4mm is always made in 3 plys. A 4' x 8' sheet of 4mm Okoume can range from 12 to 16lb (桐30-50 price range) and Meranti about 19 to 24lb. All in all, you will be hard pressed to find anything lighter than Okoume.

 

Now, the main thing that entitles to be classified as 'marine' relates to the manufacture under a set of standards, specifically to the quality of the wood as in the number and size of permissible knots and cracks, glue type, moisture content and thickness tolerances of the plys etc... Marine is sold under BS (British Standard) designation such as BS1088 or BS6566. BS1088 is made from Okoume and is of the highest quality with a defect free core and both faces of solid A surface while BS6566 standard is less species specific and is more permissive so the surface of this may show a few skin defects on one or both faces. Here is a short excerpt of the BS1088 standard.

 

What about other ? The nice thing about building your One Ocean stitch and glue kayak like the Cirrus is that we can ignore most of the BS1088 standard for it is quite irrelevant with respect to this building method, with one exception - the requirement of a 'void free' core. This suddenly opens up a whole new world of choice. Remember, that the sole purpose of the , (like the strips in a strip kayak), is to serve as a solid sandwich core, reinforced on both sides with continuous and water proof skin of epoxy and structural fiberglass. Consequently, the 'BS' rules for thickness variation, individual ply variation, wood type, rot resistance, small skin defects, and most importantly the glue type - make NO difference whatsoever. As a point of interest, the BS standard recognizes four types of glue bonds. All BS1088 and BS6566 marine use phenol formaldehyde (Weather & Boil Proof) glue.The other non-marine types are "Cyclic Boil Resistant", "Moisture Resistant" and lastly "Interior" glue which is very strong in the dry state but has no resistance to moisture.

Now, the perspective to keep in mind is that the in your kayak will always stay as dry as it was when you covered it first in epoxy and it will remain 1004 weather, moisture, air and UV proof. It will certainly not be boiled (perhaps only cycle boiled in sprint as you lean into the paddle ;)). Let me also point out that strip kayaks are made of many wood types (balsa included) and the glue used is common yellow carpenter's glue (not water resistant or 'proof'). I still wait for reports of kayaks dissolving in action.

 

The last and most important point that deserves consideration is the requirement for a void free core. This is a structural issue and large voids or cracks in the core essentially reduce the thickness of the in that area to the sum of 'thickness' of the skins and the fiberglass. So if you have 6mm Lauan on the hull with a huge crack in the core, the actual thickness of the becomes about 3/32" (2.5mm) which is very bad! BS1088 and BS6566 will guarantee a completely solid core but it doesn't mean that it is the only in existence that has it. If you look around, you will find a vast amount of excellent quality on the market which uses the same glue as BS1088, and even if it doesn't, the core and skin will be as solid, perhaps better than any BS 6566 . If you decide to build from non marine , make sure to examine the sheets from the side (perpendicular to the grain orientation of the skins) to verify the quality. In my experience, top quality exotic veneers (which is what we like in our kayaks) are not bonded to crappy cores so the sheets will generally be consistent with the overall quality and price of the veneer. So far, this gives us a decent selection but if you want something really special you can also make your own by bonding veneer (of which there is even larger variety) dierctly to 3mm or 4mm . To do this right, however, will require vacuum bagging or veneer press since the gluing will need to be done with slower setting adhesives such as Titebond II or epoxy. Some merchants also provide this customized service. So, if you are building the Cirrus, Okoume and Meranti are not your only choice and that's no 'BS'.

Longda Wooden manufacture corporation limited