low tide

The problem with exterior grade ply (WBP) over marine ply is that you cannot see the voids, they are not apparent until the sheet is cut. The top veneer is rarely a single sheet on exterior ply, which can also cause problems when cutting for something as accurate as a hull section. If it is a single veneer in order to keep the cost down the internal layers are often poor.

Remember that trhe timber merchant wants to sell you what he has in stock.  They will have to order in marine ply and their margins on it are small due to the quantities ordered.

Several Mirror dinghys have been home built using WBP, you will recognise them as the rotten lumps in the corner of the dinghy park or the ones with bubbles on the ply where it is delaminating.

I think that the 6' skiff is an excellent and bold design. I do think however that if you compromise the materials you use, (and I know that you are only going to use a certain design for a short period) you will not be able to properly test a design since it will be unable to take the loads properly.

I don't intend to be arguementative on this issue, and I appologise if I appear so I  would just hate to see something like this fall at the first hurdle or get a reputation for something that falls apart as soon as it gets going, or that people waste their money on unsuitable materials.

There is a very big difference between exterior grade and marine grade plywood, I know this because I am a carpenter. Exterior grade ply is unsuitable for boat building due to the way ity is constructed, not the quality of the finish. 

I may seem very argumentative about this issue but i still fail to see how you are going to build a hull for £100. 

I feel that this is a very misleading statement to make on a website and it cannot be backed up by hard facts. 

Whilst I wish the 6' skiff class well with its projects I really think that your should be able to provide some hard facts and advice to back up your statements.

Please explain what materials you suggest.  eg marine ply? you would need a minimum of two sheets. I can get this trade (6mm) for £40-00 a sheet (plus vat) so you are looking at £94-00 as a starting point. Thats without all the other materials.