Enterprise hull panels

[Ruskie]

I have just acquired a wooden enterprise no.15904 which is in need of restoration. I have bitten the bullet and removed the 2 bottom hull panels completely as I could see rot around the centreboard area and also the butt joints to the next panel had split both sides near to the stem.
I have got to the stage where I am about to purchase replacement plywood for these panels.
All of the suppliers I have been able to find can supply either 6mm or 9mm ply but the old panels and the transom are all 7.25mm thick (which I presume is an imperial size).
I have discounted using 9mm as although it will lap ok up to the transition joint, it will not butt properly to the adjacent existing panel to give a flush finish near the bow.
My concerns on using 6mm are that although it will bend easier, it is 15% thinner and I don't want to put my foot through it the first time I get on board! I also have the matching problem for the butt joint however this is easier to resolve by either putting a spacer behind on the chine to make the right thickness or lather on plenty of epoxy with microfibres and screw the new panel down until it is flush and let the epoxy take up the gap behind.
I would appreciate any advice as to the adequacy of using 6mm ply and assuming this is OK what is the best way of matching the new to old panels at the butt joint.

[Garry R]

I have just done the same job on 1713 and as far as I could see the bottom panels were 9mm and the other hull panels were definitely thinner - I assume 6mm (measure at the transom where the panels overlap although bear in mind that this area will be prone to oversanding if the boathas been repainted several times in its life.
As a quick calculation 7.25mm equates to 0.28" (to mix measurements) ie more than 1/4" which would be 6.35mm but not 3/8" either which would be over 9mm or 5/16" which is 8mm. Has there been some vigorous sanding?!!! It doesn't fit obviously into the imperial chart but even now 4mm ply as advertised is 3.7mm so you have to watch it. Certainly using 9mm I had no issues with different thicknesses scarfing to the good original ply left when I had cut out the rotted panels. If you scarf joint the panels (as you should) then if there is a slight discrepancy of thicknesses at the join you can sand the difference away at a taper not compromising the joint while doing this with a butt joint would remove the top laminate. The floorboards will also help in this regard strengthening the joint by spreading the load.

I have to confess though that I didn't have to deal with the curves towards the stem. If you have cut both panels away you will have to be very careful that the boat retains its shape when you fit the new panels as if it is not framed corectly it would be very easy to get a twist in the hull especially when you get tension near the stem. I cut out one side at a time and replaced it before starting on the other side to avoid this but as I said I was really just replacing mostly the flat area - the curve was just starting where my joint fell.

As regards the issue of matching the panels, if you mean colourwise I would say it's almost a non-starter due to the likely differences which have been due to weathering over the years. For my boat this would be an impossibility so I am going to paint the hull inner on the floor with non slip grey or white and the new floorboards left for varnishing . The original side panels will be varnished once I get the white paint stripped off.

Any photos?

[Ancient Geek]

Especially twenty plus years ago given ply thickness was "nominal" there were quite a few Merlin Rockets built that were very light and the planks were no 1/4" more like 5.5mm+ a bit!
I am sure Garry is right about time playing a hand in altering the thickness, however just to add confusion could it be extra layers of paint and varnish could it be swelling caused by damp wood doesn't always fully shrink back.
In any event Garry is your man he's been there and done it very recently.
My enterprise days are even further away than my other dinghy days but I seem to recall a bit of a fuss when some home builders built very fast boats one of the sins (By no means the only one - moved frames came int it too!) was light boats with thin topsides and thick bottom panels!
What do the class rules say about panel thickness and density in wooden boats?

[Ruskie]

Thanks for your comments, it seems I was being a bit optimistic to expect the plywood to stay the same thickness over 30+ years of use! I have remeasured at a number of points and have found variations in thickness of +/- 1mm on both the hull bottom sheets and the transom at points which still look to be in reasonable condition. I cannot find any reference in the rules to thicknesses of materials only overall dimensions, I guess thicknesses are given in the plans. The bottom sheets are definitely over 2mm thicker than the side panels which are 6mm and so 9mm looks to be the closest match.
On closer inspection what the builder has done forward of the transition joint (which you probably didn't as far as in your panel replacement Gary as it is just forward of the front bulkhead) is to plane the thickness of the bottom panel down to the same as the adjacent side panel thickness so that the 2 panel edges meet flush on the chine.
In any event I am glad I asked the question!

Paul