Building the Eun Mara "Skerry"
Planking
This page contains some general notes about my experiences when planking Skerry. Garboard and Scarphing are described on separate pages.
Preamble
I chose 9mm hoop pine for the hull planking, mainly because it is available locally here in Canberra so I can purchase a couple of sheets at a time and not have to worry about storage. (The 9mm is nominal. It's actually closer to 9.5mm.) I'll use a darker plywood (gaboon, the same as I used for Grebe) for the upper works.
I am not going to epoxy-sheath the planks, for similar reasons to those outlined in the Eun Mara article in SWBANS' September 2004 newsletter. I quote (with thanks to SWBANS for an interesting article):
"There is a great debate about whether to seal plywood (or any wood, for that matter) with epoxy inside and out before painting. The argument in favour is that it prevents water from penetrating and therefore prolongs the life of the wood. The argument against is that the epoxy sheathing will eventually be broken (a crack, a ding, or something) and then water will get in with no way to get out, leading to premature rotting."
Also, I don't want to mess with more epoxy than I need to. The flip side is that hoop pine is quite soft so probably should be sheathed. However, I'll take my chances and wear any wear (as it were).
As regards finish, my intention is to paint up to the sheer strake (over the hoop pine, which is too light in colour for my liking) and use Deks Olje (proved to my satisfaction in my previous boat, Grebe) on the darker wood of the upper works. I'll fit an extra rubbing strip at the bottom of the sheer strake; I like the effect that gave on Grebe, and it will provide a nice demarcation line for the change from paint to oil.
Construction
I mentioned on the Garboard page the considerable twist that must be given to each end of the plank. This became very difficult on strakes 2 and 3, with the twist at the stern being the most challenging. I used a windlass arrangement attached to the building frame to draw the plank down to the sternpost, then a long temporary screw to secure it. Things became a lot easier at strake #4.
Here one of the laminated frames has been planed flat to meet the bevel on the plank. The foot of the plane is an effective guide for assessing when it's good enough. (The wedge-shaped gap becomes progressively bigger for planks towards the sheer. I'll pack the gaps with stiff epoxy when the hull is turned over.)
I used my new rebate plane to cut the gains ("geralds", "rebates") at the end of each plank.(This plane is a beautiful tool, made by Terry Gordon in northern New South Wales. If you thought "they don't make 'em like that any more", then you were wrong!. I couldn't resist getting one of his cute little wooden mallets to use for setting it.)
For strakes 1 through 4 I cut the gains after fitting to the boat so that there was no fragile edge to damage when the severe twist was being applied. After that, when less force was required, I cut a partial gain (about 70% of final depth) on the bench, which is much easier, then finished it after attaching the plank to the boat. This finishing touch was quite easy, as the shoulder was already present to guide the plane.
When the plank was shaped and ready for fastening, I painted the appropriate parts with slightly thinned epoxy.
Then I did the same to the bevelled edge of the receiving plank (as well as the flattened section of each laminated frame, and the stem and stern posts).
I then applied a layer of stiffly thickened epoxy to these areas (just on the receiving plank), before fastening the pair together.
(I'll have to find somewhere else to park my bike shortly.)
These photos were taken in mid April 2005. Four strakes are in place, so the hull is 4/7ths complete. That sounds like over halfway (!), particularly given that the planking process becomes easier as you approach the sheer.
Notice the marks where I have filled (and not yet cleaned up) screw holes along the top edge of the plank. My planking strategy to date has been to shape the plank, and dry fit it with a few sheet metal screws (which have flat heads about 1/2" wide) so that I can confirm all is OK. Then, when the plank has been removed and the edges epoxied, it can easily be located back in place using the screws to register it. Then I used the wooden slotted clamps to hold the edges together between the screwed down places. (I never took a photo' of the clamping, but it looked very much like Dale used on Alistego:
Thanks, Dale, for the use of the photograph!)
The reason I've shown Dale's photo' and not just waited and taken one of my own on the next plank is that I've decided not to use the wooden clamps any more. Reasons:
- As you come around towards the sheer the lack of angle on the plank overlap means that the clamps need wedges inserted to stop them sliding off. I had to use wedges on a few of the clamps near the stem on the 4th planks, and it was very fiddly.
- With a ready supply of cheap electric screwdrivers, inserting and removing the screws is negligible effort.
- I don't mind spending time filling in the holes - quite a relaxing pastime that I can do of an evening. (Just gives me an excuse to spend a bit more time with my boat.) As I intend painting the hull, the marks aren't an issue. (The wooden wedges leave indentation in the hoop pine plywood anyway, particularly on the inside, and so some filling will be needed.)
- It's easier to clean up excess epoxy from inside the hull as there are no clamps covering the plank overlaps.
- When building Grebe I used the sheet metal screw technique and found it quite straightforward.
So, rather than being clamped, the plank now looks like this when being glued:
That's the fifth plank (starboard side) in place. Before the eopxy is quite set I loosen each screw a turn or two and then re-tighten it (good old electric screwdrivers again.) This seems to break any bond between the screw and the timber. In any event, I seldom have any difficulty removing the screws once the eopxy has completely set.
The marking gauge was used to mark the 2cm plank overlap
I use my little block plane to bevel the plank edges up to the marked line. The long piece of wood screwed to the side of the plane is stepped up from the foot by the thickness of the lath that I use as a guide.
(The block plane is a bit small for the task, but has never bothered me enough to change the arrangement!)
Permanent bronze screws are used to fasten the planks at the stem and stern posts, and at the laminated frames. I tend to find that I do two or three dry fittings of a plank before eventually fastening it to the boat. (Professional builders may roll their eyes at this point. Being an amateur, I don't cost my time!) For these trial fittings I use steel screws of the same size as the eventual bronze screws. That way I avoid damaging the heads of the (highly expensive) bronze screws.
24 June 2005 and six planks completed. This is the stern view and shows the completed gains. (Seven ply plywood, and therefore six glue lines.)
I didn't notice the wobble (deviation from a fair line) at the join of planks three and four until after I'd applied the fillet. I could fair things up by removing a section of the fillet and shaving about 5mm off the bottom (top on the inverted hull) of the fourth plank with the rebate plane. But am I that concerned? Probably not, as I doubt that the problem will be apparent when the boat is the right way up.
(Notice the stack of gaboon ply sheets under the building frame. I acquired these a couple of weeks ago, and there should be enough to complete the boat. Quite exciting. Note also that they are kept clear of the floor by the oregon beams that are destined for the pergola at the side of our house. Looks like I won't be able to do that pergola until after Skerry is completed!)
Six planks shown from the stem. Notice that the gains are still just the partial ones I did on the bench before the planks were fitted (only four of the six glue lines showing). It's a ten minute job to complete them (as for the stern, shown above) with the rebate plane now that the planks are in place.
Nearing the end now. Here's the top (sheer) edge of the starboard plank 7 being marked off. The bevelled edge of the receiving plank can be seen.
Finale...
These images show the completed planking (7 per side). (Completed structurally, anyway. Fillets are complete, holes filled and roughly sanded. I'll do the final sanding, and painting, after the keel is in place.)
Notice the change from hoop pine to gaboon for the last plank (sheer strake). As mentioned at the top of the page, I intend painting the lower six planks, and switching to oil (Deks Olje) for the sheer and upper works.
Stem view.
Stern view.
Starboard side view.