Thursday, April 13, 2017

Argie 15 - Fitting the Daggerboard Casing & Rub-Rails

Moving on with the Argie 15 project, I covered the bottom runners in my previous post. The runners serve multiple purposes, which I forgot to explain. The runners give some protection to the bottom when beaching the boat, by lifting it a bit when pulled onto rough beaches. They strengthen the bottom by serving as stringers but, being on the outside of the boat, they keep the bottom of the cockpit clean for a more comfortable sleeping space when camp-cruising. They also help to improve the efficiency of the planing surface by channeling the water parallel to centreline rather than losing energy by moving off to each side.

At this stage we also checked the fit of the daggerboard. It slid nicely through the slot in the hull. Kevin had glued the end spacers to the one side of the daggerboard casing but the second side was still loose. When we checked the fit, the board wouldn't go through. Checking the sides for straightness showed that they bowed inwards a few millimeters, enough to jam the board. That gave warning that care had to be taken when gluing it all together to ensure that the sides remained straight throughout the height of the casing.
The daggerboard casing glued up, including the top and bottom framing. The blue pieces at the top are spacers to force the sides against the framing, to ensure that there is no curvature in the surfaces to reduce the width and jam the board.
The casing glued in place. The blue spacers were left in place until the glue had cured, so that there would be no chance of the casing distorting and reducing the width of the slot.
Next on the "to do" list is the rub-rails. These are laminated to the outside of the hull, at the gunwales. They stiffen the hull, changing a fairly flexible plywood edge into a robust gunwale that is capable of taking a knock if needed. Some builders of the Argie 15 don't use this detail from our drawings, instead changing it to an internal scuppered inwale detail. That is a very pretty detail that is well-suited to traditional rowing boats and similar craft, adding the benefit of tie-off points anywhere that you want along the gunwales but is more difficult to do. For the Argie 15, which will be sailed with the crew sitting along the sides of the cockpit, the inwale creates an uncomfortable surface to lean against instead of the clean surface of the original design.

Kevin called on me to assist with fitting the rub-rails. The laminations are fitted in single lengths (scarphed from short pieces), so are awkward for one person to handle in a confined space. Getting them correctly positioned on the wet glue while also working with clamps calls for some ingenuity if working by yourself. It is simpler to call in a pair of extra hands.

This job calls for lots and lots of clamps. We did both sides in one evening, which needed all of Kevin's clamps as well as all of mine. If you are brave and short of time then you might want to laminate all layers at the same time. This is risky because it needs slow-setting glue that won't set before you are able to wet-out all strips, get them into place, manipulate three or fours slippery lengths into proper alignment and get all the clamps in place and correctly tensioned.

We chose instead to do one layer at a time. Rather than four layers of equal thickness, Kevin prepared inner and outer layers of poplar and a middle layer of cedar of double-thickness. This gives a nice stiff gunwale with a tougher outer surface than if all layers were cedar. It is also very pretty.
Kevin with the Argie 15 after clamping the first layer of the gunwale.
Two days later we also glued the second layer of the rub-rail. We managed to break one of the scarphs even before starting with the gluing. The epoxy was not fully cured yet so the epoxy was well short of final strength. We were able to still laminate it onto the  first layer by carefully clamping at the joint to hold it closed against the bending loads applied by the curvature to which it had to comply.

When gluing all laminations after the first one, it is best to get the bottom completely flush and let the top look after itself. The reason is that it is very easy to clean up and neatly finish the top  but much more difficult to do the same to the bottom of the rail because of the adjacent plywood.

That's all for now. To see more of this and our other designs, go to our main website or our mobile website.