My Merlin Rocket: September, 2013

Interior Construction

Getting started on the interior construction required sanding the plank joints, around the apron, the transom, the hog and the centerboard. Prior to fitting the planks I used an orbital sander on them so the surfaces were fairly smooth for the most part.

Even though I'll have to sand again once filleting is done and fiberglass reinforcements are fitted, it is worth the effort and it will be noticeable after applying paint or varnish.

The Main Spaceframe

Prior to fitting the Main Space Frame, I placed a rope across the hull and tightened it until the dimensions between the top of planks' #8 were precisely as indicated in the layout drawing.

I then placed a square against the centerboard case and the Main Space Frame. Once squared to the garboard, I marked the final location of the port side Main Space Frame. A good mix of epoxy resin with colloidal silica was then applied for bonding.

The starboard side Main Space Frame went through the same process,

The Centerboard Side Stiffeners

It is recommended that the side stiffeners be fitted prior to mounting the centerboard case over the hog. The openings on the construction frames allow plenty of room to insert the centerboard case in place.

Fitting the centerboard through the construction frames was easy. I regret not having fit the side stiffeners earlier. Clamping and handling at this point was a bit awkward. There is much better access to the centerboard when it is on the workbench or soon after being fitted to the hog.

Centerboard Bolt Reinforcements

Once the centerboard side reinforcements were bonded, I fitted the bolt reinforcements. I placed a long drill bit through the hole for alignment with the starboard side bolt reinforcement. With a small square against the drill bit and the reinforcement, I ensured the alignment reference was perpendicular to the centerboard case.

After marking the proper location of both reinforcements and verifying there were no gaps with the hog or the side reinforcements, a mix of epoxy resin with colloidal silica was applied for bonding.

This month my photographs are a bit out of sequence. I didn't take them after each step as I usually do, so I had to go back and take them after I had taken a couple more steps. Notice the filleting beads I applied throughout.

Aft Spaceframe

The aft spaceframe drawing provided by designer Keith Callaghan specifies "2 halves of spaceframe are scarf joined at the centreline (6:1 scarf joint)."

Prior to fitting the Aft Space Frame, I placed a rope across the hull and tightened it until the dimensions between the top of planks' #8 were precisely as indicated in the layout drawing. It is important that no gaps exist between the spaceframe and the hull.

So I dusted off the router jig I built to scarf the planks and proceeded to scarfed the two spaceframe halves. Prior to scarfing I placed both halves in place and marked the overlap on both pieces.

Once again, the result was a sharp and smooth cut.

Now that looks like a nice scarf joint...

Wait! What? Oh, gee! You may remember my jig had an 8:1 slope. The drawing calls for a 6:1 slope.... Oops! Fortunately, the difference is not much and I was able to fill the gap when I was filleting.

I marked the ends on both sides and the direction of the cut on each aft spaceframe half to avoid a wasteful outcome. Then, I applied clear epoxy first on the exposed plywood and about 5 minutes later I applied an epoxy and colloidal silica bonding mix to the scarf joint. Clamping on a temporary work bench was easy.

Once bonded and sure that no gaps between the aft spaceframe and the hull existed, I fitted the aft spaceframe to the hull with a bonding mix of West Marine 105 epoxy and 406 colloidal silica.

The Main Bulkhead & Bow Tank Beam

The Main Bulkhead drawing provided by designer Keith Callaghan gives a great deal of detail: "The bulkhead is made from 6mm plywood and is angled at 62 degrees to the centreline."

I also beveled and fitted the bow tank beam and added reinforcements of Western Red Cedar to support the bow tank top.

Another specification reads: "aft face is 1738 aft at bevelled surface of land #4". Beveling is a variable 3-dimensional task at each plank. Fun times indeed!

Painstakingly, I took the time to plan, prep and execute these tasks to achieve the desirable result. Beveling is important to achieve a close fit. Supporting the bulkheads at the right angle for bonding requires some time and preparation. I used a combination of Western Red Cedar blocks and temporary duct tape. The bow tank tops provide a great reference when placing the bulkhead on the hull and marking its final location. A lot of sanding before starting was required and a lot more will be required later.

Reinforcement Of Lands Between Planks #2 & #3

The land between planks 2 and 3 has only about 16 mm of bevelled land to glue to. There is a sharp turn there and I'm concerned that, if I fall (and I most likely will... several times), the epoxy will hold but the plywood may give up.

Therefore, and based on Keith's recommendation, I placed an epoxy fillet along this land, internally, from the bow tank to the aft space frame, then I applied one layer of 75 mm wide glass tape and one layer of 50 mm wide glass tape. This should beef it up sufficiently for me.

Keith Callaghan's Construction Note #8 specifies: "Each plank overlaps the next plank nearer the garboard plank on the outside. The plans show a nominal overlap of 19 mm, but where planks overlap at an angle greater than about 15 degrees (as in the bow sections near the waterline), the bevelling of the land causes this overlap to be reduced. In the bows, local reinforcement is desirable in these areas (eg glass reinforcement internally)."

And so I've reinforced the hull from bow to stern.