My Merlin Rocket: May 2013

Bracing The Building Frames

I removed the hog, the centerboard case and the bow knee to level and brace the stations. The garage floor has a very slight slope down towards the street to avoid water penetration or accumulation during storms. I leveled the jig first and then proceeded to level and brace each station, starting from the transom. I used a 2" x 2" cedar stock for the braces and wood screws to secure them.

All the stations now leveled. Notice the silver hydraulic bottle jacks I used to level the jig. This ensures the transom and the apron are perpendicular to the jig.

Mounting The Centerboard Case

Construction note #6 reads: "It is recommended that the centreboard case is assembled, inserted in the frames and joined to the hog before planking commences."

The procedure seeks to insert the centerboard case through the building frames. This was done without any problems thanks to the frame opening in station #4.

Using the centerboard case drawing and the layout drawing, I set the aft edge of the centerboard case at 3384 mm aft, the exact location of the forward face of the aft space frame.

I then proceeded to lay the hog over the centerboard case and mark the exact location of the opening for the centerboard. Four pilot holes were drilled at the corners of the opening Then, I cut the hog opening for the centerboard with the table saw and the jig saw.

The Hog, The Apron & The Bow Knee

Construction note #7 specifies: "...The hog butts to the apron, and is held in place by a small knee at this junction. At the stern, the hog is part rebated into the transom, and again held in place with a small knee."

As a next step, I mortised the area of the transom where the hog is rebated. I took away a section 6 mm thick x 12 mm tall x 98 mm wide.

To bond the hog to the apron, to the bow knee, to the center board case and to the transom, I placed PVC tape on the building frames to avoid bonding to them during this process.

I always do a dry run (no epoxy) to align all parts before bonding. This includes sanding, marking the position of the parts, bending, fitting, clamping, etc. The entire process. Once the epoxy is mixed with the colloidal silica, my focus is on bonding and ensuring the right amount of bonding mix is applied throughout.

Here is a picture after I bonded the hog to the apron, the bow knee, the center board case and transom

The bow knee fully rebated into the apron and the hog. This picture was taken after bonding.

Another view of the bow knee from underneath. Notice the hog doubler, a 12 mm reinforcement lamination forward of station #1.

Looking towards the transom after the bonding process.

The hog partly rebated into the transom after bonding.

Looking towards the bow after sanding the excess epoxy from the centerboard case opening.

The Garboards

According to the construction drawings, the centerboard case opening passes through the hog and extends 6 mm beyond the hog, exactly the thickness of the hull's planks. The garboard planks surround the centerboard case opening.

I marked the stations, space frames and overlap lines on all planks so it was easy to align each garboard plank against all reference marks from the apron to the transom. Once clamped in place, I marked the opening of the centerboard case on the garboards and made the cut using my table saw and jig saw.

The garboard planks land on the hog at different angles forward of station #4. The forward frame drawings and the building frames do a great job at referencing these angles. Beveling the hog to accept the garboards at the right angle requires a lot of attention to detail and patience.

After consulting with designer Keith Callaghan on how best to go about this task, I purchased two new tools, a spokeshave and a No. 9-1/2 block plane, both from Stanley.

Here, while trying to figure how to progressively bevel the hog, I strike a "What would Laurie Smart do?" pose imitating a picture of the renowned British Merlin Rocket builder while building Wicked 3708. Hoping to get some of his "mojo".

The first step I took was to mark the hog's final profile at each check point forward of station #4 per drawings provided by designer Keith Callaghan.

Next, using a coping saw, I make a cut across the hog at the correct angle base on the profile marks I made. Then, using the block plane and the spokeshave, I shaved off the excess material.

After carefully shaving away the excess material I achieved the specified shape at station #1...

... at station #2...

... and at station #3.

A picture of the forward section of the hog after shaving and before final fairing.

A dry run to test the bending/twisting characteristics of the garboard plank. A considerable amount of torque is exerted on the planks at the bow where they twist almost 90° to land on the apron.

Part of the same dry run exercise, I set a garboard plank over the building frame and against the centerboard case.

Forward of station #4 there is excess material towards the center line over of the hog. I used the block plane to shave off the excess material to ensure a proper fitting.

Centering and aligning both garboard planks over the hog to ensure proper fitting.

I marked the landing spots for all planks over the apron. Once bent and clamped in place, the overlap line of the garboard plank lands exactly over where the edge of the next plank will land.

I drilled holes on the building frames to insert clamps and secure the plank during bonding. This helps counter the torque exerted on the plan and ensure proper alignment to the frame.

I placed a clamp wherever air gaps could be seen so that the planks fit perfectly flat against the hog.

Having a variety of clamps really helps manage the grip against different angles and surfaces. I made 6 additional deep-throat clamps

I also bought a couple of heavy duty clamps for holding the garboard onto the apron. Great advise, Keith! Thanks!

The deep-throat clamps recommended by designer Keith Callaghan worked really well on a variety of angles when clamping the garboard against the hog.

Dealing with higher than normal temperatures

One of the biggest challenges I had this past month was the higher than normal temperatures in May. While others around the globe complain about their cold and rainy Spring, I had to deal with temperatures as high as 95°F / 35°C, making it difficult to mix epoxy for work areas that require more than 10 minutes to set.

During the dry run I realized I was going to need more time to mix the epoxy with colloidal silica, spread it over the overlap areas, set the garboard in place over the hog, twist and clamp the plan over the apron.

I decided to use West System 209 Extra Slow hardener. Here are the specification from their website.

Pot life at 72°F (22°C): 40 to 50 minutes

Pot life at 95°F (35°C): 15 to 20 minutes

Cure to a solid state at 72°F (22°C): 20 to 24 hours

Cure to a solid state at 95°F (35°C): 6 to 8 hours

Cure to maximum strength at 72°F: 4 to 9 days

Minimum recommended temperature: 70°F (21°C)

On a Saturday morning, I got up at 5 am. The temperature in the garage was 28°C, while outside it was a nice 21°F. After opening the garage door, I was able to drop the temperature inside the garage to about 26°F. I moved the epoxy, the hardeners and the colloidal silica tube inside the house the night before. The West System 209 extra slow hardener worked great and it is obviously specified for my current temperatures. I was able to mix and spread the bonding compound without any issues, clamp down the first garboard plank, clean excess epoxy, and tweak here and there forward of station #4 before the epoxy began to gel.

I protected the tips of the deep throat clamps with plastic to prevent them from bonding to the garboard and the hog.

A variety of clamps over the port side garboard plank. The larger C-clamp was necessary to counter the torque effect over the apron and the hog.

A view from the other side while I was inspecting to ensure there were no gaps without epoxy

A tight fit.

After curing, I removed all the clamps and inspected the garboard.

One garboard down, one to go!

The next day, I followed the same process for the Starboard plank. I had to remove the excess Port garboard material over the hog to allow ample space for the Starboard plank.

Although I had a better idea of what to expect, the Starboard garboard forward of station #4 proved tricky. I had to clamp over the Port garboard.

A view of the garboard planks from the transom after bonding.

I also clamped the garboard planks against the centerboard case opening to ensure a tight bond and the 27 mm wide opening. Thank you for the reminder, Keith!