December, 2013

Shaping The Foils - The 3rd Dimension

Last month (November, 2013), I shaped the foils using the profile drawings and NACA foil tables provided by designer Keith Callaghan. That step allowed me to shape the foils along their stations and ordinates.

Next, I used the centerboard's NACA section drawing provided by Keith as reference to shape the centerboard down its length below +700, at sections +500, +350 +250, +150 and +50 as the foil diminishes in size.

Example of centerboard section drawing detail at +700

Copyright Keith Callaghan

More shaving and sanding was involved. A great method to shape the foils was shared by MROA member Barnsie in response to my November update.

Barnsie says: "Shaping the foils, one option which I used when making a number of them in the 1990's, was to trace the chord and thickness stations on each side and progressively gauge a router into the the blank. This gave me the stations when planing the shape, with course sanding to get the final shape." 

Thank you for sharing Barnsie, I like your approach and plan to use it when making my next set of foils. It will save time and guess work. 

Leading edge view of the centerboard from the bottom after the initial section reductions below +700 to achieve final shape.

Centerboard view from the top after the initial section reductions below +700 to achieve final shape. Notice the reduction at the +1188 waterline. Above +1188, the centerboard foil is faired rectangular.

Next, I used the rudder's NACA section drawing provided by Keith as reference to shape the rudder below +500, at sections +300 +200, +100 and +50 as the foil sections diminish in size.

Example of rudder section drawing detail at +500

Copyright Keith Callaghan

Leading edge view of the rudder from the bottom after the initial section reductions below +500 to achieve final shape.

Reinforcing The Foils

Keith Callaghan recommends reinforcing the foils with fiberglass and carbon fiber, especially where the centerboard exits the hull and where the rudder exits the tiller stock. Here are Keith's instructions:

"Firstly, laminate some 9oz/sq.ft. (300gsm) unidirectional carbon cloth (for the centerboard: from the waterline to about one third the way down the exposed length of the centerboard, and for the rudder: from the top of the blade down to about one third below the waterline). Then lay up 2 x 6oz/sq.ft (200gsm) bidirectional twill e-glass over that."

Here is a photograph of the carbon fiber pieces I cut to lay over the sections below the water line to about one third the way down the exposed length of the foil. I don't have a tiller stock yet so I have extra length on the top of the rudder to allow for it. Once I get a tiller stock, I'll add the additional carbon fiber reinforcement to the top of the rudder.

I used West System epoxy resin to wet the centerboard and the carbon fiber cloth prior to lamination. The carbon fiber cloth is too thick and tight to allow the free flow of epoxy resin through it, even when applying pressure with a plastic spreader. Then, with an epoxy roller, I removed the air bubbles in between. Once this carbon fiber lamination was done, I proceeded with the fiberglass laminations and 3 layers of epoxy resin.

Painting The Outside Of The Hull... Green!

I selected Interlux Perfection's Jade Mist Green for my boat. It is a two-part polyurethane paint to give her a high gloss topside finish. The color I chose shouldn't be a surprise as Rob Holroyd's MR3708 WICKED has been and continues to be an inspiration to me. I just love the way WICKED looks and I want my boat to resemble her somewhat but without loosing its own identity.

There are many methods of painting, depending on product and manufacturers. I followed the roller and badger brush method recommended for Interlux Perfection. Preparations and application instructions can be found in the link provided.

Interlux recommends: "Product temperature should be minimum 10°C/50°F and maximum 35°C/95°F. Ambient temperature should be minimum 10°C/50°F and maximum 40°C/104°F". We had a couple of very cold days in Austin so I had to wait for the temperature to rise a bit. Fortunately my garage is insulated and it keeps the temperature above 10°C/50°F for the most part of the winter unless an Arctic blast reached us.

An important recommendation by Interlux: "For the best finish, the first coat should be applied thickly enough for even coverage and flow, but do not attempt to achieve full opacity." 

It really pays off to read the instructions. Especially more than once if it has been a while. I spend time reviewing the instructions prior to starting the work. There are several important steps that go in the preparation and application. Knowing not to attempt full opacity on the first coat is good to know as the white primer shines through this Jade Mist color after the first and second coats indicating the need for additional coats. Apply too much paint and it will run. Apply too little and there won't be any after sanding for the next coat.

Port side view of the bow from the mid section after the first coat.

Port side view of the rear from the mid section after the first coat.

Transom area view after the first coat.

Starboard side view of the bow from the mid section after the first coat.

Bottom view of the hull from the rear after the first coat.

Port side view of the bow from the mid section after the second coat.

Port side view of the rear from the mid section after the second coat.

Starboard side view of the rear from the mid section after the third coat.

Starboard side view of the bow from the mid section after the third coat.

Epoxy Coating The Foils

In between coats of paint there was a lot of downtime so I decided to coat the foils with epoxy resin while the paint dried. I applied the West System epoxy resin to both sides of the foils while on a workbench but then hanged them from a ladder that is hanging from a roof beam.

View of the centerboard drying after coating with epoxy resin.

View of the rudder drying after coating with epoxy resin. I really need to get a tiller stock soon so I can finish the foil, reinforce with carbon fiber above the waterline and prime it.

Happy New Year!

November, 2013

Outer Gunwhale Lamination

The outer gunwhale lamination is triangular: 15 mm wide at the base, 1 mm at the top and 25 mm high. It is made of Western Red Cedar. Detailed dimensions at each station can be found in the GUNWHALE / RUBBING STRAKE CONSTRUCTION drawing provided by designer Keith Callaghan.

To fit the outer lamination over the middle lamination, I used small wood screws to hold them together while bonding.

Once dry, I removed the screws. The angle and curvature of plank #8 makes it almost impossible to clamp the outer lamination securely over the middle lamination.

First, I held the outer lamination flush (at the bottom) against the middle lamination. Then I used a small drill bit to drill a screw pilot hole every 18 inches  and avoid splitting the stock. For bonding, I applied West System epoxy resin with Colloidal Silica to both surfaces.  Then I hand-tightened the screws. One at a time.

Port side view towards the transom.

The rubbing strake is set at a constant 30 degrees to the vertical. This mean the outer lamination is set at a constant 60 degrees to the horizontal. To help me achieve the proper angle while shaving the stock with the block plane, I cut a simple plywood jig on the band saw.

The angle at this point is (provided the lamination is cut per specification) from the bottom outer edge of the lamination to 1 mm off the opposite edge on the top. I shaved the outer lamination using the jig to gauge the proper angle and to verify it is flat so that the rubbing strake will have a flat surface to adhere to.

I made a lot of wood shavings in the process. This can be improved by cutting the outer triangular lamination on a precision table saw, thus eliminating the need to shave the angle.

Final Priming Of The Hull

Once I finished fitting the outer lamination, I proceeded to sand and fill the bottom of the gunwhales, and finished priming the outside of the hull with two coats of Interlux two-part PrimeKote. I had to do a little bit of fairing too so I used Interlux Watertite two-part fairing compound over the Interlux PrimeKote, and later applied two coats of primer over the fairing compound, as instructed by Interlux.

Port side view of the hull after priming.

From the shrouds towards the bow, the gunwhale gradually reduces in width and depth. Detailed dimensions at each station can be found in the GUNWHALE / RUBBING STRAKE CONSTRUCTION drawing provided by designer Keith Callaghan.

View from the bow towards the transom

The Bow

Mid-Section

The Transom

Shaping The Centerboard Foil

In August, I bonded Western Red Cedar strips for the centerboard and the rudder, and I also cut both profiles using the drawings provided by Keith Callaghan. While the primer on the hull cures, I've decided to tackle the shaping of the centerboard and the rudder.

It had been a while since I last studied the NACA foils table and drawings that Keith sent me, so I spent time revisiting and researching all of this information. Looking at the stations and ordinates table can be intimidating at first. What does it all mean?

I won't attempt to explain all of this (there is plenty of material in books and on the Internet) but I'd like to share a reference I found on "How To Loft Airfoil Sections" on page 6 in a PDF document called: How to Build Rudder Blades and Centerboards by the Gougeon Brothers. I hope the reference proves useful to you as it did to me.

The centerboard reaches maximum thickness at 40% of the chord's leading edge. I made a pencil mark along that line on both sides of the centerboard.

Next, I plotted the stations and ordinates on a piece of cardboard and cut a simple jig to gauge the rough shape of the centerboard while shaving it.

I mounted the centerboard on my very old WorkMate work bench and sanded the edges to achieve a smooth profile.

The block plane proved very useful for shaping the leading edge of the centerboard. For shaping the rest of the foil, however, i thought my hand power planer would do a more precise, consistent and faster job. I believe it did and I'm glad I used it. Plus I no longer have to justify owning one. Check!

Using the foil jig as reference, I continued to shave away with the hand power planer as needed until the X,Y shape was achieved.

Here is the centerboard shape I've achieved so far. These initial steps have shaped the centerboard only in two dimensions.

Next steps include shaping the centerboard to its 3rd dimension. More to come next month when I do this.

Shaping The Rudder Foil

To shape the rudder foil, I followed the same steps as with the centerboard. The rudder reaches maximum thickness at 30% of the chord's leading edge. I made a pencil mark along that line on both sides of the rudder.

Next, I plotted the stations and ordinates on a thin piece of Western Red Cedar and cut a simple jig to gauge the rough shape of the rudder while shaving it.

I mounted the rudder on my WorkMate work bench and sanded the edges to achieve a smooth profile.

Again, the block plane proved very useful for shaping the leading edge of the rudder foil and the hand power plan for shaping the rest.

Using the foil jig as reference, I continued to shave away with the hand power planer as needed until the X,Y shape was achieved.

 

Here is the centerboard shape I've achieved so far. These initial steps have shaped the centerboard only in two dimensions.

Next steps include shaping the centerboard to its 3rd dimension. More to come next month when I do this.













Happy Holidays!

October, 2013

The Bow Tank Top Reinforcements

The Merlin Rocket Owners Association website has a great reference library and photographs on boat repair, renovation and self build. I do a bit of research in the site, looking for tips and advise.

In one of those libraries I found an interesting photograph. I wondered, what would happen if I had to go under the deck to do upgrades, maintenance or repairs? The bow tank top would fail and collapse under my weight. It is made of 4 mm thick marine plywood supported by the bulkhead, the bow tank beam and top of plank land #4.

I decided to add Red Western Cedar strips next to the top of plank land #4 and a center beam from the bulkhead to the stem. Additionally, I added two vertical supports from the hog to the  beam.

The Shroud Knee

There are 2 shroud knees made of 12 mm marine plywood, half-lapped on to the bow tank bulkheads. I secured the starboard shroud knee to the bow tank bulkhead with a clamp and used an angle finder to determine the bevel angle between the shroud knee and the planks. Notice I position the angle finder perpendicular to the shroud knee and not in parallel with the plank.

I then positioned my angle finder against the band saw miter fence and read the angle on the scale. This step can avoided by using an angle finder with a built in scale.

Then, I set the band saw table at the same angle and proceeded to cut along the edge of the shroud knee. Before cutting, I made sure to mark the area to be removed. Given that my band saw table only inclines to one side, I started the cut on the port side shroud knee from the opposite side.

Before bonding the shroud knee I set it in place and clamped it on both ends. Then, I inspected the fit for gaps.

Looking at the shroud knee fit from the other side... not bad.

Another view of the starboard shroud knee.

A photograph of the shroud knees from the transom. I laid the bow tank tops to ensure the fit was right.

Filleting, Sanding & Epoxying

All these fittings inevitably come with their fair share of bonding and filleting, followed by painstaking sanding, sanding and more sanding. Afterwards, I coated the inside of the hull with epoxy. A couple of times over the fiberglass reinforcements until smooth.

A view from the bow.

Another view from the bow, this one up a bit higher.

Middle Gunwhale Lamination

The middle gunwhale lamination is 15mm wide x 25mm tall, and made of Western Red Cedar. It tapers out between station #1 & #2. Detailed dimensions at each station can be found in the GUNWHALE / RUBBING STRAKE CONSTRUCTION drawing provided by designer Keith Callaghan.

To fit the middle lamination over the inner lamination, I had to use small wood screws to hold them together while bonding. Once dry, I removed the screws. The angle and curvature of plank #8 makes it almost impossible to clamp the middle lamination securely over the inner lamination. 

First, I held the middle lamination flush (at the bottom) against the inner lamination. Then I used a small drill bit to drill a screw pilot hole every 18 inches  and avoid splitting the stock. For bonding, I applied West System epoxy resin with Colloidal Silica to both surfaces.  Then I hand-tightened the screw. One at a time.                                                                                                                                                                                                                                       

Starboard view of the middle lamination.

Port side view towards the bow.

Port side view towards the transom.