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!