Build Log 'Harpy' a free plan and Foamy Footy

[graham_mca]

Introducing 'Harpy', another footy from the ScaleSailing boatyard.
'Harpy' is available as a set of free plans in .pdf format from http://www.scalesailing.com/support.htm and as such is built using the tape-and-glue method from 1/16" balsa sheet or 1/32" ply.

But even easier is to build 'Harpy' on a foam core as I will describe here. If you are already building a Harpy please join in and show us what you did or are doing. Harpy is meant from the outset to be an 'open source' design so feel free to give your own hints and tips.

To get started the photo below shows a Harpy with a tall sloop rig. The hull shape is deliberately simple to allow easy building from the plans but also follows the 'low rocker/high volume bow' design route.

Graham

[graham_mca]

photo 1, Construction starts with the foam core. The Harpy core has two cut out areas with a 1/2" 'bulkhead' between. The core as seen weighs typically 0.4oz (12g).

photo 2, First job is to join two 3" wide sheets of 1/16" balsa, pick light but firm wood. Lay the balsa sheet on the foam bottom scrap and weight the hull core down to curve the wood. Draw around the hull.

photo 3, Mark the fin hole position (from the instructions) and cut out.

photo 4, Glue and tape the hull bottom in place. Use Titebond 2 or 3 for best results applying the glue to the foam not the balsa. Get it straight! You can put the hull in the scrap bed and apply weights to press it firmly in place.

[graham_mca]

photo 5, Mark and cut the 1/32" balsa hull sides in the same way...

photo 6, Tape, glue and press one side then the other onto the foam core.

photo 7, The transom is made the same way using 1/32" balsa.

photo 8, the stem post is 1/4" balsa, shown here after shaping to match the hull.

photo 9, Before you know it you will have a light and very strong hull.

Graham

[mr badwrench]

looks wonderful Where do I get one?

[graham_mca]

Originally Posted by mr badwrench

looks wonderful Where do I get one?

Thanks mr badwrench! You will see the Harpy Core listed on the www.scalesailing.com web site, go direct to this page if you like http://www.scalesailing.com/product.htm
If you click on the Harpy Core photo you will get more information too. I highly recommend the Core+CD option, you are seeing a few of the CD photos here. The CD will play on your pc like a web site so no special software is needed. Also most DVD players which can handle .jpg files will play it too.

photo 10, The deck is cut from 1/32" ply, draw around the skinned core again leaving a little overlap as a rubbing strake. The openings are as shown on the downloadable plan.

photo 11, A length of 2mm dia. carbon rod is used to strengthen the bridge, epoxy in place.

photo 12, The servo tray epoxied in place. There is a drawing for this in the core instructions set.

At this stage I coated the inside balsa surface with 'Z-Poxy' thinned a little more with rubbing alcohol. Two coats to waterproof and stiffen the balsa.

[graham_mca]

photo 13, The deck goes on next, use Titebond 3 or 2 again and the scrap foam as a press to ensure a good bond.

photo 14, Here the mast tube has been fitted. I chose to use an extended tube on this Harpy and mount the gooseneck/vang assembly on the tube rather than the mast. Check it is square to the deck and the foam 'bulkhead' will position it further.

photo 15, The base of the tube sits in a ply mast foot. (Short tube in this photo.)

I'll deal with the fin next time...

[graham_mca]

photo 16, I like to laminate my fins from basswood. The Harpy fin used 6 strips of 1/4" x 1/8" bass with two strips of 1mm x 3mm carbon extruded strip inserted to add stiffness.

photo 17, end view showing basic fin shaping. The two carbon strips extend beyond the fin and will be epoxed into slots in my usual half bulb castings. They could just as easily be epoxied into 1/8" drilled holes in a sinker weight.

photo 18, inside you can see how the top of the fin is held by the servo plate.

photo 19, the fin epoxied in place.

[graham_mca]

photo 20, The bowsprit is from 3mm or 1/8" carbon tube. Slot a strip of 1/16" ply and epoxy the tube into the groove and onto the deck. With a good epoxy fillet this is strong enough.

photo 21, The plastic rudder shaft tube epoxied to the transom.

photo 22, The rudder is made from 1/32" balsa with a 2mm carbon rod shaft epoxied in the slot. Sand the thickness of the balsa down to match the rod and shape to a semetrical cross section.

photo 23, After painting the shaft is inserted in the tube and the ply rudder horn is epoxied onto the rudder shaft.

Graham

[graham_mca]

photo 24, The gooseneck and vang is bound to the mast tube on this Harpy. This frees the mast to be a simpler item and reduces the cost of extra rigs. Switching rigs is still a quick enough job when you need to.

photo 25, A wider view, despite it's simple lines I think this boat has quite attractive lines. Maybe it is the attraction of 'form follows function'.

[graham_mca]

The radio installation is pretty simple in the Harpy, the external rudder servo in particular simplifies matters. Choose a basic plain bearing, plastic geared servo for the rudder control. Ball bearing servos are more likely to be water damaged, they rust. When the rudder servo is finally installed I use silicone sealant around the body and in the screw holes.

photo 26, A very simple servo link, put a 'V' bend in it if you think you may need some adjustment. If you take care to get the rudder straight with the transmitter trim central then the transmitter trim should be enough to handle any trim requirements while sailing.

photo 27, I am using a Hitec HS-81 servo on the sails. There are more powerful small servos but I have a handful of these. Using dry batteries for a 6v input will help with the torque figures, only time will tell if it is enough.

photo 28, Using a cheap 2-channel Futaba receiver I throw away the case. That actually saves 7gram which can be useful, and it won't keep the water out anyway. Put the receiver in a small plastic bag with a twisty, not waterproof but it will protect the receiver from any odd spots of water.

photo 29, The receiver tucks away neat and tidy. The battery installation is seen here too, keep the wires out of the way of the sail control line.

[graham_mca]

This particular Harpy hits the test tank.... ok the bath. This boat is somewhere between the wide 'muscle footy' style and the light displacement narrow footys. My aim being to produce a boat in the narrow trend which can still be built at 16 to 18oz if weight creeps up as it often does.

I hope this is of some interest...

Graham

[mr badwrench]

im really interested in your sails.

[Bob Starr]

Originally Posted by graham_mca

This particular Harpy hits the test tank.... ok the bath. This boat is somewhere between the wide 'muscle footy' style and the light displacement narrow footys. My aim being to produce a boat in the narrow trend which can still be built at 16 to 18oz if weight creeps up as it often does.

I hope this is of some interest...

Graham

Graham,
I think your build threads shows your exemplary devotion to quality and craftsmanship. Which is reflected in your kits.
Bob

[lgliser]

graham on the external balsa sides ,, did you use the thined z poxy to waterproof ?? and what type of paint did you use to paint the hull sides ?? meany thanks

[graham_mca]

If you have any questions mr badwrench, ask away

Crikey Bob you'll embarass me, sincerest thanks though to you for your thoughtful encouragement. We are alike I know, we only know one way to do anything.

Hi lgliser... on this hull I used 3 coats of Bulls Eye Shellac to harden the balsa, two would have been better because I got quite a shine and had to rub it back. Over that I sprayed Krylon white primer then finished with Krylon 'indoor/outdoor' gloss. The Shellac does not attack the foam so you can use that on the inside two, I was experimenting so used the thinned Z-Poxy inside only. The deck is done with Minwax Helmsman brushing varnish.

Graham