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| Introduction | I wanted to build a fast boat with more curves, style, speed and excitment. So I searched the internet for free speed boat plans and settled on "Sea Scout" from Svenson's site. I preferred to name the boat "Boss Drover". It's a 14 ½ foot runabout from Boat Builders Annual and similar in some aspects to Riviera style boats, but with less detail (see figure 1). I could not find any reference to other models built from this "Sea Scout" plan. The chine hull design meant ply laid over timber frames would be easy for an inexperienced builder like myself. Or if I was ambitous, attempt some planking. | |
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| I decided 1/9 scale would best suit my skill level and resources. Dimensions are 456 mm long by 168 mm wide. Powered by a brushless outrunner motor, ESC and Lithium polymer battery promised excellent performance. | Top of page | |
| Frames | I converted all imperial dimensions to metric and scaled them down 1/9. All frames were drawn to scale then frame extensions added to form a common baseline and reference point for alignment. The frame drawings were photocopied, cutout and stuck on 3 mm ply. Frames outsides were cut out using a bandsaw, insides using a copying saw. They were clamped against aluminium angles at 76 mm spacings along the centre line of a building board as described in the hull drawing. The bow stem was shaped from 7 mm ply and notched to fit the first 3 frames. Frame notches were also cut for sheer and chine stringers. Thin timber stringers were subsequently glued in place once alignment was correct (see figure 2). An error on frame number 2 on the original plan was discovered. This was corrected by gluing an extension to the top of frame 2 to correct the top deck height. My drawings were adjusted and are now correct. | Top of page |
 Figure 2: Sea Scout frames |
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| Propulsion | Good performance requires a boat with high power to weight ratio. A brushless motor (Turnigy AerodriveXp SP series 35-30 1400Kv 470W), ESC (Turnigy Plush 40A) and lithium polymer battery (Rhino 2350 mAh 3S 11.1V 20C) provide a powerful and efficient electric system. These components are over-rated for such a small boat and were chosen to run at low load and stay cool only by air convection. To keep weight down I did not want to use a heavy brass prop tube. Instead I supported the 4 mm stainless steel prop shaft and 35 mm plastic prop on a nylon bushing inside a brass strut. The prop was set quite deep in the water to prevent cavitation and lifting forces that were expected from such a flat bottom hull travelling over rough water. The shaft was angled as far forward as possible and sealed using a specially made gland containing three 0.1 mm teflon disks. The centre of each disk had a hole punched just undersize of 4 mm. Both sealing gland and strut were fitted to inner keel timbers glued between frames 3 & 4 and 5 & 6 respectively. The motor end of the shaft was mounted in the ball race of an old printer motor casing. The brushless motor was screwed to the opposite end and a universal coupling joined both shafts in the middle of the casing. The pre-aligned bolt holes in the old motor casing made alignment of the brushless motor, coupling and ball bearing much easier (see figure 3). | Top of page |
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| The whole assembly was attached to two aluminium angles and screwed down onto two 7 mm ply girders glued between frames 2 and 3. The bow stem between frames 2 and 3 had to be removed to accommodate the motor assembly. Strengthening gussets were fitted around the stem, girders and sealing gland inner keel. After the prop shaft was trimmed to length, flats were filed on both prop and motor shafts to land grub screws from the coupling to prevent slippage. | ||
| Rudder | An external rudder mounted off brackets on the transom was constructed from brass rod and an appropriately shaped piece of PVC plate. The rudder shape on the plan was not reproduced because of its small size and perceived inefficiency. A Futaba S-148 servo mounted inside the rear left hand side controlled the rudder via a rod linked to a tiller arm attached to the top of the rudder shaft. The tiller arm entered the hull through a slot cut in the transom. | Top of page |
| Radio Gear | A Japan Radio Co. 5 channel receiver was installed inside the rear right hand side to balance the weight of the servo. Fortunately both devices weighed 40 grams (see figure 4). It was important to install all the running gear and test its operation before covering the frames. Space limitations would hamper any modifications later on. Everything worked OK, so it was time to complete the hull. | Top of page |
 Figure 4: Rudder, Receiver, Servo, Propeller, Strut and Shaft. |
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| Planking | I could have applied ply to the frames, but some of the curved surfaces may have proved difficult to cover. So I found enough timber strips (600 x 4.5 x 2 mm) to plank the hull. I calculated I needed about 100. I started by removing all the running gear and clamping the frames on the building board. Starting from the sheer I began planking the sides until I reached the chine level. Planks were super glued to the bow stem first then wrapped around the frames and finally clamped against the transom. The bottom was next. Planking started on the keel line and spread across the bottom until each chine was reached. All planking was parrallel to the centre line of the boat. Plank ends were trimmed to suit the chine as needed. Excess material over hanging the transom was cut off leaving the rough hull ready for filling and sanding (see figure 5). Gap-filling super glue was painted across the interior surfaces to seal the timber and fill the thin gaps between the planks. The result was a very light, but strong structure. | Top of page |
 Figure 5: Planked hull outside and inside. |
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| Deck | The deck was planked in an identical fashion starting from the centre line and working towards the sides. The position of frames 2 and 3 and frames 4 and 5 were marked on the planks to guide cutting openings for the cockpit and engine hatch at a later stage. The original plan showed the engine hatch between frames 3 and 4, but I changed this to frames 4 and 5 to give better access to the rudder servo, receiver and battery compartment. Increased access would also make balancing the boat easier. After all planks were fitted gap-filling super glue was spread across the deck (but not the cockpit or hatch areas) to seal the timber and fill the thin gaps between the planks (see figure 6). | Top of page |
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| Cockpit and engine hatch openings were cut flush with the frames. The hatch cover was constructed from a frame of icy pole sticks and a block of balsa wood. The hatch was supported on horizontal timber straps glued to each frame. Then it was shaped to fit the deck contour less the thickness of one plank. Timber planks were glued on top of the hatch and trimmed for a neat fit. The entire boat was rough sanded then low spots filled with body filler. Further sanding and filling gave a smooth surface. Next all interior and exterior surfaces were sealed using gap-filling super glue. This gave a water resistant seal and a consistent surface for painting. Fittings kit 1240F from Dumas Products was purchased to help finish the boat. Holes were drilled to mount the flagstaff, lifting rings, navigation lights and exhaust pipe. Working lights consisted of a 5V bulb and clear lens for the top light and 2 sets of 2 red and green LED's for navigation. Power from a spare channel on the reciever was connected to a small bread board circuit containing a switch and four 350 ohm resistors controlling each LEDs voltage. A dashboard shaped like the top of frame #2 was cut from 2mm PVC sheet. It was attached by two screws at either side. A hole was drilled at an angle through both the dashboard and frame #2 to mount the steering wheel. | ||
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| Painting | The hull, hatch, rudder, prop shaft strut, steering wheel and dashboard were spray painted with Dulux quick drying undercoat (see figure 7). Two coats of red gloss enamel were sprayed over the hull and hatch. Next the water line was masked off and the bottom of the hull sprayed with black gloss enamel. The rudder, prop shaft strut and dashboard were also sprayed black. I only applied one coat, but two would have been better. At this stage, 3mm white automotive pin striping was wrapped around the waterline, starting and finishing at the bow. Nichrome ribbon was epoxied to the sheer to form the top rub rail. Short lengths of old stainless steel windscreen wiper inserts were epoxied to the rear chines to form the bottom rub rail. All chrome fittings were epoxied in place. Black U-shaped rubber channel was epoxied around the cockpit. Clear plastic CD case covers were used for the windscreen panes. To avoid cracking they were cut using a hot knife blade shaped from a piece of brass rod heated in an electric soldering iron. Aluminium foil adhesive was laid on glass, cut into thin strips and used to edge the hatch and windscreen panes. Another piece was cut into a "Y" shape (previously determined using a paper template) and stuck on the bow. The name "BOSS DROVER" was added to the transom using BECC white vinyl lettering. BECC chrome speed, volts, oil temp, water temp and fuel dials and gauges were added to the black dashboard. All fittings were masked and exposed surfaces and steering wheel sprayed with two coats of Plasti-Kote Super Clear Acrylic Gloss (1138) for extra durability and protection. All running gear, dashboard and steering wheel were installed ready for test runs (see figure 8). I fitted a paper Australian flag, but it was quickly smudged by water spray. I made a different flag design containing the BMBG logo and the boats name from cotton using an iron-on transfer. Total weight of Boss Drover was 1.342 kg. After optimising the centre of gravity by adjusting the battery position the model moved gracefully across the water. | |
  
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| Parts List | Turnigy AerodriveXp SK Series 35-30 1400Kv /
470W brushless outrunner (from HobbyKing). Turnigy Plush 40A Brushless speed controller. Turnigy BESC programming card. Rhino 2350mAh 3S 11.1V 20C Lipo battery. T-connectors 10 pairs (Deans connectors for battery/ESC connection). Polymax 3.5mm gold connectors (Plugs and sockets for Motor/ESC connections). 4mm Stainless Steel prop shaft with M4 thread. 2 blade 35 mm plastic propeller with M4 thread. Dumas 1240F fittings kit. BECC 6mm white vinyl lettering. BECC dials and gauges. JR Pulse Core 5 Ch Tx and NER-625X 5 Ch PCM Rx. Futaba S-148 servo. 5V bulb light and lens. 4 x Small LEDs (2 green & 2 red). 4 x 350 ohm resistors. Switch, breadboard and connectors for the light circuit. Note: Similar equipment from other suppliers would also work. |
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| Summary | My
second model boat "Boss Drover" has certainly exceeded my expectations
when it comes to appearance. The extra effort preparing super
smooth surfaces and spraying red and black gloss paint resulted in an
excellent finish. Chrome trim and fittings were a very cost effective
way of enhancing the boats appeal. Reviewing the
original plans
has taught me that a modest design well constructed can give an
outstanding result. The motor mounting system worked well and the
Teflon shaft seals maintained a low friction
water tight seal. This enabled me to keep the boat as light as possible
by not using a brass prop tube. I am still searching for suitable 1/9
figures to place in the cockpit. Commenced building November 2008. Launched May 2010. |
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