Outrigger Build
By Paul Williams.
Article posted 19th March 2008.
This article gives an overview of scratch-building a foam/ply/balsa outrigger hydroplane. The following guide shows how to fit out a 'rigger tub with wiredrive, steering servo, radio system etc.
Marking Out
Marking out should be done lightly to allow easy removal of any lines afterward. Use a pencil, steel rulers and an engineers' square, and take the time to get your marking out accurate - any mistakes here will be very difficult to make good later on.
Mark datum lines on the tub floor and transom.
The first job is to mark a longitudinal centreline datum from just forward of the motor mount to the transom. If you elect to offset the drive in order to counteract propeller torque effects, then mark this offset drive line next. Mark the transom with a driveline datum using an engineers' square. Remove the original centreline datum after you have marked an offset datum, to avoid confusion later. Fine-grade sandpaper or dry wet-and-dry paper can be used to scrub out unwanted lines.
Triangular fillet piece to allow motor to sit lower. Lowering the motor through the tub floor gets the weight of the motor as low as possible and reduces the curve on the wiredrive.
Next to the cellpack, the motor is the heaviest component in the boat. To keep this weight as low as possible, and to reduce the size of, or eliminate the need for, a canopy in the hatch, I drop the motor through the floor of the tub using by a few millimetres, or enough the accommodate the cooling coil. This has the added benefit of reducing the curve on the wiredrive.
Opening the fillet piece. Score the two angled lines of the fillet triangle on the inside of the boat, to allow the fillet halves to hinge open easily.
Transom marked with offset datum. On this boat, I'm offsetting the drive by 10mm to the right to counteract prop effects.
Drive strut mounting - aluminium angle secured with M4 stainless bolts, washers and stainless nyloc nuts.
Motor Mount
My personal preference for motor mounts in any type of boat is to spread the weight of the motor over as much of the hull as possible. In an outrigger, this means I make a motor mount that spans the width of the tub and is glued to floor and sides, reinforced with triangular balsa fillets. You can buy some very fancy CNC-machined carbon motor mounts, or you can make a perfectly adequate mount from scraps of ply.
Motor mount bulkhead from 1/16th" plywood faced with 0.6mm plywood.
Fitting The Wiredrive
I'm using a 0.062" (62thou/1.6mm) wiredrive, which is run out of the hull through a short length of brass tube. The tube is approximately 2.4mm in diameter, so I cut a slot roughly 2.5mm wide. Positioning of the slot fore and aft is something you need to guess - you may get it spot on, or you may need to elongate the slot to suit like I did here.
Fitting the wiredrive should be done simultaneously with gluing the motor mount in place. If you fix the motor position and angle first, you may end up forcing the wire to run in a less than optimal curve, which will cause friction and possibly wire breakages. The slot for the wiredrive should be long enough to allow the wire to float free and assume its natural curve.
Mark the slot for the wiredrive.
Cut the wire to the desired length, and mount the drive to the boat, with the strut at the desired height and angle. Offer up the motor bolted to the motor mount. Feed the wire into the motor coupling and secure the coupling set screws. Position the motor on its mount in the boat to achieve a mild curve in the wire, check that the mount is square in the boat with an engineers' square, and tack into place with thin cyano.
Elongate the slot if necessary.
The wire runs through the bottom of the boat in a short length of thin brass tube. This needs to be shaped to match the curve of the wiredrive, to reduce friction to a minimum. Try the tube on the wire - when it slides freely up and down the curved wire, the brass tube is ready to be glued into the boat. Roughen it first to give a good key.
I like to file slots in the brass tube to allow easy lubrication of the wire without removing the wire from the tube. You can file slots in the tube before or after gluing it into the boat.
Tack the motor mount in place with thin cyano superglue.
Brass tube - shape this to match the curve of the wire when mounted in the boat.
Masking tape over the wiredrive slot, prior to gluing the wiredrive in place.
Mask off the slot in the bottom of the tub with masking tape. The wiredrive brass outer tube should be glued in place using two-part epoxy. I like to mix some microballoons into the epoxy mixture. Apply the epoxy inside the boat, sealing the slot in the hull and fixing the brass tube in place. Use disposable gloves when handling epoxy - too much exposure to epoxy glues and resins can cause dermatitis. To make the epoxy flow smoothly, I give it a quick blast from a hot air gun - but not too much. Overheating the epoxy can cause bubbles to form. Smooth the edges of the epoxy with a finger (gloves!).
The wiredrive brass outer tube should be glued in place using two-part epoxy. I mix some microballoons into the mixture.
Wire lubrication slots filed in the brass outer.
Servo Mount
The last thing you need in a fast boat is any slop or play in the steering. This means the steering servo needs to be securely mounted in the boat. Raid your scraps box for lengths of oak strip and offcuts of plywood to make a servo mount. Small servos can often be mounted upright in the boat, bigger servos such as the Hitec HS5625MG (a standard sized, high output metal geared digital servo) that I'm using here will almost certainly need mounting on the side, unless you are building a big outrigger. This servo has been waterproofed.
Servo mount from oak block and 1/16th" plywood.
Servo mount with servo.
Rudder
The strut and rudder mounting brackets used on this boat are made from short lengths of 1/8th" (3.2mm) aluminium angle, squared off on the milling machine. I'm using a simple flat plate-type rudder, driven by a side-mounted Hitec HS5625 metal-geared digital servo.
Rudder and mounting bracket, with linkage to be finished.
Servo mount glued in place in the radio compartment.
The rudder control linkage is made from ball-joints and threaded ends glued to a short length of 3mm carbon rod. The rudder linkage is sealed through the transom using a rubber bellows glued to a short length of brass tube. Establish where the linkage centreline is on the boat, then drill the hole for the bellows in the transom. Bear in mind that the linkage will move sideways as the rudder rotates, so you may want to position the bellows off-centre a little to prevent binding at full rudder deflection.
Rudder bracket and mount.
Drill an undersized hole for the rudder linkage and enlarge to size using a hand reamer.
Isolation Loop
Fitting an isolation loop, or not, depends on whether you race and if the rules decree you must have one. However, I would strongly recommend fitting an isolator, if for no other reason than the ability to make the boat totally safe when changing propellers. This article describes how I make my own isolators.
I chose to make the loop for this boat using 5.5mm gold connectors and 6mm2 cable, even though the motor and speed controller use 4mm connectors and 4mm2 cable. The intention with this boat is to use it for a variety of different setups, so I don't want to have to replace the loop in the future if I go to a high power setup.
Isolation loop made from 5.5mm gold connectors and 6mm2 cable, supported in oak blocks.
SWAMBC broadly runs the same rules as Naviga regarding isolation loops, meaning the loop must be on the red side of the circuit and be a minimum of 20mm in diameter. To mount the loop block in the tub, I marked out a rectangle of the same depth as the loop block, but over twice as long. I cut three sides all the way through, and scored the fourth to allow this flap to hinge inside the tub. The pictures probably explain it better than my words. The block was tacked in place with cyano, then fillet strips were added top and bottom to close the hole in the tub.
Loop set into side of tub.
UPDATE:
Well, I've finished it. I added a water pickup for the cooling system (a length of brass tube silver-soldered to a strip of brass), and had to knock out the bulkhead between the motor and battery compartments. This boat was designed originally to take 12 nimh cells in two stick packs lying flat, the lipo pack is quite a bit longer.
The finished boat.
I added a couple of layers of carbon-kevlar cloth to the bottom and sides of the motor and battery compartments to strengthen these areas. A turn fin was made from aluminium and mounted to the hardwood dowels in the right hand sponson with a couple of countersunk M4 stainless socket screws. Finally, an aerial tube mount was added, this being a short length of white plastic tube glued into the hull which accepts the thinner aerial tube. With everything in place, the hull was then stripped, masked off, primed and painted, then reassembled after the paint had hardened.
Water pickup mounted in the prop cone.
Internal layout. The front bulkhead had to be removed to accommodate a 4S lipo cell pack.
Aluminium turn fin.
I'll update this when I've had a chance to run the boat and possibly get some video.
© Copyright Paul Williams and www.fastelectrics.net, 2010.
This article may not be reproduced wholly or in part without the written permission of the author and www.fastelectrics.net. If you would like to use this article or the accompanying pictures/diagrams please email articles@fastelectrics.net.
Last modified: 08th July 2010 @ 09:06
