Build a Simple RC Boat Hull A scratch built RC boat hull that is easy and inexpensive. Learn to scratch build with this simple project. Plans are now available for download. This RC boat hull building instruction goes hand-in-hand with the plans available for download (use link below). The hull, and entire boat, is designed to be a relatively easy project. Before you email me asking if I think this is a suitable project for you, I'd like to offer the following advice: Read through the building instructions and any pages that it may link to and make your own guess first. I'm willing to bet your guess will be better than mine anyways:)
Introduction Read a short introduction to this new series of small RC model boats to learn more, what materials you'll need etc.
Tools Here are some of the tools I ended up using for building this RC boat hull.
Scissors
Razor blades or X-acto knife (or both)
Steel straight-edge
Small square
Pencil
Glue
Thin CA (cyano acrylate) glue
3M Spray Mount Repositionable Adhesive #6065 or similar
Cutting out the Templates
Start by printing out all the plan sheets that you downloaded. I would recommend printing out a second set for reference and/or if a mishap happens. Next it's time to cut out the templates, starting with the bulkheads, transom, keel, deck and chine shelf (Item "A"). A word of caution, don't cut too close to the outline at this point. You can safely stay 1/16 (1.5mm) outside the perimeter of each part. In addition, parts that get thinner in the middle or are generally "spindly", (bulkheads #2, 3 and 4, keel, deck and chine shelf) are best not to cut out the internal area for the template to maintain its integrity.
Printed sheet of RC model boat templates.
Lay Out the Templates on Balsa Next lay them out on your 1/8" (3mm) balsa sheets. Try not to just throw them on if you want to conserve material, but don't place them too close together either. Leave 1/8" to 1/4" (3-6mm) between the outline of the parts. Once your happy with the layout you can pencil in the outline of the templates onto the balsa, or take a picture, so you remember where each piece go. Use the Spray Mount adhesive to glue the templates in place. Follow the instructions on the can.
Cutting and Trimming
Some of the templates laid out on balsa. Note how the paper "hollow" inside the templates is left to maintain the integrity of the shapes.
At this point all templates should be glued to the balsa with the Spray Mount Adhesive, essentially turning the templates into over-size sticky notes. Now it's time to start cutting out the parts. Separate each part from the sheet first by using a razor blade or X-acto knife and a metal straight-edge. At this point don't worry about the templates, except not to cut into them. This step is just to separate the pieces so they can be trimmed later. You don't need the straight-edge, but it is infinitely easier to make a cut if you do, and the risk of slipping and cutting into a template is greatly reduced. If you have a scroll saw or band saw it can be put to good use at this step. As the pieces are separated from each other, there will be excess material surrounding the templates. Now it's time to trim that down. I tend to do it in successive steps and using the straight-edge as much as possible. The resulting angles will be taken off at the final trim. I also tend to start with the outside shape and do any internal areas last, otherwise the pieces can break and split easily.
Making Multiple Pieces From a Single Template Also note that the deck and chine shelf templates only account for one half of the hull, so you need to make two of items "A" and "B". The same goes for the knee (item "E"). The best way to make two identical parts is to sandwich two sheets of wood under the template and cut through the stack. Two issues emerge: How to hold the sandwich firmly together while cutting?
The best way I've found is to first attach the template to one of the sheets of balsa and trim the balsa roughly to the template with a razor blade or X-acto knife. Next, leaving the other half oversize, glue it to the first half using two tiny dots of CA glue. The amount of glue is relatively important - too much glue and you won't be able to get them apart etc. How to make a perpendicular cut through both sheets? Making a perpendicular cut free hand on balsa is difficult. If you're just a little off perpendicular the two halves will be different size and the whole point of sandwiching the material is lost. The way I do it is to trim the sandwiched parts until all you've got left is an even 1/16" (1.5mm) of balsa surrounding the outline of the template. To get to finished size I trim off the last bit with 80 grit sandpaper on a hard sanding block. I often lay the balsa over the edge of my work table and that way have an easier time keeping the angle straight.
Final Trim With the exception of multiple parts from one template (as outlined above) parts with straight edges are best cut to finished size with the knife and straight-edge. For rounded edges there will be excess material coming off as angles. This is best dealt with using a wooden sanding block and 80 grit sand paper. Start at the angled peaks and work your way around the perimeter. When sanding, your strokes need to go in one direction only. from the template side towards the back so you don't lift the template off the wood. You can put some angle to it, but you get the general idea.
Here are all the parts for the RC boat hull with templates still attached.
The last thing to do is to trim mortises and the internal areas as mentioned earlier. Once all done you should have a set of parts like in the picture above.
Transfer Lines From Templates to Parts At this point its tempting to peel off the templates, but hold your horses we're not quite ready for that yet. Instead we need to transfer relative position from the templates to some of the parts to aid the assembly for accurate position and alignment. The best tools for the job is a small square and a sharp, relatively soft, lead pencil.
A small square is used to transfer alignment and position marks to the balsa.
The parts that get the treatment are chine shelf, keel, deck, and transom. Having the center line marked on the outside of the transom will help in aligning the keel and rudder. The other components need marks to give the relative position for the bulkheads. Only one line is required per bulkhead, but I typically mark the position for both edges so I don't have to remember if the bulkhead goes in front of or behind the line. With two lines, I know the bulkhead goes between.
Separating the doubled parts.
Once the necessary marks are made, you can safely peel off the templates with one exception: Leave the template on the keel in place for now. The parts that were doubled can be separated as shown in the picture. Some wood will most likely separate from one side, but it's not enough to worry about.
Dry Fitting the RC Boat Hull Dry fitting is the first and most important step as the hull is being constructed. This is a good opportunity to trim and fix minor flaws that may have worked its way in at this point. Better to remake one erroneous part than an entire assembly, so take your time. Dry fitting also helps you familiarize yourself with the pieces that make up an assemble and help you figure out which order to attach the parts while retaining good alignment and integrity.
First dry-fit of both chine shelf halves, transom and two knees.
The most important tool to make a straight hull is a flat surface to build it on. It is good if you can drive pins into it, lay weights or use magnets to hold the chine shelf down flat on the building board or table top. Lay down the Hull Alignment Template on your building board and lay a sheet of wax paper or plastic food film (Seran Wrap or similar) over to prevent the model to stick to the template and your table. I've found the wax paper resist CA glue better, so that's what I use. Secure the sheets to the board with a method suitable for the type of building board you're using - it can be pins, tape, weights etc.
Detail of the front end of the chine shelves on the building board. Three points line up perfectly: the stem, bulkhead position and inner front edge.
When I built the prototype I didn't have the hull alignment template, so you'll see the template is missing in the pictures on this page. Assembly should be a lot easier and almost self explanatory with the template. Align the two halves of the chine shelf on the hull alignment template. Pin or weigh them down once they are in position. There three most important places to check for proper alignment are: 1. The pinnacle of the stem 2. The rear edge 3. The inner edge at the stern If all three of these line up with the template, secure them in place to the board and glue them together with a couple of drops of CA glue where they join at the front. There are a few other less important points that should line up, such as the inner front edge and the lines drawn for the #1 bulkhead.
Drawing lines to high light the bulkhead positions.
Take a straight-edge and pencil and draw lines connecting the bulkhead position marks you made from the templates to aid bulkhead placement later on. Earlier we marked both front and rear edge of the bulkheads onto the balsa. Now I usually only connect one set of those tick-marks, using the other set as a visual guide for bulkhead placement.
Detail of transom, chine shelf and knees glued together.
Place the transom (item "5") in-between the two chine shelf pieces and line it up with even on the left and right hand side. Use the two knees (items "E") to establish the correct angle for the transom. The knees should line up with the inner edges of the chine shelf (see pictures), but their placement is not critical.
Sometimes the parts will stay in place by themselves, other times they need pins. Try and eliminate any gaps. Either way, once the placement is right, attach the pieces with small drops of CA glue at the joints. Be careful not to bump the parts out of position.
Front assembly of stem piece and bulkhead #1 and 2 attached to hull.
Next dry fit the stem piece (item marked "D") and bulkhead #1 and lay them in position with stem piece centered on the hull center-line and the bulkhead in it's marked position. Check and make sure they are perpendicular to the building board and each other. The position of the stem piece is more important than the bulkhead, so pay extra attention to it. Once they're in position, glue them in place. Take bulkhead #2 and align it as well. Check and make sure it is centered by checking against the edge of the chine shelf - it should over/under-shoot equally on either side. Where the tail end of the stem piece meet the bulkhead is less important.
A bird's eye view of the rc boat hull so far.
Do the exact same for bulkhead #3 and 4.
Bulkhead #3 and 4 attached.
Cut the two deck stringers from a 1/8" x 3/8" (or 3 x 10mm) balsa stick and glue in place. You can leave it long at the transom end and trim it with an Xacto Razor Saw for example.
Deck stringers in place.
The rc boat hull assembly is now fairly rigid and likely to stay straight and true. In the next installment we'll focus on the deck, keel and lower part of the hull structure before moving on to some internal installations and planking.
Continue to the next step...
Simple RC Boat Hull Follow this RC boat hull building tutorial for an easy and inexpensive balsa model boat. This is part two where the hull frame is finished and getting ready for planking. In preparing the RC boat hull for the next step, you can now carefully remove the structure from the building board. Don't worry if the wax paper sticks to the hull or rips. Even if the wax paper looks clean and comes right off, I'd opt to replace it for the next step. A spilled drop of glue or other debris can mess you up, so better safe than sorry.
This is where we left off after the previous build log. If you missed it or would like to go back, click this image.
Also, we're done with the hull alignment template that was placed under the wax paper to guide component placement and alignment. However, if your building board is really dark, or just ugly, you can lay the template upside down under a fresh sheet of wax paper. It will provide a light, neutral background when you build that makes it easier to spot things that are out of the norm or things you drop or spill.
The Deck After you remove the hull frame from the building board, remove any wax paper remnants if any. Give the deck side of the structure a light sanding with 120 grit sandpaper backed with a flat sanding block. Go easy as the only purpose is to take down any obvious high spots. Put the hull frame aside while we focus on the two deck halves (item "B" on the plans). Align them at the pinnacle of the stem and check alignment at the rear edge where they join. At this point, place a piece of tape over the joint to
temporarily hold them together and flip the deck over with the tape facing down. Pin or weigh the deck down on the building board. Mark the bulkhead locations across the same way as you did on the chine shelf. The lines will be a visual aid when aligning the deck to the hull.
RC boat hull with deck facing down.
Place the hull frame on top and position the raised part of the transom inbetween the "legs" of the deck. When aligning the frame to the deck, the stem is the most important, both in being centered and alignment front to back. Keep in mind that it is the top of the deck that after sanding should line up with the profile angle of the stem piece, so looking at it all as assembled, the frame will sit back a couple of millimeters from the foremost point on the deck. As the stem is lined up, glance at the bulkhead locations as marked on the deck. Don't expect them all to line up perfectly, but it will give you a good idea of how close to ideal you are at this point. Also check and make sure the frame is making contact with the deck along the deck stringers, transom, bulkheads and the stem piece. If care has been taken so far in cutting out the parts and aligning, nothing should be too far out of alignment. When things look good place drops of thin CA along stem piece, bulkheads and deck stringers.
Prepping the Keel
Many builders would go ahead and attach the keel at this point without a second's thought. However, when it comes to installing a propeller shaft most of those builders would be scratching their heads trying to get a propeller shaft tunnel aligned correctly. It would require a jig, extra long drill and some luck to get it right. We're going to take much of the tool requirements out of it and stop relying on luck for success, here is how.
Keel cut to shape and two pieces of basswood or hard balsa for the propeller shaft tunnel.
To do this you need two pieces of basswood or hard balsa approximately 1/8 X 5/16 X 2 inches (3 X 8 X 50mm) that will act as doublers on either side of the keel. Do as follows: On the keel, we need to stay clear of the bulkhead #4 location, so make sure the keel is well marked in that area. Next, lay the keel (template down) on a flat surface and glue one doubler to the back side of the keel just ahead of the #4 bulkhead location and line it up parallell with the bottom of the keel. If you're off by a few millimeters from either that's fine. Try not to have the doubler extend passed the bottom of the keel, it's better if you err on the other side.
First doubler glued to the back of the keel.
Next flip the keel over and trim away the area between the two phantomlines. This can be done with a razor blade and a straight edge or with a razor saw. Try hard not to cut into the doubler. The prototype used a 4mm outer diameter stuffing tube, so that's the size marked on the drawing and template. Since the keel is made from 1/8" thick material the tunnel you cut will be too tight from side to side. This can be fixed later with a long 4mm drill or a needle file and some elbow grease.
Trim away the area of the keel where the propeller will pass through it, thus creating a tunnel for ditto.
Now peel away the template (make sure all bulkhead locations are transferred first!) and place it on a flat surface with the attached doubler facing down. Prop up either extreme of the keel with scraps of material until level and clamp or place weights on top. Glue the second doubler in place and weigh or clamp to the assembly. Same rules apply as far as location - stay clear of bulkhead #4 location etc.
Propeller shaft tunnel finished - note faint pencil marks for bulkhead #4 just to the left of the doublers.
Attaching the Keel Before attaching the keel, take small pieces (1/2 to 3/4" long) of balsa, the same thickness as the chine shelf, and attach to bulkhead #2, 3 and 4 right in the center. The purpose is to provide a temporary landing and support for the next step in fitting the lower triangular parts of the bulkheads. When I built the prototype it took me a while to figure this out, so they may be missing in some of the pictures below.
Dry-fitting the keel with a square.
Time to fit the keel. Just like when the deck was attached, keeping the keel perpendicular and centered is more important than locating front to back. The easiest and best way to locate the keel front to back is to sand the front-most part of the chine shelf flush to the angle of the stem piece. This way you'll have an edge that should correspond with the front-most edge on the keel. As you can see on the picture below, I didn't do it this way, but it would have made things a little easier. Instead I eye-balled it in by looking at the profile and having the curved part of the keel tangent the angle of the stem. Either method works, but I highly recommend the former.
Transom and keel transition - note how the keel is lined up to the center line of the transom and flush at the rear.
Also look at where the keel meets the transom. By design, the keel should end at the stern face of the transom and be perfectly centered. Once all lines up, attach the keel with a few drops of CA while held perpendicular and in position. The lower triangles that make up the rest of the bulkheads don't have templates, but are taken off the triangular shape created between the keel and chine shelf at each bulkhead location, or station as it is properly called. First grab a piece of balsa a little wider than the height of the keel. At least one of the long edges need to be straight. Use a square and make a cut at a right angle to the straight edge.
Cut a square angle at the end of a piece of balsa sheet.
Hold the square corner against the chine shelf and keel at station #3 with one hand. With the other hand, with a sharp pencil, mark the edge where the keel and chine shelf intersect (see picture below). All you need are two tick-marks.
A square corner of a balsa sheet is held against the hull at each station and the edge of chine shelf and keel is marked on the balsa.
Lay the sheet down on your cutting surface and lay a straight-edge between the two tick marks and cut with a razor blade or X-acto knife. You can save a little time by using the first triangle at each station as a template for the opposite side.
Lower bulkhead "triangles" in place at station #3.
I glue each pair in as I complete them. It breaks up the laborious task of trimming and cutting a little. Then use the same process for the other bulkheads. I like to work from the center and towards each end so it adds some well needed stability to the keel.
All the lower bulkheads are cut out and glued into place.
Now the hull frame is ready for sanding to smooth out the shape some and to give the skin more edge to hold onto. After that we'll start the planking process.
The RC boat hull flipped over ready for sanding and planking.
Next, planking the hull...
Planking the RC Boat Hull The RC boat hull is now almost ready for planking. The only thing standing in the way is some final sanding of the frame to take out any bumps and inconsistencies, and to provide more surface contact between the balsa planking and the hull structure. Everybody hates sanding, I'm no exception. It is nonetheless an important step in completing a quality model hull. If done right it trues up a wobbly hull and add significant strength by better accommodating the hull planking. The process isn't complicated, but may need a thorough break-down for the novice. This page is meant to clarify the sanding and planking process for the simple RC boat hull.
The hull needs sanding and final shaping before the planking can start.
Prepping the hull
The first thing I do is to mark the edge of the deck and keel with a magic marker. It helps give me a visual indication of where I've sanded and helps give an early warning if I'm starting to take off too much material in one spot. You may or may not want to mark the edge of the chine shelf as well. I did not on the prototype for some reason.
Tools The only tools you need is some 80 to 100 grit sandpaper and a couple of sanding blocks. In the picture above you'll see a razor plane. I only used that to shape the lower part of the transom. I could just as well have used the sand paper. You also need a good sanding block. The one on the picture is technically too wide, which made the sanding more difficult than it had to be. I'd recommend a hard block about 3/4" wide. A narrow block that is swept along the hull with one of the long sides leading as its moved along the length of the hull will easier follow the changing contour. Another option here is to make a sanding stick - essentially the same thing, except the sandpaper is glued to the block/stick.
Sanding and Planking Procedure When sanding there are two main things to pay attention to: 1. The shape and fairness of the deck, keel and chine shelf 2. The transition between bulkheads and deck and chine shelf (or stringers, if any) Using the magic marker, as described before, is my best effort to take care of #1 above. The illustration below shows the steps of sanding and planking in regards to #2 above. The red dots show where attention is needed for each step. A red line shows where a straight sanding block or stick has been used. Don't take it as gospel, as some steps can be switched around without making much of a difference on the end result.
1 & 2: Sand Upper Panel First the sharp edges at the underside of the deck and upper edge of the chine shelf needs to be sanded flush with the bulkheads. Continue sanding front to back so the sanded edges on the deck and chine shelf are true in that direction. At the stem, sand the keel to an edge. You can leave an ever so narrow flat at the extreme.
It may be hard to see in this picture, but the upper side panel (between the deck and chine shelf) has been sanded, corresponding to #1 & 2 in the illustration above.
3: Plank the Upper Panel Next step is to plank the upper panel. I tend to start at the stem and work my way to the stern. Generally the tighter bends and compound curves are more pronounced at the stem and I like to get them out of the way in the beginning.
Planking under way.
Notice how I lay the first joint between balsa sheets in the middle of bulkhead #2. It will help hide the joint as there is less tension in the sheet from the steep bend. Also make sure you alternate sides when you plank: lay a sheet on the right, then the corresponding sheet on the left etc. It helps taking asymmetrical tension out of the hull as you progress.
Upper panel ready.
I determine the shape of each sheet by holding a roughly cut piece of balsa to the hull with one hand and transferring the contour to the sheet with a pencil. Then I trim the sheet with a razor blade to the line. Most often it requires a couple iterations before I'm satisfied with the fit. Before I glue it in place with CA glue, I try it on the opposite side. If it fits well I make a copy of it for the other hand to save a little bit of time.
4: Sand Lower Panel Sanding the lower panel is not that different from sanding the upper panel. It's easy to tear out parts of the balsa planking on the upper panel if you're not careful. You can lessen the risk of this happening by:
avoiding the lightest quality balsa
avoiding course sandpaper. Instead use a medium course sand paper: 80 to 120 grit
When sanding, go in the direction along the length of the hull
Just as in step one, the keel needs to be sanded to an edge as well to give the planking some flat area to land on. Go easy and try and take material equally off both sides. A narrow flat in the middle is OK.
5: Planking the Lower Panel Before planking the lower panel is a good opportunity to install the motor mount and propeller shaft. It is a lot more complicated doing after the hull is closed up. The propeller shaft I made for this boat is identical to the one I made for this plastic kit conversion, only a little longer - measure on the plan for actual length. You can also use a commercial 2mm diameter prop shaft.
Entire hull planked.
The planking is straight forward, just follow the same method as with the upper panels.
6: Sanding the Chine Transition
Last step is to sand the transition between the upper and lower panels. Generally the angle should be kept sharp at the rear 2/3 to 3/4 of the hull. Towards the stem the transition is more ambiguous and disappear completely at the first bulkhead.
Final sanding.
Later we will finish the hull by adding a keel strip, rub and spray rail.
Adding details to the hull...
RC Boat Hull - Adding Details The RC Boat Hull will have the deck finished, a keel strip, hatch coaming, skeg, rub and spray rails installed. The devil's in the details rings true even for RC boat hulls. Here we'll add some of those so we can move onto the rudder installation.
Stern Deck Filler Attach a stern deck filler, for lack of a better term. Its purpose is essentially to push the superstructure slightly forward from the transom. It's not totally necessary, but I felt it'll look better. It's made from a piece of 1/8" x 3/8" (3 x 10mm) balsa strip trimmed to length.
Add a Coaming A coaming is a raised edge that keeps water out. They also help locate the hatch. I made mine from strip balsa 1/8" x 1/4" (3mm x 6mm), but the height is not critical. I glued it in about 1/8" (3mm) proud of the deck.
Propeller Shaft and Skeg The stuffing tube and propeller shaft I intended for this model is identical to the one used on the lindberg trawler. An M2 commercial unit may work just as well. I glued it into the tunnel made earlier through the keel. Pay attention to final location as you need to make room for the rudder just behind. Also check for alignment from side to side before committing.
For the skeg a 1/8" piece of scrap balsa were cut into a wedge and left long.
On the picture below you'll see the scalloped trailing edge of the skeg. It could be left straight, but I liked the slight arch.
For final shape the skeg was sanded both in profile and thinned toward the propeller.
Keel Strip Until now the planking along the keel has been left open, and it looks pretty ugly. There are several ways to address, but my favorite is to glue in a strip of basswood for additional reinforcement. The gap at this point is an uneven "V" where the actual angle varies along the length. First thing to do is to square it up by running a square needle file up and down the joint.
As I file the groove, I dry-fit with a 1/16" (1.5mm) square basswood stick. In the picture below you'll see it glued in place. In the same picture, note how the upper edge of the hull planking (closest to the table top) has a flat sanded to accommodate the rub rail which will be fitted next.
Rub Rail The rub rail consist of a 1/16 x 1/8 inch (1.5 x 3 mm) strip of basswood, although most any hardwood strip of similar size will work. It can even be
made from styrene or laminated layers of card stock - your choice. Be sure to sand a flat surface on the upper edge of the hull planking, perpendicular to the deck. This surface should be as wide (vertically) as the strip is tall - in my case 1/8" (3 mm).
I glued them on one at a time, starting with from the stern, the starboard strip (right hand side) was glued in place first, as shown in the picture above. Joining the strips at the stem can be tricky, but here is a tip. Intuitively, most builders would aim for making a joint between the starboard and port side strips, down the center line of the hull. This is not ideal for several reasons: First, it's hard to do. Second, the strip is the most likely to take a bump straight from the front and thus will see the most shock load right where the joint is. A better way is as illustrated.
After the first strip is attached it is trimmed and sanded to blend with the surface where the second strip is meant to go. This way you'll end up with a joint that is a lot stronger and is off-set from the center line and therefore less likely to take a direct hit when you bump into the dock of other obstacles.
The second strip is also glued from the stern and gradually attached with CA glue as I progress forward. I tried to make sure the strip is flush with the deck as I went along.
Once at the stem, just continue the laying the strip passed the opposite side a fair bit.
Above is the final joint before sanding a more rounded shape.
Spray Rail The last thing to do before we move onto the rudder is to add a spray rail. I wouldn't call it mandatory, but I believe it helps performance a little and it certainly makes the boat look a lot better. It's made from 1/16" (1.5 mm) square basswood strip. Again, a lot of materials could be used, even hard balsa. Attaching it is pretty straight forward. Starting from the transom and work your way forward along the chine knee. At some point the knee will be less defined and you need to establish the curve more or less by eye. When I got to this point I took aim for an imaginary point at the stem where I felt the strip made a curve that I liked and simply followed with the CA glue. I'm sure there is a more scientific approach, but this worked well enough for me. I should point out that my spray strips ended up slightly off comparing left to right, but I doubt anyone will ever notice. Below is a picture of how it ended up.
Another thing I'd like to point out is that I did the tissue-and-dope before adding the rub rail and spray strips. The CA glue has a hard time adhering to the dense and hard lacquer finish, so I contemplated gluing the strips first and then doing the tissue-dope. After some valuable feedback (thanks Mike!), I'm back to the order presented here. Adding tissue after the rails isn't just going to be a challenge getting the tissue to conform to the rails, it will also shrink and pull away creating blisters where the planking meets the rails - so, bad idea. I overcame the adherence issue by using baking soda as a combined kicker/filler and a lot of patience. I still ended up with a fair share of CA on my hands, but the result feels solid, so I think it was worth it.
Next, we make a motor mount...
RC Boat Motor Mount RC boat motor mount
An RC boat motor can be mounted in as many ways as there are model boat builders. I've seen everything from a glob of hot-melt glue to slick and colorful anodized aluminum brackets to hold that power plant.
Surplus Mabuchi RE-280 to the left and Aristo-Craft RE-280 with a simple motor mount to the right.
Personally, I've always been in favor of a simple solution that gets the job done. That's not to say I'd glue my motors into my boats. I do appreciate the option to be able to remove or replace the motor easily, if need be. Another thing to note is that I don't build high performance boats, so copy my rubber-band mount for your Mega Power output brushless motor at your own peril. My two favorite mounts are:
A homemade motor bed with the motor held in place with a rubber band.
A commercial but inexpensive motor bracket that can be bolted down from the top
I don't like face mounting my motors. Most RC boats have a direct-drive where the motor face is pointing down towards the bilge at a shallow angle. It makes it very difficult to access the screws and almost impossible to see what you're doing if you need to remove or reattach the motor.
A scratch built motor mount installed in the RC cabin cruiser prototype. Installing the motor before the bottom was planked made alignment a lot easier.
For the prototype RC Cabin Cruiser I built, I ended up making the motor mount from scratch. If I had to do it over again, I'd get the Aristo-Craft motor with the simple, but perfectly adequate motor mount included. I would have made a simple flat piece of 1/8" (3mm) plywood with a cut-out for the keel spanning between bulkhead 2 & 3 for the mount to sit on.
Motor Coupling Efficiency Between the motor and propeller shaft a compliant coupling should be used. There are several different commercial types, but my three favorites are (from low to high torque):
A piece of silicone rubber tubing
A rubber coupling with metal inserts in each end
Universal joint
One of the most overlooked aspects when installing a motor in a model boat is the alignment of the motor and propeller shaft. Too many builders believe that because a compliant coupling is used having an angle between the two shafts is OK. This is a misunderstanding.
Proper alignment between the motor and propeller shaft is paramount in model boat building. Note the scratch-built motor mount.
The purpose of the compliant coupling is to relieve the motor from strain and side loads due to misalignment. No motor installation is perfect, so the misalignment that does occur should be kept to a minimum. A model boat with a misaligned motor will suffer unnecessary power loss and shorted life of the motor and coupling. The more power the motor generates the more important the alignment becomes. That means: The bigger the boat, the more important alignment becomes In effect, most effected motor types are: high performance brushed motors, all brushless and gas motors
Secure Motor Mounting Just as important as the coupling is making sure the motor is mounted securely. If the motor can wiggle loose, the wires may get twisted and break or short out.
A homemade motor mount for the RC cabin cruiser.
The reason I like rubber bands for small motors is that they have high friction against the motor can and prevent the motor from twisting. They also are compliant and hold the motor with spring pressure. Compliance helps dampen shock loads and is very resilient to vibrations compared to a more positive type of mounting.
Return to Simple RC Model Boats
Simple RC Model Boats - Intro
Learn to build RC model boats the easy and inexpensive way. These projects are perfect for beginners and those looking for a cheap, easy, simple and fast build. These RC model boats are based on an easy-to-build 15-inch long hard chine hull mostly constructed from balsa. These boats would make great introductions to both scratch building and RC boating. You may wonder why I keep referring to this project in plural. The reason is, this hull will become the basis for several simple semi scale model boats.
This is what the hull described here will look like when finished. It measures about 15 inches long by six wide.
Being a planing hull the speed is high enough not to be boring, but not so fast it would easily get out of control. Due to it's size it is suitable for calm ponds, large fountains or pools. For safety reasons, don't run the boat in waters where prohibited or where people or pets are in the water. One word of caution; this project is not recommended for children or young adults without adult supervision. If you are not comfortable using the tools listed further down on this page, at the very least, ask someone for help. This, and any other project on this site, is undertaken at your own risk.
The Plans The plans for this boat was developed to be easy and inexpensive to build. If you are interested in purchasing and downloading the plans, follow the link above.
Material The material used is mostly balsa, fiber board, basswood etc. A crucial aspect for this project to be successful is that the weight is being kept down. I strongly recommend that you don't substitute the materials recommended here.
Below is a list of material needed for this RC boat hull and approximate quantities. Material usage can vary widely from builder to builder. The quantity listed is fairly generous and account for some do-overs. 1/8 x 4 inch wide x 36 inch long balsa - 2 sheets minimum + 1 extra for superstructure. For those with access to metric sizes, substitute with 3 x 100 x 1000mm. 1/16 x 4 inch x 36 inch long balsa - 2 sheets. 1.5 x 100 x 1000mm. 1/8 x 3/8 x 36 inch long balsa strip (just one needed) - 3 x 10 x 1000mm for our metric friends. 1/8 X 1/4 x 36 inch long balsa strip or 3 x 6 x 1000mm. One should be enough, but won't allow for mistakes. Get a spare if you need reassurance. 1/16 x 3/16 basswood strip - one 36 or two 24 inch long - 1.5 x 5 x 1000mm. One is technically enough, but see note on material quality. 1/16 x 1/16 basswood strip - one 36 or two 24 inch long - 1.5 x 1.5 x 1000mm. Again, see material quality note below. I also used miscellaneous materials I have laying around, such as bamboo skewers, empty cereal boxes, scraps of basswood and plywood. For rudder and propeller shaft you will need stainless steel wire and some brass rod. More about this later.
A note on material quality Generally, the balsa sheet should be relatively light-weight and soft, but most importantly, straight grain and even density. It doesn't need to be the "ultra light" stuff, but for this boat, avoid the heavy stuff. Also avoid warped or bowed sheets. After a few boat projects you'll be a balsa expert. For the balsa strips I'd go for a harder quality than the sheets (if available). These strips will be used as structural stringers and for deck coaming, so there are no bends or anything to consider. These strips could be substituted for basswood or spruce if available in a pinch. I've had mixed luck with basswood strips. I order most of my wood online and thin basswood strips often has the grain run out the side of the strip causing it to split when bending. For that reason I recommend getting several spares if your ordering online. If you can pick them out yourself, you may be able to avoid the duds and thus buy less.
Tools Tools are often a matter of personal choice as there is often more ways than one to skin a cat. I've tried to list the tools I've used for each step in the building process.
Glue, Filler and Finishing Glue - only thin CA glue has been used for this model boat Filler - CA glue and baking soda Sealing - Silkspan and Lacquer Finishing - Automotive primer and good old rattle cans
Hardware There isn't much available in the US for building small RC boats like this. For propeller I've come to use one plundered from a toy (I'll get into more detail later in the build log). For propeller shaft, stuffing tube, rudder etc. I opted to make them from scratch out of brass tubing and sheet. It's not hard to do if you've got some basic tools and the means and skill to solder with a basic solder iron. If not, there are commercial alternatives, but we'll get into that later as well.
Propulsion
A single, relatively common, brushed Crest, Aristo-Craft or Mabuchi RE 280 can be used. The motor is driving a single shaft and prop through a piece of silicone fuel line tubing as a coupling - doesn't get any simpler than that. There are at least two options as far as motor mount:
Build your own from balsa, styrene, popsicle sticks or other material at hand
Buy the Crest or Aristo-Craft motor that come with a simple sheet metal motor mount
I got a low cost, light weight 20A ESC from Hong Kong that I found on ebay. Make sure the ESC is with "brake OFF" and comes with reverse. The batteries are four AA NiMH in a cobbled up holder. There is no reason a more commercial RC battery pack couldn't be used. The propeller is "on loan" from a Tamiya Submarine Motor (#70153). This is a fairly common item and there are other brands and models. It's really not
ideal as the entire unit is junked except the prop. However, propellers this size (3/4 inch diameter - about 20mm) are hard to come by in the US. In Europe I've found 30mm plastic propellers with M2 threads and corresponding propeller shafts. It is likely they would work quite well in this design. I'm in the process of researching this further, so stay tuned.
RC Controls RC Controls are my trusted Tactic TTX-404 with a Hitec HS-55 sub micro servo for steering.
Related Pages Here is a list of links to related pages on this site:
General Info & Background Design Background - Learn more about the intent and goals for this RC model boat Intro to the Build (this page)
Plans RC Boat Plans - download the plans here
Build Logs RC Boat Hull - part one - starting hull construction RC Boat Hull - part two - adding deck, keel and lower bulkheads Planking - sanding and planking the hull Hull Details - adding hatch coaming, skeg, rub and spray rails etc.
