Fibreglass 1/10 scale drag boat

[rol243]

i would go more than 6mm offset for this hull / power combo. maybe something like 20 to 30 mm as you really need to counteract torque.

[Old School]

Alas, 6 mm is the maximum offset as the motor mount is already up against the starboard deck cutout.

[rol243]

Did you look at the hydro at drag boat city ?

[Old School]

Yes. I previously linked to an image from that hull as regards an offset drive showing the underside. The canopy on that hull has the more modern eggshell shape.

[f1rogers]

Drag boat city .com says the boat is electric, AND the record is 124 mph. That little hull never went 124 mph. The 0 to 78mph was with my RedBull boat, and 124 mph is WAY WAY WAY faster. This boat was destroyed, I could not keep it on the water, and when this small hull goes over at 60+ mph, it tends to break things. My hull was 21" and was running on 6 cells, and the boat would barely float, calm water conditions were a must. Video is on youtube "brushless dragboat 2"

[Old School]

The motor mount and stuffing tube are now installed. Due limited access, I epoxied the motor mount bracket screws in position with the mounts at the correct angle. As I would not be able to access these screws, I modified the forward mount ring, cutting off the top half so that the mount needs to be sprung slightly to fit the motor. This holds the motor at the forward end.

As the battery is a relatively tight fit in the nose (second image), I epoxied a battery strap longitudinally that will assist lifting the battery out. Pulling on the aft end of the strap will lift the battery up enabling easy removal. The battery will be restrained by a lateral strap.

[rol243]

now i can see why you couldn,t get the motor over to the starboard side more. you have some serious power in this hull.

[Old School]

now i can see why you couldn,t get the motor over to the starboard side more. you have some serious power in this hull.

We will see if it will torque-screw (if there is such a word). Obviously, not a real drag boat as power will need to be gently applied to stop the hull flipping. Offset is approximately 6 mm.

[rol243]

keep the prop small otherwise she will torque screw over, like a croc doing its death roll.

[Old School]

This shows the stern with the Speedmaster strut. While I had purchased a Speedmaster rudder, I was only able to use the mount bracket. The rudder as supplied was for a right hand mounting. I had thought to simply remove the rudder blade and flip it for a left hand mount. However, the manufacturer uses an obscure size SAE Allen key and all attempts to remove came to no avail and I was unable to remove the pivot pin. I adapted a TFL blade that I had to the Speedmaster mount.

The fuel tank is simply some electrical conduit that I used, filling with resin and shaping the ends. The prop shown is for illustration purposes only.

[f1rogers]

Just curious, rudder on the left?

[Old School]

Just curious, rudder on the left?

Many prefer a rudder control rod to be in tension on a right hand turn. On a normal right hand mount the rod is in compression. This coupled with a shaft offset that really left no space on the small transom to mount a right hand rudder left me really with no choice. The ability to turn quickly is of little importance on this hull.

[f1rogers]

Very cool build. I did most of the same myself, except I had to build my hull from scratch, only because I could not find one to purchase that looked scale. I hope you get to drive this boat, as I am curious to see your results. One thing I do notice is all that weight in the front of the boat. I did the same with mine to start, but could not get the boat up "on plane" because the prop is trying to lift the rear and it just plows the nose under water. Put the batteries behind the motor, and control the nose with the strut. No turn fin needed, at higher speed, it just pulls the boat to that side. You will be surprised how hard it is to make the boat go straight, with this kind of power. I will be the first one to tell you I know nothing about oval racing, but I was able to get my boat to go straight, at over 75 mph many times, crashing many times along the way. I was using "Eagle Tree" to monitor speed, time, rpm, temp, and amp draws.

[rol243]

For this type of hull usage its not a bad idea to have the rudder on the left as well as the servo as it will help with some offset balance weight for any excess motor / prop torque inducement., probably not alot but atleast some.

[Old School]

Very cool build. I did most of the same myself, except I had to build my hull from scratch, only because I could not find one to purchase that looked scale. I hope you get to drive this boat, as I am curious to see your results. One thing I do notice is all that weight in the front of the boat. I did the same with mine to start, but could not get the boat up "on plane" because the prop is trying to lift the rear and it just plows the nose under water. Put the batteries behind the motor, and control the nose with the strut......................

The CoG is the same position as where one would expect it to be for a hydroplane so I was not thinking that it would nose down. At this point everything is permanently positioned so there is no chance of rearranging the battery. Prop choice will also be critical as a lifter prop may accentuate the nose down attitude. I can always opt for a smaller capacity battery to reduce weight if need be.

[rol243]

you can always fill up the fuel tank if needing more tail weight. lol.

[Old School]

Some cosmetic progress. Awaiting shorter screws to install hardware. My son will eventually replace the exhaust pipes with more appropriate upswept pipes plus fit the ignition leads.

[rol243]

Looks very nice indeed. this also now looks to be a static model not set for drag racing. ?

[Old School]

I filled the dummy V-8 with epoxy and securely screwed it to the deck which is backed with bonded 2 mm carbon fibre sheet for strength. It is intended to be a functional model.

[Old School]

Finally back on track after a slight diversion into building a metre long sailing boat (a new interest for me). Strut and rudder assemblies fitted. Awaiting upswept drag pipes for the dummy motor plus an ESC (most likely a Turnigy 120 amp model) to complete.

[rol243]

Looks very nice. wonder if you might need to fit a direction fin for straight tracking.? test and see i suppose.

[Old School]

Actually there is a small dagger type fin on the starboard sponson for directional stability (hopefully). There may be an image on the previous page.

[rol243]

looks like you offset the strut too. good.

[f1rogers]

Has it been in the water yet?

[hughb]

No not yet. I’m in the process of moving interstate so it will still be some time before it’s maiden run. However as shown it’s pretty much ready to roll, so soon as I get a chance i’ll be taking it down to the dam.