Fibreglass 1/10 scale drag boat
Now I know nothing of drag boats other than they should travel quickly in a straight line direction at SAW speeds. A couple of years ago my son purchased this hull from a local builder. The hull is 57 cm in length and 22 cm in width with a carbon inlay. The hull follows the high standards set by the builder for his numerous other hulls and apart from a bow in the hatch moulding (what fibreglass hull does not have a bowed hatch) Jason has done an excellent job.
My son had planned that he would some day build a fast drag hull but has of late been way laid by other boating plans so I decided while awaiting parts to finish my Osprey build to have a look at this hull. The bowed hatch and mating surfaces on the hull cutout have been worked to give a better fit than previously.
I have an SSS 3674 2075kv motor removed from my Libero when I recently upgraded the boat to 6s, plus I have several Turnigy Nano-tech 3300 mah 3s 65-130C batteries for my two Arowana self righting hulls, so thought as I am almost half there for parts why not give the drag boat a crack.
My plans are to run the 2075kv motor on 6s. As the boat will be specificially a SAW hull the high revs should not be too much of an issue. If the revs are too high then I can always replace the motor with a lower kv value. The batteries would be located in the nose section in series to give 6s. The motor will be located roughly 50% mid-length and will be offset about 1/4" to the right to counter prop torque. The ESC will be located at the rear at the transom, with strut and rudder by Speedmaster.
I have done a rough CoG placement and the CoG is positioned about two inches (5 cm) aft of the sponson vertical trailing edge. I did a float test and the boat was level with no water over either the transom or the nose. The boat was weighted with the batteries and motor in my chosen location plus lead weights in the rear to simulate the weight of the ESC, strut and rudder assemblies.
I do have a few questions.
Firstly, I assume a turnfin is not necessary as the rudder should be able to manouevre the hull at the slow turning speeds the boat will be doing. I notice that some hulls have small fins mounted to the inside edge of the sponson. I assume that these give directional stability. Are fins fitted to both sponsons or just one side (starboard side), please?
Secondly, is 1/4" shaft offset sufficient for the hull to maintain straight line stability? I assume that the drag hull would behave in a similar fashion to a hydro or is a drag hull a much different beast?
Thirdly, as the rudder is really just to maintain straight line running, is a "full size" rudder blade required or are there specific rudders designed for drag hulls, please?
Fourthly, is it preferable to slightly fill the nose section and tips with shredded carbon fibre and resin as on a catamaran hull?
Finally, a 2075 kv motor running on 6s, would the amp draw possibly exceed a T120 amp ESC capacity or would a T180 amp model be preferred, please?
My personal preference is towards a mono hull, but this drag hull looks interesting. If I did not have a hull, motor and batteries available then I would not have pursued this build.
My son has found a source for a very nice (expensive) 1/10 th scale 3D printed V8 motor that one can use a servo to operate the butterflies. Not sure that I would go that far, but the V8 motor would be essential to create the look of the boat.
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Originally Posted by rol243
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