Nautical Marine Model Perkasa 150

[Campbell Sims 1Participant @campbellsims1]

I have just completed this model after 3 yrs and did its first sail the other day. I have fitted it with the suggested motors 600 Eco Graupner (2), 7.2v NiCads an 40A mtroniks ESC, 30mm props L and R. The hull tends to rise but seems to have difficulty in maintaining the planing position as shown in Sept 2009 by Dave Abbott. I admit that I may have placed the batteries to far forward and wondered if this has been a contributory factor. I am going to place them further aft and then see if the result is any different. In the meantime I am open to suggestions as to why this is happening. Thank you in advance.

[Campbell Sims 1Participant @campbellsims1]

Lack of speed/planing

[Ray Wood 3Participant @raywood3]

Hi Campbell,

Going back to a thread on this forum 2nd October 2009 seem to suggest this model is prone to being overweight as for 7.2v Nicads are 13ozs compared to 11.1v 2200mah Lipo at 7ozs will get some more revs and perhaps 35x props?

Regards Ray

[harry smith 1Participant @harrysmith1]

Hi Campbell

The specs of the motors are 6to9.6 volts, 11,000rpm, length 57mm, dia 37mm, shaft 3.17mm and weight 220 grams.

Replacement Hobbyking motors 3639-1100kv 800Watts, 2S lipo 11,100 rpm and on 3S 12,210 rpm( no load), length 48mm, dia 37mm, shaft 5mm and weight 140 grams.

I am running one of these motors in my 865mm Gentleman's runabout on a 3S lipo 3700mah (338 grams)with 37mm 3blade prop.

Weight saving on the motors adds up to about 140 grams and a lot more power.

My Perkasa is getting a 3648-1450kv 1600Watt single motor has it was set up for a single motor.

Harry Smith

[Empire ParkstoneParticipant @empireparkstone]

Cam I'll ditto that for Harry's Perkasa motor I have one fitted that replaced 3x 850's in a 1/24 Schnellboot

Ep

[Campbell Sims 1Participant @campbellsims1]

Many thanks for your replies and advice it is much appreciated. I will go forward with the advice with optimism.

[ashley needhamParticipant @ashleyneedham69188]

Hi Campbell. The two obvious things to do are 1) shift battery 2) use larger battery (9.6V) and 3) change props to 35mm (ok, that's three things!)

30mm is quite small, and a shift to 35mm should be within the motor capability. Two blade props are available in X (course) potch, and S (`normal`) pitch. As they are very cheap, worth buying a selection. Using a wattmeter is also good. Has been suggested many times before..they are very cheap and will show you if the motor is being overloaded.

Going to a 2s Lipo will increase performance without any other changes due to their capability of delivering more current whilst maintaining voltage and being half the weight. A fully charged one will be over 8V in any case, this alone giving more revs.

Ultimately you could fit a gazillion watt brushless motor. HOWEVER please look at the motor specs first. A 600 of your type might produce 60 watts or so (correct me if wildly out), but swapping these for an 800 watt brushless……..

Brushed motors are very gutless in comparison size for size with brushless, however not all brushless motors are equal, and similar size, turn and KV specs can produce a wide range of power. The weight saving alone may be worth it, but bear in mind two motors need two ESC. As you are looking for a relatively small increase on performance, then work out roughly how much power your 600 makes and then find a brushless of a slightly higher power, but nothing with too high a Kv rating 1100-1600 seems to be a happy medium.

Ashley

Edited By ashley needham on 22/10/2018 09:16:44

[Malcolm FraryParticipant @malcolmfrary95515]

Running a motor that is rated to work between 6 and 9.6 volts on 7.2 volts will not see it give its full power. A 7 or 8 cell NiMH pack will let it use the power that is is capable of provided that the prop is not too much for it (rule of thumb – prop smaller than the motor can diameter, not more blades than motor poles). A small amount of extra weight, a lot of extra power with the extra couple of cells. If you adjusted the throttle on your car to stop at 80% of its travel, it would lose performance. Running the motor on reduced voltage does much the same.

Distributing the weight correctly also helps, and the battery is a big consideration. A larger prop, unless the existing is far too small, will only try to overload the motor, whichever type is fitted. Within limits, for the same pitch, a faster spinning prop will give a faster boat, but at the cost of reduced accelleration. A coarse prop will give more speed for a given RPM, but only if there is enough power to get it there.

Getting the balance between weight (boat plus batteries etc), power (how fast it drains the battery) and prop choice (converting power to moving water efficiently) is crucial for any hull design.

I do recall from WAY back a magazine article decribing the efforts involved in getting a larger Perkasa to plane. It involved a 12 volt SLA for " normal" running plus a switched booster battery to up the volts to 18 for fast runs. Times have moved on.

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