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[Davenotdone]

Hi, i have a RTR cheapo Ebay Police boat. I have ripped out the original ' pod ' type motors ( tank steering ) and have installed a rudder, 4mm prop shaft, 7.2v nimh 5000miah stick battery, Mtroniks Tio 15 speed controller and a 2 channel radio set. The boat is 20 inches long and i have been told it has a planing type hull ( V shaped ). I originally installed a cheap unamed 380 ( up to 18v )  type motor in with a 3 blade brass 30mm prop. The result was not very fast. I was told when i took it to the Blackpool Model boat show that the motor was not right ( it can't spin fast enough ) and that the prop was wrong. For a planing type hull i was advised to buy a Graupner speed 400 ( 7.2version ) and a plastic Graupner 2 bladed 30mm prop. I bought the motor and prop and installed them. The boat runs a lot faster than before ( just right ) but the motor is a little hot ( you can just about leave your finger on it ) I am not after all out speed, just enough to look reasonable and i would rather go for reasonable speed and endurance ( about an hour ) than very fast and the battery runs out after 15mins. When i looked at the Graupner prop package it said part No 2314.30 which i belive is a hydro type prop. The questions are,  do i have the right prop or will a more suitable one make the engine run cooler and allso do i keep the set up as is but water cool the motor? Thank you very much, regards, Dave.

[boatmadman]

Hi,

The easiest and cheapest option would be to leave it as it is, and just control it on the throttle.

Going down a size on the prop will reduce speed, reduce power consumption and increase endurance whilst allowing the motor to run a little cooler.

I would try the prop change if you have a thumb like mine that always heads for flat out! Its the next cheapest and easiest option as well.

Ian

[nick_75au]

It doesn't sound too bad if you can hold your finger on for 3 seconds before that burning sensation occurs, then the motor is still within operating specs. (about 60 degC) If you put a slightly lower pitch prop it will bring the temps down without sacrificing much if any speed.


Nick

[malcolmfrary]

I have a Graupner Lotse, about the same length and a shallow V, hard chine hull that will plane.  It runs on a speed 400 with a Graupner 2 blade prop running on its stated voltage.  Reading the label on the packet, it says "No.451.0,   High performance racing prop.  2-bladed clockwise rotating.  25mm  for shafts M4". 
On a 3700mAH 7 cell pack I get an hours cruising (not quite planing), with plenty of bursts of top speed (front third out of the water and a bit of a rooster tail).  Good for the length of Fairhaven and back (thats a 1 mile walk) with a bit of showing off. 
The motor is mounted clamped between a pair of aluminium strips each bent into something looking like a pipe clamp.  This probably acts as a bit of heat sink/cooling fin, and the motor does get warm, but not uncomfortably so.

[Davenotdone]

Thank you all for your responses, i think i will go down the route of a smaller prop and reduce from 30mm to 25mm. Malcolm, are you using the 7.2v or 6v speed 400 in your Lotse?. Once again thanks everybody.

[malcolmfrary]

Without digging it out to look at the label, I'm not sure, but previously it had a 6 volt one.  It went very fast, but soon died.  Pretty sure I replaced it with a 8.4 volt version.