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[drawknife]

Hi all,
I have a 1970's fibreglass speedboat hull 2ft long, 8in beam similar to the old Sea Scout hull profile.
Which electric motor would give it a reasonable turn of speed but not as fast as the modern fast electrics please?
I want it to be fun to use but not manic.
They do not allow fast electrics on our pond so a sports boat type speed would be best I think.
Thanks and hoping for suitable answers.

[chas]

For sedate planing speed one option ( of many) is a standard 540 motor, and 6 or 7.2 volt nimh battery.
 There are brushless motor and lipo options, but I see you need to keep the speed down. If you don't want the model to plane, ask us again. The above is cheap and simple.

[canabus]

Hi Drawknife

I have a Sea Hornet(25 and 1/4 inch) with a 28mm B28-57-15L 1900kv motor with a 3S(11.1 volt) Lipo battery.
Which I would in you case go down to a 1500kv brushless motor for a quick scale speed boat, but, still use a 2 blade 32mm prop.
The 540 motor with Nicads will only give about 10 minutes run time.
The brushless motor and Lipo battery setup will give over 1/2 hour easily.

[Tug Fanatic]

Hi Drawknife

............................The brushless motor and Lipo battery setup will give over 1/2 hour easily.

With what capacity LiPo?

[chas]

The 10 mins bit is incorrect. Assuming a decent capacity battery. I use this set up in 2 models, a cynette which has a 4 a/h sla, ( no good for drawknifes model) and runs for 1 hour. And 28 inch fire float, with 4.3 nimh, It runs for 1 to 1.5 hours.
  The 540 motors I use are from commponent shop, the standard one typicaly draws about 2.5 to 3 amps on load. I think the 10 mins bit assumes a racing 540, which is very different.

[drawknife]

Thanks folks.
If I wanted a reasonable planning speed which brushless motor would you use please, or would you still use the brushed one?
Thanks

[dazzle]

My 30 inch mtb, original motor a new 545 only lasted 2 hours then packed up,
Have now gone / going brushless in all my boats I will be posting info on them in the brushless section soon as seems theres not enough info or most is guesswork.
Mtb has a wood hull lots of brass etc fittings weighs 2.15 kilos I use a turnigy 2830 - 11 pole 1000kv works on a 2s up to 4s lipo 7.4volts to 14.8volts (fully charged lipo volts 2s 8.4v, 4s 16.8v) it has a 3.17 shaft same shaft size as a 540.

I run mine on a 2s 7.4volt nanotech 5000ma (5 amp hour) saddle pack battery, 1st escapement I used was a hobbyking 60 amp car esc with reverse, You do not need a hulking big esc That first mistake I made, replaced it with a h k 30 amp boat esc which has reverse,
I use a 40 mm raboesch 3 blade brass prop, You can also use 35 mm or 40 mm 2 blade s (standard) j p, ripmax etc plastic/glass prop.

I get same up on plane very fast speed on half throttle (not full as needed with the 545) plus can go much, Very much faster, control is excellent from the slowest hardly notice boat is moving, or a full open whack of the throttle from boat stopped to instant full speed, water cooling though fitted because needed with 545, I have bypassed it, the brushless motor and escapement are stone cold when I put the back of my little finger on them, Run time, full charged lipo 8.4volts after 2 hours non stop running
including lots of substained 10 - 15 mins full throttle runs lipo volts on the onboard checker alarm display and on my digital volt meter which reads the same is 7.9volts boat has had over 10 runs testing results are the same. lipos can go down to 3 volts per cell 2s = 6 volts, most lipo alarms go off at 3.3volts per cell, my alarm and esc cut off volts are set for 3.5volts per cell.
Have not yet done a long enough run time to get the lipo alarm to go off, so am going to try a smaller capacity 2s nanotech lipo about 4000ma.

Turnigy 2830 motor cost £8, esc £12, nanotech batterys start about £8 for a 2s 2200ma from h king uk warehouse.
Brushless motors are 90% efficient hence the much longer run times, a brushed motor is only between 30% to 60% efficient, hope this info is of help to you and others.

[dazzle]

Re my mtb post,

Forgot to say, though I am running mtb on a 2s lipo at half the motors rated voltage and way under half its maximum power ouput I do not do sharp turns above half throttle because the boat trys to do a submarine act, also 40mm prop might be to much for your boat.

On a 2s or 3s lipo a good start size prop for your boat on either lipo, 30mm 2blade standard prop change up to a 35mm if needed, brushless motors even the small ones are very powerful for there size.

[drawknife]

Thanks for the info folks. Very helpful.