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[MacGee]

Hi everyone, i am currently building a canal boat wich is my own design and ive come across a problem ive got a 12v motor fitted with a 3 blade propeller m2/30mm  the problem is she doesnt make any headway even at full throttle she barely moves. the question is  can i change the propeller or do i have to change the motor to get more power out the boat is pretty heavy and is running off a 12v 7amp lead battery. im a bit lost in this field and not sure which way to go with it.

thanks for any help in advance
mark (the brit in germany)

[IainM]

Hi Mark,
As the saying goes .... "Well you see, it all depends !"
I guess first off, how big is the canal boat and, if you have an idea, how heavy is it? and secondly what is the motor you are using?
A 30mm prop does seem a wee bit on the small side, especially given that you have room in the boat for a 12 volt 7Ah SLA.

How much you could increase the prop diameter by will depend on how much clearance you have between the end of the prop shaft and the underside of the hull and obviously whether or not the motor could take it (increase in power consumption).  Completely out of scale (but cheap to try), you could perhaps fit a 2 blade plastic racing prop that has a much greater pitch of the largest diameter you can squeeze in without fouling the hull bottom. 

I know I've had to play around with props quite a lot to get the best setup so you're not alone in this!!

Iain

[MacGee]

thanks for your quick reply, the boat is about 1mtr long and heavy i made a prat of myself at the lake on her trial run with every one watching and nothing happened lol but thats life,  ive got about 55mm clearance so ill try a new size  propeller and put her in the bath tub before i go back out on the lake. i thought about a racing one but wasnt sure. so its off to the model shop and see what hes got for me
thanks again mark

[Stavros]

What Motor have you fitted


Stavros

[Peterm]

Just a thought.   I have a 4ft scratch-built narrow boat powered by a Decaperm 12 volt motor via a gear box to a 40mm prop.   I have no problems, in fact it goes like the proverbial clappers, so there are two possible causes:   a.  Motor revs too high causing what I believe is called cavitation.   b.   You have the propeller rotating in the wrong direction,   try swapping the motor leads around.   Be interested to hear how you get on.   Pete M

[tugboyben]

hi i have a canal boat the size is 40 inch's long by 7 inch's wide i run it on a mfa 6:1 geared motor & a 50mm prop a 12v 7amp battery i have run the boat for over 2 hours  with loss of power hope it helps

[malcolmfrary]

With a home design by a newbie, I've got to ask - what is the shape at the back, just in front of the prop like?  Poor flow leading to the prop can destroy performance.  Assuming that the motor is big enough (12 volt motors come in many sizes), even a small prop like this should cause enough motion for stering.

[MacGee]

thanks to everyone for there help, i whent out and bought a new propeller and prop today and will test it out next week in the bath this time lol.
 
if that doesnt work then its a new motor but well see
thanks again mark

[MacGee]

 
a big thanks to every one who helped with my problem the prop was changed over to an M4 45mm and the shape of the hull was modified. she whent on her trial run at my local lake and ran like a dream this is my first scratch build  working from some holiday pics (no plans) and allthough not the best paint job and some problems here and there im happy with the results. here a few pictures on my website for you to look at there will be a video in a couple of weeks

http://mcglinchey.de/index2.html

thanks again
mark (brit in germany)

[GaryM]

Hi Mark

You have some wonderfull boats and I couldn't stop chuckling at the questions / comments asked.

regards
Gary :)