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Author Topic: prop recommendations please  (Read 2472 times)

rcflyers

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prop recommendations please
« on: November 17, 2006, 07:33:43 AM »

I bought a cheap mono hull speedboat (about 26" long) for my daughter recently. I am going to ditch the twin 380 motors and surface drive setup as it has no rudder and the power is either on or off. I am going to fit a nornal rudder at the stern, fit a normal central propshaft and install a 540 size 27 turn water cooled stock motor and electronic speed controller. The prop will be fully submerged in front of the rudder. What size prop would be suitable please. I may fit a more powerful 540 size motor in the future (like a 17 turn or so)
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boatmadman

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Re: prop recommendations please
« Reply #1 on: November 17, 2006, 09:28:00 AM »

Hi,
Try this site, they may be able to help, they have halped me in the past.

http://www.astecmodels.co.uk/

Or, try here, again v helpful

http://www.britnett.net/propshop/

Ian
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Bridkid

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Re: prop recommendations please
« Reply #2 on: November 17, 2006, 09:56:18 AM »

How many cells will you be using? If you are using a 6 pack then there will be one or two you can use. ASTEC sell a good P31 that will suit it but it may be a matter of buy and try. Small sub-surface props are quite expensive too. (12 each approx) Maybe a plastic or carbon filled prop at around 3 would be better.
Cheers,
Ian.
 ;)
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cbr900

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Re: prop recommendations please
« Reply #3 on: November 17, 2006, 12:00:42 PM »

I have just put a 540 19 turn motor into a boat about the same length and have used a 55ml three blade brass prop with one 25 ml pitch, it gets along quite well....



Roy
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rcflyers

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Re: prop recommendations please
« Reply #4 on: November 17, 2006, 01:13:30 PM »

Thanks, a plastic or carbon filled prop at around 3 would be perfect.
I will be using 6 cells, it doesn't have to be mega fast,
I just wanted the rough size of a 2 bladed prop size to start with.
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J.beazley

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Re: prop recommendations please
« Reply #5 on: November 17, 2006, 01:52:34 PM »

i have a C.C.Lee victory speed boat that im using 2 x 540 motors on 6 cells with a pair of 2 blade 35mm diameter props.

with a timing gun she gets up to around 30mph on the water which is more then fast enough i think.

Jay
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rcflyers

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Re: prop recommendations please
« Reply #6 on: November 25, 2006, 06:15:47 AM »

Slight change of plan, I am going to surface drive it instead, I will run a propshaft through the transom, what height does the centre of the shaft need to be in relation to the boats keel and how far back from the transom does the prop need to sit? Also will i need a bigger prop than the 35mm one suggested earlier?
Thanks for any replies.
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Bridkid

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Re: prop recommendations please
« Reply #7 on: November 25, 2006, 08:47:57 AM »

Hi.

The centre of you prop boss should be level with the bottom edge of your transom. Are you still using 6 cells?
Hope this pic helps.
Cheers,
Ian.
 8)
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rcflyers

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Re: prop recommendations please
« Reply #8 on: November 25, 2006, 09:32:25 AM »

thanks, yes still 6 cells
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Bridkid

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Re: prop recommendations please
« Reply #9 on: November 25, 2006, 10:55:38 AM »

In which case I would stick to the prop you have for the first run and see how it goes. A larger prop does not necessarily mean more speed but you may be able to uprate to say, a 37mm without any problem. The problem you may encounter is the fitting for the prop. Some of the larger ones have a dog drive and the smaller ones are screw fit. (4mm) I don't have my Ripmax catalogue at the moment (out on loan) but your local model shop should have one and you will be able to look and check. I do have a 40mm plastic screw thread prop (just checked in my odds box) so there must be something in between that and a 35mm. You may even like to try a smaller one and there are 2 or 3 carbon filled plastic hydro props that might suit. (29mm and 32mm at least) Rule of thumb is that you can always use a larger prop for surface drive than submerged because there is less drag and therefore less drain/strain on the cells/motor.
If you need more speed/fun/excitement, add a couple of matching cells to the pack.
Cheers for now,
Ian.
 8)
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rcflyers

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Re: prop recommendations please
« Reply #10 on: November 27, 2006, 09:50:12 PM »

I have got the prop, shaft, motor and rudder fitted, where roughly (in percentage terms between bow and stern) should the centre of gravity be for a mono-hull please?   I am trying to work out the best position for the cells and rudder servo. Thanks.
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Bridkid

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Re: prop recommendations please
« Reply #11 on: November 28, 2006, 08:59:56 AM »

Approximately 2 thirds of the way back from the bow (66%). Fit the rudder servo first and then use velcro to fit your cellpack (Hook on the hull and loop on the cells) so you can move the pack backwards and forwards to obtain the correct C of G. Even a move of " can make a difference and you may find that you need 2 positions marking, one for smooth and one for rough conditions depending on your speed.
Cheers,
Ian.
 8)
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