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Old Oct 02, 2012, 01:18 PM
Registered User
Slovenia
Joined Oct 2012
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Need help. Motor, prop for my 47'' boat

Hello guys.
I am very fresh on this forum, so let me introduce myself first. I am coming from Slovenia, and i built a hull 6y ago, then i had no time to go on and i forgot about it. Now i want to finish this project.
Below are some pic from the hull, it is 4kg heavy, 120cm long (47'') and it is made from polyester. i need a motor for this thing. i am looking for a gas engine from chainsaw, but i don't know. maybe 2 electrics? any idea would be much apretiated.





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Old Oct 02, 2012, 02:25 PM
Registered User
Slovenia
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Will two of these be ok?

http://www.ebay.co.uk/itm/3000Kv-RC-...#ht_2588wt_906
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Old Oct 02, 2012, 03:48 PM
Boaters are nice people.
Sneek, Netherlands.
Joined May 2004
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Quote:
Originally Posted by rakec View Post
Hi Rakec,

No, way too small and to high a Kv.

Not knowing what hullshape your boat is, my guess would be two of these on 4S at least...:
http://www.ebay.co.uk/itm/TUR-N4250-...item48404f1f4d

Got some pictures of your build?
That would making sensible suggestions a lot easier...

Regards, Jan.
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Old Oct 02, 2012, 05:37 PM
Redneck Injuneer
bill34207's Avatar
Bradenton, Florida
Joined Aug 2007
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Hi Rakec
As Jan has already mentioned your motor choice would be much too small for pushing a 47" hull would most likely result in a cloud of smoke when something (motor or esc) overheats.
It's actually cheaper to make a big boat run with a gas motor than electric (trust me, I know on this one although my big boats are electric powered) You can easily wrap up over $1000.00 in motor, esc & batteries to run something in that size range.
I'd suggest a minimum of 3000 watts (electric power) just for mild sport running. For competition, 5000 watts plus. Here's a couple of my high power - high voltage models to give you an idea.

47" mono http://www.rcgroups.com/forums/showthread.php?t=1378472

41" cat http://www.rcgroups.com/forums/showthread.php?t=1572391
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Old Oct 03, 2012, 09:07 AM
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Slovenia
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I don't know, but i don't see the pics in the first post, it must go something wrong with the upload. Here are again:





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Old Oct 03, 2012, 09:13 AM
Redneck Injuneer
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Bradenton, Florida
Joined Aug 2007
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That has the look of a submerged drive type hull.
If you're not looking for any kind of speed you can get away with considerably less power than I originally stated.
You will still want to stay with a lower kv motor like Jan mentioned though.
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Old Oct 03, 2012, 09:48 AM
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Slovenia
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well, i try hull how it's float, and it is excelent. only 1 or 2 cm under water, with 5kg weight. i still need to pull out that pu foam out, so it should have around 1kg less.
one thing, blow motor. will that be good? i first try to install motor from chainsaw, but i just don't have any
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Old Oct 03, 2012, 09:56 AM
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And my point is not the extra super duper speed, i just want that boat to go, not slow, but fast enough
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Old Oct 03, 2012, 10:53 AM
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Slovenia
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what about two of these:
http://www.ebay.co.uk/itm/1000Kv-Out...#ht_2565wt_906
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Old Oct 03, 2012, 11:40 AM
Never Fast Enough
Hamilton Ontario
Joined Oct 2005
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Is that motor good for at least 2000 watts?
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Old Oct 03, 2012, 12:35 PM
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Slovenia
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not even close, around 500W

what about motor on ethanol? i find one 10ccm and 3hp, or, O.S. Engine 3.5ccm (Model 72802)
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Old Oct 03, 2012, 03:11 PM
Never Fast Enough
Hamilton Ontario
Joined Oct 2005
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Nitro engines are greatly over rated in the power they make. You would need a gas / petrol engine or an equivalent 15cc nitro engine.

If you used the 3.5cc nitro engine, you'd only be able to spin a 38mm prop at 20000RPM. Not going to do very well with a large heavy mono. If you used the tiny brushless motor you had linked to, you'd spin the same prop at half that RPM and get no where.

Why are you restricting yourself to no power? Perhaps you need a smaller hull to place these things small motors in to? We are talking 27" in length.
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Old Oct 03, 2012, 03:29 PM
Boaters are nice people.
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Quote:
Originally Posted by rakec View Post
Hi Rakec,

Do you understand the answers that you get on your questions?

If so, why do you keep coming up with those tiny motors, when all answers indicate (much) larger ones?

The motor I suggested is 850W and the midget you came up with isn't even half that Wattage, so what don't you understand?

Regards, Jan.
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Old Oct 03, 2012, 03:32 PM
Thermite + ice = Big boom.
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Canada, ON, Ottawa
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Ryan, I'd be concerned with a motor that small in a 27" hull, maybe a hydro but still.
Look for at least 2000W of power, something like this would be a good one on 4- 6S
http://www.hobbyking.com/hobbyking/s...li_880kv_.html
You aren't going to be able to do this for less than 250$, then you have to buy a radio, a charger, and all the other peripherals.
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Old Oct 03, 2012, 03:33 PM
Never Fast Enough
Hamilton Ontario
Joined Oct 2005
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He said two of them, hence motorsssssss.

He said to me 500 watts. I looked at the link again, and it really is tiny. Lucky to even spin 200 watts. LOL
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