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Old Dec 13, 2013, 08:57 AM
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Tech Head's Avatar
Australia, NSW, Temora
Joined Sep 2008
208 Posts
Question
Prop suggestion

Hi all, I have a 70cm Hydro with a solid shaft so the prop is submerged.
The engine is a Go Tech .25 (4.1cc) and I'm looking for prop suggestions.
At the moment I have an Octura X447 3 blade and it seems to be too big as the boat bogs down and stops when I launch it.

Any ideas? Thanks.
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Old Dec 13, 2013, 05:19 PM
RC boat Rock Star
Kalamazoo, MI
Joined Apr 2004
2,895 Posts
Go down to around an X-442 or X-445.
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Old Dec 14, 2013, 02:20 AM
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Australia, NSW, Temora
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Not much difference in sizes. Does 2mm make much difference?
5mm I can see it making a noticeable difference.

Also I'm using 20% nitro content, should I go higher?

Thanks for the reply Ron.
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Old Dec 14, 2013, 07:13 AM
RC boat Rock Star
Kalamazoo, MI
Joined Apr 2004
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Yes, it really does! It's not just the diameter but the pitch also. If you do the math using 1.4 times the diameter of the prop you'll see that the pitch does down also along with the diameter.
An increase in the percentage of nitro only works so far. The smaller the engine the better they like it. By nature, nitro is a slow burning fuel so it needs the methanol to help ignite it so it works better when it has less of an area to burn in. I wouldn't go crazy as 45% is generally the most that you'd use as anything over that doesn't make much of a difference in speed but also higher nitro makes the needle a little harder to get a good setting on. Just use fuel made for boats as it has a higher oil content in it.
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Old Dec 15, 2013, 04:44 AM
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Australia, NSW, Temora
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That makes a lot of sense Ron thanks for that. As far as the fuel goes, I'm in a remote area and any fuel I get I have to have it shipped in. I'm unaware of boat specific fuel. I use a blend of 20% nitro and 20% Klotz supplied by a friend when he comes to town once a year to run his boat at a Rc boat event I've recently started here in town.
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Old Dec 15, 2013, 06:50 AM
RC boat Rock Star
Kalamazoo, MI
Joined Apr 2004
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You got enough oil then, that's good. Tower Hobbies sells Aquacraft Grimracer boat fuel that you can hae delivered to your door. Reports are that it's good stuff. I knew a guy that lived near the Wildcat Fuel plant and he'd bring us up cases of fuel every year so I'm set for a while.
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