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so confused on props, Need help!

Old 02-22-2006, 06:32 PM
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ledzep
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Default so confused on props, Need help!

Hello, I am new to the boating hobby, and I recently finished my first boat. It is a shallow mono hull about 30 in long and it has a O.S 18. in it. Fully loaded with gas it weighs about 4 pounds. I have a octura serface drive and a Octura X438 prop. I have ran about half of a gallon of 20% nitro fuel in it. I want to push this boat to the limit without hurting it or the engine. I am so confused about props it is not even funny, I dont understand what lift means, or what prop would best fit my boat if I want to go for speed. If there is a web site that I can go to or if anyone can tell me about props and how to get the most speed out of my boat.


Thank you.
Ledzep.
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Old 02-22-2006, 06:42 PM
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martno1fan
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Default RE: so confused on props, Need help!

if i were you id buy some cheap plastic props in dif sizes,find one that works well then buy a goo brass prop in same size!!.apart from that im as dumb as you
Old 02-22-2006, 07:20 PM
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Frank B.
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Default RE: so confused on props, Need help!

Hi, there is alot of info here http://rcboat.com/past.htm


Frank B.
Old 02-22-2006, 09:33 PM
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Ron Olson
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Default RE: so confused on props, Need help!

Don't be afraid to pour the nitro down its throat, my .12 runs just fine with 50%, besides it freaks out the car guys when you run that much!
There are probably other places to do some tweaking at yet like the tuned pipe length. Your boat is still a sub-surface drive and reall isn't considered a surface drive until the prop is half-way out of the water at speed.
I haven't seen one of those MRP hulls in a while, how about a shot with the hatch off?
Old 02-22-2006, 10:06 PM
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ledzep
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Default RE: so confused on props, Need help!

ron, when the hatch is off it takes on water like no other. when it turns it sprays water all over. maby cause the nose realy goes down when i turn. What prop would u sugest for this thing though?
Old 02-22-2006, 10:53 PM
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Default RE: so confused on props, Need help!

I don't know with it being just under surface drive. with most of my boats I may have to try 6 props to find one that the boat likes. You can try the X-637 or upwards of an X-440 to see what the boat likes or doesn't. I've found the biggest performance gain on mine using a larger than normal carb.
I just wanted to see an "under the hood" shot to see how you have things set up or is this one that you've shown shots of before?
It may be a little on the nose-heavy side by the way that it sounds but you'll find that a semi flat-bottomed hull doesn't handle like a deep-vee.
Old 02-22-2006, 11:13 PM
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ledzep
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Default RE: so confused on props, Need help!

Ok i will get an under the hood shot. let me clear up on thing the largeer the number of the prop the smaller the prop is?. like is a X-637 larger than the X-440. Ok here is what i have found. i get abetter all around start and run with the prop lower in the water. But it does not sound like it is reaching its max RPM. when the prop is higher it seems to slip on the start up. i dont know what that means.
Old 02-23-2006, 10:02 AM
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Default RE: so confused on props, Need help!

OK, quick class on Octura prop sizes. First, the "X" is a non- or low-lifting prop. The first number be it something like a 4, 5 or 6 is 1.x that number times the diameter in millimeters of the last 2 numbers like 37 or 40.
As an example, your Octura X-438 translates into a diameter of 38mm (1.50") and a pitch of 53.09mm (2.09").
Lifting props for hydro use use both numbers such as 14, 16, 17, etc. times the diameter to find the pitch, except the 14 is used as 1.4 when multiplied to the diameter.
Clear as mud, huh?
ABC props make it simpler as they use the actual numbers instead of the multiplication factor so they would call your X-438 something like a 5338. Forget Prather as there numbers really don't mean anything as far a size goes except we know that a 270 is larger than a 220.

OK, next questions. Prop slip is cavitation, getting air around the blades. One simple cure may be to just give the boat a "push-start" in the water or a light toss to help get it going.
On not sounding like it's reaching it's potential RPM can be a bunch of things. Fuel mixture off, tuned pipe length off, too much prop, an overcooled engine which may be rare seeing where you live or a few other things.
Old 02-23-2006, 04:02 PM
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Default RE: so confused on props, Need help!

Check out (Prop sharpening & other tips for new boaters) its at the top of the nitro boat form there is a lot of good info on props and not just for sharpening it may answer some of the questions you have. The links on it are vary helpful to its a lot of reading
Old 02-24-2006, 12:21 AM
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ledzep
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Default RE: so confused on props, Need help!

Ok I was looking at a prop chart and I understand what you mean on the pitch and diameter. My other question is if I wanted to get the most speed out of my boat with a surface drive would I want to go with a high pitch prop with a smaller diameter or a large diameter prop with a lower pitch?

Thank you.
Old 02-24-2006, 08:39 AM
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jdoug
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Default RE: so confused on props, Need help!

Nobody has "your" boat...meaning they are all different. Like the rest of us, you are going to have to get a selection of different props and try them to see which one performs best. Start with plastic or carbon, as they are cheaper...and when you find one, buy it in beryllium copper. Strut angle and depth will also play a role in the performance of a particular prop. There will be a prop that performs "best" depending on what you are after (top speed, out of the hole power, etc.) Trouble is, finding it. Small changes to a prop can make a big difference too! Like me, you might have to experiment. I tried modding my gas boat prop for the first time with excellent results. Whats the worst that can happen? ...you lose $10-20 on a prop lesson. Yes, check out the prop info pages at the top.

Just be sure that is thing balanced well and the sharper the better. I've had speed increases by thinning my props too.
Old 02-24-2006, 07:35 PM
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ledzep
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Default RE: so confused on props, Need help!

Ok, I think I am gonna try the Octura X642 prop.
Old 02-24-2006, 11:07 PM
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ledzep
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Default RE: so confused on props, Need help!

Ok, I was wondering. What does the Y mean on other Octura props, and what about the ones without letters, just numbers. Like 1453. I would like to have the prop that will produces the most thrust wether it be a X-642,1640,Y-567 or a three bladed prop. I know the X series is a non-lifting prop but I dont know what I should put on my boat, lifting or non-lifting or.... whatever else there is? I am sorry if yall are getting tired of me asking all these questions, but I just want to soak in all the info I can before I buy somthing.[&o]

Thank you.

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