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Choosing a prop

Last Post 18 Nov 2009 08:17 AM by pamnjay. 9 Replies.

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JustinScott User is Offline

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30 Aug 2009 12:41 AM
OK, so obviously there are a lot of variations in what a make a good prop. 2,3,4 blades.. pitch... size... blade shape... What does it all do? Would 2 blades produce a faster ship, as they could get more grip? or would 4 blades because there is more sources of water pressure? Pitch at first glance is easy... more bite = more go. But that's probably not true... too much bite & it'll be a paddle wheel. additionally, too much bite will put too much pressure on your motor and slow it down... there for slowing the boat down. Also a faster spinning prop cuts weeds easier, so perhaps a slow speed but fast-rotating prop would be a good thing? Would it cavitate more? Size... same as above... Blade shape... I would think a shapely blade would be more performant and less likely to cavitate(sp)... Perhaps I'm missing other things? Has anyone played around with these things? What did you come up with?

Cheers, jks DKM Tirpitz

Stokamoto

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30 Aug 2009 10:30 AM
Boy.. good questions. I played around with quite a few of them. I seen teh same type ships use different props but with the same results. It's a complex issue with no one answer but it does come down to what you feel is working for you. I was checking RIVABO prop website and I think I remember they had a detailed section on all the various types of props and what applications they are best suited for. I was able to figure out what worked well. For example Roma I had 40 pitch 3 blades it got the ship up to quick accelleration but couldn't stop on a dime. The model was too fast so I reduced the size but though it had correct speed the pitch and smaller diameter produced less wash over the rudder. I kept the size but switched to 25 pitch but with 4 blades. THis worked well. I got plenty of wash over the rudder, accellerationg was good and it could stop almost to an isntant. Speed was sustained at 24 sec over 100ft. I did not have to change gears, or motor size, or increase voltage. I didn't have to use an ESC. I could probalby get away with even a flatter pitch and a 5 blade or 4 blade and go up to a larger diam slightly to improve it further without going over the limit.

JustinScott User is Offline

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30 Aug 2009 12:43 PM
Do they make the plastic props in 3 and 4 blade? Buying a bunch of plastics and trying them out would be the only feasible way of trying out different props. Sure they wouldn't last against a fishing line... but they wouldn't have to.

Cheers, jks DKM Tirpitz

Greg McFadden User is Offline

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30 Aug 2009 12:54 PM
justin, do you have a link to the props you were telling me about? do they have plastic variants (this would be optimal, as a plastic prop of one design and a metal prop of another, will not give you the information you need)

JustinScott User is Offline

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30 Aug 2009 01:12 PM
I have a preference to octura props... The set I had on Iowa were practically indestructible. Octura is run by a guy who was very successful in r/c race boats, and doesn't believe in the internet. This is the best reference I've found to their props... www.funrcboats.com/category.aspx?categoryID=109 And even that's not that good... they make probably 4x the amount of props that are listed there.

Cheers, jks DKM Tirpitz

Stokamoto

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30 Aug 2009 03:49 PM
I used to use the plastic props from Octura and they were 2 blades. The props themselves were virtually indestructible and worked very well. There's so many out there you can choose from but research the applications first and then it's just narrowing down the kind you want be it brass or plastic, threaded or non threaded , then price.

crzyhawk

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01 Sep 2009 12:20 PM
Bumped an older thread that had some good input from Bob and JohnCA72 which might be helpful.

HMS Invincible USS Salem (CA-139) USS Belleau Wood (CVL-24)

warspiteIRC User is Online

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01 Sep 2009 06:26 PM
I think that 4 blades did not add anything to speed when I tried it vs. a two blade

JustinScott User is Offline

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01 Sep 2009 06:43 PM
Thanks for the link! I'll read it tonight when I get more time. I wouldn't expect 4 blades to add more speed... I would expect it to add more acceleration.

Cheers, jks DKM Tirpitz

pamnjay

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18 Nov 2009 08:17 AM
The number of blades does add to accelleration and to braking, but has minimal effect on top speed. (I learned that in the NAVY) The shape of the blade makes a diiference too. On Scharnhorst, I had a single 4 bladed 40 pitch prop with shaped blades, similar to speed boat props. When compared to Steve Crane's dual shafted round bladed Nagato , I took of faster and was about 1/2 a boat length ahead of him when the top speeds equallised. The down side is that it took 4-5 boat lengths to stop from full ahead. I switched to a BC round bladed prop. Now Steve can accellerate a little faster than I can but I can stop in 1 boat length. That makes a difference when you are trying not to ram anyone. J

"There it is again...kind of a BOOM sound" -short lived Allied lookout

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