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Old 07 December 2006, 08:12   #1
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quality props

If money were important, who makes the best props in the business for rib's?

If money were no object who makes the best props for Ribís worldwide, not altered or re pitched but original?

Has anyone come up with titanium one for example.... would there be a benefit in using this material over stainless? (Overcoming the inertia / weight of the stainless one on my engine must sap one or two horses?

Has cad etc improved manufacturing tolerance etc?

I'm just throwing this up in the air as I think collectively pooling resources on this (what seems to be a black art) makes sense for all of us..

JK, If the response is good maybe a better brain than mine could work out how to categorise the answers?
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Old 07 December 2006, 09:03   #2
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Would it depend what is considered "best"? I shied away from fitting a stainless prop due to the fact that there is a risk of Mr Prop meeting Mr Rock on the odd occasions. A titanium one would be even more likely to bust your gearbox I should think, and I'd rather just have to spend 100 quid on a new prop which takes 5 minutes to change

Titanium should be good for performance though what are its corrosion resistance properties in salt water?
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Old 07 December 2006, 11:12   #3
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Would it depend what is considered "best"? I shied away from fitting a stainless prop due to the fact that there is a risk of Mr Prop meeting Mr Rock on the odd occasions. A titanium one would be even more likely to bust your gearbox I should think, and I'd rather just have to spend 100 quid on a new prop which takes 5 minutes to change

Titanium should be good for performance though what are its corrosion resistance properties in salt water?
What I meant (looking at it again I'm not clear) was, for example is 3 or 4 blade better in relation to ribs? With the generally light nose heavy stern problem.

If people have found either or to be true who makes the most efficient prop etc?

Do some props when compared, slip more than others? could this be due to some being better made.?.

Does the length of hull favour one or the other that type of thing, if tit is stronger, then blades could be thinner. My understanding of increasing the blades (more surface edges) is drag robs you of top speed. If that’s true has anyone done something about it..?

If collectively the info could be assessed then we would have a clearer understanding than "you've just got to try some and see what’s best" position we are all in at the mo.
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Old 07 December 2006, 12:06   #4
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I think you're making sweeping generalizations, and applying them to specific applications.

Two very similar boats may well use two wildly different prop styles to get good results.

What I'm trying to say is that there is no cookie-cutter "best", especially when it comes to something as black-artish as propeller selection.

jky
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Old 07 December 2006, 12:37   #5
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Prop size

Ok Guys, time for a bot of lateral thinking (dont all hop off me, its only up for discussion).
You see the new planes (not sure who makes them) but the wing tips are turned up. Possibly to stop Eddie vortex`s spinning off the end of the tip. I believe that there has to be a three min wait after a Jumbo lands due to same.

Point is, if it has taken 70 years to decide that there is a better wing type, how come no one has come up with a better prop type.
It has never changed that much. You can see the Impeller type prop in a Saab Turbo, its a different shape. SO who out there is going to design a 21st century efficient prop and same people can buy a Luxury liner.

What about Ram Jet type etc.

Aidan
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Old 07 December 2006, 14:10   #6
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Point is, if it has taken 70 years to decide that there is a better wing type, how come no one has come up with a better prop type.


Aidan
Thats pretty much what i'm getting at ,is there some cutting edge manufacturer out there. state of the art normally costs a premium,
I think a lot of people would be prepared to pay it.

People talk about the pitch/dia etc what about the balance accuracy or material, (accepting the norms of S/S or ali) no one as far as I'm aware,appears to be trying to shove the envelope.
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Old 07 December 2006, 14:24   #7
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Quote:
Originally Posted by jyasaki View Post
I think you're making sweeping generalizations, and applying them to specific applications.

Two very similar boats may well use two wildly different prop styles to get good results.

What I'm trying to say is that there is no cookie-cutter "best", especially when it comes to something as black-artish as propeller selection.

jky
Actually that's what I mean, what does good results mean? one must be better than the other for a given application. the fact that we talk about good results only goes to show how accepting we all are with the comparisons/measurement of these things. why should we accept black-artish? I think the propeller manufacturers use the fact that we accept black artish to do two things

Avoid competing with one and other.
avoid investing money in developement?

Hey it's a idea, but to me it points that way, if there is anybody making props out there I'm in South Africa.
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Old 07 December 2006, 15:15   #8
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Not sure if you've seen this, but it explains how variations in props affect speed, cavitation etc. Interesting stuff:

http://ribevents.com/site/index.php?...=267&Itemid=84
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Old 08 December 2006, 13:25   #9
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Originally Posted by Aidan View Post
You see the new planes (not sure who makes them) but the wing tips are turned up. Possibly to stop Eddie vortex`s spinning off the end of the tip. I believe that there has to be a three min wait after a Jumbo lands due to same.

Point is, if it has taken 70 years to decide that there is a better wing type, how come no one has come up with a better prop type.
In truth, I think high altitude private planes have been using similar designs for a long time. I remember seeing them on Cessnas used in the Sierra Nevada mountains in the 70's (though now that I think about it, the wingtips may have been turned downwards. Something about keeping higher pressure air under the wing. Same idea.)

The 3 minute wait is not due to the wingtip configuration, but rather that the turbulence generated by keeping 400 tons aloft with air is going to be pretty substantial. In truth, all planes generate the vortices, its just that heavier planes generate more.

But, I see your point on marine prop development. If you look at the amount of research that has gone into refining the prop as it is today, I think you'll find that it is much more efficient now than when they first started using screws on boats.
http://www.boatbuilding.com/article....nofpropellers1 makes for a good read.

I think your example leads pretty naturally to the ducted propeller design (the prop mounted inside a cylinder that prevents spillage over the blade tips.) Where this idea is still in use, I think it's geared more towards heavy load/low speed applications (tugs come to mind), rather than high speed applications. The ducting itself has to generate a lot of drag, which will offset the energy retained by ducting.

The US Navy has done a lot of research into alternate propulsion methods, and none of them have really panned out. Could be that from a cost standpoint, the modern propeller is about the best we can expect?

I sure don't know.

jky
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Old 08 December 2006, 17:00   #10
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Quote:
Originally Posted by Aidan View Post

Point is, if it has taken 70 years to decide that there is a better wing type, how come no one has come up with a better prop type.
It has never changed that much. You can see the Impeller type prop in a Saab Turbo, its a different shape. SO who out there is going to design a 21st century efficient prop and same people can buy a Luxury liner.

What about Ram Jet type etc.

Aidan
Is there a better wing type? It all depends on it's use. For high speed you need a swept wing - for lift you need a totally different design - hence swing wing. Everything is a compromise.

Prop design hasn't really advanced since WWII - different materials perhaps and different props for different applications but that's about it.

Jet engines haven't advanced much over the years either.Most turboprops on commuter aircraft were designed by RR in 1956 - later became the PT6.

Modern engines tend to be far more eeconomical but the speed of modern airliners is actually down on the 1960s. They are also much quieter as the engines these days are almost like ducted fans - very high bypass ratio - big fan blades at the front. The military still use turbojets - much higher speeds but noiser and more fuel.

You mention Ram Jets - there is quite a bit of work on high speed torpedoes - some use rocket motors and they shield themselves in bubbles of air to reduce drag - maybe that's the way forward for boats - more air underneath!!!
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