5 Blade Cleavers?

[Mattwarner]

These look really cool but i cant see anyone using them? Do they just not work as well as a 2 blade?

http://www.prop-shop.co.uk/index.php?id=25&section=services&sub_section=products&product_type=25

[egneg]

They work but you need a very strong high rpm motor, check with graill for details.

[Boaterguy]

they also cavitate more.
they are used in big (full size) cats for a reason i do not specifically know (nor is it relevant in this explanation)
think of the space between each blade on a full size boat with a 5 blade prop, it is usually about 6 inches.
think of it on that prop you linked to, it's more like 1/4-1/2", so the amount of time the water has to close back in (theoretically) is very little, especially at high rpm's, so cavitation is high and efficiency drops (plus they are a pain in the arse to balance)

[TINY]

I will be using the 5 blades from prop shop for my custom mhz twin saw boat.. Takes alot of work and they need big power.... Let you know how it goes.
If your scared of pushing the limits of components then stay well away.
cheers

[Fluid]

Multi-blade props have several advantages over two-bladed props. For the same blade area they have less diameter, so have less torque effect on the boat. One blade is almost always in the water so there is a smoother transmission of power to the water instead of the distinct two-thumps-per-rev of twin-bladed props.

They also have disadvantages. They are heavier and stress the hub/blade root area more, so there is a higher chance of throwing a blade. Their efficiency is lower because the previous blade has disturbed the water for the following blade. All surfacing props cavitate - that is how they provide their high thrust - but water with bubbles and currents doesn't allow the same 'smooth' cavitation to occur, reducing blade efficiency. They are also more difficult to balance and sharpen, and the choices of sizes is very limited. Too, cupping and adding pitch is very difficult with props having more than 3 blades. Serious SAW racers want to be able to fine-tune their props to that last mph, which is tough to do accurately.

For top SAW speeds two-bladed props are normally best, but depending on the power to be delivered the smaller diameter multi-bladed props have their place. Still, current fast SAW boats almost all use 2-bladed props.


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[TINY]

Yes I remember way back when ski boat races all had outboards and 3 blade props, now they have their ass's handed to them buy turbo'd inboard big block chevs that ALL run multi blade prop's.. Funny how times change and records are made to be broken..

Guess it comes down to the "serious" saw guys and their testing?

[egneg]

This is a pair of Prop Shop 8015/5's that I modded for graill to use on his cat the Platinum Princess. He said they were hit and miss as far as hooking up but when they did...

prop2.jpg 8015-3.jpg

[Fluid]

The fastest propeller driven hydro through the measured km (220+ mph) is the Miss Budweiser, using a Dave Villwock 3-bladed prop. Even then, the propeller broke and the driver was lucky he was not seriously injured.



SAW runs are a lot different and more demanding than drag racing. Having to keep the prop together for 2 kms is problematic. Most don't realize this, but full-scale racing props running in surfacing mode get very hot! Hot enough to lose both temper and pitch. Even one of the best prop makers in the world (Villwock) has trouble meeting that challenge, see above.


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[TINY]

This is a pair of Prop Shop 8015/5's that I modded for graill to use on his cat the Platinum Princess. He said they were hit and miss as far as hooking up but when they did...

[ATTACH=CONFIG]66054[/ATTACH] [ATTACH=CONFIG]66055[/ATTACH]

Yeah i heard that,and was warned.. hence why alot of testing before the main event..

The 5's may be crap but it's worth a try.. Costing alot to get prepped though, hope they work...lol

[TINY]

This is a pair of Prop Shop 8015/5's that I modded for graill to use on his cat the Platinum Princess. He said they were hit and miss as far as hooking up but when they did...

[ATTACH=CONFIG]66054[/ATTACH] [ATTACH=CONFIG]66055[/ATTACH]

Yeah i heard that,and was warned.. hence why alot of testing before the main event..

The 5's may be crap but it's worth a try.. Costing alot to get prepped though, hope they work...lol

[TINY]

The fastest propeller driven hydro through the measured km (220+ mph) is the Miss Budweiser, using a Dave Villwock 3-bladed prop. Even then, the propeller broke and the driver was lucky he was not seriously injured.



SAW runs are a lot different and more demanding than drag racing. Having to keep the prop together for 2 kms is problematic. Most don't realize this, but full-scale racing props running in surfacing mode get very hot! Hot enough to lose both temper and pitch. Even one of the best prop makers in the world (Villwock) has trouble meeting that challenge, see above.


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Agreed'd the pitch they use is crazy and the tourqe is out of this world...

Alot different than 45 to 55 though rpm.... om tiny scale boats... you even need to calculate the water viscosity brfore final desicions...

[Fluid]

I am among other things a fluids engineer, and I can tell you that no R/C boat record holder "calculates" the water viscosity when making prop decisions. Reynolds number and density have more effect than "viscosity", but no software exists to quantify that effect anyway since surface tension has a disproportionate effect on R/C props; no one needs to do any 'calculation'.

It may surprise you to learn that the blade speed on R/C boats is far slower than on full-scale SAW boats. The tip speed on the Miss Budweiser's prop was around 550 mph, while that on a typical FE SAW boat is closer to 80 mph.



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[TINY]

Tip speed may have something to do with diameter bud? Surprised....

And no one calculates viscosity..

I'm one and no of two others.

Thanks for the info though..
Cheers

[TINY]

Fluid when I meant viscosity I also meant a few factors like density etc..

Kind of like a fast pool and a slow pool at the Olympics. The density of salt versus fresh. Yet to own a title but have bought the equipment that has got the records and am upgrading components.. Stay tuned

Cheers

[Fluid]

And no one calculates viscosity...I'm one and no of two others.

I think I said no record holder calculates viscosity. Viscosity is a measured value anyway, as is density, salinity, etc. Do you use an AntonParr 500, a Fann 35, or a Marsh Funnel to obtain your viscosity values? How you would use this subtile information for making a prop decision - when other factors like wind and waves have a much larger effect on speed - escapes me. You would need a large database of test results to make any practical use of viscosity measurements.

Regardless, good luck on your attempts. If I can assist in any way, just let me know. I've held a few SAW records myself....


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