DFB

Anybody play around with 4 blade props?

DFB

Also what is the difference between a "cleaver" and a "chopper" ??


Thanks for any and all help...

danielplace

Have run the 2714 / 4 and 2814 / 4 and Voodoo makes a nice 4 blade they were all run very successfully on mono style hulls.

There was 2814 / 4 ABC on this nitro powered Razor but they run very well with gas power also,

http://www.youtube.com/watch?v=sWMc1yRzMbA

MrMikeG

Yes I like the 4 blade ABC's as well.

Justaddwata

My Feedback: (3)

Going to depend a whole lot on what prop, what boat, and what power your taking I imagine.

Going by what Mercury are showing
http://www.mercuryracing.com/propellers/chopperii.php

Chopper...........................Cleaver

DFB

This is the boat I'm looking to put the 4 blade on... Rio 51, with a RCMK ... If correct, a chopper will promote bow lift, and a cleaver will not.??

MrMikeG

Depends on the cupping of the blades. Props have lift or no lift, it acts on the transom, lift on the transom holds the bow down, no lift lets the hull go where it wants. A boat with a lot of strakes and a no lift prop the bow will lift higher, because of the strakes though, not the blades on the prop. The only way a prop can lift the bow is if you put positive angle on your strut.

lapistola28

Props with more Rake promote bow lift despite what MrMikeG says

01VIPER27

My Feedback: (1)

I have a RIO 51 powered with Zenoah G260 PUM with an M5 head kit going at 53 MPH with its stock hardware and a VOODOO Stainless Steel XX Tater ($100.00) chopper prop on it. It will cavitate for the first 6 feet and voila, its gone.

The WHH RMB 703 Aluminum cleaver will do the same speed without the cavitation ($16.00) but will not last 3 tanks before it starts to show hair line cracks on it.

I have recently tried the Prop Shop Stainless Steel 6717 4 ($100) cleaver from my 64F project on the RIO 51 and it cavitated for about 4 feet and voila, it hit 52 MPH.

Note;
The prices are steep because I did not buy direct from the manufacturers but they normally run about $65.00.

MrMikeG

Props with more rake have less lift as more rake tightens the thrust cone. Start with a NO lift prop and put your "more rake prop" on and tell me which way the bow goes.

What your saying is like telling me the front wheels on a car push the rear end around.

danielplace

I think all Mike was saying was the only way a prop hold down the bow is because it has lift. If it had zero lift of coarse the bow would be higher than with high lift but not likely to pull the transom down. It is either lower lift allowing a looser ride or high lift that tightens it up. It is either no lift, low lift or more lift but not less than no lift. Did that make any sense at all ? Or in other words the prop doesn't lighten the front end but one with less lift allows the bow to lift. If a prop had no lift then no more bow lift would be possible by prop alone.

01VIPER27

My Feedback: (1)

I forgot to add that none of the props I mentioned above had a lift. Just set your trim tabs flat with the hull and your drive flat with the keel and you will fly...

lapistola28

Read this from Voodoo Props ......... Then tell me i'm still wrong about rake creating or reducing lift !

http://www.voodoopropellers.com/anatomy.html

MrMikeG

Rake creats or reduces lift ON THE PROP look at the picture.

Daniel said it better than I did. Lifting props lift the transom which can plant the nose, the prop doesn't plant the nose though, the prop lifts the transom which in turn plants the nose. (Sometimes)
Non lifting props let the transom settle down into the water which makes the bow run higher, the prop doesn't lift the bow though, the prop settles the back of the boat. Strut height can do the same thing, and a fast boat you will need to adjust the strut height depending on how much lift the prop has.

tropheus29

I do not totaly agree with you (MrMikeG) on this. Lifting props do not cause "planting" of the nose (read bow) as much as strut angle and adjustment (positive and negaitve) affect ride attitude. Think see-saw. Kind of off topic with a little inaccurate info, respectfully.

MrMikeG

Go try a known lifting prop (like a stock H 50) on a cat or mono and tell me what it does!

I'm not blurring anything, I'm trying to state the facts and clear up all the hype.

dicko

Lifting props do plant the bow down. They are trying to lift the transom out of the water & that in turn drops the bow. People overcome this by then putting angle into their prop to bring the transom back down & lift the bow. This is an inefficient way to run your boat. If you use a non lifting prop the thrust can be kept parallel to the keel and give you a more efficient setup which is less likely to hook in a turn.

On a hydro you use a lifting prop to get the stern of the boat out of the water for less drag and this in turn plants the sponsons (at the front) onto the water. If the lifting prop raises the bow, a Hydro would be constantly blowing off the water.

martno1fan

Have to agree thats what ive allways believed too.
Mart

Doubledog

My Feedback: (48)

I see what tropheus is saying coming from the fullscale performance boating world.
Normally when we talk rake, it means it a BOW lifting prop and can handle extra trim angle of the engine/outdrive.
Where in the rc sector, when we talk rake/back cut, it reduces lift.... oposite from what we've been taught in the initial statement. Takes a while to get used to.

lapistola28

i raced offshore powerboats for most of the 90's and that is where i was drawing my information and experience from . i just can't see why it would be the opposite with the little boats ........