Hey Kenny

[Texasmark]

Help me on this ole buddy.

Was playing some more over at the Merc Prop site and gave them a set of parameters.

They came back with a High 5 at 12 3/4 x 24P or a Trophy + 13 3/4 x 24P (4 blade).

Confused as to why the inch drop in diameter when upping the blade count for the same set of parameters.

Maybe others trying to decide between the two types might be interested in your answer.

Mark

 

[Crownie2]

Re: Hey Kenny

The additional blade area provided by the extra blade(s) means the diameter can be reduced while not adversly affecting the blade area.

 

[Texasmark]

Re: Hey Kenny

Ok my man, so what does that buy you? I would think that if you are running like the big dogs do (the ones that don't stay on the porch d ) you want that extra diam to have something to stick in the water when you are jacked up 4-ish inches and set back.

Mark

 

[Crownie2]

Re: Hey Kenny

True to a degree - but the extra blade area theoretically will help at higher elevations by keeping more blade in the water - like a Maximus prop on an ocean racer. But that is not really what the high five is meant for and they are sort of assuming you are not doing extreme elevations with a high five.

Also, this points out that a prop calculator cannot be all things to all people - just guidelines for most applications.

Bob

 

[xtraham]

Re: Hey Kenny

good question Mark, what are the advantages and disadvantages of diameter? I always assumed that diameter grabbed more water, If I were to remove the 26"X26" prop from my big boat and install lets say a 14"X26" I am sure it would not move at all........ so what dynamic effect does diameter vs pitch have? would a larger diameter less pitch be more efficient ?

 

[Dhadley]

Re: Hey Kenny

Mark, what motor are you using?

Did the parameters you provided include intended use, X dimension and hull design?

 

[Texasmark]

Re: Hey Kenny

D, if you punch in www.rivertrail.com and look at the pic in the middle of their home page, that's essentially what I'm running, except mine is custom built (by them, with minor differences) for Dallas' Travis Boating Center (Called a Travis Edition) and the Yammie is replaced with a 3 cyl 2.33 geared 90 hp Merc. Specs for the 17 footer are in the site.

It's alum and has 3 distince steps in the hull giving you a 3 step pad. At WOT you are only on the last step and only on about 3' (length) of it as the spray exits at and aft of, the corners of the chine/transom interface. Once you get over 35, prop slip goes way down and she takes off.

There weren't any questions asked about performance and all; mostly generalities. The section was for console steered, aluminum boats to 22'. I assumed that would differentiate between this and a "lard arse" BB that needed significant whoopie to get out of the hole.

I was just curious at the diversity of their answers given the fact that we were talking about an alum boat, and the big difference in dia on the 4 and 5 bladed props.

Mark

 

[Texasmark]

Re: Hey Kenny

Correction: www.rivertrailinc.com. If you leave the "inc" out you get the wrong site. Sorry.

Mark

 

[walleyehed]

Re: Hey Kenny

I think diameter, in several cases, gets blown WAY out into space!!!
We're talking 1/2" around the outside at the TIP....a very small area. Now, if we were to take 1/2" cross section out of the blade at the mean chord, well, now that would be different.
The proper blade area is built into the prop as whatever the manufacturer has found to be best for a fairly specific application...this is all taken into account in testing prototypes before they settle (in "most" cases) on a certain design.
Often times, the prop recommended is just the prop (in their line) that most closely met the needs punched in.
Mark, when ya get done messin' around and decide you want that boat to fly, let me know.....8)

 

[Ron G]

Re: Hey Kenny

dddi'm on boardddd