thoughts on this article?

[spego]

New BASS Times article....wanted to get opinions on this or see if anyone has ever tried this?

http://i41.photobucket.com/albums/e253/spego69/grind.jpg

[stoker2001]

I would like to see better befor and after pics.Roark knows his stuff

[staylor]

...since it's caused a big discussion and lots of confusion on some other boards out on the web. I read it 3 times and pulled out a Tempest and a Trophy to look at the trailing blade edge. Going to the 6 sentences that actually quote Mr. Howell on the mod narrows down the details. The only other useful sentence is when the author states that the mod is done to the "inside edge of the prop where it meets the hub". I submit that what is meant is the pressure face of the blade at the trailing edge next to the outside diameter of the hub. Mr Howell says that if you rub your nail at this edge it will stick- I submit that this is the ground edge of the cup on the pressure side of the blade-which is quite sharp on my Tempest- and it's sharp all the way out to the tips. The mod is simply to take off this sharp edge for the first 1/2 inch of the blade out from where it meets the hub. This is quick and easy to do with a file since you're only removing a tiny bit of the edge itself.The effect of this on a prop is normally to allow a bit more slippage and maybe a slight loss of bowlift. The extra slippage gains a bit of rpm, but more importantly it changes the so-called "angle of attack" of the blade, which on this particular bass boat with a Tempest appears to increase prop efficiency and therefore top end. Because it's only done on the inner part of the blade it doesn't screw up the prop's ability to bite at high engine heights. This is not a new trick, and in fact my stock Trophy Plus 23 came this way from Merc- only Merc flattened the first 1 inch, rather than 1/2 inch. I also have an old OMC SRX Chopper that has the same 1/2 inch flattened section described. Other ways to increase slip and angle of attack include a leading edge cut or just slightly rounding off a sharp leading blade edge. The key is that this mod works on a certain type of bass boat with a specific motor and prop- no guarantee says it will work on other rigs. If you try it and it doesn't work, you can always re-edge the cup in that region with a file or grinder.
Doug

[Euroski]

can you post a picture of the prop with this mod?

[spego]

Thanks for the description staylor! I think I will share this with a few people that have questions about it as well. Thanks again!

The pics would also be useful too.

[The Big Al]

One, he talking about a Triton Bass Boat!
Not a performance boat.


The only thing I agree with him on is taking weight out of the boat.
(I don't, I carry all my **** all the time)

I run a Tempest, It has a vent system, Sending the prop to Performance Propeller and spending the 150.00 will gain a lot more than his hack job on a propeller.

Do not agree with his modification.

I think leaving the prop work to the prop guys would be a better option.

Besides, if it does not work, what ya gonna do? Stick it back together?

[spego]

Just an FYI - I DO NOT plan on doing this. Just trying to understand what it means and why it works. Just so everyone knows....there is no talking me out of it because I do not plan on doing it. I just think there has been a ton of confusion on what it actually means on the internet forums and figured someone would crack it open sooner or later.

I idled over a few rocks and put some dings in my tempest over the weekend and removed the burrs with a a file....and I almost cried doing that. :(

[staylor]

...to my Trophy Plus 23. My rig currently runs best with a Boger modified 21 Tempest Plus or a 21 Trophy Plus modified by Mark's Props. Both props show relatively low slip in the 6-7% range and the calculated angle of attack for the blades is a bit on the low side of optimal for either prop. You can get the math formulas from the Merc Prop Booklet. My idea is to take the 23 Trophy and cut the blade area down, gaining more slip while adding pitch to see if I can improve overall efficiency and gain an extra mph or 2. I did this last winter via a 3/4 inch leading edge cut on the entire blade, holding the same basic contour and outside diameter as the stock blade. I finished the prop and balanced it and ran it this summer with good results. It runs about 1/2 mph slower than the 21 pitch props at the same top rpm, but loses bite at my optimum trim angle. I had the same issue on the stock 21 Trophy and had the cups altered by Mark's Props. This gave better bite and picked up 2 mph. So, this winter I'm sending the cut 23 Trophy out to Mark for the same cup change and some thinning of the blades. If this gains the same 2 mph as the 21 Trophy gained, then my experiment should get the 23 Trophy running as my fastest prop- at least on this particular rig. I'm an engineer in the aerospace industry and learned about props from my Dad, an aircraft engineer from the 1930s- he was a design engineer on piston powered fighters- with big props. If you want to see why prop work is an art, rather than pure science, look up the Navier-Stokes Equations for 3 dimensional compressible flows- there is no exact solution for flows of this type because there are too many variables- and these are the equations applicable to flows from a marine propeller with surfacing blades.
Doug

[spego]

Nice detail. Good info and thanks for sharing. I have to say I have had a few props worked and its amazing how you can tell them what your trying to do and what type of boat it is and send it across the country and get it back and its acts like its not even the same prop. It is an art for sure.

I plan to have mine blueprinted and balanced by Mark but not for a while yet. I need to hit a few more rocks first :(

[The Big Al]

I idled over a few rocks and put some dings in my tempest over the weekend and removed the burrs with a a file....and I almost cried doing that. :(

YOU DID WHAT????

Don't feel bad, I was running a XR6 gearcase and had a Laser II 26p worked by Performance Props it was bad! I mean bad to the bone.

Me and my buddy Ed were running around on lake murry talking about how great it was and wham!
Underwater rock island!

1st day out!

[spego]

I hope I dont have to live through one like that one....man that sounds bad. I would be so pi$$ed!!