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NITROZ9 Profile
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Registered: 04-2010
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Will cup improve??


A while back Jay told me that he thought is sounded like I need a little cup added to my prop.I am thinking about have him do some work on it and just want to hear what everyone thinks.

Nitro Z9
250 pro
26" tempest plus
5900 RPM
WP 12-13 @ WOT
72 MPH GPS
10" slidemaster

I have worked with the plate and the farther I raise it the better it handles and the faster it goes.Problem is H2O got low so I had to stop.Also the rooster tail is probably 2-4' above the motor.I have to trim up pretty high in my opinion to get the bow up.(no I don't have alot of weight in the front.) I don't run out of trim but the prop shaft is not very parallel with the water.

Would a little extra cup lower my tail and allow me to carry the front with less trim?

Also , would it help my loaded holeshot? It blows out on breakover with 3 people and full livewells at current plate setting.Not bad but a little. I can back out of the trottle a little when it breaks over and then get right back in it.

Should I have it BPed? emoticon

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May/25/2010, 7:57 pm Link to this post Email NITROZ9   PM NITROZ9
 
BARRY J Profile
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Registered: 05-2010
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Re: Will cup improve??


Have you tried a Trophy? Four blades should give you a little more bite and help carry the bow.
May/25/2010, 11:37 pm Link to this post Email BARRY J   PM BARRY J
 
1Nightmare Profile
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Re: Will cup improve??


I kinda think you got the questioniin' backwards, already havin' asked the prop pro but I'll point out a few things. emoticon

Having to trim all out to get the bow up would indicate (As Jay has suggested) that you could use some cup in the tips, which will get your bow up. Right now, the trim is pushing the back-end down so the front comes up. In other words you're using the trim to make up for a deficiency in the prop. You're also losing forward thrust by doing this by pointing the motor downward. Does that make sense?

Theoretically, the prop shaft should run parallel with the world for most efficient thrust. That doesn't necessarily mean level with the pad since the pad is likely running at an upwards attitude.

Ideally, the optimum hull attitude and lift is generated by hull design and prop blade geometry. Negative trim is required for most hulls to get out of the hull with any satisfaction ('cept maybe them light-butted Allys) but the further you have to get into positive trim, the worse off you are efficiency-wise.

I doubt that you really want to "lower your tail" but the front can come up w/o lowerin' the butt. Some cup on the trailing edge effectively lowers your pitch and should help with holeshot, while possibly helping get more stern up on top.

If you are still gaining speed but running out of H2O, you have a couple options. One is the first thing most guys probably think of and that is a low-water intake LU...either complete unit or modify your own. Another option, and a much cheaper one, is to get your hands on a pair of Merc water intake scoops or whatever they call'em, can't recall right off. Kind of a fancy term for 2 flat pieces of metal that get drilled, tapped, and screwed to the LU partially over the water intakes.

What they do is when the upper intakes would otherwise be exposed to air, the scoops draw water to them instead. Of course, these are only good so long as the lower intakes are still at a height that they're catching good water.

I effectively did the same thing by gluing and trimming rubber stoppers in the upper intakes on my 'Rude. Allowed me to go up a good 1/2" higher than I otherwise could have. Depending on the design of your intakes, you may be able to follow this method.

If you had the right mods on your prop and able to make best run without the extra positive trim, you may be able to keep good H2O. Hard to say.

You may have mentioned earlier with Jay what your measurements are currently but I don't see it here. I like and use a Trophy but I ain't running the performance, hp, or rpms that a lot of people do. It seems to be a general consensus among prop guys (pretty sure Jay has mentioned it) that Trophies don't do well when they are being "surfaced"...That is, the blades are coming out of the water when rotating over the top. They apparently have his habit of slingin' a blade. Otherwise, I like the torque that a 4-blade loses over a 3-blade. I'll take a wild guess but what you got hyd steering, so that's not an issue for you.

So far as the BP job, guys that have had that done can give informed opinions whether they thought it was worth it. I might think that the more things you have done to the prop and the less % of the cost that the BP adds to it, the easier it is to say WTF? emoticon

Just my non prop-work-educated opinions. As I tell people concerning a host of topics....That and a buck'll get ya coffee at the truck stop...regular price...a buck. emoticon

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Good things comin' outta Crap!


May/26/2010, 4:26 am Link to this post Email 1Nightmare   PM 1Nightmare
 
1FASTLASER Profile
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Registered: 02-2010
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Re: Will cup improve??


Where are you at as far as shaft to pad measurements??? That will help Jay out as far as whats going on....Jerry is about dead right on about where to add the cupping....not only on the tips but the trailering edge as well. Jay as told me that trailering edge cup will add to stern lift and of course tip cup will bring the nose up more ....Plus it will drop the rpms some but add more efficient thrust which turns out to a faster WOT.....as far as any mods to the lower you gotta be careful about doing them if your motor is still under warranty.One of the old tricks is plugging a couple of holes in the water intakes and that will allow you to jack a bit higher.....now that is on the older units and I cant say for sure if that applies to the newer style units....Jay could anser that better.

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LASER'S n MERCS....SETTIN THE WATER ON FIRE
May/28/2010, 8:33 am Link to this post Email 1FASTLASER   PM 1FASTLASER
 
1Nightmare Profile
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Re: Will cup improve??


Correction for terminology. I'm sorry, I'll blame this one on 0430 in the morning. emoticon

When you commented about getting the "tail" down, I was thinking "stern" --- not ROOSTER tail... emoticon Yeah, you're right that it's little high. emoticon

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Good things comin' outta Crap!


May/28/2010, 8:58 am Link to this post Email 1Nightmare   PM 1Nightmare
 
NITROZ9 Profile
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Re: Will cup improve??


O.K I know this is not going to sound right to you because of the boat that I have but I just went out and done this.

I leveled the pad and the plate on my lower unit. I took a 6' level and held it to the bottom of my pad and let it stick out to the bullet on the lower unit and the way it is right now is 2.5 inches.Now that is the way I ran it at Table Rock in April loaded to the gills.

Now before TR it was a 1/2 inch higher.The reason I droped it for TR was the week before I had three people in it and it wanted to blow out on breakover.I had 12 psi H2O pressure but and ran good and handled good.I figured that I should lower it for Table Rock because of 2 people full livewells and alot of extra crap. I had all of my poles , extra shoes, extra clothes,even had my extra seat.All stored in the front storeage.The boat ran good at the Rock ,even got my 72MPH loaded like that minus the wife of coarse.The rooster tail is way up there compared to the knee high Jay likes to have.Probably 2-3 feet above the motor.

I know different props like to be ran at different depths so should I go with cup or try a different prop ,like a trophy or something.

I know people say these boats like the 3-3.5 range on the prop height but I'm telling ya my prop won't throw a tail at all at 3.5.
Also at 3.5 68MPH is the best. emoticon

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May/28/2010, 5:47 pm Link to this post Email NITROZ9   PM NITROZ9
 
Jay Martin Profile
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Re: Will cup improve??


Cup it!!

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www.jaymartinpropellers.com
May/28/2010, 9:38 pm Link to this post Email Jay Martin   PM Jay Martin
 
1Nightmare Profile
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Re: Will cup improve??


Givin' up good info here. I'll digest a portion for ya. Short answer: the prop/shaft measurement is relative to amount of setback. Let me throw out some facts that muddy the equation:

When water comes off the rear of the pad it starts to rise since it is no longer being displaced by the hull.

A hull doesn't run with the pad level to the world. The pad runs uphill.

We use pad to shaft measurements as a standard by which to compare only.

Between the pad running uphill and the amount of trim being a constant variable, the actual vertaical seperation between pad and shaft aren't really able to be quoted in any practical sense.

In the end, the performance isn't actually derived by the distance between pad and shaft. It's the location of the prop, vertically, in the water column BUT we can't measure that.

Remember the water starts to rise when coming off the pad? For a given amount of setback and a given pad/shaft measurement, the actual vertical location of the prop in the water colum is going to differ.

Does that help you see why you set yours at 2.5" with a 10" setback whereas you've heard 3-3.5"? These may be measurements with lesser amounts of setback.

Not to mention that the more setback changes the rear to set lower.

Something to think about for now. All I got time for at the moment. If you're not totally confused yet, I'll be back! emoticon emoticon emoticon

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Good things comin' outta Crap!


May/28/2010, 10:08 pm Link to this post Email 1Nightmare   PM 1Nightmare
 
NITROZ9 Profile
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Re: Will cup improve??


I'm pretty sure that the other z9's and z8's with 10' setbacks that I have been talking to are running in the 3 1/2 to 3" range. I know all boats are diferent but I would not think that much.I can run it at 2" by myself and do good. emoticon

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May/28/2010, 11:04 pm Link to this post Email NITROZ9   PM NITROZ9
 
1FASTLASER Profile
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Registered: 02-2010
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Re: Will cup improve??


Hey son......Jay said it in a nutshell...CUP IT.......after getting it Balanced and blueprinted with some cupping added you wont beleive the difference. Trust your ole man on this one. Dont change the plate setting right now. After gettin the prop back from jay bolt her up and run her like you normally do as in load weight and everything else. Then jack her 1/4" at a time. That brief second you drop pressure while climbing on pad shoule be ok as long as when running full tilt boogie and trimmed you can make a turn and dont loose pressure. Hope I am splaining this so you can understand what I am saying. You might even be able to jack the motor back to the height you had it before you went to TR and dropped the plate.

Nightmare has a fantastic way with his splaining and his splanantion is DEAD ON ACCURATE.....

Ifn ya want gimme a holler ifn ya need some more splaining. Tell the wife and chillens I said hey.

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LASER'S n MERCS....SETTIN THE WATER ON FIRE
May/29/2010, 5:56 am Link to this post Email 1FASTLASER   PM 1FASTLASER
 


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