Need some prop advice!

Ok, we picked up a new prop with ACME's recomendation. I wanted someone in here to check this over to make sure we got the right thing:

2004 Tige Switch V
335HP 340MP
Ballast: 1500-1700lbs

The original prop was a 3 blade, 13 X 12, whatever came stock with the boat
We upgraded to a 4-blade 13.5 X 14.25, upon acme's recommendation about our ballast amount.

After trying it out tonight, it seems like the hole shot is significantly slower, but the RPM's are a lot lower. For instance, the original prop @ 30 MPH (no weight) was 3K. Now, with no weight, we are pulling 2300 RPMs at the same speed.

Does this sound like the right prop? I want to trust ACME, but I really don't know what to expect, I know very little about props.

Thanks

(Message edited by garret_s on July 03, 2007)

That's not the right prop. I think ACME made a mistake and thought your had a different gear ratio in the tranny. That would put you at about 1700 pulling a boarder and you are not going to have enough torque.

let me ask this question: how many RPM's SHOULD I be at while pulling a boarder at, say, 24?

It sounds like you have a 1:1 transmission. The prop suggested would be for a gear reduction transmission of some type. I would think you would be better suited with a 13 X 11 for your application.

Eric @ OJPROPS.COM

Ok, wait a minute:

If I am running more weight, why would I want to pitch down? My original prop was a 13 X 12 (though it was a 3-blade), so wouldn't it make sense to have a higher pitch when running more weight?

Someone made a mistake. Think of pitch as the gears in your truck. If you put a heavy load on your truck, you would have to down shift to maintain rpm. Imagine loading up your truck and starting off in second gear...that's what you are doing with that prop (simplified). I'm not an expert like Eric or Karl from Boarditup but I researched it when I upgraded. Think lower pitch=lower gear=higher rpm.

...for sure a lower number pitch.....for example when I first got my boat I had a 19 pitch prop...couldn.t hold speed or get out with weight....now I have worked my way down to an 11 pitch and have torque coming out of my ears....the boat will sink before it cant pull the weight anymore.

great! Ok, so here is the next question: Why is the prop that is listed as correct for my boat on Wakeside have a higher pitch than my stock 3-blade?

http://www.wakeside.com/page/W/PROD/tige_v_drive_propellers/acme_4_blade_propeller_857

The stock prop listed on that page is a 17.5" pitch and the loaded prop is 15.5".
The loaded pitch is much lower than the stock size. But those pitches are only used on geared transmissions with a ratio like 1:1.5 (I don't know exactly what the ratio is for that listing) and it sure sounds like yours is a 1:1. So that 17.5 pitch would be like a 12 pitch on a 1:1.

Sorry Garret, I missed one of your questions.
The pitch of the prop is the number of inches that it moves forward in one rotation. (not quite but almost) So a twelve pitch moves the boat forward 12 inches each revolution of the prop. An 11 pitch moves it forward less so it does not work as hard. If you load up the boat, that takes more work so it is to your benefit to go with the prop that is not working as hard.

With a transmission that has a gear reduction you can use a higher pitch (like 17) because the engine turns one revolution before the prop turns one revolution. So maybe the engine turns once and the prop moves the boat 12" forward but the prop has only turned 2/3 of a revolution.

There, now it's all clear as mud for you...

...i had to buy 5 props in the process of ending up where i did.....your props cost substantially more....so you will have to get as informed as possible and then hopefully pick the right prop.....if you can find anyone else with another boat maybe they can let you try their prop if it is in the range your looking for and obviously fits your boat. I did this with another guy who had the same engine as mine....it saved him buying
as he tried all mine to find the right one.