Do i need a different prop?

[msojjo]

Ok, i appreciate any help i can get on this one. I just purchased a 2000 Starcraft 2010 with a 350mag/300hp with a Bravo 1 outdrive. I just had a merc remanufactured long block put in, so i have been easy on it so far this spring trying to break it in. I have about 10 hours on it now, so i decided to try WOT for a bit, because i know i have the wrong prop on it now. First of all i started off with a 15X22 pitch prop four blade Mercury Marine Bravo 1 SS prop, with a little ding in one of the blades, does that make a big difference. I could not get the thing out of the water no matter how hard i tried with no weight in the bow. The guy i purchased the boat from had a 21 pitch prop that i tried over the weekend. I measured it, and it came to be a 14.25 X 21 pitch. The prop is a Mercury Marine Tempest three blade SS, but has been reworked, and i suppose is a spare prop now. I don't think there is any cup in it, or rake. But on this one i still can't get the boat out of the water, if there is no weight in the bow. The 21 pitch prop is the one that i tested the WOT on. so here it goes, and i haven't seen anything on any other threads about this. I can only get 4000 rpm out of the motor, and i know that i can damage the motor with that low of rpm. I should be between 4600 and 5000.

So, the performance that i want is to get the boat out of the water and get it to plane faster, pull up skiers and tubing.

Current prop is the Merc Marine Tempest 21 pitch three blade SS.

14.25 X 21 pitch, reworked.

WOT should be between 4600 and 5000, but i am only at 4000. Speed in on spedo at 58. This was not at normal load. Empty tank of gas and just me, 200lbs.

It has the 350mag with MPI fuel injection year is a 2000. Rated at 300 HP and has the Bravo 1 with the 1.50 gears.

The boat is a 2000 Starcraft 2010 fiberglass 20ft boat. On my title is states the boat is 3200lbs, so i'm assuming thats with the motor. Has a 45 gal. fuel tank.

Any help with this would be great.

 

[180shabah]

Re: Do i need a different prop?

Did you just do all of your break in time, being over propped by 3-5"

Time to look at props in the 17-18" range.

 

[msojjo]

Re: Do i need a different prop?

no i didn't finish the whole break in time, but the dealer told me as well in the book that you can start wot after about 10 hours or so, just don't do it for long periods of time.

 

[180shabah]

Re: Do i need a different prop?

no i didn't finish the whole break in time

Don't really care if you start doing short WOT runs at 1hr, my concern is that you have been running too steep of a pitch for this first 10 hours and lugging the engine during break in.

 

[steelespike]

Re: Do i need a different prop?

No sense crying over spilled milk whats done is done.I don't think gently driven we could tell the difference in a tear down. I'm not the guy to help select a big time prop but it appears you need some stern lift and little or no bow lift.
4 blades are said to assist hole shot.
Be sure it trims in all the way.Perhaps trim tabs are needed.

 

[180shabah]

Re: Do i need a different prop?

Starting point would be to drop down to a 17" to get a good baseline. Also we need an accurate speed via gps, cause your speedo is WAY off.

Do you have a prop exchange dealer in your area?

 

[msojjo]

Re: Do i need a different prop?

Well by running the motor over pitched, i really hope that i didn't do any harm. I won't run the boat until i change the prop. I know the spedo is off, i was told they could be up to 6 mph off. If that's the case i would be running in the 50 mph range. I have been asking around different dealers in the area about exchanging props, i'm told they have too much inventory of used props. I found a used Laser 2, 19 pitch prop, for $100.

 

[180shabah]

Re: Do i need a different prop?

I know the spedo is off, i was told they could be up to 6 mph off

...or more.

1.5 ratio + 21" prop + 4000RPM = 53mph +10% prop slip = 48mph

Of course you said that your tempest was "reworked" so that would through off the theoretical speed, and we don't actually know your prop slip, and.....and....and....

What we do know is that you are 600rpm low at WOT. rule of thumb 1" of pitch = 200rpm so you need to drop 3" just to get to the bottom of your WOT rating, 4" would be better.

 

[msojjo]

Re: Do i need a different prop?

So are you thinking a 17 or 18? I was told by one of the dealers that once the new block loosens up, i could gain a few hundered rpm by the end of the year?????? Do i take that into consideration?

 

[180shabah]

Re: Do i need a different prop?

So are you thinking a 17 or 18?

From first post...

Time to look at props in the 17-18" range.

When all is said and done, you want to be at the TOP of your WOT range, not the bottom. It will be better for your engine, fun factor, and wallet. There are 20+ choices for 17" props here at the iboats mall, the two most popular being the hustler and the amita 4 blade. Both aluminum. If you want to get another SS, prop There are several to choose, but I can't personnally recomend one. I'm sure hwsiii will have some suggestions when he gets back.

 

[msojjo]

Re: Do i need a different prop?

thanks for the help, that's where i'll be starting. Does the Diamater of the prop matter as much as the pitch? I'll be pushing a big boat with the bravo 1, so do i want to keep clost to a 14.5 to 15.25?

 

[180shabah]

Re: Do i need a different prop?

When looking at performance props diameters will be all over the place from about 13.5+. When we start talking about diameters of 15+, those are typically for BIG boats, cruisers etc....

Most of the props you will be looking at will fall 14.25 - 14.75 in diameter. A high five might drop below 14".

 

[msojjo]

Re: Do i need a different prop?

Thanks, i'm looking through used ss props, so i'll be looking for between a 14 and 14 diam. prop with a pitch from 17 to 18. Thanks again for you help.

 

[msojjo]

Re: Do i need a different prop?

Hey, 180shab....., i took your advice and found a 14.75X17 Ballistic ss prop, used but very nice. I'm going to be trying it out this weekend and i let you know how it's working. My only concern is if i did go to low, do i have to worry about anything (the obvious overreving of course) but it is ok to run a prop that's too low? Just not too high, right?

 

[tdrudd87]

Re: Do i need a different prop?

You are safe, just keep an eye on the tach and don't overrev.

Terry

 

[msojjo]

Re: Do i need a different prop?

thanks tdrudd87.

 

[msojjo]

Re: Do i need a different prop?

Tried out my 17p 3 blade SS prop this weekend, and performed great. My holeshot was much better, wouldn't mind more, but i realize its a really heavy boat. I got my rpms to 5000 with out any problem, i may be a bit underproped, i may look at a 18p 4 blade prop. My speedo is way off, and i forgot the gps, but my guess according to the spedo, i'm at low 50's which is plenty fast for me.
Thanks to thoes who helped me out.