Propping for 2" shorter lowers.
 

I'm considering adding 2" shorter lowers
to my boat, but am wondering what to
expect on prop issues.

For those of you have went to shorties,
did you experience an increase in RPM ?

If so, was it enough to have to increase
pitch ?


Here's my Setup

33 V bottom 575SCi's

XR's on stellings boxes.

Propshafts approx 3" below the
bottom of the boat.

Been running 32 labbed bravo's

getting on plane sux.

Cruising speed, seems to be alot of slippage

Top end, mid 80's.

Tried a set of 32 Maximus

Getting on plane.....much better.

Cruise speed......at least 5 mph better.

Top end.....a tad faster, probably more
due to the fact that I wasn't on the rev limters
like I am with the 4 blades, but only pulling
4800 rpm.

So, the $ 64K question is,

If I go to the 2" shorter lowers
will I be able to spin the 32
5 blades up in the 5200 rpm range ?

Any replies appreciated.

JT

Re: Propping for 2" shorter lowers.
 

Post your tessting / performance numbers so we run some calcs and look at propeller efficiency with your current set-up.

Julie

Re: Propping for 2" shorter lowers.
 

With the 32 4 blades ( Mazco is stamped on the hub ??)

Cruise, 3600 rmp='s around 52 mph
top end, 85.2 at the rev limters ( 5400 )

With the 32 maximus, ( assumed labbed, have the
"secret number coding on the inside of the hub ")

Cruise, 3600 rpm ='s around 58 mph

top end 85.9 @ 4800 rpm .

My thoughts are that, getting the 5 blades up
a little higher will free them up a little more,
allow them to turn a few more rpm,
also less drag, all this should get some gain
up top.

Re: Propping for 2" shorter lowers.
 

With 1.5 gears running the 32P Mazcos you have 20% slip. This is assuming that your Mazco's are true 32P props. This is an extremely inefficient set-up. With the Maximus you have 9% slip which is great, however you are at the low end of the torque band of your motor. At 9% you are at the appropriate drive heigth with that diameter of propeller. The dimaeter of your propeller, the Maximus is very relavent as to the drive heigth. If they are at the full 15 5/8ths diameter than it may explain your I would like to see two things.

1) Performance numbers with Bravo I props.
2) Your motor at 5200 RPM at WOT.

Julie

Re: Propping for 2" shorter lowers.
 

1) The "mazco's" are Bravo 1 props,
I'm assuming they've been "modified"
by mazco, sorry for the confusion.

2) I'd like to 5200 with the 5 blades too,
but 4800 is all I can get with the 32 max's.

I'm suppose to be getting 30 pitch maximus's
from the dealer I bought the boat from,
but it seems to be taking quite a while
for them to get them ????

Those might get the rpms up to the proper
range, but, what if I go to the shorties,
will I be against the rev limiters again ?

Re: Propping for 2" shorter lowers.
 

Possibly so! If you have somewere around 10% slip than I would not recommend going to the shorties. Run the 30P Maximus props and post the results or feel free to call me. You should have the info you need to make a decision then.

Julie

Re: Propping for 2" shorter lowers.
 

I have a Brand New set of Maximus 5 Blade 28" Pictch. They have been labbed, thinned and will fit a 2" shorter Bravo. This will raise your RPM's

Re: Propping for 2" shorter lowers.
 

Jaayteee,

What year and model boat do you have?

I have a feeling the Bravo 1's have been modified where there is very little cup in them. The performance numbers from them may not be indicative of a typical Bravo 1 prop. Have you ever tried a stock set of Bravo 1's on the boat? With the Maximus props it's important to state the diameter as well as the pitch.

From what I see at this point I wouldn't run out and get a pair of 2" shorties. Higher is not always faster!!!!!!

Matt

Re: Propping for 2" shorter lowers.
 

Boat is a 2002 Baja 33 outlaw.

I personally havent tried other Bravo props
on it, but the dealer I bought it from has
tried a few different sets on it.

I ran the 5's again last weekend,
played a little more with the trim,
running the trim out to 7 on the indicators
got the rpm's up to 4900-almost 5k,
speed went up about 1 mph,
was throwing alot more water,
didn't feel as "hooked up" as it does
when trimmed to 6 on the indicators
( but it was a tad faster :D )
Going past 7 didn't net any gains,
just more spray.



I'll check on the diameter of the Max's

We put it away for the winter this
weekend, I'll probably just wait 'til
I get the 30 max's and see what they
do.

I also have a 1" of adjustment in the
extension boxes to play with.

The cruise speed and out of the hole
performace is soo much better with the
5 blades, I've got to believe that they're the way
to go.

The only thing that bugs me about them is,
going in to gear, with all that blade area,
they bang pretty good.

With Stellings boxes, the factory rubber coupler
isn't there for any shock absorbtion ......I don't
know how, in the long term, what effect it's going to
have on the drives.

Re: Propping for 2" shorter lowers.
 

Shorties on Bajas can be a dangerous proposition. However, you have some great efficiency numbers for your boat. Raising the drives would free up the props to turn higher rpm. You would have less drag from gear cases and propeller material. But, your boat likes help carrying the bow and raising a stern lifting propeller closer to the surface could out weigh the gain of less drag in the stern to more drag in the bow.

If you decide to try this, remember, full size diameter Maximus propellers won't fit under some shorty lowers.

We also have test 30 pitch Maxmus if we can be of assistance.