Need some prop help
 

I was wondering where I should start with prop testing? The boats a 1989 31 bullet (knotched transom) with stock Merc 525 EFI's. right now the drives are stock brovos but I'm just not seeing good speed at all out of it I haven't found a good prop. So far the boat has done 73 with a set of 5 blades (can't remember pitch but I think they were 28's). Currently it has 4 blade 26's but it hits the rev limiter immediately and will run 70. I was wondering what other people with similar hp have seen speed wise and what drives they have? I'm thinking I am going to need XR's with 2" shortys but want to see what other bullets have before pulling the trigger.
Thanks

If you are hitting the rev limiter you need to go higher pitch. Are they standard bravo 1 non labbed out of the box props.



I highly recommend Auggie at cutting edge props in socal to lab your props. He can change your 26s to say a 28 or 29


i need to know your exact pitch, drive ratio and exact rpm and gps speed and I'll give you a better idea. Tenths count. I'm a prop nerd

I would try some stock 28 Bravo's to get a good baseline or maybe even some 30 Bravo's. You really don't want 5 blades with the deep X dimension.

Not sure. It I always thought it's way better to pitch a prop down to gain RPMs. Rather than trying to add pitch. I don't think you can get a B1 26 anywhere near real 29.

As Griff stated, Id start with a B1-28p four blade, its not a fast hull

73mph at 5,300 RPM. Drives are stock 1.5 year ratio brovos and props are stock non landed 4 blade 26 pitch. I am going to put XR with shortys on it this winter but for now I am just looking for the best props to use to run the shootout in. Next weekend.

Course is just 3/4 mile. Would you hit top speed in 3/4 mile with taller props ? Some boats may do better a little smaller.

Your slip is 16% which is higher then I like. 10-12 is good on a bravo imo



Labbing to a 27 pitch and gettting th4 slip to 12 would net 78 mph at 5200 or 80 at 5300 if it will rev that high

28 at 5100 is 79mph

Your prop slip is at 20 percent right now. you might want to try a 28 bravo 1 with extra cup. Does the boat still have trim ability at full speed. what I am asking if you try to trim the boat at speed does it slow down right as you start to trim or does the bow not seem to rise as you trim but the prop starts to cavitate?

It's at 16. How did you get 20

Hitting rev limiter is 5350 rpms @ 70mph. with 1.5 ratio and using 25.5 for pitch =19% slip.

Well he said 5300 rpm at 73mph not 70 and 26 pitch. And even if the case 19 isn't 20 lol. Either way there is room to improve the setup. He is complaining about the hull but there is a lot room to improve on the prop.


Would hydromotives work better on those hulls then bravos? I know fountains were faster with them

just got a new pair 30s to run. haven't opened it all the way up but been around 80 with more to go and at 3600 was running 60 no hop or tab. have 720+ a side but very deep with TRS.

Theoretical speed for the numbers he provided is 86.994. his speed is 73 MPH sorry its 19 % not 20%

really need to now how the boat trims with the 30s or the 26s that will help with the prop selection and blade style and then give it to Augy and he will make the perfect prop.

Re read his first post.
Bravo 1 props stamped pitch is rated 1/2" to 1" more than actual pitch. Rev limiter on a 525EFI is at 5350 rpms.
Fountains like hydromotives(Q4's) because they have stepped hull that doesn't need bow lift.
Rev limiter on a 525EFI is at 5350 rpms.

Brett, for reference, 32 AT's with HP500's run stock 28 Bravo's or labbed 30's.

Actually only early fountains had q4s and some early ones where straight bottoms. It wasn't until mercury bailed out Reggie that he had to switch to all mercury parts and they had to raise the x to use the bravos and were typically slower

Thanks for all the help! The boat does need more bow lift it rides pretty flat in my opinion. I would also like to know if hydromotices would work. I am searching for 4 blade 28's to run but I came across a set of 4 blade 29 hydromotices anyone know if those would work?

what do you mean?

Text u Brett. Go steal the labbed 28s off my boat if you need or I'll bring the other set next week.

Plug in your numbers Prop Slip Calculator

For Bravo 1 props, reduce the pitch by at least a 1/2 inch of what they are stamped.

Tried some stock Bravo 28 pitch 4 blades over the weekend. Didn't get the 79mph, the boat ran 73 at 5,300 rpm. Does anyone think the boat needs shortys?

Labbed 28s will be faster

Some -2's might help in some ways and might hurt in others. Deeper drives will bite better and lift the bow easier and the boat will respond to trim better.
Your prop slip is still high at over 19% and I think it would just go higher with shorty lowers.
I would try and find a pair of stock 30 Bravo's to test. Ideally, if you can spin 30's close to 5000 rpms, then they would be perfect candidates for labbing.
Custom labbing with some added cup and maybe rake done will get more speed and bow lift.
BBlades labbed my props. They were thinned slightly and cup added. I gained 2-3mph and 150 rpms without having to trim as high.

Also, I would check the bottom of the boat for some hook in the last 4-6 feet closest to the stern.

What did they say the boat will run with 525s? Look for carter on here he has set up a lot of bullets. I don't think you will see 80 with stock 525s.

I don't think there is a "they." He's had the boat a few years and upgraded the power to the 525's recently.