I have a 43 foot Black Thunder with twin 735 HP, Huber 1000 trans, #5 Speed Master with 3" of spacer. The hull has two steps. The current props are 4 blade 17" diam. by 28" pitch. Cruise is 3500 rpm & 50 MPH. top speed is 5200 rpm & 71 MPH. My slip is about 20%. I would like to go to something other than cleavers due to safety when swimming (3 cuts this year so far). I think I need a round ear 5 or 6 blade. Do I need to change the prop rotation to out? The original Bravo's were rotating out. Thanks for the help. Joe Murray

Joe,
Did you do a conversion from Bravo's to #5's?
If so, what were the performance numbers before and after the conversion?
What is the gear ratio?
Have you tried other props on the boat, different diameters?
You have a 3" spacer, did you test the boat with other size spacers?
Who is the manufacturer of the props on your boat?
How does the boat handle, get on plane?
Is there a rooster tail at WOT?
There are many considerations when setting up a boat like yours, many more than can be covered on this board. If you like, give us a call and we may be able to help you get the boat running better.
Matt

There are many questions to be answered. Your slip #'s and questions lead me to believe you are running bow heavy. These boats do tend to run flat and have had issues with leveraging the stern. I assume you are turning the props in (tops toward the center of the transom). If so, this will help to carry the bow. Turning them out will hurt not help. Working with the diameter will help too.

Round ear SSM props are hard to find. We just customized a set from HOSS that went on a Cigarette with Arneson drives and the boat picked up 4mph and carried better. We also do specialty round ear work on Kiekhaefer series propellers if your interested.

The boat was an original Bravo boat with boxes and drives lowered 2" when the Stellings boxes were gutted and Imco torsion shafts installed. With HP 500 per side and 1.50 ratio Bravo and 28 pitch 4 blade Bravo 1 props boat would cruise 45 MPH @ 4000 RPM and run 68 MPH @ 5200. With #5's and no spacers boat would not plane. With #5's and 2" spacers boat would plane OK except with a heavy load it was tough. With 3" of spacer on #5's boat planes fine with any load. The current props are Merc SSM cleavers 17" diam by 28" pitch 4 blade. Throttle Up cleaned up the SSM props for me last spring. With about half drive trim at WOT I do get a rooster tail. Joe Murray

Joe,

Lets talk about your motors, Do you have dyno sheets on them?
If so at what rpm is peak torque and peak horsepower?
Are they supercharged or naturally asperated?
When you trim to half trim is the boat still picking up speed?

Matt

Dyno sheets were @ TMP in Slidell, LA so they are gone. Engines are normally aspirated EFI. Peak torque should be around 3800 to 4200 RPM. More trim past 5 or 6 on the indicator does not add speed. As stated before I think I might need to go to a 5 or 6 blade with less pitch and diamater. I definatly need less slip. With the current cam power falls off above 5400 to 5500 RPM. Joe Murray

Without knowing your current gear ratio it's hard to say for sure but I think your slip is too high. The slip was excessive with the Bravo drives as well.
The 5 or 6 blades may not be your answer as they will tend to lift the stern and possible increase the slip even more than it is now.

The round ear props work well on Arneson V bottom boats to help lift the bow. The problem some of our customer have had with the Hoss round ear props is keeping the blades on. With a drive, like the #5, that has positive trim capability, you shouldn't need the round ear style props.

You may need to lower the drives even more than they are now. Considering how expensive speedmaster style props are I would hate to see you spend a lot of money for a pair of 6 blades and they be even worse than what you have now. The 4 blade props you have now should get you close to where you need to be.

Matt

Gear ratio is 1.5. Drives can not be lowered any more unless I go to SSM #3A's. The 3A's would be 3" deeper in the water. I calculated slip at 18-21% depending on RPM/MPH. I think the 3A's would be too deep in the water. The "X" was set with the nose of the bullet even with the last running surface and the spacers were added to tune the driveability of the boat. With the price of gas I am looking for more efficiency. Joe Murray

Spoke to BBlades today. I am going to try their prop rework at the end of the season and try to find my missing MPH. Joe Murray