Too much prop slip? What is too much?
06-13-2016, 12:31 PM
#1
Too much prop slip? What is too much?
Trying to figure out why boat is so slow. Current setup on my 28' Advantage V hull is 700hp(dyno proven) 1.5 ratio XR upper and -1 IMCO lower turning 26" and 28" B! 4 blades. I am seeing around 20-22% prop slip throughout the mid and upper rpm ranges. I have tried a std length lower with no change. I have tried a -2 lower which picked me up a couple mph, but blew the prop out pretty bad getting on plane. I have also tried a 27" Hydromotive 4 blade which I could blow out at will. I can turn the 26 at 5400 rpm and the 28 at 5100 rpm with around the same top speed of 71mph.
Here is where I think the problem is. The bow of this boat is heavy, I just can't get it out of the water. I cannot even trim it up high enough to make it porpoise. Once the boat starts coming out of the water, I can keep trimming up until the prop blows out without really changing the attitude of the boat any. It has always been this way with every different setup I have had on it. Would a 5 blade prop help? If so, what brand and pitch? Is 20% prop slip excessive? Transom has a small notch, but would an extension box or ITS help? I realize that this is not the fastest hull out there, but I think I should be closer to 80 than 70. I keep throwing more power at it with very little improvement in mph.
Thanks in advance for the help
Here is where I think the problem is. The bow of this boat is heavy, I just can't get it out of the water. I cannot even trim it up high enough to make it porpoise. Once the boat starts coming out of the water, I can keep trimming up until the prop blows out without really changing the attitude of the boat any. It has always been this way with every different setup I have had on it. Would a 5 blade prop help? If so, what brand and pitch? Is 20% prop slip excessive? Transom has a small notch, but would an extension box or ITS help? I realize that this is not the fastest hull out there, but I think I should be closer to 80 than 70. I keep throwing more power at it with very little improvement in mph.
Thanks in advance for the help
Last edited by snapmorgan; 06-13-2016 at 12:38 PM.
06-13-2016, 03:14 PM
#5
Charter Member # 55
Charter Member
How far is the propshaft below the bottom?????
A 5 Blade will most likely create more stern lift. Talk to BBlades about some cupping and increasing the rake on the Bravo prop.
A 5 Blade will most likely create more stern lift. Talk to BBlades about some cupping and increasing the rake on the Bravo prop.
06-13-2016, 10:10 PM
#7
Charter Member # 55
Charter Member
3" below is fairly high. My 28 Pantera single did pretty much the exact thing as you describe with your boat.
Propslip was high in the low 20%'s and very little reaction to trim.
My propshaft was 3.5" above the bottom and I had a notched transom. It would throw a 3' tall rooster tail at neutral trim as cruise speeds.
First I tried prop work as I described and it helped slightly. Then I added a 1" larger drive spacer and went to 4.5" below.
It carried the bow better and reacted better to trim and slip went down to around 17%.
I picked up about 3-4 mph at cruise speed and 1-2 on the top end. It still never felt like it came unglued from the water until you ran in a good 1' chop.
This was all with bumped up 525SC and Bravo 26" prop.
Propslip was high in the low 20%'s and very little reaction to trim.
My propshaft was 3.5" above the bottom and I had a notched transom. It would throw a 3' tall rooster tail at neutral trim as cruise speeds.
First I tried prop work as I described and it helped slightly. Then I added a 1" larger drive spacer and went to 4.5" below.
It carried the bow better and reacted better to trim and slip went down to around 17%.
I picked up about 3-4 mph at cruise speed and 1-2 on the top end. It still never felt like it came unglued from the water until you ran in a good 1' chop.
This was all with bumped up 525SC and Bravo 26" prop.
Last edited by Griff; 06-13-2016 at 10:13 PM.
