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

I have seen 76mph out of it bouncing off the rev limiter with the 26, but that is a rarity.

I have heard that these hulls have a lot of hook in them, but I have not ever checked it. Anyone have any first hand knowledge on this?

Find a proper without the diffuser ring. Give it a try

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.

Propshaft is 3" below bottom of boat. I just checked the back 6' of the hull for hook and it has none. Perfectly strait.

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.

Can't help Joe, but was good chatting with you on Sunday.

Terry

Sounds very familiar. This boat is stuck like a slot car. You cannot get it loose.

There is no change with my std length or lower, but maybe a spacer on the IMCO would help