JohanSweden

Hello guys

I have a little bit of problem with my setup and asking for your advice.

I have a Chris Craft 260 Stinger 1987 hull.
It has a Mercruiser 496 Mag, upgraded to a HO with 425hp with Whipple Stage 1 upgrade in it.
(5450rpm max range according to whipple).

Bravo One X/or XR (I dont know the exact gear ratio). Sport Master lower on a extentionbox as you can see in the picture.

I run this setup with a Bravo 4-blade 26p prop.

I see this numbers:
Speed - 50 mph
RPM - 4800 rpm

I count that the boat weights about 2500 kg/5500 lbs

The problem now is that I get a huuge prop slip with the prop slip calculator. Around 30-40% prop slip, even if I put all available gear ratios in the calculation for my drive it is between 30-40%.

Here is a picture of the transom of the boat and you can see how the prop height is.
I dont have the exact numbers of the prop height/x dimensions unfortunately...






I appreciate all the help I can get!

Thank you

JohanSweden

I tested the boat yesterday again and got these numbers with 30-40% prop slip even if I count with 1.26, 1.35 or 1.5:1 ratio.

Top speed: 42 knots / 48 mph
Max rpm: ~4500 rpm


I bought a 0,5” spacer to my Sport Master and I hope it will arrive next week.

Starting with that to see if I can get less prop slipp.

jeff32

Wow ! Wicked set up! Never heard of a big single blown 26 stinger! Had one twin 350...

you sure have a problem... or 2 !

i would firt make sure of drive ratio even only if you remove drive turn upper drive shaft one turn and see roughly how many turn it does to prop shaft, 1.5? Or even a little more? That could give you and idea if it is only s slip problem

of course 50 mph for 4800 is way to slow no matter what drive ratio is
trying to lower the drive is a good start! How was it set up before when it ran fine?

JohanSweden

Thank you!
Just trying to figure out how to make it go fast

My plans is to figure out what gear ratio it is. Then put the spacer on.

But now a guy got me confused.
He said the water pickup that is located on the right side of my drive on the bottom of the transom is located wrong. He means that it should be on the left side.... Can the water pickup be the problem with the slip??

JaniH

the water pickup sure can be problem, if the propeller covers the area where the pickup is. Sorry Johan but i have missed this picture or have not even seen it.

JohanSweden

this is so confusing.. do I buy the spacer for no reason then

JohanSweden

Here is some more pictures

JohanSweden

So my question to the experts, if you look at those pictures.

What do you think is the cause of the prop slip?
the water pickup or the high drive mount?

Oger

I am not an expert but if you want to hear my opinion on your issue.
Before I would install a spacer I would try another propeller.
May be your prop is just out of spec.
If possible I would try a left hand prop.
Then the pickup in on the correct side and you know if the location of the pickup is the problem.

JohanSweden

thanks, I can try this after I have mounted the spacer. Got it today so I will take the boat up and take the sportmaster lower off and put it on place. Then try the boat to see if it made som difference