prop slip under or over propped
 

Just got a chance to take my newly purchased velocity 260. It has a Sportmaster -2 lower with a 1"spacer that is stamped 1.36. Currently it has a 26pitch Bravo 4 blade prop. Out of the hole I get terrible prop slip at anything over 2600 rpm. Even on plane I can get it to slip pretty good. I can only get it to run about 4200 RPM at WOT and gps registers 51 mph. At 3000 rpm boat is only moving at around 28 mph. At 3500 I am seeing abot 35 mph. Does this sound under or over propped?

This lower was rebuilt so I am unsure if it is infact a 1.36 or if it is a 1.5...

First of all, get your propshaft centerline depth. Here is a website you can play around with. http://www.rbbi.com/folders/prop/propcalc.htm
Another thing, what power is it equiped with? That will give an idea of what speed to expect. Be sure to get your speed from a GPS, anything else is just a guess.

Speeds I provided are via GPS not dash speedo. It is powered by a 496 mag. From what I have read it should be running around 70. Granted I was running with a full 80 gallons of gas and a total of 3 guys all around 200lbs. Not expecting to see 70 but I would think somewhere in the 60 should be realistic.

Your slip is way too high. If it’s a 1.36 then 33% or if it’s a 1.5 then 26%.
Either way bad!

Check the prop shaft height below the bottom of the hull. You may need to space the drive down or try a five blade prop.

Given your numbers I'm surprised you can't get more than 4200rpm. You could be dealing with an engine not making full power.

What prop?????

Sounds like the propshaft height is way too high or you have the completely wrong prop.

Fixx
 

guys he is only spinning 4200 rpm's @wot..

i would say wrong style prop and may have engine issues

Here is my thinking here. I might be way off. I think the propshaft is too high. THis is causing my slip. Being propped to high is probably why I am not hitting the proper WOT. I think Velocity puts a 1.5 lower and a 24 pitch 4 blade bravo on the 260s.

I think I might be better off getting rid of the sportmaster in favor of a stock Bravo lower and putting a 24 pitch prop on it. This will bring it back to where it was when it left the factory... ANyone want to buy a Sportmaster drive???? I will sell it cheap. Just need enought to cover the cost of a Bravo Lower.

I am sorry guys I was incorrect about my WOT it was around 4500 RPM. I will be taking it out again tomorrow and will keep track of the numbers better and post.

Also the sportmaster case is stamped 1.27.....

If you have a 1.27 drive, and a 26 pitch prop with a stock 496 then you are way over proped. If stock was with a 1.5 drive and a 24 prop, it is not surprising you are not pulling more than 4,500 RPMs. Need to change that final drive ratio. You would have to have some big power to pull that kind of ratio.

The Sportmaster has already been taken off and sold. I have a new 1.5 coming tomorrow. The 26P prop is the right prop for the boat, just had wrong lower gear ratio. Not sure what the thinking behind putting that drive on this boat was...... I bought it that way so I am not to blame