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

Perhaps it was an affordable option for the previous owner to solve an issue. Either not realizing or caring what the outcome was. Regardless I would check out to see what they typically come equiped with from the factory and go from there. If I recall Merc use to put the 1.36 drives on 525's and up. You should still be able to prop for the drive you have otherwise get the 1.5 like you said, you'll be much happier. Years ago when I played around with different drives I found the 1.36's robbed power. If you were getting slippage you would be potentially over reving. Doesn't sound like that's an issue. Also be sure and check your engine over. At the very least do all the basics. Timing, plugs, wires, cap and rotor. Be sure and check your timing right away. (very important)

How does the engine sound at an idle and under a load?

Did you buy a standard XR lower? The sportmaster will just slow you down at anything under 80-90mph

There were two things happening here. First thing the X dimension was too high. Which was causing major prop slip out of the hole and even up on plane. I could go from 3000 rpm - 4000 rpm in under 1 second, without seeing any change in speed. The second issue was the gear ratio. I was turning a 26p prop with a 1.27:1 Sportmaster. This is why I was unable to reach the proper WOT. THis engine runs fine and is not the issue.

As far as throwing on a Sportmaster as affordable option, say what?:eek: That's a $5000 + lower.... I was able to sell it to a member of OSO for $2k. Which I used to purchase a new SEI Bravo lower and left me $1k in my pocket. So the boat will be back to the way it was when it left the factory.

just curious why would that slow u down? if both were 1.5 ratio whats the differance?

now you got to test props . i say a 23pitch if its stock???

The front of the case is shaped different and it has a much longer skeg.

I am learning as I go.

The Velocity 260 w/496 mag came stock with a labbed 26p Bravo 1. THis was confirmed with a call to Velocity. I have the original prop. 23p would be to small.

it funny i broke my skeg and had a new one welded on and it is longer .i was going to cut it down to size . but i try it frist and it did help from chine walking . it did that real bad when it was broke .so i am leaving it the way it is . now when i have 25gallons of fuel just me in the boat the boat chine walk a little . so now i puting longer trim tabs :drink::drink: The Velocity 260 w/496 mag came stock with a labbed 26p Bravo 1 that then would be the prop good luck:drink:

There's been heaps of debate on lowers being better than others and some being faster than others.Here's my take from real experience.The sportmaster is a stronger case and the original,not an aftermarket copy.With the skeg,if you were making a lower for a performance boat knowing that performance boaters run aggressive heights(call it the x dimension)and that skeg is used for steering and control would you want it shorter?This applies to drives run at heights to achieve maximum performance.

Good luck with it Bradley.That was a real find and as you put it a "diamond in the rough".

bajabob,
I read this post 3 times and just wondered if your were :drink::drink::drink: while you wrote it? LOL...

maybe a little:drink: but its true about the skeg. my boat at top speed there is hardly any of the boat in the water. i broke most ofthe skeg off :eek:.the new one is about 3in longer i try it and the boat handle better. http://www.seriousoffshore.com/forum...p?t=834&page=3 look at this picture of my boat and you will see there not much of the boat in the water. its just my finding about my boat.. i just thouth i put it out there about the skeg :drink:

That's pretty funny. On the flip side I see what your saying after blowing up your pic. I haven't really seen to many 24's run like that. Surprisingly your not throwing a very high rooster for your boat running the way it is. Real flat though... You need a flat step bottom. LOL... How fast do you run with your 600hp?

well i run 80mph all the time i run on the river so going with the tide and wind i got 84.6 that with 622 hp dyno drink: i got my motor redone more ponys . i will be testing in 3 weeks :drink::drink:

I got out to test it now that the "stock" set up is back on the boat. It jumped up, out of the hole perfect. I got it up to 62MPH @ 4500 RPM. I wasn't able to pull any more as the stock flame arrestor is plugged up with salt and sand...... I tried to clean it but it's junk. I am going to put a K&N on it and see how it does. It was cold, windy, and rainy so I didn't spend much time trying to trim it right. I just wanted to test it real quick so I could feel confident the repairs were worth it. So I am sure there is a few hundred RPM to gain by triming it right and a few hundred more by allowing it to breathe better. I fully expect this boat to run a bit slower than other 260s as I have a lot of weight in stereo equipment and batteries. I would be very happy with 65-67 MPH.

I put the K&N on as it was cheap. I may go back to the stock flame arrestor if I find one at the right price.

Your little extra weight shouldn't have that much of an impact I wouldn't think. What type of air cleaner are you running. Pull it off next time and do a quick test. Don't be afraid to trim it up either. Run it a little loose even until you actually even go the other way in speed and then bring it back down little by little. Not sure about your boat but I would think you should see a 3 foot rooster or so when WOT and trimmed out well. The K&N's rob about 15hp also.
Good luck,
John

I am guessing the K&N is good for 15hp over the plugged flame arrestor..... I will try it out and then without.

I am running 2 group 31 batteries (each is at least 70 lbs) and 1 group 27..... ALong with a 35lb subwoofer enclosure and another 45lbs in amp rack and amps.

I wasn't too trimmed. I was more concerned with just making sure I was heading in the right direction with the repairs...

Sounds like your on the right track and are getting some good experience along with having some fun. Any more questions and or things you would like to share please do. Did you ever check your timing?

Sounds like you may want to face your sub out the back. It may help with a little stern lift and MPH. LOL...

I did just buy and install red anodized gauge bezels and a new red anodized Dino steering wheel. That should be good for 3-5 MPH, right?:lolhit: