New to boating and need a prop recommendation

[WholesaleCabinets.US]

I just purchased a used 18' SeaArk 1860MVT that weighs about 700lbs. It's an aluminum tunnel hull that has a 88 Evinrude on it. The current prop is 14x17. The boat jumps up out of the hole great but top end is 32mph at 5200RPM's. That makes my cruising speed about 20mph. I would like to up my cruising speed to about 25-30 and still have enough throttle to be able to get out of the way if I need to. I'm hoping that I can up the speed, which will also increase my fuel economy because I will be going faster with less RPM's (my thinking at least...)

I am a bit confused on props however and would like some suggestions. The boat came with a 48 SPL and the top speed was almost identical but out of the hole was terrible if there was someone else in the boat with me sitting in the back. I'm a bit disappointed with the current motor (prop) thus far, since it is no faster but drinks a lot more fuel.

What kind of speeds can I expect by changing the prop? I was looking at turning point propellers prop wizard and it suggest aluminum 3 blade 13.25 x 19 and 13 x 19 4 blade. Does this sound about right? I would think with a current 17 pitch prop and such a light boat, a 21 pitch would give me more overall performance.

Any and all suggestions are greatly appreciated.

 

[jestor68]

Your first consideration should be the WOT rpm range of the motor; which is 4500-5500 rpm.

If it just turns 5200 with a 17 pitch, going to a 19 pitch will likely pull it down out of it's ideal(5000 rpm) power band.

It appears that a compression test is in order to gauge the health of the motor(120-130 psi would be considered good).

 

[YoungMind]

^^^+1 You will need to verify all parts are running in good order(compression test, check tach reading accuracy, get mph by gps not with on board speedometer)

Once all of those check out and you verify that everything is in good order we can go forward with a more accurate suggestion for a prop.

Just remember a couple of basic formulas when working with props;

-Going down in pitch will increase RPM's (amount can vary depending on boat type/size, prop brand change, etc.)
-Going up in pitch will decrease RPM's (amount can vary depending on boat type/size, prop brand change, etc.)
-To optimize the power of your motor you want it to be able to run in the top half of it's recommended RPM range at WOT

Happy Hunting!

 

[steelespike]

Assuming your numbers are accurate your slip is really high at 23% Very possible rpm and or speed may be suspect.
Normal slip light load is about 10 to 13% Usually a gps is best for speed.
Does the boat respond to up trim?Does it get up on the water and not lay down like it is glued there.
Don't assume that a new install is correct. Does the throttle open all the way?Timing set right and advancing as it should.
As suggested a compression test is a good point.
The 48 would use almost 5 gph (gallons per hour)at wot, the 88 almost 9 gph at wot.Thats whether pushing a house boat or a runabout.