nunbers dont add up!
 

New to this site and need some help
Just bought a 25' Donzi ragazza and think I should be getting better performance than I am. With 2 people, and 1/2 tank(35 gals) I am only getting 41 mph (gps) @ 4200 rpm wot

1988 merc 7.4 w/ bravo 1, 14 x 19 quick silver 4 blade prop, gil maniflods w/ corsa exhaust.

engine starts easily appears to run smoothly with no issues

I would think I should be able to run a 23p prop with the available hp and torque. With the current prop I should be turning close to 5,000 rpm

I should be able to push the boat to the low to mid 50's

Am I missing something or just wishful thinking

Are you trimming the boat up? Not a stupid question. I see it all the time.

Yes, I have tried throughout the range to the point of cavitation

I did see 42mph once with only myself in the boat

Also, boat has been rack stored most of it's life and continuously for the last 12 years

I am the third owner

Does it have a lot of hours on it? Go back to the basics like plugs, cap, filters, timing, etc, and possibly a leakdown test.

Just turned 500 hours

I have put about 10 hours on it and over 100 gals of fuel so that shouldn't be an issue

seems to run fine just no top end

previous owner was pretty good about maintenance

He only used the boat 5 or 6 times a year and rack stored it

Is in excellent condition for a 24 year old boat so I doubt it was beat on

I tried to find info on what prop was supplied from the factory but having a hard time finding any info about the ragazza.

The 19 seems a bit undersized, I wonder if it has had a problem for a while and they compensated by putting a shallower prop on

I know it isn't a speed hull, but it isn't a pig either

long story short: #1-check the compression and replace plugs...#2 if numbers are good check your timing and look at the drive to see what ratio you are running, maybe it was replaced? That is what i'd start with

That model Donzi is more of a mini cruiser, and was not designed for top speed. You engine package is only 300HP stock. At 4200 RPM you may be a little overpropped. I think without significant horsepower gains you will not increase your top end. I had a buddy who owned a 25' Ragazza and could not get more than 45MPH out of it no matter what he did. The X dimension is really low on that hull.

Does the boat get on plane quickly? If so, I doubt the motor is tired.

I think you are right where you are suppossed to be speed wise with your boat/motor combo. Good luck and have fun!

top end RPM should be 4200-4600 for your engine. The four blade might have been put on the boat for skiing and hole shot.

I'd guess you should be able to pick up a few MPH with a 3 blade.

Thanks for all of the input

Not sure if it is 300 or 330, title says 330 but either way not a huge difference

I know it is not a performance offshore hull, but in reading numerous posts from other with similar style boats it appears I am coming up short. They are able to produce the same numbers with a small block.

I have a friend with a 25' amberjack with the same engine combo, his boat outweighs mine by at least 1500# and has a 10' beam. He runs a 23p prop and can hit 40 mph

I just want to be sure I am maximizing what I have

any suggestions for adding hp without speeding 5k