Prop recommendation for 25' Center Console

[jwilkes]

I have a 1994 Robalo 2520 center console with twin 200 carbed Mercury outboards. The boat weighs around 6,000lbs dry, and I typically carry about 70-100gal of fuel MOST times, along with average gear and 2-6 people. The engines have a recommended rpm range of 5,000-5,600. The drives are counter-rotating and spin a pair of balanced Quicksilver Mirage 21p stainless 3-blade props.

With about 70gal of fuel or so, 5 people, light chop, and a little engine trim, I was able to pull 54mph on the gps and that was at about 5100 on the tachs. It happily cruises around 3,800-4,000rpm at 36-40mph. It will stay on plane at as low as 3400-3500rpm. No matter what the load (people, gear, etc), I've never been able to pull much over 4,900-5,100rpm's at WOT. The engines start and run pretty darn well, and I recently put new plugs in and did a good SeaFoam de-carb.

I'm not TOO concerned about top speed, but I'd like to keep as much of it as possible. I'd like to get my WOT up closer to the 5,600. I'd also like to get more "traction" in heavier waves and possibly be able to hold plane at lower rpm's.

I understand the BASIC effects of prop pitch, diameter, and number of blades. All my needs and research point me to a good pair of 4 blades. I think Mercury Rev4 props in a 19 pitch should do the trick from what I've been reading; what do you guys think?

Thanks for your insight!

 

[steelespike]

Re: Prop recommendation for 25' Center Console

There are others that can probably do better on the big twins but:
It does appear your doing really well.Slip is an unlikely very low number.
Is the speed by gps?It appears you will lose speed whether you go to a 4 blade 19 or just a 19.
I wonder if your could maybe play with the props a little remove a little cup perhaps.
You might lower the motors one hole to solve the grip.

 

[jwilkes]

Re: Prop recommendation for 25' Center Console

There are others that can probably do better on the big twins but:
It does appear your doing really well.Slip is an unlikely very low number.
Is the speed by gps?It appears you will lose speed whether you go to a 4 blade 19 or just a 19.
I wonder if your could maybe play with the props a little remove a little cup perhaps.
You might lower the motors one hole to solve the grip.

Yeah the boat doesn't do too bad; that speed was on gps, and surprisingly, my "dream-o-meter" doesn't read that far off...it's been within 1 or 2mph each time I've compared it with the gps. I've only had it since February, but the previous owner bought it brand new and claimed he'd see upper 50's out of it. He sold it to buy a newer 35' Contender.

I think I ran my numbers thru a slip calculator once and it was a low single digit number. The motors are already all the way down on their mounting holes. My last boat was a 1993 Trophy 20' center console with a single 175 Mercury. Really no comparison; this Robalo blows it out of the water in every category. I don't notice much of a difference weather I have 6 people in it or 2.

I think for the engines to operate more efficiently, they need to be able to turn some higher rpm's. If I could get a little better bite at lower rpms, that'd be a good bonus too. I keep hearing that the Merc Rev4 is the 4 blade prop that keeps your top end but also gives the typical gains in the lower end too. A lot of cabbage just to try though.

 

[steelespike]

Re: Prop recommendation for 25' Center Console

Sometimes you get a setup that seems to do well at the low end with apparently not much gained with prop manipulation.
Is the bottom clean and smooth?Painted? Sometimes boats seem to gain weight as they age,usually from accumulated gear.
Its possible "upper 50s" was a sales exageration.56 would be on the side of upper 50s.
Maybe you could find a dealer to let you try props with the understanding your buying.
Do you have trim tabs?

 

[jwilkes]

Re: Prop recommendation for 25' Center Console

Sometimes you get a setup that seems to do well at the low end with apparently not much gained with prop manipulation.
Is the bottom clean and smooth?Painted? Sometimes boats seem to gain weight as they age,usually from accumulated gear.
Its possible "upper 50s" was a sales exageration.56 would be on the side of upper 50s.
Maybe you could find a dealer to let you try props with the understanding your buying.
Do you have trim tabs?

Bottom is freshly re-painted; no trim tabs. The boat is trailered for now, so it stays relatively clean on the bottom. I'm pretty impressed with the speed already; it wasn't a huge selling point for me, but intriguing for sure.