Merc 25 Prop question

[will941s]

Have a 1998 Mercury 25hp, 2-stroke (114 pounds) on a 14' BayRayder V-hull side console fiberglass boat (650 pounds). I took it out the other day with a 13p prop and it will run 31 mph @ right about 5,800 rpm's. Thats with a Quicksilver Black Max 3 blade Aluminum 13p progressive prop. With me, motor, battery and 6 gallon tank in the back; and anchors, trolling motor, and trolling battery in the front. The boat had good hole shot (reached 31 in about 5 seconds) and planed off in about 2 seconds. Question is.....is there any way to get more top speed without running over my 6,000 rpm max? Or shoud I just stick with what I have and assume it's as good as it's going to get. I am happy with the results of the motor....just want to see what I can get for top speed.

 

[Bondo]

Re: Merc 25 Prop question

just want to see what I can get for top speed.

Ayuh,... Sounds like yer Already there...
A bigger prop will probably drop the rpms to much...

 

[steelespike]

Re: Merc 25 Prop question

That looks very respectable to me.You might try raising the motor on the transom.
The antivent plate just above the prop could be up to an inch above the bottom.
Raise it to a point just before ventilation becomes a problem
Is speed by gps?Finding a prop that might do better may be difficult.
To keep it simple you could try a Turning Point Rascal in the same pitch.

 

[will941s]

Re: Merc 25 Prop question

Thanks for the posts. Speed was confirmed by GPS, and is the same as the speedo in the boat. I think 31mph is respectable for a 25hp motor, and really can't ask for better. Have to slow down on tight curves as it is. I've heard that you can go up a pitch or two by going to a straight blade prop vs' a progressive pitch.....is that true? But then again people say you lose some of your holeshot, so it's kind of a double edged sword.....with one you gain something, and lose something. I will look at the Turning Point prop, I think now it's just a matter of "fine tuning" to get the absolute best results all the way around. I am pretty impressed with the Quicksilver...being that it's pretty much a stock prop for the motor...but I will see if I can borrow a few more and switch and run. I will post results if I get getter performance.

 

[will941s]

Re: Merc 25 Prop question

I did some research on the Turning Point Rascal....i'm not not sure accurate the data is, but some of the results are pretty impressive on their website as far as before and after switching to Turning Point. Some of the best results were with props the same size...and were like 3-5mph faster. Price is alot cheaper then I thought too. I know a good Michigan Wheel prop runs about $20 higher than those guys (never been impressed w/ Michigan Wheel). I did the calculator and they said 10 1/8" by 13p which is what I run now or 10 1/2" by 11p which I would be iff'y about. I think the biggest difference is they have larger blade diameter and cupping......which now I have long sharp swept blades, and no cupping. Do you guys guys think I should bite the bullet and switch?

 

[Silvertip]

Re: Merc 25 Prop question

One thing you need to understand is that whatever prop diameter, style, material, and pitch you have now may actually result in poorer performance with a similar prop from another manufacturer. The key word in all of this is "Design". Just like car engines -- design criteria may put emphasis on performance with economy being secondary. Another manufacturer may sacrifice a little performance for economy. With props, one design may provide excellent hole shot but not have the top end the other prop has and vs versa. Selecting a prop because top is is significantly faster should be an indicator that perhaps something else suffers -- like hole shot. Hole shot is really important as it is what gets the boat moving. If the engine has to strain long and hard to get on plane, that's not a good thing -- especially if you tend to run with a heavier than normal load. In other words, one more person in the boat may actually kill performance regardless what the top end is. Make your selection carefully and by all means try to find a shop that will let you test several props -- and then be a sport and buy from them. If it costs a bit more, consider it money saved over buying a prop that doesn't meet your expectations.

 

[will941s]

Re: Merc 25 Prop question

Thanks Silvertip....I've been through 3 already, a 4 blade (HUGE MISTAKE)....but I use it if I have to pull someone, a Michigan Wheel (Ok, slow, and not balanced), and another Quicksilver that was too much pitch and too low RPMS's....then came the Quicksilver I have now which so far seems to be the best. I had Hydofoils on the foot, then the foot went out and I replaced it and never put them back on. I had to actually hang on the the wheel last week when I took off because it too off so fast. It wasted no time at all getting on plane and hit that 31 mark in no time flat. Tomorrow I am going out with a buddy and I am interested in seeing what it does then. I am going to have to replace the prop at some point due to a small chip on the top of one of the blades because my Zinc Annode gave way and fell into the prop. It will due for now though. I will post some results tomorrow with more weight.