2002 mercury 25hp prop selection

[Eylusion]

Boat: 1992 crestliner nitehawk 14' rated for 30hp I think
Motor: mercury 25hp model: 1025311zd serial: ot54636
Current prop 3 blade unknown probably whatever came with it.

I want to buy a new prop and I'm not really interested in a replacement as I want to get more thrust out of this setup.
With 2 passengers and light gear, this setup works just fine and I have no complaints. But with the boat running heavy with gear, tackle, full well, and hell maybe a third passenger tucked in there for a quick ride to the other side of the lake to the swimming area. I could get out of the boat and walk faster.

Can someone tell me exactly what prop to purchase so that this thing can go faster than maybe 5mph when running heavy? I have no tach so I can't say what rpm it runs at and I can't give any sort of speed estimation either. I will gladly give up top end for better low end. When boat is light with just a captain it'll fly out of the damn water, I don't need that but I do wanna go faster than walking speed when heavy.

Yes I know the boat is underpowered to begin with, but I'm buying a new prop anyway as this one has seen better days, can I go to a smaller 4 blade with less pitch or something to get me going under load?

 

[Eylusion]

Re: 2002 mercury 25hp prop selection

Boat: 1992 crestliner nitehawk 14' rated for 30hp I think
Motor: mercury 25hp model: 1025311zd serial: ot54636
Current prop 3 blade unknown probably whatever came with it.

I want to buy a new prop and I'm not really interested in a replacement as I want to get more thrust out of this setup.
With 2 passengers and light gear, this setup works just fine and I have no complaints. But with the boat running heavy with gear, tackle, full well, and hell maybe a third passenger tucked in there for a quick ride to the other side of the lake to the swimming area. I could get out of the boat and walk faster.

Can someone tell me exactly what prop to purchase so that this thing can go faster than maybe 5mph when running heavy? I have no tach so I can't say what rpm it runs at and I can't give any sort of speed estimation either. I will gladly give up top end for better low end. When boat is light with just a captain it'll fly out of the damn water, I don't need that but I do wanna go faster than walking speed when heavy.

Yes I know the boat is underpowered to begin with, but I'm buying a new prop anyway as this one has seen better days, can I go to a smaller 4 blade with less pitch or something to get me going under load?

Okay well I guess from the lack of input I should just go buy an identical replacement prop and not run heavy. Come on guys, it's not my fault I can't just go to Mercs website type in my model number and have it say only buy props between 10 and 10.5 inches wide and pitches from x to y. I can't pull up an owners manual or a service manual or anything like that, I was just hoping to maybe give up some top end and gain some more lower end. I'm gonna replace the prop anyways I just thought I could find something out there that would move a smidge more water for me.

 

[steelespike]

Re: 2002 mercury 25hp prop selection

If you answer the questions at the top of the prop forum we can get you started.
I guess you tried but you didn't really get us much information we need some numbers regarding the lighter load and the heavy load.
Without we can't evern really use the Merc prop selector.
Your prop size,lightly loaded wot rpm and gps speed would be a big help.
hp,year and 2 or 4 stroke is better than numbers on the motor.
The Night hawk is 380 lbs If the motor is a 4 stroke it's about 172 lbs.
Without your present prop size we don't even know where we are starting from.
Prop size should be near the base of the blades or under the prop nut.

 

[Sea Rider]

Re: 2002 mercury 25hp prop selection

You can start by specifying if you own a 2 or 4 strokes engine to begin with. If happens to be a rebadged 2 strokes Tohatsu, you could upgrade it to a 30 HP for peanuts cost. Both 25-30 are exact same CC, being the 25 restricted. That way you could have better engine punch with 3, probably factory delivered prop will work fine. To test props at wot a induction tach is a must install.

Happy Boating

 

[pootnic]

Re: 2002 mercury 25hp prop selection

I say keep the prop you have(whatever it is)and buy another prop acouple pitches smaller for when your running "heavy".
Be careful though,if you use the smaller prop with a light load,you might go over the recommended rpm range of your outboard.

A tach,is really the only real way to get the proper prop though...

 

[Eylusion]

Re: 2002 mercury 25hp prop selection

Ahh, you guys rock thank you for the input. If im not mistaken i believe its a 10 3/8" prop 3 blade with a 13p. Its chewed up pretty good so i know im gonna get a little perf boost just replacing it. It is a 2 stroke 2002 merc 25hp. Its sticker says max 6000rpm, but i dunno what that means exactly, does that mean 6k is my dangerzone, should i set it up to run at 6k, or what So i need to figure out how to hook up a tach, and figure out what i run at. I still have some other qdjustments to make as i think my prop isnt perfectly centered on the boat and it might need a trim adjustment, etc. Also its time to pump in some fresh grease, and this engine has been running on 25:1 since i got it qnd i think ive since learned that i am only suppose to do that for the break in period and then goto 50:1 oil mix, so if running it rich in oil like that for all this time has done something bad i wouldnt know it. So ill try to get some tach readings for you guys, will my rpms differ between light and heavy loads? And ill get some gps speeds for you guys as well.

 

[steelespike]

Re: 2002 mercury 25hp prop selection

Generally you would prop for a light load and your test run should be with a light load.With your wot rpm and gps speed and the prop size we can get an idea if your setup works.
You would prop lightly loaded for near or at the 6000 figure. Once you get setup you can run at what ever speeds you prefer.
The motor will also be more powerful in general performance.
Your 25:1 ratio is no problem It wouldn't hurt to look at the plugs.
Propping near the top gives you a cushion for heavier loads and assures you won't over rev when lightly loaded.
I think the 2 stroke is something like 155 lbs.