Prop Size Help for a Rookie

dhendr11

Cadet
Joined
Apr 28, 2018
Messages
10
Hey everyone, decided to try out the boat life and purchased a "trial" boat just for family fun. However, I got too close to a sandbar at the lake and well that prop needs replacing. Luckily no damage to engine or outdrive but I wanted to get opinions on a replacement prop. Looking to replace with a stainless steel but do I need to change anything pitch/diameter wise before I just buy the same specs below? The speedometer isn't functional at moment so not sure about speed at WOT.

1991 Glasstream 180 SE (17.5 inch Runabout, 2425 lbs empty)

1991 Mercruiser 3.0L I4 with Alpha One Gen 2 drive (1.98 ratio)

Michelin Match Aluminum 14.5 x 19

4500 rpm @ WOT
 

QBhoy

Fleet Admiral
Joined
Mar 10, 2016
Messages
8,286
From what you have posted...you could stay the same pitch or even go down in pitch or two with a stainless. But my instinct and experience would tell me that normally similar boats with that drive ratio/3.0 Merc...would usually have a 21” black max as standard...unless it’s high altitude...
You will know the boat and how it performs better than anyone, but might I ask if your 4500rpm was achieved when trimmed up and running well set up ? I would have thought you could be at the max recommended rpm of 4800 with a 19” on her ?
if I’m wrong and she was well trimmed and perhaps you run the boat heavy laden...then you wouldn’t go far wrong with a laser 2” 19”. Will lift the boat and perform well. (Still think it might manage a 21” though, haha)
 

Scott06

Vice Admiral
Joined
Apr 20, 2014
Messages
5,543
Had a similar size boat with an 3.0 ran well with a 19" 3 blade or 18" 4 blade , would drop down to a 17 /3 blade or 16 /4 blade for skiing (I'm 250 lbs) . I think a 21 would be too much for that engine if you want to take the family with you. I had good luck with the Michigan vortex 4 blades which are relatively inexpensive vs stainless. find a prop shop to fix your old one so you have a spare as we've all dinged them ...
 

QBhoy

Fleet Admiral
Joined
Mar 10, 2016
Messages
8,286
Fair play guys. But similar boats like maxum 1800, bayliner 175 etc, etc with 3.0 and the same gear ratio are very common in my marina. By far the most popular boat and engine combo over here. Likely because of price and economy. Such boats sell really well here....but all the examples I know of all run a 21” black max as standard. Some of the guys have changed to a 21” high 5, but need to watch the RPMs wot...some have went to the “go to stainless” the laser 2 and run a 19” best. But with an ally...most are 21” and run well, showing around 40-45 gps depending on hull.
 
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