84 Stingray w/ Merc 3.0 140R

We recently acquired a 1984 Stingray with a Merc 3.0 140R. The manual states that the WOT operating range is 4200-4600RPM. It is currently running a 13 3/4 21" prop. Yesterday we took out for the first time. We had 4 adults (2 men, approx. 225lb each and 2 women, approx. 140lb each) and 2 small children (50 lbs each). At WOT, it was running approx. 4100 RPM and 37mph (per iphone, bc gauge is not working).

We will normally have 4 adults when we go on the lake as we like to go with friends and the whole point of getting the boat was to take our girls tubing or possibly the adults to wakeboard or ski occasionally (if possible).

I felt like with the added weight, the boat struggled to get on plane and was sluggish. Would an adjustment in prop help? Can you provide suggestions?

Thanks
JB

Re: 84 Stingray w/ Merc 3.0 140R

Looks like you may need to drop down to a 19" pitch prop with that many on board. Be carefull though, if you take it out with only two on board you could over rev with a 19". Watch that tach and you should be fine. By the way, you should realize that going to a 19" will drop your top end around 4mph. Should notice an increase in your hole shot as well.

Re: 84 Stingray w/ Merc 3.0 140R

I think a Solas Amita 17" 4 blade It will knock some speed off but when it comes to sking
You will probably think you added a super charger.You'll have to watch the rpm with a light load.
It should hold a slow plane easier and respond better around f the dock

Re: 84 Stingray w/ Merc 3.0 140R

I have the exact same boat and we went with a 4 blade 17" and the boat will do 35 MPH all day and gets on plane with ease. I highly recomend the 4 blade.

Re: 84 Stingray w/ Merc 3.0 140R

Judging from your prop size, I assume you are running a SS prop; perhaps a Mercury Vengeance?

It sounds as if your 1984 motor might be a little tired; as it would usually be able to turn a 21 up to about 4600 rpm @ 42 mph when new.

Going from a 21 to a 19 should add about 400 rpm and get you to about 4500 rpm; about perfect for your recommended rpm range.

Running a 21 at 4100 rpm and a 19 at 4500 rpm calculates to nearly the same theoretical top speed, while providing a noticeable boost in out of the hole acceleration.

I would stick to the same type/series of prop for more predicable results. A Quicksilver Silverado is basically the same thing as a Mercury Vengeance.