Baseline pitch to start tuning?

[erikgreen]

Hi guys -

I'm just getting started with my new engine. Boat is a 21 foot 1983 sea ray with a reman chevy 350, 4 bbl intake/carb on it, pre-alpha drive.

I took it out to the lake for shakedown and after a couple hours of driving I did a couple WOT runs. Prop was a 17 pitch three blade. I got up to 4000 RPM WOT, dunno speed since I didn't have a GPS with, but the other boat said he estimated 35-ish from his gps.

I then pulled my first stupid human trick (ok, maybe not first) on the way out and dinged a blade of the prop on the ramp pulling the boat.

What I'm wondering is where I should start for prop tuning.. I need to buy another prop for a backup anyway (and repair this one) and I'm wondering if I should use a lower pitch prop to get my WOT rpm or if I should be able to try something higher?

From what I know from reading here, a chevy 350 4bbl in a 21 foot boat should use something like a 19 pitch prop? Yet my RPMs would suggest I drop back to a 14 or 15? Obviously I still need to check on the other causes of low RPM, and I'm working off Don's checklist.

What prop do you think I should order?

Edit: NADA lists the boat weight at 3440 lbs.

Erik

 

[steelespike]

Re: Baseline pitch to start tuning?

I'd be sure she is well broken in and properly tuned.Having to go to a 14 or 15 pitch seems extreme.You should check tach accuracy.
Don't overlook proper heatrange plugs,plug gap etc.

 

[erikgreen]

Re: Baseline pitch to start tuning?

Roger. I'll just borrow a prop from a friend for a while until break-in is complete, then. I should be more or less ok if I can get the standard WOT rpm in the first ten hours, right? IE, I won't damage it by being a bit below the rated RPM for a while?

Erik

 

[2broke4this]

Re: Baseline pitch to start tuning?

I have a similar sized boat (Ebko 210 Biarritz SS) with a 260hp Mercruiser Alpha. My NADA weight with standard power is a bit lighter at 2800 lbs. My boat has a pretty deep vee, as I imagine yours does. The pitch on my prop is 21" and I was able to hit the upper 40s (on the speedo) at about 4600 rpms with a decent load of people/gear in the boat. To be fair, the lake was nearly as smooth as glass and we had pretty much perfect operating conditions. However, I can't imagine you'll need to go lower than 17. I ran the 21 all summer under a multitude of conditions (nearly unloaded, packed with people, pulling tubers/wakeboarders) and only when the boat was really packed did I wish I had a lower pitch. I'd keep going with your plans to find other reasons your RPMs are low. That said, break her in gently, and good luck!

-Carl