210 SunDeck Prop

[Kameroo]

Our 210 SunDeck is over-propped, and I'm only getting 3800 RPM WOT. The boat is a little heavy anyway with the aftermarket swim platform and 2 batteries. Would like to go back to Aluminum as we run on the river.

Details:
1998 210 SunDeck
5.0L Carb, 220 hp, Alpha One
Current prop: Stainless, stamped "M14 1/4 x 20", "Turbo", 3-blade

Was wondering what prop I should switch to in Aluminum? Would like to see about 4400 RPM (max spec. is 44-4800 RPM WOT).

 

[Trucky]

Someone smarter than me can correct where I'm wrong but I think it's about 200 RPM for each inch up or down. I have a 210SD with the same engine. It came with a stainless 19p prop and was a dog out of the hole, and could only reach 4400 RPM wide open. I moved down to a 17p and the hole shot was like night and day and can run right at 4800 RPM. Most of my boating is at elevations from about 1200 to 2200 feet above sea level, which definitely has an effect on your prop pitch.

 

[Kameroo]

With the 14.25x20, a switch to 14x19 would get me much closer, as there is less diameter. May just start there...

Anybody recall the conversion factor if I go to 4-blade?

 

[blaster]

Rule of thumb is 100 fewer rpm's for an extra blade. Aluminum will also turn faster than a comparable ss prop due to the flexing of the softer metal. There are so many variables involved selecting the best prop for your needs. Maybe check with some prop shopps and ask about their return policy if you buy something you aren't happy with.

 

[Kameroo]

Thanks all for the advice. A friend also told me that he suspects the aluminum would turn up more since I'm "already in the torque band at 3800." Not exactly sure how to interpret that, but I'm going to see what the 14x19 does in Aluminum.

 

[Lazy Daze]

Before you start doing any changes, let's make sure everything is operating correctly, first. With just you in the boat and a light load, what is your MAX RPM - trimmed out as high as you can go before speed drops off or it starts ventilating. Even with the 20" on there, you should really be getting much higher RPM than that. Actually, if you have the 1.62 drive ratio, a 21" would of been standard. Ideally, you'll want to get to at least the upper range of that 4400-4800.

Is the boat bottom clean? Is the prop in at least near-perfect condition? What do your spark plugs look like?

 

[Kameroo]

Dennis, very good advice. This morning, I put a 14.5x19" prop on the boat. Wanted to go 14x19, but I've got a few days off and the 14.5x19 was available. It got me to 4200 RPM. Had a friend check the ignition system. Distributor and plugs were pretty new, but the plug wires were original 1998 and showed what he considered excess resistance at something like 11,000 ohms. He had some kind of voltmeter that read something like 36,000 volts at the distributor, but only 16,000v at a few of the plugs.

New plug wires got us up to 4350 RPM. As I mentioned, the boat is a little on what I consider the heavy and aft-heavy side with its full-beam aftermarket swim platform and a 2nd battery that I installed in the stern.

Interestingly, the boat would fall off plane at 2800 RPM with the old wires, but would hold plane at 2700 RPM with the new wires. I thought 2700 RPM would be 2700 RPM regardless of how you achieve it, but the engine seemed stronger in that range (all ranges actually) with the new wires.