Propeller Choices - Suzuki 140, Thunderjet

Franko Manini

Well-Known Member
Hey folks,

I've got a 20' Thunderjet Luxor (AKA the Falcon in Canada) that runs a Suzuki DF140. The current prop is the stock Suzuki 3 blade, 14" diameter, 21 pitch model. I'm happy with the boat's performance, but always looking to tweak it here and there. I was out a couple weeks ago and the water was flat and calm so I decided to do some WOT testing. Two guys and gear in the boat, we topped out at 40MPH, but just as we hit top speed, the motor hit the rev limiter. For those of you who have never bumped up against the rev limiter, it's pretty damn shocking. The computer cuts the ignition and it scared the crap outta me!

Normal operating range for this motor is specified to be 5600 - 6200 RPM. If I hit the rev limiter that means I was over 6200 RPM. During the test, I did see the tach just inch past 6000, and then WHAMO - rev limiter.

What does this tell me? Am I under propped? Do I move up in pitch, move from aluminum to stainless steel? 3 to 4 blade? The prop stuff is so friggin confusing.

This is a family fishing/exploring boat, and I rarely do any watersports with it. Thoughts?
 
Get a 23 if keeping with aluminum props and keep the 21 for a spare
 
If you go up in pitch it will get your rpms down but you may loose out on hole shot. I agree with trophy wife.....4 blade, same pitch....may drop a few rpms and you will likely gain better holeshot with thr 4 blade.
 
Heres what I have on my 18 1/2' weldcraft with a df140. Both top out around 40mph and I havent hit the rev limiter and wound it up to 6000rpm. The four blade shoots out of the hole but I found in the rougher water the boat wasn't as responsive and harder to control as the three blade. The three blade is 14 x 20

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4 blade
Will bring RPM down slightly. May lose 1-2 mph on top end but better hole shot, carries a heavy load better, planes at lower speed, better stern lift, more efficient cruise RPM and often better fuel economy.
 
Although it can certainly seem confusing, prop design is logical and the basics can easily be learned by doing a little reading. Unfortunately I've found over the years that the guys who should know this stuff (boat dealers) are pitifully short on prop knowledge. That's a shame because the prop is a critical component of your boat and can make a huge difference in boat performance and fuel economy . Most dealers simply supply the same 3 blade prop that they sold with the last 10 motors of a given size regardless of the type of hull and its desired use. But the boat that used for salt water fishing should not be using the same prop as the bowrider that's used to entertain the family at the lake!

3 blades are most common because they do most things reasonably well but they are not always best for uses such as for our fishing boats. Our boats tend to be quite heavy for their size with gear, fuel and passengers and their use is primarily cruising to the fishing grounds, trolling, and sometimes running through choppy or rough water to get home. We do not need a high rake 3 blade prop designed for speed! We need a prop that pulls hard to get a heavy boat on plane, runs nicely at an efficient cruise speed, allows us to remain on plane at lower speeds if the water is rough, and lifts the boat to make it handle nicely. Generally, a well designed four blade prop will work better than a three blade to meet these goals. The only real sacrifice you make in switching to a 4 blade is that you might lose a couple mph at top end. But, if you're like me, you won't care. My go fast days are over!

Good luck with your prop change. It can make a big difference. When I changed the prop on my current boat to a carefully chosen four blade, it transformed the boat from a gas guzzling slug to a boat that runs faster at much lower rpm, gets better mileage and is now fun to drive.
 
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