My Cal 34 has a prop that measures 16”, pitch unknown. Engine is yanmar 3GM30F. On a recent cruise I ran 2500 rpm and only made 4.5 knots in still water. Admittedly when I hauled it today there’s lots of barnacles on hull and prop. I’m thinking the prop is undersized. There’s a chart on Marine Diesel Direct that recommends for this engine and transmission either 2 blade 17x12 or 3 blade 17x11. Advice or recommendations?
Prop for Cal 34
- Thread starter Bill England
- Start date
Growth on the prop, shaft, and hull will dramatically slow your speed. Is this speed slower than what you normally get underway? Before investing in a new prop, cleaning the prop and bottom might be well worth the effort.
Prop tip clearance is a critical dimension on a prop. If the prop is too close it creates turbulence which reduces efficiency. If you opt for a new prop, rely on more than a chart on a website. You will need clearance measurements as well as engine HP and gear ration.
Prop tip clearance is a critical dimension on a prop. If the prop is too close it creates turbulence which reduces efficiency. If you opt for a new prop, rely on more than a chart on a website. You will need clearance measurements as well as engine HP and gear ration.
Ok thanks. I was also advised to see what the max engine rpm is as an indicator of whether the prop is sized right. I’ll do that before jumping on a new prop.
Bill. Cleaning up the bottom and prop system of fouling junk will be helpful. You do not mention how the boat was moving as you increased rpm. Did the bow go up and the stern down? Prop pitch is a factor. How was your Cal loaded ? Were you carrying all the food, gear, and weight you could fit in the hull or was it stripped lean and mean like a racer? Lastly there have been improvements in prop design that impact thrust over drag.
Explore all the factors as you search for improvements.
Explore all the factors as you search for improvements.
Check the tachometer too! I had a similar issue on my Catalina 34. Then I found a free strobe tachometer app for my iPhone and determined that it was reading quite low (it was also rather suspicious that full throttle was 4000 RPM when the Universal spec sheet only claims it goes to 3200).
You’re likely looking at minor optimizations with 16” vs 17” not 4.5 vs 6 kt. I can’t imagine Cal would have matched props THAT badly, assuming it’s original.
You’re likely looking at minor optimizations with 16” vs 17” not 4.5 vs 6 kt. I can’t imagine Cal would have matched props THAT badly, assuming it’s original.
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Talk to a prop shop, like Shannon at General Propeller in Bradenton FL, she will ask your displacement, waterline length, transmission reduction (on tranny placard), engine HP, max RPM, etc. with that boat they likely have the original spec as well
Hello, I have a Yanmar 3GM30F on an ODay 34 with 16 inch two blade prop; the max RPM for engine is 3600 per manual. It does make a significant difference if the hull and prop are clean. Been there, cleaned things up and could get 6-7 kts at ~3k rpm in smooth waters. My hull speed calculates to 7.28kts in optimum conditions; hull speed is based upon length at water line (HS = 1.34 x √LWL ). Go to Sailboat Data to obtain the LWL.
Castle in Ches Bay
Thanks all for the input. I had the boat hauled and the barnacles were gnarly. After a good cleaning and painting the boat now makes 6.1 knots at 2500 rpm, versus the 4.5 I got before. Huge difference. Problem solved.
