Proper Prop Size

[Ken Keitges]

As far as I can determine my boat has a prop size 13x13. What I need to know is wither or not that is what I have to live with or can I change to a 3-blade-prop or maybe even a 14-inch-diameter blade for more speed and control. I have heard that a 3-blade-prop gives better control when going in reverse.

 

[Roland Briere]

h30 prop

Ken, I have a '77 h30 with a YSB12 Yanmar. I assume you have the same. The original prop is a 13X10 2 bladed which I still have, but was changed to a 12X12 3 bladed before I bought her 3 years ago. The RPMs are probably a bit less than they should be but, she runs nicely at 2100 doing about 5.5kts. It walks something fierce to starboard in reverse, however, but when you get used to it, it gives you great control. Hope this helps.-Roland S/V Fraulein II Tarpon Springs, Fl.

 

[T. Birchfield]

prop's

we also have an 1981 H 30,that had the 13x13x2 blade prop,that we have changed out to 13x13 3 blade prop now we have a cruising speed of 7 knots at 2400 rpm's. with much more thrust. yes we still have prop walk but,with the extra thrust we now back into our slip much easier. hope this helps. T.Birchfield (POLE DANCER) crystal river fl.

 

[Tim]

props

Any extended running of the motor should be at least 80% of the maximum RPM else the exhaust elbow and system will coke up. Small diesels do NOT want to be run at low RPMs, hence too great a pitch on the prop will limit your RPMs and eventually destroy the motor. You should leave at least 15% of the prop diameter for clearance to the hull else you risk vibration and thumping (just annoying) but also cavitation of the prop tips (not serious, but over time will damage the prop) and serious prop walk from the wash off the hull.The recommended props on my 1981 H30 with Yanmar 2GM are 13x13x2 (the original prop; OK but reverse stank out loud); the 13x10x3 (little difference in forward, reverse somewhat better.) I eventually settled on a Cruising Design 3 blade feathering. Good in forward due to a large blade area and fantastic in reverse due to a separate reverse pitch setting. (I can actually do 5+ knots in reverse. Boy, does that look silly.)With a clean bottom, I can do about 6.3Kts at 3200 RPM which is about the theoretical maximum and all you can expect from the 13bhp on a 26' waterline.Oh, and I'll give you such a deal on a used 13x10x3 if you're interested.