- This topic has 9 replies, 5 voices, and was last updated 4 years, 2 months ago by
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Will you be reusing your transmission or getting a new transmission with your new engine? You need to figure out the rotation speed of your new arrangement. The betamax runs at 2800 RPM. Assuming no change in gearing, is this shaft speed close to what you already have? A good 3-blade folding prop will provide efficiency in forward similar to a fixed-blade prop. If the gear reduction is the same, a prop with the same pitch should provide about the same performance.
I assume you read my notes. http://www.richardcarter.net/repower/Propeller.html
Rich -
I would say a 20” is the right size for your configuration. I have a 21” and it is a bit oversized for my 55hp W60. I’m at cruising speed at 1500 RPM, and that’s not a diesel’s sweet spot. I definitely recommend the feathering prop and although there are several quality brands, I can only speak to the MaxProp which has served me well for 15 years. There are of course good and bad points of a feathering prop. When they are good, they are very very good. When they are bad, they are very bad. To the good, they do assist sailing speed and reduce drag. I’ve got a couple of first in class in races to attest. They power very well in forward and exceptional in reverse. It also seems to reduce the Starboard crawl in reverse. That may be attributed to its quick reverse stern-way which gives it more responsive rudder steerage. The MaxProp is dependable and durable. I’ve wrapped my share of crab pots and have twice had major jib-sheet fouls, (stupid captain error) one so severe that it bent the shaft and strut, but no damage to the prop. The bad side is that they do not perform well at all when they are fouled with barnacles or anything else. In that respect they react worse than a fixed prop. The other perhaps negative is that they are expensive. Maintenance includes not only keeping it clean, but a simple re-greasing on haul outs.
As for your pitch recommendation, I can’t give you that but the MaxProp is Configurable and can be tweaked (changed) on haulouts. -
I got a three blade flex-0-fold. After much back and forth with the vendor we settled on a 18×12-3 L bladeset, there is some discussion in the forums about this as well:
Response #1:
“I have a Wester 58; and replaced the original 3 bladed prop with a flexofold; and, am satisfied with the flexofold prop. Jack, the US contact for flexofold recommended an 18 X 12 – 3LH; and this was too much prop (eng would not reach 3003 rpm, smoked excessively at wot). I downsized; cant find the paperwork, but I believe to a 17 X 11; and, for my boat it is the correct size.Response #2:
“Our original was 20X13, same as listed in the 424 sales brochure. I always had the impression we were somewhat over-propped. WOT gave us somewhat less than the spec 3000 RPM, and a lot of black smoke. We changed to a 18X11 flex o fold, and it seems to be about right. Certainly not too weak. However, I was cautioned by flex o fold to not compare their prop to other props vis a vis the diameter and pitch. No usable correlation.”
Note that you can try the flex-o-fold for one week and then return it. Obviously not the easiest thing to take off in the water but you might even just be able to return the blades. I worked with Csilla B. Rasmussen, cbr@flexofold.com. The exact engine specifications and transmission ratio are very important.
So far I’ve been very happy with the prop.
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Bryan Bywalec
S/V Pelican, Hull 209
Siren Engineering, LLC -
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Mine is a flex-o-fold, 18X11. Compares very favorably with the original prop’s performance. I cruise between 1900 and 2300 RPM typically, but can hit 3000 RPM or so under WOT. Smoking of course, with the exhaust well under water and making eight or more knots at that point. I’ve cruised all through the Gulf, up the East Coast to Rhode Island and out to the Bahamas with this prop and am pleased with it. Took a bit to get used to having to hit it hard in reverse to stop the boat, but it does stop pretty quickly when I roll the throttle up. Gotta’ be careful when positioning straps when hauling the boat though. The blades tend to be folded while at rest and you certainly don’t want to lift the boat by the prop blades. I ask the crew to lift very slightly while I go below and attempt to turn the prop shaft by hand, If I can’t move it, we reposition the strap by coming in from the stern a bit.
David
#189, Blue Moon -
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