I installed a new prop (and shortened stainless shaft and PSS seal) in Sheer Bliss, #1055 1990 with M-35A engine) replacing my factory 2 blade. My primary goal was to get 7 knots cruising speed without hurting sailing performance. The new prop is 15", 10 pitch, 3 blade. Here is my preliminary data:
old prop 2200 rpm 6.1 kts engine temp 170 deg
2400 6.4 175
new prop
2200 6.4 170
2500 6.8 170
2700 7.1 175
All speeds taken via the knotmeter which has been pretty accurate. Is 2600 rpm too fast for cruising? Do I need more pitch? Catalina says factory puts on 15" 10 pitch 2 blade or 9 pitch 3 blade and not to put on bigger dia.
Thanks
bruce fowler and sheer bliss
Your rpm should not excede 80% of the maximum rated rpm. My engine runs up to 3300 rpm (same engine only 2 years newer). I generally cruise at 2500 rpm. I also have installed the flex-o-fold and have experienced no difficulties in the two years that it has been installed.
Why did you shorten the shaft?
Jim Kane
The shaft was shortened because both the yard and Flex o Fold said that 3 1/2 " past the strut was too long. I was making a new shaft anyway.
Exactly which Flex O fold do you have and what is your cruising speed?
thanks
bruce fowler and sheer bliss
I have the flex-o-fold 15X10 two blade. I cruise at 6.2 kts with a dirty bottom; 6.8 when I clean it.
Jim Kane
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Jentine:
Your rpm should not excede 80% of the maximum rated rpm. My engine runs up to 3300 rpm (same engine only 2 years newer). I generally cruise at 2500 rpm. I also have installed the flex-o-fold and have experienced no difficulties in the two years that it has been installed.
Why did you shorten the shaft?
Jim Kane<HR></BLOCKQUOTE>
"Snow Goose" has had the same favorable experience. I usually cruise at 2200 rpm, but then I was a post Depression baby and always save something in reserve.
Peter
I have hull # 1554. The engine is a Universal 35MB and I cruise at about 1800 rpm. At this rpm I generally am doing about 6 kts. Based on "sound" and vibration, I believe this is the best rpm to cruise on my boat. Am I wrong? Am I doing something different? Seems to me that anything over 2000 rpms is a strain. Would appreciate comments.
Hal, in a word - YES. Diesel engines do not like to run at low speeds. They develop carbon residue in the combustion chamber. You should be cruising at the manufacturers recommended speed. They don't recommend this speed because they get a kickback from the oil companies, but because it is best for the engine. Your engine will last longer and run better if you get the rpm up to where it belongs. Diesel engines like to work.
Jim Kane
Both the yard and Flex o Fold thought that 3 1/2 inches from strut to prop was too long and could cause vibration with the heavy 3 blade folding prop. The shortened shaft seems to work fine except that there is now a noticeable but tolerable vibration resonance on the binnacle at 2000 rpm. Overall the engine ran pretty smooth before and is noticeably smoother now.
What prop do you have and what is the pitch? How do you cruise?
Thanks
bruce fowler and sheer bliss
My prop is 15" with a 10 RH pitch on a 1" shaft. I don't recall my shaft being shortened, and I haven't measured the overhang. If it's of use to you, I'll measure it this weekend.
I cruise at about 2200 rpm and get about 6.5 kts. I had a 10 1/2 pitch and couldn't reach the max. rpm of about 2500 rpm. I had the pitch changed.
No problems with the prop at all.
Peter
Thanks a lot for your responses. I assume that you have a 3 blade Flex o Fold prop.
bruce fowler and sheer bliss
Three blades it is. And she back fairly straight as well.
Peter