9.2 prop size/pitch

[Rick19354]

I'm interested in hearing what other 9.2 owners have regarding prop size. I have a Yanmar 2GM20F (16 hp) and power a three-blade 15-11 prop. I'm a few hundred RPM's short of the max rated for the engine, but get good thrust with the current prop at 2600 RPM (about my cruising RPM) and backing down is pretty strong with the current set-up. Just curious on what others have for prop/engine.

Thanks,
Rick

 

[BobM]

If I recall correctly...I am on the road in scenic Iowa...it is a Michigan 16 in two bladed right hand prop with a 9 pitch (16RH9) for my 2QM15, which is 14-15hp. Cruising is 5.5 knots at about 2800 rpm. We haven't done much backing up yet.

 

[RussB]

My prop is the same as BobM. Stock prop on a 1979 with 2QM15. I am replacing it with a Campbell Sailor CS3RH14x8x1, three blade 14 in dia 8 in pitch. I am looking forward to gaging the impact on motoring performance this spring.

 

[Rick19354]

Thanks to both of you for the responses.

Russ -- may I ask if you are switching to the Campbell prop because of sail or motoring (or both) performance? A folding prop has entered my mind, but mainly due to motoring performance as I fall a bit short of hull speed with the 15RH11 3 blade.

Rick

 

[Bob McKee]

I have an S2 9.2A, it had a Yanmar YSE12 that smoked, shook and leaked oil and water. I found someone that wanted to change from a 3GMD 20hp to a 40hp and was selling the 3GMD cheap. 20hp will make a 9.2A move at 7.2 kts on the GPS at 3400 RPM in flat water and no wind. It feels like the boat is flying! I usuall run at about 2800 RPM, it's feels more comfortable and I'm not pushing the bow wave.I had to replace the engine mounts and modify the engine cover by lengthening it about 5 1/2" but it all fits. I cut the bulkhead in the quarter berth for access to do the work and then spliced it back in when I was done. The prop is a 3 blade 15RH11, I used one of the online prop calculators, don't remember which one, there are several.

 

[Peregrine17826]

I've tried several props with my 9.2C and here is my experience in a nutshell. Peregrine came to me with a Yanmar 2GM and a RH 15D X 12P 2-blader. It wasn't enough to get into the river (maybe 5 kts in flat water) so I swapped it out for a used RH 15D X 14P Martec 2 blade folding prop and I didn't gain much on my cruising speed at 3,000 rpm. Eventually, I repowered with a Yanmar 3GM30-F with a 2.61 ratio transmission and I found 3,000 rpm to be a good speed and the extra power was a blessing. I got a used RH 16D X 14P Martec eliptic folding prop and she goes 6+ kts even in a good chop. The extra diameter made a big difference and didn't hurt anything. I tried a RH 17D X 15P folding to see what would happen and we got some vibration from the extra diameter and wash against the hull. I think that was overdoing it a bit so went back to the Martec 16D X 14P, but I could do 6 kts at 2,000 rpm with the big one. I've been told that the smoothest ride is from a 15"D X 12" Pitch 3 blade fixed prop, but it sacrifices sailing performance. The right diameter is 15" to 16" and the right pitch is 12" to 13", depending on your local conditions and expectations.

 

[RussB]

Sorry for the delay in reply. My laptop was out of comission for a week. I had to replace the DC power jack. Anyway, I am trying a Campbell Sailor three blade to improve motoring performance and do decrease vibration. I have talked to several people and read much online about vibration. It seems that a two cylinder engine coupled to a two bladed prop results in a lot of vibration. I guess we will see this spring.

 

[BobM]

Just sharing some experience here. If you are having vibration issues, don't neglect inspecting your engine beds. In my experience, the vibration can break the tabs loose from either the beds, the hull or both, especially at the back. The aft most tabs had broken loose on my boat and had to be reattached. I am also unhappy about the lack of any strong lateral connection between the two beds, either aft or forward. Forward there is a thin sheet of wood and aft there is nothing. The mounts are expensive, not the best design and also have the potential to fail.

My engine is sitting near the top of its mounts, which was necessary to achieve alignment. I have to think that must contribute to vibration as well (just based on the physics of leverage). If I ever repower her I will redo the beds entirely and buy better mounts.

 

[Rick19354]

Thanks all for the responses. I look forward to hearing Russ' outcome regarding the Campbell prop. BomM -- your last post is interesting. S2's have great glass-building reputations, but the engine beds in the 9.2 don't deserve the accolade. It's interesting to hear about the layout (and lay-up) of the engine beds. My 1985 9.2 has two stringers running forward/aft. Under the forward end is a steel (very heavy) reinforcing bar connecting the two stringers. The tabbing is weak, but the steel bar certainly helps. I too had to raise the engine for proper alignment, and did this after new Yanmar mounts were installed last year. In fact, I had to put a piece of starboard under each mount to gain an extra half of inch or so of vertical clearance. All is great now, but I do keep an eye on the engine beds. Your advice is well given...

Rick

 

[Jim5569]

Going back to Martec

My boat was built in 1982 and fitted with a Yanmar 2GM (13/15hp) engine and had a Martec 14X14 folding Eliptical, 2 blade prop on it when I bought it in 2007. Had some troubles with the prop folding and unfolding properly, but used it successfully for over a year. In late August 2008, I was running the engine at full thrust in the slip, heard a loud "clunk", followed by a severe vibration. After quickly shuting down and checking things below the water, I discovered that one blade had broken off of the folding prop! I was able to move the boat at idle speed to the nearby boat lift with one, unbalanced blade's worth of thrust. The previous owner had left me a 14 X 8, 3 blade fixed prop as a spare (I assume it was the prop which was fitted on origional delivery), which I had reinstalled.

2 Thumbs Up is noticably slower both under power and under sail with the 3 blade fixed as opposed to the 2 blade folding prop (the fixed blade is smoother running however). Martec agreed to refurbish the folding prop for $450 (their standard price; they refused any responsibility for the failure). I can't wait to get the folding prop back on (costs me 6 seconds per NM in club racing, but is worth it).

 

[BobM]

Interesting

]Under the forward end is a steel (very heavy) reinforcing bar connecting the two stringers. The tabbing is weak, but the steel bar certainly helps. I too had to raise the engine for proper alignment, and did this after new Yanmar mounts were installed last year. In fact, I had to put a piece of starboard under each mount to gain an extra half of inch or so of vertical clearance. All is great now, but I do keep an eye on the engine beds. Your advice is well given...

Rick

Very interesting. I have been thinking about improving the attachment between the two beds both in front and perhaps in back of the engine (in back is tough due to the shaft). My estimate was that my engine had to come up about a half inch in front. I thought about putting wedges under the front mounts and using longer lag bolts, but a sailor of more experience who helped me with the alignment convinced me to drop the back a little to achieve the 0.005" required. That worked, but I had a ringing sound after, which to me sounded like the shaft hitting the log. I paid big bucks last minute to have a "professional" tell me he heard the noise, but didn't know what it was! :cussing:It went away, but I plan to check the alignment again this spring and perhaps will consider raising things again. Did you do the alignment yourself?

 

[Rick19354]

Re: Interesting

I put the mounts in to solve a strong vibration problem (they needed replacement, so I thought I would start there). Well, got them in and never could get rid of the vibration nor correctly align. Spent two weeks trying. Took it to a local pro - hauled the boat to find the strut was bent. This is a heavy strut (stainless) on the S2, meaning it was probably bent in a haul out in the past. Removed it, had it straightened, reinstalled and then realized the engine was too low on all fours. Hence why it was raised with the starboard. This alignment was out of my league, hence the pro's help. Alignment was perfect, but I still had the vibration issue (clanking/sputtering in forward is a better term). Diagnosed as the drive cone slipping in forward. Had tranny rebuilt and I put it back in about a month ago. All (thankfully) if perfect now. I'll take a photo of the steel reinforcing bar for you to see --

Rick

 

[BobM]

Thanks Rick. I'd appreciate it.