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Any advice on switching from a 2-bladed to a 3-bladed prop on my 1983 Pearson 303? Valued advice would be dia., pitch, same reduction gear ratio?; all this powered by a 2GMF Yanmar. Is this asking too much of the 2-banger, and any other considerations would be helpful in a decision.
 

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Why are you considering a switch? If its poor performance, make sure your current prop is sized correctly. This link lists some suggested props for different engine/transmission combinations.

props by motor and gear ratio

I would first compare your prop to the ones listed there for your engine to see where you are. Note you need your transmission ratio.
 

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If diameter and pitch are correct a two blade is much better performancewise. Three blade is smoother than a two blader. If you are happy with the smoothness of your prop do not replace it, you will loose performance.
 

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Absolutely

If diameter and pitch are correct a two blade is much better performancewise. Three blade is smoother than a two blader. If you are happy with the smoothness of your prop do not replace it, you will loose performance.
A Pearson 303 is already "slow", putting a 3-balded prop will only make it slower. If you're really thinking about putting a 3-bladed prop, think about a feathering one.

DrB
 

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All the above comments are valid. I would add that a two blade can be positioned behind the deadwood and drag is much reduced when sailing. How much a 'grip' the propeller has on the water depends on diameter and pitch, not the number of blades. Diameter is by far the most important. The reason for a three blade is usually cavitation where the forces are so strong that vapor forms at the face of the propeller and then collapses causing severe erosion of the metal. If the propeller is sized large enough, the forces are small enough to not cause this to happen. The marine architect that designed the boat would have worked this out with the choice of a propeller that would not cavitate and would be properly sized so that the engine would transfer its peak horsepower when at maximum rated RPM. If you do not have the original engine, then we need to take a careful look at the propeller that’s there and see if it is properly matched to the engine. This takes a lot of time to work out. The original prop is a 16X10 two blade with a 13 HP engine. I would prefer a 20 HP for bucking the wind with a 10,000 pound boat. If you want the best performance and fuel economy, buy a Max-Prop where the engine torque is near maximum for a given RPM. Saves about 20% in fuel because less unused air is pumped through the diesel engine (pumping losses). A 16” two blade is about $2000 and will fully feather when engine is off.
 

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A fixed prop is never as efficient as a folding prop under sail, but a fixed three blade is a great cost effective solution if you need performance under power, if it is the proper pitch and dia for your engine. And an even better idea, if you can afford the price of admission, is a KIWI 3 blade folder. Best of both worlds and not a deal killer price. Pat
 

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Hey Julie and John....at least I think this is you!!!

I just ordered a 3 bld Campbell Sailor (15x9) for Dragonfly II and will let you know of the improvement. It will be replacing a Michigan Wheel 15x12. Norm was a pleasure to work with and the upcharge for the new prop was minimal. Be advised, there is some lead time (approx 3 weeks) on the prop build...mine will be a late XMas present!
 

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I have a 1984 Pearson 303 with a three bladed prop (not feathering) that was installed two years ago. The performance is better than the two blade and I haven't noticed any appreciable drag when under sail. The performance still isn't stellar under power (small 2gm engine) but it is improved.
 

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Ok, so the new prop is installed and so far I like it. Please note the bottom has now been freshly done so I am surely seeing some performance gains here as well. (....and don't call me Shirley!)

My testing is far from scientific but here goes.....Under power, I am seeing definite improvement in speed vs rpm. With the MW, at 2400 rpms, I averaged 5.5 kts (tide and conditions in consideration). With the CS prop, at 2400 rpm, I am seeing around 6.4+. Prop walk, in reverse gear, has not been reduced but is manageable.

The engine tag indicates max continuous rpm to be at 3200, I am seeing about 3050 rpm and suspect there may be some variance/deviation in the guage...but is close enough for me...I am happy with it!

I have also noticed an improvement with less drag under sail. This improvement is a harder to quantify but is noticeable.

In my opinion, for the small up charge in cost, the CS prop is a good upgrade over a conventional design.

Here are some pics of the MW vs CS...pretty dramatic differences in surface area.
 

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I,m curious. My Yanmar guy tells me I should cruise at around 2700PM om my Yanmar 2GM. In flat water that equates to 6.3 knots for my C&C 29. He claims that you are doing more harm than good if you continually operate at lower rpms. I motored for 19 hours straight between 2600-2800 rpms and the engine ran fine. I have a Martec 2 blade folder. The key is the right pitch and prop size along with a good alignment. I always have a clean racing bottom which probably helps too.
 

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That makes sense - it's about 80% throttle of the max continuous rpm of 3400.

But to be propped correctly you should be able to take the engine to its max rpm - if not you are over propped. And you should not be able to go over max rpm.
 

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I have a 1984 Pearson 303 with a three bladed prop (not feathering) that was installed two years ago. The performance is better than the two blade and I haven't noticed any appreciable drag when under sail. The performance still isn't stellar under power (small 2gm engine) but it is improved.
Where did you get your prop from and if you don't mind how much did it cost I have the 84 Pearson with the small 2gmf motor and it takes me 2.5 hours to get to the Long island Sound from my marina. Trying to reduce the time spent on the river.

Thanks
 

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This is a 10 year old thread ultimatedamage. Don't hold your breath waiting for wretchedsailor to reply as he has been inactive for years.

That said, someone else may be able to help you in finding a new prop. Would be helpful to let us know what prop you have now and what RPM and speed you make at about 80% of full power. I personally am not a big fan of 3-bladed props due to the impact on sailing performance. I have a 2-bladed folder.
 

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Wretchedsailor says he "hasn't noticed any appreciable drag" from his 3 blade prop. Anyone who has made the switch from 3 blade fixed to a folding or a feathering prop will tell you sailing performance is significantly improved.

My personal experience going from a 3 blade fixed to a 3 blade Flexofold is that not only did my sailing performance improve, my motoring performance also improved. Something to consider.

In terms of selecting the correct prop for your boat, be it fixed or low drag, your best bet is to reach out to the prop manufacturer. They will want to know your engine model, transmission model, boat type and shaft size. They are the ones that will know which of their products is best.



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