Prop Drag :folder vs Max

[JDAM]

I repowered my Ranger 33 with a 20 HP Diesel, and am now selecting a prop. The choice is between a Martec 2 blade folder, or a 2 blade feathering Max Prop. I understand the Max prop is excellent in reverse, but has more drag under sail. We do club race. Extra power in reverse is a good thing, but I wonder if the drag differential between the two props is significant, and might tend to hurt light air performance.

Any input would be appreciated.

[kimberlt]

did you look into an autoprop?

[paulk]

What is the cost differential? We''ve got a martec 2-bladed folder that works fine for us. Of course we don''t motor more than we have to -- we have a sailboat.

[JDAM]

The feathering Max prop is about twice the price, however reverse is reportedly quite a bit improved over the folding Martec.

We back out of a slip often enough so that reverse is a consideration, but not at the price of significant increased drag.

[Silmaril]

If you are concerned about drag under sail, the Martek 2-bladed folding prop is the best, bar none. They are worth maybe 1/10 kt over the feathering props. If all you are concerned about is getting in and out of your slip, go with the Martek.

If you are planning on cruising and using your engine for making time when necessary, go with the feathering props. They are way more efficient under power than the folding props. They act most like a fixed prop. A great help in making your fuel last longer while motoring.

I use the Martek. They are inexpensiive, and can be rebuilt. Mine has been rebuilt twice, over about 15 years. Ran about $300 each time, including labor to pull and install.

[jkumin]

The Max-prop has a touch more drag than the Martec but the difference is small, especially as compared to a fixed prop. I don''t agree the Max-prop is far more efficient in normal motoring. Max-prop blades are flat, with no twist or cup. Both tests I have seen and discussions with people who have them confirm the Max-prop is not all that efficient in forward. People who find them so are usually responding to the ability to adjust the pitch. A properly pitched Max-prop will be better than another type that might be more efficient but is not pitched right.

The Martec is not the greatest in reverse but it can do the job. How much power do you need to back out of a slip? They aren''t that bad in forward. Years ago I raced against a friend with a sistership. We both had Yanmar 2QM15''s swinging 14x14 props. I had a Martec, he had a 2 blade fixed. We were way faster under sail, but what got him was one day motoring alongside to a race start we tried setting throttles to the same rpm. At each throttle setting we would slowly walk away, including flat out. He bought a Martec after that. We learned a two-bladed fixed prop has its own compromises. Blade area is reduced on some models to lessen drag.

I''d only get a Max-prop if power in reverse was the highest priority, they are unmatched for that.

[JDAM]

Thanks for all the input.

Sounds like the drag differential between the Max Prop and Martec 2 blade folder may not be significant. The blades on the Max prop seem to have quite a bit more surface area than the Martec, but the boats rated the same by phrf with either prop.

[wwilson]

Silmaril,

Can you share where the 0.1-kt differential came from? I''m familiar with a now pretty old evaluation done by MIT that concluded there was no meaningful difference in drag between a broad set of props that included both folders and featherers. The 0.1-kt figure you offer is the first time I''ve seen a difference quantified. Is that from test, modeling or anecdotal?

Wayne

[JDAM]

Wayne

Can you share any more information about that report?

If the feathering prop was equal in drag to the folder Iwould opt for the additional reverse power and go with the Max prop.

[wwilson]

JDAM (a munition?)

Five years ago I went through the same attempt at research you are now about. After a reasonably exhaustive effort, I was able to find only one authoritative document despite any number of competing sales claims by manufacturers or owners justifying their purchases.

MIT and Practical Sailor magazine teamed and did an analysis of fixed, folding and feathering propellers. You can search the PS web for the article. The testing was done >10 years ago so the paper will not be on line, but you can have PS send you a paper copy. The "drag" results were virtually the same for the folding and feathering propellers that they tested. If you are really concerned - buy the paper and read it. It is by no means the final word on this topic, but more reliable than anecdotal reports.

Wayne