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-   -   Feathering Prop vs. Fixed Blade Prop (http://www.sailnet.com/forums/pacific-seacraft/62377-feathering-prop-vs-fixed-blade-prop.html)

Benevento 02-26-2010 06:24 PM

Feathering Prop vs. Fixed Blade Prop
 
I have a 2000 Pacific Seacraft 40, with a 3 blade Max-Pro feathering prop (18" diameter, 13" pitch) which unfortunately needs to be replaced. I am leaning towards a fixed 3 blade prop. Specifically a Campbell Sailer, (17" diameter, 9" pitch), manufactured by West by North Enterprises. The manufacture recommended the smaller diameter and pitch. Apparently this has been the case for other customers too; the claim is this prop design is more efficient and therefore can be smaller. This appears to be largely substantiated by others who have purchased this prop.

Therefore my questions are more about how much of a difference in performance I might notice moving to a fixed prop. Specifically:

1. Will I have significantly less control in reverse
2. Is there appreciable increase in drag under sail
3. Comments on this brand

Thanks!


sailingfool 02-26-2010 09:01 PM

I'd guess you'll lose .5 to .75 knot depending on conditions. I'd say a bad tradeoff but I guess to each their own.

ralopata 02-26-2010 09:44 PM

I believe Nigel Calder wrote a rather lengthy section on the prop selection for his PSC 40 in his book, but I don't have a copy with me, so I can't cite it. However, my recollection is that he discusses fixed prop diameter and pitch for the 40 quite thoroughly. I'd recommend it as a good resource.

Based on my experience, the MaxProp does provide very nice control in reverse on the 40. I've had a MaxProp on the boat the entire time I've owned it, so I can't comment on side-by-side comparison with a fixed. Based on other boats I've had and sailed, however, I'd say you'll always have better control with the folder -- and much less "prop-walk" when you back. However, it is sure to reduce your speed under sail. How much, I can't say for sure, but I'd guess that Sailingfool's .5 knot estimate is a fiar one. That said, though, you may get more speed when powering forward underway with a fixed prop.
So, if you're planning a long inland trip, for example, the ICW on the East Coast where you'll be doing a lot of motoring, a fixed three-blade may be something to consider. Some years ago, I met one sailor boat who put a fixed three-blade on his boat when he left the Chesapeake going south and then had the boat hauled and put a folding prop back on when he got south and was ready to head for the islands.

Then again, if you're voyaging to somewhere quite remote, the great thing about a fixed prop is no moving parts. Much less to worry about. If a MaxProp somehow gets toasted in a remote Pacific archipelago, repair or replacement may be challenging indeed.

All the foregoing, I guess, suggests one way to approach the the prop decision is to consider how and where the boat will be used.

Roger Lopata
JUNO
PSC 40 - #46

svsirius 02-27-2010 07:19 AM

Just have PYI rebuild your max prop... I would never go back to a fix blade except for loosing my prop.. I do keep a fixed 2 blade as an emergency spare but never would make it my primary.

niftynickers 02-27-2010 04:44 PM

Darold,
I have a Campbell Sailor Prop on my C37.I have not had a Max Prop so cannot make a comparison but I can give some comment on the Sailor prop.I have very good forward thrust and serious prop walk in reverse.My prop was delivered with the wrong pitch and had to be repitched by Campbell ( only Campbell will do the repitch)a real hassle.When sailing the drag is negligible, I sail right along with other boats and pass many.
If you are into racing the feathering prop is obviously the way to go but if you are cruising I think the simpler non mechanical prop is best.
One last note ,when I repowered and reproped the engine supplier warned me that he had had numerous problems with incorrect pitch on Sailor props and recommended Michigan props.I ignored that advice and did get a incorrectly pitched prop.

MC1 02-28-2010 11:44 AM

Replace a MaxProp with a fixed prop? Oh the humanity !! :)

Regarding question 1: Yes, no question the MaxProp is better for moving the boat in reverse than a fixed prop (less prop walk, better acceleration from a standing start).
Regarding question 2: The additional drag may not be a big deal for local short sails, but it'll add up to be significant for long distance sailing. Other previous threads here at Sailnet have discussed this point, so you may want to search for them.
Regarding question 3: I'm not familiar with the Campbell, but I'd be suspicious of a vendor's claim of greater efficiency as the science of prop design is well established. It's important to match the prop's performance with your engine to ensure it can reach its specified maximum RPM (else you risk shortening the life of your engine).

If there's a chance of refurbishing the MaxProp, possibly by sending it to PYI even (call them and ask them about it - it may be less expensive than you think), I'd consider doing that. If that wasn't feasible, I'd look at another MaxProp or perhaps an AutoProp.

MC1 02-28-2010 12:28 PM

One other thought regarding prop efficiency (stating the obvious, but since the salesperson brought it up . . .)

Fixed props are more efficient than feathering props for propelling the boat forward while motoring. If one has a power boat, he'll want the most efficient prop for providing forward motion under power.

For sailing vessels, efficiency has to be measured both under sail (weighted heavily since it's a high percentage of our usage) and under power. At least for racing or long distance sailing, the drag question becomes an important factor when considering overall efficiency, yes?

Fstbttms 02-28-2010 01:26 PM

Quote:

Originally Posted by niftynickers (Post 574839)
When sailing the drag is negligible, I sail right along with other boats and pass many.

I would argue that the drag when using any fixed-blade prop is not "negligible". While it may be true that you keep up with, or pass, other boats, this is an "apples and oranges" comparison, and of little real value when discussing the performance of the prop. But if you can keep up with the competition now, think how you'd blow their doors off with a feathering prop! ;)

ralopata 02-28-2010 03:58 PM

A Quick Follow-up Regarding Calder's Calculations

I dug out my copy of Calder's Cruising Handbook, and he has more than five pages of text and formulas he used when deciding on the prop for his PSC 40, NADA.

Bottom line: Calder went with a three-bladed fixed 18-inch prop with a 12-inch pitch. He claimed it provided 7 knots at 3,000 rpm and topped out at 8 knots (He must have really been running that Yanmar hard to do that).

Roger Lopata
JUNO
PSC 40 -- #46

MC1 02-28-2010 06:19 PM

Quote:

Originally Posted by ralopata (Post 575116)
A Quick Follow-up Regarding Calder's Calculations

Bottom line: Calder went with a three-bladed fixed 18-inch prop with a 12-inch pitch. He claimed it provided 7 knots at 3,000 rpm and topped out at 8 knots (He must have really been running that Yanmar hard to do that).

I have all Nigel's books and have read them through, but they're not handy at the moment. The information you're citing regards efficiency of the prop under power, but I'm pretty sure he assessed the drag issue as well. If you have it handy, can you remind us / summarize his feelings concerning drag?

Regardless of the efficiency issues, for me the (near) lack of prop walk in reverse is nice as I single hand a lot and it's one less thing to have to manage. I guess as with everything else sailing, it comes down to one's requirements, priorities, and preferences.


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