Prop Comparisons

[Loren Beach]

Prop Results

New prop on yesterday. Michigan "Sailor" three blade. 15 X 10.
Motored back to the moorage and evaluated it some on the way.
The old 15 inch two-blade Autostream is off the boat for the first time since '95. (I had forgotten just how heavy that mechanism is!)

Backing up is comparable but there seems to be a bit more walk to port in reverse. Something to cope with.
Forward it obviously moves a lot more water with all that extra blade area.

The propeller shop that sold it went by their own knowledge base and a modern computer application that compares hull characteristics and engine specs.
Result is that they are close enough for now, but I can see that a future haul out will involve some slight re-pitching.
Reason is that I can now only get about 2750 rpm in smooth water, for about 7.2 kts speed.

With the former adjustable two blade I could get the full 2950 (+ or -) rpms at that speed.
Now, cruise speed at 2500 is about 6.5. That's a bit high for smooth water motoring, and we will therefore have less HP available to punch through a head sea.
This is far better than the 15 X 12 two blade that came from the first owner -- that prop hobbled my top rpm to about 2600.

I imagine that reducing the pitch about an inch to 15 X 9 might about do the trick. But what would I know?

Anyhow, that's where we are right now.

Regards,
Loren

ps: see attached pics of new and old prop and Autostream hub before removal.

 

[EGregerson]

vibration

loren ; since you didn't mention vibration, can i assume that the new prop is satisfactory? and ... how can you know what you gain or loose under sail with drag?

 

[Loren Beach]

since you didn't mention vibration, can i assume that the new prop is satisfactory? and ... how can you know what you gain or loose under sail with drag?

It seems to be quieter, but that was only on a 40 minute trip back to the moorage. We plan to get out for a night or two this coming weekend and really get better acquainted with it. Sailing drag expected be about a half knot loss in light air, going by past experiences. Only time will tell, as the trite saying goes.


Loren

ps: here is another three-blade prop thread on this site:
http://www.ericsonyachts.org/infoexchange/showthread.php?t=1106

 

[u079721]

when you're contemplating swapping around props, do you usually stay with the original diameter? e.g. i have (probably the original) 15 x 11 2 blade on my e34. if i went to a 3 blade, should i stay at 15; or can i drop to a 14"?

I guess I would disagree with David's comment above about "necessarily" going with a smaller diameter. Yes you CAN go smaller when you go from two to three blades, but you don't have to. What you do have to do is balance the load - meaning that if you keep the same diameter, and move from two to three blades, you have to drop the pitch. Or you can drop down in diameter an inch, and drop the pitch slightly less. Remember that after the switch you need to run the engine tests to see whether you are possibly over or under propped.

In our case the PO went from a two blade 16" diameter 13" pitch fixed prop, to a three blade 16" diameter Max prop. Which was great, except that the yard pitched the prop at the same 13", which WAY overloaded the engine, and we could not get the rpms above 2000. Over the course of a couple of seasons we dropped the pitch all the way to 10", and finally got the engine revs back up to 2900.

If he had gone instead with a 15" diameter prop we would probably have settled at 11" of pitch.

 

[Emerald]

If you went from a 2 to a 3 blade, all else equal, you would go to a smaller diameter. Here's a nice little prop 101 write-up from a place that did a shaft for me a ways back:

http://a1discountprop.com/propinfo.htm

This is why I put in the key words "all else equal" and included the link to the prop 101 write-up. There are a LOT of variables here, and it can get very confusing to sort through. For example, depending on original tip clearance, you may or may not want to go smaller for other reasons, and this is where having someone who's got experience with your exact setup is a great time saver. I was lucky with Emerald in that someone else had already gone through all the headaches on the Independence 31 and my exact engine/transmission combination (thanks Glyn!), and the "right" prop was actually very different from the computer selected prop

 

[Captron]

Prop Comparison

In searching through my hard drive I came across an old XL spreadsheet that had the results of some tests run in Germany on several brands of folding/feathering propellers that I thought was interesting. Don't ask me what some of the symbols and measurements are, I just don't know. Also I don't know how old this data is.


http://members.toast.net/captron/propellor_test.htm

 

[gulfcoaster]

New Prop Purchase

We just purchased Flexofold 2 blade 15x10 for our '87 32-3. The thing is in the mail and hopefully will be installed this weekend. I'll add feedback next week after we get her in the water. Called Chuck Angle in Ma. and he was very helpful. 1095.00 plus shipping. We currently have a 14x9 3 blade fixed. After reading the May issue of Yachting Monthly and discovering the drag characteristics, we elected to make this change for racing purposes. We always back in to our slip. Should be interesting.......

 

[Frank Langer]

We have a 13 x 9 Varifold folding propeller on our 1984 E30+. It generally works well. Although there is no tach on the boat, I try to run the engine at about 80% of top speed judging by sound/feel. At that rate, the boat will easily cruise at 6.2 knots, and I can run it at up to about 6.8 at full throttle, though I don't do this for long.

The boat operates well in forward, but less well in reverse, with some prop walk, especially initially. Once I get underway in reverse it's not bad.

The folding prop was new in 2005. It sometimes stiffens up a bit due to marine growth, so won't open/close as freely. But working it by hand occasionally does free it up, and a good cleaning/scraping of the gears when hauled gets it operating like new again.

As it's the only prop that has been on this boat since we bought it, I don't know how it operates with another prop.

Frank

 

[Loren Beach]

Further in-use report

Just got back home from a couple weeks cruising.
Everyone said that a three blade (any kind) would vibrate less than a two blade. Except for a persistent and attention-getting vibration at around 1200 to 1400, this appears to be so. Not really a lot of difference that I can see, though.
Power (i.e. thrust) is noticeably better at all rpm's than the old two blade. To be accurate, this is not really a fair comparison, since there is no cupping on the former feathering prop blades.

Reverse is less effective, with more prop walk.

The boat is a better motor boat now and also a better motor sailor... :nerd:

Under sail, in the lower river/bay closer to the ocean, with the afternoon winds hitting 25+ true, we could only make low 8's and spent most of the time in the high 7's, broad reaching.
With our feathering prop, same conditions, we were always in the high 8's and low 9's.
While the dock gossip is that a fixed blade drags the most in light air, I am now of the opinion that it also costs up to a knot in medium and heavy air as well. (Of course, that opinion is still only worth about two cents.)

Admittedly, what with light winds on the nose all the way down the river to Astoria, we motored like a trawler! Covered ground at a faster pace than in the past.

Obviously there were bound to be plusses and minuses to this prop change over...


Our thinking now is to start budgeting for a three blade feathering prop someday.

And that's my report.

Cheers,
Loren

 

[Emerald]

Hi Loren,

this is very interesting feedback on your top speeds with the prop switch. Really makes me wonder about the 3 blade bucket I am dragging. In the interest of looking at all factors, any chance that you've got bottom fouling that could be part of the speed change? I know we have different fouling issues on the Chesapeake, but I've always been amazed how quickly we get slime build up and how much it affects speed (and it's not just me, pretty much all the boats at our marina have constant battles with this from what I can tell).

 

[gulfcoaster]

32-3 w/ 2 blade Flex O Fold.

I think I posted this on another thread already but here goes. Had a 3 blade fixed. Called Mr Angle and he said I would need a 15x10 2 blade folder. The cost was 1095.00 plus 10.00 shipping. The yard quoted one hr. labor and a quick haul. The old prop came off easily and then the new one went on. He folded the new one back and it overlapped the rudder by 1/4 inch. Pull the rudder, pull the shaft, get it shortened, reinstall. 1100.00 more and 24 hrs later we were back in the water. Just came back from a 30 mile trip with about 4 hrs of motoring. Propulsion is as good if not better in forward. Surprisingly, reverse was better. Good propulsion with no prop walk. I LIKE IT!.

 

[Loren Beach]

Hi Loren,

this is very interesting feedback on your top speeds with the prop switch. Really makes me wonder about the 3 blade bucket I am dragging. In the interest of looking at all factors, any chance that you've got bottom fouling that could be part of the speed change? I know we have different fouling issues on the Chesapeake, but I've always been amazed how quickly we get slime build up and how much it affects speed (and it's not just me, pretty much all the boats at our marina have constant battles with this from what I can tell).

Right you are to mention the possibility of fouling.
I had very little slime due to having a diver do a bottom scrub within a month of our vacation.
In fresh water we do get a build up of slime, especially the top foot of paint where the sun penetrates our murky river water. I also scrub that upper part and the rudder with an angle-head 3M pad regularly. Paint of choice around here has been Trinidad SR.
(The "SR" may "resist" slime, but no way stops it.) I also cleaned the waterline and a couple of feet under with the angle-head pad a week prior to our trip.

So, the bottom was reasonably clean, at least the upper part.

To repeat, and to be fair, the three blade sailor prop really does make for a superior powering experience in forward gear. Averaging 6.5 kts for hours at a time is easy, now.
So I did indeed gain some motoring performance... but there are observable tradeoffs.

Best,
Loren

 

[EGregerson]

gori

I checked out Captron's spreadsheet a couple of months ago; i was drawn to the gori; so i checked out the website and entered my boat data for a quote. They said a 2 blade folding would save .85 knots over a 3 blade fixed; presumeably for my E34 which i believe is pretty similar to Loren's O34 in basic respects. So, if that's the trade-off, based on their computer estimate, it's about 10%. It sounds like it might be pretty close.

 

[Loren Beach]

Another 3-Blade Prop data point

We are just back from a cruising race, 20+ miles down the Columbia River yesterday (Saturday), and with very light air we motored back home today.

While the three-blade certainly slowed us down during a 3+ hour beat to weather in 4 kts of wind that slowly built to a solid 18+, the trip back gave us a good benchmark for powering performance. The hull was scrubbed by a diver on Friday.
So the bottom was super clean. We maintained 6.8 to 7.0 knots thru the water motoring home, at 2500 rpm. It was a measurably-quicker trip than usual.

Since most all of the other boats were motoring also, it was interesting to see how many we could catch and pass. We have apparently created a fast trawler. Of course this is at the expense of sailing performance, as I mentioned earlier.

Time to start building up the boating account to budget for a three-blade featherer.

As to how we did on Saturday, we were slower than the little group of fast boats with their composite sails, and ahead of the main bunch of everyone else.
I imagine that many clubs have some sort of event like this one, and if not, they should!
There are no trophies for first, just a pair of engraved wine glasses for every finisher. "Everyone's a winner."
There were a noticeable number of other Ericsons entered, too!


Cheers,
Loren

ps: a friend of mine just emailed a picture of us churning along today at about 7 knots.

 

[Loren Beach]

3 Blade, Nearly Three Years Later

Just hauled the boat for a new bottom this week. Here's a photo of the prop.
You can see the prop and line cutter.
Line cutter still untested, but that's OK...

Still no $$ in our budget for a 3-blade featherer, so we will instead spend time and money on some overdue shaft balance/vibration problems while it's out.
The original shaft looks like it might be at the end of its life. It's actually polished down a few thousands where it fits into the bearing. There seems to be some "whip" in it, too.

This would be a lot more interesting, from an educational standpoint, if it were not so hard on the budget.


LB

 

[gulfcoaster]

3 Blade Drag

We switched to our 2 blade Flex O Fold 3 yrs ago and love it. I read a 5 page article 3 yrs ago in Yachting Magazine which compared performance and drag on many props. The 3 blade fixed prop had the drag equivalent of 2 five gallon buckets being dragged behind the boat. Try to race with that anchor!

 

[Randy Rutledge]

Last year I installed a 2 blade flex o fold prop on Rumkin and I love it. Better thrust forward and reverse with less prop walk than the 2 blade fixed, I expected delay when shifting to reverse but it is instant. The boat starts to move in light wind much better where it would lay over a little and then slowly start to move now she starts to move as the sails load. I would definitely go with the 2 blade if fitting another boat. The reviews give the 2 blade better thrust forward and reverse over the three blade Flex O fold and many fixed 3 blade props.
Flex O fold props are a work of art from a machine shop. “If you can’t tell I like it.”

 

[rwthomas1]

I've had the Variprofile 3 blade feathering prop from Variprop for two seasons now. Other than being a bit expensive I have no complaints, it works better than expected, much improved light air performance, better helm feel and better motoring in any direction or conditions. The great thing about sailing today is the sheer number of choices we have for most things we need. There is a prop for every application and budget, pretty cool I think. RT

 

[Greg Ross]

Max PROP here

I had the good fortune to acquire an experienced "Classic" Max-Prop and fitted it last year. Unfortunatlely a short Season courtesy of the lousy Spring/ early Summer weather, disrupted further by a work assignment far from home and the final insult, hurricane damage and early haulout limited my opportunity to play with it. The literature cautioned up to 15% loss of effeciency compared to an equivalent fixed prop. I pitched it one notch heavier that the 14 x 10" it replaced and it appeared to work quite well. The I-31 was no joy going astern, now with plenty of authority in reverse I could see improvement there. Didn't do enough pure sailing in the abbreviated season to get any sense around relative drag and I never did dive the boat to ensure it was feathering fully. Shifting from forward to reverse was without hesitation so the mechanism was certainly doing as asked.
The next season I will coat with grease or petroleum jelly, after only 9 weeks in the water there were a number of barnacles well established.

 

[Loren Beach]

More prop info

http://forums.sbo.sailboatowners.com/showthread.php?t=140954&referrerid=95405

Quite a "review" about the Flex-O-Fold prop.

This seems like a proper reference for this thread subject.

LB