SailNet Community banner

1 - 20 of 58 Posts

·
Registered
Joined
·
7 Posts
Discussion Starter #1
We are going to buy a new prop for our 40' Island Packet and wonder if anyone can share their opinions on these two props. We have a Prowell feathering prop that is 15 years old and we think it's time to replace it. It seems that the Autoprop will be easier to install and has the advantage of having no pitch adjustments to make. However, it's priced a lot higher than the MaxProp which seems to be popular as well. Your opinons will be appreciated!
LJD
 

·
Registered
Joined
·
660 Posts
I just saw a KIWI prop at the Vancouver boat show. I looked the thing over real good, and it is a good looking unit as far as the machining goes. It was made totally out of stainless parts. To me I like the idea of SIMILAR metals in contact with the brine. It was adjustable, foreward and reverse like the MAX but quite a bit simpler design. I am sure the drag of the KIWI will be higher, due to the design of the foils, and the 3 stops for the blades. The KIWI could be had today in Canadian currency for $1200-1400 for a 18" feathering prop out of solid stainless, with some type of polycarbonate blade? Sorry if the material is wrong (some one is liable to know what it is.) The KIWI is priced good in my point of view, It would cost me only slightly less to make one, and be a PITA with the machines I currently have. I easily could have made a MAX for what they retail. As for the AUTO PROP it was a sleeker design, almost like a stainless MAX taking into consideration who will be putting these things on their boats. People with "X" # of $, willing to give it away to go "Y" faster, and feel "Z" cooler than you in the end! haha
 

·
Seattle Sailor
Joined
·
192 Posts
I actually just put in an order for a variprop 3-blade feathering prop. After looking as several options at Strictly Sail Chicago, I was impressed by the engineering and the new low-profile prop hub. I had planned on getting a Kiwi prop (which I still think might be a good prop), but the price of the Variprop was only a few hundred $ more. I am in fresh water, though, if that makes any difference to those worried about salt-water corrosion. Sorry I don't know much about the MAxi and Auto props other than seeing them in demonstrations.
 

·
Registered
Joined
·
935 Posts
As has been mentioned the Autoprop is expensive. I put one on my Catalina 320 after a couple years and used it for 4 years happily. My Nauticat came with one and besides the feathering and Great Reverse its Auto Pitching is great for Motor Sailing.
 

·
Super Moderator
Joined
·
6,771 Posts
If you read..

If you read the MIT prop study the Max Prop develops about 2 lbs of drag and the Autoprop about 9-10 lbs of drag. If the intent of buying a feathering or folding prop is to reduce drag then I think the Max Prop is the best choice..

Of course I chose a Campbell Sailer prop to have the lowest drag in a non mechanical prop..
 

·
Seattle Sailor
Joined
·
192 Posts
"If you read the MIT prop study the Max Prop develops about 2 lbs of drag and the Autoprop about 9-10 lbs of drag."

Do you know if the props currently made are the same as the props tested in the MIT study in 1994? Several props were not even made then, and at least some of the props have undergone significant changes in the last 15 years since the tests were done.

(Disregard if there is a newer MIT prop study.)

Of course, we are talking about a slight difference in efficiency and drag, and much of the choice will probably come down to ease of use, convenience, and local experience with a particular prop.
 

·
Super Moderator
Joined
·
6,771 Posts
"If you read the MIT prop study the Max Prop develops about 2 lbs of drag and the Autoprop about 9-10 lbs of drag."

Do you know if the props currently made are the same as the props tested in the MIT study in 1994? Several props were not even made then, and at least some of the props have undergone significant changes in the last 15 years since the tests were done.

(Disregard if there is a newer MIT prop study.)

Of course, we are talking about a slight difference in efficiency and drag, and much of the choice will probably come down to ease of use, convenience, and local experience with a particular prop.

Same 1994 study but the differences in these props externally from then until now is very slight. I just finished researching props for my own boat, and I would guess the Max still has one of the lowest drags for a three blade prop.

I looked at many including Autostream (HUGE HUB), Max, Gori, Kiwi Autopop and others. I also spoke at length with my local prop shop about repairs. They sell many different brands and for them the Max Prop has been the most reliable but still gets no cigar from Mike the manager. The had a total of four feathering/folding porps in house at the time for rebuilds/repair ranging from $500.00 to over 1k.

My reason for not choosing a floder/feather prop was reliability and the fact that they do not like to hit lobster pots which can literally sheer off blades (had one in house that had happend to). We have lots of lobster pots up here.. My own prop shop talked me into a prop they don't even sell..
 

·
Seattle Sailor
Joined
·
192 Posts
Feather vs fixed

The other question I would have is why buy a feathering or folding prop if not racing. The difference in drag can be made up by chucking a few of those extras off the boat that haven't been used in several years, and a fixed blade prop is essentially maintenance free (other than cutting loose the tangled lobster pots and fishing lines). As Maine Sail described, these props are not always the most sturdy. A nice 2 or 3 blade fixed prop will nearly always perform better under motor, and will certainly last longer.
 

·
Super Moderator
Joined
·
6,771 Posts
The other question I would have is why buy a feathering or folding prop if not racing. The difference in drag can be made up by chucking a few of those extras off the boat that haven't been used in several years, and a fixed blade prop is essentially maintenance free (other than cutting loose the tangled lobster pots and fishing lines). As Maine Sail described, these props are not always the most sturdy. A nice 2 or 3 blade fixed prop will nearly always perform better under motor, and will certainly last longer.
That is why I went with a Campbell Sailer... I don't currently race and prefer the reliability over the .1 knot..

The funny thing is that a Campbell Sailer three blade at 4 knots has the same drag as a 2 blade Michigan Wheel Sailer prop and only about 1.5 lbs more drag than Martec 2 blade folder. In higher winds 12+ the hull speed is slowoing me not my prop.

I don't hear folks talk about this much but folders/featehring props only really help in lower wind speeds. Once you hit hull speed.... In 13-15 knots I can tow my dinghy with the motor on and still hit hull speed so at that point I could have a 2X4 as a prop and still hit hull speed.
 

·
Registered
Joined
·
7,302 Posts
Then again, folks that want to sail in area's with lower wind speeds, where it is harder to hit hull speed, will find that a folder/feathering prop will net you upwards of .5-1knot of boat speed in those lower wind ranges, ie less than 10 knots. Obviously if in a 20+ knot wind, the prop is not the worst thing for slowing the boat down!

With that in mind, my boat came with a max prop, and the previous owner did report .5-1 knot gains in lighter winds! In Puget Sound where I am, in the summer we do get quite a few days with winds under 10 knots during the day. So if you want to sail more, faster etc, it really will not matter if you race or not, a folder WILL allow you to motor less!

Another prop option, is a Kiwi. An identical boat to mine north of me that races heavily, he mentioned he gained a bit more speed with a kiwi over having a max prop on the boat. ALong with a bit more motor speed at the top too!

overall, I am happy with the max prop that came with my boat!

Marty
 

·
Unpaid Intern
Joined
·
992 Posts
I'm kind of in a similar position about where to go... My boat came with an old-style Martec 2-blade folding prop (no gears). It's in good shape, but once we splash the boat, I have a feeling I'll be unimpressed by it's performance in reverse, while being happy with the sailing performance. I'm also not thrilled about the potential reliability factor.

From my perspective, I'd hate to buy a replacement prop that would noticably slow me down sailing (I'm not racing, but like moving in lighter air on the Bay), but I'd like to be able to reliably back up when needed.

The Kiwi prop interests me due to the price point when compared to other feathering props, and I'd never spend the bucks for the others.

My problem is that I don't really have a clear picture of the actual performance implications of my current Martec, versus a Kiwi, versus a 3-blade Campbell sailor. I know the pluses and minuses of each, but how noticable those differences are is something I can't really quantify. That makes the choice more difficult.
 

·
Registered
Joined
·
728 Posts
I bought my boat new in 1985 (Tayana 37) and installed a 3 blade max prop. After some adjustment to the pitch after a year or so it is doing fine to this day. Everytime I haul out I repack the prop with grease which is somewhat of a hassle requireing another set of hands to get the blades properly lined up. I think the newer ones have a grease fitting. The nice thing about the pitch adjustment is that you can play with it to get the proper rpm on your engine. It is excellent in reverse and there is a slight ineffenciency in forward since the blades are flat and not curved as a fixed prop, but the difference is very hard to quantify.
 

·
"Sparkie"
Joined
·
343 Posts
That is why I went with a Campbell Sailer... I don't currently race and prefer the reliability over the .1 knot..

The funny thing is that a Campbell Sailer three blade at 4 knots has the same drag as a 2 blade Michigan Wheel Sailer prop and only about 1.5 lbs more drag than Martec 2 blade folder. In higher winds 12+ the hull speed is slowoing me not my prop.

I don't hear folks talk about this much but folders/featehring props only really help in lower wind speeds. Once you hit hull speed.... In 13-15 knots I can tow my dinghy with the motor on and still hit hull speed so at that point I could have a 2X4 as a prop and still hit hull speed.
You are correct that once you reach hull speed, a folding/feathering prop will no longer help your boat speed. Dont forget though, windward ability is a function of the lift/drag ratio. If you decrease drag or increase lift, you can point higher for the same boat speed. A folding/feathering prop will give you a few points toward the wind with no reduction in boatspeed. My 2 cents......
DD
 

·
Courtney the Dancer
Joined
·
3,970 Posts
We put an Autoprop on the last boat which replaced a three blade fixed. This was on a 34' sloop, 13000 disp. We noticed a large increase in light wind speed -app. .5+ knot. This allowed us to sail instead of motor more often in the light winds of summer here in the PNW. There was a huge difference in motoring efficiency and reverse power was amazing. There is also no prop walk, none. It made docking easy, and backing out even easier. We gained about 1 knot at the same rpm which allowed us to run just under hull speed without the noise of the engine at higher rpm. We put over 1000 hours on it over 12 years and never had a problem although I have read the thread provided above and wonder if something has changed. Seems like Autoprop would be out of business pretty soon if it was a widespread problem. The current boat has a fixed three blade sail prop, not sure if I'm going to spend the 4K for the Autoprop or not, I sure miss the ability to reverse in a straight line.
 

·
Registered
Joined
·
33 Posts
The Catalina 470 we bought two years ago came with an Autoprop and has served us very well. As stated, there is no propwalk. I couldn't tell you if it is port or starboard. Also, when the blades swing around, they give full thrust in reverse.

But to me the biggest advantage to the Autoprop is its ability to self pitch. This was discussed at some length on our C470 forum. This can result in fuel savings, especially when motorsailing. As the sails add speed to the boat, the blades dig in deeper, keeping the engine under a more proper load and RPMs lower.

For reference, we usually cruise at 2200 RPM at 7.2 kts in flat water, burning 1.08 GPH with a 28,000 lb boat (Yanmar 75 horsepower).

So far, we have had no maintenance issues, just grease and change zincs.
 

·
Registered
Joined
·
5,491 Posts
I am (finally) installing my VariProp this year. Long story, but I expect great things from it. As for "why", my steel full keeler will benefit from it under sail probably more than my fin keeler did with a Gori folder (and that impressed me), and the ability to have separate forward and reverse pitch settings that I can adjust with an allen key and a snorkel (in the water) makes it worth my while. Basically, I want to stop the boat and maneuver better than I can with a fixed blade, and I have seen most feathering props perform very well in this regard.
 

·
Registered
Joined
·
188 Posts
Kiwi

I've had it two seasons & like a lot. Less drag, way better reverse & forward than my previous two blade fixed. Lots less $$.
 

·
Registered
Joined
·
2,498 Posts
Buy a long-keeled double-ender, mark the prop shaft so that you know when the prop blades are vertical, and turn the prop so that the blades are in line with the keel.

On the point about "hull speed", drag always slows the boat. At higher speeds the fractional contribution of the drag from the prop drops off as there is so much drag from the hull shape, but the drag from the prop is steadily rising.

With a lot of wind around, you won't notice it much, but it will be there.

At very low speeds I reckon you won't notice it much either, as the vast majority of the drag will be from surface drag, and the prop, though an obstruction, does not wet much area. It obstructs (from form drag), but do you not need a decent bit of speed to see that one? There should be a good graph to plot in there somewhere?

Next time I am out in light airs I will try to turn the prop in line with the keel, and then perp to the keel, and see if it gets noticed. It should be a good experiment.
 
1 - 20 of 58 Posts
Top