propeller change??

[lindsay]

In the midst of some work on my Volvo 2020 (on a Sadler 29) after 3000 hours of trusty service, it has been suggested by a keen French mechanic that I should also consider changing the standard two blade propeller to a folding version.

I have always understood that these improve performance under sail, with less drag, but diminish performance in reverse.
Since I sail always singlehanded, and do a lot of ins and outs of often new ports, I am loathe to part with the Sadler's quite reasonable reversing ability, but of course am tempted with an increase of speed under sail.

What experience does anyone have in changing propellers? How much speed increase and how much lack of reversability?

Thanks in advance

 

[davidbains]

If you use a Kiwi prop your performance in reverse will improve a lot!

 

[rob2]

Changing a prop is largely a matter of having plenty of penetrating oil and a strong puller - otherwise easy enough.

My folding two blade prop gives noticeably better sailing performance, and just needs a good, positive burst of power to kick it open in reverse. Once open, though, it powers along nicely and steers well. This, of course will in part depend on the hull configuration of your boat. Mine is fin and skeg.

The suggested Kiwi is rated by many but like all pitching props, will have a little more drag than an equivalent folder.

I was lucky that my previous (1986 vintage) prop came from Darglow who were able to supply to the details kept in their ledgers!

 

[boatmike]

Knowing the Sadler quite well I would say the maximum improvement from a standard 2 blader to a fully folding prop might be up to but certainly not exceeding a knot at best. Probably realistically about half that. The loss of speed in forward gear when motoring though will be more than that with most folders and even with the best a loss of at least 1/2 knot is inevitable. In reverse they are mostly simply dreadful. Feathering props are a compromise and the loss of power less noticable, but greater drag when sailing. Sophisticated self pitching props like the Brunton Autoprop make the best of all conditions but are bloody expensive. Personally I would say "if it ain't broke don't mend it"

 

[ebbtide]

[ QUOTE ]
My folding two blade prop gives noticeably better sailing performance, and just needs a good, positive burst of power to kick it open in reverse. Once open, though, it powers along nicely and steers well. This, of course will in part depend on the hull configuration of your boat. Mine is fin and skeg.

[/ QUOTE ]

Ditto ditto ditto and a big vote for Darglow - plus virtually zero propwalk. Perfick!

 

[ditchcrawler]

I changed from a standard 2 blade to a Kiwi prop on my Moody31.I have noticed no change in my forward speed,but a slight increase in fuel consumption.My sailing speed is better by av half a knot & sometimes more,but the thrust in reverse is amazing.I reverse out of my berth in tickover.No association just a satisfied customer.I had a Maxprop on a previous boat & the Kiwi is as good for alot less money.

 

[doug748]

I considered this when I changed my engine, as a lot of similar boats to mine have adopted various styles of new tecnnology in this department.
In the end I decided I did not need the complication or the risk that sooner or later it would not work - just when you need it most.
Anyway you are lucky, I can't do backwards at all.

 

[Marsupial]

A difficult one to answer but you must decide what you want the propellor for?

Is it to get in and out of marinas or do you intend to motor for hours.

If its the latter then a three blade folder will help you motor. As for speed, that depends on what dia and pitch you have now compared to what you might buy. The rule is size the prop to the engine NOT the boat, in other words the propellor should deliver as much of the engine HP as possible to the water - how fast the boat will go is physics.

A three blades will make better headway than a two blade; into a sea.

I ve had 3 blade maxprop feathering and volvo folders, my boat went backwards with both! and faster forwards because they were correctly sized.

Fuel consumption is difficult as you wont be comparing like with like but the engine wont use more because of the prop as such, it may use more because its delivering more power into the water and hence the boat is now going faster. Again its physics.

My advice for what its worth, get a proper appraisal on the prop size vs the engine output that you currently have and see if you could increase the thrust by changing the prop. If the prop you have is already delivering all the engine HP to the water dont change it. If you change it fit a folder, they're cheaper.

 

[NormanS]

If you can possibly justify the expense, go for the Brunton's Autoprop. Excellent piece of kit. I fitted one last year, instead of a fixed three blade prop, and it's given me about 1kn faster motoring (at lower revs), probably about ½kn faster when sailing (difficult to be precise). It really comes into its own when motor-sailing, when it automatically sets its pitch to suit the speed that you are already making with the sails. Admittedly, my boat is a motor-sailer, but it's well worth looking into. You do need the type of gearbox which can stop the shaft from turning when you're sailing.

 

[PeterGibbs]

Q - are you satisfied with you boat's performance now? Sounds like you are, so why go to the expense and complication of a folding prop?

These posts are loaded with good folks who can't stop fiddling with their lovely boats, and spending money that produces mixed results at best...hope you don't join their ranks!

PWG
Also a practiced single hander.

 

[Marsupial]

But wasn't that my point? and we dont fiddle we improve, my boat sails faster and motors faster. In my case I was dragging a 20" diameter disc through the water under sail - my folding prop presents a 3" dia disc not strange then that under sail I get a good two knots faster in light airs!

These guys who tell you folding or feathering props make little or no difference have obviously not tried them. AS for mixed results if go to the university of the pub, you will get mixed results. (Thats where boatbuilders in the 1970's and 80's went)