Lavezzi 40: Folding Props

[MKB53]

Hi DragonLady

I fitted Seahawk feathering props to my Mahe and have been very happy. 3 years and a lot of hours so far.

Sails much better than fixed - quicker and tacks easier. Top speed under motor is also up close to 1 knot.

I prefer feathering to folding for astern performance and I am also wary of wear on the exposed gears on the folding ones. Feathering are more complicated but may well be more robust.

You should send SeaHawk an email with your boat details. They are very responsive with recommendations. When I bought them my boatyard sourced them for me at trade and passed on a small handling fee which saved some $s.

[wolfenzee]

Even though fewer blades of the same area is more efficient, the limiting factor is sailboats is useually diameter, builders also have a tendancy to install props smaller than a boat really needs. That said more blades of the same diameter will give you more thrust. I have a 16" fixed 3-bladed prop in a full keel heavy displacement boat, the effect of the fixed prop is insignificant compared to the relyability. My boat just happens to back in a straight line with no noticable loss in power. The biggest advantage I have seen of a folding prop is that the leading edge remains the same in reverse as well as forward.

Originally Posted by Mark Johnson

According to the extensive study and prop comparison done by MIT...

"More blades" makes a LESS powerful prop in theory, IF they have the same square inches of blade surface area. (Apples to Apples)

A three bladed prop of 12" might be equal in size to a two bladed prop of 16".

Thrust wise, the most efficient prop would be a ONE bladed prop, but it would not balance, and is utterly impractical. The best "practical" solution would be a two bladed. THEN a three. This is regarding "thrust efficiency" for a given cumulative amount of blade area.

As is well known, a large prop going slow has more grip than a small prop going fast, but it gets complicated...

The reason for going with more blades, and/or smaller, faster props, (in spite of their being less efficient), is that after a point it becomes impractical to have a prop beyond a certain size, due to the hull's design constraints. There is just so much space for an aperture in the skeg, and it needs to be well clear of the bottom as well as the hull. Multiple blades then become the logical compromise.

IF, however, you CAN fit an appropriate sized two bladed prop, it will be more efficient than the exact same blade area of a three bladed prop, because there is less propwash for the blades to contend with. The two bladed prop will possibly have a bit more vibration, but this need not be an issue.

In the MIT study: Comparing the two bladed FLEX O FOLD folding two bladed prop to numerous other props, including a "Michigan Wheel" fixed two, fixed three, other brands of folding or feathering props, AND the two and three bladed feathering Max props... The Flex O Fold was more efficient than ANY of them, in forward!

IF it is sized correctly, YOU WILL NOT LOOSE ANYTHING BY SWITCHING TO A FLEX O FOLD in forward, you will probably gain... but you do loose a bit of reverse thrust compared to a feathering Max Prop.

Other brands of folding props have different results, but they all will improve your sailing and make it less likely to snag a crab pot line as well.

It is the most bang for your sailing buck!

Mark

[Pieter]

Originally Posted by yeloya

Hi Dragon Lady,


To be more precise, I wasn't even attemting to sail if the wind were at least 12-13 kts. Now, I can sail at 8-9 of wind kts and make 4 to 5 kts of speed..
I've also bought a new assymetrical and with this alone (no main sail) and folding props, we did 8-9 kts at 15-16 kts true from 160-170 degrees..


Cheers

Yeloya

I also use a lot my assymetrical (138 sq m), but i certainly dont use it over 10 knots wind... As i use a shute to open or close, try to close the sail at over 10 knots makes it a very hard task.. And also, i know FP uses this table of windspeeds and reefs, so i keep thinking that flying the assymetrical at higher wind speeds certainly will have its impact on the rigging. So i may err on the safe side, but feel that at over 10 knots winds i can use the two standard sails and develop adequate speeds.
Comments, anybody on using the assymetrical, windspeeds and rigging issue on the Lavezzi?
Best rgds
Pieter

[Le Doume]

We have the " standard" 2 blades prop ( non folding} on our Lavezzi , when considering the expense of replacing them with folding props , I did look at the so called ' gain of performance" under sail . Having had the opportunity to sail in convoy with another Lavezzi with folding props , The decision was made for me , it is NOT worth the expense , further more , seing hos the other boat operated in reverse at the time of berthing , I was very happy to have the props installed by the factory.
Both Lavezzi are equipped with Volvo's 30 hp.

Cheers

[Dragon Lady]

Originally Posted by Le Doume

We have the " standard" 2 blades prop ( non folding} on our Lavezzi , when considering the expense of replacing them with folding props , I did look at the so called ' gain of performance" under sail . Having had the opportunity to sail in convoy with another Lavezzi with folding props , The decision was made for me , it is NOT worth the expense , further more , seing hos the other boat operated in reverse at the time of berthing , I was very happy to have the props installed by the factory.
Both Lavezzi are equipped with Volvo's 30 hp.

Cheers

Thanks that is very interesting, what wind strength were you sailing in when say there was no significant speed difference?

[Le Doume]

We were sailing in a 12 to 15 knots SSW on a broad reach the other cat never got away from us . Once we got back to the YC , it became ' obvious" that in reverse , the difference in thrust is quite significant when berthing stern in .

Cheers

[Dragon Lady]

Even more interesting, do you know what props they have?

[zeehag]

8+kts in my brick is fine with me--LOL--- in 60 kts breeze from mostly--nnw to nw, quartering seas from essentially same direction... reefed mizzen and reefed jib....LOL..was coool and smooth for her--we beoke some seas over her waist but nothing into cockpit... goood ride...only had one major but not really major thing break on that leg-- was a bit of decorative cap when the wind came up and the preventer i had made tugged....i use a huge heavy 3 bladed wonder.... but i am not into racing or seeing how fast i can sail to somewhere else..... the sailing is actually FUN and relaxing...and i dont care how fast i dont get somewhere, nor do i flog my boat.
oh, my prop is i think 18 in 3 blade and way heavy !! i love it--it works!!!

[Dragon Lady]

Thanks for sharing Zee, unfortunately I have to work and that means doing passages in chunks as quickly as is safe, always safety before schedule!

[Rapanui]

Yeloya,
I am interested on your long term experience with the Radice folding props on your FPs after your post a few years ago.
In particular:
*Any issues on reliability?
*Some people have reported problems removing grub screws and shaft nut. What have you found?
*How does the prop perform compared to standard prop in fwd and reverse?
Would you recommend these for my Athena?
They are very reasonably priced and hence attractive if they work ok.
Many thanks
Stephen