Prop replacement advice

[Moderator]

We’ve got a fixed 3 blade prop, which is badly corroded and needs to be replaced. We’re thinking of splashing out to buy a feathering prop, for example, maybe the Kiwiprop, Flexofold or Autoprop.

Does anyone have a feathering prop, or some other fancy design prop? We would really appreciate any advice on whether paying 5-10x the price for a feathering prop vs. a new fixed prop is worth the cost, based on how they fit and perform in the Nic 38 aperature arrangement.

Does it make noticable difference for speed under sail?
Does it make improve helm control when backing up?

[Ronar M]

I have thought about a kiwiprop for Ronar M but I think you will find the aperture in the rudder is too small to take the prop when it’s folded.

Trevor

[svgosling]

You might want to consider the Max prop or other feathering prop designs. There has been a lot of discussion on other groups such as the SSCA and the Southbound group (Yahoo groups). I highly recommend these sources of info when considering changes such as yours.
Cheers, J-G

[Jeff]

Hi folks,
I went into this some time ago. Since changing over to a VP D40 engine with h the 2.65 ratio g/box, the original 16×11.5″ prop was hopeless so I changed to what was calculated to be the correct size of 18″x12″.(also 3x bladed)
It was fantastic in ‘ahead’, the torque was amazing & up to about 2000rpm was pretty quiet too. Problem was that as soon as you approached 2500rpm the noise & vibration multiplied ridiculously, & I couldn’t get anywhere near the recommended max rpm of 3,200rpm & couldn’t get over about 5.5Knots. I had the new prop cut down to 17″x12″ with a chamfer on the leading edges to reduce the noise & I think this is the best she’s going to be, without more lift-outs(£££)& fine-tuning.
I contacted Bruntons about all this 9 months ago & gave them the details, displacement of 10 tons in cruising trim etc, & they were happy to sell me a folding prop for over £2500 but stated they didn’t think there would be any increase in performance. No refunds if no improvement, either.!
Needless to say, I didn’t take it any further.
BTW, I still have a nice 16×12″ undamaged prop for sale, (quite cheap)
Jeff

[La Tortue]

Good afternoon sir,

Very interesting experience. Could you give the adress for this prop.

Pierre André

[Jeff]

Hello Pierre,
The Prop is with me on Sea Eagle, here in Penarth Quays Marina-Cardiff Bay-Near Cardiff-South Wales.I can email a photo if you can send your email address.
If you’re definitely looking for a replacement prop, I’m going overseas on another 6 month assignment soon, so you’d probably want to make a decision quite quickly.?
If I have to leave urgently I can leave the Prop with Marina Manager for you/someone to collect, if necessary.
Jeff

[La Tortue]

Bonjour Jeff,

désolé, je m’exprime en Francais car je ne me suis pas bien fait comprendre en Anglais ( je peux lire mais c’est difficile d’écrire).
En fait, je constate que le montage d’origine ( helice de 16″ )est un peu juste pour le tonnage du bateau.
J’envisage de remotoriser ma Tortue et je me pose la question pour la taille d’helice.
Les calculs montrent 18″ mais votre experience est tres interessante et je comprends que la taille de 17″ est le maximum possible compte tenu de la petite taille de la cage d’helice.
Je suis toujours interessé pour connaitre le fournisseur pour votre helice de 17″ .

Cdt

Pierre André

[Jeff]

Hi Pierre,
My new 18″ (later 17″)propellor was bought & fitted while I was on assignment in Australia, & it was already installed before I came back to UK.
Sorry, but I don’t know where it came from.
18″ WILL fit in the aperture but it’s quite close to the hull (20-25mm clearance)which may be responsible for a lot of the noise that’s transmitted through into the aft-cabin, & possibly cavitation as well.
However, it didn’t allow my engine to get past 2,600 rpm & I couldn’t get anywhere near her hull-speed either. I still can’t, & would need to be going down-wind to get 7 knots or more out of her. I’m not happy with this but I’m unwilling to keep spending money on something that may only produce an extra 1-to-1.5 Knots.
Regards…Jeff

[Chihili Q]

I have been reminded of the potential advantages of a feathering prop upon re-reading the Yachting Monthly article about feathering and folding props published a year or two ago. The potential advantages of a 1/2 knot increase in speed, reduced prop wash, and sparing of the cutlass bearing and gearbox suggest such an investment would be well worthwhile. Jeff looked into this and reported that the Norton Autoprop would offer no improvement in performance, by which I presume this means no increase in top speed? Their great claim is that you achieve a similar cruising speed for slower engine speed, and if this is achieved in addition to the above then the package looks very appealing. The article suggests to me that either the Autostream or the Max Prop might be marginally better choices, but I should be most grateful if anybody can offer thoughts based on personal experience. Here is a link to the article: http://www.flexofold.com/upload_dir/docs/Test_YachtingMonthly_low.pdf

Adrian.

[Van]

Hi Adrian,

We looked at this issue a while ago and opted for a fixed prop, from Axiom. It has good thrust, and is sized correctly for Rainshadow, allowing us to get to the recommended 3200 RPM at top speed of 7.5 kts. We do have some noise at higher RPM, but we can comfortably cruise at 5 kts (2000 RPM) – 6.5 kts (2500 RPM).

Where it really shines is in reverse. No prop walk to speak of, and we can reverse Rainshadow confidently and easily, with plenty of power. That was what attracted us to this prop. The previous screw prop was horrible.

Also, Axiom support was super – the first prop sent was incorrect so true to their word, they sent us a new one at their own expense. Really a pleasure to work with them in spite of the first prop not being quite right (the issue was the aperture was smaller than they realized so the blades came too close to the deadwood).

You can see more on our blog at http://svrainshadow.com/?p=827

We felt that the benefit of the extra 1/2 knot was not enough for us to justify the cost. In general, if you have enough wind, there is more than enough power in the sails to drive the boat faster and overcome the drag from the prop. Or put another way, the 1/2 knot effect probably is only important in light air. Our philosophy with that is to get a big light air sail (more on that later).

Finally, we also talked with Darglow Eng about their Featherstream prop, which looks quite interesting and not as expensive (at that time) as the MaxProp, Autostream, etc. See http://www.darglow.co.uk/html/products/feather.htm
If we had not gone with Axiom, we probably would have tried the Featherstream.

Let us know what you decide and how it goes!

Van

[Chihili Q]

Hi Van,

I am thinking (since my current prop is in good condition) of deferring any change until next year or even later in favour of a windvane! I agree with your thoughts about the 1/2 knot saving being rather slight, and value your comments; I was also rather put off feathering props because of the recommendation that they should be serviced annually. The Axiom, in light of your experience, looks a good choice. And I meant prop walk, rather than wash!

Incidentally I intend to order a Hydrovane.

Adrian.

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