Propellor types - fixed blade or folding

[Vivaldi 53]

Hi,

I currently have a 12 x 9, 3 blade fixed prop on my boat (29 foot yacht), being pushed by a 23hp Nanni. The 3 blade has a wicked prop walk when reverse is engaged, making it almost uncontrollable. The boat also came with a 13 x 8 bri-ski 2 bladed folding.

I was wondering if changing to the 2 bladed folding would fix the prop walk issue but I'm not sure of the performance of the prop and if 12 x 9 fixed will be similar to a 13 X 8, 2 blade folding. Any prop experts out there?

 

cheers

[rigger 47]

Sounds pretty bad.

 

On the tranverse thrust - you can use it to assist when you manouvre.

That is position the boat in such a way that the astern affect helps you.

In my job I use the transverse thrust to assist in bringing a vessel alongside, angled approach to the berth good kick astern and the stern lifts towards the berth whilst slowly the boat down.

Another way is to get the bow to swing the opposite way to what happens when you go stern just before you go astern, hopefully the initial swing is cancelled by the astern movement.

 

Not sure which prop will cause less effect.

[Bimini Babe 0]

I'm no prop expert, but I also have wicked prop walk on my boat, and I understand it's more to do with hull shape than prop type. So, long story short... you're pretty much stuck with it, and the best thing you can do is adapt to it.

 

That said, I also believe that fixed props generally deliver better performance than folding props when it comes to prop walk. That's because when you engage astern, prop walk will be worst when the boat is moving slowly (because you're just creating wash, and there is little or no flow of water over the rudder to enable steering), and best when you develop a bit of motion (because now you're actually creating flow over the rudder to help you steer). Fixed props should get your boat moving faster than a folding prop in astern, and as such, should deliver better astern performance on a boat with prop walk. That's roughly the theory anyway, which was backed up in my case when I switched from a 2-blade folding (horrible prop walk) to a 3-blade feathering Kiwiprop (manageable prop walk).

 

You might also try giving it more juice when you first engage astern - it can be a bit worrying, especially in a confined space, but it does help overcome that prop walk.

[rigger 47]

prop walk will be worst when the boat is moving slowly (because you're just creating wash, and there is little or no flow of water over the rudder to enable steering), and best when you develop a bit of motion (because now you're actually creating flow over the rudder to help you steer).

 

The pivot point shifts depeneding upon the forces applied.

Very smuch simplified:

If moving ahead the pivot point moves fwd.

If moving astern the pivot point moves aft.

 

So if you have slight headway (or are steming the tide) when you engage engine astern the effect will more pronounced.

The faster astern you move the further aft the pivot point shifts. So the transverse force has less effect as the lever that the force acts through is shorter.

 

Anyway, will leave it at that and hopefuly someone with knowledge about the actual props you have will come along.

[Bimini Babe 0]

The faster astern you move the further aft the pivot point shifts. So the transverse force has less effect as the lever that the force acts through is shorter.

...and in English?

[rigger 47]

Sorry ship / boat handling is a hobby and job for me - I like the technical aspect and throughly enjoy the art of ship handling.

Heading off for a week long ship handling course soon

[Jon 360]

Hi C

I had a Carpenter 29 for 5 years, great little boats.

You will find it will be worse with the folding prop but sail faster

I found the trick was to set the boat up so the prop walk will bring you back to straight and don't move your tiller until you are moving astern

You have to avoid the desire to correct the prop walk with the rudder as this will just allow the stern to come around and you need to wait till you have good way on astern then you will be able to steer it any where.

The best place to practice this is out in a bay away from advice and other boats.

Good luck

It's just practice.

[Atom Ant 0]

Just seen D's post which went up while I was typing this. If presume you are in a marina as this is where prop walk affects you most. Used to have a boat with fairly noticeable prop walk when going astern. We used to engage reverse and then pull on the opposing stern line to "offset" the prop walk and then back out with no problem at all. That's kind of what BB was saying when she suggested living with it.

 

On another matter with said props is that you have a yacht so what are you doing with a fixed 3 bladed prop? Carpenter 29's are nice yachts but their sailing performance will be affected by a fixed 3 blader. At the very least I would suggest a folding prop and if 3 blades are your thing then a 3 bladed feathering prop. I accept that 3 bladed props in general will give better motoring performance. But if that is what you are after then a launch is a good option.

 

Your best bet would be to talk to the people at Henleys, or Craftmaster, or Kiwi Feathering Props. All the best with it.

[wheels 543]

First of all, "prop walk" is all about angle of the shaft. But yes, prop design either accentuates prop walk, or can lessen it.

The number of Blades, Diameter, Pitch, Blade design/shape/thickness all have an affect how a Prop works. However, there are always many fudges when it comes to a Prop for a Sailboat, because ultimately, you want the best sailing performance. So Props are always secondary. Although it does also depend on budget. If you have the dollars to spend, then Variable pitch/Feathering blade designs can work extremely well. Very simple self feathering props are really a simplistic approach to application.

So what am I saying??? Well there are so many variables, you can not easily just answer the question by saying, a 2 blade will give you less prop walk. Because the real answer is, It depends.

Taking this back to rigger's post though, I would give my back teeth to have some decent prop walk on my boat. Using it as a tool to berth your vessel against a wharf or another boat can make you look an absolute pro.

[Guest]

Hi,

I currently have a 12 x 9, 3 blade fixed prop on my boat (29 foot yacht), being pushed by a 23hp Nanni. The 3 blade has a wicked prop walk when reverse is engaged, making it almost uncontrollable. The boat also came with a 13 x 8 bri-ski 2 bladed folding.

I was wondering if changing to the 2 bladed folding would fix the prop walk issue but I'm not sure of the performance of the prop and if 12 x 9 fixed will be similar to a 13 X 8, 2 blade folding. Any prop experts out there?

 

cheers

 

Gee 12 x 9 seems like a small prop... I got a 15 x 8 with a 21 nani

 

3 blade will be way better motoring (2 knots better in a big blow) also, the 3 blade will give less prop walk

 

Your shaft is out. If you let the tiller go when motoring will it shoot off in one direction?

 

Only thing you can do is get use to it and use it to your advantage as others ubove have said. Good luck

[Mothership 6]

Sorry ship / boat handling is a hobby and job for me - I like the technical aspect and throughly enjoy the art of ship handling.

Heading off for a week long ship handling course soon

 

Does this help in assisting ass-backward ships found wandering down the harbour?

[rigger 47]

Where did you see that happening?

[Terry B 71]

I have a Whiting 29 and had similar prop walk problems when I first bought her.

 

Once reverse motion was achieved I could steer no problem, but before that motion was achieved the bow drifted solidly to one side - which was a nightmare in a marina with little room.

 

Then I figured out (only took me 6 months ) that if I ensure the stern is into the wind when starting to reverse then the bow doesn't drift away anywhere near as much.

 

Also, once you work out which way the prop walk forces the bow (starboard or port) away you can use that to your advantage - instead of lining the boat up dead centre of the pier water before reversing, you line up on the side that the prop walk forces you away from - gives you more room while you wait for the reverse motion to takeover from the prop walk effect. And, angle the boat in the causeway the "wrong" way from the prop walk as well - prop walk straightens the boat up as you wait for the reverse motion to take over.

 

And hey presto, problem solved! It does mean I sometimes have to start reverse in the main causeway and back towards my pier entrance - but that's not a problem. I'm used to embarrassment

 

The rest was just practice - and an empty bay with a few mooring buoys strewn around is an excellent training ground!

[PaulR 3]

Doing figures of "8" when going astern is another thing to practice.

 

Learning to watch on a transit to see when the boat is actually moving astern is a key ingredient. It can happen a LONG time after the engine/prop is put astern.

 

KEEP your rudder amidships until one has good water flow OVER THE RUDDER by seeing you are acutally moving astern BEFORE trying to steer.

 

Also don't be afraid of giving your engine full power astern. Diesels work better with a good load.

 

There is an agruement that after a period of constant running, the engine should be run at higher revs to clean out crap etc. See your engine manual.

 

Yes it helps to open it in the language one use's most

 

So after some constant steady running e.g. comming into the harbour, then a "Full Speed Astern" cleans the engine just before you shut down after reversing into one's berth.

 

Once moving astern, slow down the engine / stop prop turning and just a quick kick ahead will stop one exactly in the desired position. A spring line around the sheet winch is also VERY useful. Bow and stern lines don't really matter and can be done once the yacht is no longer moving.

 

PANIC SLOWLY

[PaulR 3]

The rest was just practice - and an empty bay with a few mooring buoys strewn around is an excellent training ground!

 

 

+1

[Kestrahl 6]

Those fixed 3 bladed "Sailor" props are a pet hate of mine. The first boat I crewed on was a Noelex 30 with one. We used to complete with the Noelex 25's on line but after changing to a folder we were in with the Y88's! Also with the fixed prop when the boat got hit by a gust it would just heel over and spin out instead of surging forward.

 

We have a 2 bladed geared folding prop on the Davo35 and can back out of berths okey if you give it a short burst with the tiller hard over Then you can straighten up and steer out. A Kiwi prop is probably the way to go if you have the $

 

cheers

 

Gee 12 x 9 seems like a small prop... I got a 15 x 8 with a 21 nani

 

3 blade will be way better motoring (2 knots better in a big blow) also, the 3 blade will give less prop walk

 

Your shaft is out. If you let the tiller go when motoring will it shoot off in one direction?

 

Only thing you can do is get use to it and use it to your advantage as others ubove have said. Good luck

[Vivaldi 53]

Also with the fixed prop when the boat got hit by a gust it would just heel over and spin out instead of surging forward.

 

cheers

 

Thanks all for the advice - Kestrah - do you mean this is what happened while you were sailing - as in the 3 blader interferring with the rudder?

 

in terms of manouvering, I'm okay getting into the marina, i just use it to my advantage as suggested. I find the problem is with anchoring. If I want to motor backwards to set the pick the prop walk will always take the bow off to starboard and then the wind takes us around sideways so i have trouble going straight back in the direction I want to set the anchor. i'm learning to live with it but i thought that the extra diameter and lower pitch on the 2 blade might not be as bad as the higher pitched 3 blader.

Seems my thought were wrong...

[wheels 543]

The size of the prop is stipulated by the area it has to fit into. There is a percentage of distance between tip of blade and bottom of Hull and the distance from Keel to Blades, and the diameter of shaft to Hp/and prop diameter and finally the distance from Strut to prop.

If the distance between blade tip and hull us not enough, you will get a hydraulic affect between the prop and hull and it can become a very loud hammering noise.

[Kestrahl 6]

It restricted the boat accelerating in the gusts, which turned into heeling force. And as the N30 is a light tippy boat with a small rudder (original) In gusty conditions (marlborough sounds) it was a real handful. The handing improved a lot when the folding prop went on.

 

Also with the fixed prop when the boat got hit by a gust it would just heel over and spin out instead of surging forward.

 

cheers

 

Thanks all for the advice - Kestrah - do you mean this is what happened while you were sailing - as in the 3 blader interferring with the rudder?

 

in terms of manouvering, I'm okay getting into the marina, i just use it to my advantage as suggested. I find the problem is with anchoring. If I want to motor backwards to set the pick the prop walk will always take the bow off to starboard and then the wind takes us around sideways so i have trouble going straight back in the direction I want to set the anchor. i'm learning to live with it but i thought that the extra diameter and lower pitch on the 2 blade might not be as bad as the higher pitched 3 blader.

Seems my thought were wrong...