Prop walk

[Storyline]

I have a 36' fin (longish) keeled sloop (Westerly Conway) and am considering getting a new prop as we are currently under-propped. At the moment we have a considerable amount of prop walk in astern with the stern moving sharply to port. I frequently find this very useful as I can spin the boat nearly in her own length (provided I want to go clockwise) and also can reverse out of a confined space (provided we are moored starboard side to).

I like the sound of a Brunton Autoprop but they state one of the advantages is having much less prop walk in astern. I think we will get better torque in forward and of course be able to reverse anti clockwise but what are peoples opinions about the loss of the times when the existing prop walk is very useful ?

 

[Resolution]

We have a feathering Maxprop. There is still a bit of propwalk (to port), enough to help in close quarters manoeuvres if needed but not so much that we cannot go back pretty straight when we want to do that. And when sailing we gain perhaps half a knot compared with a fixed prop.

 

[Woodlouse]

We have a darglow featherstream which has been set up to give a coarser pitch in astern to give the same kick as it had with the fixed prop.

 

[onesea]

Use what you have got.

I have sailed boats with large prop walk, present boat has next to none. Which would I prefer, probably the present boat even with large propwash but she handles better all round.

On the boats that have had large prop walk I found I would arranged life so it would work for me not against me. The hard part is when you have to get used to one after the other, I guess doubly so when its the same boat!

 

[dovekie]

You may not lose the prop walk if you switch to a Bruntons Autoprop. We have an Ohlson 38. Used to have a fixed three-bladed prop. Quite marked prop walk astern. And no change in the propwalk when we switched to an Autoprop. Others with different boats / hull shapes may have differing experience.

 

[Dirk.Watson]

Feathering props are very expensive and Barancle up.

May the pitch is to great - check on the net - horspower, reduction, vessel length - places on the
net can calculate and they are very close.

 

[jmaude]

You may not lose the prop walk if you switch to a Bruntons Autoprop. We have an Ohlson 38. Used to have a fixed three-bladed prop. Quite marked prop walk astern. And no change in the propwalk when we switched to an Autoprop. Others with different boats / hull shapes may have differing experience.

I recently got an Ohlson 38 and am thinking of changing the fixed prop so would be very interested to learn more of your experience with the Autoprop. What sort of difference did it make? I thought there might be space issues, what size did you get? Which engine do you have? Many thanks

 

[nigelmercier]

Feathering props are very expensive and Barancle up...

I don't see the point of them, the gain in speed is minimal at best. Slightly quieter below decks when sailing perhaps.

 

[ianj99]

Feathering props are very expensive and Barancle up.

May the pitch is to great - check on the net - horspower, reduction, vessel length - places on the
net can calculate and they are very close.

Kiwi props aren't. http://www.vectamarine.com (around £1100)

A 17" model works well on my 10t 36' long keeler.

Its been 100% reliable, although I excercise it fortnightly during the winter season (that's 9months in Scotland)

I use one with good results - more speed for the same rpm, better slowing due to astern having more pitch, easy to adjust yourself by a 4mm socket screw near each blade root. Easily replaceable blades, few moving parts.

There is more prop walk due to the higher pitch going astern but my long keeler goes where she wants to anyway when backing out of my berth!

 

[NormanS]

I have a Bruntons Autoprop, and have noticeable prop walk. Unfotunately, it pulls the stern to starboard, and I prefer berthing port-side to. Ho hum.

 

[Leighb]

Feathering props are very expensive and Barancle up.

I don't see why feathering props should be any more prone to barnacle growth than fixed, if you mean that the barnacles affect the feathering ability it is not my experience this past 3 years.

I haven't noticed any great difference in the prop walk (Except at first as it was the opposite way which took a little getting used to!)

I have noticed that the stopping power is much better though.

 

[chubby]

Interesting thread and happened to be pondering the same things: I have a 32ft long keel motorsailor which doesn`t go predictably astern and I am beginning the think more about the cost of fuel: would either a kiwi prop or bruntons autoprop give me benefits worth the price: better sailing, better economy under power and quieter would all be welcome. I am concerned about manoeuvrability: I had got used to the idea she doesn`t go predictably astern but have learnt to use the prop wash effect to turn almost in her own length: if I can`t reverse up a marina alleyway I come out of the berth, see which way she goes and turn as needed to come out ahead. Would I loose that with less prop wash?

I am inherently lazy and often tow the dinghy and motor when sailing gets slow, how many years would it take for fuel savings to offset the cost of the prop and should I just pull the dinghy aboard?

Is it more important to keep he prop clean during the season: do owners do a mid season clean?
Interested in feedback from any autoprop or kiwi prop owners with similar boats

 

[mainsail1]

I have a Brunton Autoprop and think it is great. When sailing the propellor drag is greatly reduced. When going astern there is a little prop walk but nothing like the problem with a 'normal' prop. You can almost go astern in a straight line for long distances and that must be worth more than the loss of prop walk. Haslar visitors marina pontoons is a good example. Impossible for me to reverse in before the Brunton came along.

 

[Tranona]

Interesting thread and happened to be pondering the same things: I have a 32ft long keel motorsailor which doesn`t go predictably astern and I am beginning the think more about the cost of fuel: would either a kiwi prop or bruntons autoprop give me benefits worth the price: better sailing, better economy under power and quieter would all be welcome. I am concerned about manoeuvrability: I had got used to the idea she doesn`t go predictably astern but have learnt to use the prop wash effect to turn almost in her own length: if I can`t reverse up a marina alleyway I come out of the berth, see which way she goes and turn as needed to come out ahead. Would I loose that with less prop wash?

I am inherently lazy and often tow the dinghy and motor when sailing gets slow, how many years would it take for fuel savings to offset the cost of the prop and should I just pull the dinghy aboard?

Is it more important to keep he prop clean during the season: do owners do a mid season clean?
Interested in feedback from any autoprop or kiwi prop owners with similar boats

An Autoprop is generally better for motorsailing as it adjusts pitch to the speed and load. You therefore run at lower revs motorsailing for the same speed than with a fixed prop. Whether this translates into significant savings in fuel to justify the high cost is debatable! The main reasons for choosing it are quieter motoring (ie at lower revs) and reduction in drag under sail. However you may find reversing not so good.

You may wish to consider a feathering prop like the Featherstream. This does not self pitch, but you can have the pitch set differently forward and reverse. I have mine set with a coarser pitch in reverse to improve the thrust at low speeds. As yours on a long keel, and the prop walk is the same as the old fixed prop. Overall motoring performance is at least as good as the fixed prop and sailing better at low speeds in light airs. Substantially cheaper than an autoprop.

 

[duncan99210]

We get a marginal improvement in fuel consumption with the Brunton (1800 rpm as opposed to 2200rpm for 5.4 knot Brunton to standard two blade prop) but that won't pay for the prop unless you're planning on doing multiple circumnavigations..... It gives about half a knot when sailing, is quiet as its not turning the gearbox over and is much better for close quarters maneuvers, as it seems to bite better, especially when changing direction. Still prop walk but not as much as with the two bladed one.

Downside is that it suffers when fouled. I don't think it fouls any faster than other props, just that the effect of fouling is marked. We can loose three quarters of a knot for the same engine speed when the prop has a layer of fouling built up on it. Takes about ten minutes to clean with a scotch pad and well worth doing. Never had the two bladed thing on for long enough to see if fouling creates as big a problem....

 

[charles_reed]

Interesting thread and happened to be pondering the same things: I have a 32ft long keel motorsailor which doesn`t go predictably astern and I am beginning the think more about the cost of fuel: would either a kiwi prop or bruntons autoprop give me benefits worth the price: better sailing, better economy under power and quieter would all be welcome. I am concerned about manoeuvrability: I had got used to the idea she doesn`t go predictably astern but have learnt to use the prop wash effect to turn almost in her own length: if I can`t reverse up a marina alleyway I come out of the berth, see which way she goes and turn as needed to come out ahead. Would I loose that with less prop wash?

I am inherently lazy and often tow the dinghy and motor when sailing gets slow, how many years would it take for fuel savings to offset the cost of the prop and should I just pull the dinghy aboard?

Is it more important to keep he prop clean during the season: do owners do a mid season clean?
Interested in feedback from any autoprop or kiwi prop owners with similar boats

I've had an Autoprop since 1992. Whilst it offers far greater economy over the previous 2-blade fixed prop - I don't think one could make a valid cost/savings comparison. If doing 1000 hrs/year the Autoprop would return its additional cost in about 8-11 years.
You should not confuse the Kiwiprop (variable pitch) with the Autoprop (self-pitching). Two different beasts, with the Kiwi having a big price advantage but only a few few of the Autoprop benefits.
The big benefit with the Autoprop is its effectiveness when motor-sailing, great in the Med where wind is either too great or insufficient.
Under sail you gain considerably over a fixed prop but the Autoprop is not as slippery as a folding prop or one such as the Maxprop.
Rather than needing cleaning the Autoprop stays clear if it's used sufficiently - barnacles are the big problem.

 

[Tranona]

You should not confuse the Kiwiprop (variable pitch)

Not a variable pitch, but a fixed pitch with feathering blades. Pitch is however adjustable in forwards, but once set is fixed. Also fixed (at a different pitch and non adjustable) in reverse.

Variable pitch propellers can be adjusted (usually by mechanical means) when in use, just like many aeroplane propellers. Not now common on small boat engines because of cost and complexity, but still used on commercial vessels.

 

[davidej]

I have a Bruntons Autoprop, and have noticeable prop walk. Unfotunately, it pulls the stern to starboard, and I prefer berthing port-side to. Ho hum.

Ditto for me but for port read starboard and visaversa.

Nothing to do with the prop - depends on which way the shaft rotates

 

[dovekie]

PM sent

I recently got an Ohlson 38 and am thinking of changing the fixed prop so would be very interested to learn more of your experience with the Autoprop. What sort of difference did it make? I thought there might be space issues, what size did you get? Which engine do you have? Many thanks

 

[cmedsailor]

We can loose three quarters of a knot for the same engine speed when the prop has a layer of fouling built up on it. Takes about ten minutes to clean with a scotch pad and well worth doing. ..

I don't think there's any difference in speed drop if it's a fixed or a Brunton. It's really amazing what a thin layer of fouling built up can cause in speed. And yes, especially if you sail in warm places (Med for example), ten minutes with a scotch pad and it's back in action.