In praise of the Brunton Autoprop.

[Trevor Lyons]

I was impressed by the Brunton Autoprop when I saw it demonstrated at boat shows. Decades ago, I even considered fitting one to my 41' Mindon cruiser-stern narrowboat. Ultimately I decided the benefits were too marginal. However, I recently experienced the performance of an Autoprop on a large ketch motorsailer, where the Brunton propeller exceeded my expectations. With its original 3-bladed fixed prop, she averaged around 7 knots under power and sail, its 120hp 6-cylinder Isuzu engine turning over at 1,650 rpm. Once an Autoprop was fitted, 6 knots was achieved on engine alone at a mere 1,000 rpm, with a concomitant reduction in noise, vibration and fuel consumption. A friend was so impressed that he proposes to fit a pair of Autoprops to his sea-going catamaran.

 

It might still seem extravagant to fit an Autoprop to a narrowboat (except possibly to a new-build); but I am considering fitting an Autoprop to my 12' wide 54' river barge which I propose to take across the Channel. Since I'll navigate not only canals but also fast-flowing European rivers, it seems that the Autoprop might give significant advantages over the current fixed prop, namely greater oomph in tricky conditions, a reduction in prop-walk, and better performance in astern.

Edited November 4, 2019 by Trevor Lyons
typo

[dmr]

A friend has an "antique" variable pitch prop they he found in a boat jumble, they really are works of art and should probable sit on the mantelpiece rather than under a boat.  Probable good for sailing but would not last long on the canals, especially the BCN or Manchester.

 

................Dave

[Slim]

I've got a friend who has one on his Bruce Roberts 44' ketch. It eats bearings. Also I was with him when he approached a pontoon in Brighton Marina and it jammed. Another friend got some serious rope burns trying to stop the boat tee-boning a jetty. Wasn't there when it was lifted so didn't see it jammed first hand. A lift, bearings, anodes etc. Not cheap. 

 

Frank.

 

Should add that I've got one of their SigmaDrive 150 flexible drives on my NB. Works fine.

[Trevor Lyons]

19 minutes ago, Slim said:

I've got a friend who has one on his Bruce Roberts 44' ketch. It eats bearings.

The early Autoprops had open exposed roller bearings that were cooled and lubricated by water. The current Mk II version (as illustrated above) has a sealed greased bearing that one is expected to inject new grease into ever couple of years. Of course, the Autoprop is primarily aimed at sailing boats on the sea, whereas canal boats are motorboats in fresh water. That is why I'm interested to hear if any one has any experience of one on a canal or river barge.

[Trevor Lyons]

Narrowboats and their wide-beam siblings both have shoal drafts so as to operate in shallow canals, and they have weed hatches to cope with the detritus collected on the prop. By contrast,  wide-beam river barges such as Dutch barges will normally operate in deeper water, and I suspect that flotsam and churned-up muddy water would be less a problem to an Autoprop on such a craft.

[BEngo]

3 minutes ago, Trevor Lyons said:

Narrowboats and their wide-beam siblings both have shoal drafts so as to operate in shallow canals, and they have weed hatches to cope with the detritus collected on the prop. By contrast,  wide-beam river barges such as Dutch barges will normally operate in deeper water, and I suspect that flotsam and churned-up muddy water would be less a problem to an Autoprop on such a craft.

Crap in the water will be less of a problem to any craft as the water gets relatively deeper  with regard to draft  regardless of the prop type. That is why ocean going ships worry little about debris on their thrust devices, either in design or operation  and deal with it by divers as needed.

Any variable pitch propelling device is going to be more complicated, more vulnerable to failure and more expensive than an unvarying lump of aluminium or bronze.  There has to be an essential benefit which makes this extra complexity worthwhile.  For the Royal Navy's gas turbine powered frigates an destroyers it was the ability to not have a reversing gearbox.  In use they were a continuous PITA.  For a sailing yot in open water the benefits of reduced drag may be worth it.

  For a powered craft on any dimensionally restricted inland water I would take a lot of convincing.

 

N

 

 

[Chewbacka]

On 04/11/2019 at 15:33, Trevor Lyons said:

 

Doesn’t look like it would survive whacking a shopping trolley or bike lurking just below the surface of the canal.....

Edited November 5, 2019 by Chewbacka

[Detling]

Often on a canal you are floating in a soup of fine clay type dust sometimes it is abrasive like metal polish. This could get into the bearings and gradually abrade them. You also often hear the swim being sand blasted by fine gravel kicked up by the prop.

[Trevor Lyons]

I've been in touch with Bruntons, who say they've produced many thousands of these Autoprops. Apparently they're not recommended for speeds over 10 knots. They have a dealership network in the Netherlands, and they will get back to me on any experience of Autoprops on continental river boats and Dutch barges. (Of course, I accept that the Autoprop is both unsuitable and probably pointless on a narrowboat on narrow canals).

[peterboat]

36 minutes ago, Trevor Lyons said:

I've been in touch with Bruntons, who say they've produced many thousands of these Autoprops. Apparently they're not recommended for speeds over 10 knots. They have a dealership network in the Netherlands, and they will get back to me on any experience of Autoprops on continental river boats and Dutch barges. (Of course, I accept that the Autoprop is both unsuitable and probably pointless on a narrowboat on narrow canals).

I am in talks with them for my electric boat, I am looking at the same version you showed, I am on deep water here so should get some good benefits from it without many drawbacks. The bearing life is very long, also they wont recommend one if they think it wont work for you