Autoprops

[cliff]

As per previous post (below) I am planning on changing the engine in my Sadler 34
and am considering fitting a Brunton's Autoprop™.

Anyone have and experience of them? - Both Bruntons and/or their Autoprop™

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[ChrisE]

Following recommendations of users on this board, we had an Autpprop fitted to our Rival 38 this spring. I found Brunton's to be extremely helpful both pre and post sales.

The prop has given Rival Spirit about half to threequarters of knot on her boatspeed and, as you would expect, light airs performance is the most noticable improvement.

In terms of her performance under power, we now need more revs than before with the fixed prop due to the prop being physically smaller. Interestingly though, the self pitching gives us a higher top speed. There is now a latency when going between forward and reverse that has meant learning a new technique for tight turns in marinas.

Initially, we found that the prop was singing in a certain rev range and Bruntons were very helpful in diagnosing the problem and offering solutions (possibly shaving some bits off the blades). In the event the singing has now stopped.

All in all am thoroughly impressed and consider it the best £1500 we have spent in terms of improving the boat's performance.

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[Robin]

We inherited a 3 bladed Brunton Autoprop with our present boat, fitted with a Yanmar 44hp, having previously had a fixed 3 bladed and 50hp on our earlier W33.

The autoprop takes a little getting used to, but overall is excellent. There is no doubt that sailing performance especially in light winds is much improved with the feathered blades. Under power the prop also performs well, and the problem of matching the prop size (diameter & pitch) is much simplified because the prop self adjusts pitch underway. The self pitching feature means that the slightest bit of wind assist (even with no sails up, but especially motorsailing) allows the prop to increase pitch and boatspeed increases for the same engine revs. Conversely, wind or wave hindrance causes the prop to 'drop down a gear' and boatspeed drops, needing an increase in revs to maintain the same speed, much the same as you would do going uphill in a car. Like a folding prop, you need to give an initial burst of revs when engaging gear to get the blades set, most notably when changing from forward to reverse and vice versa since the blades actually reverse completely. Reverse performance is excellent and the brakes work exceptionally well, Brunton I believe claim a 6kt crash stop in one boatlength, I have not dared try it but don't doubt it could be possible! Prop kick is still there but is not as great, especially in reverse if the revs are initially applied gently since the prop will set a fine pitch. If you need the prop kick effect for a tight turn it is still there, just give a hard burst astern to set a bigger pitch and there it is!

I have had some discussions with a fellow Sun Legende 41 owner who has a fixed prop and the same Yanmar 44hp. By comparison with him, we cruise at a higher speed for the same engine revs, have a higher maximum speed and lower cruise speed fuel consumption - just what it says on the Brunton box.

I have spoken with Brunton several times, initially concerning servicing ours and adjusting the bearings and found them very friendly and helpful. Spares are not cheap, I bought a complete bearing service kit and tool and also a special prop puller, ouch! Our prop is now about 10 years old and the bearings had not been adjusted in the 7yrs before we bought the boat, however having bought the bearing replacement kit I found it was not actually required (adjustment was sufficient) so I still have everything as spares.

I hope that helps.


<hr width=100% size=1><font size=1>Sermons from my pulpit are with tongue firmly in cheek and come with no warranty!</font size=1>

 

[alan]

Fully agree with the other replies. The only "negative" feature that I have found is that toward the end of the season when the prop is fouled it is not possible to reach maximum revs anymore. (Incidently this true of all feathering props, to the best of my knowledge.) This is solved by cleaning the prop; I usually go under the boat and give it a clean a couple of times a year as well as the normal clean-up when the boat is out of the water. Of course living in the Med makes this job much more enjoyable ...................



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[Robin]

We bright polish ours before launching. Originally it had been antifouled, we removed this and rubbed it down with wet/dry progressively from 320 to 1200, then finished with Brasso. If I'm swimming around August I will give it a quick brush, there may be a little (ie patchy and very light) 'grass' no more, not enough to affect performance. When we lift out, usually February, there will be a coating Of slime/limescaley stuff overall and the odd barnacle by the roots of the blades, not enough again to prevent max revs or noticeably affect performance. I normally scrape of the prop crud before it dries on with an old plastic sail batten whilst the boat is still in the slings, it goes back to the bright polished finish. Bringing back the shine before relaunch takes about 45mins with 1000/1200 grit paper then Brasso. We do use the boat every weekend until about November and the hull (International Optima) stays very clean, even slime free, so is not itself detracting from performance, this is though in ther colder waters of the Channel!

<hr width=100% size=1><font size=1>Sermons from my pulpit are with tongue firmly in cheek and come with no warranty!</font size=1>

 

[charles_reed]

I've had one on my boat for about 12 years and can vouch for the propellor's benefits.

Fouling can be a problem, but, I suspect no worse than any normal prop. I find to clear of the worst of the crud it's worth putting it into reverse and forward gear a few times whilst alongside.
Last year the prop grew a whole lot of coral, during the summer recess, which definitely reduced thrust - from 7 knots to about 4.5.
I polish it every season, eschewing ever using wet and dry but use a 3M metal finishing pad, followed by metal polish - this seems to prevent fouling far better than any spray antifoulings, hot applied lanolin or grate blacking.

The delay going from forward to reverse is most notable - exacerbated by the lower ratio you have in reverse - however when it does kick in the propellor is considerably more efficient than any fixed propellor and of a different order of magnitude to a folding prop. There is a real danger, whilst getting used to it, of tossing expectant foredeck crew overboard when stopping by reverse.
To reduce prop-walk, low revs should be employed - alternatively, if you want to use it effectively to walk the boat sideways, use considerable bursts of throttle.
The additional weight of the prop might increase cutless bearing wear (it has on my boat) and I find that the blade-bearings need adjustment every season (about 200-250 hours) or the whole train becomes very noisy.
On a 29'10" LWL I get about 7.2 knots flat out in still water from 18 bhp and, in normal give-and-take situations, about 1.25 litres/hour using 1/2 throttle. Sailing performance is improved by about 15% compared to the fixed 3-blader I had before.
The greatest benefit I've found is for genuine motorsailing (having both main and genoa drawing) when I'll get between 1.2 and 2.6 knots of enhancement at just above idling speeds.
Equally it's tactically short sighted to try and plug direct to windward on motor alone, using the main, I find my best VMG results in a tacking angle of about 60 degrees and I was 1 of only 2 boats out of 7 (the other was one of the ex- Kreigsmarine Rasmussens) that managed to get into Lagos with just over 40 knots out of the R Benasfrim.
For the blades to feather it is essential to leave the boat in forward gear - if I don't my prop starts rotating at about 3 knots.

In purely economic terms, I doubt the fuel saving will ever justify the additional capital cost, but my under-power range has effectively been doubled - if you keep out of marinas (as I do) this is a very real advantage.

Do ensure you have an effective shaft anode - Brunton's spares prices are truly astronomical and saving the boss anode has to be an economic strategy. I do have a spare bearing set (mine is one of the earliest, with water-lube bearings) - but I managed to adjust up the bearings sufficiently this season, without replacement, and after 80 hours there is virtually no bearing rumble.

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