Bruntons auto prop

[Jackattack92]

Hi everyone, currently owner of a hunter 306. It has a 2 bladed bruntons folding auto prop and a 18hp yanmar. It performs fine but does seems to struggle when motoring into big waves and strong winds. Would the 3 bladed feathering propeller improve this?

The boat was initially designed with a fixed two bladed propeller.

I’ve had the quote from bruntons and very tempted to proceed but it’s quite an investment which I would like to see a return to.

 

[rotrax]

The bit about 'big waves and strong winds' gives me a clue.

With 18HP the boat will struggle.

Early today, 7AM, off Start Point, 24 Kts from the NE, over 2 metre swells our heavy motorsailer was being 'stopped' now and then. 6Kts down to 3.5Kts.

We have 110HP and a 17X21 three bladed prop.

Work it out for yourself.

Ten hours later, off St Albans Head we were doing 10Kts motorsailing. Wind E, only 6 Kts true, sea smooth, a good tide up our chuff.

 

[NormanS]

Bruntons Autoprops are excellent, particularly if you do any motor--sailing, when they really come into their own. They do have this one disadvantage, that if the boat is slowed down while motoring against a head sea, the prop automatically adopts a fine pitch until the boat's speed increases. Catch 22. I have a Bruntons Autoprops on my boat and I'm delighted with it, but am aware of this slight problem.

 

[Tranona]

The Bruntons does not do well on boat/engine combinations like yours. The boat hull shape is not good in heavier seas and the engine is marginal (it is rated at 16hp). As Norman describes it adjusts pitch as you slow down when you go into a head sea and you don't (unlike his boat) have the power to get the speed up quickly. The trade off is no drag under sail. Bruntons are effective and popular on bigger boats, particularly for those intending doing a lot of motorsailing as it is good at matching revs to power demand which mens lower revs for a given boat speed.

For best motoring performance you need a 3 bladed fixed blade prop. probably a 13*10 if you have the common 2.2:1 reduction, although a larger 2 blade with a large blade area would be almost as good and bit less drag. If you want the best of both worlds, no drag and good motoring then a 3 blade feathering prop like a Featherstream is the best.

 

[Metalicmike]

I've been banging my head with the same problem and my engine is 28hp on a 1/2 tonne class. I antifouled 2 months ago and increased the pitch of my Maxprop. On testing my engine failed to accelerate past 1500 and was very unhappy. Down the rabbit hole we go, changed filters discovered partial blockages in some fittings cleaned out the the lift pump and ended up ordering a replacement Inspiring my first posting, waiting for a delivery may as well make some mast steps. Also decided to replace the injector nozzles sourced via Autodoc.es (another item to get stuck in Madrid customs because they were posted from Germany). Ok fitted the injectors and the pump and the engine starts and I am getting better performance but the Injectors need calibrating as it is kicking out an embarrassing amount of black smoke. Being a hard up pensioner I have had to wait till now to afford the calibration which hopefully I can get done this week.

 

[Baggywrinkle]

I've been banging my head with the same problem and my engine is 28hp on a 1/2 tonne class. I antifouled 2 months ago and increased the pitch of my Maxprop. On testing my engine failed to accelerate past 1500 and was very unhappy. Down the rabbit hole we go, changed filters discovered partial blockages in some fittings cleaned out the the lift pump and ended up ordering a replacement Inspiring my first posting, waiting for a delivery may as well make some mast steps. Also decided to replace the injector nozzles sourced via Autodoc.es (another item to get stuck in Madrid customs because they were posted from Germany). Ok fitted the injectors and the pump and the engine starts and I am getting better performance but the Injectors need calibrating as it is kicking out an embarrassing amount of black smoke. Being a hard up pensioner I have had to wait till now to afford the calibration which hopefully I can get done this week.

Why would Madrid customs be interested in goods posted from Germany? Just curious.

 

[Sandy]

As everybody above has said, no.

How often are you out in such conditions?

I replaced my two bladed fixed prop with a two bladed Bruntons 'Flexifold' on my Volvo Penta 2002 (nominally 18hp) and the difference to overall sailing was fantastic. No prop rotation at greater than 4.5knots, the whirring sound was driving me insane, a greater average speed through the water and no affect on reversing.

Save your beer tokens.

 

[Ian_Edwards]

Just to reinforce what's already been said.
I had a 2 blade Autoprop on my Parker 275.
When I first got it, I got black smoke and couldn't make more than 4.5knots. It was over pitched. Sent it back to Darglow and they re-pitched it, which solved that problem.
But getting the boat moving in a strong head wind and a steep sea was always a problem. The best solution I came up with was to motor sail with 3 reefs in the main and tack upwind.
Motor sailing a 30 degrees or less to the wind, and pinching into the gust, I got a surprising amount of power from the main and reduced the slamming, it also allowed the Autoprop to pitch up and provide more drive.
The Parker had a 1GM10, so it wasn't over powered!

 

[Tranona]

I've been banging my head with the same problem and my engine is 28hp on a 1/2 tonne class. I antifouled 2 months ago and increased the pitch of my Maxprop. On testing my engine failed to accelerate past 1500 and was very unhappy. Down the rabbit hole we go, changed filters discovered partial blockages in some fittings cleaned out the the lift pump and ended up ordering a replacement Inspiring my first posting, waiting for a delivery may as well make some mast steps. Also decided to replace the injector nozzles sourced via Autodoc.es (another item to get stuck in Madrid customs because they were posted from Germany). Ok fitted the injectors and the pump and the engine starts and I am getting better performance but the Injectors need calibrating as it is kicking out an embarrassing amount of black smoke. Being a hard up pensioner I have had to wait till now to afford the calibration which hopefully I can get done this week.

That is a completely different type of propeller from the Autoprop as it is fixed pitch, although adjustable and you seem to have set it at too steep a pitch. do the sums and set it properly for your boat/engine/reduction ratio.

 

[Tranona]

As everybody above has said, no.

How often are you out in such conditions?

I replaced my two bladed fixed prop with a two bladed Bruntons 'Flexifold' on my Volvo Penta 2002 (nominally 18hp) and the difference to overall sailing was fantastic. No prop rotation at greater than 4.5knots, the whirring sound was driving me insane, a greater average speed through the water and no affect on reversing.

Save your beer tokens.

FlexoFold is not made by Bruntons, Their folding propeller is called Varifold.

 

[Sandy]

FlexoFold is not made by Bruntons, Their folding propeller is called Varifold.

Thanks @Tranona - the post was made before my second mug of tea of the morning - I stand corrected.

 

[johnalison]

I got the impression that the Bruntons was most useful for larger boats who motor or motor-sail at close to seven knots. While it is true that a 3-bladed fixed prop will give the best motoring performance, any boat with any pretension to sailing performance or pleasure is going to want a folding prop of some kind. It sounds as if the OP is getting much what one would expect and I doubt if throwing money at it will be worthwhile.

I have a Volvo 2-bladed folding prop which is not ideal, but good enough. Yesterday I found that in my 34 my motoring speed was down about half a knot due to fouling but when I needed to motor against the wind towards Harwich I was able to keep up to 6-6.2 knots against a true wind of about 18 knots through water that was a bit bumpy. I have the impression that in these conditions it is worth giving plenty of wellie. I was doing 2700 rpm, but if I had dropped it to a gentler 2400 my speed would have plummeted and the waves would have stopped me.

 

[Kwik Decision]

Just to reinforce what's already been said.
I had a 2 blade Autoprop on my Parker 275.
When I first got it, I got black smoke and couldn't make more than 4.5knots. It was over pitched. Sent it back to Darglow and they re-pitched it, which solved that problem.

This doesn't make sense, the whole point of an autoprop is it automatically changes pitch depending on the conditions; you can't get them re-pitched. They are also made by Bruntons, not Darglow.

 

[vyv_cox]

We have had a 2-blade Bruntons Autoprop, the feathering type to save any confusion, for more than 25 years. Sadler 34, 3GM30F engine. It has been an excellent choice, no problems at all. On the rare occasions that we motor upwind in biggish chop I find I need to increase engine revs to about 2500, which keeps us moving well.

 

[Metalicmike]

That is a completely different type of propeller from the Autoprop as it is fixed pitch, although adjustable and you seem to have set it at too steep a pitch. do the sums and set it properly for your boat/engine/reduction ratio.

The prop was set at 18deg which would have been right for 18hp Engine so at 28Hp I figured some horses had escaped the corral.

 

[Ian_Edwards]

I stand corrected on the manufacture. But Burtons did effectively re-pitch the prop for me.
I don't known the details, I didn't ask, but my guess is that they altered the balance of the blade, perhaps by changing the angle.
All I can say is, that as delivered, it showed all the signs of being over pitched. The 1GM10 couldn't reach maxs revs, and produced lots of black smoke when I tried.
When I got it back, it was OK, and no wind and flat water, I was able to get about 6.5knots, the same as I could with the original 2 played fixed prop.
After that I was quite happy with the prop for the following 10years until I sold the boat.
Over that period, I didn't have to dodge to wind very often, like everyone else I try and optimise the wind and tide. But on several occasion coming back from Orkney to Stonehaven, I had to motor sail against a strong Southerly and a short steep sea, to get home in time for work the following day.

 

[Tranona]

The prop was set at 18deg which would have been right for 18hp Engine so at 28Hp I figured some horses had escaped the corral.

Rather the opposite - using the pitch for a 18hp on a 28hp would be underpropping whereas your symptoms are overpropping (lack of revs and black smoke). suggest you go back to basics and determine the prop diameter and pitch for your current boat/engine/reduction combination.

 

[Tranona]

I stand corrected on the manufacture. But Burtons did effectively re-pitch the prop for me.
I don't known the details, I didn't ask, but my guess is that they altered the balance of the blade, perhaps by changing the angle.
All I can say is, that as delivered, it showed all the signs of being over pitched. The 1GM10 couldn't reach maxs revs, and produced lots of black smoke when I tried.
When I got it back, it was OK, and no wind and flat water, I was able to get about 6.5knots, the same as I could with the original 2 played fixed prop.
After that I was quite happy with the prop for the following 10years until I sold the boat.
Over that period, I didn't have to dodge to wind very often, like everyone else I try and optimise the wind and tide. But on several occasion coming back from Orkney to Stonehaven, I had to motor sail against a strong Southerly and a short steep sea, to get home in time for work the following day.

I think what they do is flatten the angle of the blades, effectively reducing the minimum pitch.

 

[Metalicmike]

Rather the opposite - using the pitch for a 18hp on a 28hp would be underpropping whereas your symptoms are overpropping (lack of revs and black smoke). suggest you go back to basics and determine the prop diameter and pitch for your current boat/engine/reduction combination.

I will know when the injectors have been calibrated, I expected this problem when I changed the injector nozzles so the black smoke was not a surprise and if they are not balanced i am not going to get them horses back in the corral. You are not wrong about the Propeller possibly being over pitched but I would rather do 4 Knots at 1500rpm than 3 Knots at 3000rpm and that is in normal conditions. My problem is compounded by having a Hydraulic drive.

 

[Jackattack92]

Thanks for all your input everyone.

I think for the time being i will keep as is, most likely is that I need to motor sail when met with these conditions instead of trying to power through. I do try to avoid bad conditions as much as possible but do occasionally get caught out as is the nature of cruising.