Braunston auto propeller

[Esso6]

BiL has recently bought a Fisher30 with a Braunston auto propeller, he's not sure how well it will perform, so is considering changing it before launching.
Any experience or views appreciated.

 

[Deleted member 36384]

If you mean these guys http://www.bruntons-propellers.com/ (Bruntons) then they are considered to be very good quality propellors. I will be fitting a new propellor and these guys are on my short list.

The propellor pitch can be adjusted in situ so that fore and aft thrust is best matched for boat and engine, normally set up at time of installation.

 

[oldfatgit]

Fitted an autoprop to my last boat, a Westerly Konsort. Result was, faster under engine with lower revs, faster under sail as prop feathered, brilliant when motor sailing, again at lower revs than before. They are brilliant pieces of engineering which I would never replace. The reason why they cost so much is because they are quality items. Clean it up, fit the correct anode and keep it as it cannot be improved on.

 

[Robin]

Excellent prop and the self pitching makes it even better for motor sailing. There is no setting required at all, it self pitches to suit the conditions. If the wind is assisting it will increase the pitch and give more speed for the same revs (or reduce revs to conserve fuel), if into a headwind/sea it will drop the pitch, like changing into 3rd gear, to maintain the thrust so increase revs a bit to put the speed back. Under sail it feathers and reduces drag, quite automatically. We had one on our 41ft cruiser racer and it does everything it promises.

Why BiL should be thinking of changing it I have no idea!

 

[Esso6]

Thanks for the replies.
My initial thoughts were, why design something which didn't improve on the original. So I will advise that he sticks with it,at least for the first season.

 

[NormanS]

If you mean these guys http://www.bruntons-propellers.com/ (Bruntons) then they are considered to be very good quality propellors. I will be fitting a new propellor and these guys are on my short list.

The propellor pitch can be adjusted in situ so that fore and aft thrust is best matched for boat and engine, normally set up at time of installation.

No, that's not right. The Brunton's Autoprop automatically adjusts its pitch to suit the conditions. (The clue is in the name). It's an excellent piece of engineering, and particularly with a boat which may do some motor-sailing, is worth every penny.

 

[Coaster]

BiL has recently bought a Fisher30 with a Braunston auto propeller, he's not sure how well it will perform, so is considering changing it before launching.
Any experience or views appreciated.

If you really mean a Bruntons Autoprop it may be worth more than the boat! These are superb pieces of kit, particularly well suited to motorsailing.

A Bruntons Autoprop is self-pitching, and is often compared to an automatic gearbox. In calm, flat water our 34' boat is driven at 6 knots when the engine is producing as little as 1500rpm. In rough, broken water the engine can produce much more power, at say 2500rpm, resulting in the same boatspeed. Hence the automatic gearbox analogy.

One word of warning. An Autoprop must be properly maintained. Keep it clean and regularly grease the pivot points. We have a screw in attachment to allow the connection of a conventional grease gun.

Good luck.

 

[Deleted member 36384]

No, that's not right. The Brunton's Autoprop automatically adjusts its pitch to suit the conditions. (The clue is in the name). It's an excellent piece of engineering, and particularly with a boat which may do some motor-sailing, is worth every penny.

I believe they set the pitch stops when its installed for the first time. I understand that the pitch stops, if set wrongly will impact the performance of the auto prop.

 

[vyv_cox]

I believe they set the pitch stops when its installed for the first time. I understand that the pitch stops, if set wrongly will impact the performance of the auto prop.

No, there are no pitch stops. Each blade rotates 360 degrees when the prop is stationary. Like this -

 

[Robin]

I believe they set the pitch stops when its installed for the first time. I understand that the pitch stops, if set wrongly will impact the performance of the auto prop.

No that is not the case, there are no pitch stops on the normal Brunton.

I think the prop you are thinking of is the Maxprop and there may be others where the pitch has to be set, even a separate pitch for forward and reverse. We had friends with one of these (bought because the Brunton wouldn't fit when feathered in the aperture available on their boat) and they had to lift out 5 times for adjustments before it was correct, not happy bunnies.

 

[Deleted member 36384]

Thanks folks for the correction. I have looked at a few propellors and Robin has certainly thrown light on my recollection which is of a boat having its stops adjusted a few times. It may even have been from a posting on this forum in my research.

Thanks

BlowingOldBoots

 

[Coaster]

Further to Vyv's photo of a two-blader, this is our three blade Autoprop:













Photos taken last year, much grubbier now.

 

[Esso6]

If you really mean a Bruntons Autoprop it may be worth more than the boat!

Ah!...the mist is clearing.....perhaps you have stumbled upon the reason for him thinking about changing it!

It looks very similar to the one in the photo's, I will go and have another look later, and take a photo or two.

Cheers

 

[mobeydick]

Most seem happy with their Autoprops. A few (mostly Americans it seems - why?) claim to have endless problems, but certainly worth trying.

MD

 

[dulcibella]

Not entirely Americans that have problems. On some boats the Brunton, however well-maintained, seems to produce a lot of shaft vibration. I had this problem on my Rustler 36, and was told by them wot know at Rustler that this seems to be a recurring problem with this particular marque. I've now replaced it (the prop, not the boat) with a Darglow Featherstream which behaves much better.

 

[Coaster]

On some boats the Brunton, however well-maintained, seems to produce a lot of shaft vibration. I had this problem on my Rustler 36, and was told by them wot know at Rustler that this seems to be a recurring problem with this particular marque.

What diameter is your propshaft? When we fitted our Autoprop we installed a new 1 1/4" shaft in place of the original 24mm one, whilst uprating the engine from a nominal 28hp to a new 38hp unit. Dependent on the distance between shaft log and prop, and taking into account intermediate support such as a P bracket, I suspect the rather vigorous action of the Autoprop might cause slender shafts to vibrate.

 

[mobeydick]

What diameter is your propshaft? When we fitted our Autoprop we installed a new 1 1/4" shaft in place of the original 24mm one, whilst uprating the engine from a nominal 28hp to a new 38hp unit. Dependent on the distance between shaft log and prop, and taking into account intermediate support such as a P bracket, I suspect the rather vigorous action of the Autoprop might cause slender shafts to vibrate.

Hey I like that theory. I followed various threads on the Autoprop when concidering one, and was never happy with the conclusions I saw when there WAS a problem with vibration (wrong size prop, too close to hull/skeg/p-bracket etc).

md

 

[HermanD]

Brunton disadvantageous

1. As mentioned by others, it can give vibration= noise=irritation

2. You can not go slow, because is automatic changes pitch
minimum speed sometimes is 3 or 4 knots. That means every
time you have to switch to forward-free etc. to keep the
speed low, for instance in a small canal or habour.=irritation

 

[Robin]

Never had any vibration nor any problem with being unable to go slow. That was on a Sun Legende 41 with a Yanmar 44hp with a 30mm dia shaft, 3 bladed Autoprop. This prop has done around 25,000mls.

 

[NormanS]

Likewise, no problems with vibration, or going slow, or anything else. The only problem that I once had was that the prop started to rotate when sailing, and it had a strange effect on the rudder. Easily sorted -- stop the prop.