Autoprop blues

[Danny Jo]

Earlier this year I splashed out on a Brunton Autoprop , which "automatically adopts the most efficient pitch setting, taking into account the driving force of the sails". My cruising speed under engine alone at 2400 revs went up from 5 to 6 knots, but the biggest benefit for me was the ability to add a couple of knots to the 5 knots under sail and allow me to make otherwise impossible tidal gates, harbours before nightfall, etc.

After 200 hours use, however, my new pride and joy is playing up. The first thing I noticed was rather more vibration than normal while motorsailing to Bardsey last week. When I slowed the engine, the prop started vibrating more, and making a lot of noise, as if it was cavitating. Ditto going into reverse. It seems OK at my regular cruising revs under engine alone.

My diagnosis is that one or more of the blades has ceased to rotate to its optimal pitch. I'm a bit loth to shell out 400 GBP for a liftout just to have a look at it, so I'm proposing to dry out against a harbour wall somewhere.

Has anyone else had this problem, or got any tips?

 

[Robin]

My Brunton is an early one with open bearings and I've not had any problems and my guess is yours has sealed grease packed bearings.

Maybe the prop is weeded or barnacled up?
Is there a rope cutter fitted and could this have been damaged?
Is there rope or plastic debris on the prop?

Can you not make up a kind of underwater periscope (mirror + PVC drain pipe) to get a look from the dinghy? We use a diver to clean our bottom and he is quite reasonable, if you have one locally that might save a lift or drying out?

 

[Amari]

Why not snorkel, with or without wet suit, to have a look?

 

[Danny Jo]

[ QUOTE ]
Why not snorkel, with or without wet suit, to have a look?

[/ QUOTE ] Good point. My Aldi wetsuit needs putting to the test. I just need to find some clean water - not to keen on doing it in the dock.

 

[Danny Jo]

[ QUOTE ]
Maybe the prop is weeded or barnacled up?
Is there a rope cutter fitted and could this have been damaged?
Is there rope or plastic debris on the prop?


[/ QUOTE ] Thanks. Fouling by weed or barnacles is a possibility - I did not antifoul it, and never got round to polishing it. I don't have a rope cutter. Rope or debris was my first thought, but against that the prop seems to perform as normal in its normal motoring-only pitch.

 

[Robin]

I never antifoul our Brunton but I do bright polish it....

 

[ChrisE]

I'd agree with the diagnostics from above. We dry out about twice a year, we're in a heavy fouling area, and clean the prop. It present hull is like the hanging gardens of babylon as is the prop and both the boat and autoprop performance have dived. I fully expect that once the grot has been vanquished we will be back to normal.

Incidently in the past we've had the anode in the centre of the prop start to come off (the nylon screws go through the thinnest piece of the anode, doh... ) and that has caused vibration and funny noises.

 

[Robin]

Chris

Brunton told me to paint around the anode screw holes with Primocon, it stops that bit vanishing first. Certainly since doing that 4 years ago we haven't had one fall off between haulouts.

Robin

PS D you know if there are any visitor buoys left in Lymington for this weekend, most seemed to be taken by the boats moved on them whilst the dredging work goes on when we were there weekend before last? We had thought about a last trip to the market!

 

[Danny Jo]

Many thanks for all the suggestions and advice.

 

[npf1]

A question for the Bruntons Autprop owners: how long have your anodes lasted?

Thanks

 

[Robin]

The one on the prop is about 60% used at the end of the year and is replaced annually, but we also have a hull mounted anode that is connected to the shaft/prop, that lasts 2 years.

 

[vyv_cox]

We comfortably get two years out of ours but we have an additional shaft anode. This is consumed after two years.

 

[DavidMcMullan]

Do you have a shaft anode? If so, could it be loose?

 

[Danny Jo]

The photo shows the arrangement of anodes before I fitted the Brunton. I replaced both shaft anodes this year and used sealant to backfill the bolt sockets.

 

[jon]

Er......... does not look like a Brunton Autoprop to me !?

 

[ChrisE]

Don't know about the buoys, you could try ringing the Lymington HM 01590 672014.

Hope you can make it, it looks like a settled if cloudy weekend.

And thanks for the tip about the anode. I'd heard that it isn't strictly necessary, if you have appropriate hull or shaft anodes and they only put it on because customers asked for it....

Chris

 

[fireball]

No, RFTP ... he said BEFORE he fit the brunton ...

 

[boatmike]

Have found they only last one season. Painting around the screw holes is a good idea. I think this bit wastes first and the buggers drop off!

 

[jon]

Ok, should have read the post properly, must remember to engage brain on getting up.