Propellor balancing

[mlines]

We have a vibration in the boat that occurs above 3000 rpm. Its of the form that causes "loose" items in the boat to buzz (i.e. catches and popup cleats).

Its a Bravo III drive with a stainless Duo prop . The boat is a Regal 2250 with a 350MAG.

It has been suggested that this could be a couple of things:

1. Props not balanced
2. UJ worn/stiff

The UJ was removed and greased etc. in the spring and Tompamarine is going to have another quick look at it over the next few weeks.

The props are maintained (in terms of cosmetic) to a high standard. They are polished each year by a professional polisher (but not a propeller professional, a metals specialist). There are no obvious dings or bends but we did hit a pushchair last year which came between the rear prop and the skeg. Is it possible that they are out of balance? What are the symptoms of out of balance props. We do seem to be using a bit of drive oil which might suggest that the vibration is letting oil past a seal which might point to the props.

A balance costs £158.80 so reluctant to take a punt on this being the issue without some more definite idea,

Martin

 

[BruceK]

I doubt it's a prop balance issue that would cause this and that you couldn't visibly see with the props. Bent or significantly chipped blade. However if it's anything like my VP 290 leg, what can happen is the inner prop shaft going to the outer prop is susceptible to getting bent on a prop strike with SS blades on. Check for a bent shaft.

 

[mlines]

Is this something a dial gauge would show?

 

[BruceK]

yes

 

[oldgit]

A balance costs £158.80 so reluctant to take a punt on this being the issue without some more definite idea,

Martin

Cripes that seems a bit steep considering you have got to get both props off then get them round to their workshop and all they have to do is true them up
Have you tried Steel Developments...or is that their price. ?

 

[mlines]

That's Steel developments price

£74.40 per prop, its a duo prop + £10 p+p

 

[Ian h]

Sent my duo props to Steel developments a year ago to have some dents removed, Prior to going away boat easily did 47 knots when they came back max was 43 knots, they really messed them up, Have spoken to a few people whom all say the same, Steel developments are no good with duo props - steer clear,
I called them after they went back on boat and they said it was not what they had done it must be the engines, ..........
Engines are fine nothing changed, Engineer checked them out, Its the props,
The previous owner of my boat had to send the props back 4 times before they were sorted .

 

[mlines]

So is there anyone else you would recommend for balancing?

 

[tico]

Streamlined props? did a good job on my duoprops

 

[mlines]

Streamlined, they are close to me so I can drop them in - £160+VAT makes them more expensive. Hmm - decisions

 

[mlines]

I have a dial gauge so went over to the boat to take some measurements, first the props. This is not very scientific, I just chose a high spot on the blades to measure the difference.

The rear prop of the Duo Prop pair showed two blades on "0", the dial gauge is a 0.01mm gauge, and one on 0.58mm, so one is offset slightly.

​I then did the "front" set of blades, again choosing a random high spot on the blades and checking the difference. Starting with a "reference" blade, one was 0.10mm different and the other was 0.36mm different.

I then removed the props and measured any rotational run out (i.e. shaft bent) on the concentric shafts. The first (inner) shaft was a steady 0 all round and the second (outer) varied by 0.1mm but it was on what appeared to be a dirty, slightly unfinished surface so probably can be excluded.

So it doesnt look like a bent shaft but is the sub-millimetre differences on the prop blades going to be a balance issue and do they "balance" to this level of accuracy??

 

[BruceK]

Well that's great news it's not the shaft then. I wasn't so fortunate

 

[mlines]

Yes, and feedback from the Regal forum suggests that a variation of 0.5mm or less on the props is not the issue either. Therefore its to the top of the drive and the UJ.