4 Blades

[MauriceMynah]

I suppose this one is aimed primarily at Griff.

I remember you waxing lyrical about the four bladed prop. What I would like to know is... What's better and what's not?

How much did it cost to change? tell it like it is!  Should I go for the conversion?

[BroadAmbition]

Morning,

What's better - A big improvement at slow speed manoeuvring as the bite is more instant for kicking the stern in / out

What's not - four blades to clean / polish during the biannual AMP

Cost - Not a scooby but it will be in our receipts somewhere or t'other.  Jason Hatch (Aka LBBy back in the day 2007) organised the new prop and took the original 3 x bladed affair in part exchange.

Originally we were going to keep the 3 x bladed prop with just a bit more pitch added so we could slightly over-prop.  We inherited 'B.A' with a very tired 4108 which should produce 34bhp when new in tip top condition.

Once we had made the decision to upgrade to a 50hp Beta Marine, it dawned on us that somehow or other we had to deliver that 50hp into the water.  We didn't have room to use a larger diameter prop so four blades was the way to go.

If we had stuck with the original prop size and three blades for 50hp we would have been hugely underpropped, which uses lots more diesel for no improvement in progress.

So it was a huge no brainer and one of the best upgrades we have done

Hope that helps,

Griff

 

 

[BroadAmbition]

[annv]

Hi you could look at a Axiom Propellers 01832730457 very pleased with mine quirter, more control over maneuvering and heavier built to resist knocks. John

[BroadAmbition]

Something else - Picking / choosing the correct propeller really is a 'Black Art'  Yes I know there are many websites that have formulas for this sort of thing but rarely are they spot on first time, and they struggle with hull and draft shapes

In our case I wanted 'B.A' over propped slightly.  We had information to hand, that is that the Beta is flat out at 2'600rpm, that is to say with just a shaft and no propeller attached the engine will not run over 2'600rpm.  We also knew we had a Borg Warner 2:1 reduction gearbox.  I've been informed that with a gland packed stern tube, the shaft must not exceed 1300rpm, so even at 2'600rpm on the engine we would not over speed the shaft 1'300rpm limit

So, I asked Jason to provide a 4 x bladed prop that would allow the Beta to get to nearly 2'600rpm when flat out (After it had been run in).  I was sceptical he would hit the target with the first attempt - we would see.

Much to my surprise, amazement and subsequent admiration, he did just that.  Flat out 'B.A' and her Beta achieved 2'400 rpm, in deep water.  After being run in she managed 2'450rpm.  Since the Beta is now fully run in and with an administration of ZX1 she now manages in deep water 2'500rpm

He got it spot on first time of asking     Which is just plain and simple showing off if you ask me

Griff

[Vaughan]

5 hours ago, BroadAmbition said:

Something else - Picking / choosing the correct propeller really is a 'Black Art' 

It is indeed! It makes an enormous difference when you get the right one, though.

To MM I would say - why not try it out for a couple of years until you haul her out again, and see what you think?  The boat has been going around on hire quite happily with the present one, plus you are now going to take the speed limiting off the engine, which will also make a difference.

[BroadAmbition]

How many of us have seen / heard boats revving high and not really making much progress?

This is due to being under-propped, especially with hydraulic drives.  No doubt it gives plenty of charge to the batteries, the cynic in me thinks that under propping also aids the yard in diesel sales.

'B.A' fully laden with f/w, diesel and a full complement of crew / stores etc will weigh in at around the 9 ton mark.

That's 9 x tons of the finest biodegradable 40 x 12ft being pushed along at 4mph for only 1000rpm (500rpm on the shaft), 1200rpm gives us 5mph.  This easily charges the six domestic and one cranking battery.  The Beta is under gentle load only.  Slightly over propping is what to aim for

Griff

[JennyMorgan]

Perhaps asking those nice engineers at Richardsons would be a plan, after all they do know the boat. I would also re-read and take onboard the very wise words of Vaughan: 

14 hours ago, Vaughan said:

To MM I would say - why not try it out for a couple of years until you haul her out again, and see what you think?  The boat has been going around on hire quite happily with the present one, plus you are now going to take the speed limiting off the engine, which will also make a difference.