PBO prop test

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afterpegassus

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This was done almost 9 years ago.
Is the information still current or have there been improvements that might make the findings obsolete?
(I am considering a prop replacement)
 
The only major development since then has been the introduction of the Featherstream which is more competitive against folders than other feathering props.

If you post what boat you have and what you want to achieve you might get some useful owner's feedback.
 
I seem to recall it was based on tying the boat to a pontoon & measuring the pull ( if that was the test in question)
That is itself makes it a pointless test. My Brunton, for instance would give a measured amount of pull & seem excellent. However, once at sea the boat hits a bit of chop it stops dead & the prop looses its pitch & there is a few seconds wait whilst it re pitches & gains momentum. By that time the next wave comes & the boat stops again. Hence in a 1 metre chop in , say, Fishermans gat, I cannot make more than 3 kts flat out esp if there is a head wind. In this state fuel consumption rises from 2-2.3 litres per hour. non of this came out in the test. In flat water in a canal I can do 7.2kts flat out.
But as a motor sailing addition it is fantastic, as even at tickover it provides drive to a yacht under sail because it pitches to just a bit faster than the sailing speed.

Only one example but if that was the test in PBO, then ignore it because unless the prop is tested underway similar effects may/may not happen with other props.
 
Daydream believer said:
Only one example but if that was the test in PBO, then ignore it because unless the prop is tested underway similar effects may/may not happen with other props.
Click to expand...

I am about to order a 3 blade Flexofold based on that test, it is replacing a 2 blade VP which on this boat struggles against headwind and accompanying chop, I am happy to base my choice on the level of thrust achieved in the test, in what other way would you try to measure a propellor's efficiency? It was a good well conducted and measured test and involved the test boat being lifted in and out for each prop tested, they measured thrust as pull both ahead and astern , top speed achieved, and kick to the side when going astern, what more could they have done?
To comparatively measure performance in open water against wind wave and tide is surely close to impossible. They used a standard 3 blade fixed prop as a benchmark and looking at how each related to it on the various aspects of performance is really useful.
At the time I had a 33' boat which performed excellently with a D1 30 and a VP three blade folder but VP decided not to submit their products to the test so in my opinion they missed the opportunity but then my satisfaction with it was as much with the big engine as the prop. The boat was a typical Baltic design with limited beam and a thus very easily driven hull which allowed close to 8 kts. if I was prepared to burn the fuel.
Darglow assure me that three blade folders will always outperform 2 in adverse conditions and that makes sense but it is twice the price (or 7 times a fixed blade) so it will need to.
BTW Darglow ( and some others) are offering a discount which ends at the end of the year.
 
Quandary said:
I am about to order a 3 blade Flexofold based on that test, it is replacing a 2 blade VP which on this boat struggles against headwind and accompanying chop, I am happy to base my choice on the level of thrust achieved in the test, in what other way would you try to measure a propellor's efficiency? It was a good well conducted and measured test and involved the test boat being lifted in and out for each prop tested, they measured thrust as pull both ahead and astern , top speed achieved, and kick to the side when going astern, what more could they have done?
To comparatively measure performance in open water against wind wave and tide is surely close to impossible. They used a standard 3 blade fixed prop as a benchmark and looking at how each related to it on the various aspects of performance is really useful.
At the time I had a 33' boat which performed excellently with a D1 30 and a VP three blade folder but VP decided not to submit their products to the test so in my opinion they missed the opportunity but then my satisfaction with it was as much with the big engine as the prop. The boat was a typical Baltic design with limited beam and a thus very easily driven hull which allowed close to 8 kts. if I was prepared to burn the fuel.
Darglow assure me that three blade folders will always outperform 2 in adverse conditions and that makes sense but it is twice the price (or 7 times a fixed blade) so it will need to.
BTW Darglow ( and some others) are offering a discount which ends at the end of the year.
Click to expand...

We went for the 2 blade flexofold and we have had no complaints about it's performance in adverse conditions / punching a tide etc. Very pleased with it after 6 years of use and the best money we spent on the boat apart from a new set of sails.

Another test by Berlin Uni:

SUMMARY - TEST CONDUCTED BY TECHNISCHE UNIVERSITAT BERLIN
Eff @ 6.5 kts Eff @ 8 kts Drag @ 8 kts
Flex-O-Fold 2-blade 60% 68% NA
Flex-O-Fold 3-blade 57% 63% 2.7
MaxProp 46% 44% 3.0
Autoprop 48% 54% 16.9*
Gori 52% 52% 2.7
Fixed 53% 59% 94.5*
Stopped. If allowed to spin, Autoprop drag was 150 lbs, fixed blade drag was 40.5 lbs.
 
I think that the suggestion that static tests are unhelpful is probably correct. I have a 2-bladed Volvo folder which is adequate at marina speeds and as far as I can tell, becomes more efficient with increasing speed. I seem to use no more fuel per hour at around 2700 rpm than at a rather gentle 2300 but go half a knot faster. I also struggle against a head sea, perhaps not to the same extent, but I suspect that the 3-blader would be an improvement in this respect.
 
Daydream believer said:
I seem to recall it was based on tying the boat to a pontoon & measuring the pull ( if that was the test in question)
That is itself makes it a pointless test. My Brunton, for instance would give a measured amount of pull & seem excellent. However, once at sea the boat hits a bit of chop it stops dead & the prop looses its pitch & there is a few seconds wait whilst it re pitches & gains momentum. By that time the next wave comes & the boat stops again. Hence in a 1 metre chop in , say, Fishermans gat, I cannot make more than 3 kts flat out esp if there is a head wind. In this state fuel consumption rises from 2-2.3 litres per hour. non of this came out in the test. In flat water in a canal I can do 7.2kts flat out.
But as a motor sailing addition it is fantastic, as even at tickover it provides drive to a yacht under sail because it pitches to just a bit faster than the sailing speed.

Only one example but if that was the test in PBO, then ignore it because unless the prop is tested underway similar effects may/may not happen with other props.
Click to expand...

After about 4 years with my Brunton, I discovered the secret in a seaway was to change the revs (usually increase) it makes motoring through a chop much better. The pitch seems to vary less.
 
I would have another VP three blade folder if it were not for the anodes, even with the boat berthed in 'fresh' water I never got more than one season out of them. Really well engineered product otherwise, even after 8 years use the prop had no discernable wear but it means lifting every year. Price is attractive too about 70% of the Flexofold, but the anodes are just too small.
 
Gladys said:
After about 4 years with my Brunton, I discovered the secret in a seaway was to change the revs (usually increase) it makes motoring through a chop much better. The pitch seems to vary less.
Click to expand...

This was suggested by Brunton, but under autopilot this is not possible . in addition in a 1 metre chop the period between waves does not allow one to rev up & slow down within the cycle.
 
Of course it was the YM test - my mistake.
On the basis of its findings I was going to order a 2b Flexofold, possibly direct from Denmark for my 20hp Sadler.
I'd love the 3rd blade but it's almost as much as the other two for an apparently marginal performance increase.
 
Quandary said:
To comparatively measure performance in open water against wind wave and tide is surely close to impossible. They used a standard 3 blade fixed prop as a benchmark and looking at how each related to it on the various aspects of performance is really useful.
.
Click to expand...

The point I wanted to make is that the tests lead to a misleading result. it is not impossible to take a boat out into open water. Having gone to the trouble of taking the boat out & fitting a different prop many times over it seems a major omission when measured against the effort taken in the first place.

Incidentally-- i would probably have another Brunton Autoprop, but a 3 blade next time, if i were to buy a larger yacht. I think most of my problem is lack of blades.
I would certainly go back to Brunton for the prop, whatever it was.
 
afterpegassus said:
Of course it was the YM test - my mistake.
On the basis of its findings I was going to order a 2b Flexofold, possibly direct from Denmark for my 20hp Sadler.
I'd love the 3rd blade but it's almost as much as the other two for an apparently marginal performance increase.
Click to expand...

You will find it very satisfactory in that application, although 20hp is rather underpowered for the boat, but you should get better performance than a 2 blade fixed. I expect Darglow will have good data on what size to recommend and what you can expect to achieve.
 
afterpegassus said:
Of course it was the YM test - my mistake.
On the basis of its findings I was going to order a 2b Flexofold, possibly direct from Denmark for my 20hp Sadler.
I'd love the 3rd blade but it's almost as much as the other two for an apparently marginal performance increase.
Click to expand...

I have current quotes from Darglow and from Denmark, not much difference as the exchange rate fluctuates but the telephone conversations with Nick, the sales engineer at Darglow, swings it in their favour. My delayed decision is really between the two and three blade I might need a heater and could nearly get two Planars for the difference.
I contemplated buying a VP thee blade at half way between and getting the anode grooves turned to twice their width and then having a go at casting double weight anodes with a bit of meat added to the depth ( sort of loaf of bread profile) but life is getting too short for that.
 
Daydream believer said:
The point I wanted to make is that the tests lead to a misleading result. it is not impossible to take a boat out into open water. Having gone to the trouble of taking the boat out & fitting a different prop many times over it seems a major omission when measured against the effort taken in the first place.

Incidentally-- i would probably have another Brunton Autoprop, but a 3 blade next time, if i were to buy a larger yacht. I think most of my problem is lack of blades.
I would certainly go back to Brunton for the prop, whatever it was.
Click to expand...

How do you propose to replicate the conditions?
This summer going through the Cally, where there is no tide, I ran the engine at various revs and recorded boat speed, in Loch Lochy with a light (>5kt.) following wind the speed was around 6% - 8% faster than the next day in Loch Ness, still a following wind but a tad lighter. Smooth water both times and no sails in use.
 
Daydream believer said:
This was suggested by Brunton, but under autopilot this is not possible . in addition in a 1 metre chop the period between waves does not allow one to rev up & slow down within the cycle.
Click to expand...

I didn't mean that, just set your revs higher or lower to suit the conditions. It turned a very unpleasant wind over tide motor towards Sovereign Harbour into bearable, and the average SOG went from 3 knots to 5 for about 250 rpm increase.
 
Gladys said:
I didn't mean that, just set your revs higher or lower to suit the conditions. It turned a very unpleasant wind over tide motor towards Sovereign Harbour into bearable, and the average SOG went from 3 knots to 5 for about 250 rpm increase.
Click to expand...

I often have to rev as hard as the engine will go to get much forward momentum. Plus the extra 250 RPM adds a lot to fuel consumption- ie about .3 litres per hour up from 1.9/2 litres to 2.3 litres.
 
Last edited:
Quandary - in case it’s of use, we have a Flexofold three blade prop. Used it for 3 years so far and been very happy with its performance, in flat water (including Crimean with your help!), punching waves and in reverse Can’t compare directly to any other props, but if the budget allows won’t go far wrong with this.
 
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