Just learnt something!

[johnphilip]

Following Boo2's thread on which rope cutter to fit I followed the recommendation and checked out the Ambassador cutter. It was on their site that I realised the prop on our saildrive is a Volvo rather than the Flex-o-fold I had thought, (because the spec for the boat said it was a Flex-o-fold )
Now I have always been disappointed about the loss of thrust when pushing into a stiff breeze with any chop. You expect the boat to slow but on occasion the boat has suddenly lost drive to the extent that we have to pay off and go at an angle to wind and sea until the prop started working again.
I had read the very good YM test on different props ( which you can see on Flex o fold site) and this showed that this prop was very good, giving thrust at least as good as many 3 bladed ones. Unfortunately they did not have the Volvo prop to test. As I thought I had the F-o-F prop I thought there was little I could do about the problem. Now I find there is another spending opportunity. Has anyone else had isues with the Volvo saildrive 130 leg with their own prop?
As often the difficulty is that you cannot tell the extent of any improvement until you have spent a lot of money.

 

[Stork_III]

Following Boo2's thread on which rope cutter to fit I followed the recommendation and checked out the Ambassador cutter. It was on their site that I realised the prop on our saildrive is a Volvo rather than the Flex-o-fold I had thought, (because the spec for the boat said it was a Flex-o-fold )
Now I have always been disappointed about the loss of thrust when pushing into a stiff breeze with any chop. You expect the boat to slow but on occasion the boat has suddenly lost drive to the extent that we have to pay off and go at an angle to wind and sea until the prop started working again.
I had read the very good YM test on different props ( which you can see on Flex o fold site) and this showed that this prop was very good, giving thrust at least as good as many 3 bladed ones. Unfortunately they did not have the Volvo prop to test. As I thought I had the F-o-F prop I thought there was little I could do about the problem. Now I find there is another spending opportunity. Has anyone else had isues with the Volvo saildrive 130 leg with their own prop?
As often the difficulty is that you cannot tell the extent of any improvement until you have spent a lot of money.

Do you have 2 or 3 blade VP prop. I changed from 2 to 3 blade and had significant improvement in forward drive and even greater improvement of reverse power.

 

[johnphilip]

Do you have 2 or 3 blade VP prop. I changed from 2 to 3 blade and had significant improvement in forward drive and even greater improvement of reverse power.

Two blade.

 

[Stork_III]

Two blade.

When I changed from 2 to 3 blade VP prop, same speed at 350rpm less, with total confidence in reverse. With 2 blade never knew if boat would stop when applying reverse. Blades and hub (15x9) quoted at £1300 from Volspec, £1650 from Marine parts. Volspec gave me 25% discount for ordered prop against full price for in stock. Worth asking. No experience of Flex-o-fold for comparison.

 

[Daydream believer]

I bought a brunton autoprop 2 blade
If in a 1 metre chop the boat would stop
The prop would loose its pitch as there was no forward progress & it would feather
Then as it began to pitch up the boat moved forward
But on the next wave it would stop again & again the prop would feather
Max speed was 2.5 kts against 6+ with a fixed prop
Brunton changed the prop for one with a greater pitching action & it solved the problem
Trouble is that max revs are down by 800 & fuel consumption is up from 1.66 litre per hour to 2+ per hour
I suggest that your problem is a prop with a pitch that is too fine
I suggest you compare it with a fixed prop on a similar boat & see what the pitch is
The boat tests were not definative as they did not test the results in a chop
In flat water my first prop was faster than a fixed one. In a chop it was useless

 

[johnphilip]

I bought a brunton autoprop 2 blade
If in a 1 metre chop the boat would stop
The prop would loose its pitch as there was no forward progress & it would feather
Then as it began to pitch up the boat moved forward
But on the next wave it would stop again & again the prop would feather
Max speed was 2.5 kts against 6+ with a fixed prop
Brunton changed the prop for one with a greater pitching action & it solved the problem
Trouble is that max revs are down by 800 & fuel consumption is up from 1.66 litre per hour to 2+ per hour
I suggest that your problem is a prop with a pitch that is too fine
I suggest you compare it with a fixed prop on a similar boat & see what the pitch is
The boat tests were not definative as they did not test the results in a chop
In flat water my first prop was faster than a fixed one. In a chop it was useless

I thought that the static or bollard pull is giving a pretty fair test of the performance when facing wind and sea. This is indeed the issue for me, the amount of thrust from the prop when it has stalled and the boat is almost stationary. Regarding the pitch I had always believed the contrary to be true, slow moving needs a lower pitch or the engine is struggling to achieve the revs. Could the Brunton be a special case or is the issue more to do with cavitation increasing as the boat slows? Conventional wisdom has always been 3 blades give more low speed push but the YM test gave the 2 blade Flex-o-Fold almost the same figure as the 3 blade. Still not sufficiently convinced of the best solution.

 

[johnphilip]

When I changed from 2 to 3 blade VP prop, same speed at 350rpm less, with total confidence in reverse. With 2 blade never knew if boat would stop when applying reverse. Blades and hub (15x9) quoted at £1300 from Volspec, £1650 from Marine parts. Volspec gave me 25% discount for ordered prop against full price for in stock. Worth asking. No experience of Flex-o-fold for comparison.

I have a Volvo MD2020D (20 ps engine power, 18 ps shaft power) is this the engine size for your prop?

 

[Stork_III]

I have a Volvo MD2020D (20 ps engine power, 18 ps shaft power) is this the engine size for your prop?

Yes but B version. I also have 3 blade on my current boat 2030C.