Tigers,
must decide 16x12 or 15x13 in 3 blades. Current 16x13 two blades, and I am guessing it is badly damaged. To much vibration and not efficient at all. The aim is a top end speed with less rpms of course. Planing to motoring to Pittwater for a weekend family trip.
Tried to Google it but just can not figure out the difference. I am scared that 15x13 would be to much pitch even Hunter has recommended (via email). All I know is that 16" will grip better on water but an extra pitch will push further.
Very confusing. I know that are some calculations but I just haven't come across an engineer who can explain it simply in two min. Porters and Austral sad no differences at all but anybody who has 3 cyl in 6.5 t boat can give me some light here. I am sure that there is a difference. There are many Hunters in USA but can not find any forum about upgrading the original 2 blades prop. Regardless, both will perform better than current one. Thank you my dear tigers.

shaggybaxter said..
Serb,
You didn't need another thread mate. I'll give you my numbers.
- Cruising mode: 6+ ton.
- Length: 41'.
- Wetted surface: Way more than a Hunter.
- Engine: 30Hp 3 cyl.
- Prop: 2 blade folding.
- Prop size: 15/16 x 10 (can't remember which diameter, I think it was 16)

Interesting fact:s:
- I wouldn't ever run over 3000 rpm. And only for short runs. With a clean bottom that would be 7.8 knots, 8 on a good day;
- With a dirty bottom, you wouldn't get much above 6 knots.;
- IIRC, the biggest pitch you can get on the Volvo 2 blade is 10"; and
- The biggest diameter is 16".

And that was enough to push a 6+ ton over 7.5 knots with a clean bottom.

If you think your 2 blade is badly damaged, maybe you should look at getting your existing 2 blade repaired first?

Thanks mate, 8 knots Woow that is a big difference..

shaggybaxter said..
Serb,
You didn't need another thread mate. I'll give you my numbers.
- Cruising mode: 6+ ton.
- Length: 41'.
- Wetted surface: Way more than a Hunter.
- Engine: 30Hp 3 cyl.
- Prop: 2 blade folding.
- Prop size: 15/16 x 10 (can't remember which diameter, I think it was 16)

Interesting fact:s:
- I wouldn't ever run over 3000 rpm. And only for short runs. With a clean bottom that would be 7.8 knots, 8 on a good day;
- With a dirty bottom, you wouldn't get much above 6 knots.;
- IIRC, the biggest pitch you can get on the Volvo 2 blade is 10"; and
- The biggest diameter is 16".

And that was enough to push a 6+ ton over 7.5 knots with a clean bottom.

If you think your 2 blade is badly damaged, maybe you should look at getting your existing 2 blade repaired first?

It doesn't look damaged but under pitched for sure. Now I understand why on 2000 rpms I am moving few knots only instead of 5. will see how will 15x13 three blades with prop speed on it push the boat.


Will get back in two weeks. Honestly, moving 4.7 knots on 3000rpm is nonsense. 21 years old propeller vibrates like a washing machine. This is 16x11 in my opinion. It should be 16x13 in two blades. Can not wait to see the difference. keep in touch

shaggybaxter said..

Serb1980 said..

shaggybaxter said..
Serb,
You didn't need another thread mate. I'll give you my numbers.
- Cruising mode: 6+ ton.
- Length: 41'.
- Wetted surface: Way more than a Hunter.
- Engine: 30Hp 3 cyl.
- Prop: 2 blade folding.
- Prop size: 15/16 x 10 (can't remember which diameter, I think it was 16)

Interesting fact:s:
- I wouldn't ever run over 3000 rpm. And only for short runs. With a clean bottom that would be 7.8 knots, 8 on a good day;
- With a dirty bottom, you wouldn't get much above 6 knots.;
- IIRC, the biggest pitch you can get on the Volvo 2 blade is 10"; and
- The biggest diameter is 16".

And that was enough to push a 6+ ton over 7.5 knots with a clean bottom.

If you think your 2 blade is badly damaged, maybe you should look at getting your existing 2 blade repaired first?

It doesn't look damaged but under pitched for sure. Now I understand why on 2000 rpms I am moving few knots only instead of 5. will see how will 15x13 three blades with prop speed on it push the boat.


Will get back in two weeks. Honestly, moving 4.7 knots on 3000rpm is nonsense. 21 years old propeller vibrates like a washing machine. This is 16x11 in my opinion. It should be 16x13 in two blades. Can not wait to see the difference. keep in touch

Sorry Serb, I don't see the logic.
Volvo's maximum pitch on a 2 blade is 10'. And that pushed my much fatter arsed girl to 7.5+ @ 3000.
When your only reference to near the same prop is one that 'vibrates like a washing machine'....why are you not trying to fix it first before jumping to a 13'?
I'd argue the vibration is what is killing your speed much more than the pitch.

Spot On Shaggy..Investigate why the prop iis unbalanced and vibrating and get it fixed.
As this is certainly the cause of loss of speed.
Otherwise Serb it will be a very expensive and unnecessary change.

Cheers

Lazzz said..
A good clean of that prop wouldn't hurt - for a start anyway!!

Yep, there could be a knot gained just be cleaning the prop blade.

0llie said..
Serb could it be the prop shaft bent or out of line as well? Is there any leaks around the stern tube or stuffing box?

No leaks. I was thinking of fixing this prop but it it worth it? Does age reduce quality of components?
By memory, old prop from Tasman turned into almost in terracotta.

"Spot On Shaggy..Investigate why the prop iis unbalanced and vibrating and get it fixed.
As this is certainly the cause of loss of speed.
Otherwise Serb it will be a very expensive and unnecessary change."

Cutlass bearing. It was in the survey. To be done next haulout as I understand.