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Serb1980 said..

MorningBird said..
You are way over propping the boat. My S&S34, 6.5 tonnes, had a 20hp engine with a 15 X 10 two bladed folding Gori prop. I bought it from Porters to replace the worn out 15 X 9 that was on it. Porters were fantastic in their advice and the prop was exactly right.
The 15 X 10 pushed the boat at 7 kts (hull speed) at or near max rpm. She cruised at 5.5 kts at 2200rpm. If you overload the engine with a big prop you will go slow, use heaps of fuel, and have lots of unburnt fuel coming out the exhaust to make the cockpit uninhabitable.
Assuming you have a 20 bhp or so engine a 15 X 10 or maybe a 16 X 9 two bladed prop is what you need.

Read your post, gave another call to Austral and David did the calculations again. His words: 15x13 in 3 blades fixed will be a bit too much. 15x12.5 will be perfect for 29 hp. so you are not too far 20 hp = 15x10.

First you have mentioned engine power. I still believe you won't be able to achieve full power/rpm with that size prop.the engine will labour, waste fuel and smell of unburnt diesel.
Ask themif they will take the prop back and give you a full refund if it is the wrong size.

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MorningBird said..

Serb1980 said..

MorningBird said..
You are way over propping the boat. My S&S34, 6.5 tonnes, had a 20hp engine with a 15 X 10 two bladed folding Gori prop. I bought it from Porters to replace the worn out 15 X 9 that was on it. Porters were fantastic in their advice and the prop was exactly right.
The 15 X 10 pushed the boat at 7 kts (hull speed) at or near max rpm. She cruised at 5.5 kts at 2200rpm. If you overload the engine with a big prop you will go slow, use heaps of fuel, and have lots of unburnt fuel coming out the exhaust to make the cockpit uninhabitable.
Assuming you have a 20 bhp or so engine a 15 X 10 or maybe a 16 X 9 two bladed prop is what you need.

Read your post, gave another call to Austral and David did the calculations again. His words: 15x13 in 3 blades fixed will be a bit too much. 15x12.5 will be perfect for 29 hp. so you are not too far 20 hp = 15x10.

First you have mentioned engine power. I still believe you won't be able to achieve full power/rpm with that size prop.the engine will labour, waste fuel and smell of unburnt diesel.
Ask themif they will take the prop back and give you a full refund if it is the wrong size.

Got the confirmation from Hunter. 3 blades are 15x13. I can ask 15x12 to make sure that engine can spin till max revs. If 2 blades prop is 16x11 than 3 blades will be 16x10 (drop a pitch for an extra blade) or 15x12 (for each diameter down two pitch up)You are spot on when over pitched. It burns double of diesel for the same results.

Today spent all day on the boat and diver didn't come to remove the propeller. Will try tomorrow morning. New prop 3 blades (15x12)will cost me $870. I will take the old one to see if we can repitched and make it sexy again.

I seem to recall you achieved your happy boat speed after the engine re-build?

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southace said..
I seem to recall you achieved your happy boat speed after the engine re-build?

Yes I have, but 26 footer wasn't big enough for family to cruise around and spent school holidays

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Serb1980 said..

southace said..
I seem to recall you achieved your happy boat speed after the engine re-build?

Yes I have, but 26 footer wasn't big enough for family to cruise around and spent school holidays

Ah now I see, you upgraded your yacht not trying to put a hunter prop on your old one. I have a autostream adjustable pitch prop and have adjusted it 3 times now and it's just about maximum pitch and I'm doing 8 knots at 2800 rpm cruising at 6.2 at 2000rpm. Very happy with it however the engine manufacturer recommended 3000 rpm cruising which I find absolutely ridiculous and now I can't even reach 3000rpm with the pitch I have. I have a theory my taco maybe incorrect. Also I have a friend with a phantom 33 he's just replaced his 2 blader for a 3 blade with more pitch, she's zipping round now at 6 knots easy and really didn't effect sailing performance. I suggest you enjoy the boat and don't change things much until you slip and re-antifoul and see if this makes a difference before you spend more money on re-propping.