Prop size for Irwin 34 Citation.

[sengland]

Can somebody help me out with the prop size for my Irwin Citation 34ft, with a new 20HP Yanma and 2.61 Ration Kanzaki gearbox.
If somebody has a boat with similar length, displacement of 11,500 pounds and a 20hp engine, tell me your prop size if your happy with it. Or thoughts on a feathering prop? (I don't race)

The yard got it quite wrong with a Chris Craft Equipoise, 3 blade bronze, RH 14"D x 14"P, 1 1/4" bore. The engine can only reach about 2200rpm, (Yanmar recommend around 2500-3000 cruising), with this prop it wont rev any more than 2200rpm, if I try she smokes, being flooded.
Also, at idle around 500-700 it will just stop, a nightmare when maneuvering around a marina.
Its not the engine because she purrs away nicely at 3300rpm.
Thanks
Stuart

[JimsCAL]

Prop pitch looks close to me, though I would like to see a inch or two larger in diameter if your installation can accommodate one. I wonder if you have engine issues. Shouldn't stall once its warm. And might not be making full power.

My boat is a Cal 33, 11,000 lbs with Yanmar 3GM30F with 2.6 gear ratio. Prop is a Martec folder, RH 16x16. It's a bit over pitched, but engine easily pushes boat to over 6 kts with no smoking or other problems. Prop came with the boat (I'm 4th owner) and I think it's been on her for a long time.

[tkeithlu]

Your diameter probably is limited by space. You have too great a pitch, similar to too high a gear, so the engine bogs down. So, go to 13.5 or 13 inches of pitch. Aim for a maximum RPM just a bit below the red line.

Purring under no load does not a happy engine guarantee. You have not completely convinced me that you do not have a compression problem, but I hope not.

[sengland]

Originally Posted by JimsCAL

Prop pitch looks close to me, though I would like to see a inch or two larger in diameter if your installation can accommodate one. I wonder if you have engine issues. Shouldn't stall once its warm. And might not be making full power.

My boat is a Cal 33, 11,000 lbs with Yanmar 3GM30F with 2.6 gear ratio. Prop is a Martec folder, RH 16x16. It's a bit over pitched, but engine easily pushes boat to over 6 kts with no smoking or other problems. Prop came with the boat (I'm 4th owner) and I think it's been on her for a long time.

Thanks for quick response, I could go bigger by about an inch but my issue is the engine getting bogged down so I was thinking I need to go smaller. You have 1/3 more HP than me and two bladed correct? This has three blades at 20HP.

[sengland]

Originally Posted by tkeithlu

Your diameter probably is limited by space. You have too great a pitch, similar to too high a gear, so the engine bogs down. So, go to 13.5 or 13 inches of pitch. Aim for a maximum RPM just a bit below the red line.

Purring under no load does not a happy engine guarantee. You have not completely convinced me that you do not have a compression problem, but I hope not.

Engine is new with maybe 10hrs on it max. (Hr meter not hooked up yet) so am not going there yet. We we're in some rough weather with a 1/2full fuel tank so, if its anything to do with the engine am looking at the 10micron filter first. Am sort of ruling compression right now because since having the new prop its always had issues at the higher revs when gearbox is engaged.

[Compass790]

I've found this free prop calculator to be good;https://vicprop.com/free-propeller-sizing-calculators?
Just input your parameters, got our boat right.

[EWOL Props]

Originally Posted by sengland

Can somebody help me out with the prop size for my Irwin Citation 34ft, with a new 20HP Yanma and 2.61 Ration Kanzaki gearbox.
If somebody has a boat with similar length, displacement of 11,500 pounds and a 20hp engine, tell me your prop size if your happy with it. Or thoughts on a feathering prop? (I don't race)

The yard got it quite wrong with a Chris Craft Equipoise, 3 blade bronze, RH 14"D x 14"P, 1 1/4" bore. The engine can only reach about 2200rpm, (Yanmar recommend around 2500-3000 cruising), with this prop it wont rev any more than 2200rpm, if I try she smokes, being flooded.
Also, at idle around 500-700 it will just stop, a nightmare when maneuvering around a marina.
Its not the engine because she purrs away nicely at 3300rpm.
Thanks
Stuart

Clearly the prop you have is overpitched, difficult to give an advice on prop diameter without knowing the gear box ratio in forward.
However typically a boat of 34' installs props of about 15"-16" diam 3 blades with a diam/pitch ratio of about 1.5, (e.g. 16" x 10.6"), this is just a ball park indication obviously that doesn't take in consideration important data.
A feathering prop with external pitch control will allow you to optimize the pitch right for the real characteristics of your boat, not only it will be calculated for the optimal theoretical diam and pitch, but you will be able to fine tune its performance to the absolute best pitch through a simple and quick trial&error test.

[JimsCAL]

Originally Posted by sengland

Thanks for quick response, I could go bigger by about an inch but my issue is the engine getting bogged down so I was thinking I need to go smaller. You have 1/3 more HP than me and two bladed correct? This has three blades at 20HP.

Yes, the Martec is a 2-blade folding prop.

One thing you don't mention is the speed you are making, just the engine RPMs. If you are making 5-6 knts as you approach the point that the engine starts to smoke, then that is indeed an indication that the engine is overloaded by an overpitched prop. However if the boat speed is much lower, I would think it's more likely an engine issue. You say engine is "new". Is this new or a rebuild? Has yard that put this engine and prop in looked at things to see why you are having this problem?

[GordMay]

Originally Posted by EWOL Props

Clearly the prop you have is overpitched, difficult to give an advice on prop diameter without knowing the gear box ratio in forward...

sengland specified a 2.61 ratio [2.61:1], so possibly a KMP35P ➥ KM35P?Hydraulic Equipments,Transmissions and Marine Gears?Products?Kanzaki Kokyukoki Mfg. Co., Ltd.

[EWOL Props]

Yes, you are right, I did not see that before. So supposing the engine model is a 2YM20 with gear ratio 2.61:1, considering an LWL of 27.33' and displacement at full load (fuel, water, crew) of 14200 Lbs, we would suggest a prop 15"x 9" (pitch to be then fine tuned with pitch setting after the first test). Expected boat max speed 6.0-6.2 knots.

Originally Posted by GordMay

sengland specified a 2.61 ratio [2.61:1], so possibly a KMP35P ➥ KM35P?Hydraulic Equipments,Transmissions and Marine Gears?Products?Kanzaki Kokyukoki Mfg. Co., Ltd.

[sail sfbay]

Suggest contacting the propeller manufacturer for the correct propeller sizing that matches your engine (hp and recommended cruising rpm) and transmission. Engine rpms and pitch are inversely related. Increasing the pitch will decrease engine rpms and decreasing the pitch will increase engine rpms. On everyone of my sailboats I installed a 3 blade fixed Michigan Sailor propeller. With proper propeller sizing you will have plenty of low speed maneuverability at low rpm and top end speed at high rpm.