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-   -   Tartan 27 propeller (https://www.moyermarineforum.com/forums/showthread.php?t=11353)

Chica 12-11-2019 05:46 PM

Tartan 27 propeller
 
2 Attachment(s)
I replaced my old, chipped two blade with an Indigo 3 blade. Did not recognize an improvement. Furthermore, after light use over one season the three blade was evenly pitted on both leading and trailing edges, more pronounced on the trailing edge. I suspect serious cavitation. I think the prop is too close to the deadwood. Deadwood is 3" thick, Indigo blade is 4" long beyond a 1 inch shaft. 1 inch of the available 4 is directly behind the deadwood. My choices are:

1- Move the three blade aft by cutting the shaft and adding a spacer at the transmission, or...

2- Purchase a new two blade.

I want motoring performance above everything else.

What are your thoughts?

Chica 12-12-2019 09:17 AM

i figured wrong with regard to what amount of the blades lay behind the deadwood but the principal is the same.

Administrator 12-12-2019 10:34 AM

Maybe it's no big deal, but is that jack stand chain stressing your rudder post?

Bill

Dave Neptune 12-12-2019 10:36 AM

Careful proping
 
Chica, I assume you are a direct drive with the Indigo. There is not much room for the small diameter to bight on and what it bites on is disturbed water flowing around the deadwood. What was the original prop and crusing RPM's before?
And what RPM's are you getting with the Indigo? The Indigo runs at a higher RPM's to get to the power ccurve of the engine. Comparing speed at a given RPM is not what to look for. What you want is around 21~2200 RPM's for fast cruise. Choosing a 2 or a 3 blade is problematic for finding a flat enough pitch and diameter (usually larger) to achieve good power RPM's.

Before changing anything be sure of the tune of the engine. With the Indigo you should get to 24~2500 RPM's if the engine is tuned properly.

Dave Neptune :cool:

indigo 12-12-2019 10:56 AM

Propeller Deterioration
 
The pitting you see on the prop is the result of Galvanic Activity. Since you do not have a zinc on the shaft, the prop is the sacrificial element. That is the concept behind the Indigo "No Barnacle" solution. The prop material has no zinc in it thus the pitting was very limited. The good news is that you had no barnacles.

To follow up on Dave's question, what was your WOT RPM and what boat speed did that yield. We have a least 20 Tartan 27s with our prop installed and no complaints.

Tom Stevens

Chica 12-12-2019 12:49 PM

Thanks all-

Bill, I'll check the stands and chain but I seem to recall the chain having some play...still not an ideal location.

Dave, i don't know the answer to these questions but I'll keep them in mind when i restart things. It had a 13"X8" and it appeared to work well.

Tom, I came to my cavitation conclusion because of the evenness of the deterioration and the shiny metal exposed, especially on the trailing edge of the prop. It looks like someone ran a 36 grit board over it. I did have the boat on a marina dock for the summer. Do you think the distance between deadwood and prop could be an issue? Is this prop still serviceable?

Thanks again-

Chica 12-12-2019 06:27 PM

Choosing a 2 or a 3 blade is problematic for finding a flat enough pitch and diameter (usually larger) to achieve good power RPM's.


Dave, Could you either elaborate on this or put it in terms a carpenter can understand? :)

indigo 12-12-2019 08:58 PM

Indigo Prop
 
Since I have had no negative feedback from other Tartan 27 owners with the Indigo prop, I can only assume that the clearance you have from the deadwood is sufficient.

You should hand dress the leading edges especially to restore decent performance. Try to create a nice parabolic leading edge, not something razor sharp.

You can probably get a zinc of some sorts on either the shaft (a thin "Donut" model) or one of the "Nut" types on the threads. The addition of a zinc will prevent the Galvanic Action on the prop, however you will get barnacles which make a mess of performance as well.

Tom

Chica 12-13-2019 09:17 AM

Thank you Tom.

Al Schober 12-13-2019 10:14 AM

Chica,
The prop in the photos is corroded, and shows impact damage on the leading edges at the tips. The corrosion can be due to an engine/battery grounding issue. I've seen a 12" propeller reduced to 9.5" by stray ground current!
Your best powering performance will be with a 3 blade prop (more blades gives you less vibration), as big as you can fit in there while maintaining adequate tip clearance to the hull. As diameter increases, you have to reduce pitch so the propeller performance curve matches the engine power curve.
The performance of a propeller can be adjusted somewhat. Diameter can be reduced by machining the tips of the blades, and pitch can be adjusted somewhat by twisting the blades. These are both jobs for a good propeller shop. A bronze propeller has limited ductility and will only stand so much 'adjustment'. River tug boats frequently damage their propellers, but select stainless propellers that can be beat back into shape numerous times.
I recommend you consider a DriveSaver https://www.globemarinedirect.com/pr...01-12-0020.htm
This unit will stop any stray currents in the shaft/propeller, as well as moving the propeller aft bit, giving room for a zinc forward of the propeller hub.

HOTFLASH 12-14-2019 09:42 PM

Room for thin anode on a Tartan 27
 
Chica,

There is very little room for an anode, other than a thin donut collar type on the 1" shaft of a Tartan 27. Boatzincs.com carries "LC-3 Micro Thin Collar Zinc Anode - 1" Shaft" which is 11/16" thick. Install it on the shaft just forward of the prop leaving a margin on both sides. But it could be your new prop takes up more space on the shaft that the original prop, leaving no room for even a thin anode.

I have a Tartan 27 in fresh water with original prop and I have not found a magnesium nor an aluminum thin (11/16") anode for a 1" shaft, so I have to use a 25mm one designed for a Beneteau. It only comes in zinc or aluminum. I use the aluminum, and the 25mm one fits fine. Boatzincs.com has those too.

Mary

Chica 12-19-2019 09:13 AM

Thank you Al and Mary. Very helpful.


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