propeller position

[cloy]

Had new port d,shaft made, stbd straighten. Had wheels reworked. As I started back together I discovered port shaft is longer than stbd. Anyone have a clue where the face of the wheels should stop?

 

[psneeld]

Someone may have the actual measurement which I think is based on diameter...but I would say the average I am used to is no closer than 2.5 to 3.0 inches behind the cutless bearing for good flow.

You might get away with closer...but not sure what the absolute would be.

 

[cloy]

2" to 3". Looks like I had about 1" on one and 1 1/2" on the one I replaced. Had a couple of ol timers say not less than one inch.

 

[cloy]

We hit something hard on the 3rd on the way to fireworks show in Biloxi on a low tide.
After pulling the boat next morning and start demo, found a lot of mixed matched parts. Even two dif. Length trans, surprise,surprise. Oh well, time to do a little more diggin.

 

[mbevins]

My research for line cutters required a minimum of IIRC 1 " clearance to the cutlass to maintain proper water flow. So I would think with a prop hub you'd like closer to 2" clearance.

 

[psneeld]

The minimum could very well be pretty small...I think most of the time the 2.5-3 inches and maybe a touch more is so you can get a collar zinc in here....then the clearance is only about an inch anyway.


For displacement speeds...probably not a lot o cavitation and on single shafts...mine has a positive pressure water feed at the top end to help.

 

[Donsan]

We hit something hard on the 3rd on the way to fireworks show in Biloxi on a low tide.
After pulling the boat next morning and start demo, found a lot of mixed matched parts. Even two dif. Length trans, surprise,surprise. Oh well, time to do a little more diggin.

Your survey didn't mention anything about that???

 

[AusCan]

This is what Yanmar recommends.

 

[LarryM]

This is what Yanmar recommends.

For our boats, Yanmar, and just about every other shaft manufacturer, propeller manufacturer and design source I have ever encountered are in agreement. Ideally, 1-1.5 shaft diameters. Beyond that, any propeller imbalance or shaft distortion can be magnified and shorten the life of the cutless bearing. Shorter and the water flow into the bearing and shaft log can be affected. In extreme cases, the propeller hub can actually contact the cutless bearing shell because of shaft movement fore and aft if very flexible engine mounts are used.

As for shaft zincs. If you don't have an exposed shaft, where the zincs are typically installed forward of the strut, then a prop nut zinc is sometimes recommended.

Obviously, OB, IO and specialty racing drives and props are excluded.

 

[psneeld]

Exactly...I think that why you see a tad more room as to allow the engine under higher loads moving forward on its isolators.

The 1 to 1.5 I think is the minimum so it would be under load?

If the boat is being used...you can see it on the shaft...shiny from the cutless.

 

[markpierce]

So, how does this "stack up"? The propeller looks farther away from the rudder than recommended in post #8.

 

[LarryM]

So, how does this "stack up"? The propeller looks farther away from the rudder than recommended in post #8.

Mark, a quick search of my reference material indicates the distance between the propeller blade and the leading edge of the rudder should be no more than 10-15% of the propeller diameter.

In general, the distance from the propeller to the rudder should be kept small to maintain good steering control, but if Coot's steering is adequate, I wouldn't be concerned.

 

[markpierce]

Larry, the Coot steers good. Thanks to large rudder and propeller, and "displacement" speeds?

 

[mbevins]

 

[cloy]

Missy did a little searching sunday evening and came up with 3 different ARTICLES FROM 3 different high in people that do a little racing and boat building.
This morning when me and bubu headed to the boat yard, I ran into a couple of the old local shrimpers and talked, or rather listened to them.
What Ive came up with is, no more than 50 percent of shaft dia. From end of strut to prop hub. 1 1/4" shaft equals 5/8" clearance.

 

[cloy]

I do want to give thanks to all you ol water hobos for putting in on the subject. Now, if I could get yall to come help a couple days, well now that would be just fine...

 

[Nomad Willy]

I'm close to the minimum but I have a PSS and seawater pressure fed stern bearing.

 

[Manly Q.]

Hi Eric.

I know next to nothing about propellers but is that one in your attachment on back to front. It appears to be left handed but the shape is facing the other way.

I am sure I am wrong here. And I am sober.

Regards.

David.

 

[Nomad Willy]

"shape is facing the other way"
You must be seeing something wrong .. thinking it's from a different angle than it is or?
Definitely a left hand CCW wheel.

 

[Manly Q.]

Thanks Eric.

Always happy to be wrong.

Regards.

David.