# Propeller position?



## ereuter (Aug 31, 2006)

I race a P30 PHRF cruising, and have the adjustment for a fixed 2-blade prop.

I've often wondered if the position of the prop when I shut down the engine makes a difference in drag - i.e. whether the blades are pointing vertical or horizontal or in between.

Does anyone know if it matters? 

I always sail with it in gear so that the prop doesn't spin freely.

Thanks-
Eric


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## sailingdog (Mar 19, 2006)

Yes, especially if the keel and prop are close together, since a horizontal prop won't be shielded by the keel, and will generate more drag as a result. If the prop is stopped in the vertical position, most of the area of the prop will be "shadowed" by the keel—resulting in far less drag.


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## ereuter (Aug 31, 2006)

Well, it's a fin keel, so the prop is pretty far away. Looks like this:









The rudder is turned around backwards in that photo.


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## paulk (Jun 2, 2000)

Even with such distance between the prop and keel, vertical is probably better than horizontal. Things like entrained flow and turbulence along the hull surface may mean that having a blade closer to the hull doesn't slow you down as much as having both blades sticking out horizontally into relatively less turbulent water. What with heeling and wave motion, though, it might be worth testing with the blades in both positions to be sure. You'd need a fairly finely calibrated speedo to tell the difference, though.


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## maestro (May 3, 2002)

*what we do*

on our boat, we have marked the shaft near the transmission (while the boat is out of the water) where the prop is in the vertical position. Then all we do is set the prop so that the 2 marks line up and put it in reverse.


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## DavidWhitney (Jun 13, 2007)

I always set mine straight up and down, before I put a folding prop on.
I also removed that raw water strainer and raised my rudder up until it just cleared the hull. That and wet sanding seemed to make a major difference in my finishes. I now win more that I lose..Dave Whitney 1975 P30


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## ne57301 (Mar 7, 2000)

*Nice Bottom*

Wow Eric, that bottom looks great, nice job.

Mark the coupler between the shaft and the transmission with white paint. A line fore/aft on top of the coupler when the prop is vertical, two lines for either blade up.

Here's the big tip. You can see the coupler if you take the bottom out of the top step (use a flashlight). Make a little tool to turn the engine over using the pin in the middle of the flywheel (the thing you would use to manually start the A4). The tool I have is a couple of pieces of (3/4" ?)pipe connected with a 90 degree elbow. Use a hacksaw to cut a couple of notches in the end of one of the pipes. Now you can leave the engine in gear, look over the top of the engine at the coupler, turn the engine over by hand until the white line is on top. Prop centered. (really helps with the folding prop)


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## ereuter (Aug 31, 2006)

ne57301 said:


> Wow Eric, that bottom looks great, nice job.


Thanks. I had it soda blasted, but it was still a lot of work.



ne57301 said:


> Mark the coupler between the shaft and the transmission with white paint. A line fore/aft on top of the coupler when the prop is vertical, two lines for either blade up.
> 
> Here's the big tip. You can see the coupler if you take the bottom out of the top step (use a flashlight). Make a little tool to turn the engine over using the pin in the middle of the flywheel (the thing you would use to manually start the A4). The tool I have is a couple of pieces of (3/4" ?)pipe connected with a 90 degree elbow. Use a hacksaw to cut a couple of notches in the end of one of the pipes. Now you can leave the engine in gear, look over the top of the engine at the coupler, turn the engine over by hand until the white line is on top. Prop centered. (really helps with the folding prop)


That's good to know. I currently have all the paneling out of the quarter berth because I've been doing work on the engine. I'd been wondering how I'd know where the shaft was. So you've eliminated the floor to the little storage compartment?

I actually found the original hand crank for the A4 under the port settee. Justin didn't even know it was there. It's rusty, but I've been able to start the motor with it, even with that short throw.

Which folding prop do you have? Have you found that it's worth the hit you take on your PHRF rating?

Thanks-
Eric


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## sailingfool (Apr 17, 2000)

I don't think it matters a bit the prop orientation if it isn't in an arpeture...but do yourself a big favor and get a folding prop. They are far and way well worth the 6 second per mile rating reduction, if they were not, you'd see the hotshots cheating the rule with fixed props. Never happen, a knowledgeable racer will have a folding or feathering prop.


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## maxmunger (Dec 29, 2005)

Yes vertical behind the strut is better.
But all this really matters is in light air. Once a boat can get near hull speed the prop doesn.t matter much.
Those old P30s can still beat most boats1


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## sanctuarysam (Sep 16, 2006)

*how would you know...*

absent a folding prop, how can you tell which way the prop is oriented when you shut down the engine...
looked all over my boat for the "align prop vertically" switch, but i can't seem to find it.
really, when it gets down to it, unless you have a prop suitable for racing, i'm thinking one should worry more about a clean slippery hull, and spot on trim, than negligible drag from your prop.
i have an offset 2 blade, sail w/ it in R...not a lot i can do about the effect it has in the water, ergo, i try, (try being the operative word) to focus on eeking out all the speed from sail trim and weight distribution.
anyway...my $.02
great day of sailing on the bay yesterday, worked my new crew hard(i think they'll be back)..now boat projects to finish.
have a great sunday all.


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## Sailormon6 (May 9, 2002)

sanctuarysam said:


> absent a folding prop, how can you tell which way the prop is oriented when you shut down the engine...


When the boat is on the hard, align the prop vertically, and then mark the prop shaft inside the boat, so that you can see, visually, when it is aligned after you shut off the motor. When my boat is under sail, I can easily turn the shaft by hand to align it.



> ...really, when it gets down to it, unless you have a prop suitable for racing, i'm thinking one should worry more about a clean slippery hull, and spot on trim, than negligible drag from your prop.


 The fixed 2 blade prop on my boat isn't set in an aperture. It's very similar to the prop and shaft in the above photo of "Figment." I can't prove it, but believe that, if the prop isn't aligned properly, it sometimes causes the boat to point higher on one tack than on the other. Since I have been aligning my prop, it hasn't done that. I suspect that, if the prop is not upright, it creates turbulence over the surface of the rudder that creates an imbalance in the pressures over the rudder's surface. If the prop is upright, it minimizes the imbalance.


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## sanctuarysam (Sep 16, 2006)

*with an offset prop...*

on my boat, i can't seeing it mattering a whole lot...assuming your rig is tensioned properly and balanced, rudder, rudder post and wheel/tiller are also properly aligned, and of course your rudder and keel faired, then maybe there is some measurable drag..i can't, nor really care to try to get upside down in the engine compartment to hand turn the shaft...frankly it's just not practical, and as i don't intend to pull my boat anytime soon (bottom done late nov w/ periodic swim-bys of a diver to check my ablative)..so i think a clean bottom and putting my boat on a diet would affect my boat speed more than 20 degrees off on a prop..
but..we all try to squeeze every bit of boatspeed..if it works for you..hey great.


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## Rockter (Sep 11, 2006)

On a long keel ship, mark the propshaft coupling so you will be able to align the prop with the keel. I reckon it makes a difference in lighter airs. It would help a bit in all circumstances though, particularly on a long haul, so it's worth doing. 
Often I have got to stop the ship in order to align it. If the ship is moving, the forces are simply too high for my poor wee fingers.


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