Small Prop as Temporary Solution

[Pendragon35]

Originally Posted by skipperpete

For a kickoff, ¾” is pretty slender for a 3GM 30 propshaft unless its Aquamet or some similar alloy, I don’t recall ever seeing a ¾ shaft even on much smaller engines. The bigger issue is getting the taper and key to match and being able to easily get it all snugged up correctly underwater….. and knowing that its fully engaged on the taper, not getting this right will at the least mean vibration and at the worst, loss of the prop.

It's an old installation. I think, long before I bought the boat.I have no way to check these things until we put a prop on it. But I really appreciate the thought and will keep it in mind.

[SailingHarmonie]

With knowing the size and shape of the aperture…. Normal clearance requirement is 10% of prop diameter between blade tip and hull. If you were to jump to a 14 prop would you still have that clearance?

If not, or if that question was never asked, I would not trust any other recommendation from that source.

[NorthCoastJoe]

Check with " Blue Pelican " in Alameda CA. Last time I was there they had a selection of used props. They are always helpful, give them a call they have a massive amount of gear not listed online.

If you don't have a prop shop nearby I would bring your old and new props to a machine shop to check the taper and keyway for matching fit.

https://bluepelicanmarine.com/

[skipperpete]

Originally Posted by Pendragon35

It's an old installation. I think, long before I bought the boat.I have no way to check these things until we put a prop on it. But I really appreciate the thought and will keep it in mind.

I guess its an Arlberg 35 and damn thats a tight aperture. If it was me installing the prop, I’d undo the coupling , push the shaft BACK enough to remove the gearbox.. its easy on a 3GM, the brackets are on the flywheel housing so the mounts stay bolted in place and no alignment issues…… then slide the propshaft inboard enough for the diver to get the prop into the cutout and onto the stub. Finally, slide the propshaft back out and into the prop hub, install the nut and “ it’s Miller time”. Refit the gearbox at your leisure but only after you pull the propshaft back to the correct position and verify that its clear in the aperture with enough tip clearance. Since I’ve not removed the gearbox from a 3GM in an Arlberg its possible that my suggestion could be very difficult to implement and a shaft anode adds an extra level of difficulty for the diver. If its impossible to remove the gearbox, my fallback position with the coupling released would be to slide the engine forward on the beds a few inches, it means doing an alignment but still probably way easier than dropping that rudder.

[Don C L]

The Alberg 35 originally had an Atomic 4 and the aperture in the rudder was sized with props for that in mind I think (i.e. has the right size boss). Have you looked at props like this one?
https://www.atomic4.com/propeller.html

I have no idea if that would work well for your diesel engine.

Out here we have a good prop shop and the guy seems to know everything about props; I bet he'd know an answer that would keep you from moving the engine or rudder. https://valleypropellerservice.com/

just throwing it out there

[MJH]

Originally Posted by Pendragon35

I have an Albert 35 with a Yammer 3gm30F engine, the standard transmission which I believe is Kazakh 2.1. The prop is an aperture in the rudder. The shaft is .75 in.

Last summer, I discovered I'd lost a blade on my 3 blade prop. After many false starts, I finally had a diver get the prop off, went to a prop manufacturer who recommended a 14R14. The one that came off with was a 13R, not sure of the cup. In the event that's what I bought, from Millers Island Props in Baltimore. It's a thing of beauty. But when the diver attempted to put it on, it would not fit. We've tried lots of things, it's just no go short of dropping the rudder, which I'm not prepared to do.

So I'm going to buy a 13R prop at some point. However, I'd really like to get sailing. Last week I bought a 2 bladed 12R7, a little prop, because it was cheap and immediately available.

My question is: is this ok to use with the Yammer 3GM30F? I know it's not big enough, I know the boat won't go very fast but I just need to get in and out of the marina and get back to at least day sailing while I work on getting a bigger prop.

Things I already know and don't need discussed:
1. 2 blade vs 3 blade - I'm going to get a 3 blade for the final
2. folding props - won't fit
3. I can sail without an engine - no, my marina is such that I can't get out that way without endangering others
4. drop the rudder - just no, not doing that

Thanks for any/all helpful comment!

I would place my emphasis on solving this issue first (rather than day sailing) by hauling the boat and getting the correct prop installed; you have already bought one prop that doesn't fit and paid a diver for at least two dives. Everything is easier with the boat out of the water.

Sizing the correct prop can be an involved process of matching the engine, transmission, and drive train limitations. Take it one step at a time and do it right the first, (correction) second time.

Good Luck.

[j.g.evans]

Go to vicprop.com and look for their propeller calculator. It is the only one that I have found that I trust. In general you want a large, slow turning prop which is not an option for you. My 3GM30 has a 2.4:1 gear box. Check yours for you will need this information. Consider as 4 blade prop for more thrust and smoother operation. I just put on a 3 blade feathering prop for which I increased the pitch in reverse and now I can stop the boat in a fraction of the boat length.
Before I started my own propeller calculations I went to 8 propeller shops and got 8 RADICALLY different quotations.

[marcjsmith]

since you are in maryland also check anchors and oars in Stevensville (kent island area) for used sailboat stuff..

[Rothblum]

Originally Posted by boatpoker

Propeller cup is not the same as pitch.
https://www.miwheel.com/propeller-cu...9Ccup%E2%80%9D.

Sounds to me as though "cup" is the camber of the blade -- the curvature which allows a higher angle of attack without the blade stalling -- probably irrelevant to this discussion. I can't imagine that running with a smaller than ideal prop could possibly do any harm other than lack of thrust. I also imagine that the number of sailboats that have an ideal prop is negligibly small.

[boatpoker]

Originally Posted by Rothblum

Sounds to me as though "cup" is the camber of the blade -- the curvature which allows a higher angle of attack without the blade stalling -- probably irrelevant to this discussion. I can't imagine that running with a smaller than ideal prop could possibly do any harm other than lack of thrust. I also imagine that the number of sailboats that have an ideal prop is negligibly small.

The cup is at the trailing blade edges only and not related to camber.
https://community.brunswick.com/area...up/article/557

[Rothblum]

Originally Posted by boatpoker

The cup is at the trailing blade edges only and not related to camber.
https://community.brunswick.com/area...up/article/557

Here is a quote from the URL you referenced: "When done correctly, the face of a cupped prop blade is completely concave." Not just the trailing edge. I couldn't right off-hand find any actual drawings of cupped blades, but the 3-D representations I found of the Mercury cupped blades don't show any evidence that the "cupping" is only at the trailing edge. In any case, it would still come under the heading of camber. Here is the definition of camber, from NASA's website: "camber -- A measure of the curvature of the airfoil. The mean camber line is an imaginary line which lies halfway between the upper surface and lower surface of the airfoil...."

[boatpoker]

Originally Posted by Rothblum

Here is a quote from the URL you referenced: "When done correctly, the face of a cupped prop blade is completely concave." Not just the trailing edge. I couldn't right off-hand find any actual drawings of cupped blades, but the 3-D representations I found of the Mercury cupped blades don't show any evidence that the "cupping" is only at the trailing edge. In any case, it would still come under the heading of camber. Here is the definition of camber, from NASA's website: "camber -- A measure of the curvature of the airfoil. The mean camber line is an imaginary line which lies halfway between the upper surface and lower surface of the airfoil...."

You may have cup without camber or camber without cup. As I said ... two different things.