Replacing Prop Shaft for 84 Hunter 31

[anelso29]

Hey everyone,

I apologize for the basic questions, but I truly appreciate everyone's knowledge on this forum. I'm relatively new to boat ownership and am tackling most of the maintenance on my boat myself for the first time, with guidance from YouTube and this forum.

I own a 1984 Hunter 31, and last season my anodes detached early in the season (not sure exactly when), and unfortunately, my prop shaft suffered significant damage (I've attached pictures).

I managed to remove the damaged prop shaft myself and have already bought a replacement, along with all the necessary parts. While removing the old shaft, I quickly realized the rudder is in the way. I’m not sure how to remove the rudder or if it’s even necessary for installing the new prop shaft. Does anyone know if there’s a way to install the new shaft without removing the rudder, or if removal is necessary, how to go about it?

I understand it's a complex question and hard to answer without seeing the boat and having more details, but any advice or support on this project would be greatly appreciated! Thank you.

 

[Ralph Johnstone]

have already bought a replacement,

I hope this is not to late, but if the shaft is not Aquamet 22, it is not worth proceeding with :

https://www.aquamet.com/grade-comparison

All reputable boats today are made from similar alloys with the high Cr and Ni.

I can't speak about rudder removal from an '84 model but the rudder removal from a '99 H-310 was quite simple.

 

[anelso29]

Ralph

Thank you for your response!

I purchased the prop shaft from this website, as it was listed among the stock parts in their inventory:

Hunter 31 (83-87) shaft, fitted with yanmar coupler

Hunter 31 (83-87) shaft, fitted with yanmar coupler

shop.hunterowners.com

 

[Tally Ho]

Hopefully you got the shaft from a reputable shop that sold you the right stuff…including the coupling. Also a very good time to replace the cutlass bearing…and consider a dripless shaft seal.

I don’t have a Hunter, but when I replaced the shaft, coupling, cutlass bearing and added a Volvo Dripless shaft seal on my O’Day 322, I did it with the rudder in place. Of course, the shaft lined up directly with the rudder, but I found a few tricks to get the new shaft in without dropping the rudder.

1) remove the cutlass bearing to give you a little wiggle room at that point on the shaft. Also, remove any shaft seal or stuffing box, so you don’t bind there.

2) Depending on the geometry of your rudder, P bracket and the shaft log (hole in the hull where the shaft goes in) you may be able to just slide the shaft in. I got mine through the P bracket fine, but really had to pull it to get the end of the shaft into the shaft log…I was worried about bending the shaft, but once I got it into the hole, and the other passed free of the rudder, it was easy to finish the job.

I didn’t film too many details of getting the new shaft in….but maybe this gives you some ideas…

You want to be careful not to break or move the P bracket. Having someone to lend a hand working the shaft past the rudder and into the shaft log would be Good. I did it myself, but just barely.

Good luck,

Greg

 

[dkinzer]

I watched a YT video where someone replaced their prop shaft (while the boat was in the water!) by raising the engine enough to be able to remove the old shaft and install the new one from inside the cabin. Depending on the configuration of your boat you may be able to adapt the technique to your situation.

Sailing Naida - Replacing the Prop Shaft

Also, don't forget that the new prop needs to be lapped to the taper on the prop shaft. It is relatively easy to do. I'm sure that you could find YT videos on the topic.

 

[anelso29]

You want to be careful not to break or move the P bracket. Having someone to lend a hand working the shaft past the rudder and into the shaft log would be Good. I did it myself, but just barely.

Good luck,

Greg

Thank you so much for your post and video. This is all perfect advice. I am replacing everything you listed during this project so this is perfect thank you.

 

[anelso29]

I watched a YT video where someone replaced their prop shaft (while the boat was in the water!) by raising the engine enough to be able to remove the old shaft and install the new one from inside the cabin. Depending on the configuration of your boat you may be able to adapt the technique to your situation.

Sailing Naida - Replacing the Prop Shaft

Also, don't forget that the new prop needs to be lapped to the taper on the prop shaft. It is relatively easy to do. I'm sure that you could find YT videos on the topic.

This was a great find thank you!

 

[dario_hunter31]

Ralph

Thank you for your response!

I purchased the prop shaft from this website, as it was listed among the stock parts in their inventory:

Hunter 31 (83-87) shaft, fitted with yanmar coupler

Hunter 31 (83-87) shaft, fitted with yanmar coupler

shop.hunterowners.com

Hey there!

What engine you running? I have a 2GM 13hp and, after the propeller change, seems to be over sized/pitched...

What propeller did you buy? Results??
Thanks !!

Dario

 

[Ralph Johnstone]

Hi Dario,

Of course, numerous questions here.

I see you had a two blade prop and have now changed to a three bladed prop.

My original prop was two bladed which came with the boat :

The new three bladed prop is :

I didn't get a picture of this prop. The D.A.R. is the disk area ratio which decribes the area covered by the prop blades as being 45% of the area the prop describes in one revolution.

This now felt as if the prop had fallen off due to reduced vibration and I made 3600 engine RPM.

The big question for you now is (drum roll please) are you able to make 3600 engine RPM with your hull and prop reasonably clean? Probably more important than that, can you make 3600 RPM with the engine in neutral ?

 

[dario_hunter31]

This now felt as if the prop had fallen off due to reduced vibration and I made 3600 engine RPM.

As soon as the boat keeps moving - that sounds fantastic !

I did have a 3 blade - rotten - which lost 1 blade.

Replaced it with this below: Unknown size and pitch - recommended by "best guess" from local mechanic.

Now when engaging forward, RPMs stale, throttle up -> not RPM increase above 1500RPM (but water is flowing) > TONs of black smoke > engine dies.

If I rev up on neutral - RPMs goes around 3000s (Havent put much attention on the actual MAX rpms).

So, based on my engine and transmission: 2GM 13hp with KM2-A 2.62 ratio. (Do you have this one as well?)

1) What would you select as a proper propeller size/pitch?
2) Im seeing propellers with a for a "TAPERED" shaft (ie 1 IN TAPERED SHAFT-7/8") -> is this standard?

Thanks so much for the agility!!
Dario

 

[Ralph Johnstone]

based on my engine and transmission: 2GM 13hp with KM2-A 2.62 ratio.

Our engines are different. Your engine is rated as a13 HP (2GM) while mine (2GM20) is rated as 18 HP for 3600 RPM. Different Xmission but same ratio of 2.62

1) What would you select as a proper propeller size/pitch?

Wouldn't even guess for your boat. Way above my pay grade. My recommendation would be to see a dealer specializing in props.

When I had mine manufactured, I filled out a multi page questionaire which asked everything you can imagine regarding my particular engine and boat hull.

 

[Brian M H23]

I watched a YT video where someone replaced their prop shaft (while the boat was in the water!) by raising the engine enough to be able to remove the old shaft and install the new one from inside the cabin. Depending on the configuration of your boat you may be able to adapt the technique to your situation.

The benefit to this approach is that the coupler can be installed ahead of time. Fighting the coupler onto the shaft in the limited space between engine and stuffing box is a bit of a chore.

 

[anelso29]

Hey there!

What engine you running? I have a 2GM 13hp and, after the propeller change, seems to be over sized/pitched...

What propeller did you buy? Results??
Thanks !!

Dario

Hi - so sorry for the delay. I have a Yanmar 2GMF Engine, I have linked the propeller I purchased LINK: https://shop.hunterowners.com/hp/part.php?m=31&c=12&p=52590

The propeller has worked fine for me so far as this is exactly what I had before.