Prop Shaft woes

First couple of days on my new project 44, and already some "interesting" finds.

The prop shaft alignment is very poor, rubbing on the bottom of the stern tube where it exits the hull (think the engine mounts may be too low/have collapsed, as the shaft is low in the forward edge of the P bracket also), and also the port side of the tube inside the hull.

The stern tube has crenellations on the inner edge. Is this something to do with the original stuffing box?

The shaft is a write-off with huge amounts of damage.

Prop has issues too.

The stern tube seems to be angled to the side slightly. Is this normal?

For some reason, the phots I attach are not appearing?

Forum is a bit touchy, you need to upload photos in JPG which do not exceed 4.0 mb (opened), so check the file you want to upload, or send it to me and I will downsize it to correct dimension.

matteo (47/069 Vanessa)

Dear Sweyn,

I have seen the photos you uploaded on facebook, the prop looks to be corroded by galvanic corrosion  and I think the shaft could have been  triggered by a strong friction, you should investigate why.

matteo(47/069 Vanessa)

Yes the shaft is rubbing on the stern tube edge pothole in the lateral plane at the forward end of the tube, and in the vertical plane at the aft end of the tube.. The stern tube seems to be angled a bit to port, and I'm wondering if this is normal on a Swan?

Dear Swey,

I am not sure, but maybe with the original engine (Perkins 4.108 27 KW) it was decided to have the angled shaft.

Anyway the alignement is very important and should be carried out by someone who knows his job, I think the tolerance is less than 1/10 of mm, or, as Marco suggested you on Facebook, you can inastall a device as Aquadrive in between the engine and shaft.

You have a galvanic corrosion problem, and the zinc itself is not enough, so the propeller was corroded too.

matteo (47/069 Vanessa)

I thought the angle might be deliberate, thanks. It's too large to be an accident. Currently the engine is at least 10mm low and more than that off line with the stern tube.

She's spent years in the water without anyone changing zincs, so the anode problem is not a worry in the fiture, just hoping the prop can be reconditioned.

Hi.

Looking at the pictures my 2 cents worh of thougts after also seeing your pictures is:

- check the HP between old and new engine. If they repowered and changed to more powerful torque on the engine, that propeller is likely not correct. If higher torque on new engine, then the difference can be significant i performance. I did change from old Maxprop like you have to a larger Flexofold, reduced rpm for 6 knots cruising speed from 1850 rpm to 1450 rpm and with unbelievable grip in tight quarters manouvering.

- I would consider to install a thrust bearing with a flexible coupling to your engine. Thrust bearing will carry the push force from the propeller, not the engine mounts. You will need to have built a small but strong mini mount/bulk head to anchor the thrust bearing on. After aligning your engine (likely change engine mounts) you will have worry free alignment of engine and shaft.

I would also put extra anod on the shaft. My guess is that you will replace shaft.

All the best,

Robert

Thanks Robert. I think the original engine is probably similar HP to the Beta 38 that's on it now, but definitely ask the people refurbishing the prop (assuming that's possible) to check if they have a suggestion that will be better re the pitch. I know you have to be careful altering pitch to achieve low RPM though. If the engine cannot achieve rated RPM then it's not good for the engine.

Dear Sweyn,

original engine was Perkins 4.108,  37 HP, 3,000 RPM, with a Borg-Warner hydraulic gear 2.1:1.

Original prop diameter 17".

Max Prop is certainly able to fix the propeller, but be very careful as they often do big mistake when suggesting pitch.

The engine, with engaged gear and a correct prop pitch, should get not less (about) 10% less of max engine RPM (e.g. Beta 38 HP is rated at 3,600 RPM, which means with a correct pitch you should get circa 3,250/3,300 RPM).

Ideal  should be to get all the engine RPM, but, as said, 10% less is still accettable.  I talk to many S&S Swan owners who got from MaxProp a pitch  so that they take 20/30% less than the engine RPM, which is very harmful for the engine.

matteo (47/069 Vanessa)

Hi,

Regarding pitch, I agree with both of you. Ideally, have several experts have a calculation at it. 

I considered the torue curve on the engine. I have a Nanni 50 HP (on a 41) with a max on torque at 1300 rpm, so I wanted to be above it around 6 knots in calm conditions, which means 1450-1550 rpm. I can reach hullspeed at 2100 rpm in calm conditions. The engine in my opinion, is actually slightly too powerful for the boat. The hull is really easily driven for its weight (until you get close to engine hull speed). It is a very big difference i power required if you motor against wind and sea.

My guess is that you should consider sticking with the "original" setting as power cureves of the engines I asume would be similar. With that, renovating the propeller is what I would go for. 38 HP and 17 inch blade seems well balanced as far as what I learned in my process...

Glad to hear of your committment on the project!!

All the best, Robert

Thanks Robert.