Bavaria 31 Cruiser - Stock propeller + upgrade options

[reystos]

Hi everyone!
Having recently become the owner of a Bav31 Cruiser (2000, J&J)  and the boat finally out of water, I am going through an extensive list of repairs to be done.
Starting with the prop that was in bad shape. It is a two blade prop that probably came originally with the boat, on a Volvo Penta MD2020D and a 120S saildrive.

I have gone through all the manuals I could find for it, but the size is not mentioned anywhere. In Bavaria's lists, only boats produced after 2005 are mentioned and it seems similar sized ones came with 16x11.

It measures about 14", so I can only guess it is a 14x11. Do you know if that seems correct? On water it felt a bit underpowered, making about 5knots at 2k rpm.
Instead of just try to fix it, I would prefer to keep it as a spare and upgrade to a larger diameter. Would 16x11 make sense?

Many thanks in advance!  Its great to see there is an open owners forum, so I thought I should ask.

[Symphony]

If it is the original you will find the size stamped on the boss, probably hidden under coats of paint. Suspect though it should be a 15*10 as I am not sure there is a 14*11. However the speed you report at 2000 is spot on. The engine revs to a maximum of 3600 and the normal cruising revs is 2400 which would give you a speed of around 5.5 knots. You should be able to achieve at least 3500 flat out and a speed of just over 7 knots in flat water. You would get this performance with either a 14*11 or a 15*10, but the larger diameter would be better. A 16*11 would be far too big - that is what is commonly used with a 2030 or D1 30.

If you are buying a new prop there are aftermarket suppliers like Lake Sterngear or T Norris who are cheaper than Volvo at around £250. However if you have the budget consider changing to a folding prop such as FlexoFold, although this is about 3 times the price.

Although The size (15*10) I quote is almost certainly right, checked with propeller size calculation programme, best to just give your boat and engine details to your supplier so they are responsible for supplying the correct size.

Hope this helps

[reystos]

Thank you very much Symphony.

After using a wire brush to clean all the coats of paint accumulated over the years, here is what I have found.
The prop has a 16 13 stamp on. But it measures a max of 36cm wide, which is about 14" (and initially made me believe it could be a 14x11).
Does the prop outline in the photo seem a bit irregular to you too? I am afraid it may be a lathe job on a beaten prop from elsewhere, during the boat's charter years that went unnoticed.

Here is what I saw:


and:

[Yngmar]

Does the prop outline in the photo seem a bit irregular to you too? I am afraid it may be a lathe job on a beaten prop from elsewhere, during the boat's charter years that went unnoticed.

It does look like it! If you look up the shape a Volvo 2 blade prop is supposed to have and compare it with yours, it definitely seems this one has been trimmed to size a bit

Edit: Add picture.

[reystos]

Thank you for verifying my suspicions Yngmar. In this case, I will keep this onboard as a spare and look for a new prop.
What size would you recommend that I go for? 15x10 seems very reasonable, according to Sympony's suggestion.

Next reasonable step for me will be to completely remove the engine and saildrive and have a good look, check the gears for visible marks of damage. Cover-ups are not really my thing, specially now that I am getting to know the boat better. Would you agree?

[Symphony]

That has been really butchered. Would I be right in thinking that the boat was on charter in Greece as that is just the sort of "engineering" that some Greeks like to do! It is a 16*13 that has been chopped down to 14" either because it had to be fixed in a hurry or simply to save money. The blades may have been flattened a bit although that is not easy to do (even with a Greek hammer) without cracking the casting. Anyway it needs replacing as suggested above.

Not sure why you want to take the engine and drive out unless you want to replace the diaphragm. Rarely does the reduction box give trouble other than the clutch pack failing which usually results in wrecking the whole drive. However it is worth taking out the lower housing apart and replacing the seals in the end cap. If the oil is clear and not milky with water then the rest of the drive should be OK. It is worn seals that allow water in, hence the need to check and change them. Plenty of You Tube on how to do the job plus repair the shaft if you do find wear.

[SYJetzt]

I comply with Symphony, no need to take anything apart except for changing the diaphragm.
I guess, if it is an ex-charter boat (like mine) , there will be a lot of hours on the engine and maybe a lot of wear.
I suggest to:
1) Perform a compression test to check if all cylinders show the same compression ratio.
2) Check the engine cooling (inner circuit), if there are any losses of coolant
3) Check the outer (seawater) cooling system ( impeller, elbow, exhaust,..) for proper function, tightness and cleanliness.
4) Check proper funktion of all alarm circuits of the MDI (Oil pressure, Temperature,...). If one machines the prop on the lathe, he maybe disconnects  the alarms to pretend proper engine state.

If you perform these checks, you will get a little more familiar with your engine.

[reystos]

New propeller in, I aimed for a 16x11. It seems like at 2300rpm the boat is getting roughly about 5.4knots or so. Does that sound correct?
Run the whole summer with it, feels much better than the old chopped prop. No smoke coming out of the exhaust, everything seems normal.

Should I dare go for a larger pitched one? When the conditions get choppy or the wind is against me, I cannot seem to beat 4ish even at 2300. I keep reading about owners running it in the 2500rpm range, not sure if that is the best exercise for multi hour trips.

[symphony2]

16*11 sounds too big, although the speed you are getting is about right. The important test is whether you can get close to 3600 rpm and a speed of about 7 knots at full throttle. BTW i have a 16*11 on a 30hp in a much heavier 33 and it is just right. A 2020 which I assume you have would normally have a 15" prop.

The downside of having a prop that is too big (overpropping) is that you cannot use full power which limits your ability to make progress in adverse conditions. It is a requirement of Volvo that the prop allows your engine to achieve a minimum of 3400rpm in flat water and the factory fitted prop which was probably a 15*10 or 15*11 will do this.

[reystos]

Got it. Probably even 3200rpm would be too much to ask of my 20year old Volvo anyways, so I will stay with what I have for now.