Prop Sizing

[Sunharvester]

I am buying a Vision 46 with a well maintained d255 that specs a max rpm of 27-3000, however she maxes at 2500. It also has the wheel pulsing issue from prop wash found on some others.  Is it possible this could all be related to an oversized prop?  We are upwards of 10mph at 2500rpm.  Looking at Gori folding prop and I'm not sure the existing 18-16 is the right prop.

Anyone have any insight?

[symphony2]

Going down 1" in pitch to 18*15 will raise revs by 250-300 bringing it back up to the recommended range. You should be able to achieve a maximum of 8.5 knots with this engine/propeller.

If you are buying a folding or feathering propeller take the recommendation of the maker or dealer as it will almost certainly be different from the standard fixed size because of the difference in design of the blades - and different from other folding designs!. Suggest you consider a Flexofold, probably the most common make on Volvo saildrives after the one Volvo offer (which has a variable reputation).

[Sunharvester]

How does that compare to a Gori? 

We definitely have the speed. The uneven prop wash tells me there is room for improvement.   Surveyor suggests sometimes production boats dont get the right prop out of the factory.  That wheel wiggle can't be good in the long term.

[symphony2]

In my view probably better. It came out better in the tests run by Yachting Monthly a few years ago, although I have no direct experience of the Gori. My recommendation is based on several year's good service on 2 boats, numerous positive comments from owners when I was involved in a related business, and commonly offered by builders as an option (Jeanneau for example). Bavaria have fitted them in the past but have also offered other makes such as Volvo.

Generally speaking Bavaria do get the factory prop sizes spot on because the boat needs to pass the commissioning test to get Volvo Warranty, which means it must achieve revs within the recommended range in flat water. I was on my boat when this was done, partly because I supplied the non standard FlexoFold which was not the same size as the standard fixed prop. Fortunately it passed achieving 3100rpm (range 2900-3200 on a D1 30).

Don't think the prop wash is anything to do with the size of the prop, more likely the location of the drive in relation to the rudder. Wear in the rudder bearings may also have an influence. it is more useful to find out if other owners of the same model have the same issue.

[Sunharvester]

Thanks for that valuable feedback. I ordered a Gori but went 2 from a 16 to 14 pitch.  Then I found out the original owner bought her with a volvo folding prop. Trying to figure out where that ended up and what size it was.  Regardless, this is not the original prop that's on it now which is an 18-16.  Goris calculator suggested an 18-16 or a 20-something.  Considering the existing 18-16 only hits 2500 I felt the move to a 14 wouldn't hurt and might help.

I have read that some with same boat experience the condition and some dont.  That tells me it's not a foregone  irreparable and unsolvable characteristic of the boat.  I confess I am the type that can get hung up on something like this.  However it's really noticable except at lower rpms.

On haul out the rudder shaft seemed really solid and turned freely.

[Jake]

I recently changed out my fixed prop (17x13) for FlexoFold 18x14.  The new prop allows the engine to get close to 3,000 rpm.  I think the pitch is just about right.  It certainly has a better bite than the standard prop.  It can feel it through the rudder, which isn't a real problem.  It's only noticeable when starting out from a stop.  Once you get under way there isn't any noticeable vibration.  It makes sense that the prop wash hitting the rudder would cause this.  Not much can be done, except buying a boat with twin rudders (but that comes with its own issues).  I can use the prop wash to kick the stern around a little bit too.

Jake

[Diga]

I have a Gori 3bl. 20x13 mounted on my VP D2-55 (Bav.42, 2007) and it works really well. In particular the "overdrive" feature is remarkable - reduce approx. 500 RPM (~3000 to 2500) at around 7 knots.

/Bo

[Jake]

Bo,

Going to a 20" prop is a big change, assuming that your boat was equipped with a 17" prop from the factory.  I was concerned with maintaining the proper tip-to-hull clearance when I installed the 18" prop.  It has worked out well.  The generally accepted clearance for propellers is 10-20% of the propeller diameter.  I have just over 2" of clearance with my new prop.  Improper clearance can result in unwanted hull vibrations as the blades pass too close to the hull.  I hope this is not the case with you setup, but it is something everyone should be aware of when considering a prop change.

Jake

[Diga]

Jake,

Take a look at the attached report (actually from Gori) and you will find that this is the recommended size for a Gori prop to a Bav. 42 Cruiser.

/Bo

[Jake]

Bo,

Thanks for sharing the report.  The rpm drop in overdrive is nice.  I'm sure that makes for quieter motoring.  Glad you're happy with it.

Jake