Dual prop installation

[Scott Danforth]

Volvo has no position on this. Even Mercruiser doesn't say you have to time them.
Timing has nothing to do with anything.
Venting can lead to cavitation, which over a period of time causes blade erosion, or cavitation burn

If your getting prop burn your over trimming causing the water to boil on the prop edges
8 years of installing my F5's just by slapping them on every year in whatever position they go on and none of these issues

correct, Neither VP or Mercruiser have any official stance on this. however it is in published documents by both Abermarle and Carolina Classic regarding VP duo prop drives and prop burn (possibly stemming from the same VP blog site contributor that Maclin commented about)

on the 3 different boats with lat 80's / early 90's DP drives that I have had the pleasure of putting props on, I can tell you it makes a difference regarding prop burn and is noticeable in a short time frame. When I first bought the current boat, by not clocking, I got prop burn on a new set of B5's in under 2 hours. found out about clocking from a few VP owners as well as the late Don S. after repainting and clocking, the props lasted until a collision with a sunken sail boat (about 250 hours) bent the blades on the forward prop.

as for the suggesting that it is operator induced ventilating causing the prop burn.... my pig of a boat is too dang heavy and drafts too much to get the prop close enough to the surface to ventilate without bringing the drive up to the transom (45 degrees up).

if anyone wants to clock their props or not clock their props. I know it makes a difference in my own experience, so I will continue to clock them

 

[tpenfield]

I have done my B3 props both sync'ed and not sync'ed . . . sync'ed being where the blades did NOT cross while directly under the ventilation plate. The boat seems to like the sync'ed better :noidea:

My thoughts were that it had something to do with the props having to cross while they are under the ventilation plate :noidea:

 

[bruceb58]

The boat seems to like the sync'ed better :noidea:

Curious what that means.

 

[Ryland3210]

At the end of the day, there are those that have seen good results by clocking, and those that say it makes no difference. To me, since the flow of water through the props is not radially symmetric, the relative position of the props as the front one's blade is vertical must have some effect. Advocates of clocking claim good results. I shall clock mine.
I appreciate the lively discussion and comments.
Thanks

 

[bruceb58]

Now the question is which of the many clocking points should you use since there is a lot of discussion of just that! Bottom line, they will always have some portion of their blades crossing under the cavitation plate.

 

[alldodge]

It's all clocked up ound:

 

[bajaunderground]

I feel like clocking your duo-props is the chiropractice of boating...some will believe it works and other won't!

 

[Ryland3210]

My understanding is that when a blade of the forward prop is pointing at 12 o'clock, a blade of the aft prop should be pointing at 6 o'clock.

 

[bruceb58]

How many splines on a Bravo 3 rear prop? I think you should divide by 3 and then try in all those positions and get back with us!

 

[Ryland3210]

LOL!