Does boat with Duoprop plane different than single prop?

[High Cs]

Hello, newbie here, my first post on this site. I asked this same question on another site but I wasn't enlightened so, if you don't mind, get on your thinking caps, hit the books and set the record straight. Here it goes!

I'm hoping someone can explain to me the difference in planing characteristics, if there is any, of a boat using a VP Duoprop vs that of a single prop; all things being equal other than the drive.
I have been told that a boat with a DP planes at a slower speed and at a more pronounced "bow down" attitude or that the stern is less prone to "digging a hole". Help me to understand this. If two boats are going the same speed (SOG)and everything is the same other than the outdrive, then is there really any difference in the "angle of attack" (for lack of better words) of the two boats, and aren't they both planing equally?
Wow, I know this sounds stupid but I won't rest till I understand!!
Don

 

[dvan1901]

Re: Does boat with Duoprop plane different than single prop?

Ok, let me take a stab. I own both a single prop and duo prop (Bravo III). One thing I have noticed is the duo prop "bites" much harder and makes acceleration almost instant. With the single, there seems to be a bit of a hesitation/slip. Now, this could just be the prop on the single, but who knows. Also, the duo tends to track straighter becuase of the counter rotating props; this allows for straighter tracking at slower speeds. I can see that because a duo moves more water at a slower RPM that it would plane much quicker than a single. Make sense? There are more scientific answers than mine, but mine is simply based upon my own experience. Hope it helps...
Something I forgot to mention; on the single prop, when I go to accelerate (like pulling a skiier) the boat has a tendancy to drift to one side. This is due to the torque of the single prop as well. Not a big deal though, just throws you the first couple of times.

 

[High Cs]

Re: Does boat with Duoprop plane different than single prop?

dvan, thanks for the reply. It was helpfull to hear from someone who has both outdrives. I currently don't have a Duoprop drive but I am very iterested in it's pros and cons.
It makes sense to me that the Duoprop has better exceleration, better tracking and planes at a slower RPM. But will it enable a boat to actually maintain plane at a slower speed as well? It doesn't make sense to me that it would. And, if two identical boats (other than the drive of course) were traveling at the same speed, say just prior to getting on step, wouldn't they both assume the same angle?
Come on guys, there's gotta be a Voplvo Penta guru out there somewhere. Maybe I should have posted this in the prop topics instead...
Thanks ahead for helping me solve this "urban myth?".
Don

 

[QC]

Re: Does boat with Duoprop plane different than single prop?

A Duo-prop or Bravo 3 drive, for the same reason that they get better hole shot, also respond more to trim. So at the same trim position the bow is more effectively "pushed". This is why they can plane at a lower speed. Some of this is because the combo is longer, and that length gives the drive more leverage on the hull, the other is more total blade surface. . .

The down side of these drives is they lose their effectiveness above 60 MPH. This is why most go fasts have a Bravo 1 or derivative.

 

[High Cs]

Re: Does boat with Duoprop plane different than single prop?

QC, so they really do plane more effectively at a slower speed? I was a skeptic before, but I think that might change. I'm hoping to be on the water next summer pushed along with a VP Duoprop. I won't have to worry about the loss of effectiveness above 60 MPH, I will be doing 22 - 26 knots (25-30MPH).
Thanks for your perspective.

 

[Solittle]

Re: Does boat with Duoprop plane different than single prop?

Another factor is drag. Twin engines have two gear cases in the water vs. one for the Duoprop.

 

[Drowned Rat]

Re: Does boat with Duoprop plane different than single prop?

Don't forget the handling characteristics of the Duoprop. In the right hands a single engine Duoprop can handle nearly as well as a twin screw inboard boat. One of my tow boats was a 26' Privateer single screw with the Volvo Duoprop and no one could believe it had only one engine. It's only limitation was the inability to rotate while station keeping, but there are ways around that. Otherwise the performance was amazing.

 

[erie_guy]

Re: Does boat with Duoprop plane different than single prop?

Can you explain why most offshore racing boats, go-fast boats, and high performance drives use a single prop and not duoprops? Could it be the restricted availability of props, drive horse power restrictions, or speed limitations? I have twin engines with vp sx drives and have thought they were optimum for an express cruiser. Perhaps I should consider the duoprop as an upgrade.