DuoProp

GodSmile · 07-06-2016, 04:53 PM

Would someone please explain the advantage of a duoprop outdrive? I've had a single prop and now a Duoprop, and while they are very different boat designs I'm hard pressed to detect any difference in the handling characteristics.

DesertDweller · 07-06-2016, 05:14 PM

Don't have any real world experience but dual props are supposed to have better slow speed maneuvering and better acceleration.

ITD · 07-06-2016, 05:21 PM

http://www.volvopenta.com/volvopenta...f_duoprop.aspx

Discuss.

fatlazyless · 07-06-2016, 05:22 PM

Supposedly, duoprops on motorboats came from duoprops used on torpedos shot from submarines, if one believes the Volvo duoprop advertising from 1988?

Descant · 07-06-2016, 05:25 PM

Counter rotating props offset the directional torque you get from a single prop spinning in one direction. The boat is thus better balanced. More acceleration, power, with two props taking a bigger bite of water.

GodSmile · 07-06-2016, 05:28 PM

Good to know, the only thing I'd question is backing is straighter... I still can't control the boat the way I'd like when backing....

ITD · 07-06-2016, 06:12 PM

Quote:

Originally Posted by GodSmile

Good to know, the only thing I'd question is backing is straighter... I still can't control the boat the way I'd like when backing....

Nudge it, if you slam into reverse and keep it there you will go where the boat wants no matter what you have.

Descant · 07-06-2016, 08:30 PM

My experience is that most deep vee's back straight, AFTER the hull assumes an angular attitude. (Crab angle) Or you can reset the angle every few yards as you would do with a single engine inboard. This is usually a function of the hull design as much as it is the propeller. Go out in the bay, throw a cushion overboard for a fixed point and try backing various distances with various throttle positions. You will find a stable position for your boat. Next week, people will say "How does he do that? What a great helmsman" (Actually, nobody around here says "helmsman" but the Navy folks will say "Bravo Zulu"). The key, in part, is throttle. That's why you practice in the bay. Being too tentative with the throttle can give poor control, just as much as too much. Unique to each boat.

VitaBene · 07-06-2016, 09:10 PM

Quicker acceleration, better reversing, less top speed. I gladly sacrificed 5 mph for the ability to come out of the hole with 12 on board. But there are others that prefer the speed.

radiocontester · 07-06-2016, 10:23 PM

Quote:

Originally Posted by GodSmile

Would someone please explain the advantage of a duoprop outdrive? I've had a single prop and now a Duoprop, and while they are very different boat designs I'm hard pressed to detect any difference in the handling characteristics.

I have a duoprop on my cruiser and in addition to what's already been mentioned it helps keep the boat straight at slow/no wake speeds and provides better control in reverse. The downside: Replacement cost, so be extra careful out there!

Blue Thunder · 07-07-2016, 07:32 AM

Quote:

Originally Posted by GodSmile

Good to know, the only thing I'd question is backing is straighter... I still can't control the boat the way I'd like when backing....

That's been my experience as well since owning a DP for 17 years. I could thread a needle in reverse with the 3 mercs I owned over the years. I back my boat into my slip and it just doesn't act the same way as a single prop. 50% of the time I have to correct what I'm doing by putting it in forward. That said, the performance and control with a DP is superior to a single prop.

BT

BroadHopper · 07-07-2016, 08:18 AM

I have experience with 3,4,5 blade props as well as duo counter rotating props (usually 6 blades) Generally speaking the more blades applied the better the torque but you sacrifice top end. Counter rotating props balance the torque thus gives you better maneuvering.

How the boat maneuver is another matter. Lots of practice and paying attention to boat drift, wind, current as well as throttle response. the more blades you have the better the throttle response. So the duoprop gives a much better response. Big reason why heavy boats have duo props or 4 blades.

Most bass boats respond well with 5 blades. Tournament fishing requires hole shots and great maneuvering. The boats do not require duoprops because they are light weight.

If you have the need for speed a 3 blade is the way to go. I know of no performance boats with duoprop set up.

GTO · 07-07-2016, 09:04 AM

I pulled a duo prop unit from the lake last year after someone went on the wrong side of the markers. They are still attached to the drive unit. Props are a little damaged but a marina said they are fixable. If anyone is interested in spares and want to take a look and make an offer......I just want it out of my basement now. Just PM me it is a merc Bravo 22p. I can give other identifying numbers that are also on it

8gv · 07-07-2016, 09:07 AM

In the last year I have replaced both of my stern drive boats. The two previous ones had Mercruiser Alpha drives. The two new (to me anyway) ones have Mercruiser Bravo III drives with their counter rotating "duo" props.

My findings:

Time to plane is much quicker. For me this makes the two prop syatem worth the cost. Being able to plane the boat nearly instantly means less bow rise and less time making a big wallowing wake.

Top speed? I don't know because that's not how I like to run my boats.

Backing down into a slip is "different". After years of experience with the Alpha drives my technique relied on either using or countering the wheel effect. The Bravo drives don't seem to have any of this.

07-06-2016, 04:53 PM	#1
GodSmile Senior Member Join Date: Apr 2014 Location: Alton Bay Posts: 192 Thanks: 94 Thanked 58 Times in 38 Posts	DuoProp Would someone please explain the advantage of a duoprop outdrive? I've had a single prop and now a Duoprop, and while they are very different boat designs I'm hard pressed to detect any difference in the handling characteristics.

07-06-2016, 05:22 PM	#4
fatlazyless Senior Member Join Date: Apr 2004 Posts: 9,173 Blog Entries: 1 Thanks: 310 Thanked 1,103 Times in 812 Posts	Supposedly, duoprops on motorboats came from duoprops used on torpedos shot from submarines, if one believes the Volvo duoprop advertising from 1988? __________________ .... Banned for life from local thrift store!

07-06-2016, 05:25 PM	#5
Descant Senior Member Join Date: Mar 2006 Location: Merrimack and Welch Island Posts: 4,597 Thanks: 1,418 Thanked 1,705 Times in 1,109 Posts	More bite, better balance Counter rotating props offset the directional torque you get from a single prop spinning in one direction. The boat is thus better balanced. More acceleration, power, with two props taking a bigger bite of water.

07-06-2016, 05:28 PM	#6
GodSmile Senior Member Join Date: Apr 2014 Location: Alton Bay Posts: 192 Thanks: 94 Thanked 58 Times in 38 Posts	Thanks for the responses Good to know, the only thing I'd question is backing is straighter... I still can't control the boat the way I'd like when backing....

07-06-2016, 08:30 PM	#8
Descant Senior Member Join Date: Mar 2006 Location: Merrimack and Welch Island Posts: 4,597 Thanks: 1,418 Thanked 1,705 Times in 1,109 Posts	Backing My experience is that most deep vee's back straight, AFTER the hull assumes an angular attitude. (Crab angle) Or you can reset the angle every few yards as you would do with a single engine inboard. This is usually a function of the hull design as much as it is the propeller. Go out in the bay, throw a cushion overboard for a fixed point and try backing various distances with various throttle positions. You will find a stable position for your boat. Next week, people will say "How does he do that? What a great helmsman" (Actually, nobody around here says "helmsman" but the Navy folks will say "Bravo Zulu"). The key, in part, is throttle. That's why you practice in the bay. Being too tentative with the throttle can give poor control, just as much as too much. Unique to each boat.

07-06-2016, 05:14 PM	#2
DesertDweller Senior Member Join Date: Aug 2011 Location: Las Vegas, NV and Moultonborough, NH Posts: 405 Thanks: 27 Thanked 96 Times in 80 Posts	Don't have any real world experience but dual props are supposed to have better slow speed maneuvering and better acceleration.

07-06-2016, 05:21 PM	#3
ITD Senior Member Join Date: Apr 2004 Location: Moultonboro, NH Posts: 2,953 Thanks: 484 Thanked 703 Times in 393 Posts	http://www.volvopenta.com/volvopenta...f_duoprop.aspx Discuss.

The Following User Says Thank You to ITD For This Useful Post:
GodSmile (07-06-2016)

The Following User Says Thank You to fatlazyless For This Useful Post:
GodSmile (07-06-2016)

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07-06-2016, 09:10 PM	#9
VitaBene Senior Member Join Date: Jul 2007 Location: Moultonborough Posts: 3,644 Thanks: 1,718 Thanked 1,662 Times in 861 Posts	Quicker acceleration, better reversing, less top speed. I gladly sacrificed 5 mph for the ability to come out of the hole with 12 on board. But there are others that prefer the speed.

07-07-2016, 08:18 AM	#12
BroadHopper Senior Member Join Date: Oct 2004 Location: Laconia NH Posts: 5,668 Thanks: 3,282 Thanked 1,132 Times in 814 Posts	Props I have experience with 3,4,5 blade props as well as duo counter rotating props (usually 6 blades) Generally speaking the more blades applied the better the torque but you sacrifice top end. Counter rotating props balance the torque thus gives you better maneuvering. How the boat maneuver is another matter. Lots of practice and paying attention to boat drift, wind, current as well as throttle response. the more blades you have the better the throttle response. So the duoprop gives a much better response. Big reason why heavy boats have duo props or 4 blades. Most bass boats respond well with 5 blades. Tournament fishing requires hole shots and great maneuvering. The boats do not require duoprops because they are light weight. If you have the need for speed a 3 blade is the way to go. I know of no performance boats with duoprop set up. __________________ Someday may never be an actual day.

07-07-2016, 09:04 AM	#13
GTO Senior Member Join Date: Apr 2004 Posts: 1,096 Thanks: 340 Thanked 354 Times in 162 Posts	used duo prop I pulled a duo prop unit from the lake last year after someone went on the wrong side of the markers. They are still attached to the drive unit. Props are a little damaged but a marina said they are fixable. If anyone is interested in spares and want to take a look and make an offer......I just want it out of my basement now. Just PM me it is a merc Bravo 22p. I can give other identifying numbers that are also on it __________________ GTO

07-07-2016, 09:07 AM	#14
8gv Senior Member Join Date: Jan 2012 Posts: 2,195 Thanks: 63 Thanked 764 Times in 497 Posts	In the last year I have replaced both of my stern drive boats. The two previous ones had Mercruiser Alpha drives. The two new (to me anyway) ones have Mercruiser Bravo III drives with their counter rotating "duo" props. My findings: Time to plane is much quicker. For me this makes the two prop syatem worth the cost. Being able to plane the boat nearly instantly means less bow rise and less time making a big wallowing wake. Top speed? I don't know because that's not how I like to run my boats. Backing down into a slip is "different". After years of experience with the Alpha drives my technique relied on either using or countering the wheel effect. The Bravo drives don't seem to have any of this.