"Bert and Marvin....., Forgive
"Bert and Marvin....., Forgive me .... and let me add some clarity to that earlier comment!
Quote:"At sea level, and on certain hulls, the DP is similar to adding 80-90 horse power. Much better bang for the buck, IMO."
There is no hard data to support 80-90 HP gain at the prop.
It was an example only saying <font color=""0000ff"">"similar to adding 80-90 horse power"</font> as to compare what I've seen when going from a 5.0L to a 5.7L (for example) yet staying with a single prop drive.
The Duo Prop suggests more performance improvement over that of what the larger 5.7L w/ single prop drive may gain us.
Volvo's 1983 literature suggested a gain in economy and performance of 25-30% if memory serves me.
I've installed these on my own boat, my son's boat, his friend's boat and on customer boats........... all but one (and we don't quite know why) showed quite an improvement.
As a comparison:
On my own 28' SDN F/B twin engine boat, the difference was night and day.... both in reduced planing distance, more top speed, more ability to be up on step (and then some) and ability to remain on step at a lower engine rpm.
The boat previously struggled to get on step with the single prop drives (and this is w/ two new 5.7L engines)
Now with the Duo Prop drives, it comes up in a very short distance..... and acts as though it is not working as hard to remain there.
We did one to my son's 24' SDN F/B boat..... the gain was well worth it!
We also did one to boat which belonged to a friend of my son's.... of which was also a 24' SDN F/B boat..... again, tremendous gain. It was all that boat could do to get on step with the sp drive.
It would be very involved for me to take the time to river run each boat and collect before/after actual data.
I also participate on a boating forum where many members have done the Duo Prop upgrade! Some were to SDN F/B's.... some were to Single Station models......... all with very positive results. In fact, I don't recall reading where any one was disappointed.... and there have been several long threads about this topic.
I helped one man convert a 460 OMC KC drive to a complete DP C drive. This was in a 28' single station boat! Of course he had to do a complete installation to go with an AQ series drive.
He is also extremely happy with the improvement.
Here is a reverse engineered scenario for you:
<font color=""0000ff"">Short story...
I owned a little 24' SDN F/B.
Heavy... but a fun little boat.
Engine was a 200 HP 5.0L
I installed a Duo Prop drive and used it in the interim while I was finishing the 28'.
The boat surprisingly scooted right along @ 37/38 mph tops with the Duo Prop.
I removed the DP to sell the boat w/ a single prop.
I had never operated this boat without the DP.
Went for a river test.
It was all that boat would do to get out of it's own way w/out the DP.
I don't believe that a 5.7L would have helped this hull like the DP did!
I was lucky that I found a buyer who was OK with the performance!</font>
So, with all of that being said...... I can only suggest that going from a 5.0L to a 5.7L (while staying with single prop) would not render as much gain as though you added the Duo Prop to the 5.0L!
I am also not able to comment with any experience as to the gain for high altitude use. I would speculate that there would still be an improvement!
Keep in mind that the Volvo Duo Prop does not perform as well as the BIII will at speeds above 40/45 mph.... but does better than the BIII at speeds below this. This has to do with the pattented propeller design.
."