DuoProp choice ?

[Tafflad]

Have a bowrider with a VP 280-C DPS
For this motor the WOT range is 5400-5800
The prop set has to be changed under warranty, due to corrosion on the SS blades.

The dealer did some test runs with new prop set (original pitch)
And with a set with next pitch down.

The results are ...
Original pitch prop
Max speed 48.8 @ 5560
3040 - 24.1mph
3560 - 29.4
4080 - 38.5

New Prop. (Down 1 pitch set)
Max speed 47.3 @ 5800
3000 - 21 mph
3580 - 27.9mph
4000 - 31.8mph
4570 - 36.6mph

VP Dealer recommendation is to go with lower pitch as it has better pick up, but stays in power band limit.
My use is towed watersports most of the time around 18-22mp

What do you think ?

 

[alldodge]

Motor will burn based on HP needed to sustain speed under a given load. Motor will burn more fuel under a given at a load lower rpm then the same load with higher rpm.

Like climbing a hill in 4th gear, would be easier in 3rd gear.

Cruising at 4000 rpm can burn less and be easier on the motor then same speed at 3000 rpm if the motor depending on loading.

My 10K (4500 Kg) cruiser likes it best at 3800 rpm (WOT 5200)

 

[Tafflad]

The dealers advice was that as most of my use is below 30mph then having the lower pitch would give me better hole shot and flexibility.
i don’t ‘cruise’ as such ... its stop - pop a skier or boarder out of water - few minutes run .... repeat.

Not sure which way to go hence the post.

 

[Faztbullet]

Go with the lower pitch ...you the operator and those on the end of the rope will like it

 

[Tafflad]

Go with the lower pitch ...you the operator and those on the end of the rope will like it

That is what Dealer is suggesting

 

[Scott Danforth]

rehashing this again? go with the lower pitch set

 

[Tafflad]

I'll go with that lower set then... that is what is on it now, just had option on either set.
As I had the test data, thought it worth checking.
Thnx

 

[Sea Rider]

The dealer and many others as well recommends the lower pitch prop over the other, thumbs-up for that!! If pulling toys, skiiers top hole shot is what it takes.

Happy Boating​

 

[alldodge]

Agree lower set, and could add a bit of cupping on the set which would help reduce the slip. In turn the cup would lower the WOT rpm slightly (maybe 100 rpm) and may get the speed up at WOT. Only issue is reducing the bite of the prop in reverse

 

[Tafflad]

Cupping is set on the VP set ..... don't want to change that.

 

[QBhoy]

Likely said this before...but quite unusual to hear of an original set up VP DP to be wrongly propped. Were those numbers with the dealer testing it out or yourself ? I presume there is nothing your missing to see more rpm from her ? Like trim tabs left down (if you have them), outdrive is trimmed out when full speed etc etc. Sorry to ask.
For me personally, if the boat wasn’t lacking in low down acceleration as it is...I would leave it perhaps. But if as you say...want it for pulling power and it is lacking a little low down...100% drop in pitch.
You could even ask them to try a set of Ally duo props on her. You might find an almost perfect happy medium. Stick the shiny props up on the wall in the garage ! The standard VP ally DP’s are great props and in what I’ve seen...rarely drop noticeable performance, if any, compared to the stainless equivalents...on boats with moderate power like this. Should you have a stonking big block turning them. By all means...stainless are the way. V6’s...maybe not so much a real benefit. Then of course...there is the bloody eye watering price of them, should you ever have to replace them.
I had a lovely wee classic sealine 218 cabin cruiser with a AQ205 v6 and DP with B5 ally props. As she came with. She seemed propped to perfection. Revving to around 4800 rpm and topping out at around 35/36 mph at her best. Fella I knew had the same boat (220 newer model but same boat) down south from me. He put C5 stainless equivalent props on his. It ruined it. Dropped top end and acceleration and obviously rpm. He then tried C4 props. They saw her no better than the B5 ally originals. Anyway...Enough from me.

 

[Tafflad]

The data above is what the dealer found during testing .... an average of several runs on each set.
There are no trim tabs ...and dealer advised they trimmed out as much as they could. They got higher rpm than I did when I tested ... I use in open water .... with swell & chop. Dealer has a freshwater locked marina.

There is no way I would remove stainless the SS set and put on aluminium.

 

[QBhoy]

The data above is what the dealer found during testing .... an average of several runs on each set.
There are no trim tabs ...and dealer advised they trimmed out as much as they could. They got higher rpm than I did when I tested ... I use in open water .... with swell & chop. Dealer has a freshwater locked marina.

There is no way I would remove stainless the SS set and put on aluminium.

Ok. Do what you like then. Think we have been over this conundrum a few times now.

 

[KD4UPL]

I would also vote for the lower pitched set. I would guess the dealer tested with just a driver, possible a second person. When you operate the boat it sounds like you might have a family or tow on board plus toys, cooler full of drinks, etc. This makes the boat heavier and which could possible reduce the WOT a bit. Maybe enough that the higher pitched set drops the 160 rpm to the low end of the design spec.