Duo Prop Issues

[Rtiny33]

I have a powerquest SLS 240, Volvo Penta 5.7 gxi f with F6 duo props. My issue is I have nothing coming out of the hole once it planes after 30 to 40 yards) I'm only getting about 3600 to 3800 max rpm. Volvo Penta 5.7 gxi F is 4600 to 5000 RPM WOT. The props need a little care after i purchased the boat. I had a prop shop working on a stainless steel props and they cupped them. Can duo prop be cupped and if so or if not why is my performance so poor should I drop sizes looking at F5 or F4. My biggest issue is I can't hardly even pull a skier up let alone plain out at a max speed or wot.

 

[Rtiny33]

2004 Power quest SLS 240
Engine 2004 Volvo 5.7 gxi 320hp DP F6 props

gear ratio dp-sm 1.78 m22
3868912
4202127047

Sx-MBAC
3869298
4151078155

boat was purchased in 2009 new, less than 300 hours when I purchased in 2015.

 

[Scott Danforth]

make sure your running on all 8 cylinders.

are you saying your only getting 3600-3800 at WOT when on plane?

single props are cupped, Duo props do not get cupped. if you cupped your F6's go back to stock F6's

if you want to pull a skier or two, maybe drop down to F5's

 

[tpenfield]

I'd go with the 'he who touched it last' theory on this . . . props should not have been cupped. Why did they (prop shop) do that?

 

[QBhoy]

Have a look at the Diz cap and fuel system.

 

[Maclin]

With a ratio of 1.78 I think an F5 set is closer to what you need in that size boat. DP units I am familiar with were all 1.95 for V8 and 2.2 for V6. Diesels were 1.78 as they had much more torque but lower top rpm. Your GXI has top RPM of 5000, put on the lower pitch F5 or maybe F4 and let 'er rev man.

 

[Rtiny33]

So they cupped the props thinking that it would be better in the performance area. I had a friend that had a similar set up and his props were cupped and his boat did the same thing lost the performance on both ends no hole shot or WOT. Or should I stay at the F6 have them un-cupp them or see if they would trade for maybe F5 props. I really hate the performance that I getting it almost embarrassing to even be on the water ..... Running like a slug//// Thank you everyone that replied your AWESOME!!!!

 

[Rtiny33]

Have a look at the Diz cap and fuel system.

what is that...and what does it do

 

[Rtiny33]

With a ratio of 1.78 I think an F5 set is closer to what you need in that size boat. DP units I am familiar with were all 1.95 for V8 and 2.2 for V6. Diesels were 1.78 as they had much more torque but lower top rpm. Your GXI has top RPM of 5000, put on the lower pitch F5 or maybe F4 and let 'er rev man.

called the prop shop they said bring it in and they'd take the cupp out of it, thanks

 

[Rtiny33]

make sure your running on all 8 cylinders.

are you saying your only getting 3600-3800 at WOT when on plane?

single props are cupped, Duo props do not get cupped. if you cupped your F6's go back to stock F6's

if you want to pull a skier or two, maybe drop down to F5's

So you think the F5 would be the better prop....

 

[Maclin]

Have you ever run it with a vanilla F6 set, before any mods were made to them?

 

[Maclin]

Volvo put a lot of engineering into their DuoProp propsets, they are pretty much dialed in from the factory. Without you having run a non-modded set (if that is the case) then I am hesitant to recommend anything. I would want to see what it did with a bone stock F6 set first for a baseline.

I had a 22 foot Cuddy with DuoProp, the previous version of the drives DP-A. It had the 1.95 ratio. I used B5 (alum version of F5) for water sports as I was usually fully loaded and tubed a lot, and the lake was small. It was a 275hp 5.7, hitting about 48mph at 4800 rpm. It could swing B7's and hit 51-52 or so, took a little longer to get there, never tried towing with that set.

 

[Maclin]

what is that...and what does it do

Distributor cap, and rotor. If you have the crab style there have been problems with those with early onset corrosion.

 

[Scott Danforth]

the crab style dizzy needs to be replaced every 2 years regardless of how it looks. the cap breaks down internally and shorts out and you loose power

as for the props, like Maclin asked, what did the boat do with a stock set of F6 props. not sure why you had a $1300 set of props turned into paper weights by having them cupped.

stainless props are not something that are cheap to play with.

as for F6 vs F5, see if your local volvo dealer has a test set of props.

here is the volvo prop guide
https://www.volvopenta.com/content/...r-owners/parts/propellers/Propeller Guide.pdf

 

[QBhoy]

As mentioned above...I should have explained...the Diz cap it notorious for gathering moisture on these MPI/GXI GM engines. If it’s not to blame just now (I suspect it might be), it will be to blame soon enough. As mentioned, best to replace them every couple of years.
Whats worse is they can have many symptoms, from loosing power like you, to a little almost unnoticeable miss fire, trouble starting or even not starting at all. Then sometimes, the engine will run apparently ok, and then let you down come home time !
for the sake of about $80-100, best to replace it now in any case.

 

[Rtiny33]

make sure your running on all 8 cylinders.

are you saying your only getting 3600-3800 at WOT when on plane?

single props are cupped, Duo props do not get cupped. if you cupped your F6's go back to stock F6's

if you want to pull a skier or two, maybe drop down to F5's

So you think the F5 would be the better prop....

 

[Scott Danforth]

I am not saying that.

your looking for answer only you can give

however for the rest of us to give you an answer, you need to help us help you.

first, how did the boat run with un-molested and stock F6 props? this is the critical base-line information that we all need to be able to answer if you should stay with F6 or go to something else. specifically, we need to know RPM and speed with your unmolested F6 props

second, is your motor running 100%? did you replace the dizzy cap and rotor if it is the crab style cap? is your fuel pressure correct? what is your compression readings on all 8 cylinders? any CEL codes?

if your boat ran ok with F6 props, however was a little low on WOT and not hitting the RPM band recommended, then yes, get a set of F5's

however I would get a loaner set to verify before I spent $1300

 

[Rtiny33]

Well took props back to have the cupp taken out. When I purchased the boat it was in bad shape it's never really ran as I would have liked. Having said that, prior to cupping the props I added from tabs, waxed the under side of the boat. I'm headed to the lake it the morning. I appreciate all of the positive inputs. I will post my results from the lake.

 

[Silverbullet555]

It is my understanding, and I could be wrong, that duoprop sets are more complex to work on than single props. Something about variable pitch. If your local prop shop isn't set up for duoprop, it might be worth looking into another shop if the uncupped set gets you closer.

and do the recommended maintenance above to ensure motor is running well.

 

[Maclin]

Silverbullet555 Yes, they are very complex. They do act like variable pitch with the action of the rotation and size differences in the set. I was amazed at how my (previous) boat took off, hardly any slip, the boat moved out right away and speed increase was in synch right away with the engine revs during acceleration.

Merc Bravo 3's are basically same props and pitch, not quite as much engineering at the prop level as Volvo. Volvo's are kinda like Texas I guess, don't mess with 'em.