Can I find what the original prop was used?

[Kevinhilkey]

I recently got a 1992 Gibson 37 Sport series with a Volvo Penta 570. It has a duo prop. The outer is missing and the inner is damaged. Our local prop guy replaced them for me but I don’t think it’s right. The manual for that engine says top RPM range is 4200-4600 although it doesn’t say if that changes with type of boat. With new props I only get 3800 RPM wide open. Doesn’t seem right. Is there anyway to find out what was originally used?

 

[Sea Rider]

An original prop whether factory delivered or blindly installed afterwords is no indication tha will perform top, need to install any prop that will make engine to run middle to max wot rpm range factory stated dialed with a tach.

It's same as buying your own shoes, shoes bought per other person for you probably won't dial a comfy fit, sort of LOL!!

Same engine installed on 2 different same length boats with same prop will perform much different, the one that has the less hull drag will rev more than the other.

If engine is running strong and healthy need to drop several pitches from current prop to pull wot revs up as usually loaded. Engine is revving -400 wot revs from min range and -800 from max range.

Happy Boating

 

[Kevinhilkey]

Do I look at adjusting the larger inside prop, the smaller outside prop, or both?

 

[Sea Rider]

Do I look at adjusting the larger inside prop, the smaller outside prop, or both?

Sorry, can't answer that issue, only play with standard props. A prop guru should answer that tricky question for sure.

Happy Boating

 

[Sea Rider]

Don't have any experience whatsoever with duo props, but assume that both should be same diam/pitch whether counter rotating or turning CW both. A matter to check both stamped prop numbers..

If with no information on prop, take it to a prop shop and have both measured. In real boating world whichever prop engine was delivered with specially if new, should be a medium pitched prop which could perform good, but not excellent for your current application. A top prop maximization is something you need to find out for yourself testing different prop pitches from current one.

Happy Boating

 

[Maclin]

You would need input from Gibson for any meaningful discussion on what they chose for delivery for their boats.

What size is your boat? I and others here can provide some experience from previous and current boats with the 570.

The VP DuoProps have to be in matching pairs. Volvo does not categorize them in pitch, just a number in a series. The Volvo prop user guide has the Speed at differing RPM's in a table.

Do you know what series/number they put on? Aluminum series will be tagged as Bn, like B5, B6, B7. Higher numbers indicate a higher relative pitch.

Stainless are Cn, like C5, C6, C7. Same relative pitch numbers as B series.

Choosing them is the same basic process, you need to start somewhere and run it, which you have done. Assuming you have an engine in a good state of tune, then if your RPM's are too low you go with the next lower number in the series. If RPM's are too high you go with the next higher number in a series.

What altitude do you boat at? Can make a difference.


Found a post with the guide attached...:
https://forums.iboats.com/forum/general-boating-outdoors-activities/prop-questions-and-topics/539405-what-size-duoprop?p=5531833#post5531833

 

[Kevinhilkey]

Thanks for the great info. It’s a 37 foot Sport Series Gibson Houseboat. The engine is a gasoline stamped as a 570A with an RPM range of 4200-4600. The local prop guy put on an A1 set. Based on your chart looks like I should be looking at B1 or B2. Great place to start. On the chart, what does the GL, GSi, Gi, and GS refer to? And the SKW numbers following?

 

[Maclin]

The A series is same as B series, but have thicker blades, used by Diesels. You pretty much need to stay with those.

For GL, GSi, Gi, and GS...

The G means GM based engine.
GL is always a Carbed engine I seem to remember the L means "limited"
The others are variations on fuel injected models, though not real sure what just GS is.

SKW is power rating in Kilowatts instead of Horsepower.

 

[Maclin]

The next thing to ask about is the actual Drive ratio. In sport runabout boats the DuoProp is usually a 1.98 for the V8's and 2.3 for V6's. If yours has a 1.98 then one (expensive) option is to go to a 2.3 ratio for your large boat.

 

[Maclin]

I just keep thinking about a 37 footer with a 570, 5.7l 350 V8. Just the one engine?

 

[Kevinhilkey]

Yep. One engine. Gear ratio of 1.95:1
si what does the DP280 and DP290 designate? Horsepower? How would I know? I don’t see any of those designations in my paperwork.

 

[Maclin]

The 280 and 290 are the older DP drives, yours is the next generation called DP-A or B or C. The 280 came first, then the 290. Yours is a lot like a 290, shares some external parts.

Your 570 engine is a later version of an AQ271C, both 5.7l GM350's, brochures show 275HP (at engine) for both. Parts are identical. There was an AQ290, which was a 290hp version of the 5.7. I have read about them as to what made them the extra 15hp, but memory fails on what the differences are, and what they were used in.

 

[Maclin]

Sorry about mixing up the 1.95 with 1.98. I had a 570/DP for several seasons, knew it was 1.95. I got a Merc this time and it has poisoned my brain.

 

[Maclin]

Hey, I just opened up my prop guide as it had been a while since I looked anything up there, and I see there is an A0, I bet that is what you need. The B series starts with "1" , C series starts with "2", I never noticed the A series staring at "0", cool.

In that prop guide there is no separate section for the DP-A like what you have, but in this guide it is the same as the 280 and 290 for all intents and purposes. Or even intensive purposes

 

[Kevinhilkey]

Excellent information. I found paperwork to suggest the drive is a DP-C. Based on your prop guide, everything seems to point to the B1 prop set for gasoline 5.7 GL with RPM 4200-4600 and gear ratio of 1.95:1. Thank you so much

 

[Maclin]

The A1 and B1 should be the same pitch. The A0 intrigued me, as it will be one step lower pitch than what you have now, which should get the RPM's up 2-300 or so. Right now, with that heavy of a boat, the gear ratio is affecting your choices. That is a huge boat to have a single engine with the 1.95 ratio. I bet it looks lonely in the engine compartment! Seems most boats like that have dual engines with Vdrives.

I just wanted to be clear that the A series, although usually specified for Diesel applications, are fine for use in all the 280/290/DPA drive applications.

Now, we need some pics of that monster...

 

[Kevinhilkey]

Okay so I got a B1 set and no improvement. Matter of fact max RPM dropped to 3700. Ouch!!! I’ll look for the A0 set.

 

[Kevinhilkey]

Just to cover my bases, I had a friend advance the throttle by hand to verify I wasn’t having a cable issue. I also checked compression on the engine. It was fine. With my friends help I was able to determine the tach showed about a 200 RPM increase at the helm compared to the flybridge. I will have to look into that. So I found a set of A0s and they brought my RPMs up almost an extra 400!!! I’m now hitting about 4600!! Which is the top of my 4200-4600 range. Wow. Water was too choppy to determine if they will increase speed much. I doubt it. Thanks for the help.

 

[Scott Danforth]

its a houseboat. your limited to displacement speed.

 

[Maclin]

Well, now we know why Volvo made the A0's Good deal.