Volvo penta b6 duoprops

[seanfoster]

Hi all,

Not posted on here for a good while,

I'm starting a refurb of my Cranchi Derby 700 which I bought a few years back, it has a volvo penta aq271 engine with a dp290 out drive.
The duoprop props have a fair amount of damage so I'm going to get them repaired, but after taking them off I noticed the rear prop is considerably bigger than the front one (diameter) I would say nearly 2 inches larger.
They are b6 props, I can't find any details about pitch and Dia for them, does this sound right or does it look like one has been 'bodged' on?
There are markings on the front but not rear prop.

Can anyone shed some light on this?!

 

[QBhoy]

Hi all,

Not posted on here for a good while,

I'm starting a refurb of my Cranchi Derby 700 which I bought a few years back, it has a volvo penta aq271 engine with a dp290 out drive.
The duoprop props have a fair amount of damage so I'm going to get them repaired, but after taking them off I noticed the rear prop is considerably bigger than the front one (diameter) I would say nearly 2 inches larger.
They are b6 props, I can't find any details about pitch and Dia for them, does this sound right or does it look like one has been 'bodged' on?
There are markings on the front but not rear prop.

Can anyone shed some light on this?!

That’s perfectly normal. The rear prop is always larger on these. The B series is now not available, but the J series (I think) is the replacement. Most would replace with aftermarket props from Michigan marine, I’d say. They do a direct replacement and are every bit as good in quality as the VP oem props. Half the price nearly too.
alternatively most would just send away their damaged props to castle marine for a refurb. About £70 per prop last I heard. Mind and replace that anode at the back, whilst they are off. Take care.

 

[seanfoster]

Thank you for the reply,
Yes I'm going to send them both to be repaired, was a bit confused as they are quite different.
Having looked at the Michigan Marine website, I can see that the front has a 14.25" dia with 23" pitch, the rear 13.25" dia with 22" pitch.

 

[QBhoy]

Thank you for the reply,
Yes I'm going to send them both to be repaired, was a bit confused as they are quite different.
Having looked at the Michigan Marine website, I can see that the front has a 14.25" dia with 23" pitch, the rear 13.25" dia with 22" pitch.

Not sure about what particular inches of pitch the reference refers too. But last I knew, each number represents roughly an inch of pitch on the props. Best info I’ve ever found anyway. So an example would be that going from B6 to B5 props, you might expect to gain around 150-200 rpm, some acceleration, but perhaps lose top end and run the risk of over revving the engine (under propped).
ive never known Volvo to actually put a number on their dp props that represents an actual pitch in inches perhaps.
your particular VP271 will be 5.7l 350ci GM engines. And with a 4 barrel carb (likely quad raker or less likely Rochester). The usual rpm range for these are about 4400-4800 rpm. Or 4200-4600 rpm on occasion. If you’re in the range there and happy enough with the performance as she is. Just get direct like for like B6 equivalen or repair what you have.
all the best. Allan.

 

[QBhoy]

Also add that I’m particularly keen to hear and get involved in how you get on and what rpm and speed you see just now. I think comparing what I know already of personal close comparisons, you’re likely not far off with B6 props on that boat. Added to this, I’m not aware of too many or any at all perhaps, originally propped from new, set ups on a VP DP boat to be wrongly propped. If it helps you any. What I do know for certain is the following;
On mine and another guys previously owned sealine 218/220 (7m deep v hull OAL of about 1800-2000kgs) with a 4.3l 205hp V6. They had B5 props and were perfectly set up running around 4800 rpm at about 35/36 mph trimmed up and flat out.
I’m also presently familiar with a 28ft heavy deep v princess with twin 5.7 engines. She has matching twin 290/DPA/DPb family DP outdrives...but some where along its life, has been under propped with a set of B3 props on each drive. For one of two reasons. Either it’s the original props for the original 271 5.7 engines, but she has since been re powered with 300hp 5.7 more modern engines...or she has been down pitched for a previous life in slower inland waterway at some point.
regardless of which, as she is with the B3’s, she will easily over rev to 5100/5200 rpm close to, but not quite at full throttle. So in the danger zone for the engines. The owner and I both decided to go to B5s to lower the rpm by around 400 rpm at a best guess. We will soon find out how she runs.
hope that helps with some perspective

 

[seanfoster]

Hi Allan,
Thanks for your reply, my boat has a single AQ271 engine, the carb is a Holley 4150, I've not had the boat flat out as I currently run it on the river with a 6mph limit, so not really getting much out of it, but will be moving to the south coast in the near future so will be able to open her up then and see what sort of performance I'll get out of her (I'll be rebuilding the engine as well before hand).

I have an owners manual which has the aquamatic and duoprop prop guide, it has a chart showing what sort of prop will give out what speed, other than that the info is a bit vague, but according to the chart the B6 is correct for my setup:

 

[QBhoy]

Hi Allan,
Thanks for your reply, my boat has a single AQ271 engine, the carb is a Holley 4150, I've not had the boat flat out as I currently run it on the river with a 6mph limit, so not really getting much out of it, but will be moving to the south coast in the near future so will be able to open her up then and see what sort of performance I'll get out of her (I'll be rebuilding the engine as well before hand).

I have an owners manual which has the aquamatic and duoprop prop guide, it has a chart showing what sort of prop will give out what speed, other than that the info is a bit vague, but according to the chart the B6 is correct for my setup:
View attachment 108027

I’d imagine it will be to be fair. As far as I can tell, each number incline is similar to going up an inch or so in pitch. Be about right you’d think. Like I say. They are normally pitched and propped perfectly on these things from new.