Change to J Series Props?

Scubadoo

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Hi All,

Thinking of replacing my A6 duo props when the boat is lifted soon, as my current props are nearly 10years old and looking worn etc.

So, considering changing to J series props and read a few posts on this forum, and now can't make my mind up if it is a straight swap from A6 to J6 or not. Some seem to have done a straight swap and complained about reduction in top end performance/speed and suggested going up one size, in my case that would be J7. Getting it wrong will be an expensive mistake.

Anyone get recent experience of changing to J props and any recommendations etc, e.g. top end and "getting on to the plane".

The alternative is to simply buy new A6 which are still available, but more expensive based on a recent quote from my local Volvo dealer. Not interested in refurb either but plan to keep my old props as spares.

Lastly, can anyone recommend a supplier for the best price?

Thanks all.
 

Momac

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So, considering changing to J series props and read a few posts on this forum, and now can't make my mind up if it is a straight swap from A6 to J6 or not. Some seem to have done a straight swap and complained about reduction in top end performance/speed and suggested going up one size, in my case that would be J7. Getting it wrong will be an expensive mistake.

I have also heard sticking with the same number reduces top end speed, which suggests going up a number may be the way to go.

Ask Paul Jenkins at Volspec for a propeller enquiry form. They will then advise. I don't know whether it will help but could be worth a try.
paul@volspec.co.uk

To be honest I think the final decision will remain with you.
 

[2068]

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If it were my boat, I’d go for J7 assuming I had healthy engines and turbos that could hit the right RPM range at full throttle with A6.
If I was a couple of hundred of rpm down, I’d go J6.
But don’t blame me if it all goes horribly wrong - you have to be happy with your own decision.
 

Scubadoo

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I have also heard sticking with the same number reduces top end speed, which suggests going up a number may be the way to go.

Ask Paul Jenkins at Volspec for a propeller enquiry form. They will then advise. I don't know whether it will help but could be worth a try.
paul@volspec.co.uk

To be honest I think the final decision will remain with you.

Thanks, will email Paul and see what he comes up with.
 

Scubadoo

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If it were my boat, I’d go for J7 assuming I had healthy engines and turbos that could hit the right RPM range at full throttle with A6.
If I was a couple of hundred of rpm down, I’d go J6.
But don’t blame me if it all goes horribly wrong - you have to be happy with your own decision.

My single engine is a AD31 which reaches the max rpm of 4100 for most of the season on A6. The only thing it is no pocket rocket getting on to the plane ie 150HP 25ft boat, so does make me wonder if a J7 would exacerbate this. But I am leaning towards J7.

As said trying to get an idea from others before taking the plunge. Thanks.
 

rlw

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Some of the aftermaket stuff is not bad. I think I paid 1300€ for 2 sets of new duoprops on my previous boat. Blades seemed to be a bit thicker.
 
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I changed mine last year from A5 to J5 and have lost some top end speed and cruising speed RPM is also higher (21 knots @3400 now), it picks up a lot better though.
Personally I will opt for one number up next time around but I won’t know if that’s the correct decision until after the first trip out.
 

NBs

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If the speech in the Volvo Penta duo prop J series I would not buy these propellers for two reasons. The claimed paint is better than before, has its own experience of lying! Another view of their own specific exchange B-series VP professional J-series propeller, the same RMP and -3 knots I think, poor rank, buy propeller set stainless steel, J series is a joke!
NBs
 

[2068]

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If the speech in the Volvo Penta duo prop J series I would not buy these propellers for two reasons. The claimed paint is better than before, has its own experience of lying! Another view of their own specific exchange B-series VP professional J-series propeller, the same RMP and -3 knots I think, poor rank, buy propeller set stainless steel, J series is a joke!
NBs

Can someone translate this for me?
I’ve just run into the language barrier.
 

QBhoy

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I think you might be lucky here.
The stainless Js will undoubtably drop your rpm at the top end but it looks like you have RPM to play with.
Also as it happens, I think you might find a fair improvement not only in top end but in acceleration too. The stainless props will not flex and loose pitch the way the ally ones will opening the throttle. Add the advantage of the Diesel engine you have demanding load on it to spool up the turbo quicker....you can’t loose I’d think.
Only down side is the massive cost to buy. I can’t remember seeing any decent quality non VP stainless Props though. Maybe Michigan Marine do them now ?
Really cannot remember the ally to stainless models but there is either “C” or “J” to choose from. Perhaps one is for petrol and one diesel. Haven’t looked. Just remember that mine were B5 and the stainless equivalent was C5. That was a petrol though. A series were the standard diesel as you know.
I don’t think you will loose much more than 100-200 rpm tops. Also save fuel too.
Since the VP I have had many mercruiser and always go to stainless. The difference in performance, economy and refinement is tangible in every respect over the year
 

QBhoy

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If the speech in the Volvo Penta duo prop J series I would not buy these propellers for two reasons. The claimed paint is better than before, has its own experience of lying! Another view of their own specific exchange B-series VP professional J-series propeller, the same RMP and -3 knots I think, poor rank, buy propeller set stainless steel, J series is a joke!
NBs

I have no clue what this means, but I’m intrigued
 

NBs

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Can someone translate this for me?
I’ve just run into the language barrier.

Sorry my bad English,

Old B-series propellers 36 kn, I changed the new J-series speed only 33kn, 2 x KAD44 RMP in both 3600 B- and J-series.
 

Greg2

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I think you might be lucky here.
The stainless Js will undoubtably drop your rpm at the top end but it looks like you have RPM to play with.
Also as it happens, I think you might find a fair improvement not only in top end but in acceleration too. The stainless props will not flex and loose pitch the way the ally ones will opening the throttle. Add the advantage of the Diesel engine you have demanding load on it to spool up the turbo quicker....you can’t loose I’d think.
Only down side is the massive cost to buy. I can’t remember seeing any decent quality non VP stainless Props though. Maybe Michigan Marine do them now ?
Really cannot remember the ally to stainless models but there is either “C” or “J” to choose from. Perhaps one is for petrol and one diesel. Haven’t looked. Just remember that mine were B5 and the stainless equivalent was C5. That was a petrol though. A series were the standard diesel as you know.
I don’t think you will loose much more than 100-200 rpm tops. Also save fuel too.
Since the VP I have had many mercruiser and always go to stainless. The difference in performance, economy and refinement is tangible in every respect over the year

My understanding is that the J series are not stainless, they are aliminium and replace the old A and B series. The C series stainless props are still available from VP
 

Scubadoo

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Some of the aftermaket stuff is not bad. I think I paid 1300€ for 2 sets of new duoprops on my previous boat. Blades seemed to be a bit thicker.

My current props are aftermarket "PowerTech" and lasted well, but the supplier is no longer available (I think).

Who did you contact for your aftermarket props?

To date simply not sure the best course of action at the moment, I am beginning to think maybe I should simply stick with buying new A6 props.

So far everyone thanks for your comments, very helpful.
 

volvopaul

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I’ve just swapped 2 pairs of J series they are less than a year old , I think there J 5s I& anyone is interested. Client is going down a size as it’s not pulling full rpm. Selecting the right size is an art form, I’ve yet to find info from any VP dealer that’s got it right first time calculation. At first VP said it’s a straight numbers swap , then they said go up 2 sizes .
I’ve swapped many over the last 2 years with very mixed results that have given better and worse overall speed and fuel consumption figures .

Every boat is different, every engine is different, builders spend thousands on trials with different props, I’ve seen diesel boats go better on petrol props and vice versa. Don’t take what the dealer says as gospel, you would be very lucky if it’s right first time .

The J series is more robust as it has no bush and it’s a lighter prop so will spin up with less Effort, I’d surmise that’s where VP got the idea to go up 2 sizes at the outset , that might have worked if you were initially on stainless C series as boy are they heavy.

Younpays your money and takes your choice.
 
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