VP J propsu

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Sailorsam101

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I need a bit of advice after changing my props a single the results are not good.

Volvo Paul serviced my legs and arranged for 4 new props. I had A7 props that were nackered and J7s looked like a straight swap like for like....that's what Volvo say in their bumf.

No let me state that I've no issue with anything Paul did and he is aware of the problems I having but is also stumped.

So the figures..

Last year....freshly painted hull and legs with old A7 props..

Half fuel and half water with three adults on board. 2900 rpm gave 21 kts on an average run up and down tide.

Same as above but with very dirty bottom and badly chipped props...2900 gave 20 kts.

Now to this year with 4 new J7 props fitted and fresh painted hull and legs.
Half fuel and half water again with three adults on board. 2900 rpm hives 18kts on an avarage run as above.
3000 rpm gives 20 kts again.

I have not touched the engine In away way....one weekend I was getting 20 kts at 2900...then paint bottom and replace legs and I loose 2 kts.

Once again VP state that the J prop is a direct replacement for the A.

Any ideas welocme folks befor I go off to VP to ask.
 
Here is an extract from the service bulletin.

- The Marine Propulsion Software (MPS tool) should be used to determine which set in the J-series to use. Depending on application type, boat size, weight etc., it’s not certain that for example an A6 kit can be replaced with a J6 kit.
- The MPS tool is found on Volvo Penta Partner Network under Sales & Marketing, and it is updated with the J series propellers.
 
Perhaps get in touch with the dealer who supplied them as I would assume they have access to the right info ? an expensive thing to get wrong, if I were investing in new props I would only want to by once
 
Several people have reported a small speed reduction when going with like-for-like Ax to Jx, which is probably a good thing if you couldn't quite hit the recommended revs with your A-series.
Bumping up one size seems to work well if you can gain a knot or so (e.g. A7 to J8) and you can still hit recommended revs, just so long as you weren't previously overloaded, otherwise you are making it worse.
It depends on what figures you were getting to start with, but the J-series don't appear to be direct equivalents - Volvo only claim that they are "approximately" equivalent.

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I would rather calculation based on economical cruising speed rather than max speed, how often does too speed really matter ?
 
I agree so that why I'm a bit concerned that I'm getting less speed for more rpm.

I've also noticed that my fuel burn is a little higher than before.
 
It's not a same to same swap so you need to put some thinking into it before you decide which J series prop you want. In practice its usually one size up or down and iirc around 150rpm's per size. Read the rpm at WOT and if in spec stay on the size but if not then do the 150rpm up or down as appropriate.
 
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