would you get the reference of the blades that we need to buy to go from 3 to 4 blades on our duoprop 290? thanks a lot ? any material we shall go for? price range? thanks a lot ;)

https://www.facebook.com/mbjohnsteed/photos/a.1416977208565140.1073741828.1416915105238017/1744496862479838/?type=3&theater

Hi Alexandre

Why would you like to get a four blade for you DP? You already have six blades in total :)
The outer propeller was four bladed on older VP diesels, but I think that they stopped with that when the KAD series was introduced.

people did it here and they certified me i will go plan much faster and use much less fuel

Hi
Never heard of this actually. I think that the reason VP used four blades on outer propeller was for balancing the shift from vibrations that came from the diesel engines.
Four bladed propps can increase acceleration, corse stability etc on single prop outboards and sterndrives. Regarding fuel economy it doesn't really affect anything to have three or four bladed prop. The important thing is to have the right size.
I don't think you will get anything from this on you DP dive. If you feel that you don't get the right performance with current prop, try a different size set.
What boat, engine and prop size do you have now?

After reading through your nice link with pictures I assume that you have a 5.7 v8, 270bhp or more. Most common gear ratio for this is 1:1.95 and I would like to say that a set of b6 props would be perfect for this setup. B5 if you would like to get better acceleration and maybe b7 if you have 300+bhp. Stainless C series might give a bit more performance but approx three times more expensive.

you can see the engine in the page. I changed a VP 231 a for a home made built v8 5.7 liter chevy long block. we get 270hp+ i think. but if it push nicely, i would expect more punch and going to plane more easily. now i go plane around 20 knots. i was told changing propellers will get me to plan around 10 knots. if i add my recently bough trim flaps as well. so B6 stainless steel is what you recommand?

https://www.facebook.com/mbjohnsteed

page 21 it seems

http://www.volvopenta.com/SiteCollectionDocuments/Penta/Propeller%20guide/Propeller%20Guide.pdf

At what speed your boat goes into plane has very little to do with engine and prop, it's all about hull and weight. Trim tabs will not do you much good either, maybe you can keep plane at a bit lower speed. Tabs are more for balancing weight distribution and get the running angle that you want. To go into plane at 10kts with a 24' midi I would say is impossible, more like 16-18 at best.
I never been riding in a Coronet 24', but a number of C 21',22',26' most of these with a 5.7L V8 270hp+, DP 1:1,95 and a set of B5 or B6 and never really felt that it was hard to go into plane even with 4-5 persons and full tank.

Can you figure out what size you have now? Since your old engine was a 5.0L and about 230hp it might been equipped with b3-b4 propps, which is way to small for your current configuration. Do you reach max RPM on full throttle? On 5.7L it would be about 4600-4800 RPM. If you get there and over your props are to small and the other way around.
It's impossible to say what props you should buy without having the experience of similar setup, but my recommendation for you would be a set of b5 if you'd like more punch.
I would also recommend you to test out with B series (alu) props at first and when you have the right size buy C series for extra performance since these are 3-4 times more expensive.

thank you so much for your time Jonas. Very precious and informative to me.
my current vV8 5.7 is home built. and what surprised me is that when im plan and nearly 30 knots, the engine is around 3800rpm. and then when i push to go higher, the engine suddendly goes down in rpm. i asked to the motor builder ( afriend) and he asked to the block supplier. and the answer is: the block is designed with max 3800 rpm. is it possible? i thoigh V8 could go until the end...

thanks for feedback

which size it is according to you?

I don't know about this max rpm but 3800 seems low for a 5.7, but it's for sure possible to design a engine this way.
Sounds more like your ignition doesn't follow, at higher rpm it should adjust closer to TDC.
What about if you give full throttle with no gear?

Regarding your current prop size its impossible to say from a picture. Older models of DP props has a marking on the side of the hub, newer model has both on the side and at the back of the hub.
It should be both a six figure nr and letter+nr like b6.

I can read now in the boat service historic that the previous owner changed one propeller (the back one, bigger then the front one) and it is written (2014 invoice):
- Propell B6 indre

What will i gain to go for stainless steel?

Hi
If the inner one was replaced with B6 I'm sure that outer one is B6 as well. Outer one is always smaller than inner prop but they are a set of B6 anyway.

If you have a set of B6 and max RPM is 3800 I would try a B4 set, then you would reach 4200-4400 at least. B6 seems to big for you. I don't really believe that your 5.7L V8 cannot go over 3800 RPM.

What you will gain from stainless props is a much harder material that allows blades to be thinner and cut the water better, and since it's harder the blades cannot flex in the way alu can.
Stainless is not going to solve your current issue. Try out the set that fits your hull, engine and drive that matches your preferences regarding acceleration and speed with regular alu props at first. And when you are happy with the configuration you can think about spending 1500 USD on the extra 2-3 knots and grip that stainless might give you.

ok. i will follow your advice. Thanks a lot for your time. Very precious.
And now, last time, the V8 (code name "Purdey") went smootlhy to 4200 rpm...
But now i do have a over heating problem. The water is boiling in the expansion tank each time i go over 3500 rpm for a while. Very strange. to be tuned

Hello Alexandre

I read your last post regarding overheating. Are you getting a "high temp." indication at the same time the water inside the expansion tank is "boiling"?

If you have a leakage between the top and the engine block, you will get the same condition (boiling water) with a broken head gasket. But you wrote "after a while" and that indicates something different might be the problem..

Good luck.

Sincerely Wilhelm