Duo Prop Choice

[Greg2]

Our Sealine S34 has KAD32s and currently runs on A4 aluminium duo props. I am thinking of making the switch to stainless props from the VP C series but am not sure which size to go for. One the one hand I have been advised that it is a straight swap to C4 but I have also been told that dropping a size to C3 might be best.

Can anyone help with this? Particularly interested if someone has done this on an S34 with our set up.

 

[[2068]]

Prop guide suggests C3 would be roughly equivalent.
But I’m not sure it’s worth it on an S34 - stainless props have the advantage at higher speeds.
Disadvantages are the need to have extra anodes as everything nearby apart from your props starts dissolving.
They are also really quite heavy, and if you go run aground or hit something, the shock load to the drive will be higher, as the blades are much stronger.

https://seastriper.com/Propeller_guide_2006.pdf

 

[Greg2]

Prop guide suggests C3 would be roughly equivalent.
But I’m not sure it’s worth it on an S34 - stainless props have the advantage at higher speeds.
Disadvantages are the need to have extra anodes as everything nearby apart from your props starts dissolving.
They are also really quite heavy, and if you go run aground or hit something, the shock load to the drive will be higher, as the blades are much stronger.

https://seastriper.com/Propeller_guide_2006.pdf

Thanks for the link - had seen that guide and your are right that the inference is that C3 would get the right speed range but oddly it isn’t shown as an option.

Good friends had stainless on a Sealine 328 and he swears by them. No corrosion on the props (which is the PITA I want to avoid), no problems with corrosion elsewhere - anode changes annually but happy with that although he did moor in fresh water so maybe worse in salt. He reckons that with the props being stronger with finer blades they got him out of trouble several times with ropes/nets as they just cut through them. No idea if the last point can be quantified and I take the point about them being stronger so maybe a greater risk on a grounding but I tend to try to avoid such occurrences and I think I am right in saying that they do still have the rubber bush system that would give way on a major impact?

 

[Dill et Bound]

Good friends had stainless on a Sealine 328 and he swears by them. No corrosion on the props (which is the PITA I want to avoid), no problems with corrosion elsewhere - anode changes annually but happy with that although he did moor in fresh water so maybe worse in salt. He reckons that with the props being stronger with finer blades they got him out of trouble several times with ropes/nets as they just cut through them. ?

I have been running C3 s for a couple of seasons.
They can be fouled same as the old props... a rope is a pain anyway...
I tried J series.... Just lost about 4 knots top speed. Great up to the plane though.
And my rev limit up to the plane was more than I wanted it to be.
I can’t say I have noticed any corrosion issues.
Anodes fizz away just the same.
I am aware that they may cause a bit more damage to the drive if you ground.
So I am just a bit more careful...
C. 3s not being as cheap should your have a slight accident.
Performance wise they are pretty impressive.
Although the boat is capable of 30 knots.
I like most people cruise at about 21 22.
They match the J series on acceleration, which is the reason I swapped to them

 

[Greg2]

I have been running C3 s for a couple of seasons.
They can be fouled same as the old props... a rope is a pain anyway...
I tried J series.... Just lost about 4 knots top speed. Great up to the plane though.
And my rev limit up to the plane was more than I wanted it to be.
I can’t say I have noticed any corrosion issues.
Anodes fizz away just the same.
I am aware that they may cause a bit more damage to the drive if you ground.
So I am just a bit more careful...
C. 3s not being as cheap should your have a slight accident.
Performance wise they are pretty impressive.
Although the boat is capable of 30 knots.
I like most people cruise at about 21 22.
They match the J series on acceleration, which is the reason I swapped to them

What were the props that you had on before the J series?

 

[Dill et Bound]

What were the props that you had on before the J series?

It’s a bit of a sorry story I am afraid.

Due to corrosion in the shield I had to replace the engine on the boat.

I was on A5s then J5s ... replaced the engine.. went to B5 reccomended for the KAD 42 and drive I fitted.

Could not pull the revs and did nt have... at the time B4s so put on C3 s instead.

No help for you...

But as a general comment on props..

Volvo designed J series for the latest engine drive combinations they produce..

If your boat ... when new... was on A5s

It’s because at that time.. it got the best performance from the drive/engine package you had.

I don’t think that has changed.

What has changed is the availability of VP props.

Genuine or aftermarket.

And there I think I would like to leave it.

 

[Seastoke]

if you are ever in north wales ,there is a selection of them free to a good home courtesy of BruceK

 

[BruceK]

Only if you can dive them up though.

 

[BruceK]

Our Sealine S34 has KAD32s and currently runs on A4 aluminium duo props. I am thinking of making the switch to stainless props from the VP C series but am not sure which size to go for. One the one hand I have been advised that it is a straight swap to C4 but I have also been told that dropping a size to C3 might be best.

Can anyone help with this? Particularly interested if someone has done this on an S34 with our set up.

I have KAD42's in a 34ft sports boat. Heavy at 8 ton. Engines are old and probably lost a bit of HP but rated at 230hp each. Not sure what hp your 32's are.
C3's were way to light. Didn't need superchargers and I could cruise along at any speed I chose up to ~18-19 knts WOT including riding the hole. C4's are just right. B5's I can reach WOT but I think the engine loads too much. Certainly the temps were higher than I'd like at 92ish C rather than 87ish although my gauges do read slightly high. It's a bit of a loose connection but if your boat weight is the same as mine or less and the engines roughly equivalent in hp if not torque you may be able to draw some correlations on what you might expect.

 

[Greg2]

I have KAD42's in a 34ft sports boat. Heavy at 8 ton. Engines are old and probably lost a bit of HP but rated at 230hp each. Not sure what hp your 32's are.
C3's were way to light. Didn't need superchargers and I could cruise along at any speed I chose up to ~18-19 knts WOT including riding the hole. C4's are just right. B5's I can reach WOT but I think the engine loads too much. Certainly the temps were higher than I'd like at 92ish C rather than 87ish although my gauges do read slightly high. It's a bit of a loose connection but if your boat weight is the same as mine or less and the engines roughly equivalent in hp if not torque you may be able to draw some correlations on what you might expect.

The ‘32s are 170hp although I have read that in reality they pull nearer 190hp - can’t verify that though. The boat is lighter than yours - 5.8 tonnes according to what I can find online. Taking your experience compared with our boat weight and engines and the prop guide posted by FlowerPower I am wondering whether C3 would be the right ones to go for.

 

[BruceK]

Tough call. They are wildly expensive to take a punt on too. However Im inclined to agree. If nothing else you can still enjoy a season on them. If C4s are too coarse your season is finished until you lift and change them.

 

[QBhoy]

I used to know my VP props and details when I had a VP...but something in my mind is saying that the B series and C series (stainless equivalent of B) were maybe for petrol engines ? They almost certainly had 3 blades on each instead of the usual 4 and 3 of the usual diesel A series of the age ?
Maybe I’m wrong.

 

[Greg2]

Tough call. They are wildly expensive to take a punt on too. However Im inclined to agree. If nothing else you can still enjoy a season on them. If C4s are too coarse your season is finished until you lift and change them.

Yes, it is a tad pricy to take a punt! There is sense in what you say though -I will see what a dealer advises although given people’s experience with the J series I am not sure how much weight to put on that.

 

[Greg2]

I used to know my VP props and details when I had a VP...but something in my mind is saying that the B series and C series (stainless equivalent of B) were maybe for petrol engines ? They almost certainly had 3 blades on each instead of the usual 4 and 3 of the usual diesel A series of the age ?
Maybe I’m wrong.

You are right about the number of blades but I haven’t heard that the stainless props were for petrol engines - no reference to it in old and current VP ‘blurb’ and I know of Diesel engined boats that have used them.

 

[BruceK]

I used to know my VP props and details when I had a VP...but something in my mind is saying that the B series and C series (stainless equivalent of B) were maybe for petrol engines ? They almost certainly had 3 blades on each instead of the usual 4 and 3 of the usual diesel A series of the age ?
Maybe I’m wrong.

I think it's more complex. To my knowledge. Series A was the choice for most diesels but not all. My KAD 42 for instance was B series. C is not a replacement for B but C was recommended for boats capable of speeds in excess of 30 knts

 

[Greg2]

I think it's more complex. To my knowledge. Series A was the choice for most diesels but not all. My KAD 42 for instance was B series. C is not a replacement for B but C was recommended for boats capable of speeds in excess of 30 knts

Yes, we had B6 props on our Targa with KAD42s

 

[QBhoy]

Good read. Seems there are multi use for them. Perhaps the kad engines behave more like a petrol with the power down low available from the supercharger ? Maybe ??
I had B5s on a gm petrol engined boat. Just remember a bit about the C5 being the stainless like for like perhaps. I didn’t bother changing for two reasons.

The price
The risk that my engine would no doubt drop a few RPM, typical of going from ally to stainless on all but real performance orientated hulls. My rpms were perfect with the original B5’s and didn’t think it was worth messing with.
Oh and I’ll mention the price again, haha.

 

[Greg2]

Good read. Seems there are multi use for them. Perhaps the kad engines behave more like a petrol with the power down low available from the supercharger ? Maybe ??
I had B5s on a gm petrol engined boat. Just remember a bit about the C5 being the stainless like for like perhaps. I didn’t bother changing for two reasons.

The price
The risk that my engine would no doubt drop a few RPM, typical of going from ally to stainless on all but real performance orientated hulls. My rpms were perfect with the original B5’s and didn’t think it was worth messing with.
Oh and I’ll mention the price again, haha.

Think you might be right on the KAD performance point with the supercharger - not the first time I have heard it said.

Think you are also right on the point about price of the stainless props