Unmatching Duo Props

[Dazzajohm]

Bit of a vague question but thought I'd ask in case someone can give some pointers

I've had my boat for a year and discovered during the summer that it's not as quick as it should be so when I take her out for maintenance planned on getting the props looked at and changed. With this in mind I've done a bit of research to get an idea of price and I think she has the wrong props on.

I've got a KAD 44 and DPE drive and looking at my props the inner one has 3 blades but the outer one has 4 blades. Looking on the VP website there is an A series of prop with this configuration but apparently not compatible with the KAD 44.

Until I get the boat out I won't know exactly what ones are on there but my question to those of you with lots of experience is on the basis on the assumption of the wrong props currently being on there, what damage could this cause to the engine / drive?

 

[Ian h]

this may help

https://seastriper.com/Propeller_guide_2006.pdf

 

[[2068]]

Newer version:
http://www.volvopenta.com/content/d...r-owners/parts/propellers/Propeller Guide.pdf

Take a look at page 20 ... if the prop blades have the edges squared off a bit, they could be the newer type “J” propellers, which replaced both the type “A” (3 and 4 blades) and type “B” (both three blades).

Type “A” props on a KAD44 is definitely wrong - it won’t damage anything in the short term. Just not optimum performance at higher speeds.

However, if you are achieving 3900rpm+ at WOT and they are “J” props, maybe you could go up one size.
If you are not achieving 3900rpm+ at WOT, then that needs to be fixed first.

 

[Dazzajohm]

this may help

https://seastriper.com/Propeller_guide_2006.pdf

Thanks I will have a look just now.

 

[Dazzajohm]

http://www.volvopenta.com/content/d...r-owners/parts/propellers/Propeller Guide.pdf

Take a look at page 20 ... if the prop blades have the edges squared off a bit, they could be the newer type “J” propellers, which replaced both the type “A” (3 and 4 blades) and type “B” (both three blades).

Type “A” props on a KAD44 is definitely wrong - it won’t damage anything in the short term. Just not optimum performance at higher speeds.

However, if you are achieving 3900rpm+ at WOT and they are “J” props, maybe you could go up one size.
If you are not achieving 3900rpm+ at WOT, then that needs to be fixed first.

That's really helpful, thanks I'll have a look. The person I got the boat from said they props were B7's which clearly they are not plus I've had numerous other issues with things not being as they should so needless to say I'm sceptical.

The problem I've been having is that I can achieve 4000rpm to 4100rpm WOT but might just push 22-25knts on a princess 266. That means at cruising RPM of 3200ish rpm against the tide I'm lucky to get 15-17knts.

I'll have a look at these J props.

Have also tried to attach a photo of mine although it's not a very good one.

 

[[2068]]

From the photo, it looks like someone has stuck on a set of A-series props, which isn’t the best choice.

 

[zt260]

On my targa 37 with twin kad44 I ran stainless c4 with no problems

Regds ash

 

[inception]

What's the maximum RPM you get? does it reach the maximum RPM which I think for your engine is around 3900?

 

[petem]

On my targa 37 with twin kad44 I ran stainless c4 with no problems

Regds ash

'c' series is correct for Kad44 but suspect the op has 'a' series or 'j' as suggested above.

 

[petem]

What boat is it?

 

[Dazzajohm]

What's the maximum RPM you get? does it reach the maximum RPM which I think for your engine is around 3900?

When the bottom is clean around 4000 to 4100 WOT. always cruised at around 3100 rpm though and would do around 15-18knts

 

[Dazzajohm]

What boat is it?

Princess 266

 

[petem]

Princess 266

Max rpm for Kad44 should be 3800 so you do seem to be under propped. If you lift the boat the prop size should be stamped on the props.

 

[inception]

When the bottom is clean around 4000 to 4100 WOT. always cruised at around 3100 rpm though and would do around 15-18knts

You are under-propped if getting that rpm.

 

[NBs]

Newer version:
http://www.volvopenta.com/content/d...r-owners/parts/propellers/Propeller Guide.pdf

Take a look at page 20 ... if the prop blades have the edges squared off a bit, they could be the newer type “J” propellers, which replaced both the type “A” (3 and 4 blades) and type “B” (both three blades).

Type “A” props on a KAD44 is definitely wrong - it won’t damage anything in the short term. Just not optimum performance at higher speeds.

However, if you are achieving 3900rpm+ at WOT and they are “J” props, maybe you could go up one size.
If you are not achieving 3900rpm+ at WOT, then that needs to be fixed first.

hi, in my previous boat 2 x kad44 B4 propellers WOT 3900 and speed 36kn. I had to change the propellers because of this bad condition, I picked up the J5 propeller series. WOT still 3900 rpm but the speed of 32-33kn, the travel speed is not so big difference between the rmp and the speed. I thought the J series of pots are thick versus the B series of propellers. I would remember the instruction of KAD 44 not to use A- series of propellers because KAD too big torgue and power!

If you walk in clear waters without the danger of propellers hit the stone, then definitely worth buying the high quality stainles steel propellers with the best performance.

NBs

 

[NBs]

Max rpm for Kad44 should be 3800 so you do seem to be under propped. If you lift the boat the prop size should be stamped on the props.

Hi, i think Volvo say KAD 44 EDC rmp area 3600-3900rmp, from the point of view of the engine life, it is better to reach the largest RMP boat in full travel weight. 3800 rmp is approved by the manufacturer so it's Ok.

NBs

 

[CLB]

Princess 266

Ah, so the boat has been re-engined. I guess whoever did it cheaped out on the props and used whatever was available. Running right, I would have though you would see 30 knots top end.

One you know what A size is in their, go up at least one size in the C series. That should reduce your top end by around 200rpm and increase your top speed.

 

[BruceK]

I'd take a step back and verify your drive and drive ratio's before committing to anything. You may find that the drive once belonged to the previous engine(s) (I see some at least came with twin 3.0l inline 4 motors) and that you need a lower leg / gearbox change before changing props to bring it within a correct diesel vs petrol gearing ratio ... if that makes sense, I'm PUI at the moment.

 

[CLB]

I'd take a step back and verify your drive and drive ratio's before committing to anything. You may find that the drive once belonged to the previous engine(s) (I see some at least came with twin 3.0l inline 4 motors) and that you need a lower leg / gearbox change before changing props to bring it within a correct diesel vs petrol gearing ratio ... if that makes sense, I'm PUI at the moment.

Good point. If the boat was changed from petrol to diesel, and the drive not changed, the ratio will be wrong.

 

[BruceK]

well at least the lower gearbox gearing. Not that it's cheap mind. My props freewheel in a 4knt river estuary current year round and so the seal gets to eat into the shafts and I've had to replace those twice now. Might be cheaper to look for a good reconditioned lower as the engineering costs weren't cheap either.