Ventilating Prop

[Virgo67]

Looking for some advice, I just purchased a used Seapro RIB with a Mercury F60 4 stroke EFI, both well look looked after and serviced. The RIB was bought from Highams in 2012 I believe.

I took it out yesterday on my first trip with it (I was solo so it was light) and had nothing but problems with what I believe was prop ventilation. I’d get some speed up then it would fade, rev high and loose speed, loads of splashing at the rear transom too. It felt like a slipping clutch on a car. No matter how I trimmed the engine up or fully down, I got the same issues. Never really got any speed going, and same issue when turning.

I’m no expert on engine trim and performance,

I am wondering

1) Tube pressure – I pumped up all the tubes to around 1.5 PSI as they all felt a bit soft, wondering what pressure the Seapro 520 should be and if this had caused the boat to sit higher in the water than normal?

2) Prop – looks clean, no pits can you confirm the prop is matched to the engine? I now the previous owner towed big inflatables so maybe prop was aligned to fast take offs.

3) Would fitting a hydrofoil help?

4) Ventilation plate alignment - how can I check alignment of the engine height with the hull?

5) Engine Jack plates – how would I know when to get one fitted and if its needed at all?

6) Prop shaft spline – worth checking if it spinning at high revs?

Aim is good top speed, not bothered about towing. I’d really appreciate your opinions and guidance as I’m very unsure what I need to do to remedy this.

[Pikey Dave]

Is it the correct length leg for the transom?
Could be slipping prop on hub.
A photo showing the AV plate/prop/keel would help, preferably with a straight edge along the bottom of the keel projecting to the AV plate.

[Virgo67]

Thanks,

just noticed that the prop has 4-5mm of horizontal play on the shaft, heard that can cause issues with air gaps.

I'll get my spirit level out and take a pic of the allignment

[Pikey Dave]

Originally Posted by Virgo67

Thanks,



just noticed that the prop has 4-5mm of horizontal play on the shaft, heard that can cause issues with air gaps.



I'll get my spirit level out and take a pic of the allignment

When you say “horizontal play” do you mean side to side or back to front? I.e. port to starboard or fore to aft?
Where is the play? Is it the prop on the shaft, the prop on the hub or the shaft in the gearbox? The only play that should be evident is a few thou fore/aft between the prop shaft & the gearbox. The prop/hub/shaft should be tight to each other.

[Virgo67]

Originally Posted by Pikey Dave

When you say “horizontal play” do you mean side to side or back to front? I.e. port to starboard or fore to aft?
Where is the play? Is it the prop on the shaft, the prop on the hub or the shaft in the gearbox? The only play that should be evident is a few thou fore/aft between the prop shaft & the gearbox. The prop/hub/shaft should be tight to each other.

prop play is fore to aft, prop moving back and forward on the shaft by about 4-5mm (that seems very excessive) and think it would explain the ventilation? up/down play is marginal.

[Pikey Dave]

Originally Posted by Virgo67

prop play is fore to aft, prop moving back and forward on the shaft by about 4-5mm (that seems very excessive) .

That’s not right, unless it’s some oddball system. The prop should be torqued onto the shaft, tight against the thrust washer.

[Virgo67]

Originally Posted by Pikey Dave

That’s not right, unless it’s some oddball system. The prop should be torqued onto the shaft, tight against the thrust washer.

makes sense, I'll get it checked out, sounds like maybe the thrust washer is missing or something. Odd, cos the seller got the engine serviced like clockwork and was quite fussy with everything (except the prop). can't imagine they didn't notice how bad it was, unless they swapped out a rubbish prop for a newer one just to sell it. It was running like a bag of spanners yesterday.

thanks for the info and advice

cheers

[Voodoo]

Definitely something not right with that...I was going to say a spun prop bush but the play would let exhaust gas out and aerate the prop.

[chipko]

Originally Posted by Virgo67

Thanks,



just noticed that the prop has 4-5mm of horizontal play on the shaft, heard that can cause issues with air gaps.

If you have a Mercury Black Diamond prop with the Flo-Torq II hub then, strange as it sounds, this play is quite normal. A good few mm play along the shaft plus a few degrees axial play to boot. Even when properly torqued against thrust washer the play is there in the Flo-Torq ll hub.
Under load it pushes back and centres against thrust washer, allegedly this reduces vibration. Sounds mental but it does seem to work and definitely does not generate any ventilation issues.


Edit:

Think I’ve got this slightly wrong as it might be the Flo-Torq Reflex drive hub which has this play and not the Flo-Torq ll

[Virgo67]

Originally Posted by chipko

If you have a Mercury Black Diamond prop with the Flo-Torq II hub then, strange as it sounds, this play is quite normal. A good few mm play along the shaft plus a few degrees axial play to boot. Even when properly torqued against thrust washer the play is there in the Flo-Torq ll hub.
Under load it pushes back and centres against thrust washer, allegedly this reduces vibration. Sounds mental but it does seem to work and definitely does not generate any ventilation issues.


Edit:

Think I’ve got this slightly wrong as it might be the Flo-Torq Reflex drive hub which has this play and not the Flo-Torq ll

its a 2011 F60, so not sure about the Flo-Torq hub, but the vibration is bad, the kind that is out of balance and not improving anything