Cabo 43 FB Performance with 28x40 props

Gents,

firstly, thank you for your swift reply's, all very greatly appreciated.

Now to address a few questions raised. No, I don't mean leaning to one side or another. I have found this is inherent to most fast boats that carry a deep v all the way aft. This customer's last boat was a 38 Express with CAT C12's and it had the same problem. You just have to play with the tabs a lot. I have several customers with Palm Beach 32's, 50's and a 55. These hulls are more like a New England lobster boat style, like the Hinckleys etc, and have an extremely deep V forward but it flattens out dramatically as you run aft. These boats have no tendency to lean at all.

I am talking about a 2002 Cabo 43 FB. And those are the consumption figures we measured pretty accurately on a recent 8 hour run. Engine and gearbox specs in the OP.

I fail to see how a 1/2 inch increase in diameter can cause ventilation. The gap between the hull and the blades has only decreased by 1/4 of an inch, that gap now is about 3 and 1/2 inches or more. I gave Veem the hull gap information in the ordering process and they didn't seem concerned by this at all.

I believe the problem I have is ventilation not cavitation. My understanding is cavitation is generally (but not always) caused by poor blade design, creating tiny bubbles of air which can erode the props surface in extreme cases.

Ventilation is caused when air is "introduced" to the propeller from an external source causing a much more aggressive loss of "bight" or "grip", and the revs rise sharply and the vessel turns towards the side that is slipping. Please correct me if I'm wrong on these definitions.

My problem happens mostly on the port side, and is most prevalent when you try to accelerate beyond 2100 RPM not matter how gently you accelerate. Once or twice I have managed to get it to "stick" up to 2250 for several seconds, the speed rose to an encouraging 32.9 in that short space of time. Several times it has ventilated whilst accelerating around 1500 - 1600 RPM just as the boat is "climbing out of the hole". I put this down to being too aggressive with the throttle. It seems to make no difference where the tabs are, full up, partially down or full down.

So generally I feel that Veem have nailed the sizing of the props spot on, we seem to be right in the ball park of all the sea trail data I have seen for this engine/gearbox/hull combo. The lack of top end is disappointing but not the end of the world. It is wonderful just to have a boat that is finally performing as it should at cruising speeds. But I would like to cure this ventilation if possible and was wondering if anyone has come across this problem before and if so how they went about fixing it.

It is important to note that we have installed a new Furuno 1 kW Chirp sounder with a fairing block on the port side. It is slightly inboard of the prop shaft, I'd say at least a foot. It's about a foot in font of the main engine so at least 15 - 20 feet forward of the props. All of the other sounders on board are not "through hull", they are the internal "oil bath" style that attach to the inner skin of the hull so their signals must penetrate the hull laminate. I hope to hell that this is not the problem but am starting to suspect it as the port side is definitely worse that starboard.

I look forward to hearing your thoughts. Thanks again.

Sherwy.

I think you have identified the issue with the port side 1kW transducer fairing block. At this stage you can either move it to centerline within the transducer's specs or use one of the new style that transmit through the hull.

Cabo used to have mold inserts for factory installed transducer blocks that would then be flush mounted and would not through turbulence into the propeller as you are experiencing.

I was told that the new CHIRP sounders don't perform well unless they are mounted through the hull. (externally) The internal "oil bath" style was not an option.

I spoke today with a friend who is a naval architect. He feels that the sounder is most likely the issue. The vertically mounted fairing blocks end up being asymmetric in shape because of the vee in the hull. This causes a directional swirl which disturbs the flow in front of the prop. He has seen this style of transducer cause issues even when they were mounted a "long way" forward of the props.

I guess I'll have to move the bugger!

Talk to the engineers at Cabo as they will tell you the perfect location to mount the transducer and where they recommend. Keep in mind the fairing block for the 1 kw is quite large. I don't remember ever seeing a transducer mounted that far foward on a Cabo from the sounds of it. But I cannot remember. Center bilge under the generator seems to ring a bell for locations of transducers on some, in the center bilge at the front of the engine room on others. In the Lazzarette was where the oil bath ones were always mounted.

All the transducers on this boat are mounted just off centre at the front of the engine room so we have run out of room there.... I might have to go under the generator at the back. And you are right, the fairing block for a 1kW CHIRP is bloody enormous! I guess I'll need another one.

Sherwy.

Call Cabo and see what they have to offer for you. They are very knowledgable about their boats and where to place things and many times even have drawings and measurements.

That's where the plot thickens, I have zero faith / confidence in the local Cabo Rep. Does anyone have any good contacts at Cabo?

Sherwy.

Just call or email the factory directly with the phone number on their website and ask to speak to one of the engineers there.......tell them what you're trying to do and they'll get you to the right person.

Hello Gents,

I won't bore you with the sordid details of the saga that has played out since my last post in April but here it is in a nutshell. Moved transducer - still ventilating - port gearbox failed - remove, rebuild an re-install gearbox - yay happy days! 36.2 knot top speed @ 2350 RPM and 25 knots cruise @ 1750 RPM @ 150 LPM.

So it was the gear box slipping all along, not ventilation from turbulance from the transducer.

We have started developing some cavitation burns near the roots of the blades on both sides of each blade. The prop speed had almost completely eroded away after only 50 hours. Now at 100 hours the blades themselves have started to errode.

I have given the props to Colin Lough at performance propellers here in Brisbane, he is confident he can tweak them to fix the issue, he has had good success in recent months on similar vessels. I'll keep you posted.

FYI if you are interested in hearing my rant / saga over the last 7 months let me know and I'll post the full story. Get a couple of beers and big bucket of popcorn, you will laugh, you will cry, it is an epic tale of triumph despite some of the worst customer service and advice I have experienced in 20 years in this industry.

I would talk to Veem on the prop burn first as they should warranty it and come up with a fix for the prop burn. Usually the Veem equipped Cabo's didn't get prop burn, just the Michigan wheeled ones.

A lot of the hub burn I've seen has been attributed to mismatch between hub and strut diameter or incorrect location of shaft zincs. If the wheel hub is larger than the strut it will likely cause this issue but Veem usually asks this question specifically to avoid it. If the wheel is larger, a chamfer on the leading edge of the barrel may help. A shaft zinc located too far aft will also cause turbulence that can lead to burn and can also restrict water flow to the strut cutlass bearing causing premature failure, I always locate them 1-2" behind the shaft tube on the forward end of the shaft and never at the aft end (like I see all too often!).

Do tell.........

Please do tell.

You just cannot leave an intro like that hanging...

CAptn J,

I've been in touch with Austal props and the Veem engineer who spec'ed them for us, sent them a whole heap of photos and had zero response. Very disappointing when you pay top dollar. I'll give the Teinbridge's a go next time!

I'll post my rant about customer service later tonight! Sorry to keep you hanging, I've been flat out.

Really? Every boat I've ever worked on has had shaft brushes AND zincs on the shafts.