Cabo 43 FB Performance with 28x40 props

Did the RPMs & speed recently change or is this the way it's been? The advertised speed generally means new, and light so you're not too far out depending on current and sea state. Having the props tuned may get you closer.

If you're bottom is clean and the boat does not have tons of added weight to it. You're missing some horsepower somewhere and would look at the engines as to why you're not achieving 2350 rpm's. How many hours do the engines have on them? When was the last time you're fuel filters were changed and what is the condition of your air filters? When was the last time the engines were serviced by a MAN certified mechanic?

It's been a few years since I've run a 43' FB, and I do remembering them cruising at 30-31 knots with the 800's. The Cabo's like to run with a good amount of trim tabs down in order to achieve their cruising speed. The difference is usually about 2 knots between having no tabs and having the trim tabs down in the right position.

There's a lot of pounds in that "except". Add a thousand or so in people....
What did the Man guy say about it? Tuning the props can get you an extra knot or 2. Between that and the tabs and stripping the boat you'd be just about there.

That shouldn't be enough weight to effect speed this much. We did a survey seatrial on a 43 with 900 common rails and had 6 people on board and tools and gear and it didn't effect our speed any. It looks like you're going to have to cut the props as long as the engines are making power. I would have someone inspect the turbo's and make sure they're 100% before cutting props.

You all have it correct in new filters, clean bottom, full tanks and check the tabs. Are those the "stock" props?

Good to hear, what is your cruise and top speed now?

How fast is it running now? I spent a few days at the 2005 Miami Boat show running against a 43 Cabo in a boat that had lower cruise and top end speeds than the cabo did yet I was faster. According to the guy that designed the 43, Cabo was a little "optimistic" in their advertised speeds.

Depending on engines they used to run around 28.5 cruise and 32 top. I think the one with 900 common rails that I seatrialed did 34 knots tops......It's been a while and a lot of boats in between. CABO never uses trim tabs in their testing. Most boats are run as delivered to the dealer. No hardtop or anything, 100 gallons of fuel, full water. I did some of the seatrials and tests where those numbers came from. When you factor in that with trim tabs the boat picks up 2 knots, it more than makes up for the weight/drag differences of fuel and hardtop. So the factory numbers should be a touch lower then what you see in real life. However I've run about 75-100 Cabo's since I've run the last 43' I ran, so I cannot remember what performance numbers were with each engine package. But I ran them with C12's, 820 mans, 900 mans, etc etc etc

That sounds about right. The engine manufacturers consider cruise "rpm" to be 80% load, or 1950rpms with non-electronic diesels which is what Cabo would have published as their figures. Which put it around the 27.5 knots which is what I think those did with the smaller engines......

Hello Gents,

some clients of mine just imported a 43 flybridge to Australia. The props were massively undersized (long story) so we have just bolted on a brand new set of Veem Seastar's, 28.5x37 to go with the MAN 2848 LE 403's. (14.6 litre v8, mechanical injection, 800HP 1:1.733 ratio g/box)

Boat is finally performing like it should in the cruising RPM ranges 1800 RPM= 26.5 knots and 162 litres per hour.

However we now have a ventilation problem in the upper RPM ranges, above 2100. Seems to happen on the port side more than the stbd.

Any ideas out there?

Cheers,

Sherwy.

By "ventilation problem" do you mean a dynamic instability at the higher speeds with the boat leaning to one side (port, predominantly in your case) or are you describing something else?

The 43' Cabo did have a tendancy to lean towards one side or the other at cruise, which had to be corrected with trim tabs. More weight and windage up top amplified this, such as a tower.

To the poster with the Veems. I think the problem is in the propellors and the increase in diameter. Cabo never used over a 28" diameter on the 43' to the best of my knowledge and the increased 1/2" has put them too close to the pockets and is creating cavitation between the blades and hull pockets when spinning the engines beyond 2100rpm. The boats would already have issues from propellor burn near the hubs on the backside of the blades about an 1" above the hub and the length of the blade in that section with the 28" Michigan propellors, but not the 28" diameter veems. I believe this was caused by the propellors being too close in proximity to the hull pockets. It also tended to show up more on the Michigans with owners who were good at using the trim tabs to maximize speed at cruise rpm, which reduced slippage and loaded the propellors a touch more than not using the trim tabs. Although many other brands of fast SF tended to have this issue as well.......

The increase in 1/2" pitch means the props sit 1/4" closer to the hull, so big deal. Having had a lot of experience with propeller root burn, I can tell you that most of it was related to propeller design, especially at the root where the blade geometry meets the hub and had nothing to do with tip clearances to the top of the propeller pocket. The older Michigan Wheels had issues until they redesigned them, and the Veem's always managed the root cavitation much better than MW and did not have the subsequent "burn" at the propeller hub. This was more a design challenge to handle the incoming flow off the Strut Barrel/legs into the Propeller. I don't buy into any of your Trim Tab comments as they relate to propeller root burn or performance, you are not affecting what you term "slippage" and "loading" of the propeller.