Pershing 5X surface drives

[jointventureII]

To be fair on the 108 we have the tabs about half way "down" on the gauges, in reality the difference between fully up and fully down is probably 10 inches. On the gauge it gives you the impression that the tab is being fully immersed at 90°!

 

[PowerYachtBlog]

Amati didn’t design it . .

Seriously how far backs the ER , the balance and ……are the tabs really functioning in terms of the drives/ pitch playing a part in running attitude?

With surface drives it does not make much a difference. Infact most if not all surface drives boats have aft located engines.
Some exceptions coming from the eighties and nineties....
old Pershing 54 and 48, some of the few Itama's fitted with sds (like the few 46, 38, 54, and 56 made).

Tabs work perfect with the Rizzardi.

 

[Portofino]

There’s nothing wrong with a bit of tab down running in my book .No criticism implied from me .
Its a balance ( no pun intended) of running angle versus speed / fuel efficiency .
Most fast leisure boats by fast those designed to run around 30 knots + run better when trimmed flat .
The extra theoretical drag , well real drag of dipping a flap 1/4 or so in a 45 ftr or even 1/2 in a P108 ftr is way overcome by the better / flatter running angle .
I notice it .
For those with full instruments you also see the load decreases as well as fuel burn when a bit of flap is applied to increase the speed a few knots .
Similarly as Jointventurell pointed out running tipped up on one side is inefficient.They run better flat in the transverse plane too .According to the instrumentation I see .

For those with lardy FB s chugging about in the 18-25 knot speed range you probably find your flaps are either 1- pretty ineffective or 2- alway needed just to get up and cruise at any semblance of level ness to see forwards .Or just don ‘t bother playing around and run around with the bow high all day .Which is pretty common practice from what i see .Or just don’t have the instrumentation to see fuel burn , load and dare I say it EGT s ……..Oh Yeh the high speed running attitude has an effect on those too .


For me in my particular boat because the engines are in the middle ( there is a second cabin + en-suite in the stern areas ) , I stand on the helm on one it means the fuel tanks are behind the motors .This means 2000 L of fuel on a 14 M hull has a noticeable effect on the balance so I use more tab down after brimming , which ease up to zero as the fuel weight burns off .By say a 1/4 full I need no tab at all , or it just works the other way drags it down .
The 500 L water tank is under the saloon floor ….on or around if not Fwds of the CoL make no difference Wether full 500 kg or not .

How ever for me personally with surface drives in a 45-60 ftr as I said I would be disappointed with mid to low thirties cruise .
It needs to be N of 40 somewhere between 40-45 cruise to gain a wider efficiency benefit for the aggro / maintenance of the stern gear .Like the OTAM I posted .
A massive P108 is a different kettle of fish you have to compare that with its size competitors other 110 ftrs .
A San Lorenzo A 96 or SL 110 ( or eq ? ) is never gonna see 30 - 35 + knot cruise all day .

 

[Portofino]

To the OP by way of example here is a Pershing 56 on Arnesons the boat LHS of shot slowly catching me.I followed him out of our marina a French chap returning to France that day .
I am running from memory around 29 knots ( 78 % load - under 1800 rpm something like 1780 rpm ) but is that speed difference in this case significantly worth it ??


Itama vs Pershing 56 vs aeroplane.

Now if he creamed past me at 40 + knots like a OTAM or magnum than I would be impressed and all over “ yacht world “ that evening .



Additionally PYBs vid of the Rizzardi 45 running at 1910 rpm would be in the 90 % load range fwiw , certainly over 80 % .As we have the same engines and similar hull sizes for me to make a meaning full comparison.

 

[MapisM]

To be fair on the 108 we have the tabs about half way "down" on the gauges, in reality the difference between fully up and fully down is probably 10 inches. On the gauge it gives you the impression that the tab is being fully immersed at 90°!

I never checked the fully up/down difference in terms of absolute excursion, but 10" sounds like a helluva lot to me, even with the large and long flaps that I suppose you must have on a 108 footer.

What I am more familiar with are the BCS tabs which based on the gauge must be fitted to the Rizzardi in the video, because that's what I have also on my boat.
And their mechanical gauges are razor accurate - forget the Bennett's stuff, they are toys in comparison!
If properly installed, when you see anywhere between -2 and 12 degrees on the gauges, you know for sure that they are exactly in that position, within a one degree error at most.

Now, that Rizzardi was doing 33 kts with 6 degrees of tabs.
Of course, every hull is different, but to put it in perspective, in my boat that corresponds to the WOT speed with zero flaps, and by lowering them "only" 6 degrees at that speed, she loses at least a couple of kts.
And if the boat is listing a bit, typically due to crosswind, 2 or 3 deg on one side is more than enough to straighten her.
In other words, even a few degrees do make a difference, with those trim tabs.

These are the reasons why I found unusual such (relatively) strong usage at 30+ kts.
But PYB already addressed that, when he said that he sacrificed a bit of speed based on sea conditions.
I didn't consider that because the sea seemed pretty good in the video, but it's always difficult to assess the waves based on onboard videos...

 

[MapisM]

Three hours for 100 nm is not bad, and about 5.7 liters per nm consumption is better to IPS in similar size.

Agreed, that's indeed remarkable.
Out of idle curiosity, is that boat powered by the 730 or the 800 hp MANs?
I'm only asking because, while 5.7 L/Nm is pretty good in absolute terms, if calculated on the 35 kts average it corresponds to 200 L/Hr, which at 1900 rpm means a rather substantial engines load, possibly triggered by the surface drives.
For comparison, my V8/800 burn about 10 L/Hr less at the same rpm, even if of course at slower speed, due to larger size/weight, so ultimately with a higher L/Nm (7.5, give or take).
There's a hope that less stressed engines will last longer - fingers crossed!

 

[Portofino]

I think they run 730 s with 730 Hp .I run the slightly earlier 700 s ( same block ) in essential the same hull size .So a meaningful comparison is applicable.
200 L hr 1/2 tanks would also be in the lower 1900 rpm range but equates to low thirties knots .Let’s call it 31 but equally depending on sea state etc could be 32/33 ? It’s never going to equal in identical conditions and weight ( liquids ) carried because iam dragging shafts , P brackets and although tiny something they call a rudder .Well looks like rudders.
So like for like cruising in Co the Rizzardis only got a small fuel efficiency gain .

That was my opening point to the OP is a 1000 Hp on surface drives in todays ( if available) P 50 really enough to make the difference?? .
As said I get Miami - Bahamas @ 40 knots or better 42-45 knots .No shaft drive equivalent size can do that .
I get the inter island inc Med island hopping thing .
I get and regularly do 100 miles in 3 hrs along with many other sports boaters on as well even in the Med .

If it’s fuel saving as we all know the sum of fuel very quickly dissolves into the over all costs of running a boat upwards of 15 M
So back to outright speed going at such others on shafts can’t reach and dam the fuel bill , the extra bill if that P 50 had a pair of 22 L V12 MAN 1500 s and could sit all day at 42 knots throwing up a pretty rooster tail .

But it’s got a pair of 12.8 L inline CATs rated at 1000 Hp with the assistance of a supercharger .
The cooking 12 . Something in-line CAT churns out a ball park todays industry 850 Hp sans supercharger.

Now any one coming from a 40 ft sports cruisers ….now is the time to ditch superchargers imho .Not wed with them !
As they say there is no substitute for cubes .Applies to boats with sporty intentions too .

 

[PowerYachtBlog]

Agreed, that's indeed remarkable.
Out of idle curiosity, is that boat powered by the 730 or the 800 hp MANs?
I'm only asking because, while 5.7 L/Nm is pretty good in absolute terms, if calculated on the 35 kts average it corresponds to 200 L/Hr, which at 1900 rpm means a rather substantial engines load, possibly triggered by the surface drives.
For comparison, my V8/800 burn about 10 L/Hr less at the same rpm, even if of course at slower speed, due to larger size/weight, so ultimately with a higher L/Nm (7.5, give or take).
There's a hope that less stressed engines will last longer - fingers crossed!

Man r6 - 730hp. The load was kept at 80/82% give or take. The 5.7 number was taken at 33 knots consumption 190 lph total.
I usually take the higher number of consumption and the least in speed when working litre per nm.