Propeller tunnel: yes or no?

[PowerYachtBlog]

Aside from being disturbed (and rudders even more so) by an awful P-bracket installation, as your pic clearly points out.

You really want to go there... Actually now you arrived. It is too late

I spoke to a couple of guys who worked with Amati about this P-bracket thing after the post here some months ago. Was it March?
But anyways it is a thing from the eighties or before which he carried in his boats, and he never bothered of changing.
If it is not broken why fix it. May boats of that time are like that to be honest.
I was also told about a story about a client who was buying a 56 back in the days, and wanted to move away cause of the purchase (year 1999) and after a sea trial by Mr. Amati himself changed his mind.

In the end the only Itama build in Rome (Cantieri Navali di Roma) with P-brackets mould box was the 55, which was designed by Gianfranco de Mennato and also is on V-drives, with Amati directing the project.
All FG Itamas have the P-bracket mould box.

Honestly P you make a storm in a tea cup about these P-brackets thing. It does not really effect navigation does it. You have the virus now be careful.

 

[PowerYachtBlog]

Tunnels allow engines to be placed further aft in the hull. That creates more usable real estate forward of the engines. Likewise v drives for that matter.

Hull shape is a whole other kettle of fish. Cigarettes might be fast but it’s tough to sell them to folk who want to drive their family and friends to a quiet anchorage to spend the day playing in the water and enjoying fine food and wine.

nah you really do not need them for that.

I think a lot of the famous designers like Olesinki saw performance benefits in them during testing, and how in the nineties he actually stepped up to use them.

Since going on with tunnels BO started going for a deeper Vee hull, eighteen versus the fifteen closing of the previous models.
Interesting the less deadrise hulls do perform better then the deeper ones in rough waters. The 36 Turbo is fifteen (a perfect weight distributed boat and considered among the best to come from Oundle) as the old 50 (not Squadron) flagship.

The problem with tunnels is that they are weight distribution delicate.

Try a Fairline 36 Corsica and a 37 Phantom.
These boats have an identical hull design (both close at 18), with Fairline moving the engines further aft in the later 1994 to 96 37P model for a more spacious second stateroom.
The difference in bow high ride is impressive, about over five degrees in planning speed 18-25 knots, which reduces to a couple degrees above 26/27 knots.
Interesting though the 37 Phantom does give a bit more performance (top end) when it gets going, as with identical engines I did reach one knot more in performance. in similar conditions.
Both tested boats had Cat 355hp six cylinder engines and the 37P reached 32.5 knots WOT versus the real hard to get 31 knots of the 36 Corsica.
For this test I had no data about propellers, if identical etc
It is possible that once you go up and running the further aft located engine helped with clearing the hull forward, hence the boat ran more after a certain speed.

 

[Portofino]

I think I just watched a video clip of a dog’s water bowl?

Tunnels allow engines to be placed further aft in the hull. That creates more usable real estate forward of the engines. Likewise v drives for that matter.

Given that - in comparison to, say, automobile design - naval architecture is a mix of back-of-a-fagpacket inspiration and post-hoc rationalisation the consequential effects on running angle, comfort and handling then get addressed by lumping weight forward, adding interference etc.

Hull shape is a whole other kettle of fish. Cigarettes might be fast but it’s tough to sell them to folk who want to drive their family and friends to a quiet anchorage to spend the day playing in the water and enjoying fine food and wine.

The water level in the bowl is acting as a spirt level .Sorry for not pointing that out .It’s not spilling hardly moving back .Illustrates the AoA .

NA is an exact science no “ fag packet drawings “
The guy with the book was the very first professor ( head of Dept ) of NA iirc Harvard or MIT or both .
American gov sponsored a load of tank testing + hull pressure testing during WW2 .It’s all maths and graphs .
Before WW 2 it’s alleged the mafia commissioned his boats to out run the cops in prohibition with his “ rum runners “
In all weathers .
He was about to go down , then Pearl Harbour happened and he ended up designing MTB s and many other military projects .Cos he could and his boats were better .After the war became the first proff of NA .

But it’s like a menu or ingredients you can mix n match bits my “ segments of orange “ and yes there are some abominations out there …..you see them every day .

Just depends which compromises you want , or won’t accept .Or more accurately did not know existed.
Ignorance is bliss ay boat shows these days .Not wrong with that …..if you are attracted to the fold down flap to enlarge the cockpit or the IPS joystick to park it ….fine as long as you are happy .

 

[benjenbav]

The water level in the bowl is acting as a spirt level .Sorry for not pointing that out .It’s not spilling hardly moving back .Illustrates the AoA .

NA is an exact science no “ fag packet drawings “
The guy with the book was the very first professor ( head of Dept ) of NA iirc Harvard or MIT or both .
American gov sponsored a load of tank testing + hull pressure testing during WW2 .It’s all maths and graphs .
Before WW 2 it’s alleged the mafia commissioned his boats to out run the cops in prohibition with his “ rum runners “
In all weathers .
He was about to go down , then Pearl Harbour happened and he ended up designing MTB s and many other military projects .Cos he could and his boats were better .After the war became the first proff of NA .

But it’s like a menu or ingredients you can mix n match bits my “ segments of orange “ and yes there are some abominations out there …..you see them every day .

Just depends which compromises you want , or won’t accept .Or more accurately did not know existed.
Ignorance is bliss ay boat shows these days .Not wrong with that …..if you are attracted to the fold down flap to enlarge the cockpit or the IPS joystick to park it ….fine as long as you are happy .

Ah, gotcha with the bowl of water. Have indeed heard of Lindsay Lord and, whilst not meaning to disparage naval architects, it does have to be admitted that back in the day it was more about graph paper, “let’s see what happens if we do this” and then rationalising the outcome, rather than VR modelling.

Anyway, if called on to put money on it, I’d still bet that on something like a Princess 52 (as per the OP) the tunnels are more about helping to gain interior real estate than performance. Might be wrong, though. I often am.

 

[marcochi76]

Anyway, if called on to put money on it, I’d still bet that on something like a Princess 52 (as per the OP) the tunnels are more about helping to gain interior real estate than performance. Might be wrong, though. I often am.

I was hoping for the opposite. But I have to admit that the interior layout, with the full beam master cabin, is very generous.

 

[ari]

The advantage of tunnelled props is to reduce shaft angle. This does (as mentioned) reduce draught slightly, but it has a greater advantage that no one has mentioned, which is to reduce the height of the saloon (or deck if a sports cruiser) floor above the engines as they're not sticking up as much at the front as they are flatter. The knock on from this is reduced deckhead height, reduced flybridge height above it, etc. Very helpful given today's obsessions with maximising interior volume.

Someone mentioned that they move the engines further back increasing space in front of the engines - I'm afraid I can't see that, perhaps they are thinking of vee drives?

Portofino always makes me laugh with his not at all biased opinions

 

[benjenbav]

Someone mentioned that they move the engines further back increasing space in front of the engines - I'm afraid I can't see that, perhaps they are thinking of vee drives?

That would be my confusing up and down with forward and back, I think.

 

[MapisM]

Honestly P you make a storm in a tea cup about these P-brackets thing.
It does not really effect navigation does it.

Actually, it would have never popped to my mind again if it weren't for your claims of "gold standard" and "props free in the water flow".
So, if you think it was a storm in a teacup, you're barking up the wrong tree, 'cause I'm not the one who started it.

Ref. affecting navigation or not, I don't have the faintest idea, but obviously you also don't.
In fact, if your rudders are useless at speed (and I'm just referring to what you said - I wouldn't even dream to make that up!), there must be some weird reasons.
Now, whether disturbed water flow hitting the rudder blade is one of them and to which extent, that's anyone's guess, obviously.
The only thing I'm sure of about that behaviour, is that it's neither normal nor desirable.

 

[Portofino]

I was hoping for the opposite. But I have to admit that the interior layout, with the full beam master cabin, is very generous.

It’s a pity you can’t go on a no obligation test drive in the prospects in the sea states you want to realistically improve upon the ride with your existing Prinny .

Find one that works in your sea states first then reshuffle the pack of cards of “ must haves “

Try before you buy .
The Med brokers are more amenable to this .U.K. are still stuck in 1776 with deposit first then sea trial second.

We looked at the dock hauled out at a Rivarama 44 at Monaco marine .Deep V , MAN 700 s Rolla SSteel props , had it all but the engine access was terrible and it was hotel wise one large open plan space down below .
I knew it was a great sea boat having seen them slice through waves / seas that my stern drive Portofino 35 was slamming forcing me to back off .

later we went out on a Rivale 52 a three cabin boat solving the hotel thingy , MAN V 8 s yummy I thought.

We had just the day previously has a ride in a Itama 54 off S Tropez in big seas.

This Riva 52 dreadful .It was calm with a slight swell , but started to slam in the mid twenties .The sea tbh looked pretty calm .This was 2013 .Before we got 2 miles out of Monaco ( dealer lives there ) the look on wife’s face killed the deal .
I just turned round and went back in .

Then I new nothing about boat hulls , indeed thought S/Sker back in the Braithwaite days and a zillion Queens awards for industry and glossy adds in the back of Sunday Times supplement must know what they are doing ?

Only to find out I had to slow down / back off while others just sliced through…..more or less like for like sizes .

Thats what piqued my interest quest to find out why the differences .

Sounds like you are in the same place .

 

[Portofino]

Actually, it would have never popped to my mind again if it weren't for your claims of "gold standard" and "props free in the water flow".
So, if you think it was a storm in a teacup, you're barking up the wrong tree, 'cause I'm not the one who started it.

Ref. affecting navigation or not, I don't have the faintest idea, but obviously you also don't.
In fact, if your rudders are useless at speed (and I'm just referring to what you said - I wouldn't even dream to make that up!), there must be some weird reasons.
Now, whether disturbed water flow hitting the rudder blade is one of them and to which extent, that's anyone's guess, obviously.
The only thing I'm sure of about that behaviour, is that it's neither normal nor desirable.

Just to clear this rudder thing up ……over last winter following PYBs advice I got engineers to have a look .
Diagnosis was the helm pump was failing ( some seal wear thingy ) They sent it off for rebuild but the rebuilder said it was toast that we simply fitted a new part , lubricated the stern gear , linkages , arms etc and hey presto the steering is back to normal .It turns at speed now as enough hydraulic pressure is generated .

Not sure why you harbour these grudges P if iam honest and keep regurgitating ancient by forum stds stuff , you re looking very anti Porto so some reason only known to you ?

 

[marcochi76]

It’s a pity you can’t go on a no obligation test drive in the prospects in the sea states you want to realistically improve upon the ride with your existing Prinny .

Find one that works in your sea states first then reshuffle the pack of cards of “ must haves “

Try before you buy .
The Med brokers are more amenable to this .U.K. are still stuck in 1776 with deposit first then sea trial second.

We looked at the dock hauled out at a Rivarama 44 at Monaco marine .Deep V , MAN 700 s Rolla SSteel props , had it all but the engine access was terrible and it was hotel wise one large open plan space down below .
I knew it was a great sea boat having seen them slice through waves / seas that my stern drive Portofino 35 was slamming forcing me to back off .

later we went out on a Rivale 52 a three cabin boat solving the hotel thingy , MAN V 8 s yummy I thought.

We had just the day previously has a ride in a Itama 54 off S Tropez in big seas.

This Riva 52 dreadful .It was calm with a slight swell , but started to slam in the mid twenties .The sea tbh looked pretty calm .This was 2013 .Before we got 2 miles out of Monaco ( dealer lives there ) the look on wife’s face killed the deal .
I just turned round and went back in .

Then I new nothing about boat hulls , indeed thought S/Sker back in the Braithwaite days and a zillion Queens awards for industry and glossy adds in the back of Sunday Times supplement must know what they are doing ?

Only to find out I had to slow down / back off while others just sliced through…..more or less like for like sizes .

Thats what piqued my interest quest to find out why the differences .

Sounds like you are in the same place .

You are right to the point Porto. I am super happy and in love with my V39. It is really perfect for the size.
But as usual in life we want to look further.

At the last Cannes yacht show I visited a lot of boats, even budgets that I will probably never be able to afford:
Princess V55: the wife's choice. It's a hotel. It has everything: shafts, enclosed salon, open air salon + sunbed, full beam master cabin ...
Pershing 6x: simply too much (I wanted to visit the 5x but it was not displayed).
Sunseeker Superhawk 55: I was disappointed. It looks too much an expensive toy.
Fairline Targa 45: I prefer my V39
Fairline Targa 50: I realized I prefer the Princess style.

I had an appointment to visit the RIzzardi InFive but I had no time. A shame.

But I found a jewel: Filippetti s55.
I had the pleasure to discuss with the creator: GIovanni FIlippetti, super nice guy.
For info, his father Fausto was co-founder of Pershing.
And effectively the s55 reminds a lot of a Pershing (old 56?).
I also managed to organize a sea trial the following week.
What an experience! Arneson + 2 MAN V8 1200 !!!
Unfortunately, the sea was super flat. I would have loved to test it in rough conditions.

That could be a very good candidate....in 10 years...when maybe I can find it at half the price and I will have won at the lottery !!!

 

[marcochi76]

Snapshot from a video of the sea trial

 

[MapisM]

Not sure why you harbour these grudges P if iam honest and keep regurgitating ancient by forum stds stuff , you re looking very anti Porto so some reason only known to you ?

And how can I possibly know the reasons why I'm looking whatever I'm looking to your good self?!?
See, everything I mentioned was referred to something you said, not ne.
Christ, as when you pretended it's normal that deep vee boats can't steer unless you slow down first (go figure! ), just to make another example.

That said, I wasn't up to speed on this matter: if eventually you found that the culprit was "only" the steering pump, good for you.
Doesn't change the fact that the exposed P-bracket support is a nonsense, anyway.

As well as going for the man rather than the ball if I say something you don't like: that's another thing that doesn't change hard facts, I'm afraid.

 

[MapisM]

Unfortunately, the sea was super flat. I would have loved to test it in rough conditions.

Actually, that's just a cliché, in spite of its popularity.
For checking the attitude/behaviour/reactions of a planing boat, you NEED a super flat sea.
A boat can have a tendency to list on one or both sides, or be too sensitive to load distribution, or start porpoising at some speeds, to name but a few classic defects.
But, good luck in noticing all that, when you are hanging for dear life!

 

[Portofino]

You are right to the point Porto. I am super happy and in love with my V39. It is really perfect for the size.
But as usual in life we want to look further.

At the last Cannes yacht show I visited a lot of boats, even budgets that I will probably never be able to afford:
Princess V55: the wife's choice. It's a hotel. It has everything: shafts, enclosed salon, open air salon + sunbed, full beam master cabin ...
Pershing 6x: simply too much (I wanted to visit the 5x but it was not displayed).
Sunseeker Superhawk 55: I was disappointed. It looks too much an expensive toy.
Fairline Targa 45: I prefer my V39
Fairline Targa 50: I realized I prefer the Princess style.

I had an appointment to visit the RIzzardi InFive but I had no time. A shame.

But I found a jewel: Filippetti s55.
I had the pleasure to discuss with the creator: GIovanni FIlippetti, super nice guy.
For info, his father Fausto was co-founder of Pershing.
And effectively the s55 reminds a lot of a Pershing (old 56?).
I also managed to organize a sea trial the following week.
What an experience! Arneson + 2 MAN V8 1200 !!!
Unfortunately, the sea was super flat. I would have loved to test it in rough conditions.

That could be a very good candidate....in 10 years...when maybe I can find it at half the price and I will have won at the lottery !!!

Tnx for mentioning
Filippetti Sport 55 : that's how a wonder sails | Yachting News.
I must say every day is Indeed a school day on here.Lots of complimentary articles and history on the internet .

The only caveat I will throw in is from reading a MAN FB forum who’s members are MAN techs ( Eng speaking) the perceived wisdom is NOT to cruise them over 2000 rpm .This inc todays new ones as well as old.
Wether there’s anything in this is another matter but imho it’s should be taken seriously.Personally I set my cruise under 1800 rpm , just over reaches 30 knots .

Surface drives are no doubt super efficient and especially the faster you go as there’s minimal parasitic drag from a shaft in front or rudder behind .Also Uber manoeuvrable at speed as you angle the drives FWIW .

But if you scroll down the link above to the rpm / speed spreadsheet and where to listen to MAN factory trained techs on there helpful FB site ( quick @ sorting customer out issues WW ) then 2000 rpm = 30 knots .

Yes it can wrung out do 40 knots lightly loaded or what ever but I will wager you will blow your engines PDQ .Or get on personal terms with the warranty team techs as they will be always calling in to fix stuff .

Not sure in a 5 yr old used modal ( zero warranty ) I would be comfortable even setting them @2200 rpm for a long cruise .
Of course nowt wrong with the occasional Italian tube up a bit of WOT or near …..I am just questioning the cruising speed .Yes it shows exactly just how efficient Arnesons are esp in the top end …..

If those MAN guys wouldn’t have said what they preach about this 2000 rpm thingy then I wouldn’t be telegraphing this info on here .As said Personally I am “ in the clear “

 

[marcochi76]

To be honest, it was not a very useful sea trial. The broker drove the boat. To my impression, he was not very skilful with Arneson.
He did not take car to correctly look for the best setup. He left everything in auto (which by the way should work as well).

He did not push the boat over 1890 rpm. At that revs, we were doing 35knots, burning 190 l/h per engine. Ouch!!!
Looking at the MAN specs, that means the engine were at approx 95% load. I was expecting a better efficiency with Arneson.

 

[marcochi76]

Tnx for mentioning
Filippetti Sport 55 : that's how a wonder sails | Yachting News.
I must say every day is Indeed a school day on here.Lots of complimentary articles and history on the internet .

Porto, be careful, those data are from the version with IPS.

This is a test with the MAN 1200. The numbers are better than per my sea trial.
https://www.powerandmotoryacht.com/boats/boat-test-and-review-of-the-filippetti-s55

 

[marcochi76]

And if I compare numbers of the IPS version vs the MAN version, I would certainly go for the IPS, which is non-sense for that kind of boat !!!

 

[Portofino]

Porto, be careful, those data are from the version with IPS.

This is a test with the MAN 1200. The numbers are better than per my sea trial.
https://www.powerandmotoryacht.com/boats/boat-test-and-review-of-the-filippetti-s55View attachment 165472View attachment 165474

Arh those are better The 1950 / 1980 @ 37-38 knots is more like it .
Safe if you listen to the MAN techs .I could live with those numbers .

Yep IPS it’s just a marketing gimmick they are not slamming the door @ Flourida shows in the face of newbies .

Its great he’s mimicking Pershing but I wonder from a touch / feel ( I don’t know ) what the actual differences are with the FG Pershings? Also not sure wether you realise Amarti meddled with Arnesons and made a few for clients .
The Itama 75 a FG born boat made in same factory as Pershings @ Forli is also a surface drive boat with MTU V16 s .

Talking to a FG guy a few yrs ago at the Monaco show and he told me they have a special NVH division which reckons to be constantly working on refinements , once perfected are broadcast across the groups range of boats .
Thats fine in a huge multi group funded by a Chinese bank ….but can a small down the road family firm keep up ? Poring €€ into the black hole of R+D ?

Anyhow @ Genoa you see loadsa of small family builders, dad the sons and daughters standing by there boats .
They all look excellent to touch and feel and it’s a wet show so if you are keen they will take you out .
TBH I have missed this guy .

 

[Portofino]

To be honest, it was not a very useful sea trial. The broker drove the boat. To my impression, he was not very skilful with Arneson.
He did not take car to correctly look for the best setup. He left everything in auto (which by the way should work as well).

He did not push the boat over 1890 rpm. At that revs, we were doing 35knots, burning 190 l/h per engine. Ouch!!!
Looking at the MAN specs, that means the engine were at approx 95% load. I was expecting a better efficiency with Arneson.

View attachment 165470View attachment 165471

load is % fuel used compared what’s available.
So if you divide the 193 into 240 ( est ? burn at WOT ) it equates to spot on near as dam it 80 % .
Thats about right .80 % load .
If you press that house button top LHS you could have accessed more data inc the load .But as said a rule of thumb is to mentally % the fuel burn with a clean boat .

That broker knows his onions ……under 2000 rpm and he’s set them on 80 % load .= good man .

The knots varies depends on fouling , weight - tanks and trim + sea state .But as I said 35 , 36 , 37 ….I could live with those numbers .

For perspective my 14.5 M x 4,2 M 2 cabin 13 L boat at 1890 rpm will do 30 knots and burn 100-L per side .
I get 1/2 the fuel burn but loose 5 knots .

Normally and sympathetically I run them 1780 @ 28 knots and 85 L per side approx ( fouling / weight depending) 75 % load .They are 2003 and 1100 hrs .So I err on sympathy.l
Max fuel burn WOT is 140 L / hr per side and we see 38 knots 100 % load …..but obviously I never really go there .

Rated WOT is 2200 …..you should be able they say just go over a little as we did ^ .This is 3 months after it’s lift in btw .

You have time as we had I know it’s tricky the pull of a fifty something over a step up to a forty something.
Wife told me a fifty something was too big .We have property in Antibes as well so the hotel side card slipped to the bottom of the deck in our circumstances. So the cards that surfaced in the top 10 were performance and seakeeping orientated…..so we could widen our scope of usage go out when others were port bound , not be afraid of lumpy seas blowing up in the afternoon etc travel in comfort etc etc .

On those rare occasions excess folks turn up they hotel themselves on dry land .

So think carefully over the 2 vs 3 + cabin conundrum…….you are left funding the berth + maintenance + and as you already have seen @ potential 380 L / h fuel bill cruising .

We framed Portofino 53 , suckered in by local dealer , Pershing s .50, s , not the Arnesons one the shaft , Riva 52 .
It got even sillier when we were shown round a Manhattan 60 ….until Wife banned me from looking .

The money we saved we tipped into property.

The more time elapses since 2013-2014 when I switched the more and more sure we made the right decisions.No regrets .