Fairline squadron 58

[MapisM]

For MapisM --nevermind fussing over flywheel size in your recent post ! ,it's the hull form In my view that's more important

Oi, I never said that the fw is a crucial issue in a boat choice - more a curiosity than anything else.
Besides, if we should always stick to what really matters in a boat, the whole forum could be hosted on a notebook computer, I reckon.
Clue scattered cushions, u/w lights, ancam... You name it!

 

[jfm]

Its those flat bits that generate the lift

There is a lot of stuff written on hull form by people who don't understand fluids and physics so beware what you find on the internet and in some books. The above statement is a typical example and it is obviously 100% wrong. Spray rails deal with spray and have but a marginal impact on lift. Portofino, if I removed the spray rails and the chine flats from your boat she would still plane just the same as she does today. Apart from the annoyance of spray rising up to at least the chine, you wouldn't even notice. If you extended WL's ferretti spray rails back to the transom, no-one would notice the effect at all.

 

[stillwaters]

I think the 58 runs at displacement speed better than many other planing boats due to its low profile and therefore low cg - so it doesn't roll at these speeds as much as other planing boats. I travelled at 10 knots on our 58 for about 30% of the time but often had to speed up to take advantage of the hydrodynamic stability one achieves when on the plane. So it's never going to operate at slow speeds as well as a displacement hull would, so personally I think I'd be inclined to go for a boat designed to go at 10 knots if that's what you intend to do 90% of the time. There must be something that meets your accommodation needs? Trader? Fleming?

As far as the forward cabin is concerned, they're definitely noisier but at least you can more easily tell if the wind picks up overnight - in the midships cabin I've found I'm blissfully ignorant!

Thanks for that, it really confirms my own thoughts, and even though I was trying to talk myself into thinking that I might be able to keep the other half happy with the interior she wants, I guess she will just have to put up with the Taiwanese-style that seems the norm on SD's after all.
Btw, I hate being blissfully unaware whilst on board - if I wake up at night in total silence, then I know something's wrong.
J.

 

[Cheery]

There is a lot of stuff written on hull form by people who don't understand fluids and physics so beware what you find on the internet and in some books. The above statement is a typical example and it is obviously 100% wrong. Spray rails deal with spray and have but a marginal impact on lift. Portofino, if I removed the spray rails and the chine flats from your boat she would still plane just the same as she does today. Apart from the annoyance of spray rising up to at least the chine, you wouldn't even notice. If you extended WL's ferretti spray rails back to the transom, no-one would notice the effect at all.

Indeed, it's a spray rail, not an aileron!

 

[Portofino]

There is a lot of stuff written on hull form by people who don't understand fluids and physics so beware what you find on the internet and in some books. The above statement is a typical example and it is obviously 100% wrong. Spray rails deal with spray and have but a marginal impact on lift. Portofino, if I removed the spray rails and the chine flats from your boat she would still plane just the same as she does today. Apart from the annoyance of spray rising up to at least the chine, you wouldn't even notice. If you extended WL's ferretti spray rails back to the transom, no-one would notice the effect at all.

Agree- did not mean ALL the lift ,- the correct name for those flat sections in the V (which is 23degrees Btw ) are Lifting strakes – these are different from spray rails in that, besides deflecting some water and spray from the hull, they are also intended to provide dynamic lift to help lift the hull higher out of the water. That is not the intention of spray rails, which are only designed to deflect spray - not to provide any dynamic lift. .Apologies for the misleading nomenclature .

Just trying to make it a little more understandable , highlighting there's an overlap in roll resistance at D speed with some (not all -agree) between planning boats and D speed boats .
In fact chines ,lifting stakes and spray rails can contribute to that compared to a round bottom with these features abscent.
@ anchor on a calm bay when a wave comes in from a passing ferry etc ( comparable boats ) seem to roll a lot more and ours ,does not .Indeed you can hear the wide chines slapping down at near enough right angles to the water a few times as they quickly damp the roll .lifting strikes stay underwater resisting roll all the time .
Where as a less chined and "lifting streaked " boats just bob about from one side see /sawing about longer and with grater swings -albeit a lot .quietly -ATBE as much as poss .
Running @D speed the anti roll characteristic is amplified making for a surprising comfatable flat level ride @8-9knots or so.
So what iam saying is look at the underwater hull sections for wider chines and wide ish lifting stakes -going all the way to the transome - you will tend to find them more in the deeper the V .
Shallower deadrise or V ,ie flatter lift generating sections like the Ferretti pic ,with abscent lifting strikes and a not so pronounced hard chine will roll more , than a comparable FB with those features in the hull.
Of course with a FB there's other factors like higher CoG issues , but the OP can compare different FB hulls ,

I just saying yup a P boat @D speed does not necessarily roll about -any more ,infact sometimes less in my case to the extent that he should dismiss buying a P with the intention of 80-90% usage @D .

I,know I look at things from unusual angles , but for me start at the hull , every time which will translate into ride /seakeeping ,which translates into enjoyment and usability and increase acceptance of all who sail in her.
Mid cabin vs bow cabin , internal FB stairs vs external , SS chain vs gal ,all these things ,though nice -in the marina -- any perceived benefits they bring are blown away by poor ride /seakeeping ,-crash bang ,walup , rock n roll etc .
AIMHO

 

[jfm]

Agree- did not mean ALL the lift ,- the correct name for those flat sections in the V (which is 23degrees Btw ) are Lifting strakes – these are different from spray rails in that, besides deflecting some water and spray from the hull, they are also intended to provide dynamic lift to help lift the hull higher out of the water. That is not the intention of spray rails, which are only designed to deflect spray - not to provide any dynamic lift. .Apologies for the misleading nomenclature .

Erk, we are at risk of serious thread drift that I don't have appetite for. All I wanted to correct above was the notion that lift comes from flat surfaces, because that is wrong. Spray rails or lift strips (they are the same thing whatever name you choose) do have an impact on hull performance at high speed because they separate the water flow from the hull earlier, and that impacts drag (materially, at high speed). But that is a different thing from the suggestion that flat surfaces provide lift while angled ones by implication (the surface of a V hull) don't. I don't want to get into a big discussion on drag and flow-separating edges/strips at high speed, because that's a whole different topic.

.lifting strikes stay underwater resisting roll all the time ....the Ferretti pic ,with abscent lifting strikes and a not so pronounced hard chine will roll more , than a comparable FB with those features in the hull.

Spray rails/lift strips make ZERO difference to boat roll at anchor, really. The idea that spray rails have an impact on at-anchor roll is pure fantasy.

.

 

[Portofino]

Lifting strakes are not the same as spray rails ,it important to recognise the difference .
How ever in the interest of not wanting to thread drift I,am happy to stay in the diff camp and will let readers make there own minds up
http://www.aeromarineresearch.com/tbdp6/strakes_and_sprayrails.html

 

[Chris_d]

Lifting strakes are not the same as spray rails ,it important to recognise the difference .
How ever in the interest of not wanting to thread drift I,am happy to stay in the diff camp and will let readers make there own minds up
http://www.aeromarineresearch.com/tbdp6/strakes_and_sprayrails.html

FWIW I agree, I'm not an expert but I always understood that the perfect hull for planning is completely flat, however water is rarely flat hence the compromise of a vee section. The flatter the vee the faster the boat, but the deeper the vee the better it is through waves, hence the lift rails to regain lift lost to the deep vee angle.

 

[MapisM]

All I wanted to correct above was the notion that lift comes from flat surfaces, because that is wrong.

Yes, as long as it's only Archimede's principle at work to provide lift - i.e. statically.
But dynamically, it's a different story, and I think the point Chris_d is making is a good one.

Spray rails/lift strips make ZERO difference to boat roll at anchor

Agreed.

 

[jfm]

Lifting strakes are not the same as spray rails ,it important to recognise the difference .
How ever in the interest of not wanting to thread drift I,am happy to stay in the diff camp and will let readers make there own minds up
http://www.aeromarineresearch.com/tbdp6/strakes_and_sprayrails.html

The writer of that article defined spray and lift rails differently from how we all define them, so of course they're different, based on his/her definitions. Did you actually read and understand the thing you linked to? Seriously?

 

[jfm]

the lift rails to regain lift lost to the deep vee angle.

But dynamically, it's a different story, and I think the point Chris_d is making is a good one.

Can you explain why lift is lost by a V hull surface compared with a flat one, if both have the same horizontal component of surface area (and AoA and everything else are equal)?

The rails/strips direct the water flow off the bits of the hull out of the water, and at high speed (ie not a Ferretti 150) that reduces drag and increases lift, but the lift increase is a result of that process of separation of the water flow that is being pumped across the hull surface frictionfully; it is not due to the flatness rather than V-ness of the strips.

 

[[2068]]

When people talk about lift, they usually mean trim, i.e. how the upwards force produced by the water in contact with the hull varies from stern to bow on a hull that has a pointy bow and a flat stern. In flat conditions, the hull / surface area not in contact with the water is mostly not relevant.

It's fairly well known that flattening off the hull at the stern will generate increased lift there at moderate speeds and above. Also, imagine replacing the forward 50% of the hull with something that tapers rapidly to a knife edge: the bow will drop until enough hull is in the water to support it.

 

[Deleted User YDKXO]

Shallower deadrise or V ,ie flatter lift generating sections like the Ferretti pic ,with abscent lifting strikes and a not so pronounced hard chine will roll more , than a comparable FB with those features in the hull.

Only one thing wrong with that. Its not borne out in practice at least not in my experience. I've had 13 different boats including 10 flybridge boats and without question size for size my 3 Ferrettis have been more resistant to rolling than any other boats I've owned despite their lack of lifting strakes, spray rails or whatever at the stern. Why? Firstly they're wide, secondly they're heavy and thirdly wherever possible major weights are placed low down along the centre line of the boat. I'm no expert but IMHO factors like that are far more important to resisting roll than elongated spray rails and lifting strakes

FWIW size for size the worst boat I've had for resistance to rolling was a Targa 48 which had a reputation for being an excellent sea boat. So it was if you were going into a head sea or with a following sea but in a beam sea, particularly at slow speeds, or at anchor, the thing rolled like a pig. This was due to the fact that it had a relatively narrow beamed deep V hull and that was far more of a factor than having loads of lifting strakes or spray hulls nailed on the hull

 

[Portofino]

Can you explain why lift is lost by a V hull surface compared with a flat one, if both have the same horizontal component of surface area (and AoA and everything else are equal)?

The rails/strips direct the water flow off the bits of the hull out of the water, and at high speed (ie not a Ferretti 150) that reduces drag and increases lift, but the lift increase is a result of that process of separation of the water flow that is being pumped across the hull surface frictionfully; it is not due to the flatness rather than V-ness of the strips.

V vs flat : - re lift V looses lift because the force is vectored away from the vertical ,so the steeper the v the more lift is lost .
The flat shoe box lid type all of the lift force is perpendicular (90degrees) to the water and the lid and lifts it more ,or it sinks less .
Extrapolating take a piece of paper lay it flat on the water and a another ,this time -fold itin two and place it side on , one will float ,t,other will not float ,the side on ,one .
But the flaw here is the variable beam that you have written in with "same surface area "
Carry on folding the paper from flat through various deadrise angles -V,s- to eventually fold it in two ,you are reducing the beam .
With boats you can have the same beam and different deadrise V therefore a greater wetted area with more friction .
As I said earlier I think we are in different camps re deffintions ,differences of let's call them hull appendages other than perfectly smooth and round .

I recognise the difference in spray rails and lifting strakes .It's I bit like me speaking EN and you insisting to speak Fr at an EU conference ,insisting it me using the wrong language

Lifting strakes improve lift ( handy when you start to fold that paper ) and can deflect spray .
Spray rails just deflect spray .

Here's sorry another article on lifting strakes .--pretty self explanatory
https://books.google.co.uk/books?id...AA#v=onepage&q=lifting strakes design&f=false

 

[baylabayla3288]

Can you explain why lift is lost by a V hull surface compared with a flat one, if both have the same horizontal component of surface area (and AoA and everything else are equal)?

The rails/strips direct the water flow off the bits of the hull out of the water, and at high speed (ie not a Ferretti 150) that reduces drag and increases lift, but the lift increase is a result of that process of separation of the water flow that is being pumped across the hull surface frictionfully; it is not due to the flatness rather than V-ness of the strips.

Compare this with how effectively Volvo's vertical blade trim system is able to create lift. Longitudal strakes that extends all the way aft on a deep V acts the same way as the water flow is more diagonal versus the bottom panels. For slower or medium speeds the drag caused by stakes extending all the way aft is probably higher than the countering lift effect so therefore in sub 30 knots speds the stakes are shorter i guess. Large flat chine sections with negative angles stabilizes the transversal heel at speed in turns. I've heard that these are used commonly with IPS drives to fight the heel. This is why pods usually do not work well on an un-modified shaft drive hull. Also vide spray strakes in the bow causes slamming, Look at Botnia Targa, they use very narrow strakes and chines. They run very soft in a head sea but very wet.

 

[Portofino]

Only one thing wrong with that. Its not borne out in practice at least not in my experience. I've had 13 different boats including 10 flybridge boats and without question size for size my 3 Ferrettis have been more resistant to rolling than any other boats I've owned despite their lack of lifting strakes, spray rails or whatever at the stern. Why? Firstly they're wide, secondly they're heavy and thirdly wherever possible major weights are placed low down along the centre line of the boat. I'm no expert but IMHO factors like that are far more important to resisting roll than elongated spray rails and lifting strakes

FWIW size for size the worst boat I've had for resistance to rolling was a Targa 48 which had a reputation for being an excellent sea boat. So it was if you were going into a head sea or with a following sea but in a beam sea, particularly at slow speeds, or at anchor, the thing rolled like a pig. This was due to the fact that it had a relatively narrow beamed deep V hull and that was far more of a factor than having loads of lifting strakes or spray hulls nailed on the hull

I did say All Other Things Being ,Equal

I thought I explained ,kinda appolgied for the F150 pic as it was in my P bucket .
Yes you need to do a proper sea trial ,to see if it suits you .
Recently we we're very disappointed with a Riva52 ,slammed to 8uggery .
I,ll be hunting one down on the hard and expect to see why at first glance of the hull.
Of course your past and current Ferettis have nice wide beams which will contribute to roll resistance ,because of the increase in wetted area and general bouyoncy that has to pushed in as it tries to tip .

 

[MapisM]

Can you explain why lift is lost by a V hull surface compared with a flat one, if both have the same horizontal component of surface area (and AoA and everything else are equal)?

Well, if by "can you explain" you mean in theoretical terms (with vectors and so forth), I'm afraid the short answer is no, I can't.
At least, I should try harder and stay awake for longer than I would like to...
...with no guarantee of a proper scientific explanation, anyway!

Otoh, in empirical rather than theoretical terms, I would have thought that Chris_d post already said it all, albeit briefly.
I'll try to make another example anyway, including your constraint on the same H component of hull surface and same AoA.
Let's assume to compare a deep V hull with a flattish V hull - both with no rails at all, to keep things simple.
Same beam, same LWL, same H component of hull surface, and same AoA while on the plane.
Empirical evidence tells us - as I'm sure you will agree - that the deeper V hull "slams" less, when hitting waves at speed.
But now, think about it: isn't what we call wave slamming just the result of a higher dynamic lift of the flatter hull?
I mean, it's just a matter of action-reaction, at the end of the day: if the deeper V hull cuts through the waves more, and "rebounds" less than the flatter one, then by definition its hydrodynamic lift is lower.
Btw, in turn this means that it's also less efficient and burns more fuel, but that's another matter altogether...
...and when Magnum installs engines as big as yours on their 50 footer, they know that fuel burn ain't a big concern for their clients, anyway!

PS: fwiw, I agree that in principle rails can ALSO reduce the wet surface, hence drag.
But I suspect it's a bit of a side show, at any speed. For proper hull ventilation, they didn't invent steps for nothing...

 

[jfm]

V vs flat : - re lift V looses lift because the force is vectored away from the vertical ,so the steeper the v the more lift is lost .
The flat shoe box lid type all of the lift force is perpendicular (90degrees) to the water and the lid and lifts it more ,or it sinks less .
Extrapolating take a piece of paper lay it flat on the water and a another ,this time -fold itin two and place it side on , one will float ,t,other will not float ,the side on ,one .
But the flaw here is the variable beam that you have written in with "same surface area "
Carry on folding the paper from flat through various deadrise angles -V,s- to eventually fold it in two ,you are reducing the beam .
With boats you can have the same beam and different deadrise V therefore a greater wetted area with more friction .
As I said earlier I think we are in different camps re deffintions ,differences of let's call them hull appendages other than perfectly smooth and round .

I recognise thdifference in spray rails and lifting strakese .It's I bit like me speaking EN and you insisting to speak Fr at an EU conference ,insisting it me using the wrong language

Lifting strakes improve lift ( handy when you start to fold that paper ) and can deflect spray .
Spray rails just deflect spray .

Here's sorry another article on lifting strakes .--pretty self explanatory
https://books.google.co.uk/books?id...AA#v=onepage&q=lifting strakes design&f=false

That explanation holds no water. Excuse pun. Your "vector" sentence isn't correct. Sure there is a horizontal component to the vector if the hull surface is angled, but the port and starboard sides cancel each other out, and you're left with the vertical component of the vector, which is the same on a flat hull as a deep Vee.

I didn't say same surface area, I said "same horizontal component of surface area", which is a rational assumption when comparing flat//shallow Vee/deep Vee hulls, AOTBE. Obviously a deep Vee has more surface area, but that isn't the point. It's the horizontal component of the area that matters in this context.

As I said, strips do have an effect at higher speed, but the effect is nothing to do with "more lift because they are flat not angled". The effect arises mostly because the strips throw the water off the hull, the main effect of which is that there is less drag (less pumping losses, if you like). There are also other hydrodynamic effects, at high speed.

After wasting 3 minutes reading your previous link I hope you don't mind that I haven't clicked on your new link above and read it. As your pervious link showed, you just see one sentence that you think supports your argument and then post the link, when in fact if you had read the whole thing you'd have seen that it didn't. (In case that is unclear, the previous article you linked to defined V hull spray rails as rails on the boat's topsides, between the chine and the side deck, and it defined lift strips as the ones under the hull, that we are discussing here. It most certainly didn't say there are 2 sorts of strips under the hull, which is precisely my point as regards the nomenclature). If you wont read your own linked-to articles please don't expect me to!

I love your "I recognise the difference in spray rails and lifting strakes". Under the hull, they are both toblerone sections stuck on the hull surface - both exactly the same. How can they be different when they're the same thing? If I show you a load of boats in a boatyard can you say to me "That one's a lift strip but that one's a spray rail"? Of course you can't. Well, perhaps you can

 

[[2068]]

That explanation holds no water. Excuse pun. Your "vector" sentence isn't correct. Sure there is a horizontal component to the vector if the hull surface is angled, but the port and starboard sides cancel each other out, and you're left with the vertical component of the vector, which is the same on a flat hull as a deep Vee.

This would be relevant if a deep vee hull had the same deadrise angle from stern to stem, but that's not the case.
Most boats have flatter sections at the stern, more weight at the stern, and the deeper vee sections of the bow spend most of their time out of the water, or only slighly in contact with the water.

With a pointy bow, effectively you are creating a forward section of the boat that is flying most of the time (i.e. doing nothing) but then will have to "go deeper" to generate more lift, compared to the flatter sections behind it, causing a softer ride in the chop.

 

[jfm]

FP, I think you're working on the premise that a flatter hull generates more Newtonian lift than a deep Vee, for the same horizontal component of hull surface area. But it doesn't. On an AOTBE basis, the lift of the flat hull is surely the same as the deep Vee, isn't it?