Portofino
Well-Known Member
Stern lacks lift !
Bernard O should have listened to Ray Hunt /Sonni Levi -et al - carried the V all the way to the transome and ---- fitted "lifting Strakes "
Sorry couldn,t resist
Fairline squadron 58
- Thread starter brannan77
- Start date
Stern lacks lift !
Bernard O should have listened to Ray Hunt /Sonni Levi -et al - carried the V all the way to the transome and ---- fitted "lifting Strakes "
Sorry couldn,t resist
PowerYachtBlog
Well-Known Member
Stern lacks lift !
Bernard O should have listened to Ray Hunt /Sonni Levi -et al - carried the V all the way to the transome and ---- fitted "lifting Strakes "
Sorry couldn,t resist
Much worse is that the Squadron 58 moves a lot of water forward till about 22 knots. Considering the position of the engines, and it has semi-tunnels, I just about do not get why it does that.
Some details which where deemed spectacular in its best days look 50/50 nowadays.
Example is the flybridge line of extension (+1 foot) looks an after thought, and that central radar arch nowadays make her look old.
What is very good is the following; cockpit and deck connection, galley in that position, and fore cabin layout is also great.
It sill sold a lot considering it was in many ways an improved 55 Squadron with a larger fly-bridge.
None the less apart my critical eye it is a lovely boat.
stillwaters
Well-Known Member
Firstly, thanks to all for the valuable input about the Sq58 which following on from the OP's interest (was it really that long ago?), I had subsequently asked about its displacement speed usability. Good job there's an adjudicator in the madhouse.
However, this lift thing, fwiw, it surely isn't that difficult to see that a V hull couldn't possibly impart as much lift pro rata as a flat-bottomed one, is it?
Imagine that there are 3 flat panels of equal size and weight, and they are of sufficient weight that they only just float on water. Now bend one of them down its centre line at 90 degrees, thus giving it a 45 degree deadrise on either side if suspended V down. Next, suspend all 3 panels at the same height over water, one suspended horizontally so that it will fall exactly flat with its full face on the water, another suspended vertically so that it will fall edge first onto the water and then the final one suspended so that it will fall on the point of the V at an angle of 45 degrees either side (the median between the other two). The horizontal one will hit the water with very little disturbance, just a shock wave in all four directions. Also it will hardly submerge beyond the surface of the water, if at all. The vertical one, however, will enter the water with virtually no disturbance but will submerge significantly before returning to the surface horizontally. The V shaped one, though, will submerge less than the vertical one but more than the horizontal one before bobbing back to its buoyancy equilibrium. It will also throw more water out on each side than either of the other two. This is because the reactionary forces of all three are different. Reactionary force, or lift if you prefer, is the force that each individual molecule of water imparts back to any object imposing force upon it. So, when an object with a flat horizontal surface presses its weight down on the water molecules below it, they can only compress so much before they try to pass the weight/force to their adjacent molecules. However, all of the other molecules for a distance down in the water are also receiving similar forces so, apart from those near the edges, which are able to dissipate some of the imposed force outwards towards unburdened molecules, they then impart their reactionary force in the only remaining direction left to them, upwards. With the vertical panel, though, only a small proportion of molecules, those under the edge, will be subject to this force and can far more easily dissipate it via unaffected adjacent molecules. It's easy to see (isn't it?) that the 45 degree median between these two examples will react approximately somewhere between them, mixing as it does, both vertical and horizontal force. The water molecules below the two angled surfaces which are having force imposed on them will therefore end up dissipating this force both upwards and outwards in approximately equal measure, ie reactionary force will be on average at 90 degrees to the surfaces, or 45 degrees from vertical.
Still a reactionary force (lift), of course, but less than that imparted to a horizontal surface. Of course, with the flatter deadrise angles typical of the sort of boats we have, the ratio of lift will be between these two examples. V hulls are always actually a compromise. Racing hydroplanes utilise virtually flat hulls because they produce more speed with less power input than V hulls. However, flat hulls produce a series of problems that are not desirable to pleasure boaters, Firstly, they are hard to steer or manoeuvre. They would also be uncomfortable in anything but flat conditions, not to say dangerous if travelling at speed when hitting waves or wash. V hulls are the compromise that provide an acceptable level of lift, speed & fuel economy whilst also providing an acceptably comfortable (and safe) ride together with acceptable handling.
Strakes surely have to be for another day, if ever, don't they?
J.
However, this lift thing, fwiw, it surely isn't that difficult to see that a V hull couldn't possibly impart as much lift pro rata as a flat-bottomed one, is it?
Imagine that there are 3 flat panels of equal size and weight, and they are of sufficient weight that they only just float on water. Now bend one of them down its centre line at 90 degrees, thus giving it a 45 degree deadrise on either side if suspended V down. Next, suspend all 3 panels at the same height over water, one suspended horizontally so that it will fall exactly flat with its full face on the water, another suspended vertically so that it will fall edge first onto the water and then the final one suspended so that it will fall on the point of the V at an angle of 45 degrees either side (the median between the other two). The horizontal one will hit the water with very little disturbance, just a shock wave in all four directions. Also it will hardly submerge beyond the surface of the water, if at all. The vertical one, however, will enter the water with virtually no disturbance but will submerge significantly before returning to the surface horizontally. The V shaped one, though, will submerge less than the vertical one but more than the horizontal one before bobbing back to its buoyancy equilibrium. It will also throw more water out on each side than either of the other two. This is because the reactionary forces of all three are different. Reactionary force, or lift if you prefer, is the force that each individual molecule of water imparts back to any object imposing force upon it. So, when an object with a flat horizontal surface presses its weight down on the water molecules below it, they can only compress so much before they try to pass the weight/force to their adjacent molecules. However, all of the other molecules for a distance down in the water are also receiving similar forces so, apart from those near the edges, which are able to dissipate some of the imposed force outwards towards unburdened molecules, they then impart their reactionary force in the only remaining direction left to them, upwards. With the vertical panel, though, only a small proportion of molecules, those under the edge, will be subject to this force and can far more easily dissipate it via unaffected adjacent molecules. It's easy to see (isn't it?) that the 45 degree median between these two examples will react approximately somewhere between them, mixing as it does, both vertical and horizontal force. The water molecules below the two angled surfaces which are having force imposed on them will therefore end up dissipating this force both upwards and outwards in approximately equal measure, ie reactionary force will be on average at 90 degrees to the surfaces, or 45 degrees from vertical.
Still a reactionary force (lift), of course, but less than that imparted to a horizontal surface. Of course, with the flatter deadrise angles typical of the sort of boats we have, the ratio of lift will be between these two examples. V hulls are always actually a compromise. Racing hydroplanes utilise virtually flat hulls because they produce more speed with less power input than V hulls. However, flat hulls produce a series of problems that are not desirable to pleasure boaters, Firstly, they are hard to steer or manoeuvre. They would also be uncomfortable in anything but flat conditions, not to say dangerous if travelling at speed when hitting waves or wash. V hulls are the compromise that provide an acceptable level of lift, speed & fuel economy whilst also providing an acceptably comfortable (and safe) ride together with acceptable handling.
Strakes surely have to be for another day, if ever, don't they?
J.
Portofino
Well-Known Member
+1all agreed .
I,tried that route in more general terms with post# 34
" 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 of hull all of the lift force is perpendicular (90degrees) to the water and the lid - so lifts it more ,or it sinks less .
Extrapolating take a piece of paper lay it flat on the water and another ,this time -fold it in 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 ."
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PowerYachtBlog
Well-Known Member
You are going into to much complications for a Fairline 58 Squadron which btw is not the first seventeen meter motor yacht with a Vee shape, and is not even a deep Vee.
It closes at 17 degrees aft and a lot more boats have come before her with a similar shaped hull. 10 - 19 degrees closing aft is called a medium Vee shape hull.
Most boats of the same size and type have a similar closing Vee 15-18.
When you have a photo like that for me it means a few things, the most obvious is that the balance of weight (usually it is the engines and fuel tanks) is not at the optimal position.
That means that the designer first designed the hull, and the other came after.
It can also be that the designer had an optimum position for the engines but then Fairline for accommodation selling reasons moved away from it. A foot backwards can make a difference as well.
You can be impressed how much every little detail can be challenging in hull design, and then designers also tend to work different to one another.
It closes at 17 degrees aft and a lot more boats have come before her with a similar shaped hull. 10 - 19 degrees closing aft is called a medium Vee shape hull.
Most boats of the same size and type have a similar closing Vee 15-18.
When you have a photo like that for me it means a few things, the most obvious is that the balance of weight (usually it is the engines and fuel tanks) is not at the optimal position.
That means that the designer first designed the hull, and the other came after.
It can also be that the designer had an optimum position for the engines but then Fairline for accommodation selling reasons moved away from it. A foot backwards can make a difference as well.
You can be impressed how much every little detail can be challenging in hull design, and then designers also tend to work different to one another.
Portofino
Well-Known Member
Many thx to Sillwaters ' reminds me of A level Chemistry -days -ultimately everything can be broken down and explained at a molecular level .
I ve got some pics to further contribute
To JFM (and anybody ) -- what's the correct description and more importantly the function of those flat sections approx 1/2 way up the V .
JFM has referred to them as " bits of Toblerone " tacked on ,or words to that effect .-see post # 38 -bottom para
They sure don,t look tacked on to me ! Or vaguely Toblerone in x section !
Here's the stern of a sq58 for PYB
I ve got some pics to further contribute
To JFM (and anybody ) -- what's the correct description and more importantly the function of those flat sections approx 1/2 way up the V .
JFM has referred to them as " bits of Toblerone " tacked on ,or words to that effect .-see post # 38 -bottom para
They sure don,t look tacked on to me ! Or vaguely Toblerone in x section !
Here's the stern of a sq58 for PYB
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petem
Well-Known Member
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MapisM
Well-Known Member
Apologies to the OP for coming back to the rails o/t, but I owed you a follow-up.
Back to the time point, I don't think it's just a matter of "split second".
The fact that time is essential, as you also confirm, does not translate only in a softer wave impact. It's the whole hull behavior that is affected.
If it were just a matter of "delayed" dynamic lift in deep V hulls, eventually (over a given period of time) the pitching in a head sea of a deep vs. a flat V hull should be the same - the only difference being that the latter has a more hectic/sudden reaction than the former.
But this is not the case. As we all know, the pitching of the deeper V hull is not only smoother, it's also significantly lower, overall.
To my simple mind, this means that the deeper V hull is less affected by (i.e. has a lower) Newtonian lift.
And again, if there are other reason, I'm missing them completely.
Besides, I vaguely remembered to have read something that Levi (RIP) wrote in his book "Milestones In My Designs" on the subject of rails (among MANY other components).
Unfortunately I don't have the whole book, but after a bit of digging in my files, I found some abstracts - though only the IT version, I'm afraid.
I tried to quickly google for the original EN version, but I couldn't find it online.
Anyway, just in case anyone has the real thing, what I'm going to mention is taken from his "Technical Appendix A".
First of all, there is a short but clear sentence that summarizes very well what we were discussing:
"The purpose of longitudinal rails is to increase dynamic lift and reduce the wet surface."
For the records, this is my own translation, backward from the IT version that I found, but I'm reasonably sure that it's accurate - assuming that also the EN->IT was, that is!
Now, it's worth noticing the "and": Levi clearly mentions both these distinct effects.
And he goes on suggesting that in his experience it's better to have rails running longitudinally along the whole hull, all the way to the transom (as in the Itama pic posted by Portofino), though with some pros and cons, on this point.
But again, also this recommendation clearly comes through as based on both these distinct pros of rails: dynamic lift increase AND wet surface reduction.
All that said, to be honest, I couldn't find in his writing any explanation of the rationale behind the lift increase part, while he goes in further details about the wet surface reduction - which to me is as intuitive as the lift, actually.
Maybe he was also blinded in his theories by the flat surface "myth", as you called it. Who am I to know...?
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MapisM
Well-Known Member
Mmm... I'm not sure to agree, W.
To my eyes, that photo just seem taken at lowish (barely planing) speed, or even decelerating. And while steering to stbd, on top of that.
Totally impossible to draw any meaningful conclusion just based on that single image, imho...
MapisM
Well-Known Member
Just out of idle curiosity, do you remember what sort of boat was that red one on your port side?
Thanks for the nice pics anyway, well worth watching in a cold November night! :encouragement:
PowerYachtBlog
Well-Known Member
Agreed!
But taking away that my other opinions came after helming a Squadron 58.
Which I think has a sweet spot of around 24 knots, it really does ride well at around that speed and above it.
Uricanejack
Well-Known Member
Nick_H
Well-Known Member
I've spent 20 or more hours cruising alongside a Sq58 at 20 knots, and I don't recognise that behaviour at all. I've just looked at a video I have of it, and it runs beautifully at this speed, with level trim and no excessive bow wave. I wish I could post the video, but not sure how.
Uricanejack
Well-Known Member
Funny, the whole argument about why a boat planes is much more interesting than a Fairline 58(I have no clue what one of those is).
Or what the heck a spray strakes is.
Just applying a bit of logic.( which might be completely wrong) Lift? would that not come from power? speed? angle of attack? A boats max speed being a function of its length, breadth and depth. long narrow shallow boats being the fastest. until they reach a max where they just wont go any faster. a nice smooth shape reduces drag.
To go faster the boat needs to come out the water. Now the fast boats are short fat shallow boats instead of canoe shapes?
In order to plane you need a lot of power. you need to to have an angle to rise up out of the water. so the boat is no longer floating but lifted out of the water, the lift has to equal the proportion of the weight equal to the lost volume of water being displaced.
Anything which adds resistance would add drag and slow the boat down.
Surly a nice smooth shape would be the most efficient because it would have the least drag.
The angle of attack would presumably need to be steep to get up onto the plane in the first place when going slowly?
As speed increases wouldn't you need the angle of attack to be much less? to reduce drag.
So logically the ideal shape for a boat to plane efficiently.
A bit of an angle at the front to start getting some lift when going slow to get up on the plane in the first place.
Then a very shallow angle a bit further back.
A wide relatively flat smooth surface at a slight angle for supporting the boat near as possible parallel to the water surface.
The bigger or deeper a V shape would increase drag, making the boat slower and less efficient.
Greater V the less surface to provide lift compared to the depth increasing drag.
I would also presume an efficient planning hull would produce a much smaller wake than an inefficient hull at the same relative sise and speed
Or what the heck a spray strakes is.
Just applying a bit of logic.( which might be completely wrong) Lift? would that not come from power? speed? angle of attack? A boats max speed being a function of its length, breadth and depth. long narrow shallow boats being the fastest. until they reach a max where they just wont go any faster. a nice smooth shape reduces drag.
To go faster the boat needs to come out the water. Now the fast boats are short fat shallow boats instead of canoe shapes?
In order to plane you need a lot of power. you need to to have an angle to rise up out of the water. so the boat is no longer floating but lifted out of the water, the lift has to equal the proportion of the weight equal to the lost volume of water being displaced.
Anything which adds resistance would add drag and slow the boat down.
Surly a nice smooth shape would be the most efficient because it would have the least drag.
The angle of attack would presumably need to be steep to get up onto the plane in the first place when going slowly?
As speed increases wouldn't you need the angle of attack to be much less? to reduce drag.
So logically the ideal shape for a boat to plane efficiently.
A bit of an angle at the front to start getting some lift when going slow to get up on the plane in the first place.
Then a very shallow angle a bit further back.
A wide relatively flat smooth surface at a slight angle for supporting the boat near as possible parallel to the water surface.
The bigger or deeper a V shape would increase drag, making the boat slower and less efficient.
Greater V the less surface to provide lift compared to the depth increasing drag.
I would also presume an efficient planning hull would produce a much smaller wake than an inefficient hull at the same relative sise and speed
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jimmy_the_builder
Well-Known Member
Upload it to youtube then paste the video reference within youtube tags here eg if you take this link
https://www.youtube.com/watch?v=shKGIR65rvs
after the v= is the identifier for the video; code it like this in your post
[youtube]shKGIR65rvs[/youtube]
and you get this
Nick_H
Well-Known Member
Here goes:
OK, it worked!
This was on a long trip from France to Menorca, and we did the entire 11 hour trip at 20 knots, so I know that's the speed the Sq58 is travelling.
OK, it worked!
This was on a long trip from France to Menorca, and we did the entire 11 hour trip at 20 knots, so I know that's the speed the Sq58 is travelling.
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stillwaters
Well-Known Member
My previous post, #63, surely demonstrates that as a surface plane becomes more vertical, the reactionary force of the water molecules below it becomes progressively less vertical and more lateral. Hence, there would be maximum reactionary force (lift) upon a horizontal plane and only a minimal reactionary force upon a vertical one ( caused by frictional drag of water molecules as the vertical surface submerges). Therefore, as the deadrise angle increases, vertical lift correspondingly reduces.
benjenbav
Well-Known Member
OK, this is how stupid I am: I watched Nick's "20knot steady-state" video and, at the end, the youtube suggestions which popped up embedded in this thread were: (1) a buyer's guide to the Porsche Cayenne diesel and (2) a couple of live performances of different songs by Leonard Cohen.
And for about 10 seconds I thought: "NickH spookily shares my tastes, except I'm kinda moving towards a petrol..."
stillwaters
Well-Known Member
OK, this is how stupid I am: I watched Nick's "20knot steady-state" video and, at the end, the youtube suggestions which popped up embedded in this thread were: (1) a buyer's guide to the Porsche Cayenne diesel and (2) a couple of live performances of different songs by Leonard Cohen.
And for about 10 seconds I thought: "NickH spookily shares my tastes, except I'm kinda moving towards a petrol..."
You didn't make it to the other live performances, then?
benjenbav
Well-Known Member
You didn't make it to the other live performances, then?
No, dead men singing the blues and planet-killing cars seems to be what youtube thinks I enjoy.