Hull shape how aware are you ?

[Portofino]

On what do you base that statement? It's just your hunch PF; it isn't actually true. If your clinker or smooth dinghies are is sitting at anchor and then a wave comes, the last thing you want is grip on the sea, because that will make you roll in line with the wave. You'd rather have slippy. In any case, the drag/grip effect of all the chines/rails at these water velocities is immeasurable except with instrumentation

As for the rest, you are lost in the fantasy world where you think that a deep vee hull needs lift strips for lift, because in your world a sloping surface doesn't provide enough lift. That defies physics, though I agree it is an oft-quoted concept. If it were true the addition of spray rails to a V hull would cause the boat to sit higher in the water at rest, which obviously is not what happens.

The function of a rail is to shed spray, which is critical to (a) drag in the context of fast boat performance, and (b) dryness on less performance-oriented boats.

Here you can see that the flat chines resist roll or multiple clinks on a clinker .
Plus other stuff about deep V,s static stabilty ---
it's blatantly obvious a round smooth hull section will roll more than a hull with any flat bits to resist
Please read post # 74 and MapishM responce then reconcile it with my point about "hard chines " or wider then normal chines --- more flat bits to resist .

Ray Hunts team and my self be sharing the same fantasy JFM
http://huntyachts.com/mythbusters-the-real-truths-about-the-deep-v-hull-2/


Here it explains the difference between a spray rail and a lifting stake --- some how I think you and MapishM do not realise there's a difference ,or accept lifting strakes exsist or have any function ? I,am talking extra wide ones to look out for that do not peater out .
Remember it's what you can tell looking at the hull form with Mk 1 eyeball ---before diciding of course for a test drive .
http://www.aeromarineresearch.com/tbdp6/strakes_and_sprayrails.html

What's wrong with looking for a few subtle "Hunt " Q,s ------------ it's a boat forum and the hull staring you in the face
(if it's not skirted @ a show )

 

[Portofino]

For those fascinated by hull form ( like Darwin and beak form )
Here's some more evidence from Ray Hunts team -link ---- take a look at the bottom 4 lines below ( sorry I can,t highlight them ) ---- "some are so small they do nothing ----- " etc etc

But my point is some arn,t and you can see that looking around yards --- bit more than subtle .
Btw this stuff is 50 y old Ray Hunt died years ago ,but his legacy live on

Goto discover then ride
http://huntyachts.com/discover/the-ride/


CHINES, LIFTSTRIPS, SPRAY RAILS, ETC. WHAT DO THEY DO?
Primarily their job is to shave water off the hull. A planing boat is trying to out run the ocean, leave it behind, and climb on top, so we want to get the water off the hull quickly. Water attached to the hull means drag and pushing it aside makes waves. Both are wasted energy. A big bow wave may be dramatic but it takes a lot of HP to push water around like that, and the top of that bow wave usually blows back in your face! We want to snuff out bow waves. That is the job of the chine and the lift strips (as we call them) and spray rails. The primary chine is where the topsides meet the bottom; where the hull turns the corner. It defines the running surface. It runs bow to transom. We vary its size and location depending on several factors. We add liftstrips forward on the bottom and run them aft at varying lengths. These strips peel the water off reducing wetted surface cutting skin friction (drag) and redirect the water traveling up the hull to add a lifting component that in turn has two benefits: it helps lift the boat out of the water, and it adds stability. A survey of spray rails at a boat show will turn up every possible shape. Some are so small and round they do nothing. Others are under water all the time, and also do nothing. Some actually are indented into the hull. The water just passes these by. Hunt strips are large and sharp to effectively do their job giving the boat great control, dynamic stability, and a dry ride.

 

[jfm]

Portfofino, you have remarakable ability to think that (a) something written on the internet must be right because its on the internet, and (b) someone is agreeing with you when actually they are disagreeing.

The stuff you have quote supports my position 100% and yours 0%. It says spray rails shed spray. It also says critically "[spray rails that] are under water all the time, ... also do nothing". That is my point: you get the same lift from a deep V as you get from a flat bottomed tea tray, for the same horizontal component of hull surface area and at any given speed (your hand in the sink analogy is deeply flawed but if you can't see that then so be it), despite the many pages written to the contrary on the internet. Spray rails do not contribute meaningfully to lift, despite the fact lots of internet commentators say they do.

I note the article says also that spray rails can "redirect the water traveling up the hull to add a lifting component". That is a completely unexplained and unsubstantiated statement and I don't agree with it so far as normal spray rails are concerned. If the author explained himself we could discuss it more. It might be that the hinkley lift strips peel off the water and direct it slightly downwards, which would create some lift but that is hardly exciting because there is no efficiency gain due to the pumping cost of that and the amount involved isn't meaningful.

The article you linked to also said this: "It’s also important to understand that hard chine boats are generally more stable than round bilged boats. This is because the hard edge of the chine is more resistant to rolling than a nice soft round edge. A hard chined boat equal in waterline beam to a round bilged boat will be stiffer." That is another half-story you get on the internet these days. A hard chine boat will of course have more roll stiffness than a round bilge boat AOTBE, but that comes at a price: if a boat is sitting at anchor in flat water and a wave comes, the hard chine's greater "grip" on the sea will cause the hard chine to lift more than the round bilge. The initial roll is therefore higher. It's all a bunch of compromises and lightweight internet journalism gets nowhere near explaining roll and stiffness properly.

The Hinckley article also says this: "Deep-V has the added advantage due to the deadrise because the planing forces are always working to right the boat. These forces are acting normal to the surface of the hull through the center of lift. On flat bottomed hulls these forces are acting normal to the bottom also, but do not counteract a roll". That is just plain wrong. I don't care that Hinckley wrote it; it's just wrong on every level and completely misunderstands the physics.

Anyway, and I know we have discussed it before, but spray rails do not in general create lift. The very important purpose of a spray rail is to shed spray - that keeps a leisure boat dry, and at high speeds it is critical to efficiency because if the spray is allowed to continue up the hull skin then you have to burn diesel to pump it. Once you shed the spray with a spray rail, you stop burning diesel to pump it. Anyway, we are at "done to death" stage so let's agree to disagree. Best wishes

 

[cvt]

I'm enjoying this pi$$ing contest but if you really want to stir the pot let's introduce the question of placement of strakes relative to the chine (...and the onset of the dreaded "chine-walking"); or an even more controversial subject: the bustle, and what constitutes a "real" bustle and it's hydrodynamic performance.

 

[Capital_R]

Jfm:-

On the unwelcome risk of having to endure your disbelief on two different threads...

(1) you make a good point that righting motion shouldnt be blended with stability, so much as it is. The most comfortable boat in the universe is a giant vertically bouyant pole, right? No tilt at all, even im a hurricane.

(2) I think, as Hinkley say, a V hull planing does give righting motion, and more stability over a round bottom hull. Like a canoe. Physics wise, you're impossible to argue against, using a tea tray with boxed sides as a better form of stability (but not comfort).

3. On your spray deflectors, however, i dont follow you. The water that was once travelling up with force X will either travel until gravity overcomes it.. or it will be deflected by deflectors. The declectors will add some lift by the change in direction, and the absorption of force X by the deflectors, rather than by Gravity, no? Sorry to stick my beak in here, please ignore if that is betrer for everyone. R.

 

[Deleted User YDKXO]

I'm getting the popcorn and beer in because this one looks like it could run and run

 

[Portofino]

Pics hopefully show the difference between a spray rail and lifting strip /rail

These are easy to spot on a hull .

That's a lifting strake /strip running from the stern
It a wedge shape in x section .
The lower one starts at the bow and peters out as you can see - that's a spray rail at the bow 1/3 but in this pic the lower one has morphed into a lifting strip before it ends .

Ps -great pic of underwater exhaust btw and the chine

Spray rails out of the water @ bow 1/3 rd --- ish

Riva --a pancake could n,t be flatter
If I would have seen that 1st I would not have wasted a day in Monaco --95 % certain that's a slammer
Seriously not there's nowt starting @ the stern running fwds --- defo not a "Ray Hunt " job

Lower one that bisects the bow thruster --- any takers .? Spray rail or lifting strip ,or both? -depending position and profile ?
Ends between the straps it quite a wedge shaped there under the mid section and Tolberone shaped as it nears the bow .

What's that wedge cum triangle do -sticking out in the deadrise ( 23 degrees btw ) -RHS on the hull under the last name letter a look below . NB -there one on the other side not visable in pic sorry .
It's not the chine and it sure ain't a spray rail ?

Better pic here
JFM what is it called by most boat designers and what's its function .
Why is it flat ,pararell to the surface water ? What does that fairly wide bit bring to the party .

Hmmm wonder if it has any effect on roll resistance ?
Think Ray Hunts team know .

 

[Portofino]

JFM and MapishM

Do you agree Ray Hunt designed hull work ?---- as they describe on the web link ,

What features can you see on a Hunt style hull ?

Are the features visable ?

Any body has this post raised your awareness of hull shape ?

 

[Bouba]

The obvious difference I see is that the Riva has tunnels

 

[Portofino]

The obvious difference I see is that the Riva has tunnels

Tunnels destroy stern lift .You loose any lift in the V by the props impeding the flow of water in that section .
End up riding bow high ,attitude all wrong .

You can see that - they have had to mess about with the trim .Adding those w shaped premantantly trim tabs and those boxes to mount the movable trim tabs more aft .

Yup is a post production bodge . That's what all that trim stuff tells me

Low deadrise was the ref to pancake .
No lifting strakes /strips it so flat does not need em ---- so they thought the low deadrise would provide the lift .It did ( with the help of the post production bodges to get the right attitude ) but they sacrificed the ride - awfull slammer .
We had to use an awfull of + ve trim too -all the time to keep the bow down .





Plus side you lower the shaft angle -- less fuel burn more efficient in fwd propulsion .
This is even with a v drive gearbox ,cos they shuved the engines as for back as they dare to fit the aft cabins in -twin ,twins from memory .

Easy to get hooked @ a boat show --- what's not to like it's not moving and the griddle looked like a great place to do prawns

 

[stillwaters]

Any body has this post raised your awareness of hull shape ?

No, nothing new yet................but keep going, you're doing a fine job. :encouragement:

Btw, do you run marathons as well?

 

[Blue Sunray]

The most comfortable boat in the universe is a giant vertically bouyant pole, right? No tilt at all, even im a hurricane.

Yep, probably: http://www.ship-technology.com/projects/flip-ship/

 

[jfm]

On the unwelcome risk of having to endure your disbelief on two different threads...

Hi C-R. Hey if you cant take the heat stay out of the kitchen. You write fantasy claiming it to be true; I point out it is fantasy, which you of course know is correct. I don't get the "endure" part and I'm sorry if it is painful, but it's just heat and kitchens Top marks for the entertainment but repeating the same joke isn't a great strategy long term. You could have done a better job writing the fantasy, tbh, then you would be less on the back foot. No worries; beer offer is still open if we find ourselves in same pub

The most comfortable boat in the universe is a giant vertically bouyant pole, right? No tilt at all, even im a hurricane.

Yep

I think, as Hinkley say, a V hull planing does give righting motion,

I don't agree, but we are in "done to death" territory so I'm happy to agree to disagree. Here's a thought to consider though: imagine you're in big beam seas where the face of the wave is more metres than the beam of the boat. If the deep V has more stability, how does it know what horizontal is? Does it just offer stability whereby the boat is kept level to the wave face, rather than to the horizon? What is the point of that? The boat will roll as it is alternately on the face and the back of the wave. A stabiliser system knows what horizontal is and keeps the boat horizontal.

3. On your spray deflectors, however, i dont follow you. The water that was once travelling up with force X will either travel until gravity overcomes it.. or it will be deflected by deflectors. The deflectors will add some lift by the change in direction, and the absorption of force X by the deflectors, rather than by Gravity, no?

Yes that is correct. The amounts are not meaningful, and you are paying fully for that tiny amount of lift by burning diesel so there is no net benefit, but the principle you cite is correct. Thing is, the quantities are tiny, whereas the drag reduction in removing the pumping losses by breaking off the spray is meaningful and "free". The Hinkley article said that: it expressly says the function of the rails is to cut off the spray from rising up the hull surface, and you can see that happening in plenty of pictures.

It follows from this, and Hinckley expressly say it in the linked article, that spray rails that are permanently submerged are totally useless. PF talks of the virtues of his lower rail that goes all the way to the trnasom, but that is a design mistake in a boat that does the modest speeds of his boat. The correct way to design a non uber fast hull is to end the spray rails amidships, which is how my big fat boat is done and many others are done, because once they are 100% submerged rails just induce drag. PF's itama would go faster (not meaningfully of course) if he sandpapered off the back half of his spray rail, but I doubt PF will ever agree that so I'm in agree to disagree territory. :-D

I really think this is done to death now and I'm happy to agree to disagree

 

[Bouba]

Hi C-R. Hey if you cant take the heat stay out of the kitchen. You write fantasy claiming it to be true; I point out it is fantasy, which you of course know is correct. I don't get the "endure" part and I'm sorry if it is painful, but it's just heat and kitchens Top marks for the entertainment but repeating the same joke isn't a great strategy long term. You could have done a better job writing the fantasy, tbh, then you would be less on the back foot. No worries; beer offer is still open if we find ourselves in same pub


Yep


I don't agree, but we are in "done to death" territory so I'm happy to agree to disagree. Here's a thought to consider though: imagine you're in big beam seas where the face of the wave is more metres than the beam of the boat. If the deep V has more stability, how does it know what horizontal is? Does it just offer stability whereby the boat is kept level to the wave face, rather than to the horizon? What is the point of that? The boat will roll as it is alternately on the face and the back of the wave. A stabiliser system knows what horizontal is and keeps the boat horizontal.


Yes that is correct. The amounts are not meaningful, and you are paying fully for that tiny amount of lift by burning diesel so there is no net benefit, but the principle you cite is correct. Thing is, the quantities are tiny, whereas the drag reduction in removing the pumping losses by breaking off the spray is meaningful and "free". The Hinkley article said that: it expressly says the function of the rails is to cut off the spray from rising up the hull surface, and you can see that happening in plenty of pictures

I really think this is done to death now and I'm happy to agree to disagree

Its good to see jfm and Capital R talking:encouragement:

 

[jfm]

Its good to see jfm and Capital R talking:encouragement:

Haha! We're talking and we have a tentative pub date. I just call spades spades = in this case am distinguishing fiction from fact. Nothing wrong with a fantasy novel if it is in the right section of the bookshop

 

[Capital_R]

Hi C-R.

I really think this is done to death now and I'm happy to agree to disagree

Agree. And on all your examples above. I think we all just had different specific situations in mind - but the outcomes we all agree on.

Look forward to that beer. And to taking you deep sea fishing off the back of my mobo. Should have called it Ocean Fantasy.

 

[Portofino]

Yes that is correct. The amounts are not meaningful, and you are paying fully for that tiny amount of lift by burning diesel so there is no net benefit, but the principle you cite is correct. Thing is, the quantities are tiny, whereas the drag reduction in removing the pumping losses by breaking off the spray is meaningful and "free". The Hinkley article said that: it expressly says the function of the rails is to cut off the spray from rising up the hull surface, and you can see that happening in plenty of pictures.

It follows from this, and Hinckley expressly say it in the linked article, that spray rails that are permanently submerged are totally useless. PF talks of the virtues of his lower rail that goes all the way to the trnasom, but that is a design mistake in a boat that does the modest speeds of his boat. The correct way to design a non uber fast hull is to end the spray rails amidships, which is how my big fat boat is done and many others are done, because once they are 100% submerged rails just induce drag. PF's itama would go faster (not meaningfully of course) if he sandpapered off the back half of his spray rail, but I doubt PF will ever agree that so I'm in agree to disagree territory. :-D

I really think this is done to death now and I'm happy to agree to disagree

The article said "some "spray rails submerged are useless along with hull features .I linked that
You have taken that out of context - it was the last few lines .

You have dodged the difference between the under water sections and the bow sections

The lifting strakes / strips --(the underwater bits ) - if done correctly generate enought lift to raise the hull up more out of the water thus reducing overall drag and making the boat go faster .Not slow it down .

If I sanded back the upper lifting strip in the pic torte same L as the lower one , the boat would go slower .lose it's lift and sink more ,creating more drag .

Evidenced here
http://www.totalsimulation.co.uk/spray-rails/


You need to provide evidence to substantiate what you say ,
perhaps with your boat with a shollower deadrise ,less ratio of wetted area compared to a same size with a 23 degree deadrise ,more Kg ratio in terms of hull size and superstructure ,it's just not worth fitting lifting strips as you say to lift it a bit .There are too many other things working against you over 30 knots to nullify and small lift advantage .

Any lift reducing drag is amplified the deeper the V -the same lift gets more wetted up and out .
Taller superstructures will also cause air drag ,so as you say net gain for you marginal .

That does not mean the concept of lift from correctly designed ,placed ,shaped chines ,spray rails and most importantly the submerged lifting strakes ( note the terminology LIFTING ) does not apply to other boats
Mines an old boat rough antifoul etc I can see 38 knots easily cruise all day 32 - Engine load guages mid 80,s %

Yours is good hull too fine entry mod below 20 degree deadrise ,flatter aft sections ,not really a "Ray Hunt " deep V
Gets enough lift from the aft sections ,as said not worth chasing abit more to cruise 1knot faster .
I guess yours is cruise is mid 20 ,s and rarely see 30 + ---that's real world ,cruising stores kg,s +++ fouling etc .

Any ways lets agree to disagree if you wish .

Just for the record the taken out of contexts again below from my post # 82 {{{ this bit }}}




CHINES, LIFTSTRIPS, SPRAY RAILS, ETC. WHAT DO THEY DO?
Primarily their job is to shave water off the hull. A planing boat is trying to out run the ocean, leave it behind, and climb on top, so we want to get the water off the hull quickly. Water attached to the hull means drag and pushing it aside makes waves. Both are wasted energy. A big bow wave may be dramatic but it takes a lot of HP to push water around like that, and the top of that bow wave usually blows back in your face! We want to snuff out bow waves. That is the job of the chine and the lift strips (as we call them) and spray rails. The primary chine is where the topsides meet the bottom; where the hull turns the corner. It defines the running surface. It runs bow to transom. We vary its size and location depending on several factors. We add liftstrips forward on the bottom and run them aft at varying lengths. These strips peel the water off reducing wetted surface cutting skin friction (drag) and redirect the water traveling up the hull to add a lifting component that in turn has two benefits: it helps lift the boat out of the water, and it adds stability. A survey of spray rails at a boat show will turn up every possible shape.


{{{ Some are so small and round they do nothing. Others are under water all the time, and also do nothing. Some actually are indented into the hull. The water just passes these by. Hunt strips are large and sharp to effectively do their job giving the boat great control, dynamic stability, and a dry ride.}}}


I,ll send over a beer next time we meet @ anchor ------ in our real boats

Promise won,t raise this

 

[jfm]

The article said "some "spray rails submerged are useless along with hull features .I linked that
You have taken that out of context - it was the last few lines .

You don't half make me laugh PF! The text you linked to did not say SOME fully submerged spray rails are useless. It said fully submerged rails are useless full stop, ie all fully submerged rails are useless. Which is of course 100% correct, and the back 5m or your lower spray rails is therefore useless according to me and to the article YOU linked to. And all that is self evidently true - there is no spray in the permanently submerged part of a hull.

Here is the text quoted again. It is crystal clear that the author is saying (correctly) that all fully submerged rails do nothing:

{{{ Some are so small and round they do nothing. Others are under water all the time, and also do nothing.}}}

Offer of beer @ Lerins Islands happily accepted, thanks! The sea will soon be warming up!

 

[MapisM]

Fwiw, I also would definitely prefer to continue the debate with a cold beer in hand - either around Lérins, possibly in a day (if any! ) when there's enough space between all boats to have a swim, or maybe around CF, if you would fancy coming there and enjoy a more quiet environment.
But as of now, we can only continue along the lines of cold winter night armchair debates when TV is rubbish, I reckon...

So, ref. this point:

It said fully submerged rails are useless full stop, ie all fully submerged rails are useless. Which is of course 100% correct, and the back 5m or your lower spray rails is therefore useless according to me and to the article YOU linked to. And all that is self evidently true - there is no spray in the permanently submerged part of a hull.

Funnily, I agree that the article supports your rather than PF point, but that's actually one point of the Hinckley webpage I don't agree with.
Not the only point btw - the one you quoted in the second to last para of your post #83 being something they should be ashamed to have written, for instance.

But ref rails length I disagree on two levels:
Firstly, and quite simply, there's no such thing as a fully (i.e. permanently) submerged rail, in P boats - and the faster they are, the more this is true, for very obvious reasons.
Secondly, rails are not just "spray" rails. We already disagreed to some extent on this point, but I still believe that dynamically rails can increase lift because of their different AoA vs. the water surface, compared to the same hull with no rails - even if I understand your point ref the horizontal component of the surface being the same.
And in the previous discussion on this matter, I also quoted in this post what Levi wrote about that.

But let's leave lift aside for a moment - happy to agree to disagree on that.
Another thing Levi highlighted in his book is that rails extended up to the transom (as in most of his hulls), have distinct advantages in terms of higher dynamic stability, both directional and transversal.
So, I would think that Amati had good reasons to choose "full rails" (so to speak) for his hulls, and I very much doubt that by sanding out the back half of Fiammetta rails she would go even 0.001kts faster.
Btw, you might have noticed in PF pics that the internal rail is already interrupted well before the transom, in order to minimize the water flow interference in front of the props.
It's not like Amati earned his reputation for nothing!

Besides, you can find "full rails" on just about any real fast P hull, from my old lake toy (see pic below), all the way up to 200+ mph turbine cats.
And I don't think any of those builders would have dismissed a chance to gain even a hair of additional speed by interrupting rails, if it were that easy.

All that said, I fully agree that when talking of P boats designed for cruising at a reasonable combination of comfort and speed, what we are discussing is firmly in the "hair splitting" league, and none of these effects would be relevant enough to be perceivable.
The only exception is maybe the one summarized by the "Rivale vs. Itama" comparison, 'cause you can definitely feel the difference between a true deep-V hull and a flatter modern hull designed around the interior requirements, when banging into a head sea at speed. But that's just about it.

And even in much faster boats like the Fountain above, I don't think anyone could say just by looking at her hull how "good" it is.
Sure, when you see a stepped hull, a padded keel and a notched transom you expect the hull to be fast.
But if you put it near a similar hull of another yard, you are likely to find similar solutions.
Truth is, there are only three ways to find out which performs better: test, test, test.

For this reason, my personal answer to PF question "has this post raised your awareness of hull shape" is...
...sorry, but nope. Not one iota, I'm afraid.

 

[MapisM]

As a totally o/t comment, I very much like those transom rudders! :encouragement:

During my boat search, I only came across a couple of f/b boats with the same setup - and it's no coincidence that they were a Baia and a Italcraft.
Can't get my head round the reason why they never became more popular also on f/b hulls...