How wide is your bottom?

MapisM

MapisM

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Funny how after decades of boating you can still see something which you never noticed.
A distinct difference between the hull shape of my boat and a larger Ferretti stored nearby grabbed my eye just recently.
As the pic shows, the max beam of the latter at deck level is significantly larger than at the hull chines, while the topsides are almost perfectly vertical in my DP.
TBH, I can't think of any reason why in principle either one or the other solution might be better.
But out of idle Sunday curiosity, I thought to ask: did you ever notice if in your boats the topsides are more or less angled outward?
Not sure if that's a builder's choice or rather depends on the specific model, for some reasons...
gHC5q14L_o.jpg
 
MapisM said:
Funny how after decades of boating you can still see something which you never noticed.
A distinct difference between the hull shape of my boat and a larger Ferretti stored nearby grabbed my eye just recently.
As the pic shows, the max beam of the latter at deck level is significantly larger than at the hull chines, while the topsides are almost perfectly vertical in my DP.
TBH, I can't think of any reason why in principle either one or the other solution might be better.
But out of idle Sunday curiosity, I thought to ask: did you ever notice if in your boats the topsides are more or less angled outward?
Not sure if that's a builder's choice or rather depends on the specific model, for some reasons...
gHC5q14L_o.jpg
Click to expand...

As you know I am a bit of a newby. Just a thought though, would the more angled boat not be better if you have a beam sea. Not sure if that's the right term but does the angle better deflect waves than a more vertical one? Just putting it out there.
 
derekbland said:
As you know I am a bit of a newby. Just a thought though, would the more angled boat not be better if you have a beam sea. Not sure if that's the right term but does the angle better deflect waves than a more vertical one? Just putting it out there.
Click to expand...
Depends short ans No
Long ans when planing the water deflects in a chevron cum V looking in the longitudinal axis and detaches from the antifouled area ,not much above the chine or at chine height .( looking down )

So it’s the below the chine part that’s important in assessment of a hull that planes
How ever your query is specific to beam seas and I assume when it’s possible planing too ?

Depends on relative wave heights striking part of the hull above the chine .
For clarity the chine is the sharp angle where the side meets the bottom .

It’s submerged at rest ar the dock , but risers up when planing as the water escapes while it’s providing lift to plane .
In theory any beam wave hitting above the chine when planing will express itself in energy - to tip the boat and some component will drag .

So the one which can get rid fastest with the shortest contact will be better - if better means less ability to slow it ie drag it .
I reckon the Ferretti will hold it for less time due to its more over perpendicular chine angle than the DP in the same sea state ,Throw it out earlier and further = bigger wash

How ever there a secondary wave drag effect caused by a bigger wash .
The Ferretti wash will be greater and net sum of drag more therefore the DP and generally any other straighter beamed boat will be the more efficient .

It’s all about management of the secondary effect of draggy wake .
The DP is the better more efficient performance boat hull
The Ferretti is the better interior volume .
There’s no such thing as free lunch :)
 
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Portofino said:
Nope not related
Click to expand...

Out of interest, why not? If the beam is narrower at the water line it can afford a steeper dead rise to compensate for less buoyancy lift. Similarly for a wider beam at the waterline then equivalent dead rise would potentially create too much buoyancy lift.
 
BK, as I understand, it's the static buoyancy that you have in mind. But that's just a side show, on a P hull.
In both boats above - as well as any others - the static w/l is well above the chine, i.e. just a tad under the boot stripe in the Ferretti and under the upper border of the lighter area (where the previous a/f was removed) in my DP.
In other words, both hulls could have had a higher deadrise without risking to sit too high in the water, so to speak.

I'm not sure if PF reasoning about efficiency is always valid, but I believe he's right in saying that the choice has nothing to see with the need/possibility to go for a deeper vee, which is essentially driven by dynamic rather than static considerations.
 
Portofino said:
There’s no such thing as free lunch :)
Click to expand...
Yeah, that's always a given.
What are the topsides like in your Itama, straight or diagonal?
I half recall that you posted some pics of your hull from a similar perspective, but it's quicker to ask than search for them... :rolleyes:
 
BruceK said:
Out of interest, why not? If the beam is narrower at the water line it can afford a steeper dead rise to compensate for less buoyancy lift. Similarly for a wider beam at the waterline then equivalent dead rise would potentially create too much buoyancy lift.
Click to expand...

Chine width is the important dim in planing hulls - theses two are more - less the same ,
Is that beam or chine width P ?
This chine width on the Ferretti is very different to max beam .

Lifts produced between the chines only .The “ caravan “ sat on top is irrelevant.
The steeper deadrise ( is normally associated with steeper fore foot ) the the more - ve lift or suction occurs at the last 1/4 or so of wetted planing area .
So you can,t go deadrise mad so to speak
If you do you will have higher planing speeds and need more Hp, —- as well as obviously better seakeeping - but seakeeping is a given but comes at the expense of the above .

Flatted rear= more lift

The explanation is thus - you get decreasing lift toward the aft end of the plane, there’s a change in the directional momentum of the water particles sticking the plane so that kinetic energy is transferred.Any change in the thermodynamic conditions are negligable the entire energy is impressed on the moving hullon the water is kinetic .
Ultimately,of course all work degenerates into heat .But this takes time and in the immediate vicinity of the forefoot of the hull practically all of the work is accounted for in changes in kinetic energy of the water .
Every action has a equal and oppersite reaction - Newton’s 1st law .,
So the max lift ( kinetic energy ) is being impressed on those parts where the water is displaced down the fastest at the deepest V at the firefoot .
Succeeding aft sections encounter the same water flow allready deflected from the horizontal and therefore tend to reduce the potential angle of defection , smaller units of resistance force are changed to kinetic energy, lift decreases as the water moves aft tending to become - ve .
Here’s a pic ( shown this recently on another thread )
View attachment 71163
Black lift / White suction or -ve lift
Top pic has a V - deadrise
Bottom a plank of wood
 
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MapisM said:
Yeah, that's always a given.
What are the topsides like in your Itama, straight or diagonal?
I half recall that you posted some pics of your hull from a similar perspective, but it's quicker to ask than search for them... :rolleyes:
Click to expand...
Pretty vertical like your DP
View attachment 71165
It’s all about reducing wake and secondary drag and minimising excess topside Kg s
Sum of a lot of individual tiny bits .
Each on its own nothing but the sum something
Regarding the V forfoot and deadrise .
Deadrise you can see - here 23 degrees .
But you can’t see the V in the black area of the pic above .

In simple term think this —- the harder and faster the hull hits the advancing water and the deeper the water particles are deflected down the more lift .
 
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