Getting up onto the plane with a flybridge boat

Hot Property said:
By way of comparison, my displacement speed is 6 knots at around 1500 rpm.

To get on the plane I open up to around 5,000 rpm which rapidly gets over the hump then ease off to cruise at 19 knots at 4,000 rpm. The outboard is supercharged so pretty instant power is available.

Should I wish to increase my carbon footprint and reduce my bank balance I may go to WOT at 6,400 rpm @ 35 knots for a few minutes....
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This is typical for a petrol boat, the torq goes up with rpm, while a diesel engine has nearly max torque available from lower rpm. So with a diesel you can increase rpm gradually and go on the plane, while with petrol boats, you need high rpm to get over the hump.. (at least that is my personal experience)
 
BartW said:
This is typical for a petrol boat, the torq goes up with rpm, while a diesel engine has nearly max torque available from lower rpm. So with a diesel you can increase rpm gradually and go on the plane, while with petrol boats, you need high rpm to get over the hump.. (at least that is my personal experience)
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Your reasoning on torque is absolutely correct B, but sheer size/weight has much more to see with how the boat behaves in the transition between D and P speed, rather than the torque curve.
I mean, the larger the boat, the flatter she stays also at transition speed, while smallish hulls tend to climb their own wake a lot while getting over the hump, with the bow pointing to the sky.
More torquey engines would not change this behaviour, because it's mostly driven by the hull length/shape/weight.
 
kashurst said:
Local Volvo guy recommends full throttle then back off. Apparently it saves fuel - I seriously doubt that.
As per others I like to let the boat accelerate in it's own time feeding in more power/revs as it goes - just in case something goes bang. I tend to do it in stages, 900 rpm in/out the harbour, 1500rpm, then 3200rpm
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Actually, it can and this would be for modern electronically controlled engines, overthrottling means the boat relies upon its electronics to reign it back and only give enough fuel based upon load and speed, as the boat accelerates it constantly monitors the parameters and the engine runs optimally at all times. There are numerous variables and his statement is quite a general one though.
 
rafiki_ said:
Nice article P. Looks a cracking boat!
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I knew you would have liked it! ?

PS: Btw, according to it, she was capable of 30kts with the 3116, while as I recall you've got the 3126 on yours.
What sort of WOT speed does she reach, out of curiosity?
 
MapisM said:
I knew you would have liked it! ?

PS: Btw, according to it, she was capable of 30kts with the 3116, while as I recall you've got the 3126 on yours.
What sort of WOT speed does she reach, out of curiosity?
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She was advertised at 32 Kn P, but of course that would have been before ownership loads up the boat with all the junk that seemed like a good idea at the time. And of course having a proper sized fridge/freezer means quite a lot of additional fluid on board. Max I have seen is 30 Kn, with clean bottom and sterngear/
 
That's not bad at all, considering that tests are usually made in the most optimal conditions, light load, etc.
And the power difference isn't so big, anyway...
 
MapisM said:
Your reasoning on torque is absolutely correct B, but sheer size/weight has much more to see with how the boat behaves in the transition between D and P speed, rather than the torque curve.
I mean, the larger the boat, the flatter she stays also at transition speed, while smallish hulls tend to climb their own wake a lot while getting over the hump, with the bow pointing to the sky.
More torquey engines would not change this behaviour, because it's mostly driven by the hull length/shape/weight.
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In general I agree with you P, but just a few comments:

my 26ft 2 x D3 Karnic, despite mutch too much stern heavy, (2 diesel engines in the stern in a small 26ft boat) this boat accelerates much less bow high then previously owned smaller boats (23 and 25 ft sport fishers, but petrol engined )
With the Karnic, I'm never urged to accelerate at high rpm, the boat smoothly goes from displacement on the plane, over the hump, its bow up behaviour doesn't feel too bad.

secondly, my answer to " hot property" was typically explaining his experience with his petrol boat, needing WOT to get over the humb

and finally, the OP's question was not referring to boat behaviour, but just "whats the best procedure", I have a funny feeling that his previous boat was a petrol boat,
moreover, if you accelerate a diesel boat at wot; with old fashion mech injection, you will have loads of black smoke (overfueling), while with a modern CR diesel, the electronic injection will controll the acceleration,
 
BartW said:
the OP's question was not referring to boat behaviour, but just "whats the best procedure", I have a funny feeling that his previous boat was a petrol boat,
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Yup, in terms of procedure I agree that I wouldn't hammer the throttles with the DP (as well as I didn't on the previous boat), other than for testing purposes.
Otoh, I regularly did that with all the petrol boats I had, to go over the hump, easing the throttles as soon as they were steadily on the plane.
Then again, it's also true that petrol engines are only used in smallish boats (particularly this side of the Pond), so we are a bit at cross purposes on that...
 
MapisM said:
Yup, in terms of procedure I agree that I wouldn't hammer the throttles with the DP (as well as I didn't on the previous boat), other than for testing purposes.
Otoh, I regularly did that with all the petrol boats I had, to go over the hump, easing the throttles as soon as they were steadily on the plane.
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that is exactly the point I'm trying to make (y)
 
Actually, I don't have to floor the throttle to get on the plane. The hump starts to take effect from around 9 to 16 knots. I don't get much, if any, bow rise, but out of habit I have traditionally opened up to go on the plane. It's really the trigger I have to get my brain in gear for higher speed travel and to keep my wits about me. Going from a DS of 6 knots to say 28 in a small cruiser is a whole lot different than being in my mates 48 ft when he does that.....
 
Planing .what do you all mean by the term ?

A planing hull is simply one so shaped that a degree of dynamic lift is added to its natural buoyancy during the time when its speed of advance exceeds that rate at which solid water can close in abaft of it .


I think we all first need to agree that there is no one binary point of planing. It is not either on or off. It is a transitional regime, and therefore, any attempt to define a point of planing is somewhat nonsensical.


What actually defines planing using the most widely accepted definition is —-

The fact that if the speed increases the trim angle will decrease.

If you aren't planing, increasing speed in the sub planing regime results in an increase in trim angle, for a planing hull. Again, for a semi-planing hull that might not happen at all, but for a true planing hull, the speed where it attains planing status is the point where the trim angle decreases as the speed increases.

Look guys this is pretty simple.
Think about an airplane wing. To supply a given amount of lift at a given speed you need a specific angle of attack. If the speed increases you have to decrease the angle of attack or you will get an increase in lift. As you approach planing speed the trim angle doesn't decrease and indeed, the lift is increasing since you are supporting an ever increasing portion of the hull with hydrodynamic lift.
But once you are on the plane, even though the hull may be heavy and still have a significant portion of displacement lift, if &the trim angle drops as speed increases, it has attained planing status.
This is why using arbitrary measures like % of weight or amount of lift, are not appropriate, a heavy hull might have a different lifted height when compared to the same hull when lightly loaded. But in both cases, when the trim angle decreases, planing has been realized.

How much of the displacement volumn must be above the surface to be "on plane"? all of it, most of it, half of it, any of it? What % if any ?
Since planing begins to occur when hydraulic forces lift the hull, how much until it is actualy "planing"? Any lift replaces displacement forces with dynamic ones, so some say the begining of planing occures when there is any lift not associated with displacement.

Therefore to some they see no reason for any of the qualifiers at all. Many shapes can plane to one degree or another, no reason to put those conditions on it. I also do not see why 50 percent is the magic number either, if any portion of the weight is lifted out of the water by hydrodynamic lift you will reduce the drag and increse speed.

Some say that planing occures if any of the weight is suppored by the dynamic forces on the hull from the water. A little or a lot of the weight being supported is illrelevant, the fact that the hull is not fully in displacement mode means that lift forces on the hull are partially supporting the weight of the boat.

I think the real problem is the word "planing" itself is obsolete and based on archaic ideas about fluid mechanics. The origin of the word assumes it is even possible to be above or "on" the plane of the surface. We know a lot more about the process and forces involved but are stuck with these obsolete terms.


Getting back to the topic some suggest taking into account the “subjective feeling “ of the persons on board, I believe that anyone who has been on board a planing vessel can witness that it's movements became "stiffer" and more jerky when encountering waves at high speeds than it was during low-speed navigation. A mathematical explanation for this behavior is that the perturbation of hydrostatic lift component is in linear relationship to the vertical speed of the incoming wave disturbance, while the dynamic lift component increases as a square function of the vertical speed of the perturbation. Hence, the vertical accelerations become much more severe in high-speed regime.
It makes me think that perhaps it can lead us to a completely different criterion for the definition (by convention) of the planing, based on the vertical acceleration response of the vessel to incoming waves, or to a single standardized perturbation which could be reproduced in towing tanks. The planing regime would then be indicated during sea trials by the on-board accelerometers, rather than through the GPS readout .

Just some food for your creative minds.
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I think that at the end, it is a matter of semantics and not physics or engineering. It would be better to say, for example, "this vessel at a speed of 54 knots has 93% dynamic lift to displacement ratio", rather than argue whether it is planing or not

I think we can all agree that, when looking trim angle it becomes pretty clear where planing starts.

The more you think about it one soon realises this becomes different for every hull, and for every load condition, every thrust angle, and for every offset of the thrust vector from the line of the planing surface, as well as things like prop rake. It's possible to significantly change the onset of planing by modifying those variables.

When all things are considered, it is far more complex than a simple % of lift. For lightly loaded short, wide hulls, the change in trim angle happens much more quickly with increasing speed. For much larger hulls with heavier bottom loading, the curve will likely be more of a gentle hump, but the reality is, when you are past the peak of the trim angle curve the hull is now in the planing regime. Since there a any number of variables that can push the actual speed at which the trim angle starts to decrease - that's not a bad thing to use for a rule of thumb .

Maybe planing is like time: we all know what it is, until we think about it
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Brilliant Porto
When I first opened your reply and saw the length of it
I thought
‘Oh No, here we go’
It’s brilliant and all makes sense
Last line tops it off properly too
Great Post
Top marks
Love it
 
rafiki_ said:
My Azi just rides majestically up onto the plane at about 16kn. no need for tabs or messing with the throttle. No nose up, and no drama.
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lets talk about Hp .
The more you have @ your disposal along with bigger pitched props and engines to swing them the faster it accelerates .
Twin 700 s approx 17 tonnes 13 M WWL + minimal air draft .23 degrees deadrise so about a deep V as you can go for a off the shelf production boat .

What I do is warm them up to 60 degrees + jacket temps by pushing a bow wave at say 11 knots watching the EGTs rises as well .
This is what the MAN manual suggests ....the 60 degree thingy.
Max D speed is approx 9 knots so 11 is enough over D to get some heat in .

Then once up to 60 degrees .........just gun it .Yep just push fwd both sticks

My Itama gets up from 11 knots to 26 knots in approx 4 seconds ......FOUR .
“No fuss no drama .” either .
11 to 30 knots in less than 10 seconds .

We don’t need tabs theres only a minor perceptible bow lift or stern sinking it just flys Fwds and lifts up and away .
Any bow lift drops from 24 knots awards ....what little there is .

Before getting her up I ask guests to sit down and grab hold ....wife holds the dog too .

They say a pic paints a 1000 words .....apologies for the unsteady hand but if you mess about freeze framing you can see where I get the 4 seconds from 11 to 26 knots from . Glad I found this vid :)



once up I normally run cruise at 80% load .
 
This has turned out to be a good thread, and I'm happy that I've been doing the right thing, last couple of boats were a semi displacement 38 footer and before that a 7.4l V8 petrol so this was new to me and glad I listened to advice.



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