Can a planeing hull acheive any speed? What is a planeing hull

[justdrifting]

Will a planeing hull be capabale of any speed depending on power?

Lets say a Bertram 28 will do 20 knots with a pair of 240 hp engines. If a magic spray is used and the engines put out 1000 hp the drive train and props optimize to maximize the the power to thrust,would that boat then travel at 40 / 60 / 80 knots or more?

On the same stretch of water in the same conditions?

Sailing dingys plane, if you take a 470 under sail it will plane if you put a 100 hp engine sprayed with a magic spray so that it weighed nothing and again was mounted in the best spot the drive train in the perfect configeration how fast could it travel??

When ive been sailing dingys as the speed increases so does the bow wave is it possiable to get over that that it dosent push the hull back?

What is a planeing hull??

Please forum thank you

 

[gjgm]

well the hull needs to be stable and strong enough I guess, and those are some of the compromises the designer has to live with.
Id take a planing hull to mean one where the boat rides more on top of the water, rather than displacing/pushing the water out of the way, generally by having a more "flat" aspect at the stern. But that needs alot of power,affects handling and so on. An extreme racing hull is one design limit, but most leisure boats need more from the boat that pursuit of that one goal, and so the hull is changed to meet other priorities

 

[Major Catastrophe]

This will of course degenerate into a col regs or feathering prop type spat, but I am led to believe that you cannot exceed the design speed of a hull. Not sure that works, but some clever chap will be along in a mo.

But one thing that can happen is the hull starts bouncing from side to side. Can't remember what the technical term is, but that chap over there does.

 

[jhr]

Chine walk.

Not sure if the limitation is due to any formula, but presumably there is a diminishing return as air and water resistance increasingly thwart the power of bigger and bigger engines. I don't know where the final barrier lies but I've not heard of many conventional powerboats capable of more than about 130 mph.

A Bertram 28 will probably hit the wall at a lower speed, much though I admire them. /forums/images/graemlins/grin.gif

 

[ValleyForge]

Dimly recall mono's get a bit skittish much over 90 mph, hence cats & 3 pointers for more. 50 in a Bertram 28 would make an adequate, if expensive martini shaker ....

 

[Nautical]

Technically yes but you wouldn't want to try it, with that kind of power it would be airbourne half the time and in any kind of sea it would probably break apart, also you'll find boats capable of 70 knts + have a heafty deep V even at the transom so when it hits the water it slices it up, with a modified or medium V at around 14 degrees at the stern it would slam like you wouldn't believe till it fell apart.

A planing hul is designed to ride on the water or on top of it enabling it to reach higher speeds but first you need enough power to heave it up over the 'hump' and up 'onto' the water rather than push through it like a displacement hull aka trawler or workboat. With a displacement hull no matter how much power you add it will not go past its design speed (maybe 9 - 10 knts 9knts on a 40' ) all you'll do is dig yourself deeper into the water and shift more displacement.

 

[PowerYachtBlog]

depends the range of the hull
a range of speed is much important nowadays
while as Nautical poointed out a 70 Knot boat is usually deep aft (not always the case) it surely is usually flatter forward them most motor cruisers, as when reaching a high speed this is hardly used
while I think you mentioned one of the best hulls around with the Bertram 28 I think it has a superb range from 20 - 50 knots as still give you one of the best clean rides, not many boats have this capability
many motor cruisers nowadays have an optimun hull efficency of 25/30 knots

 

[Salty John]

A planing hull is designed to lift out of the water and ride on top of it. To do this it has to climb over it's own bow wave. This is what takes the power. A displacement hull achieves it's lift only by displacing water and cannot normally ride over it's own bow wave. The speed of a displacement hull is determined by it's waterline length because it can't pass the point at which the bow wave extends from bow to stern. This speed is around 1.3 times the root of the waterline length. Sometimes a bit more, perhaps 1.4 times if the hull is so designed.
I don't know what the ultimate speed of a planing hull is determined by, but someone will be along shortly to explain.

 

[justdrifting]

Can all none disolacement types get over the "hump" with enough power?

Take a bosten whaler for example a small 16 footer with a 5 hp its a runabout, 10 hp it might be pushing water and say with 20 hp its planeing quite fast,put a 40hp on and it will go much faster,that is if anyone can hang on before their pounded to death

I suppose with an 80 HP it would just keep getting faster untill it became a airborn! They are ment to fast plane.

Supposeing then the 470 or a wayfarer which has a "v" hull were to have an 80hp engine would that as well get over the hump and just keep getting faster untill that became airborn? Assuming it dident break up.

NEXT:

If two rowing boats were fitted with 20hp engines one being 15 foot the other 30 foot both produced at the same yard therefore the longer one is also the heaviest which would be the fastest?

Same question if a 40hp were installed in both would the lenght make a difference? Or is it only displacement boats that are limited by hull length

Why cant something small such as a merry fisher 25 for example plane if enough power were applied?

 

[Major Catastrophe]

[ QUOTE ]
Why cant something small such as a merry fisher 25 for example plane if enough power were applied?

[/ QUOTE ]

Not sure what a merry fisher 25 is, but the 625 certainly planes at about 12 - 14 knots to get it over the hump.

 

[justdrifting]

Then its weight and power? Take 2 displacement boats say a fisher 25 which weighs about 2 tons im told that has a 20 hp diesel and potters in and out collecting his fish pots at a reasonable speed but with a large bow wave if that had a 1000hp from the same engine could it plane????

I imagin something like a trawler yacht or Grand banks could NEVER plain given any amount of power???

Or is it also a question of weight

 

[PowerYachtBlog]

[ QUOTE ]
Then its weight and power? Take 2 displacement boats say a fisher 25 which weighs about 2 tons im told that has a 20 hp diesel and potters in and out collecting his fish pots at a reasonable speed but with a large bow wave if that had a 1000hp from the same engine could it plane????

I imagin something like a trawler yacht or Grand banks could NEVER plain given any amount of power???

Or is it also a question of weight

[/ QUOTE ]

Grand Banks do plane, having a planning hull with a keel, what would never plane is something like a Norhavn which has a full displacement hull and similar
GB plain at relatvley low speeds at 14 knots that is very good compared to some modern planning boats which need about 8 knots to go up
add to that the drag of the keel and its fantastic

 

[Salty John]

I think you can get any boat onto the plane if you can apply enough power.
Below the planing point it's all about waterline length, after that it's about power to weight ratio, prop design and the subtleties of the hull design.
Some quite big sailboats plane when they have enough wind and they are surfing down waves, but it's only momentary. A 60' racing boat can surf at 20 knots or more although it's theoretical displacement hull speed is only about 12 knots.

 

[Kawasaki]

In simple terms (do do any other sort) A Displacement hull's speed is governed by it's waterline length.
A Semi displacement ,Oh! sorry Salty just looked up and saw Your good Post!

Yer Boston Whaler type hull will plane at about 12 upwards.
So lets say a 16 footer of that type will plane ok with a 40 .
Stick an 70/80 on and she will get onto the plane quicker even if loaded with peeps.
Just going bigger and bigger does not mean that the boat will go faster and faster.
There becomes a point where the hull will become unbalanced even on glass like water.
The weight of the "too big a lump" will upset things also
Tis a balance thing with planing hulls, balancing the correct amount of power and how the power is delivered ie right prop for the job etc.
Just shoving bigger lumps on the back, well, law of diminishing returns, kinda.
The ultimate speed of a planing hull is determined by the hulls shape , type , length all sorts of stuff.
The ultimate shape aint been shaped yet!
Next time someone breaks the World Water Speed record, I suppose We will know the answer but then someone else will break it again so We won't know the answer. I don,t suppose that was the Answer you were looking for.
In answer to Your question "is it only displacement boats that are limited by hull length?" Basically Yes, is the short answer.
Hull types and props and stuff like that, well, blimey what a subject, needs a Forum of it's own.
Probably is one somewhere!
Probably a Tome on the subject too.
In simple terms you have had some good answers already.

No doubt a hull "Boffin" will turn up in a bit, don't know how fast though /forums/images/graemlins/grin.gif

 

[MapisM]

[ QUOTE ]
I think you can get any boat onto the plane if you can apply enough power.

[/ QUOTE ]Correct. Even a stone can plane.
BUT, it obviously doesn't make sense to use any sort of miracle spray to make a displacement hull planing.
Even the reason for asking is actually beyond me...

 

[justdrifting]

I was interested just that,and with such a great forum i thought id get & got a good answer

I think what i wonderd was the longer the boat the better and faster it can go? But that dosent seem to be so

The other reason was watching "fishermen" that some years ago used 6hp on say a 5 meter wooden "fishing" boat having removed the inboard petrol when it was worn out (i found his old 6 hp at the scpap yard) he then fitted a 20hp and today hes got a 40hp on the same boat or had since ive now got his old boat and hes got a plastic one im useing a 6hp which is fine

As many boats which would once have a 6hp now have 40 / 60 hp i wondered at the usefulness and weather any boat would go faster as more power was applied

On the fisher the 6hp is perfect and on the boston the 25hp is more than enough for me!

 

[Sneds]

Surely a long narrow dispacement hull will go faster than a short fat one?

 

[Salty John]

No; it may get to it's hull speed quicker but it isn't inherently faster - that's down to waterline length.

 

[Gludy]

The slimness of the hull does matter. Its mainly waterline length but the slimmer the hull the higher the displacment speed for a given WL length.

The boat with the highest displacment speed will be a long slim one.

 

[Bajansailor]

Re: Can a planing hull acheive any speed? What is a planing hull

My two cents worth of just general random and erratic comments, not in reply to anybody in particular.

The generally accepted formula (around 1.4 x square root of WL length or thereabouts) for maximum speed of displacement boats really only applies to 'conventional' displacement boats, ie those with a Length to beam ratio of around 3.
Or in other words, relatively tubby boats.
As you make your displacement hull skinnier (less beam) for the same length, its max theoretical displacement speed will increase.

Take this to the extreme with racing rowing boats (aka 'shells') - they might be 50' long and perhaps 18" wide on the waterline - a L/B ratio of 33! They can really shift, and their maximum speed is now governed by the amount of power that can be generated by the rowers on board.

Or powercats with long skinny hulls - the hulls of the power cat in my avatar photo have a L/B ratio of 15, for a waterline length of 47', and they are still happily in displacement mode when travelling at 20 knots and producing very little wake.

Or think of an even more extreme skinny power cat - such as two 47' long and thin rowing shells lashed together with an outboard engine on the 'bridgedeck' for propulsion - a boat like this should be capable of relatively high displacement speeds.

Whereas a 'conventional' 47' displacement hull might have a max. displacement speed of around 9.5 knots, and kicking up a huge wake at this speed.

Wake height is proportional to the bashing that credit cards or pockets get when filling up fuel tanks.
So, the next time that somebody with a humungous wake zooms past you and causes your dinner or drinks to go flying off the table, try to console yourself with the thought that he is just an (ignorant) Bottomless Pocket Prat (BPP)....... never mind that he probably thinks that he is an Absolutely Perfect Poser (APP).......
Hopefully not all BPPs are APPs, and vice versa!

Why dont these monohull racing shells with L/B ratios of 30+ just topple over when static (ie not underway)?
Because you could say that they are a sort of trimaran, in the sense that the oars form effective outriggers for stability.
Once they have built up speed they are relatively stable, sort of in the same way that a bicycle is stable when underway, yet falls over when stationary.

Sorry, am digressing..... the basic requirement for a planing hull is that (once the power is available) it needs to have sufficient planing area to generate enough lift to get the boat up out of the water and onto the plane.
Once the hull form can do this, then it becomes a 'blood and thunder' machine as a pal of mine calls them - a very apt description I think!
Or in other words, if it can get up on the plane via sufficient power and planing surface, then it will be capable of high speeds with lots of extra power, subject of course to the various constraints and limiting factors mentioned in previous posts above.

And do remember that the graph of fuel consumption versus speed is not linear! It rises steeply - you do pay extra for every extra knot of 'high' speed. 'High' in this context is relative - I am using 'high' to indicate once you get past the most efficient cruising speed.