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Old 09-19-2009, 09:05 AM   #21
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RE: how much hp to plane?

Once one gets over 10 knots or so a wide heavy boat acts like a plow pushing water aside and creates the hole you guys have been talking about. The stern falls into the hole, the angle of attack gets steep and just like an aircraft it takes lots of power at high angles of attack to move forward. Add trim tabs and it takes even more power but you loose some drag w a decreased angle of attack on certain hulls at certain speeds. So if you want medium speeds you've got to get a long narrow boat. Put a little rocker in the bottom and one can even go gracefully and relatively efficiently forward w a long narrow hull. Walt, I kept the techie talk out to please you.

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Old 09-20-2009, 08:59 AM   #22
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RE: how much hp to plane?

The simplest lowest cost solution , probably less than the interest on a $100,000 dollar bastardation job is a call to BOAT TRANSIT ,

about $1.50 to $2.00 per mile plus a bit of travel lift at either end.

If it keeps a 2GPH boat wholesome . instead of lugging a 40GPH engine , and destroying it thru severe under loading, and keeps da bride happy its cheap indeed.

Second choice is a simple delivery guy to bash the boat thru the rough water and a rent a car to get you there and the capt home.

Cheap & EZ.

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Old 09-20-2009, 10:13 AM   #23
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RE: how much hp to plane?

Even cheaper,
If you look out over bow at 7 knots most of the time it looks like your'e not moving at all. Look over the side and it looks a bit better especially if one looks down. But look over the stern and it frequently looks like your'e going 15 when only doing 6. I do it all the time. I just look aft, watch the wake for a few seconds and feel like I'm making real progress.

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Old 09-21-2009, 04:48 AM   #24
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RE: how much hp to plane?

Once one gets over 10 knots or so a wide heavy boat acts like a plow pushing water aside and creates the hole you guys have been talking about. The stern falls into the hole, the angle of attack gets steep and just like an aircraft it takes lots of power at high angles of attack to move forward

Fine description on a displacement hull that's overpowered , but the wide box shape of a true plaining boat works like the wing of an aircraft , wide but narrow fore and aft is a good lifting surface , IF the boat is light enough and powered enough.

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Old 09-21-2009, 02:32 PM   #25
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RE: how much hp to plane?

Actually it dosn't Fred. 70% of the lift on an AC wing is generated on the upper surface. And if you don't have enough power to push the wing through the air fast enough it won't fly** ..* nor will a planing hull plane without enough power to push itself out of the hole. A 35X12' boat is 420 sq ft and a boat 42X10' is the same size but the 42X10' boat will go 10 or 12 knots with much less power. With it's wider beam and higher angle of attack the 35X12' boat will make a much bigger hole to climb out of but at 10 or 12 knots it will be in the hole consuming loads of power. Medium speeds demand a narrow boat. Have you looked at the Atkin site lately? Remember the long narrow boats requireing very low levels of power? I have an 18' FG outboard and I'd like to replace it w a 26' Atkin boat (Wader) useing the same 60 hp outboard. I'd get 15 knots instead of 25 but I'd have a nice big (and long) boat. What do ya think Fred.

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Old 09-22-2009, 04:32 AM   #26
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RE: how much hp to plane?

I am using the underbody of the Atkin River Belle ,computer squezed to 7.6 beam for the test basis of our "box boat". 30LOA

The advantages of skinny boats is well known , but the efficiency of the box keel and reverse deadrise is quite hard to model test in a facility.

The numbers can only be pulled with a prop powered model , or perhaps a couple of Cray's with a specially written program.

We have a model, but without building a dozen more to compare against , it mostly is usefull for being sure our desired interior will fit.

The box keel does have a huge advantage for our use as the boat will be very EZ to get in the box with simple pipe rollers.


If you want to see a real fuel efficient boat Google the Rescue Minor , and the quite fancy version (about 20ft) built that gets 20 30 mpg at speed bu Robb White?


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Old 09-22-2009, 09:40 AM   #27
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RE: how much hp to plane?

Yep, it is the beam on these IG's that keep them from truly planing. It also a variable that doesn't appear to be included in the prop calculator. The Mainship 35/39s have the same issues....3xxhp and still only 12ish kts.
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Old 09-23-2009, 04:45 AM   #28
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RE: how much hp to plane?

"70% of the lift on an AC wing is generated on the upper surface."

There are about 5 theories ,why a wing works , vaccume is one.

Guess my launch will always be limited to 12K as we have had hard water on the deck, but never have been able to get a smooth flow from bow to stern over the pilot house. DARN!

There is a huge difference on boats at SL 2 or 3 , and fast boats of SL3 and way faster in terms of how the bottom (length, width) affects the pressure pattern that holds up the boat.

With a proper plaining hull , mostly weight is the determinant of the speed or efficiency.

Less IS more , if you can afford it.
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Old 09-23-2009, 09:00 PM   #29
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RE: how much hp to plane?

Hey Fred,
Are you telling me there are millions of people flying airplanes w wings holding them up and we only have "theories" about how they work?
A year or two we talked, argued and discussed wing lift and it's possible we had considerably more than five theories.
Yes yes on the rest
Boeing must have sent Marin to mars** ..* I actually miss the guy.

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Old 09-24-2009, 04:05 AM   #30
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RE: how much hp to plane?

"Are you telling me there are millions of people flying airplanes w wings holding them up and we only have "theories" about how they work?"

Aircraft defy gravity (while they work) and there is not yet a good theory on gravity.

Or a good "Unified Field" theory that has any more proveability than "God did it!".

Just because we dont have full knowledge on a subject does not mean we cant build something.

This months PBB has a great article on a Dutch research lab , and their "new" cruising hull shape.

Sad reading for anyone looking for a "fast trawler" , even after 5000 years of boats , and a gang of Cray's working on the problem, with decades of tow tank observations.

"we only have "theories" about how they work?"

Anyone that is foolish enough to go in an Airbust may soon realize not all theories of flight will get you to a destination other than Valhalla..


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Old 09-24-2009, 06:06 AM   #31
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RE: how much hp to plane?

There is no such thing as gravity. The earth sucks.
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Old 09-24-2009, 07:25 AM   #32
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RE: how much hp to plane?

Quote:
FF wrote:

"Are you telling me there are millions of people flying airplanes w wings holding them up and we only have "theories" about how they work?"

Aircraft defy gravity (while they work) and there is not yet a good theory on gravity.

Or a good "Unified Field" theory that has any more proveability than "God did it!".

Just because we dont have full knowledge on a subject does not mean we cant build something.

This months PBB has a great article on a Dutch research lab , and their "new" cruising hull shape.

Sad reading for anyone looking for a "fast trawler" , even after 5000 years of boats , and a gang of Cray's working on the problem, with decades of tow tank observations.

"we only have "theories" about how they work?"

Anyone that is foolish enough to go in an Airbust may soon realize not all theories of flight will get you to a destination other than Valhalla..


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Old 09-25-2009, 06:32 PM   #33
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RE: how much hp to plane?

John,
That may be a very good point about the beam being missing from the prop calculator form. If one had a 1 to 1 relationship between the beam and length and more than a bit off on trim it would be almost impossible to plane.

FF,
Feb 05 in PMM there is an article on the Shannon SRD 38. This is a very modern RD hull that works very well. The RD boats of old called Sea Bright Skiffs are'nt as efficient as a conventional hull as there is more wetted surface and the aft section presents too many places where the water needs to change directions too abruptly. The Shannon dosn't have this problem and at moderate speeds is more efficient. I think your'e talking about the Sea Bright types that have a whole sack full of advantages** .. but not efficiency.

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Old 09-25-2009, 09:41 PM   #34
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RE: how much hp to plane?

Am I reading this correctly - "there is no good theory on gravity?" FF is that your "final answer?"
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Old 09-26-2009, 05:28 AM   #35
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RE: how much hp to plane?

Am I reading this correctly - "there is no good theory on gravity?" FF is that your "final answer?"


Yes , we can work with 32ft /sec , but ca't explain yet WHY.

For folks that believe the top surface of the wing is important I suggest you look up Lanier.

Seems Mr. Lanier invented the ice cream cone , and got very rich.

As he was tossing them out a window one day he discovered that cones closed on the top fell faster than the open ones.

LIFT difference had to be the answer , so he had built an entire series of small air craft with conventional wings , that were left uncovered on top!

The most interesting part was with this configuration the planes did not stall or spin.

The then concluded (like the FAA about todays commercial seat occupiers) that pilot training would not be needed , and folks could drive air cars with almost no training.

More power goes up , less power goes down, done.

He even had plans for gas stations next to highways , so folks could IFR distance driving (IFR = I Follow Roads)..

70 % of the lift from the upper surface ?, not always.

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Old 09-26-2009, 08:22 AM   #36
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how much hp to plane?

Regarding gravity cannot be explained:

32 ft/sec/sec (the correct terminology) is* explainable and understood - at least to the extent NASA, Einstein*et al need to understand it. For hundreds of years many learned scholars doubted Newton's findings, falling back on the "you can't explain to me" logic that permeated the times. The ability to read and write, do complex math and understand the relationship between mass, acceleration and force led to f=ma. This relationship*took the physics world by storm several centuries ago. And then came along the theory of relativity with the notable e=mc2 100 years or so ago. And integral to each is "m" or mass.

Which leads us to why a heavy motor boat needs more HP to go fast than a lighter boat of the same hull and prop shape - "m." And explains why a fast light trimaran recently set an Atlantic crossing record of about 32 knots - average speed! Yes, the trimaran relied upon lift - "f" - using those things called sails or better known as vertical wings - indeed having greater pressure on one side of the sail as compared to the other.*

Now for "a" - I'm outta here!

-- Edited by sunchaser on Saturday 26th of September 2009 08:25:11 AM
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Old 09-26-2009, 06:28 PM   #37
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RE: how much hp to plane?

Yea Friendly Fred,
Your'e right. There are many or so theories about lift** ..* I even have my own** ..* has to do w inertia, and if it's right it's supports your missing upper surface idea. I noticed on one of the hang gliders I flew wrinkles on the upper leading edge tward the tip didn't seem to cause tip stalling or any other strange stuff and the wing was of very high performance for it's type. Seems to me we talked about this for about a month quite awhile back.

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Old 09-26-2009, 09:12 PM   #38
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RE: how much hp to plane?

There is only one thing a person needs to know about why a wing develops lift and that is that a wing moves air down. An airplane flies not because of the Bernoulli Theorem but because of Newton's law of action and re-action. The Bernoulli Theorem or Principle is just one factor that helps a wing move air down, but the bottom line is that a wing moves air down with a force that opposes the weight of the airplane. You can design a wing to fly with no difference between the upper and lower surfaces at all--- remember the little flat wing, balsa wood, rubber-band powered airplanes we used to build?

A sailboat sail operates the same way. The sail, using a variety of aerodynamic and physical principles, moves air down, or away in this case, and this force in combination with the hull, keel, etc. design moves the boat forward.

We have a terrific piece of film in our library illustrating the moves-air-down principle of lift. It's of the prototype 757 skimming the top of a flat cloud layer. The camera plane was out front of the 757 looking straight back at it and when you see the reaction of the cloud layer behind and under the plane, the whole lift thing instantly becomes crystal clear. NASA and the National Air & Space Museum both use the "moves air down" explanation of lift on their websites.

I have a drawing sent to me by one of the at-the-time chief aerodynamicists at NASA which illustrates what a 747 wing would have to look like to develop enough lift to fly using the Bernoulli Theorem alone. In order to get the required pressure differential, the upper surface of the wing would have to have a curve on it that stuck up higher than the tail. Needless to say, this configuration would generate so much drag the airplane would never be able to get off the ground.

So a plane does not fly because there is lower pressure across the top of the wing, it flies because the wing, for a whole host of reasons, moves air down with the same force required to oppose the weight of the plane.

As FF said, there have been wings designed with no upper surface at all. Many of the early planes, including the Wright's, had only a single surface--- the upper and lower surfaces of the wing were exactly the same. The first successful seaplane, Fabre's Hydravion in France, not only had a single-surface wing but had a thick cross-hatched box beam at the leading edge that stuck up above the wing. Using the Bernoulli Theorem plus the smooth-airflow-over-the-top idea, this wing should not have flown at all, but in fact it flew very well. Because, regardless of how many "rules" it broke, it moved air down with the same force as the weight of the plane.
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Old 09-30-2009, 04:22 PM   #39
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RE: how much hp to plane?

Quote:
sloboat wrote:

It is my understanding that semi-displacement/semi-planing boats never really achieve true plane. While the hulls are designed to provide a modicum of lift, such that less of the wetted surface is below the water line, they never actually get on a true plane.
It's been my observation-- and from what I've read by marine architects--- that you are correct. I suppose you could force a boat like a GB onto a full plane if you put huge engines into it, but for the types of engines typically used in today's "trawlers," even the relatively high-power engines, they cannot force the hull to go fast enough to achieve a true plane.* The deep forefoot and keel of the typical trawler-type boat adds a great deal of drag, so a sort of plowing "semi-plane" is the best these boats can achieve.

The main benefit of the semi-planing hull on a trawler-type boat is that it can be driven faster than hull speed.* So even though there is a significant fuel burn penalty, one can have the advantages of a trawler-type hull (large interior volume, heavy, stable) but still cruise at higher than glacial hull speeds.* For example, the stock GB42 of the late 90s/early 2000s with Cat 400-something horsepower engines could cruise at about 14-15 knots.* It burned 23-25 gallons an hour to do it, but you got where you were going sooner than if you ran the boat at 9 knots and some 8 gallons per hour.* To people who have limited time available, the ability to get to and from their destination quickly is an advantage as it gives them more time to spend at their destination.

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