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post #1 of 13 Old 04-10-2008 Thread Starter
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Natural Speed

I read an article in a boating book years ago about what was called a boat's "natural", speed . . . not to be confused with hull speed.

My boat, at the time had a "natural" speed of about 2+ knots.

If I remember right, the "natural" speed was a speed at which the boat could move with virtually no effort to keep it going once it reached this "natural" speed.

If I retire to a boat, as I hope to, I plan on using the idea of "natural" speed on excursions that will allow . . . hopefully saving a lot of fuel.

I have never been able to relocate this article, although I've been looking for years and was hoping someone here might know about this "natural" speed or the formula to determine it.

If I remember right the weight and beam pretty much determined the natural speed.
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post #2 of 13 Old 04-10-2008
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I googled "Natural Speed" and came upon a research paper that mentioned the formula. I can't paste the link because I dont have enough posts yet so I have included the quote. Hope this is what you are looking for.

Ed

"When talking about hull design it is important to consider the natural speed of a boat. The natural speed is simply the speed at which a boat will easily travel though the water without the use of excessive external forces. In order to assess the natural speed of a boat this equation is applied: take the square root of the waterline length which is the measure of the waterline on a boat. This formula will give the boats' natural speed in knots. To then convert nautical miles (knots) into miles per hour, multiply by the knots by 1.15. For example, a boat with a 25 ft water line will have a natural speed of 5 knots or 5.75mph. "

EDIT: hs.riverdale.k12.or.us/~hfinnert/exhib_04/bryang/paper/paper.html#naturalspeed
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post #3 of 13 Old 04-10-2008
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Of course, that formula probably doesn't apply properly to multihulls, since most of the formulas are designed for monohulls only.

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post #4 of 13 Old 04-11-2008
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Anyone else think the term "excessive external forces" is just a tad bit ambiguous?

Seems like it would be talking about an inflection point on a force to speed graph - but just before that we would be using less force...
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post #5 of 13 Old 04-11-2008
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Anyone else think the term "excessive external forces" is just a tad bit ambiguous?

Seems like it would be talking about an inflection point on a force to speed graph - but just before that we would be using less force...
Is it where force to speed becomes exponential vice linear??

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post #6 of 13 Old 04-11-2008
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lol - good point. Guess I was reading it wrong
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post #7 of 13 Old 04-11-2008
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Natural speed, I never heard of this however every boat that I ever sailed had a "sweet spot." This would be be where everything fell in to place. One of the boats I am most familiar with has a water line of 25 feet. At 10 kts of wind I can get mid to high 5's of boat speed out of her. This works out very close to what the "formula" says it should be. To push the boat speed to the mid 6's I would need wind in the 15 kts range. That is a 50% increase in energy and only 15% increase in boat speed.

This holds true wither boat is under sail or power. For instance my boat burns a 1/4 gallon a hour of diesel at 5.2 kts, if i push it up to 6.5 kts i am burning 1/2 gallon a hour.

Other sailors I know refer to it as being in the "groove."

Last edited by bubb2; 04-11-2008 at 06:48 AM.
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post #8 of 13 Old 04-11-2008
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Quote:
Originally Posted by L02314564 View Post
I googled "Natural Speed" and came upon a research paper that mentioned the formula. I can't paste the link because I dont have enough posts yet so I have included the quote. Hope this is what you are looking for.

Ed

"When talking about hull design it is important to consider the natural speed of a boat. The natural speed is simply the speed at which a boat will easily travel though the water without the use of excessive external forces. In order to assess the natural speed of a boat this equation is applied: take the square root of the waterline length which is the measure of the waterline on a boat. This formula will give the boats' natural speed in knots. To then convert nautical miles (knots) into miles per hour, multiply by the knots by 1.15. For example, a boat with a 25 ft water line will have a natural speed of 5 knots or 5.75mph. "

EDIT: hs.riverdale.k12.or.us/~hfinnert/exhib_04/bryang/paper/paper.html#naturalspeed
How is this different than hull speed?
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post #9 of 13 Old 04-11-2008
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Natural Speed
. . . and I thought Surv69 was announcing a new source for "natural" adrenaline boosters - legal speed!

After all, his moniker suggests he's a Woodstock survivor. (g)

True Blue . . .
sold the Nauticat
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post #10 of 13 Old 04-11-2008
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Quote:
Originally Posted by bubb2 View Post
Natural speed, I never heard of this however every boat that I ever sailed had a "sweet spot." This would be be where everything fell in to place. One of the boats I am most familiar with has a water line of 25 feet. At 10 kts of wind I can get mid to high 5's of boat speed out of her. This works out very close to what the "formula" says it should be. To push the boat speed to the mid 6's I would need wind in the 15 kts range. That is a 50% increase in energy and only 15% increase in boat speed.

This holds true wither boat is under sail or power. For instance my boat burns a 1/4 gallon a hour of diesel at 5.2 kts, if i push it up to 6.5 kts i am burning 1/2 gallon a hour.

Other sailors I know refer to it as being in the "groove."
Bubb,

From 10 kts to 15 kts is a 125% increase in energy. Kinetic energy increases with the square of the windspeed. That would reinforce your point about fuel consumption, which you said doubles from 5.2 kts to 6.5 kts.

Hud
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