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Old 02-19-2019, 02:18 PM   #381
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While your efforts to reduce the conversation to the vernacular are admirable I have serious doubts it'll work regardless of my agreement with you.
Fish53,
We vary widely to the degree of knowledge we have about this. Probably isnít a good subject for this forum as many (perhaps most) seem ďsnowedĒ and donít take part. Others interupt the the thread w jokes and some get onboard and try to understsnd. But thatís really hard when those that seem to know most about it and have the knowledge to argue ... do just that. And disagree on even basics. So most are frustrated and probably donít read any of it.

I have had an attitude that thought those that are interested would take part and others would go elsewhere. Most subjects on TF donít interest me so I tend to get involved in those that do.

So no ... I disagree w myself. Not a poor subject and weíre all learning .. even while arguing. And those that dislike the subject can go to others.
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Old 02-19-2019, 02:20 PM   #382
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Something thatís been missing from this discussion is observations.

When I repowered Willy I kept track of all the boats I saw as I went about on the floats, on TF, in magazines ect ect.. I even observed the numbers posted on a plaque on the bulkhead of an Alaska State Ferry. And when I didnít know how much power the boat had or what the WLL was or the boatís displacement I tried to find out and usually did. What I paid attention to most was how much hp a boat had per ton of displacement. I quickly found out there were quite a number of boats that had considerably less power than most. And observed their performance. This led me to determine how much power per ton was required to push a FD hulled boat. The average was a wide range of 4-7 .. for boats that I thought were powered well. The KK42 has 7. Once and awhile Iíd find a boat w only 2hp per ton. Most ofthose were large. I chose for Willy a 37hp engine that delivered 5hp per ton of disp. I knew 4 would do from my calculations and observations but I was too chicken to risk being underpowered. But now I know Iíd have been fine w 33hp. Interestingly thatís what Willard gave the 30í boats. It was a 36hp engine but they overpropped all the boats so only had about 33hp ďon tapĒ. But Iíd probably be running at 24 to 2500rpm instead of 2300. Or gone slower. So Iím glad I choose to get close to the edge but not too close.

But it was observation that led me to what I needed to know.
2hp per ton is the traditional number and many sailboats have less than that. I powered my 3 ton boat with a Lister rated at 20hp@3000rpm and adjusted the fuel stop at 2600rpm for 18hp so I could go up an inch in propeller diameter so now I have the most diameter that will fit the aperture, 18 inches. I'll share something from the UN of all places that you may find interesting.www.fao.org/3/i2461e/i2461e.pdf
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Old 02-19-2019, 02:27 PM   #383
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This is interesting as well.....

How to “Right Size” the Engine. Most displacement-hull commercial fishing vessels in Alaska are overpowered; that is, their engines can produce more power than is needed to propel the boat at its “hull speed” and do the required work. Hull speed is the rate through the water at which a displacement hull vessel starts to encounter excessive wave resistance forces and requires disproportionately more power. Hull speed (in knots) is calculated as 1.34 times the square root of the waterline length in feet. (The 1.34 multiplier applies to a typical hull with a length to beam ratio of approximately 3:1. A lower multiplier would apply to a beamier hull, whereas a slimmer hull would have a larger multiplier.) For example the hull speed of a boat with a waterline length of 36 feet would be calculated as follows: the square root of 36 is 6. Multiply 6 x 1.34 and the result is a hull speed of about 8 knots. Hull speed for an 80 foot hull would be 12 knots based on the following calculation: 80 has a square root of approximately 9. Multiply 9 x 1.34 and the product is about 12 knots. Hull speed for a typical boat in calm sea conditions (that is, steaming power demand only) requires about 4.5 hp per displacement ton. Increasing speed by one knot increases horsepower and fuel requirements by about 50%, and at speeds above hull speed the increase is even steeper. At a speed:length ratio of 1:1 only about 1 hp per displacement ton is required. Add a 15% horsepower “sea margin” to overcome adverse wave conditions, and a 36-footer that displaces 12 tons needs only 62 hp to achieve an economical 8 knots. Since a diesel engine is most efficient running at about 80% of its rated horsepower, the
A seiner is steaming at about hull speed. The “bone in its teeth” shows that it is using more fuel than necessary.
7
nominally correct size of engine for this vessel would be 77.5 hp. Most Alaska fishermen are unwilling to settle for such a small engine—they like the feel of additional power, they believe that it’s easier on the engine to run it well below its 80% output rate,1 or they simply feel they need to go faster. But additional power comes at the cost of greater fuel consumption. Right-sizing an engine at replacement time or during new construction can save in both capital and operating costs. This was from a booklet about fuel savings for Alaska fishing vessels from Seagrant. This all pertains to fishing vessels but is nonetheless pertinent to our discussion.
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Old 02-19-2019, 02:32 PM   #384
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While your efforts to reduce the conversation to the vernacular are admirable I have serious doubts it'll work regardless of my agreement with you.
53 - I agree wholeheartedly... with your serious doubts mentioned above!

Reason I enter this confab is due to my desire for TF to remain my adjunct of boating knowledge and reading pleasure during hours of my busy and often fun filled life!

TF enables me to somewhat take the edge off... while my mind still plays with other items of which I'm involved.

Regarding boating and many other circumstances in my life... I usually try to keep taking the helicopter view. I like to see the forest... not just the trees!
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Old 02-19-2019, 02:38 PM   #385
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Sadly I'm mortally fascinated by this subject, so much so I know the SL ratio of my Mazda 3 and my horse. Unfortunately my life is seldom busy or fun filled as you may have guessed.
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Old 02-19-2019, 02:57 PM   #386
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I think everyone pretty much agrees about the behavior of different hull types. But it became apparent to me that almost no one here save two, maybe three other posters, understood what those hulls could look like, and the design elements that lead them to look that way and as a result behave (or have the ability to behave) a certain way. And equally, what design elements in and of themselves have little to do with it.
Is it draft? No, look at a Great Harbor.... Is it nice rounded chines and cross section? No, look at the hauler... is it an above waterline transom with a rounded, tapering bottom, no flattish sections? No, look at the Nordhavn 62.... and so on and so on.

Certainly, most rec boaters and not a few pros, don't care, they just want to know what the boat's range of behaviours are not so much what causes them. Nothing wrong with that, I'm certainly the same way about most contraptions.
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Old 02-19-2019, 03:32 PM   #387
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Fish53,
We vary widely to the degree of knowledge we have about this. Probably isnít a good subject for this forum as many (perhaps most) seem ďsnowedĒ and donít take part. Others interupt the the thread w jokes and some get onboard and try to understsnd. But thatís really hard when those that seem to know most about it and have the knowledge to argue ... do just that. And disagree on even basics. So most are frustrated and probably donít read any of it.

I have had an attitude that thought those that are interested would take part and others would go elsewhere. Most subjects on TF donít interest me so I tend to get involved in those that do.

So no ... I disagree w myself. Not a poor subject and weíre all learning .. even while arguing. And those that dislike the subject can go to others.
Your response to the quoted comment of mine leaves me wondering how exactly you are interpreting what I said? However I agree with much of what you said, I share your disinterest in curtain colors, countertops and sundecks. The subject at hand is one that throughout my professional career was one of great interest and importance, hence my enthusiastic, opinionated and to some even annoying participation.
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Old 02-19-2019, 04:50 PM   #388
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Fish53,
You have no idea how glad I am that you came along. For the most part you’re helping me propagate much of the things I’ve been talking about for about ten years. Went to town but not the bookstore. Not feeling well .. came home. Hold the fort.

PS. What’s Gerr’s first name? Dave?
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Old 02-19-2019, 04:55 PM   #389
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I hope you're OK, take care of yourself. I was serious that I enjoy your posts, and that you don't seem to take offense to my twisted humor.
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Old 02-19-2019, 05:35 PM   #390
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reply to fish53...pitcarin island, where bounty ended up! back in the later 60`s, i`d had my ham call for a coupla yrs+, was on one afternoon, i lived near bremerton, wa, in my [inherited] mom`s house, right on the water, had a 70 ft rohn tower, with a small antenna farm on it, ran collins gear, with a 1000 watt heathkit linear...early in an afternoon, winter time, was on 15 meters i think, there was a pile up, swung my beam around to east/south est, to improve my signal, heard lady with a qst request, turned till i had her good, went back to her, she answered, she was on pitcarin, was a decendent of the bountcrew, i was her first ever contact!! never forget...clyde
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Old 02-20-2019, 10:33 AM   #391
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For those that thought this thread was a bit of a mystery and for those still trying to expand their scope on it consider that there are numerous roads to understanding.

When I was in the Navy in electronics school basic electronics was taught using various analogies. For electron flow and resistance current flow was presented to be like water flowing in a pipe and resistance as the narrowing of the pipe or an adjustable valve in-line in the pipe. But the usual method was numerical through formulas and other numerical relationships and mechanics.

For the hull speed questions the same is true. I use numbers a lot for relationships that expand understand but me being a visual person like my mother that was an artist I lean toward visual concepts to relate to complex issues and even the world at large.

The speed/length ratio is expressed numerically and Fish53 relates well to numbers and thus his road to understanding is through numbers. The range of hull designs is identified with fractional limits that relate to wave lengths that a boat creates as she moves through or over the water.

So if you read something that makes you wonder what they’re talking about try another source that will give you a different perspective. The light may go on.

Hope this is heplful.
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Old 02-20-2019, 11:34 AM   #392
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Originally Posted by Nomad Willy View Post
For those that thought this thread was a bit of a mystery and for those still trying to expand their scope on it consider that there are numerous roads to understanding.

When I was in the Navy in electronics school basic electronics was taught using various analogies. For electron flow and resistance current flow was presented to be like water flowing in a pipe and resistance as the narrowing of the pipe or an adjustable valve in-line in the pipe. But the usual method was numerical through formulas and other numerical relationships and mechanics.

For the hull speed questions the same is true. I use numbers a lot for relationships that expand understand but me being a visual person like my mother that was an artist I lean toward visual concepts to relate to complex issues and even the world at large.

The speed/length ratio is expressed numerically and Fish53 relates well to numbers and thus his road to understanding is through numbers. The range of hull designs is identified with fractional limits that relate to wave lengths that a boat creates as she moves through or over the water.

So if you read something that makes you wonder what they’re talking about try another source that will give you a different perspective. The light may go on.

Hope this is heplful.
Eric - Well put.

Myself being a [self described] airflow expert [over 45 yrs. hands-on study, learning, planning, building] regarding chimney design, temperature conditions and venturi as well as flex fabric vertical and horizontal tunnel airflow effects... I'd like to mention the following:

Moving items through and movement of and displacement in and separation from-like-kind and rejoining of like kind and capability to enclose or support foreign objects... regarding water and air are not really all that different. In that both have weight and molecules that flow in a fluid/path/state and that both have properties wherein they would rather not be separated; but, if done so will try to immediately rejoin via simplest means/path... unless somehow diverted too faraway so no re-contact capability is afforded. Also in similarity; air and water can join forces with any of the same no matter where they may be introduced for contact. And, both can somewhat alter composition for becoming capable to be mixed together and/or with other liquid or gaseous items.

Like I mentioned: "... water and air are not really all that different."

Hot air balloons at the whim of air currents [with a little assistance from heat torches] can be likened to powerless barges that are at the whim of water flow [awaiting barge assistance]. Dirigibles that have low hp. propulsion engines can be likened to really deep draft FD hulls. Cessna and other privately owned prop planes' speed through air can be likened in similarity to SD hulls. Semi-fast pleasure boats resemble really fast propers - i.e. WWII Spitfire, Mustangs, Zeros etc. Over 100 mph racing boats are not too unlike fighter jets... think Blue Angles.

Point I'm trying to press here: Designs and power-installed of floating or flying units have pretty simple individual criteria regarding their capability of speed, handling, and worthiness in air and/or water. In effect, there is no set [exact] design criterion that connotes fast or slow, nor good or bad handling for any craft. I.e. - each hull-product design and propulsion-scope enabled is extremely individualistic regarding performance capabilities that can be realized.
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Old 02-20-2019, 11:48 AM   #393
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Eric

If you'd followed D Gerr over the years, and today go to his website, you'll find that some on TF get more wrought up about this subject than Gerr does.

Look at a few of his and his fellow Westlawn grads' designs. There are hundreds or more . You'll see some real pros in yacht design who have often ventured into the gray areas and built marvelous craft with often barely decipherable by "our" terms hull designs.
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Old 02-20-2019, 02:11 PM   #394
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Sunchaser,
Great tip I’m sure and I will follow up on that. Can’t bookmark a post but I can put you in “notes”. •

Thank you my friend
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Old 02-20-2019, 02:26 PM   #395
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Art,
Great stuff there mate;
The biggest difference between air and water that I know of is that water is not compressible .. air is. Air brakes and fluid brakes both work but they feel different.
Both tend to follow a curved surface but airfoils and hydrofoils have considerably different chacteristics. Hang gliding and flying ultralight aircraft in addition to my experience w boats gave me opportunities to see these fluids in action and be well aware of many of their differences.
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