Hull Speed
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It has been a long time since I did the "naval architect" thing but I seem to remember that hull speed (kts) is 1.34 times the square root of the waterline length in feet.
Converting Kts to MPH
Also, the multiplier for Knots to MPH is 1.15077945 (1.15 for argument sake!). Thus 6.46 kts hull speed = 7.44 MPH. So you had the conversion math correct in your original post, but I'm unclear where the original hull speed datum came from.
Also, the multiplier for Knots to MPH is 1.15077945 (1.15 for argument sake!). Thus 6.46 kts hull speed = 7.44 MPH. So you had the conversion math correct in your original post, but I'm unclear where the original hull speed datum came from.
Here's the hull speed answer and more
Potential is one thing. Luck, timing and a stinkin' blow under too much sail will add to most detailed calculations. Or...screw the reef, stow the gear, pull up the CB, everybody on the windward stern side and crack off....wahoo. It's no Hobie but it'll do better than hull speed in a blow. With this big old flat bottom on the 260 I've had ours over 8.2kts with 5 guys on the tail under full sail heading off the wind in the gulf. It was surprisingly well behaved if you can find some flat water. Drain the FW tank in the bow(not the ballast), leave your fine china and all the porky stowage on the dock for a little extra bump
Good calc site with extras. http://www.sailingusa.info/cal__hull_speed.htm Have fun, Michael
Potential is one thing. Luck, timing and a stinkin' blow under too much sail will add to most detailed calculations. Or...screw the reef, stow the gear, pull up the CB, everybody on the windward stern side and crack off....wahoo. It's no Hobie but it'll do better than hull speed in a blow. With this big old flat bottom on the 260 I've had ours over 8.2kts with 5 guys on the tail under full sail heading off the wind in the gulf. It was surprisingly well behaved if you can find some flat water. Drain the FW tank in the bow(not the ballast), leave your fine china and all the porky stowage on the dock for a little extra bump
Good calc site with extras. http://www.sailingusa.info/cal__hull_speed.htm Have fun, MichaelExceeding Hull Speed
There was some hot debate on the subject of exceeding hull speed a few years ago. There were those of us who had done it and thus understood the formula to be a guide and those who insisted it couldn't happen because of the laws of physics. I may get the terminology wrong, but ultimately it turns out that the hull speed calculation is for full displacement hulls. The smaller boats most of us sail can act as semi-displacement hulls and will exceed hull speed in the right conditions. In one of the message threads someone provided a link to another site explaining all this, but I can't find in in the archives. My h26 exceeded 8knots for a number of minutes on a broad reach once and others have done same. See link. Ron Mehringer h26 Hydro-Therapy
There was some hot debate on the subject of exceeding hull speed a few years ago. There were those of us who had done it and thus understood the formula to be a guide and those who insisted it couldn't happen because of the laws of physics. I may get the terminology wrong, but ultimately it turns out that the hull speed calculation is for full displacement hulls. The smaller boats most of us sail can act as semi-displacement hulls and will exceed hull speed in the right conditions. In one of the message threads someone provided a link to another site explaining all this, but I can't find in in the archives. My h26 exceeded 8knots for a number of minutes on a broad reach once and others have done same. See link. Ron Mehringer h26 Hydro-Therapy
The constant of 1.34 was developed
many years ago and based on a hull whose shape few boats resemble today. It follows that the results for hull speed obtained from the waterlength of your boat are not exact. The good news is that dealing with such slow speeds the percentage of deviance is small thus rendering a somewhat meaningful figure. Which way does the error manifest itself? Are today's boats faster that what the formula yields or slower? It seems smaller, lighter boats are faster while longer, heavier boats are slower, that is in average terms. You have to define speed over water as a guideline as it is very easy to attain speeds over 8 knots over land in a small boat when sailing with a current of 2-3 knots. Is the math important to 2 or 3 decimal points? Given the limitations of the constant, not at all. The best way to prove if one boat is faster than another is to get both of them out in the water and ovelook the ability of the sailors.
many years ago and based on a hull whose shape few boats resemble today. It follows that the results for hull speed obtained from the waterlength of your boat are not exact. The good news is that dealing with such slow speeds the percentage of deviance is small thus rendering a somewhat meaningful figure. Which way does the error manifest itself? Are today's boats faster that what the formula yields or slower? It seems smaller, lighter boats are faster while longer, heavier boats are slower, that is in average terms. You have to define speed over water as a guideline as it is very easy to attain speeds over 8 knots over land in a small boat when sailing with a current of 2-3 knots. Is the math important to 2 or 3 decimal points? Given the limitations of the constant, not at all. The best way to prove if one boat is faster than another is to get both of them out in the water and ovelook the ability of the sailors.
Speed restraints and potential
Ahh, the laws of design. Benny is right to point out that there are design limits of bigger full keel boats vs "smaller lighter" shapes. My point and the orig question was regarding the potential of the portly, wide flat bottom 26/260 which (very)remotely resembles the faster, flatter stern section, hull shapes of the Open 30/40/50/60 designs. While I don't expect to be skipping along at 30+kts, with a little attention to weight distribution, drag and max sail area some hull designs will perform beyond a generalized rule. In the mean time I can usually gain 1.5kts+ over the "general design law" for a brief sprint in flat water(without a current or even surfing). Light air is a whole other story in which I get spanked often due to my attention drifting when boat speed reduces to under 3kts. *zzz too peaceful to be uptight. All for fun, Michael
Ahh, the laws of design. Benny is right to point out that there are design limits of bigger full keel boats vs "smaller lighter" shapes. My point and the orig question was regarding the potential of the portly, wide flat bottom 26/260 which (very)remotely resembles the faster, flatter stern section, hull shapes of the Open 30/40/50/60 designs. While I don't expect to be skipping along at 30+kts, with a little attention to weight distribution, drag and max sail area some hull designs will perform beyond a generalized rule. In the mean time I can usually gain 1.5kts+ over the "general design law" for a brief sprint in flat water(without a current or even surfing). Light air is a whole other story in which I get spanked often due to my attention drifting when boat speed reduces to under 3kts. *zzz too peaceful to be uptight. All for fun, Michael
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