hull speed ??
- Thread starter sunset lady
- Start date
this is a theoretical number based solely on the waterline length of the boat... it may be more or less depending on the underwater shape of the hull, weight and any protuberances or other hydrodynamic fouling that may be present on any particular boat of that waterline length...
Are you suggesting the correct answer should be an empirical value? The length of the waterline determines the length of the wave that the boat will ride in, and so determines its maximum through-the-water speed as a function of that wave length (ocean physics, so I'm told). It might go slower if there is excessive hull friction or inadequate power; it shouldn't be able to go faster if in that wave length. Could go faster if surfing, however.
I am NOT suggesting you are wrong, because you arent
and even though I quoted you, I was replying to the OP....
.
my thoughts are... someone who is asking what their hull speed probably doesnt know the limiting factors of their boat, and to offer them the posted theoretical number for their waterline length isnt wrong by any means, but in an attempt to give them a better understanding of why their boat may not get there, or may go a bit faster, i posted what i did....
and according to the definition in the dictionary, I guess i am absolutely suggesting its an empirical value....
"empirical, adj.
1 derived from or relating to experiment and observation rather than theory
2 (of medical treatment) based on practical experience rather than scientific proof
3 (Philosophy)
a (of knowledge) derived from experience rather than by logic from first principles
b (of a proposition) subject, at least theoretically, to verification"
(probably a much better definition elsewhere)
there are many forces that work on a boat hull that will determine its actual speed rather than just the length of the waterline, but the waterline length is the only actual single measurement that has a formula that can be used to determine theoretical hull speed of any given boat...
and even though I quoted you, I was replying to the OP.... .
my thoughts are... someone who is asking what their hull speed probably doesnt know the limiting factors of their boat, and to offer them the posted theoretical number for their waterline length isnt wrong by any means, but in an attempt to give them a better understanding of why their boat may not get there, or may go a bit faster, i posted what i did....
and according to the definition in the dictionary, I guess i am absolutely suggesting its an empirical value....
"empirical, adj.
1 derived from or relating to experiment and observation rather than theory
2 (of medical treatment) based on practical experience rather than scientific proof
3 (Philosophy)
a (of knowledge) derived from experience rather than by logic from first principles
b (of a proposition) subject, at least theoretically, to verification"
(probably a much better definition elsewhere)
there are many forces that work on a boat hull that will determine its actual speed rather than just the length of the waterline, but the waterline length is the only actual single measurement that has a formula that can be used to determine theoretical hull speed of any given boat...
I've always presumed that hull speed is a theoretical speed as calculated above. And boat speed as being related to hull speed pluse the other factors; friction, sail trim, helmsman, wind, sea state, etc.
Hull speed derived front the formula is for a boat on an even keel. On many boats, as it heels the waterline length increases, thereby increasing the theoretical hull speed.
If a boat is not reaching its theoretical hull speed, the first thing to check is the knot meter calibration.
The traditional hull speed calculation is about 300 years old, and was used to sus out the max speed of British sailing warships.
Today many more factors come into play than the calculation allows, and it is widely unused by modern naval architects. Several people have tried to come up with a better formula for existing boats (Gerr), but none are exact. There are too many variables. Most modem boats can slightly exceed their 'hull speed. Our First 260 has a waterline of 24 feet. That's a hull speed of 6.5 knots. We routinely sail at 7.5+, which is the hull speed of a boat with a 31 foot waterline.
Modern top-end raceboats (Volvo, etc) use models based on CFD (Computational Fluid Dynamics) and are very close.
Today many more factors come into play than the calculation allows, and it is widely unused by modern naval architects. Several people have tried to come up with a better formula for existing boats (Gerr), but none are exact. There are too many variables. Most modem boats can slightly exceed their 'hull speed. Our First 260 has a waterline of 24 feet. That's a hull speed of 6.5 knots. We routinely sail at 7.5+, which is the hull speed of a boat with a 31 foot waterline.
Modern top-end raceboats (Volvo, etc) use models based on CFD (Computational Fluid Dynamics) and are very close.
Thanks for the calculator: I feel a bit offended it calls my boat a bathtub. I knew she was a fat girl, but that calculator borders on insulting :O)
Well, that is a big first step! Have you ever sailed? If not, you might consider some dinghy lessons! They are so much fun, and they forgive you for being a little rough and uncultured at first!
As for the 272, this is my first season with my 272. I really am enamored of the boat! It feels fast and responsive. It has a nice cabin.
Enjoy!
Thanks,
Andrew
Have sailed 38 morgan few times. Also operated a 105ft crew boat several years. Enjoy sailing, think 272 would be good starter boatWell, that is a big first step! Have you ever sailed? If not, you might consider some dinghy lessons! They are so much fun, and they forgive you for being a little rough and uncultured at first!
As for the 272, this is my first season with my 272. I really am enamored of the boat! It feels fast and responsive. It has a nice cabin.
Enjoy!
Thanks,
Andrew