SailNet Community - View Single Post - How do you measure the waterline
View Single Post
Old 07-27-2012
johnnyquest37's Avatar
johnnyquest37 johnnyquest37 is offline
Senior Member
Join Date: Feb 2012
Location: Houston, TX
Posts: 396
Thanks: 1
Thanked 6 Times in 6 Posts
Rep Power: 4
johnnyquest37 is on a distinguished road
Re: How do you measure the waterline

Originally Posted by rbrasi View Post
So, if at 25' LWL, my hull speed calculates to 6.7 Kt. What is the best measure? I currently use a Garmin GPS to get my speed readings, but that is speed over land. How does that translate? I routinely exceed 6.7 with current and a decent wind, according to my Garmin.
The GPS is giving your speed over ground. Hull speed is your theoretical maximum speed through the water. If we are doing 6.9 knots (hull speed for the Hunter 29) through the water, but the water itself if moving with say, 1 knot of current in the direction we are travelling, then the GPS would measure 7.9 knots of speed over ground. Current can help you go faster than hull speed and so can waves. As you slide down the face of the wave, your boat speed will increase. I once clocked 12 knots of SOG while surfing down 5-6' waves and my boat has a theoretical hull speed of 7.4 knots.
[/B]S/V Wind Orchid
Catalina 350 (hull# 273)
Annapolis, MD

Reply With Quote Share with Facebook