What is a faired keel worth?

[dlochner]

Great input. Thanks. The topic comes up because the boat is out of the water and getting a bottom job. I enjoy all the technical stuff and the science that goes into the sport. One interesting thing I came across is the practice of fairing the through hulls. This is to use filler to build up a tear-drop shape fairing around each through hull kind of like wheel pants on a sporty airplane. Anyone out there done this?

If the through hulls are mushroom shaped then maybe? Mine are all flush and adding a fairing would increase drag not decrease it.

As for fairing the most important areas are forward. The goal is to maintain smooth laminar flow across the hull surface. Once the flow gets detached it pretty much stays detached, so water around the sail drive, strut, or other fittings will be disturbed and the water behind those structures will be turbulent, fairing won't be as important.

To be clear, I'm referring to a reasonable bottom profile and by rough or unfair, I'm thinking of the kind of stipple you get from using a roller to apply bottom paint and a few minor imperfections in the hull surface, not a hull that has lots of growth or layers of old flaking bottom paint.

 

[Davidasailor26]

But is it really? Especially in SF Bay where the winds are consistently in the high 20s. My feathering prop gives me a HUGE boost over similar boats at low wind speeds. Like pass em right by. But at higher wind speeds where sails are producing big power, the advantage fades away. I don’t race, don’t have a rating, just lots of observed.

Probably depends on the boat. I know our rudder with a fixed prop started to lose effectiveness in higher wind ranges, because the prop was causing turbulence right in front of the rudder. That all led to extra drag and round-ups, which aren't fast. With the folding prop the turbulence is less, so we need less rudder angle and have more control at high wind speed. Looking at the boat speed differences between fixed and folding, they are big at low wind speeds (way more than the PHRF penalty), minimal when the wind is in the teens, but then they grow again as wind gets into the 20's.

 

[jon hansen]

back in the day dennis conner would pull his personal boat out the water every week to 2,000 grit sand it before the weekly club races in san diego. this was a new vessel yet when your dennis, everyone is gunning for you. you need to keep your street cred.
every detail counts

if , like you said, you enjoy learning the science of these things. 'high performance sailing' by frank bethwaite will take it down to the molecule of every detail of your boat. then teach you the most important skill of all, 'how the wind crosses the surface of the earth and interacts with a sailboat.
if you want to 'WIN' , you'll need to learn what the winners know

 

[Gunni]

If you are rounding up in a beneteau cruiser your problem is too much sail and the drag you are experiencing is the rudder you are dragging sideways through the water to keep the boat off the wind. I put an old IOR sailer at the helm and this happens on a regular basis. Got to sail them flat.

 

[markwbird]

The friction through the water increases with velocity. In fact, it is proportion to the velocity squared. So doubling the speed increases the friction by a factor of 4. Hull speed is hull speed so it won't matter so much then.