Chew Files

[Neil C.]

Thanks to Paul for posting those excellent videos.

I was looking at the 2nd one - Atum in 11knts breeze. It got me thinking about the whole T-foil thing. Now I may well have got this wrong, but I believe the theory goes that the downward displaced water under the hull rises again behind the transom, and in doing so exerts a force on the T-foil resulting in a bit of forwards propulsion. But looking at the video, I'm not sure I buy that. I think Atum's T-foil is pretty close to the bottom of the rudder blade - is that right? So presumably something approaching a metre under the water's surface. It doesn't look like the hull could possibly be doing much to the water 1 to 2 metres below the hull skin, I would say 50-60cm at the very most. So unless it's a + Foil with the element close to the surface, all it can be doing is taking a bit of displacement out of the hull, thus exchanging a bit of hull form drag for a slightly more efficient foil form drag, plus the extra skin friction of the foil. Can somebody enlighten me?

[kevin_ellway]

Thanks to Paul for posting those excellent videos.
" but I believe the theory goes that the downward displaced water under the hull rises again behind the transom, and in doing so exerts a force on the T-foil resulting in a bit of forwards propulsion."

At low speeds where the bow wave comes up towards the transom, the theory you've mentioned is correct. However, this is not the main effect of the T foil. At speeds above 7 knots, the lift to drag ratio of the T foil is much better than the hull. So it's advantageous to carry load on the T rather than the hull. So you pull some angle on the T, and then move aft to keep the hull at its optimum trim. So the T foil is actually reducing the displacement of the hull. You can carry around 60-70kg on the T if you move well aft. It is important to keep the boat at optimum fore and aft trim. Do not allow the bow to push down too much or the hull drag will rapidly increase.

I wrote a detailed article on this for Y&Y and it used to be available on the Cherub site.

[Neil C.]

Thanks Kevin. So taking the reduced hull displacement concept further, surely that should mean there is more potential gain from sticking a T-foil on a relatively fat '91 Rules boat compared to a skinny E5 or the like?

[Phil Alderson]

I wrote a detailed article on this for Y&Y and it used to be available on the Cherub site.

The article can still be found here , or follow the link at the bottom of this page

to view the page, you need to be an association member and logged into the wiki using the same login details as you use for the forum

[roland_trim]

A weeekend of 2 halfs:

Sat. We finally found the sweet spot setting for EJ's recut main and had a very nice time. It was very nice to see 10.5 knots on the velocitek when trucking upwind and to find the groove in the boat again. When the wind dropped we found the boat tacked when hit with light gusts.

Sunday - blowing old boots and had Maf on board. Sweet spot delivers power. Sadly when not on the money the rig delivers drag and is in generally far too on/off to be manageable in gusts. Boat tried to tack as big gusts hit, if you survive those then she motors.
Many thanks for Maf's extreme patience and willingness to put his body on the line. Short outing ended with a gusty power up-helm off the rear - crew through the jib carnage. Time to end playing with different sail plans for now and fit the sensible set.  Lots of lessons learnt, not necessarily giving up on the bat wing, but now's the time to get sailing again.


Team Atum tuned up and monstered about. Eventually even they had one swim too many and headed in. Then someone turned the wind off and rain intensity up.

[phil_kirk]

Due to a gentle forecast team Kirk joined team trim at Chew on saturday for a gentle sail. The first since last August.  Our challenge was to remember how to rig the boat, which we did eventually.  There was enough wind for single wiring up and down wind and the cobwebs were quickly blown away.

The larger chute and sock certainly make kite hoisting/dropping much easier. other small improvements also worked and make the boat a bit tidier. We do need to adjust the cunnigham and kicker (which were guessed when we put the controls back on) and possibly the caps. Everything else was as we left it.  I think a bit more practice is due before we hit the race course but the learning curve is less steep than last year.

[paul_croote]

Shame Atum could not make to the training weekend (couldn’t manage whole day with family commitments), looks like you had a great time. Managed to sneak off Sunday afternoon for a play with the camera. Bowsprit Cam: the way of the future! see- www.youtube.com/watch?v=0P5BY3kIDj8

[Stuberry]

That is excellent! How did you stop the camera/pole rotating?

[paul_croote]

 We went out with it hanging under the bowsprit thinking it would get in the way of the kite but on the first hoist it rotated around onto the top and it turn out not to be a problem. It only seemed to turn whilst hoisting and dropping, we just straighted it after each

[paul_croote]

To be fair to the crew, having posted him dropping the main,  I have posted the results of the helm not paying attention as we sail into a lull www.youtube.com/watch?v=I1jzBl5464M

[Phil Alderson]

That is nice clear video, and a good view point. I have put the first one on the Video page.

[Banshee Ambulance]

Are there any Cherubs based at Chew these days?

[paul_croote]

Hi Gordon
Yes there are two of us, although we tend to migrate to Thornbury  for part of the summer when the water gets low and the weed gets to high.

[roland_trim]

We are there for the Winter and Summer is Thornbury/events. You are more than welcome to come down to either club as a guest to see if you like them.

Sailing at Chew over the past few weeks has become weed city. This generally means that you get bored with clearing weed of the T-foil and sticking it in the other way around. Paul C. very kindly took the vids below to show that that the E5 with a Spoiler does work.

http://www.youtube.com/watch?v=_WyOXi9HPDM
http://www.youtube.com/watch?v=P8oIGHlNZdQ&feature=mfu_in_order&list=UL

[roland_trim]

Its 5.50 am and im sitting at the departure gate of Bristol airport.
Still have the massive grin from yesterdays sail plastered all over my face. The other passengers think i may be derranged, i probably am.

Not sure if it was the full bow up salute during the start sequence, the epic 2 sail death zone reaches on the course or going from starting in the wrong starting sequence and then sailing down the fast fleet.
Our luck ran out when we hit the front to discover neither of us knew either the course or where the mark was if we asked!

Lots of swimming and some massive laser terrifying 3sail reaches. No
capsizes on gybes, but many on the corners.