About speed

Guy Rossey · 24 Sep 2011, 18:48

Sailing pleasure is not speed dependent, outside racing. Yet. Cruising recently on a flat sea at 10-12kt of wind, my BR was running at 5,5-6,2 knots (GPS). I thought this is nearly her critical speed (V¨6m x 2,43 = 6 knots). With stronger winds and rougher sea the BR should start surfing. I never experienced this so far but would like to know under which conditions this can occur. Would some share their own experience in speed limits and surfing?
Thanks.
______________________
Catchando Bay (BR 48)

Jeremy · 24 Sep 2011, 22:00

If this was the GPS speed, it may not have been the speed through the water, so, depending on the current, the boat may have been going a little slower.

Where I used to live, on the South West coast of Scotland, it was pretty common to get 7kts indicated on the GPS when sailing my old 22ft boat North or South. About 2kts of this was the tide running up or down the North Channel, though, so the boat was only really doing about 5kts through the water.

Jeremy

Guy Rossey · 24 Sep 2011, 22:22

Quote from: Jeremy on 24 Sep 2011, 22:00
If this was the GPS speed, it may not have been the speed through the water, so, depending on the current, the boat may have been going a little slower.

Jeremy,
you are right. But here I sail on lake of Thau, close to Sète (FR) where there are no tides nor currents. The GPS should show pretty much the real speed.
Guy

Graham W · 24 Sep 2011, 23:27

My record GPS speed so far is 8.2 knots on a broad reach in an F5 off Corfu. Against a permanent current which is probably about 0.5 knots but down the front of a large wave. I have done more than 7 knots on a sustained basis in the same general area - exhilarating!

However, I am sure I read somewhere that Matt has done more than 10 knots.

Peter Cockerton · 26 Sep 2011, 08:29

Graham

I recently installed the NASA Clipper log and depth instrument which uses a paddle wheel transducer to determine speed through the water. Last Friday with full jib, main and mizzen close hauled i recorded 5.2 knots on the local reservoir. Beam and broad reach about the same. One of the reasons for fitting this bit of kit was to enable me to improve my sail trim, not sure how i'm going to get to the dizzy 10 knots though or even if enough water exists at Draycot. I must get around to fitting the centreboard mod to stop the fountain of water coming in just in case i start surfing.

Peter

Guy Rossey · 26 Sep 2011, 09:09

[quote I must get around to fitting the centreboard mod to stop the fountain of water coming in just in case i start surfing

Quote

Peter,
I installed door brushes face to face as shown. They reduce quite a bit the fountain but also prevent ropes and lines to get tangled in the centreboard.
Guy
_____________________
Catchando Bay (BR48)

Graham W · 26 Sep 2011, 10:59

Quote from: Guy Rossey on 26 Sep 2011, 09:09
[quote I must get around to fitting the centreboard mod to stop the fountain of water coming in just in case i start surfing
Quote

Peter,
I installed door brushes face to face as shown. They reduce quite a bit the fountain but also prevent ropes and lines to get tangled in the centreboard.
Guy

Interesting! I wonder if something like your brushes would also work on the underside of the slot and therefore suppress turbulence at source, allowing the boat to go even faster?

What is the purpose of the blue line coming out of the end of the spinnaker pole?

Guy Rossey · 26 Sep 2011, 11:58

What is the purpose of the blue line coming out of the end of the spinnaker pole?

Quote

Graham,
the red line pulls the pole out, the blue helps to pull it in.
Guy

Graham W · 26 Sep 2011, 14:08

I thought it might be an adjustable tack line, threaded through the pole to keep it out of the way...

Peter Cockerton · 26 Sep 2011, 21:15

Guy

I like the look of your brushes, can you let me know where i can aquire some for my boat, after my access hatch fitting (see forum entry on mizzen stainless bracket fitting) i allergic to messing around under the boat for a while so fitting on the top of the case is very appealing although i do see the case for reducing the turbulence at source as well.

Thanks

Peter

Guy Rossey · 26 Sep 2011, 22:05

Peter,
these are ordinary brushes which I got from the DIY shop (door insulation ). They carry different kinds of them, aluminum, plastic, etc... I bought brown plastic ones for some 5,-€ a piece and cut them to the wanted length. Nothing fancy really. When needed while sailing, you can slide them out without unscrewing the fitting . You should find them but if not I can send them to you.
Guy

Colin Morley · 27 Sep 2011, 21:50

Thanks an interesting discussion. My BR GPS frequently shows a speed over 10 kts. As has been said it is difficult to know the exact effect of the tide. In July I was sailing on lake Windermere (no tide) on my own with no water ballast and had a speed of 11.3 kts.

The BR has a good turn of speed and picks up very quickly with gusts.

Quote from: Guy Rossey on 24 Sep 2011, 18:48
Sailing pleasure is not speed dependent, outside racing. Yet. Cruising recently on a flat sea at 10-12kt of wind, my BR was running at 5,5-6,2 knots (GPS). I thought this is nearly her critical speed (V¨6m x 2,43 = 6 knots). With stronger winds and rougher sea the BR should start surfing. I never experienced this so far but would like to know under which conditions this can occur. Would some share their own experience in speed limits and surfing?
Thanks.
______________________
Catchando Bay (BR 48)

Jeremy · 27 Sep 2011, 22:37

I don't know about the conditions on Windermere specifically, but do know (from some work I did back in the mid 90's) that a lot of deep UK lakes have fairly strong seiches that can induce significant apparent surface flow rates from the standing waves they produce. The best example I personally measured was in a deep Scottish loch, where some colleagues recorded flows of around 1.5kts at the surface in one direction and deep water flows of a similar magnitude in the opposite direction. We had been doing some deep water sonar trials and found that the hydrophones were picking up lots of low frequency noise from being dragged sideways through the moving water.

Seiches are pretty common on big lakes and it isn't unusual to find the water at one end of a lake to be higher than that at the other because of the standing wave created by a steady breeze.

Guy Rossey · 27 Sep 2011, 22:56

[quote author=Colin Morley I was sailing on lake Windermere (no tide) on my own with no water ballast and had a speed of 11.3 kts.

Impressive Colin !
This is exactly the point. Even assuming 2 knots of confidence level, the speed is quite above the theoretical hull speed and the BR must be planing then, do you agree ? From what speed on does she start to, if so ? Could you tell us more about her behavior at 11 knots ? One day it would be interesting to see a video of that moment.

Guy
______________________
Catchando Bay (BR 48)

Graham W · 28 Sep 2011, 11:41

When I was doing my 7-8 knots (solo, full sail, no ballast), the boat was clearly planing, as 5.7 knots is the theoretical maximum hull speed. But the impression I got was that the stern was dug in more than usual and the steering became noticeably heavier, which felt reassuring I was sitting aft and possibly if I had shifted weight further forward these effects might have diminished and the boat probably would have gone even faster. I can only dream of 11 knots....