Thread: solving a mystery

Would the same thing happen, to some degree, with BETH as well? (I think the flat bottom, vertical sides are similar.)

Brian,
I'm not sure, but...

I think, your capsize depended on few several factors:

1. width of the boat,
2. height of center of weight above the waterline
3. transfer center of weight giving rise to a large heeling
4. wind giving rise to a larger heeling.

I remember: one time I've almost capsized my BETH due to careless sit on sidedeck while paddling - no wind and main dropped.

Originally Posted by MichaelB

Would the same thing happen, to some degree, with BETH as well? (I think the flat bottom, vertical sides are similar.)

Could be, but she is much narrower, so better immersion and the angle sweeping round to the bow much shallower.

Raid41 was so light, with such a "large hull bottom area" she had a tiny amount of immersion and sat on the surface just like an autumn leaf.

Brian

Originally Posted by robhosailor

Brian,
I'm not sure, but...

I think, your capsize depended on few several factors:

1. width of the boat,
2. height of center of weight above the waterline
3. transfer center of weight giving rise to a large heeling
4. wind giving rise to a larger heeling.

I remember: one time I've almost capsized my BETH due to careless sit on sidedeck while paddling - no wind and main dropped.

width of boat - yes - although she was narrow in respect to a normal 16' dinghy, so was so light she had no immersion.

Wind was light, sailors around me were amazed I capsized and dumbfounded as I was.

When a boat heels it's important she remains under control, still steerable and able to straighten up. Here the situation is - slight heel anf around she went. If you have ever broached in a yacht under spinnaker when it's very windy. Like that but this was not windy and no spinnaker.

[ame=http://www.youtube.com/watch?v=4w3QwJdzwsE]YouTube - Sailing in Heavy Weather - wiping out and getting into trouble[/ame]

It's connected to the way she behaved when capsize testing her. Pulling down on the gunnel standing beside her, she would depress a bit and then shoot away from me as the bottom lifted off the water and her deck spun towards me.

Doing the same thing in an Oughtred Gannet was entirely different. With my 90kg weight on the gunnel she heeled, bouyancy moved towards me, until the gunnel was depressed to water level. At this point the boat was in complete balance. My 90 kg pressing down, and the 90kg of the Gannet pressing down on the other side of the centre of buoyancy. This has to be described as perfect behaviour, and enables a sailor to roll back on board after a capsize with the gunnel at water level but stable.

Filled with water ballast Raid41's behaviour was so much better. It easily supported me sitting on the gunnel and almost held two of us sitting there! If only Chris had put the ballast tanks under the floor where MIK wanted them! Because Bryan got in trouble with ballast under the floor I did not follow up on this.

She still had this handling quirk.

Brian

Originally Posted by keyhavenpotter

After I gybed in 5 knots of wind onto starboard to be on the correct gybe for the up and coming turning mark, she heeled slightly and simply rounded up to starboard and fell over. There was nothing I could do. She rounded up and was over on her side, with completely bemused fellow sailors sailing by in the light winds. And yes, try to get back on board was a trial and only achieved with the rescue boats help.

Was it her flat bottom - well Goat has a flat bottom and she does not do this.

Was it her 90 degree sides?

Brian

Hi Brian, one other thing, did you have the centreboard all the way up?

My feeling is that with the boat being flat all the way across the bottom, and such light displacement, as the sail tries to make the boat round up, and you try to correct it with the rudder, if there is no centreboard in the water, there is nothing to grip at the front, so the boat keeps rounding up in spite of the rudder, and starts going sideways, then just at that moment you get some heel, and that outside edge forward catches and over you go.

It happens to some extent with other boats if you pull the centreboard up all the way, but most boats have a bit of a V forward, or like the GIS, the sides are quite flared forward so the effect isn't so extreme.

Beth is so much narrower, at not much less displacement, so it will be relatively deeper in the water along it's length and those chines will be immersed that much further forward, so there won't be the same lack of lateral grip forward, followed by sudden grabbing at the moment the boat is going sideways.

Ian

Originally Posted by IanHowick

Hi Brian, one other thing, did you have the centreboard all the way up? Ian

Good question. This was the second lap of the race. On the first lap I had the board mostly down. no problems, no problems at teh gybe for the mark. Perhaps the wind was even lighter.

Some of the Solo's and Enterprises around me had run downwind a little faster.

On this second lap I raised the centreboard to about half way and move forward to raise the stern to stop drag. Perhaps just a little bit more wind. Still light though.

Interestingly I spoke to Ken Rayford who is a very very experienced boat builder about having problems with my Raid41.

He started on clinker Scows as an apprentice at Berthons in Lymington and was involved in building the first grp boat, an Elizabethan 29, in the UK. He built a Keyhaven Punt, a flat bottomed duck hunting skiff, and left off one bit. They normally had an external keel, something like a 3" x 2" or similar, to make her "faster". She did not work at all and he had to add the shallow external keel to give her the grip she needed, and then she was fine.

It's almost as if she had a lack of grip and them too much grip as she heeled?

Brian

Hi Brian

I can only comment on the way the Goat behaves in a gybe. I have capsized twice while gybing in strong winds, once when hit by a bullet at the moment of gybing so they are not really related to your light wind capsize. There are strong similarities with the hull forms, so I'm thinking about this too. The Goat's bow doesn't have any tendency to dig in because she has plenty of rocker, but in a fresh breeze she does need to be flat during the gybe and countered with plenty of rudder to bear away and keep her flat or she will heel violently and tend to round up. However, this is not really uncommon behaviour in boats, but we are talking about this happening to you in a light breeze. A curved side will create the required pressures to cause the steering to windward. I guess it's the degree that it happens with the Raid41.

Other things like when she broached, how was the mizzen sheeted? If over sheeted a bit, perhaps it contributed if the bow sliced into a wave? Also was the rudder blade down all the way for grip? No grip means no control.

I have found that the Goat is happier running downwind (dead run) when there is a little bit more board down than most other boats I know. In very light winds the runners provide enough grip, but as the wind freshens to around 15 knots, about 1/2 the board is required, at least.

The other thing to remember is that she was always going to be a relatively tender boat due to her length and quite narrow beam. This tenderness disappears to an extent with the ballast, which is also the case with the Goat as Christophe has reported. Also, you were alone. Climbing aboard a narrow-beamed boat without somebody on the other side applying some mass would indeed be difficult.

Howdy,

The most mysterious part of this is that the capsize happened in lightish wind when you would expect sail forces, hull forces and rudder and centreboard forces to be quite low.

The difficulty always is trying to figure out just what causes strange behaviour in any boat.

Usually the best way to identify is try to duplicate it. When it happens really fast it can be pretty hard to work it out

A bit like the old windward roll on a run and the natural tendency to try and move inboard pushes the gunwale down further, whereas if you stay put and steer the boat under the mast it becomes relatively easy to handle - but if you don't quite know what is happening then it becomes mysterious and difficult to handle. I remember the time it dawned on me how it worked.

That is an example of how things can be difficult to interpret - not the reason Brian had trouble with the boat - he's been steering his way around that problem for years like the rest of us

I really have no idea what happened to Brian. Particularly that it was happening in relatively light wind.

My feeling is that it is probably multi factorial. I sailed the boat two up, though only a short time one up, but it included some reasonably intricate manoeuvring in light winds and flat water and a medium wind reach where the boat got up quite some speed and included a couple of gybes in rougher water - I was a little tentative because the boat did not have a tiller extension. I had some board up on the rougher water stuff, but followed my normal practice of leaving about half the board down.

There are some differences that I can point to and some other bits which I think are a blind avenue and my reason for thinking that

Centre of Gravity
The most noticeable departure from my other boats is that the centre of gravity is much higher because of the raised self draining floor. This means that the boat will reach the point of no return a fair bit easier when heeled towards the crew weight on the gunwale.

Movement of Centre of Buoyancy as the boat heels
Because of the square section there is little warning of the centre of gravity moving outside of the centre of buoyancy, and it will go over. Because of the initial stability of the square section it can be hard to detect. With Beth the centre of gravity is much lower and the beam tends to make you very aware that going over is a strong liklihood. HOwever she will heel over to almost 45 degrees before you have nothing left and she flips over.

I really don't think the little bit of flare in the Goat makes much difference at low angles of heel. From a water point of view, the boat is so shallow the difference is millimetres. Particularly at the bow.

By the time the boat is heeling over a fair amout the Goat would behave differently, but at low/medium angles of heel I would not expect much difference

Light displacement
It may have been possible to think it was my style of hullshape plus the effect of light displacement. That may be a doubtful thesis because of Bruces 105lb hull. lighter than the RAID by 10lbs or so.

Shape of the bow.
As a comparison I have put a drawing below that compares the RAID to the Goat and to BETH. I will just leave it up for a little and then probably get rid of it as it contains quite a bit of info that I've worked hard to develop.

In the first 500mm of each boat there is surprisingly little difference. At the 500mm point back from the bow the RAID and the Goat are about 30mm different.

Also if the bow produced a sizeable force then the centreboard would act as a pivot and the boat turned significantly. But Brian describes the feeling as "sliding sideways"..

In the end I really don't know what caused it but the area where the RAID is most different is the centre of gravity of the sailor. But I do suspect it was multi factorial, otherwise we would have seen some of the same behaviour in the other boats.

Best wishes
Michael

Thanks MIK for your thoughts.

Just a couple of pointers.

With the side tanks filled, about 80kg, she was completely different. So sailing two up would equate to the same. Sharpies would normally be fairly heavy construction, and sit in the water. RAID41 with two or with tanks full is behaving like a sharpie. I feel RAID41 with just one one board is still in super-light floating leaf territory.

"Sliding sideways" - sorry MIK I may have confused things. Sliidng sideways was testing her behaviour when I was standing in the water pulling down on the gunnel.

The actual light wind capsize was not that. Digging in and broaching round and simply falling over. As soon as she started I knew I would not be able to straighten her up and watch her helpless as she bore round and fell over.

I agree it was multi causal.

No idea what the mizzen was doing for instance. That tended to look after itself. That might has contributed.

Difficult, but it would be good to understand what makes a lightweight sharpie more forgiving.

MIK, how do the rockers compare? RAID41 changed an increased rocker in the early stages. I sometimes wish she had Goats rocker, perhaps she had?

Thanks, Brian

Originally Posted by Boatmik

Howdy,
Shape of the bow.
As a comparison I have put a drawing below that compares the RAID to the Goat and to BETH.

In the first 500mm of each boat there is surprisingly little difference. At the 500mm point back from the bow the RAID and the Goat are about 30mm different.
Michael

MIK,

In your attached picture - which line is the Raid and which is the GIS?

Thnks

Originally Posted by tommyboy

MIK,

In your attached picture - which line is the Raid and which is the GIS?

Thnks

Red one is Raid41.

Interesting that the GIS and the Raid are so similar at the waterline. I was aware of this having seen/compared the two and seen the waterline beam was practically the same, but interesting to see the curves side by side.

I agree that what the water will see is practically the same for both boats, the flare of the GIS is barely in the water at moderate angles of heel. In that case, the main difference is the narrowness at Gunwale level, and how close it puts your bum to the centreline in the Raid, and how high it is. Because of this, any heel will move the centre of mass in the heel direction more quickly. The flared sides of the GIS put your bum further from the centreline so more chance to react.

Yawl rig so more weight aloft also a factor?

I agree many contributing factors likely.

Ian

About center of gravity positioned high above waterline - look there:



This is a MIK standing in cockpit of his original BETH. I've sailed standing in cockpit of my BETH "YuanFen" too - I have no photos of it .

I think - flat bottomed BETH (and Raid41 also) have really good initial stability, and her behaviour most depends from skipper.

Good point Robert. RAID's wider flat bottom might not give the same feedback as a semi-circular easily rolled hull.

Perhaps before the gybe, with the rig on starboard I was central but more to port. Certainly fairly well forward. When I gybed did I stay on the middle/port side, perhaps not enough mainsheet out, that would start a heel as the mainsheet stopped the mainsail. Would a heel to leeward then start her rounding up and rolling over?

I do know the classic capsize is when the mainsheet catches on the stern quarter on the hull, boat capsizes very quickly. In fact that also accounts for the only racing capsize I had in the Scows - mainsheet caught on the stern quarter and see was over in a flash - that was in quite windy conditions though.

From my windsurfing days I remember when planing you would lean into a carve and carve her round, but at sub planing you heeled the other way. have I remembered that correctly? Think so. First time I saw Raids hull upside down I remarked just how her bottom looked like a windsurfer shape.

Brian