Radical new mini

It has been pointed out that the scow needs to be sailed well heeled to perform well. It has also been reported to do poorly upwind.

Is the poor upwind performance due to an upwind handling probem, an inability to punch through opposing waves without stopping, or just because there is insufficient wind on the beam to cause adequate heel?

If the latter, I would have thought that problem could be solved in a boat with a canting keel . . . which could explain Raison's extraordinary success.

 

That certainly sounds logical-- cant the keel and it creates heel-- reducing punching that blunt bow thru a sea. Maybe I should have installed a canting keel in my stubby blunt bow lifeboat conversions

 

Heeling upwind means less lift and more drag from the sails as well. Exactly the time when you're doing your best to do the opposite

 

That would certainly be correct on a reach but IMHO not when working into the wind. Look at the sail as a wing: the entire span of the sail is approximately normal to the wind direction regardless of the angle of heel.

There is some loss of available air speed as the sail is closer approaches the surface but it is a second-order effect. There is no additional aerodynamic drag, and for this scow there would be less hydrodynamic drag.

 

Just want to reiterate that the 747 Mini 6.5 scow designed by David Raison did well in all conditions thruout the transat....

click on image:

 

You are right, of course. The more upright a boat sails, the more of the lift vector is pulling the boat forward, not up or down.

But, if you look at most keel boats while they are sailing up wind, they usually have a noticeable heel to leeward.

The amount of heel to make a scow pound and slam less is in that class or lower.

In fact, I have an interest in deep rockered scows, where the rocker extends well above the DWL, so the boat can heel up to to 30 degrees, before the lee transom corner immerses.

The idea being that, at the time, the boat is producing its greatest righting moment, presenting an asymmetrical 'V' to to the water and presenting its longest possible waterline.

The waterline on most pointed bow boats shortens as the boat heels and the water plane curve gets sharper to leeward, so at the very time the boat has the most 'horsepower', it is presenting its worst hydrodynamics.

That is the advantage of shifting ballast, such as canting ballast keels. They are used to keep the boat as upright as possible.

With a scow, the same type of keel might be used to INDUCE heel, in light winds and lumpy seas.

Attached is a drawing of a deep rocker scow I designed.

 

Anyone taking note of the sea conditions in those photos--I know this machine is designed for racing but lets face it racing conditions are not always as shown. I would like to see it matched with it's pointy nosed competitor in sharp close together 4 to 6 foot seas. I'm not convinced it would be quite as successful.

 

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If you go to the other thread about this boat and read the "log" of Raisons progress you will see that he was subjected several times to the worst conditions possible. The guy got second in the first half and first overall on a very, very long course across a rather turbulent Atlantic Ocean.

 

Good old phil bolger had a theory about the heavily rockered scow hull form. In light airs it sits on its "belly" and has reduced wetted surface. As the wind builds, it heels, extending its waterline and narrowing its beam for higher speeds. Such a heavily rockered boat could prob never plane though... and righting ability would be in some ways similar to that of a catamaran

 

Without a doubt.

Ever wonder why most boats have pointed bows?

All the scow virtues I mentioned earlier still stand. But they do little good when bashing into a short head sea such as mentioned.

Over the centuries, bows have become sharper and sharper.

The ability to slice through a head sea pretty much negated the less than ideal hydrodynamics of a pointed bow hull.

 

Well I certainly can't argue when the proof is in the pudding so to say-- Just mind boggling, seems to counteract most of the modern logical boat design. That canting keel must be playing a bigger role than I think in terms of controlling heel. Interesting gonna have a closer look at this for sure. Bet it doesn't take long before one of these show up in "The Americas Cup". I can see it now a canting wing keel

 

With positive control of heel angle, the hull could be presented to water in any (within limits) attitude;
This possibility change some ground rules and design boundaries we are so well used to;
This boat do exploit those new territories -most of talking about too bluff bow (I used an opportunity to keep silence before the boat did prove it's worth ) is to large part irrelevant, when you can heel her far enough to lift this bluff part up, above most wave impacts, at any moment.
And when you need extra volume forward to prevent pitchpole when damn-crazy-headless reaching with spinnaker in heavy weather, you can set the heel to zero.

A far as I remember, in Volvo Open class there is a tendency for bluffer bows, started by Juan K with his first pair of VO70. The point is, at some level of driving force/weight ratio, the danger of nose-dive or dive in the wave appear. Extra volume forward help to prevent this. So with more power versus more wave impact resistance for ability carry this power.... net speed gain could be positive.

 

Yup and that i can see now that is exactly what is occuring. Wonder what that ride to windward is like, one imagines a bucking bronco but the video seems to show otherwise. Should have put more sail area on those old bluffed bow lifeboats and entered the Trans Atlantic

 

- very wise of you!

I have noticed if a heavy gust catches a boat on a broad reach, many boats tend to round up into the wind. That might be considered a safety factor, de-powering the sail. However, when sailing at the limit the sharp bow could be forced down and made to dig in, slinging the boat around uncontrollably and causing an upset. I have seen dinghies do that in races and it seems to happen too fast for the skipper and crew to control.

During the turn, the direction of the airflow over the sail rotates; possibly this causes the sail to become a more efficient wing, resulting in a feedback mechanism as thrust and heeling moment both increase. If that is indeed what happens, it might explain why it seems to be difficult or impossible to control once the turn is initiated. With its reduced lateral grip on the water the blunt bow might be less inclined to dig in and do this.

On the other hand, the scow may not be the ideal boat for around the buoy races. There seems to be a great deal more going on here than I had realized . . .

 

If you heeled your boat until the sail was perpendicular to the water, you'd have 0 lift pulling you upwind. If your sail is 90 degrees to the water, you have maximum lift.

If we took an airplane, flying level gives maximum lift from the wings. As we tilt the plane, the lift goes down until the plane is flying on its side and it falls from the sky because the wings are no longer producing lift in the direction we want.