Lessons from a Beer Can and a Sail

[schoonerdog]

Just wanted to pass this on. We have beer can races here in Annapolis every year. People basically can use two beer cans and make them into any shape they want. These boats are then put into a large shallow pool with some big industrial fans behind them and raced. The whole contest is for charity and it's a lot of fun. The winning designs are typically catamarans or tri's, but one thing was interesting to see. Many people would make their catamaran hulls nice and narrow and long and fairly stable, but connect them with cross beams that were joined at about half way up their hulls. The result is that the boat would only have a small amount of clearance underneath the boat. As the races would start, these boats would start moving very well. Then as they gained speed their bow wakes would hit their low crossbeams and stop them dead. The boats would then start again and stop again all the way across the pool. Interesting lesson on wakes in boats. A larger boat would have more mass and momentum, but still would be hampered by the wave action. I used to own and older PDQ 36 that had the step down into the main cabin that caused it to have 10" of clearance. When fighting up wind to get into the chesapeake it would struggle to make any forward progress at all, I suspect because of the bridgedeck hitting the waves. Down wind it wouldn't be much of an issue, in fact waves could push you along. My present boat has far better clearance and is much faster up wind, around 9 knots in 14 knots of wind sailing 55 degrees into the wind. Anyway, when people discuss how bridgedeck clearance is important in catamarans, that's what comes to the front of my mind. Not the slap, but the lack of ability to beat into the wind.

[Intentional Drifter]

Hi, Schoonerdog --

Just noticed this post and since we have the same kind of boat I thought I would chime in. I've seen the same phenomenon, but with a bit of a twist. When we've encountered wave slapping in chop to windward, it has almost always been a problem when we were going a bit slow -- 5 or 6 knots or so. I've found if I bear off just a bit, just enough to get us up to 8 knots, the slapping diminishes. If I get her up to 9 knots, it seems to become almost no issue, as the wakes get farther back. If anything, I've found that I tend to try and pinch her too much and then pay the price, not only in speed through the water, but in slapping if we're in chop. It's been a bad habit I think left over from monohull days...

ID

[44'cruisingcat]

This sounded interesting, so I thought I'd try it out.

I quickly emptied a couple of beer cans and taped some dowels to them to form a "bridgedeck". Unfortunately the waves got into the openings of the cans and they sank.

So I emptied a couple more. This time the sticky tape got wet and fell apart and the cans sank.

So I emptied a couple more. This time I stuck the dowels into the cans so they wouldn't come apart. But water got in where I had made the holes, and they sank.

I had run out of cans, but still had a couple of bottles of beer, so decided to give them a try. After emptying them I taped some dowels on with duct tape. The bottles went quite well, but I had accidentally put the boat in the water upside down. Then the bottles filled up with water again and sank.

No more beer left in the fridge, but there was a couple of bottles of red wine in the pantry... they took a bit longer to empty, and floated quite well, but I couldn't remember why I was throwing them into the pool..

[Maren]

Originally Posted by 44'cruisingcat

This sounded interesting, so I thought I'd try it out.
...
they took a bit longer to empty, and floated quite well, but I couldn't remember why I was throwing them into the pool..

That was good.

Keep trying.

[solarbri]

Originally Posted by 44'cruisingcat

This sounded interesting, so I thought I'd try it out.

I quickly emptied a couple of beer cans and taped some dowels to them to form a "bridgedeck". Unfortunately the waves got into the openings of the cans and they sank.

So I emptied a couple more. This time the sticky tape got wet and fell apart and the cans sank.

So I emptied a couple more. This time I stuck the dowels into the cans so they wouldn't come apart. But water got in where I had made the holes, and they sank.

I had run out of cans, but still had a couple of bottles of beer, so decided to give them a try. After emptying them I taped some dowels on with duct tape. The bottles went quite well, but I had accidentally put the boat in the water upside down. Then the bottles filled up with water again and sank.

No more beer left in the fridge, but there was a couple of bottles of red wine in the pantry... they took a bit longer to empty, and floated quite well, but I couldn't remember why I was throwing them into the pool..

Nice one,
Maybe you should try bottles of rum. I think they are used to being out at sea!

[TaoJones]

Heh! Classic, 44cc. You clearly have the enterprising spirit and inquiring mind that has epitomized mankind's quest for knowledge and progress! You're an inspiration to your fellow sailors - carry on, Captain!

TaoJones