Long Narrow Planing Hulls

[Retired Geek]

Originally Posted by FAST FRED

"
Plus the unfortunate inverted stability of the cats & tris.
FAST FRED

While I don't keep an active eye on power cat or tri rollovers, can't think of one instance in the past 30 years that I have heard of.....anyone else heard of such an event?

[taniwha]

if that is the case why are only monohulls circumnavigating?

[tom28571]

Originally Posted by Retired Geek

While I don't keep an active eye on power cat or tri rollovers, can't think of one instance in the past 30 years that I have heard of.....anyone else heard of such an event?

Yep,

Just this spring a powercat capsized less than one mile off Bogue Banks. One crew member made to shore and the others (three I think) drowned.

I would not claim to be a forensics expert but there are some features that seem to make small trailerable powercats more susceptible to this problem than other monohulls or wider beam multihulls. A high center of gravity and a high initial stability coupled with a low righting moment at large angles of heel can make such a boat unsafe in certain conditions.

Trailerable powercats have much to offer but in really rough wave conditions, they would not be my first choice boat to be out in. They make charging into fairly rough water pretty easy and comparatively comfortable but when the water gets rough enough that it starts to slam into the bridgedeck, things get nasty.

[im412]

retired..have a look on ausfish.com
off qld they have one of the new planing 5m cats flipping every weekend
the older displacement sponsons are a better deal though

[Retired Geek]

[quote=tom28571]Yep,
A high center of gravity and a high initial stability coupled with a low righting moment at large angles of heel can make such a boat unsafe in certain conditions.

Just for giggles I did a comparison in GHS of equal beam trailerable monohull and cat, same displacement...there is not much in it except for that due to VCG and even then its not much more than a 7% difference in the zero RM angle. Not Sure the bridgedeck slamming makes much difference either unless your beam on to a breaking wave, then either design is in trouble. Inverted stability for same beams is also not a lot different assumming both interiors are flooded also....then again Im making a huge number of assumptions in the models and have no idea of the configuration of the boat you quoted.

Bottom line is probably down to the users experience and knowing when its a good time to run for home when it gets past the point where its safe to stay out in such vessels.....and I'd agree that the point where you realise that is probably later in a multihull than a monohull

[tom28571]

I was thinking about the typical center console boats that are used here on our coast. Such boats are open with no overnight accomodations. Both will certainly be very stable upside down. I did not use any math and have no data to work from. Just a guess from looking at both boats on the trailer.

[Guillermo]

Originally Posted by FAST FRED

At the price of 2X or 3X the drag ....

And X-X the price, marinas fees, maintenance expenses, etc.

[messabout]

Recently, I read of an Alaskan legislative act that limited commercial fishing boats to 32 feet LOA. There are numerous fishing areas in Alaska that the legislature deems worthy of protection. The 32 foot rule applies only to those areas. Those areas happen to be fertile fishing grounds. As you might guess the fisherman have responded to the rules by making their boats 32 feet long and 20 feet wide. I'm Thinking that boats may morph into 32 foot LOA by 50 foot beam travesties. Talk about clueless politicians....... All this makes for extra work for game and fish officers and Coast Guard personell while encouraging the construction of boats that are either very slow or very costly to operate. To their credit, the commercial fishing boats make no pretense at being Marina Queens.

Gene

[tom28571]

One important thing I forgot to mention is that most monohulls heel to the inside in turns. All hard chine V hulls heel inwards while some round bottom hulls may heel outwards. Catamarans tend to heel toward the outside of a turn which can turn a normal situation into a dangerous one. Some cats have active stabilization foils or canted outboard motors to induce a safer inward heel but they are in the minority. An outward heel combined with a higher CG would be a bad thing. Even some monohulls with too much upper works have capsized in this way.