New (possibly) idea for monohull stability in rough seas

USA2 all the way!! Naaah, too simple and obvious.

 

Hello everybody, I am new here. That's an interesting discussion.

htom said:
"Shoal waters, pull the bulb up, put in a reef or three to bring the center of effort down a bit; deep waters, bad weather, put it way down with only a trysail."

well, there is a Sweedish (I think) cruiser racer that does just that (a big bulb in a very narrow fin keel), except that the mast is fixed.

usa2 said:
"how about putting an oversized centreboard or daggerboard on the boat rather than lowering the mast through the hull? The area the board would present to the sea would slow down rolling. "

well, I think this will certainly slow down rolling but I think that it would also make a boat to be more easily capsized by a really big wave. Remember that cats bring the centreboards up when they encounter big waves.

Also the guys at Northshore recommend to the Southerly owners to bring their ballasted keels up, or at least half way up if they get really very nasty sea conditions. That way they can slide sideways on the wave wall, making them more difficult to capsize.

 

Discussing draft and rig height without including displacement and hull shape makes no sense. They are all interrelated. Also, comparing the behavior of ultra light multihulls to displacement monohulls is difficult at best.

 

Right Gonzo, we are supposed to be on a single hull sailboat of normal use.-------------And ROUGH weather, not hurricanes and storms.

 

sorry...


This was the original post "....regarding the stability of monohull boats in rough seas, and the writers seemed a bit paranoid about rough weather in smaller craft (< 40')”.

He is not talking about ultra light displacement boats.

I guess that it all depends on the definition of "rough" weather and "normal" and also on the size of the boat. I had assumed we were talking about boats between 32 and 40ft, perhaps because I don't think that boats smaller than 32ft are meant to handle rough weather. I assumed also that we are talking about oceangoing boats because nobody likes to be outside in rough weather, and if you are a coastal skipper you got plenty of time to stay away of it, not to mention accurate weather reports.

An oceangoing boat should be designed to handle almost any kind of weather, so "normal" conditions are very wide.

For capsizing a 32ft light displacement boat you don't need a big wave. A four or five meter breaking wave on the side is probably enough, and for that you don't need a hurricane.

 

that was the first post here if im not mistaken

 

How about computer controlled extra drop down fins (like bow trusters) ??

 

I don't know about the computer controlled part, but that's a cool idea, especially if connected to wheel steering...perhaps it could improve manuverability...

 

why not just sail the boat in rough weather to prevent it from being rolled, and not worry about making the boat more stable?

 

I recon you should have a canting keel controled by a gyroscope and some sort of servo hydraulics. Should be possible to keep the boat dead straight in medium rough conditions.

 

What about the Sydney-Hobart? Canting didn't save the multi million $ boats in that...although you did say "medium rough." Still, if it's medium rough now, just wait five minutes...

 

I think the cataramans have shown what happens when you bild in a lot of initial stability into a design - the response in catastrophic situations often gets worse - as in quite stable at the wrong time.

A "twenty foot" keel in 30 feet of water in breaking waves is not a good thing - "clawing" your way off a windward shore with everything "stuck down" due to some malfunction might easily become what is better described as a Pogo stick ride.

 

Boats sink when it is breached.Water inside the boat alters the inherent stability of the boat.

Ever heard of a buoy, submarine or fish sinking? They are all watertight.
Why not put sail on submarine and ballast it so it remains upright?

Or why not thik like a fish? Have two stabilizing fins below waterlineline that can be retracted when the ship is sailing but can be spread out like a fan when there is bad weather. The oversized fins will reduce the rolling motions.

 

is this concept going to be used on racers or cruisers?

 

it is about arc!! Moment of inertia

Lowering the mast reduces the arc. But I like the idea as I had a similar one for a multi hull where the mast....or an extra poll, was lowered with a wieght and this poll was fixed by guy wires at 4 points, to each corner of each hull. 50 poounds, 30 ft down would disallow capsize almost completely and not be all that hard to do. What do you think??, yes, I only smoke the good stuff!