skip-novaks-storm-sailing-techniques

[wheels 543]

I bet it's another one of these so call 'guru sites'

Yes there are many in the Marine game like that. I think it works on this principle. Start a career say...refrigeration, buy a Boat, drop out of society and live on Boat, write Book on Boat Refrigeration, suddenly you are the Guru of Marine Refrigeration. Or the other principle is, Sail across a Sea with the least prepared vessel you can find and write a book about it. Suddenly you've become a Heavy Weather Guru.

And don't get me started on them Internet Forums.

[Guest]

We were chatting last night about what's better in a big blow, a heavy boat or a light one. I've not thought about it too much as every blow I've got into out there didn't come with the option to change boats so I had what I had.

 

But with my tweak I'll have the ability to take on board, in tanks, approx 450-500kg of water, maybe 700 depending on how I finish one bit. On a boat that's 2500kg all up that's quite a nice load.

 

The question is, If I found myself in a blow out in the deep blue that was predicted to hang around for a bit and I wasn't in a position to go for the hell downhill slide*, would you or wouldn't you load that 400 odd kg of water aboard in an effort to make the boat more sticky?

[Island Time 1,214]

the water would add to the inertia of the boat, making a rollover (slightly) less likely and, dependent on it's location might make it stiffer. The further it is from the roll center the better for this. Of course at or below your COG if possible! You can always try it and see what it does! Easy enough to dump it if you don't like it...

[Black Panther 1,579]

Intuition tells me go light. The heavier you are the harder you'll get hit????

[wheels 543]

Well I certainly ain't putting myself onto a class of BP or IT, as both have had far more sea miles. But I have had a fair share of the lumpy stuff now and so I will venture a comment, all be it from the very cheap seats.

First off, I don't think weight is as much an argument as design is, but weight does certainly make the motion totally different. I get that comment so many times from anyone on board my Boat when we are in something a little brisk. People comment on the slow motion.

I have also noticed in any boat I have been on, that any significant weight change, makes a significant difference to motion. Our Boat weigh's in at 22Tonne with a big volume Bow and when I removed the old 65Kg plough from the Bow, it made a very noticeable difference in the motion into a Big Sea.

The negative with our boat is that the Big Bow will slow us down dramatically when we start to thump into a head on heavy Sea.

[Island Time 1,214]

True BP, but light boats get pushed around more. The more you are moved around the less comfortable, and can be more dangerous.if the structure is a problem though, better to Move! Everything is a compromise!

[Guest]

Heavier means sticker so more wave influenced where lighter means bobbing around more so more wind influenced. I suppose it's another one of those things where say 50klts light is good but at 70 if your too light you just blow away so to speak meaning heavier would be nicer.

 

Agree on the boat shape as well, that has to have an input.

 

It was a interesting discussion that never came to an solid conclusion.

[Island Time 1,214]

Knot entirely KM. Heavier means less movement. Compared to the same hull shape lighter. Any external force (wind or water) will move a heavier object further/more than it will move a lighter one...

 

This has made me think about offshore boat safety. Knot aimed at you KM, just thinking aloud here.

 

This is a brief outline of my understanding of the differences in comfort and safety for offshore boats, for anyone who may be interested.

 

You can reduce movement of your boat in a given sea state either by adding weight, or reducing the surface area upon which the force acts - ie if wind, then take down anything you don't need - furled sails, canvas etc. Not much you can do about the hull etc. BUT if you ad weight, as BP said, you are adding resistance to the forces, which is harder on the structure of the vessel. Think how slowly a swamped craft moves - due to it's change in mass.

 

Too much movement can incapacitate the crew, and or cause the vessel a catastrophic failure - like surfing out of control down a large wave and broaching at the bottom, then being rolled. Rolling a boat is bad at any time, but worse at speed of course.

 

Part of the benefit of a parachute anchor is in effect to give the boat extra weight, and to slow it's motion in the waves. A drogue does this as well, just not as much as a parachute. Many sailors don't think about that, but it is an important point. Because of the extra weight, the waves wash past the boat better, without picking it up and throwing it down wave as much. Most think of this as the drogue or parachute pulling the boat, or holding the boat toward the wave - when in fact it is of course the boat pulling the drogue/anchor! A boat moving fast has a lot of energy - if it is stopped by a wave - or anything else - that energy has been transferred (lost) somewhere. Lots of energy can quite easily be dissipated by rolling the boat over! For a stationary boat to be rolled, the energy has to be first given to the boat - overcoming the inertia to get it moving, and then built to a point where there is enough energy to cause the rollover (or pitchpole or whatever). It is much easier to transfer the existing energy (boat going fast) into a roll or pitchpole than it is for a stationary boat to gain that energy first, then lose it in the same manner.

 

So, this is the movement/comfort part. That is not seaworthiness, although it sure helps the crew!

 

In resistance to a breaking wave, tests have shown that an old, heavy, narrow, low freeboard, long keeled boat is less likely to be rolled buy a beam on breaking sea than the more modern light, high freeboard, fin keeled boat. Despite the fact that most modern designs have higher righting moments.

 

This is due to several factors. The 1st is inertia. The old, heavy boat takes longer to begin moving due to its greater mass, therefore it is "inside" the breaker for less time (presuming the wave passes, and does not carry the boat along) It's topsides are small, so present less area to the breaking wave, so are "pushed" less... It's narrow beam and other design features mean that once capsized is more likely to self right.

 

The modern (fin keel, high freeboard) designs had FAR more righting moment in all normal sailing angles, mostly until well passed 100 degrees of heel. But it will take a harder and more prolonged hit from a breaker, due to the surface area available to be hit, and the mass of the vessel. Modern designs have huge buoyancy reserves compared to the older designs, and are therefore more "lively" in a seaway. They are also more likely to remain upside down for longer.

 

However, once the breaking crest reaches about 30% of the waterline length of the vessel, ALL the designs tested were rolled. Regardless of design. And remember that I'm talking about vessels of similar size.

 

Naval Architects have a lot of issues to contend with, and that is why there is no perfect boat!!

 

Happy to discuss, have data added, or be corrected on any points!