How to reduce slamming

[cmedsailor]

I don’t want to hijack the “weight in the ends of a boat” thread, so I start a new one. Besides of course avoiding heading on waves and have a boat with no flat sections in front of the keel is there a way to reduce bow slamming? Probably something with the weight distribution (I mentioned in the other thread that more weight at the bow - eg full water tank - probably reduces it but I am not sure if it's just my imagination) or maybe using more genoa out or something else that has worked for you?

PS: I have sailed with many boats that seem to have a flat section in front of the keel but have never understood why in some of them the bow drops slowly without hitting hard the sea and in some others the bow simply drops fast with a big bung. I don’t get it.

 

[sailorman]

My boat IOR design, flat forefoot, is 50% BR she doesnt slam
I would suggest light ballast ratio + high volume hulls dont help

 

[agurney]

.. PS: I have sailed with many boats that seem to have a flat section in front of the keel but have never understood why in some of them the bow drops slowly without hitting hard the sea and in some others the bow simply drops fast with a big bung. I don’t get it.

Tidal conditions? I rarely experience slamming, but when I do it's usually in short steep seas generated by wind against tide.

 

[Deleted member 36384]

I found this article useful: -

http://www.yachtingworld.com/sail-f...techniques-series-part-5-helming-skills-76323

The technique is different in big waves on modern boats with flat-bottomed bows. In this case, to avoid slamming, gently steer to windward up the face of the wave and bear away slightly off the top. This creates more heel so you land on the stronger side of the boat.

It really is down to practise helming, small movements is all that it takes to work the boat up and over the wave.

 

[Fr J Hackett]

Or bearing away not trying to sail to close hauled.

 

[johnalison]

I found this article useful: -

http://www.yachtingworld.com/sail-f...techniques-series-part-5-helming-skills-76323



It really is down to practise helming, small movements is all that it takes to work the boat up and over the wave.

How do you teach an autopilot to do this? Actually, my boat hardly ever slams, usually when motor-sailing into very steep seas, which ic generally seek to avoid, but found myself caught out when leaving the Roompot with the ebb last year and an unforecast short blow.

 

[Bobc]

How do you teach an autopilot to do this? Actually, my boat hardly ever slams, usually when motor-sailing into very steep seas, which ic generally seek to avoid, but found myself caught out when leaving the Roompot with the ebb last year and an unforecast short blow.

My autopilot does a great job of steering up and down the waves. Never ceases to amaze me how well it does it.

 

[Deleted member 36384]

How do you teach an autopilot to do this? ....

No idea! When I am slamming it is usually one of two things: pinching at the top of the wave that requires a bigger correction or over steering. I find it takes a lot of concentration and looking directly ahead/upwind at the next wave and tell tell tales, more so than feel, to make the small helm adjustments required to work a wave so that speeds stays up and slamming does not happen.

The best helm I sailed with and one of the best races I participated in was on a Contessa 34, a boat that you can slam. When beating his helm movements were tiny, rapid adjustments, no more than a few mm each way, just small clicks as if it was tiller play causing the movement. He did not slam and maintained very high boat speed over hours. I could not last the pace of concentration and easily lost a 0.1 kt after an hour of helming in similar conditions upwind.

 

[cmedsailor]

it's usually in short steep seas

The Med where I live and sail is ALWAYS short steep seas......

 

[cmedsailor]

I know of course that bearing away and not heading directly on waves or slow down is the way to minimize slamming; my question was whether there's anything you can do on the boat to cope with this horrible thing better.

 

[Deleted member 36384]

Short of changing hull shape, no, there is very little you can do beyond steering. My own Rival 41C has slammed in big seas and she has a very deep and rounded forefoot, the solution was steering better in heavy seas.

Folks are sailing modern hull forms without slamming and the point I was trying to make indirectly is that it is shit helming that causes regular slamming.

 

[lw395]

You can effectively change the hull shape by heeling it more or less.
Better steering is the right answer though.
Sometimes a change down or reef might help, to avoid stuffing up to depower.

 

[Foolish Muse]

The yachting world article mentioned above says to to avoid slamming, gently steer to windward up the face of the wave and bear away slightly off the top When I do this I'm just laying the boat over on its / side for when it slams on the bottom of the wave. It seems the boat slams much more on its flat side then it does if I put the pointy V bow-hull into the water. Am I getting this wrong? It seems to me that a better way would be to bear off and gain power when moving up the wave face, then head up and level the boat at the top of the wave to have the bottom V shaped hull of the boat hit the water, rather than the / shaped side of the boat. Thoughts?

 

[sailorman]

it's usually in short steep seas

The Med where I live and sail is ALWAYS short steep seas......

Try the Southern North Sea :encouragement:

 

[johnalison]

The yachting world article mentioned above says to to avoid slamming, gently steer to windward up the face of the wave and bear away slightly off the top When I do this I'm just laying the boat over on its / side for when it slams on the bottom of the wave. It seems the boat slams much more on its flat side then it does if I put the pointy V bow-hull into the water. Am I getting this wrong? It seems to me that a better way would be to bear off and gain power when moving up the wave face, then head up and level the boat at the top of the wave to have the bottom V shaped hull of the boat hit the water, rather than the / shaped side of the boat. Thoughts?

You could try it, but you would soon find out why you are wrong. When you (gently) bear off on the wave crest you are effectively reducing the steepness of the wave, and gaining speed, which you would not achieve when going uphill.

 

[Poey50]

Might be worth making the first part of the rudder turn to bear away a bit sharper to see if that helps a bit. With the boat heeled the rudder turned to bear away will tend to lift the stern and push the bow down keeping better contact with the water. Worth experimenting with the timing of this with regard to the wave crest.

 

[Resolution]

You could try it, but you would soon find out why you are wrong. When you (gently) bear off on the wave crest you are effectively reducing the steepness of the wave, and gaining speed, which you would not achieve when going uphill.

Is there not a difference depending on the wavelength compared to boat size?
Helming in strong winds when the waves are big (relative to the boat) and steep there is lots of scope to change heading up or down the waves. And the blanketing effect on the wind in the troughs is another factor to consider.
But in my part of the Eastern Med we seldom get waves that big or long (at least not when I venture out!) but we often get the steep short chop referred to earlier. We find when beating into this that each wave results in a heavy impact felt throughout the boat. And I have a fairly rounded very rigid bow section and highish ballast ratio. Is the only answer to either reduce speed or to bear away?

 

[johnalison]

Is there not a difference depending on the wavelength compared to boat size?
Helming in strong winds when the waves are big (relative to the boat) and steep there is lots of scope to change heading up or down the waves. And the blanketing effect on the wind in the troughs is another factor to consider.
But in my part of the Eastern Med we seldom get waves that big or long (at least not when I venture out!) but we often get the steep short chop referred to earlier. We find when beating into this that each wave results in a heavy impact felt throughout the boat. And I have a fairly rounded very rigid bow section and highish ballast ratio. Is the only answer to either reduce speed or to bear away?

I think that sometimes the wavelength is just "wrong" for my boat, but you are losing a lot of speed and proportionately even more VMG when slamming, so it will probably help to sail freer. It may sound like the last refuge of a desperate sailor, but when coastal cruising, if the going is that unpleasant, it may be worth furling the jib and motor sailing steadily at about 30 degrees to the true wind. My boat is fairly moderate, at 5.3 tons for 34ft and a fairly fine entry, but I am sometimes impressed by some newer designs which seem to just kiss the water as they pass over it rather than through.

 

[cmedsailor]

But in my part of the Eastern Med we seldom get waves that big or long (at least not when I venture out!) but we often get the steep short chop referred to earlier. We find when beating into this that each wave results in a heavy impact felt throughout the boat. And I have a fairly rounded very rigid bow section and highish ballast ratio. Is the only answer to either reduce speed or to bear away?

Absolutely agree with the description of the steep short chop of the Med. It's the kind of sea that you cannot really steer up the face and then bear away. You need to change direction, slow down, change boat (!) or suffer the slamming.

 

[Resolution]

Absolutely agree with the description of the steep short chop of the Med. It's the kind of sea that you cannot really steer up the face and then bear away. You need to change direction, slow down, change boat (!) or suffer the slamming.

Yes, ideally something about 65ft long would solve the problem!