Quicksilver 580 Or 630

[Mike Fox]

Some interesting reports about control issues when being overtaken by large waves particularly. As you might imagine, Frisky as a displacement vessel gets overtaken by large waves quite frequently, as have my other yachts over the years.

 

I have only experienced real problems when the waves have been breaking as they came past. I put this down to having a large, well supported, rudder at the stern, which gives the stern section more lateral resistance, preventing the broach that has been described here. A full length keel, as on my previous boat, can give a similar effect.

 

However, breaking waves aren't nice, as being aerated, do not afford the same "grip".

 

I have seen some pilothouse boats with a shallow full length keel, and I would suspect they have better handling characteristics in a following sea.

 

Does anyone have one, and could they comment?

 

Mike

Edited November 26, 2006 by Mike Fox

[TomBettle]

Mike

 

You are pretty much spot on.

The heavier a boat sits in the water the harder it will be to "spin" it round.

A keel really helps counter this effect, but is not the total solution on smaller boats.

Where possible a smaller boat needs to have the nose trimmed very slightly up and the power applied to insure the boat stays ahead of the sea.

 

This can be quite hard work with the boat being driven hard up the wave and then backed off a little on the crest allowing you to surf safely down the other side. If the power was held on you would tend to leap off the top of the wave and slam into the next (or dive into it).

 

If the boat isn't trimmed effectively (nose down) and the boat is driven fairly hard as you clear the crest of the wave, instead of surfing down it using the hull, she will plough down it using the nose to create a furrow. It is as the nose digs in that the boat will broach, often when the wave you have just beaten catches back up with you and gets underneath the stern, simply picking it up whilst the bow stays glued down.. You will more than likely be caught up as the braking effect caused by ploughing into the next wave will slow you down too much.

 

Trimming the boat out alone isn't quite enough (as mentioned above), for if you have the boat nicely trimmed, but run too slowly a wave can still pick up the stern and spin you, however this is less likely to happen than the other situations described.

 

The above are not scientific and more based on trial and error experience. Some of the more experienced skippers on here (Shytalk or some of our Charter Skipper friends who have or do spend thousands of hours a year on the water) may be able to give a better answer.

 

Tom

 

PS: I tried to demonstrate this to Paul J and Bob F during last years training day when we had a very interesting "break" out at the entrance to the harbour. I think the idea kind of worked although the conditions were a little extreme.

Edited November 26, 2006 by TomBettle

[Swainiac]

Forgive me if I'm wrong, guys, which I probably am, but surely the length to beam ratio must be a major factor, which determines when a vessel broaches?? The shorter vessel will surely broach before a longer vessel??

 

Also, centre of gravity is a major player here, inboard dieseels carry far more weight lower in the craft than the weight of an outboard stuck on the stern, and so help stability.

 

Rich

[TomBettle]

Rich

You are pretty much right, but good driving and using the theory in my post above will help stop most potentially dangerous incidents.

 

Tom

[Afishionado]

A fine bow entry coupled with a broad stern are the hull features that engender broaching in a power boat. The other big factor is too much speed. In the sort of conditions that most of us go fishing in, the likely hood of a steep and clapotic sea unexpectedly knocking the Stern round is slight. IMO with the amount of power available to us with modern engines coupled with the wider stern sectioned day fisher type of hull belting along over a following sea of any size raises the possibility of a broach to quite a dodgy percent. Where as keeping steerage way and steadily plodding through a nasty following sea is much safer. Indeed if the following sea is very bad trailing a very long (100ft) loop of warp tied to between the two stearn cleats is recommended by the RYA & RNLI as a method of keeping the stern from skidding round .

 

Mad Mike

[Paul D]

Mike,

 

I wouldn't fancy trailing 100 ft of warp behind my boat over christchurch ledge - the place is like a minefield !!

 

This thread has been well interesting, since I have learnt how NOT to trim the 520 ( Mark B will be glad to hear ). It is quite easy to make Neo broach if the engine is trimmed in to far and then too much power used and at the same time your crew member stands up ( affecting the centre of gravity ).

 

The trick on Neo is to trim the engine out and slow down a bit. Trimmed in too far and the boat will try to tilt and turn as the nose digs into the wave. Learnt that lesson after nearly throwing Mark B overboard.

 

 

[Adam F]

Mikes last piece of advice is well worth remembering, but the addition of a bucket makes this far more effective - even a jacket or towel will enhance the sea anchor effect.

[Afishionado]

Mikes last piece of advice is well worth remembering, but the addition of a bucket makes this far more effective - even a jacket or towel will enhance the sea anchor effect.

I was only quoting the RYA and RNLI, I guess they know what they are talking about. As for a bucket I think that would create too much drag and break its handle. A sea anchor or droge is the ideal thing. The RYA advice is based on what a day sailer might have aboard that could be of use in an emergancy. In any event a towed warp will only be in the first 3 or 4 foot of water any snag it encountered would have taken the bottom of the boat out about 30 seconds earlier.

As for pot markers I guess I am assuming that the helmsman has enough about him to keep clear of them anyway. It's always easy to do the "Ah but what about...." stuff when someone offers some advice based on not a few years of building, owning and using small boats. Perhaps those with more up to date expertise could Volunteer their knowledge as well.

 

Mad Mike

Edited November 26, 2006 by Afishionado

[duncan]

a lot here - important to keep each component in context..........

 

 

re sea anchors and drogues - you wouldn't be using them under power...............trail an open floating line, possibly adding a fender if you don't have long lines? these are very much open water tactics of course

Edited November 26, 2006 by duncan