Following Seas and Stablisers

[Gludy]

My previous boat a 59 foot planing boat was great in a heavy following sea - in fact I could do 26 knots in an f7 and not slam.

SD boats whilst better in head seas tend to be worse in following seas - I think this is a generally accepted fact that I agree with.

However, I am told that stablisers mean that a boat with them will perform much better in a following sea. I am told any tendency to twist and hence roll either way will be counteracted by the fins hence your backend will not swing around.

I have searched the web but could find very little on this subject. I do remember reading something last year about being careful not to swithc the stabilsers off in a following sea - a false sense of security etc but I may be imagining it - so there is my questions - does anybody know? If you do not know what effect do you 'think' the stabilisers will have.

In trying to prevent this developing inot a typical Gludy thread row my position is that I do not know and at this point could argue the issue either way /forums/images/graemlins/ooo.gif

 

[hlb]

My boats no problem in a following F7. But then, I can outrun it.

I wonder how fishing boats go on. Maybe worth asking them??

 

[No1_Moose]

pah, well I disagree with you. I think you do know the answer but you're not telling us.

 

[Talbot]

stabilisers have less effect in a following sea than in a other points of sail because the relative speed of the stabiliser to the wave is considerably slower. That is why you can be doing a reasonable speed over the ground, yet experience a rudder stall where the water speed at the rudder is so slow as to be tottaly ineffective.

 

[Piers]

I have TRAC stabilisers on my Fleming which are simply stunning at killing roll. However, in an emotional following sea, although the boat won't roll, she will certainly yaw (twist) if the sea is anything but from dead astern. The autopilot works really hard to counter, but the lag means yawing happens.

My experience is that the stabilisers do not stop the yaw. They only kill the roll.

 

[Gludy]

Nope I do not know the answer.

I can run up to 25 knots with a following sea so to some extent also outrun it but what I am after is truly understanding the effect of stabilsers.

 

[Gludy]

At what speeds are you talking about with the yawing? What strength seas? Is there any danger of broaching?

 

[Piers]

Yawing is worst when in a quartering following sea when at my cruising displacement speed of 8.5kts. The worst I have experienced was when travelling East with a SW F7 wind and a following sea from the same direction. Swell was probably 1.5 metres. The autopilot was on high setting which gives max speed of rudder response, but at 8.5 kts the bite is nowhere near fast enough.

Was there a threat of broaching? No. It was just uncomfortable to experience the slewing effect. However, I suspect that if the autopilot failed, I might not have been able to turn the wheel as fast as the pilot, and certainly not to have kept going for the three hours this was happening. Hence, I would have had to divert.

But the boat never rolled. The TRACs are simply excellent.

Finally, if I was travelling faster, say 12 knots, I am sure matters would have been better.

 

[Gludy]

Piers
What autopilot did you have?

 

[Piers]

Simrad AP20 with rate-gyro. Hynautic hydraulic steering.