following sea

[Fanie]

Guys, put a boat in a river and go downstream as fast as the water. You won't steer any. Same happens in a following sea, there has to be water movement over the rudder or you can just as well not have it.

[urisvan]

it is the sense of feeling which makes you steer in following seas.
the centerboarders and windsurfers has got that feeling. try to sail a surfing centerboard like lazer or 470 for 6 months it will give you the feeling and then you can use the tiller with one finger.
i usually take it from quarters when i climb to the waves and at the moment i pull the tiller sharply to surf from the wave. it is easy for me and i dont use power it is about the feeling and the technique.
but untill you got the feeling i think it is safer to take the waves from quarters to prevent unexpected behaviours.

Not sure how to "link" but if you google theHullTruth.net, and then search Water Dog accident, you should find it. 40 photos of a fatal broach in Jupiter Inlet.

Originally Posted by fg1inc

Not sure how to "link" but if you google theHullTruth.net, and then search Water Dog accident, you should find it. 40 photos of a fatal broach in Jupiter Inlet.

I did not find it.

But when you know howto, what is so difficult? Copy and paste the link.

[srimes]

Here is the link to page 9 of the thread:

http://www.thehulltruth.com/boating-...r-inlet-9.html

I think it contains the link to the pictures, but that link is blocked here at work and I won't be able to see in until I get home.

Sorry, here's the link (if i did it right)http://pnyr.big1059.com/cc-common/ga...lbum_id=249965

[Small Wally]

Originally Posted by Fanie

Guys, put a boat in a river and go downstream as fast as the water. You won't steer any. Same happens in a following sea, there has to be water movement over the rudder or you can just as well not have it.

It is my understanding that in a following sea the water stays in place horizontally and moves only vertically so that, as you travel down the wave, the water IS moving past the rudder.

of course, I could be wrong.

[tom28571]

Originally Posted by Small Wally

It is my understanding that in a following sea the water stays in place horizontally and moves only vertically so that, as you travel down the wave, the water IS moving past the rudder.

of course, I could be wrong.

All the analysis I have seen show the water moving both back and forth horizontally. They show water particles in a vertical orbit with forward motion at the crest of a wave. That is why a shallow rudder has little control down wind but a deep one does work better. We often underestimate the speed of waves, especially in shallow water such as inlets.

[jehardiman]

Originally Posted by Small Wally

It is my understanding that in a following sea the water stays in place horizontally and moves only vertically so that, as you travel down the wave, the water IS moving past the rudder.

of course, I could be wrong.

Originally Posted by tom28571

All the analysis I have seen show the water moving both back and forth horizontally. They show water particles in a vertical orbit with forward motion at the crest of a wave. That is why a shallow rudder has little control down wind but a deep one does work better. We often underestimate the speed of waves, especially in shallow water such as inlets.

Tom is correct here, water particle velocity is actualy an orbital, with back and forth as well as up and down motion, that almost closes. There is a good picture of this in Weigel, Oceanographical Engineering, where they time lasped a photograph of markers at different depths in a wave tank. Because of viscosity effects there is a little drift in the direction of travel; i.e. the mass drift. This viscious mass drift is what produces the large oceanic surface currents, as well as the overrunning breaking crest formation in shallow water.

[7228sedan]

I didn't realise that my original question would prompt such a response. That being said I really appreciate the feedback. My particular boat is a 1972 28' Luhrs flybridge sedan. Underway she gets the best efficiency bow down (weather permiting). I have been out several times since the first post and I have been experimenting. If I raise the bow & apply more power, the boat handles the following sea much better. When running with the bow down; there is not alot of stern in the water at all. The boat is a single screw 17 inch diameter 3 blade, and her beam is 11'6". The boat does "wonder" quite a bit when under way. If I lift the bow (squat the stern) the rudder is far more responsive. She still seems drastically under powered with my motor a merc 454. This boat was originally powered by a single small block; I would not want to try to push her with that. I am used to running Deep V full planing hulls with ample power. As this boat is a modified V, there are specific characteristics that I need to gain experience with.

[viking north]

Power boats in following seas, now theres an endless topic with no real answers only for gods sake use common sense. You now have a good idea of your boats handling for a given sea state with your experience. Either you need to hire a more experienced boat handler and gain experience (no insult intended we all have to learn to handle different sea states) or You have the accumilated experience and now know what sea state with your experience combined with your boats characteristics you can handle. Properly built sail boats are sometimes a handful in following seas even when they are built with narrow sterns, long full deep keels and rudders but a powerboat with that big wide stern sometimes can be a nightmare. As a past Newfoundland fisherman with more experience than i want in big following seas miles out, my best friends have always been reading the waves, picking your angular trail thru them and be fast on the wheel and faster on the trottle,Learn how to use the prop wash against the rudder to kick her ass around.(power steering, a boat steers by re positioning her stern) Anticipate ahead how you will attact two seas at a time, one your into and the one thats following. After 10 to 20 hrs. of this your muscels will cry in pain but the funny part you still function and you sort of get into a rhythm. Now there could come a point where you sense it's getting too dicy and thats when you have to make the big manover, be patient, read the seas, decide weather it's to port or starboard, wait for that longer than usual space between them, it will come and in that longer spaced trough,using the trottle for prop wash against the sweet spot on the angle of the rudder( not hard over, find this in calm weather) kick her around counter steer if necessary but get her fairly straightened out and into it, trottle up to get up and over the next sea, and it starts all over again but now you'll feel much more in control as now you only have to contend with one sea at a time,the one coming at you and you'll develop a new rhythm, read the sea, if it's breaking trottle up, put her nose into it, if not trottle up, attack it at an angle, straighten her up over the crest and get ready for the next one. Now head for that altermate port you pre planned for before heading out or let the sea carry you on your origional course while you maintain control one wave at a time. Above all don't panic, afterall you are in control and hoping for the best but prepared for the worst. Put on my survival suit on a few ocassions,Lets see, liferaft within easy reach and release, survival kit other than whats pre packed in the raft, close by, notified family and friends of my route and ETA,(important for quick rescue) Yup, i'm going to survive this.
Geo.