Am I right?

[wheneverIcan]

Went out a few days go and started thinking over correct trim for boat as weather was a bit dodgy. Just to set it straight in my mind can someone confirm my beliefs or if not put me right.
A head sea is one where I am going against the tide and the bow should be raised to soften the impact
A Following sea is one where the tide is behind me and a "surfing feeling is felt - the bow is then lowered.
At present i adjust the trim tabs for optimum speed with compfort and nearly always have then right up with bow up and planing.
By the way its a semi-dis, single engine cruisng at around 23knts.
Is it also true that in F4/5 its sometimes more comfortable to speed up than to slow right down?
Just getting used to the newer boat - last year we seemed to have flat seas whenever we went out.

Thanks - hope questions aren't too stupid!

By the way does anyone else venture alone on their boats or always with another? I ummed and arred for ages this week and finally went for it alone - it was great but I seemed to hear all sorts of noises that I normally don't hear!

Simon

 

[whisper]

Other way round methinks. Nose down into the waves to give a softer ride, nose up with the waves so you dont bury it if you slide down into the trough.
Re. noises you don't normally hear, I hear them as well. They are a safety measure built into many boats and are designed to prevent you nodding off at the helm.

 

[hlb]

You are just arsed about face. No Offence meant. But Think this way. If not sure. No trim, or if in difficulty, trim bow up. Now in head sea. Trim bow down. But in following sea, trim bow up. If not sure. keep bow up. A Right manufacurered boat should be correct, when you buy it with no trim. Course if you add six peops to a 16 ft boat, it will be different. There is two different reasons for triming. First is to keep the boat safe. Second is for maximum speed. Decide what you need at the time.

<font color=blue> Haydn

 

[hlb]

Now if you notice the picture of my boat. It is presented with bows up. This is because we were taking pictures at the time and on flat water. So no need or time to put bow down. Putting bow down gives more bouiancy in the boat. So you rise faster when wave approches. Also keeps you from nose flying into air. But that dont matter. If sea is from behind you MUST have bow up or else it will slam you into the first wave and roll you over with the second. Of course this may only happen in extreem circumstances.But anyway is pritty unnearving if you get it the wrong way about.

<font color=blue> Haydn

 

[MedDreamer]

My Trim tab buttons have a warning on them that you must not trim down in a following sea for exactly the reasons made by Haydn

Martyn

 

[kimhollamby]

Head seas bow down

Following and head seas nothing to do with the tide direction (although the tide direction might have a significant part to play in the size of the waves).

Head sea = you are heading into the waves
Following sea = you are running in the same direction as the waves

General rule is put the tabs down (known by some as trim the bow down) in head seas; for many common hull shapes this presents the sharper, forward sections of the hull to the waves and helps to minimise slamming. You might want to compromise a little on a semi-displacement boat as the further the bow is trimmed down, the wetter it will get.

Take all of the tabs up (otherwise known as taking the tabs off or trimming the bow up) when running downwind, especially on a semi-displacement boat. Also be cautious on your boat of running too fast downwind; I don't know what you have but many semi-displacement boats can be quite a handful to steer off the face of waves (almost impossible to steer if you leave tabs all the way down) and there can be a danger of a broach (where the wave picks up the back-end of the boat, the bow digs in the the boat swings broadside onto the wave). The answer is to go more slowly. Sometimes the difference between the helm being hard work and fully under control is only a knot or two.



kim_hollamby@ipcmedia.com

 

[Renegade_Master]

Re: Head seas bow down

Good sound advice there Kim my semi dis has no tabs anyway, and is wet in a head sea. In a following sea the steering is difficult and vague and takes a lot of work. Have managed to keep from broaching so far, came close when I dropped and engine whilst zig zagging past Beachy Head toward Brighton in 5-6's, damn awfull it was.



"Sun Coast Marine sea school in the sun"

 

[kimhollamby]

Re: Head seas bow down

Too much lift off the stern with the tabs down and nose starts to dig. Some of the older semis also have really broad keel sections, which are big enough to actually contribute to lift and hence, the problem if you go too fast downwind. Many crates of beer in the forecabin also probably not a good idea /forums/images/icons/smile.gif

Forgot to add that it pays to play with tabs in flatter water on this kind of boat; you can often find an optimum setting that adds a knot or two and/or saves the engine(s) from sooting the transom. All goes out the window if the seas kick up, but can make a difference on those quieter days.

Incidentally another beginner's tip with trim tabs. There is no standard wiring convention for switches (and even when the switches are marked it pays to check if they were wired correctly). So first, check which way brings the tabs up and then mark it if necessary. Then, when at sea and you have forgotten whether they are set, bring them all the way up and start again.

kim_hollamby@ipcmedia.com

 

[Renegade_Master]

Re: Head seas bow down

Like I said Kim I dont have trim tabs Broom Crown 37 semi dis

aslo shes got a big keel so effects steering on "planning" and indeed when the sea is following

"Sun Coast Marine sea school in the sun"<P ID="edit"><FONT SIZE=-1>Edited by Sun_Coast on 08/02/2003 14:28 (server time).</FONT></P>

 

[kimhollamby]

Re: Head seas bow down

Yup, saw your comments on tabs and guessed you were referring to Crown; hence big keel comment. I like the Crown very much but a lot of boats of that era with keels can be a bit of a handful when pushed. Believe the 'Y' form version of the Princess 37 (the one with the keel) can be the same although never tried one myself.

Have you sold yours yet?

kim_hollamby@ipcmedia.com

 

[Renegade_Master]

Re: Head seas bow down

Sadly not yet Kim (and I've had to put a deposit on the F36) Just agreed which Broom that she'll go a lot quicker up at Brundall as they've sold two recently and people are coming in looking at 10/70's cos the Crowns not there. Will be planning the trip to Brundall once I get a weather window.

Never sailied the east coast before reckon the best apart from no wind, would be
W or SW off the land, or even S from behind , wadda yer reckon

"Sun Coast Marine sea school in the sun"

 

[kimhollamby]

Re: Head seas bow down

Out of Thames Estuary either suggest go in one or stop at one of the Orwell/Stour marinas (Shotley Point convenient if just transiting). And yes, leave with the wind out of the west if at all possible. Find something vitally important to do in a warm, sheltered office if it's old boots out of NE.

NE is the killer on that coast. When I did the round Britain I was very lucky to get nothing much out of E at all. Had fog, and rain as well as some sunny days, but wind was in all the right places. Left the Wash in a big W blow but the weather chart showed it was likely to stay there for as long as I needed and that saw me around to Gt Yarmouth. Only felt the full force when crossing Breydon Water and heading back into it (a plate containing heavy duty doorstep sandwiches took off from below the shelter of the flybridge windscreen and there were waves of tidal proportions in my tea that took it from scalding to artic in three seconds). Went all the way up to Brundall that same day because it was the first place we could find on the Broads with enough trees to keep the gale out of the cockpit! So Boston to Brundall in one, not a bad log entry. Never has a pub dinner tasted so good.

Anyway I digress...

If you want to call it quits as soon as you get to Norfolk Coast Lowestoft is more leisure boat friendly and you can always make your way to Brooms inland from there - Mutford Lock is now on electrics and the keepers there are helpful. I hear the marina (usefully to seaward of the A12 road bridge and run by the Royal Suffolk and Norfolk Yacht Club) is now full so worth pre-booking.

Look out for fishing markers and nets all the way up, especially above Harwich.

kim_hollamby@ipcmedia.com

 

[wheneverIcan]

Re: Head seas bow down

thanks for your really helpful guidance

One question remaining just to clear in up in my mind. The state of the sea (either following or head) is not caused by tidal direction (although this may make waves bigger) but is due to wind direction? i.e a southerly wind with me leaving for France would see me heading into a head sea so bow down.

Hope this is right - if not what causes the sea states?

Thanks

 

[hlb]

Re: Head seas bow down

Hmm. Think you might need a bit more knowledge before hopping off to france. Cant explain all about it here, but it is comon sence. So. If on south coast and wind is from the South. It's blowing the sea all the way from France. So Big sea even if only say F4 wind. Now Lets say you set off for france. Sea will become calmer all the way till it bacomes dead flat at france. Now lets say you are in Plymouth and wind is from SWest. Then, no france there, only America or where ever, so if it's been blowing a long time over say 4000 miles of water, even bigger sea. Notice. You do not get enourmous waves on duck ponds. Then theres wind over tide. Sea going one way. Wind the other. Big nasty waves. Then Overfalls. Shallow sea current over uneaven bottom. AaaRRrGGg! Very rough. Waves in all directions. Dangerous sea. Is that enough for now???

<font color=blue> Haydn

 

[wheneverIcan]

Re: Head seas bow down

OK so that very big sea coming from France then is a head sea then when going south and would become a following sea if going north?

 

[hlb]

Re: Head seas bow down

Correct.

<font color=blue> Haydn

 

[BrendanS]

Re: Head seas bow down

Want to tell him next about convergent and divergent effects if wind coming from west, which leads to different wind directions on each side of channel, even though the main wind direction is the same /forums/images/icons/smile.gif

 

[hlb]

Re: Head seas bow down

Dont know nuffink abou them, but I suppose your right.

<font color=blue> Haydn

 

[wheneverIcan]

Re: Head seas bow down

Jolly good. I hate to say it but I did a Day skipper course a few years ago and can't recal any mention of head or following seas - did I miss that evening or is it something people just know?

Thank you very much anyway. I have until recently just done relatively short passages around the solent and the tide is the thing i keep an eye on as well as the wind force. I've been aware of wind over tide and have lots of experience of this. Its probably just the winter period thats clouded my brain - I need to get out there for bit more practise!

Thanks again

 

[BrendanS]

Re: Head seas bow down

I knew the yachtmaster course would come in handy one day.

With a SW force four (F4) forecast you may experience F3 on the English Coast and F5 on the French Coast, and the wind direction will be a little different.

Wind is slowed by friction with the earth's surface. This slowing causes the wind to back (turn anticlockwise, at least in the Northern Hemisphere ) by as much as 30° over land, where friction is greater and around 10° over open water, where friction is less. This has a big effect on wind that blows parallel to the coastline, where land and sea meet.

If you are on the south coast of the UK with a westerly wind blowing, the wind that is in contact with the land will back by 30°

The wind in contact with the sea, however, backs by only 10°. The result is that the coastline splits the wind flow and causes the flow to diverge. This has the effect of reducing the gradient wind by approximately one Beaufort force and is known as a diverging air stream.

On the other hand, if you are on the south coast with an easterly wind blowing, the wind that is in contact with the land will still back by 30° whilst that over the water backs 10°. This has the result of causing the air stream to converge across the coastline and increasing the gradient wind by approximately one Beaufort force. This is known as a converging air stream.

If you are crossing the English Channel with a SW gradient wind, the wind will diverge across the English coastline but converge across the French coastline.

The weather forecasters forecast the wind-speed measured above 600 meters and no allowance is made for friction. Thus, with a wind blowing parallel to the coast it will either be stronger or lighter than predicted.

Over land the speed of the wind can be reduced by up to 50% from that forecast, whilst at sea the reduction is only about 10%. That's why wind always seems stronger out at sea than that inland for any given wind-strength.