MERLIN ROCKET FORUM

Topic : Neutral Helm?

Thoughts Please!!

I'm looking for a little extra feel uphill.

After messing with the rig a little I've concluded I need to look at the centreboard pivot location.

Current thinking I believe is the pivot point is directly between the shroud plates.

Were was it is on older merlins?

Can it be obtained on a CT or does the hull shape only give neutral?

Is neutral best?

What are the side effects of moving the centreboard up or down a CT?


Posted: 31/01/2005 09:56:25
By: Carl Whitehill
Try raking the rudder back for extra feel!
Certainly moving mast back or centerboard fwd will increase weather helm. Try a "gybing centreboard which used to increas weather helm too and if it worked was magnificent.
Alternatively stop wearing gloves!


Posted: 31/01/2005 10:54:56
By: Proper Yotter
the best merlin sailors rock the boat a little to increase feel when it is light.  it makes things sooo much easier than having to fiddle with the rig or foils

gybing boards used to help until 2002. they no longer work.


Posted: 31/01/2005 11:23:08
By: i prefer neutral helm
I think people dislike the gybing board because of the ‘clonk’ noise it made when they were rocking in light winds.  Worse than that pesky ratchet block click down wind.


Posted: 31/01/2005 11:35:44
By: Loud
'the best helms rock the boat to increase feel'

a good exmple of how it is done was encapsulated at Ranelagh as you can see these helms increasing their feel against the tide

http://www.ranelagh-sc.co.uk/Images/rscmerlin05g.JPG

Posted: 31/01/2005 12:38:45
By: Rock Stars
that really is appalling


Posted: 31/01/2005 13:40:28
By: still sitting still near Blackstone
I think you'll find that this is illegal propulsion other than the natural action of wind on the sails and water on the hull. However john Harris has been doing it for 50 years or so, so you could consult him. Of course a bad back would be a good excuse and what dinghy sailor hasn'e had one of those?
However feel is personal thing and every degree of weather helm is a brake!


Posted: 31/01/2005 15:10:05
By: Proper Yotter
Sorry to get back to the point.....
How much does the centreboard shape affect the helm?

What is the best way to tell if your mast is in the wrong place or if your centreboard (or centreboard position) is rubbish?

Answers greatly appreciated!


Posted: 31/01/2005 15:25:27
By: Tim Male
Very few people move the centreboard pivot bolt in a boat by a recognised builder.  One good guide is to measure another similar boat known to be going well upwind.  You can always rake the board fractionally forward if you want, but it is likely to make the boat a little harder to tack.  What about the rudder?  Some rudder designs are balanced to reduce weight of the helm, but in an old boat I would have a look at the pintles and check there isn't too much friction there.  Is your mast rake correct?  If it's too upright it will reduce weather helm.  What exactly do you mean by feel?  If I have the boat set up properly I reckon to sail upwind in flat water holding the extension quite lightly between finger and thumb, if I am heaving on it there is something wrong (usually too much heel).


Posted: 31/01/2005 16:03:55
By: Andrew M
OK it’s very simple.

The boat has a centre of effort from the rig (main and jib combined).

The boat has a centre of lateral resistance from the c-board/rudder and hull form combined.

If the centre of effort of the rig is in front of the centre of resistance of the underwater stuff the boat will have lee helm. (and visa versa)

You can move the centre of effort of the rig by moving the mast foot or raking the rig.

You can move the centre of resistance of the underwater stuff by
- moving the foils back/forward
- changing their shape
- changing the hull shape

Heeling the boat to windward will give you lee helm
Letting the boat heel will give you weather helm.

Don’t move anything significant until you’re rally sure. If the boats old then the board/mast foot are probably not far out. Chances are the rake is wrong or you’re not sailing the boat flat. ‘Feel’ means you’ve got the handbrake on.


Posted: 31/01/2005 16:12:06
By: Is good
building on the centre of effort theme...

rocking the boat around the axes noted causes your boat to be moved forward.

you do not need too much 'feel' to be able to rock, but when you win you 'feel' great!


Posted: 31/01/2005 16:59:56
By: rocker
Is it not true that sailing to windward, perfectly balanced, there should be some pull on the tiller, due to the hydrodynamic effect of the rudder creating lift (combination of angle of attack, leeway and rudder profile) which if not resisted would turn the rudder?

If I understand that correctly, then a completely neutral feel would mean that the boat isn't quite 'right' and wouldn't make as good ground to windward as a boat with lift generated from both teh c/board and rudder?

I'll re-read my Bethwaite, if I can't get to sleep.


Posted: 31/01/2005 17:20:43
By: Alan
Manfred Curry is better science he helped design the Porsche & VW Beetle Car bodies for Adolf! His frien werner Von Bruun put Neil armstrong on the moon.


Posted: 31/01/2005 18:31:52
By: Proper Yotter
OK as Corrie is on, and I don't watch soaps Betwaite says 'All our experience suggests that when sailing to windward the fastest trim for the tiller to lie is at about an angle of 0.75 to 1.0 degree to winward of the centre line ( ... or relative to gybing c/bord or keel with tabs etcc para phrased)


Posted: 31/01/2005 20:40:06
By: Alan
.


Posted: 31/01/2005 20:46:18
By: Alan
Many Thanks for all the replies.

All the fast boats I've ever sailed have always had just a tad(thumb and little finger) of weather helm - some people I've spoken to feel strongly that neutral helm is fast!

I think I'll move the..........


Posted: 31/01/2005 22:06:35
By: Carl Whitehill
He talks some good stuff, and he talks some…

…and we can easily measure 0.75 to 1 degree of tiller offset, possibly in a lab or detailed surveying situation, but on a boat? Comedy boy.


Posted: 01/02/2005 09:16:57
By: Bethwaite Bollocks
Probably best to do that "boat speed" thing and get some boat time in, remember Arnold Palmer the more I practice..................! You'll be amazed how it will begin to feel right after a while. Once you've got boat speed you'll be amazed hoe "lucky" you get and how "right" the yot feels.


Posted: 01/02/2005 09:27:26
By: Proper Yotter
Ok, Bethwaite goes on to say, wait for it .......................... place a rubber band on your tiller extension, (as you can feel where a band is) where the extension overlaps the gunwhale and the tiller is dead centre, then says that when on the beat the band should never be much more than about an inch or so outboard otherwise the rudder will be acting more as a brake than a lifting device.


Posted: 01/02/2005 09:38:02
By: Alan
and if you want to buy a weather helm indicator device as described above, send a £5 note to me and I'll ship you one the next day


Posted: 01/02/2005 09:41:18
By: Sailing Bits Ltd
Does this bargain include postage and insurance?


Posted: 01/02/2005 10:04:26
By: Ever the Sucker for a gadget
It's been established that a Merlin makes very little leeway going to windward.  Bethwaite's 0.5-1 degree is so close to neutral I would challenge you to feel the difference!  The rudder makes a small contribution to lateral resistance, but that correlates with a small amount of weather helm with the boat flat, you are looking at lift from the foil not a turning force.  Lee helm has to be wrong, but so is excessive weather helm


Posted: 01/02/2005 10:20:28
By: Andrew M
Of course the weather helm ("fee"l)can also be increased by tightening the leech of your mainsail (increasing its power) when its blowing "feel" will not be your problem!


Posted: 01/02/2005 14:39:54
By: Proper Yotter
So a summary:
1) it is very unlikely that your boat has been built with the centreboard pivot in the wrong place.
2) older boats had the centreboard bolt in the middle of the blade, on new ones, the pivot is at the leading edge. The bolt one a new boat is therefore lower and further forward to keep the board in the same place overall.
3) Yes Canterbury Tales do normally have weather helm.
4) You need a slight amount of weather helm otherwise the boat is too slow to tack. The amount of weather helm you want is dependant where you are sailing.

First things first though. You imply that the boat is currently neutral, so surely it won't take much fine tuning to get a bit of weather helm?

To get maximum weather helm you need to
a) move the mast foot as far aft as possible - remember to recalibrate the rig to achieve the correct rake afterwards otherwise it'll have no net efect.
b) make sure the centreboard is right down. Laurie Smiths book says that you should start with the board angled 3degrees forwards. You need to put the boat on it's side and calibrate the handle so that you know when it's fully down.
c) make sure the boat is flat and that the sails are set properly etc
d) Bethwaite know's his stuff about boats, Manfred Curry a good car designer.

It is possible that the centreboard in your boat is not orignal or is suspect. Why not try comparing it's shape and profile with another boat?

PS Propper Yachter et el who are you?


Posted: 02/02/2005 09:31:08
By: Tim Male
To fill in your obvious lack of background Manfed Curry wrote the two seminal works on Yacht Performance long before Ian Proctor Laurie Smith et al they have all of them recycled what he wrote and added modern materials. They are collectors items and very expensive but can be found in specialist 2nd hand boat book shops. We all have day jobs Manfred was as an aerodynanamist that's all.
As to my identity I'm closer to you than you think! But I prefer to stay
ANON.


Posted: 02/02/2005 09:58:42
By: Propper yotter
One other point if moving the mast significantly aft, it will effect the spreaders length and angle and could leave you with insufficient support for the mast downwind! An expensive trial!


Posted: 02/02/2005 12:47:23
By: Rig master
Thanks Gents, am working my way through the list starting with the rudder pintle, one thing that is plainly inadequate is my calibration of the mast, could do with V 12 15 18, of course it would good if I didn't ignore it! - suspect I'll have to revisit the spreaders.

I had given up the quest for "feel" after speaking with someone who prefers neutral.


Posted: 02/02/2005 21:21:53
By: Carl Whitehill
"RIGOTEN" look it up. A new way of calibrating rig tension using harmonics rather than displacement of the wire.


Posted: 04/02/2005 10:13:47
By: Mad scientist
Not sure its such a new way. Always used to check the 'pitch' of my GP14 rig to check the tension. I don't bother on the Merlin as it is adjustable on the water and I use the floppy leward shroud technique, i.e take up the slack.


Posted: 04/02/2005 14:26:17
By: Alan
Ah but did you use a Sony Pitch Meter to calibrate?


Posted: 04/02/2005 17:29:59
By: Mad Scientist & Geek.
Human ear is far more precise! HA HA


Posted: 04/02/2005 20:16:03
By: Alan

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