CLR AND CE = ???

[Lori]

Hello boaters.
OK, Got weather helm so found an article about balance.......SO far so good.
Find the CLR, do I have to scale a drawing down, of lay the boat against a pile (with no wind) to find it please??? Then the CE. Pull all the sails down? Measure them? do the einstein equation..... Probably manage that ok. BUT.
Then what do I do with it? Sorry but a bit new to all this and they don't teach it a sea school....... Is there a simple way please? Or am I just being dense?


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[boatless]

Well, since you already have the boat, it's not a design excercise!

Weather helm is caused by all sorts of things, but a boat with that pedigree should not have a problem by design. (I said shouldn't..)

Most likely cause is sail trim/condition. What are they like? Big baggy genoas are a prime cause.

<hr width=100% size=1>my opinion is complete rubbish, probably.

 

[Lori]

Hi, The Genoa is big (ish although) it seems to be cut high, we have managed to sooth her a bit by reefing the main down x1. the rigging is to the outside of the deck so we are unable to sheet the genoa in very tight making winward very hard work. I have a hydrovane steering system (willygofar) that seems unable to cope when the rudder has to be pulled over hard. I am sure she wasn't designed for the furling headsail. Hopefully Mr Maas can help me out with that one. Apparently his office say he is happy to help with his early 'babies' and our boat was buit as the flotilla leader for the Dutch Navy. (bet they had no trouble holding the helm!


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[Mudplugger]

It is possible to get a rough idea of CE /CLR by using those traditional assets, paper, scissors, pencil, string & sealing wax (sellotape), cut out usual sail plan on graph paper, get centre of effort fom each sail, join the two points, & CE will ly along this line. CLR can be found in similar method by cutting out Hull & Keel shape and suspending from the point at which the shape hangs level....if C/E forward of CLR... Lee helm, aft...Weather helm (I think)....Probable cause for weather helm, Mast raked to far aft?, Sails baggy, trim of hull etc. IMHO most cruisers sail better with mast verticle & a tad of prebend. HTH Tony W.

<hr width=100% size=1>Tony W.

 

[Anthony]

I am sure there was an article in PBO or YM last year, as part of a series on yacht design, it talked about how to easily calculate these approximatly using paper and pencil etc.

Anthony

<hr width=100% size=1>The difference between men and boys, is just the price of their toys...

 

[Roberto]

**if C/E forward of CLR... Lee helm, aft...Weather helm (I think)....**

Sailplan CE is always (very rare exceptions) forward of CLR, by say 5-15% of lwl, depending on various boat characteristics (stability, sail aspect ratio, etc): the main reason being that most weather helm is generated by heeling, if you imagine looking at the heeled boat from above, and picture the force on the sail at CE (say 1/3 of the mast up), the forward component of this force will create a weather helm momentum with an arm equal to the horizontal component of the distance of CE from CLR

sorry unable to explain without a drawing: imagine pulling forward a heeled boat at half mast, the bow would turn to windward...

putting CE fwd of CLR is a way to try to balance this momentum



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[snowleopard]

while you could work out the CLR and CE by a lot of tedious measuring and drawing, the results are only approximate and would get you no nearer an amswer to your problem.

what you need to do is adjust the rig to cut down the weather helm. first thing is to try to flatten the sails as a big camber high up will cause the boat to try to round up when heeled. if the sails are ok you then need to consider raking the mast further forward though the scope is limited to the range of the bottlescrews without changing fore/backstays.

if you can persuade a sailmaker or racing expert to have a look at your sails whne under way you may get some useful pointers.

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[Mudplugger]

Thanks Roberto... Tony W.

<hr width=100% size=1>Tony W.

 

[William_H]

Hello Lori I agree with most commentators that the weather helm is probably not a design problem. All yachts should have weather helm when they lean and are hard pressed. The more modern fin keel type even more than traditional shapes. Leaning when hard on the wind also reduces lateral resistance and you go sideways more than you should. The answer is to reduce sail area. If you do the CLR CE calculations you would be horified to see how they are changed by sail change ie reduce jib size yet most boats sail even more hapily with less sail when pressed. ie reduce jib area should give more weather helm but in fact reduces weather helm by reducing heel. The over powered aspect is exacerbated by the excessive camber of old sails. I don't know if you have smaller jibs put away and if you would be willing to remove the furling headsail I reckon this will largely aleviate your problems especially as you may be able to get sheeting point more inboard with smaller jib. The furling systems (and I presume reefing ) has enormous disadvantages in stronger winds. The sail made for light winds is rolled in a way that may not give a good shape and may not allow really tight sheeting. The ideal sheeting point often moves forward and this is often not adjusted. I have sailed with a friend who has roller reefing of the jib and I don't like it. I prefer on my own boat to change jibs and really make the jib work properly. I am sure I am a minority in saying this though.
We havn't started on getting the mainsail flat with mast bend outhaul and sheet tension traveller position. I am assuming all your problems come in stronger winds so forgive me if that is not the case. The trick is to keep fiddling and don't be afraid to be radical. regards will

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[Lori]

Thanks chaps for all your replies. Have been out this weekend on the Humber in light winds (as opposed to the Force 7 that I had on my first run out !. We fiddled about and found that she was making 5 knots with half the furled genoa and no main!. and against the tide ! Main seems a bit baggy along the foot so we may change that. Still thinking about hanking on sails to make best use of the smaller sails. The maths thing showed us way out of 'wack' will keep on trying tho!.
She has a long keel but seems to sort herself out . Will have to work on the heavy winds problem tho. Off round the world around May time. South until the butter melts.... then make a right to something big..... like the USA !.


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