Rounding up under pressure

Re: rolled part genny .... now look at this ....

My ten-penny-worth;

If you're regularly getting your cabin windows washed you're not sailing, you're capsizing!
It's cold, wet, hard work, uncomfortable and frightening.

That's not my idea of cruising.
It's also inefficient and argueably un-seamanlike.

A dinghy is designed to sail most efficiently upright, a yacht when heeled to within a few inches of the gunwale, any more and not only are you risking a knockdown in the gusts and loosing way fighting weather helm that is designed in for safety anyway, but you are also making a lot more leeway. When heeled to much, the sails are presenting less area to the wind so you may as well not have so much up anyway. Make haste slowly!

You become tired more quickly, can't leave the boat to sail itself while you do something else and if anything does go pear shaped due to the massive stresses and loads involved, there is much less time to react before it goes REALLY pearshaped. Good seamanship says that you should set canvas for the maximum gust expected, not the average wind.

If you find that you are having to beat into the wind for hours on end you've either made a mistake in your sailing plan, mis- read the weather or you're racing.

A deck sweeping genoa may be fine for the racer bods with something to prove but on a cruising boat just gets in the way and obstructs vision, which is pretty important, particularly when short handed.

I sailed a Nijad 34 with a smallish high cut yankee this year. Never had to furl it, could see under it and from a force 3 through to 7 we did a consistant 9 knots in comfort under varying amounts of main.

As a rough rule of thumb, if you can't make a cuppa without risk of spilling it, you've got to much canvas up.
I was in the Fastnet in '79 and we had a hot meal 3 times a day. (Okay, it was a very experienced crew of instructors of whom I was the most junior, we got knocked down inumerable times and we did spill some tea but it says something about the difference between seamenship and racing)

All IMHO, of course.
 
Re: rolled part genny .... now look at this ....

That's some genny!

/forums/images/graemlins/smile.gifAre you saying you don't want race her? /forums/images/graemlins/smile.gif
 
Incredible beast !!!!

They surely walked that one round when tacking ?????

Racing ... after beating the pants of a Westerly Chieftain last time out .... and making 8 kts downwind Yarmouth to Ryde .... I am starting to think about it !!!
 
Great Thread

I've enjoyed the discussion in this thread. For those who moan about lighthearted or pointless threads it's should be a relief.
For the rest of us who are more rounded in our outlook it's been a fine counterbalance
 
Re: Great Thread... wasn\'t bad and wasn\'t mine ... AND Deck sweepers

Must admit got a bit bogged down with see-saws etc. in the middle ....... but sort of got it back on track again ...

Well done that man ... aitchw - I think it was who started it ... well done.

It has given me more resolve to sort out my genny ... Seateach s/hand stock here I come .....

If it wasn't for the convenience of furling gear - I would revert to hank on ... I still have a few sails from my race boat ....

To the poster about deck sweepers not hoisted on broa reach .... and no good anywhere of the the wind ... Tell that to the Baltic Regatta lot that I stomped all over in 2003 with my sweeper up on ALL points of sailing ... we even didn't bother with a spinny that day for the final and romped home .... Marvelous .........
 
Re: Great Thread... wasn\'t bad and wasn\'t mine ... AND Deck sweepers

Twas the result of a comment of yours, Nigel, in another thread. I have enjoyed it too and it has given me plenty to look at in finding a workable solution. I am sure will return to it when I have some results to offer.

As I think I mentioned before it has been a surprise to me how many of us suffer similar handling problems which is why it has struck such a chord, maybe. It certainly appears to be highly relevent to owners of small sail boats.

Thanks for all the ideas.
 
[ QUOTE ]
Will, I have been wondering if remodelling the steel plate blade to a proper aerofoil section would have any impact on the problem and may well try it following your comments.

[/ QUOTE ]

Sorry, I had missed this information.... Definitely try this - ISTR that a flat plate stalls at a really small angle - maybe 3 or 4 degrees ?? A proper aerofoil section will make the rudder much more efficient, and keep it operating over a much greater angle of attack - maybe 15-20 degrees. There are pukka profiles available if you must, but I'm sure a freehand job will be much better than you have now. Thickest point maybe 10-15% (of the chord) thick. Leading edge well rounded, trailing edge tapering gently...

I'm certain you'd notice an improvement.
 
FWIW I used to sail a Carter 30, with a small main & big genny typical IOR shape with tiny transom. There were 2 mainsheet tracks:one right across the cockpit for racing and a shorter one one forward of the hatch for cruising, so as to keep the cockpit clear. Handling, weather helm etc were unchanged regardless of which track we used: only difference was we could get more twist adjustment on the long track.

IMHO the weather helm is to do with 1/. centre of effort of sailplan and 2/. immersed shape when heeled. AWBs round up way too easy if you let them heel very far- need a heavy crew on the rail to keep them controllable, because when heeled the fat stern creates an unbalanced underwater shape
 
Fully endorse suggestions by 'misterg' that flat-plate rudder has very limited efficiency before stalling partly, then fully, at angles of attack over 12º-15º. It should be quite easy to modify the profile - using foam and glass - as suggested. Certainly, a smooth shape that 'looks right' will be a significant improvement.

Find and look into a copy of Marchaj's 'Aero-Hydrodynamics of Sailing' for an explanation of what profile-proportions - and shape of leading edge - are likely to be most suitable. Also, the Amateur Yacht Research Society has a series of publications, some of which address this issue. There's lots of research in this area - but it is accessible really only to engineer-geeks who can converse in calculus.

A max thickness of about 18% of chord (leading to trailing edge), positioned about 20-25% of chord length back from the leading edge, and a 'fat' - rather than sharp' - leading-edge radius profile is desireable. I would also taper the profile by about 10%-15%. Leave the trailing edge square-cut. Also, effort invested in achieving a 'perfect' and highly-polished 'first third' is VIP to efficient performance.

If you cannot find, PM me and I'll arrange something for you.

The idea of 'barbour-hauling' your headsail sheet inboard is also an effective control of sail efficiency and power, and worth doing, but is unlikely to result in an improvement of rudder authority. Reshaping over the winter - as above - is both cheap, easy, and likely to be quite effective.
 
Aerofoil ??

Laminar, NACA, turbulated ..... if anyone is interested - I can probably dig out all the aerofoil data I have which covers various book-fulls !!

Its an interesting idea ... but would like to point out :

In the world of wings ... flat plate wings have worked - despite the apparent non-aerofoil shape. They work when leading edge is raised and an angle of attack is presented, the angle increases as the speed reduces ... until a stall point is reached.
The best example actually of this was a model F-15 built purely out of 3/8 balsa flat plates a few years back in UK ... it was featured in RCM&E magazine ... A couple of model flyers I knew and flew with actually built one each. It flew VERY WELL ... in fact was a match in aerobatics with my full aerofoiled Mirage 2000 ... but not in speed.

MIRAGE1.jpg


Sorry don't have a piccy of the F-15 ....

I only mention the above - as at the angles of attack that I am experiencing and I think aitchw as well - whether aerofoil of flat plate is acedemic I think .. as the angles are extremely high ... well mine is anyway !!

Problem with sorting out from the rudder perspective ... is that the actual problem is not cured, only compensated for ... The true solution has to be the remival of the problem itself ...

Excellent stuff ....
 
Re: Aerofoil ??

WhilstI cansee why you have reservations, Nigel, the task of extending slightly and reshaping my blade is easy enough to be worth trying anyway. I will let you know how it goes. It could be sometime though before I can evaluate it's effectiveness.
 
My blade ...

I have an inbuilt fault .............. the stupid guy who fitted the rudder originally offset the tiller and stock by about 3 -4 degrees ... never quite figured out why ... unless he thought it would compensate for the engine ??

So building up a rudder blade with a profile would give me opportunity to remove that ... I also feel a rudder should have a leading balanced edge / part .... which assists with turning the rudder ....

Have to think about it ....
 
No, Seaboots, you misunderstand.
Simon is quite right. The position of attachment of the mainsheet is irrelevant. The position of the Centre of Effort is all that matters, viv a vis the CLR.
Mainsheet simply transfers the sideways force to the hull. The hull is inflexible and so where it takes the force just does not matter.
I suggest that your "try it" is far too subjective to have any value.
Ken
 
I am going to jump in here at the risk of having my ignorance exposed.

I agree with SimonCR that the location of attachment point for the mainsheet doesn't make a difference - but I will add on the assumption that the track is directly below the attachment point on the boom. But I wonder if the would be a difference if (as in the original photo) the mainsheet is led aft to the transom?

I wonder whether this might have an effect because in very heavy airs spinnaker running it is common practice to choke down the spinny sheet. Partly to control the sail better, but I also thought part of the reason was to avoid the tendency for the boat to round up. There is, after all, a huge force that is pulling the leeward quarter forward if the sheet is not choked down (with a barber hauler or even flying it off the guy).

I appreciate that the dynamics of load transfer are completely different for a spinnaker than for a main - but is there something in this - at least for the spinny?

Comments?
 
"choke down the spinny"
I think that it is the change of shape of the spinny which is significant here - and it moves C.E. forward, giving the effect that you need.
Ken
 
Transom mainsheet horse ...

As seen in Superanne photo ... my mainsheet is at quite an angle back to the horse. not so much a problem when close hauled ... the boom tends to stay in line and fair with the mainsail. But as the sheets are slacked .... the boom starts to lift and "hook" ... you get a "belly" in the aft lower part of the sail. This I believe is because the sheets are working at such an angle and also near flat ..... Now what difference moving sheets forward would make apart from making it harder to sheet in and probably needing more blocks to increase the tackle power ... I do not know ....

I do notice that when I fit a preventer ... I normally do it at about 45 deg down and about 60 deg forward .... based on the deck fittings ... this actually reduces tendency of boom to lift and hook at the outer end ... and psychologically I feel boat sails better .... but of course this is now downwind sailing we are talking ....
 
Re: Transom mainsheet horse ...

re. the sheeting angle;

I agree that it can't help to have the sheeting angle as shown in the photo as it will tend to allow the boom to lift and slacken the leech of the sail. Idealy the track or bottom block should by directly under the attatchment point on the boom.A decent kicking strap would help but remember,the forces at play on a tight kicking strap can be enormous.

The main generally needs to be flatter when going to windward and in stronger winds. This can be achieved by using haliard tension/tack downhaul, clew outhaul and kicking strap.

The center mainsheet will only flatten the sail is you have a boom that bends enough to pull the middle of the sails foot down, thereby flattening the belly of the sail.

I think it was PBO that had an article about setting up the rig on a boat this size and mention of sheeting angles/rig tuning in a review of a Hurley 20, both in the past 12 months.

I still think that if the weather helm is that bad you're either over canvassed of the sails aren't balanced.

Aerofoiling the rudder will help the sympton but not the cause.
 
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