Quick question guys and girls. New to RC Sailing. At the weekend, variable wind conditions. Went from a B 1 Rig to my ultra light weight blackmagick A rig sails - with the conventional A Rig, boat beautifully balanced, from neutral to just a tad of weather helm.
Then had a play with the A Swing Rig. Love the idea, the simplicity and the physics of it but… - slotted into forward mast step. It was okay on a broad reach or run, but upwind was a bit of a dog. Too much weather helm, too much rudder thus too slow. The wind strength was light but a bit variable - in some very moderate gusts the weather helm was very apparent. Dog to tack, too; rudder is deep, thin and semi elliptical so does need gentle turning, but I guess tacking with a swing rig needs to be learnt too…
I can’t rake the mast forward, there is hardly any rake on it it’s basically straight …I can’t easily try the rig in the conventional mast step (i e move it back aft) as it’s a bigger carbon section.
Is this a Swing Rig phenomenon (I’m guessing not)? Any suggestions?
Chose a day that is generally right in the middle of the tuning range of your rig (I.E. for the A-Swing rig, it’s probably around 5mph.) Tune the swing-rig normally as you would based on that days conditions
Come close-hauled and travel upwind. Once set on the tack and the boat traveling at full speed on that direction, take your hand off of the rudder.
It depends on preference, but at this point the boat should travel 10 boat lengths before it begins to stall “in-irons” This sets the boat to hunt. A well tuned boat will take a rudder adjustment to keep it on that tack aproximately every 10 boat lengths.
Do that and report back how far the boat travels before it gets in-irons. That’ll tell just how severe the weather helm is, and therefore how severe the response is to fix it.
DON’T Change the mast step Untuill you absolutely have to.
Thank you breakwater…great advice. With all other rigs, even the little C2, she hunts upwind after 7-8 boatlengths and needs only the slightest touch to get back into the groove. So the swing rig weather helm was noticeably - I used the “fine tune” on my Spektrum which I normally use only to centre the rudder to counteract the weather helm with a constant helm down attitude and that helped me brake less but of course it’s still slow…
Here is another way of looking at the situation. The main is contributing too much power, or the jib is under-contributing. You could reduce the power in the main by easing it out, or adding more twist . . but reducing power does not sound right. . .so I suspect the jib is under contributing, either by being set too close in (stalled) or too far out. . .
but you did not complain of the jib luffing, so I suspect that the jib is set too close (let it out a bit) or the leach is too tight (add more twist) .
John - I think your onto it. I looked at some very poor (too poor to post on here) footage of my Marblehead with the Swing rig - and the jib is subtly flapping / not drawing; so in the light I’m running it too flat with too little shape forced in with the t.lift. Cool - will pay some attention to careful sail trim and report back!
It may be also another way to look at it , although improbable, and this is the jib/main sail area ratios.
In attachment the usual jib percentage for various rig :
Cheers
ClaudioD
Put the boat in the water, Put the rig on it. Then, get the sails trimmed the way the sails should be trimmed regardless of the weather helm. Then see how the boat reacts to those sails.
If you don’t sail the boat the way it should be sailed, you’ll never figure out if there is an actual problem to be solved or not. Instead you’ll chase around sail trim.
As mentioned, and especially noteable, Keep in mind you want to see if the boat “Hunts” at the 10 boat length when fully powered-up.
Many, Many boats will round-up to windward when powering up or hit with a gust. This isn’t what you’re trying to solve. You are trying to solve weather helm.
Boats rounding up on a gust can have to do with alot of things, but most likely is from hull form shape. (Narrow bow, Eliptical Stern)
Boats rounding up on a gust can have to do with alot of things, but most likely is from hull form shape. (Narrow bow, Eliptical Stern)[/QUOTE]
Thanks Breakwater, and Claudio, too. In the tradition of academic interest can you comment on my M’s hull shape? As far as I know it’s a one-off, built in possibly 2007. I am told it’s fast in the light and downwind; all I can offer so far is that she’s stable and beaut to sail with the B1 rig and a decent breeze…
Every Marblehead 50/800 ever made is a one-off. Even the ones that are supposed to be identical.
Each boat was built by the designer/builder what have-you to improve slightly upon the last one.
Anyways.
With that said, do I know exatcly what it is?
No.
But all that Matters is that it’s very clearly a Marblehead. It’s also very clearly a Modern boat. It’s probably a little earlier that 2007, in an era when hulls were super-narrow. This is similar too, and may even be an ORCO Skinny. I’d have to go back and look at the skinny lines to be sure.
Anyways, It’s very clearly a Modern M, and should be sailed/scored with boats such as the Pinter/Viper/Paradox and etc.
I bet it would do very very well.
I also bet the guy who had it before thought it was “obsolete” haha.
Looking at those Stern sections, this could very well be one of those boats that fiercely rounds-up when hit with a puff.
It should be a great light-air flyer. Fast upwind and downwind.
Be careful tacking. It might not carry enough mass to really carry through tacks like the bigger guys.
Thanks a lot, I think it might have been classed as getting obsolete. It certainly seems skinny to me but I can only compare with images and you tube videos of M’s. I’ve put an EF Guyatt winch in, have had some new sails cut, this Sunday will be it’s first outing against some other M’s. So sensitive to sail trim! Cheers
If a hull like that was classed as getting obsolete, you bought it from a nut-job who trades his car in when it needs the first oil change.
If this boat was an automobile, it is an off-lease 2-3 year old model with 25,000 miles on it.
Good job. That’s how I buy cars too! Make the wackos drive them off the lot.
That is a super-deep fin, super narrow keel modern M.
It’s going to like smoother ponds due to the low displacement, and it’s going to be a screamer.
Breakwater - my apologies don’t check in much. Well, you were so right as to pedigree; this from the original designer in South Australia:
David Hi,
wow you appear to have the real deal… that boat won a couple of state M and 10R titles…
The original boat was made out non pigmented (read CLEAR) hull so it was actually like a floating gold fish bowl… hence the name poverty pack… I digress… may I ask whom you may have bought it from ??? just checking its linage…
The original design called for a hull that could be a good all round “regatta boat” and work a wide range of conditions over a two day regatta… with a minimum of tuning …so it it has lots of rocka and thin lines for drifter work and as it heals over the displacement actually equalised or diminished at times to allow the hull to sink into the water and increase L W L. But deep lines and enough freeboard that stays out of the water and have the gunnel’s soft … thus the tumble home sides…
What we ended up with was a boat that did pretty close to that…
the carbon boats built from the mould were to a commercial/regatta quality and definitely NOT throw aways…
the boat is blindingly fast in under 5 knts and the trick to making it work to windward when using the swing rig …is to bring the jib boom in towards the centre line…then camber the foot of the sail to about 15% + and twist the head off just enough so as to back wind the main… do that in pretty much all conditions and it will go like a cut snake…
As to how we’re going - well it’s all learning! In other words I have a long way to go
Hi,
I just jump back to the first message and realize now that you used for the “swing rig” the same mast step position of the “classical rig”
This is not correct.
The “swing rig” mast step shal be positioned ahead of the “classic rig” mast step of about 5 to 6cm.
This is necessary by the “swing rig” dynamics.
Cheers
ClaudioD
Typically a swing-rig mast step will be 5-6cm ahead of the traditional step.
The only thing that actually dictates a mast-step position is the Center of Effort on the sail-plan and therefore the balance of the design.
If one was to make an oversized jib, it’s essentially the same as moving the mast-step forward.
Almost all behaviour of the boat can be corrected with adjustments in the sailplan on the water… Unless the designer completely goofed on the step position.
Mast-step is your last resort and the indicator of a poor design.
I don’t think you have that situation on your hands.
I too don’t check in too often. But that’s no reason not to check-in.
Breakwater,
The reason why the Swing Ring shall move forward is because this rig cannot use a Jib larger then 22/25% of total sail area (see type A &B) while the Classic Rig can use a larger Jib, under the same conditions, of 36/38% of total sail area.
ClaudioD
Breakwater ,
sorry, probably I misunderstood your writing : ‘Not true’ at post #14
Cheers
ClaudioD
PS:
For better understanding of persons ignoring this design detail, the below image can explain better what 's happen between a Classic Rig and the Swing Rig :
Since the Swing Jib cannot be as big as the Classic Jib due to the “wind wane effect”, the combined CE is obviously shifted backward being the result of the sum of the 2 sail’s CE, where the Main surface is increased and the Jib surface is reduced.
Of course the CE on the Swing Rig can be shifted forward by shifting forward the Jib.
Doing this the full efficiency of the two sails working together is lost.
To remember : 2 close sails (main+jib) are producing a better lift then 2 separated ones !!!
Hi,
I am trying to get to the bottom of my serious lee helm problem.
My own design and build, I’ve raked the mast as aft as possible, raked the foils forward as much as I dare and I still need to tune the rig, not for fast sailing but to counteract the lee helm. Sigh.
The above measures help in A-Rig, but B is still bad.
My question is what other factors affect the ‘helm’? Ie the design factors: the relationship between hull bouyancy (fore/aft) and helm, weight placement - bow up/down. Is the design beyond redemption or is there anything I could try?
Thanks in advance.
Tony
