extending a gantry

[john_hamilton]

with the help of the baking temperatures today, i have extended the tiller, fixed the board trailing edge, made a kicker hardpoint and more! it all cured in less than 2 hours from mixing!

[Phil Alderson]

Has anyone ever tried to get the whole leading edge of their rudder forward of it's pivot point? Keel boats do this and it makes the steering much lighter. It would be fairly tricky to do on a dinghy though.

I have seen some fixed rudders setup like that, and if you look at the setup of some pivoting rudders, they can have the same effect.

[john_hamilton]

pray tell?

[andy_paterson]

I  'normally' put 2.5 degrees of fwds rake on a daggerboard blade vs the the pivot line - giving a light feel.

But with a T- foil, there are big loads and changes as the boat heels, so it doesn't matter much now.

The i14 with a  T from the hull will unload the rudder and make the tiller loads much less.

[Will_Lee]

Hi Andy,

Can you explain how adding a t foil can increase tiller loading please?

I understand the loads on the rudder fixings will increase a lot. I understand that if you hit something with the end of T foil there may be big tiller loads.

To add tiller loading you need a force which is acting tangentially to the rudder pin line, right? I cant see how adding a T foil can increase that. (Beyond increasing speed possibly meaning increasing rudder loads.) Endplating the rudder may make the rudder less draggy, but that means less angle for the same steering, which probable wont increase rudder loads.

Effects whereby leeway makes one half of the t foil work better than the other (I think the windward half) might cause an effect whereby there is more induced drag on the liftier half, but I would expect this to be small.

Thanks!

[PaulJ]

The loads on the tiller increase as you rake the rudder forwards and backwards to alter the angle of attack of the t-foil. I guess the highest tiller loads will be experienced downwind with the t-foil right off in waves. If you add a bit of leeward heel at the same time they would be reasonably high.

[Torchy]

Loco's rudder loads are tiny...comparable with an Enterprise, which is the lowest rudder loaded boat I have ever sailed. I've not twin-wired or used the T-foil yet tho'

What was the load like twin wiring and with the T-foil John? Is it sailing Loco which has prompted your re-evaluation or does it load up with the power on?

The big difference between Loco and current boats is mast position and size of jib...and therefore main. Apart from a bit of extra rocker (which is mostly up front?) the hull is just a modern boat with wings not racks...I think.

It's worth noting btw that Ben and Daryl very quickly moved the dagger board back about a foot from its original position.

[Phil Alderson]

The loads on the tiller increase as you rake the rudder forwards and backwards to alter the angle of attack of the t-foil. I guess the highest tiller loads will be experienced downwind with the t-foil right off in waves. If you add a bit of leeward heel at the same time they would be reasonably high.

It depends on the mechanism used to adjust, with mechinisum on the boat the center of pressure of the rudder does not move with respect to the steering axis of rotation of the rudder, so there will not be a change in the balance of the rudder.

If you have the mechinisum on the stock then you do change this relationship and do change the feel quite a bit.

[phil_kirk]

Unless raking the foil forwards which will not be possible all the time if rudder rake also controls the t-foil angle it will be difficult to get the leading edge of the rudder in front of the pin with the current dagger style stocks.

Perhaps we are destined to go back to blades which pivot in the stocks however controlling foil angle will be trickier. Most dinghy rudders i have sailed with on different styles of boats have felt light if the boat is kept flat.

[andy_paterson]

Not sure I can explain why...  but i can report that:

Using a canting gantry ( so the pivot line is constant wrt the blade )
with neutral setting of lift, windward heel gives a little lee helm, flat is balanced, leeward heel gives a little weather helm, and very light tiller loads.
Using several degrees of lift on the T foil, sailing flat is still balanced and light tiller load, but windward heel gives lots of lee helm, lee heeling gives lots of weather helm, and with much higher tiller loads.

so perhaps it's just the amount of lee or weather helm, having to push/pull the tiller a long way off centre and keep it over to make the boat sail straight.

in moths, the windward heel changes the leeway on the fwds angled strut, so that the strut provides no side force - all the sideways  force normally supplied by the daggerboard is transferred to the (now inclined) horizontal foil. ( this reduces the surface piercing drag from the strut considerably )

[john_hamilton]

Perhaps we are destined to go back to blades which pivot in the stocks however controlling foil angle will be trickier. M

Or, just get fixed rudders! what could possibly go wrong

[Will_Lee]

Thanks Andy - I think I can offer an explanation for what you describe. When the boat is heeled the T foil will be giving inclined lift, but the weight of the boat is still acting straight down. This will give a resultant force pushing the stern of the boat to the side because the boat is constrained to be on the surface of the water. This steering force needs to be opposed with rudder movements if the boat is to stay going straight.

This process acts in addition to the other main force of heel related weather and lee helm, which is the centre of drive of the rig moving off the centre line (and has v little or nothing to do with chines, contrary to popular belief - try taking the rig off your boat and towing it around heeled and level).

This means there are genuine extra drag losses when the boat is not level because the T foil and the rudder are creating drag to make lifts which  cancel each other out (not much though). This loss might be less than the losses induced by having some dihedral on your T foil. Hmmm. Any gains would get less as you get better at sailing the boat flat though.

Another thing about this that smaller rudders would be expected to suffer from this more, because more angle would be required. Don't what this does to tiller force though. Could be more, less, the same or (my favourite) it depends. I think it is the last one!

[Will_Lee]

in moths, the windward heel changes the leeway on the fwds angled strut, so that the strut provides no side force - all the sideways  force normally supplied by the daggerboard is transferred to the (now inclined) horizontal foil. ( this reduces the surface piercing drag from the strut considerably )

I made this observation to a collection of foiling mothists on the beach in Saundersfoot in the NB days, so it must have been August 2004. I was subjected to hoots of derision and given many (internally contradictory, mutually contradictory, or just incompatible with physics) explanations as to why I was quite wrong. I take it mainstream Moth thinking has caught up with us? 

[Torchy]

I've just reviewed most of the posts on this thread...really interesting. Weight on steering seems to be coming from T-foil and I can see how... as soon as you heel it is pushing the stern one way or the other.

I thought T-foils were used mostly (exclusively?) upwind yet PaulJ talks about letting it off for gybing and it was to let the '...bow come up...' - I thought if T-foil was used down wind it was used to keep the bow up ie avoid nose dives.

A couple of questions:

Do people use them down wind?

If so +ve or -ve? (+ve = bow down)

[john_hamilton]

i use the t foil so that when we are both stacked at the back, the stem is a few inches out of the water, obvioulsy i use less in waves, etc/...