extending a gantry

[john_hamilton]

As anyone who saw my boat at the end of the nationals will know, the tiller is quite petite... about a foot and a quarter long. with my new adjustable caps, we are faster in heavy wind, but i find myself not having enough time to do anythin but battle the tiller loads, leading to two broken tillers, an broken uj, and a dead footstrap, all in a matter of weeks.

I cut down the tiller to give myself room in heavy wind gybes, and have experimented with having it longer many times since, always ending up going back to the shorter one... so either me and digby are rfeall fat, stand too far back, or just have a shorter gantry than everyone else ( it was taken off a different mould made by phil kirk for the specific job, and could be slightly different? So would there be any massive problems with just building a longer gantry so i can get my easy steering back? heres a picture of one on the new killing 3 int 14

many thanks, john

[JimC]

Halo had a 540mm tiller, which was pretty short as they go, and I don't ever recall getting complaints from helms about the loads, although maybe Will, who did an event with that setup would disagree. Of course that was with the 97 sails, which will change things a fair bit, but I can't help thinking that if you are running into such severe tiller loads as you describe then you need to look for a root cause in the boat setup.

[Tim Noyce]

John, measure up your gantry from transom pin to rudder pin and I can compare it to the E5 moulded one.

I think that generally the gantrys have got shorter since the move to the swinging gantrys, I can't remember the measurements from the Badger but that had quite a sizeable one, maybe 600mm or something.

[andy_peters]

We too have a very short tiller on the E5.  What I have noticed is that it loads up mainly for 2 reasons:

1. not keeping the boat flat - especially on any other course than a beat
2. having any t-foil on a white sail reach

When the gantry is back on the boat I'll measure the gap and let you know but in general the tiller loads aren't that bad.

[Clive Everest]

The bending moment on the tiller will not be effected by the length of the tiller.
If you are breaking a short tiller you are just as likely to break a long one but will not have to pull as hard to do it.

[john_hamilton]

im not breaking the tiller clive, just the extensions. A longer one will obviously make problem less... and jim, this is only 380mm long, with 05 rules sails, and its nothing wron with the rig, just if we arent exactly flat (and we sail on a n inland, gusty lake), then the problems surface

i'll measure the distance tommorrow

[Phil Alderson]

Very high tiller loads sounds like a problem with the balance of the rudder. For a balanced rudder it should be raked fwd with respect to the axis of the rudder pin. i.e. the opposite way to a Laser.

As you move the top hole in the rudder stock away from the rudder, it becomes progressively more balanced, and the steering loads drop. Up to the point where it over balances and they reverse which is V hard to sail with.

[Will_Lee]

Slop in the rudder stock can cause the appearance of high loads because the blade can snatch from one way to the other. Not nice.

Misplaced kite ratchets (too far forwards) can cause extreme lee helm downwind in marginal conds.

Mostly though it is keeping the boat really flat, and as Phil says, balancing the blade. You defnitely want some of the area to be in front of the continuation of the rudder pin. My memory says a third, but that seems like an awful lot. Thinking about Norwegain's, Atum's and Antidote's, 10% seems to be the minimum.

If the footstrap is breaking it suggests it is lee helm you are struggling with. If so, you can try using more main sheet downwind and/or kicker, which may help a bit. You can roll the boat to leeward a bit to balance the rudder downhill. Easing a it of jib may also help.

However, the magnitude of the problems suggest there is something big going wrong. If your main is very deep with a hard leech downhill you might be stalling the whole thing?

Good luck!

From memory, Atums gantry is 450mm, and I think  Antidotes is 350mm. It might have grown a bit later too.

I don't know why the 14s have been going for such long gantries. It may be ergonomics.

[phil_kirk]

two things to consider.

A longer pivoting gantry will increase the loads on the control line purchase and the loads on the fittings on the boat.

This will also mean that the foil is further back and it will be harder to get the helm's weight over the foil.

If I am correct john i think you are saying that the boat is normally balanced but lee and weather helm are felt when the boat heels in gusts and lulls. The forces from lee and weather helm are larger and more difficult to cope with because you have a short tiller.

I think my tiller is just under 600mm from the rudder pin.

The gantry mould that I made for you is very similar in dimensions to the original E5 gantry mould.  You would had drilled the pivot holes without access to an existing E5 gantry to measure from.

[JimC]

I wonder (completely evidence free theorising)  if there could be too much side load on the rudder and not enough on the daggerboard. Its good to have the rudder loaded up to an extent, but it must be possible to overdo it. Unfortunately that's a really major deal to resolve: I fear it likely  the best solution is moving the daggerboard case.

This sounds as if its the sort of thing you need a second opinion on. I don't know who the current best setters up of boats are in the fleet, but if you can entice one to go for a ride in your boat to give you a second opinion it can only help.

[PaulJ]

When are you getting the very high tiller loads, upwind or downwind. Kite up or down. Mark roundings, twin wiring. It it weather or lee helm.

It sounds to me that the rig and foils aren,t in balance, I expect it can be sorted by playing with the rake a bit assuming the foils are in the same place as the other E5s....

Post edited

Having re read the thread a bit more I think I understand your problem better

From what you have said the boat is nicely balanced most of the time, but you have problems with gybing in windy weather. You have shortened the tiller to give you more room which has worked but caused other handling issues that require possible major boat mods. Cure worse than the original ailment I think. A shorter tiller has increased the loads on the tiller plus it will make the boat much more twitchy as a small movement on the tiller has a greater effect on the rudder angle compared to the longer tiller.

In windy weather we have developed a safe gybe technique as follows :-

1. I tell Peter that we are going to gybe to make sure he knows what is happening and doesn't follow me in at step 2.
2. I come into the boat and sit on the wing and unhook.
3. Ease the t-foil off to get the bow out of the water to stop it steering the boat
4. Get the boat dead flat and more importantly still going fast
5. Tell Peter we are now going to gybe
6. Turn the boat in a smooth curve as Peter comes in, I cross the boat just before him and head for the new wing.
7. Both get on the wing and and steer as necessary to keep the boat dead flat.
8. Peter gets straight out on the wire and sheets the kite.  I follow when I've sorted out the main sheet and pulled the t-foil back on.

I would suggest before you get into major boat work you put a longer tiller back on and spend an afternoon working on your gybing technique.  The main things to get right are keeping the boat flat, steering smoothly and predictably, and keeping the boat moving quickly. 

[john_hamilton]

interesting.

Phil and will - i found an off-cut of 8mm tube from the plumbing (or something) similar about a meter long, and put it through the rudder pin hole, when extended it touched the joint between the tip of the vert blade and the "torpedo" fairing for the t foil, so definitely something to look at as there is precisely 0% of the rudder in front of this line!

Mr Kirk - How do you sail with a tiller that long? i have found when it gets gusty in gybes downwind i tended to trip on the longer tiller. This may be due to Sarahs diminutive frame in comparison to 6ft2 digby... i have measured my gantry as 300mm from pivot to pin, and i have a 420mm tiller... so a bit different, i think i could manage alot better with a 400mm gantry and a 550mm tiller (the original size, suprisingly)

Jim - the dagger board slot and rake is identical to e-numbers, which seems pleasant to sail, and fast, when the flat, the boat is well in balance, all i am looking for is a soution to the tiller loads (and broken universal joints)

the plan for now is to play with the pin angle a bit, then see if i can cope with the short tiller in that set up, thanks for all the informative replies...

[Will_Lee]

I think Paul's answer was the best. I shortened Norwegians tiller for the same reasons you describe and we swam basically every gybe until I lengthened it again (one event!). I took to opportunity to crank the end of the new bit of tiller down a bit so the outboard ends of the extensions were higher. You might find a photo or two on the website of NB with seaweed decorating the shrouds. It was that event!

[BenR]

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.

[john_hamilton]

sorry paulj, i never saw your reply, looks like we posted at the same time! technique is definately the problem, combined me and digby are 12ft3 and so crossing the boat at different times will help, longer tiller going back on, you have convinced me! (its the crews fault and the not the fault of whoever built this speedy boat ;-) )

although i will be looking at pin angles thanks to will (i cant help but fiddle with things a bit ;-D )