Mast ram...I'm still foggy

[Greenheart]

Some nice footage of a 505 going well upwind, here...

http://www.youtube.com/watch?v=IXSFiFbNgVU

...but to be honest, I'm still not clear what good the ram does, ahead of the mast.

Is the main purpose, to counter the mast-bending influence of the boom, pushing on the same spot in the other direction?

I guess not being able to see its effect in use, is making me slower on the uptake than I ought to be.

Is there a quick explanation?

And, does the deck-end of the ram need special support - some sort of under-deck chassis, to take the strain?

 

[dunedin]

The mast ram controls the amount of mast bend.

Pull on hard and it pushes the front of the mast back, causing it to be straighter- giving a more powerful mainsail.

Ease it off and the mast will bend more - flattening the shape of the mainsail and allowing the leech to free off, both allowing excess power to be eased without just flogging the sail, which would be slow

Re strengthening, the Foredeck needs to be strong anyway to avoid the forestay tension bending the bow up, but will be designed to have the ram on a big rig boat like this 505

 

[uxb]

How does 'bending the mast' flatten the main?

I can see how the leech will open but simply bending the mast will put more 'belly' in the sail. Don't you need to increase the luff tension as well?

 

[Quandary]

How does 'bending the mast' flatten the main?

I can see how the leech will open but simply bending the mast will put more 'belly' in the sail. Don't you need to increase the luff tension as well?

Forget about changing luff tension for a moment. Imagine a triangle of cloth. Pull out the edge to a convex shape. the material to make the curve has to come from somewhere, that is why the sail flattens. It is the reason boats have adjustable backstays.

 

[Bobc]

This is actually a mast strut rather than a ram. A ram acts on the mast at deck level, whereas a strut acts a gooseneck level.

The idea is that the sail is cut with maximum draft with a fairly straight mast. Applying kicker without any strut acting will try to push the boom forwards into the mast, bending the lower sections and flattening-out the "belly". So it acts as a reliable and accurate way of restricting the mast bend hence changing the fullness of the lower sections of the main to give you the right amount of power.

With some, att the deck end of the strut is a lever which goes vertically down through the deck with a pivot pin at deck level. There's only a couple of inches of lever above the pin, but about a foot below, giing quite a bit of leverage. With others, the deck-end is fixed and there's a slider on the front of the mast. Tension is applied by a block system (typically 4:1), so you can really grind the load onto it (which you need to when pushing back against the kicker loads. Boats with struts will have a load-bearing beam under the deck (front to back), but then almost all dingies do anyway because of load triangulation.

A lot of boats have taken to using adjustable lower shrouds (from the gooseneck down to the chainplates), or D2s (from the 1st spreaders down to the chainplates) these days instead of a strut, because they are lighter, and also support the mast sideways.

Hope that helps

Bob

 

[Greenheart]

Certainly does help, thanks. I already had an idea that a mast 'ram' works on the mast foot, which is adjustable in classes like the Flying Dutchman (I think), allowing immediate adjustment of mast rake.

Whereas, this strut appears only to reduce the huge pressure caused by the boom pushing forward on the mast in heavy weather.

Though, it seems surprising that serious mast bend should be visible or measurable or controllable (or have influence on sail shape) in such a short length of the spar - not like the gradual, even curve that we're used to seeing in Laser masts, etc - though it makes sense that any bend will be less localised in a rig that's unstayed.

Cheers.