Bimini damage caused by boom

[csm]

I have the same problem with bimini wear from boom contact. I have other spots on the bimini that are rotted due to neglect by the PO, which I've halfast patched. I plan to replace the fabric soon so this topic is timely for me. I have a couple yards of ballistic nylon hanging around somewhere, so a wear strip would be super easy, but I'm not a big fan of bandaids. Would it be crazy to consider cutting a relief out of the bottom of the boom? Seems to me structural integrity wouldn't be an issue aft of the bail. Been way too long since I've had the mast up (####POLAR VORTEX) so I'll have to study this when the weather clearz

[seahouse]

I have the same problem with bimini wear from boom contact. I have other spots on the bimini that are rotted due to neglect by the PO, which I've halfast patched. I plan to replace the fabric soon so this topic is timely for me. I have a couple yards of ballistic nylon hanging around somewhere, so a wear strip would be super easy, but I'm not a big fan of bandaids. Would it be crazy to consider cutting a relief out of the bottom of the boom? Seems to me structural integrity wouldn't be an issue aft of the bail. Been way too long since I've had the mast up (####POLAR VORTEX) so I'll have to study this when the weather clearz

Yeah, I've noticed that this wear happens frequently on other sailboats too, but I think most of them are just in need of adjustments.

Barring that, a quick and dirty fix might be a roller mounted along side the boom, set slightly lower than it. Could even be set on a springy bracket to absorb the shock in case of unintended jibe-type violent passings. It would then just roll over the material with minimal abrasion to it.

But all that to avoid setting the rigging up properly?

[DaveC426913]

A curved mast denotes problems.

A Mac's mast is curved by design. A non-curved mast denotes problems.

[DaveC426913]

Sorry was away from puter past two days.
Appears your Bimini is way to high for boom to clear the Bimini while sailing. How do you sail at all with Bimini up?

Under sail, the boom goes under the bimini, but the sail does not come as far astern as the boom does. So, there is no interference. The only problem I have is when I drop the sail and shorten the topping lift - I need to swing the boom out around the bimini to raise it.

[March]

DaveC426913 wrote:
Under sail, the boom goes under the bimini, but the sail does not come as far astern as the boom does. So, there is no interference. The only problem I have is when I drop the sail and shorten the topping lift - I need to swing the boom out around the bimini to raise it.

I am having a hard time picturing that: the boom under the bimini, under sail, and the topping not interfering with the bimini before, during, or after you shorten it. But then again, your mast is curved.

[yukonbob]

DaveC426913 wrote:
Under sail, the boom goes under the bimini, but the sail does not come as far astern as the boom does. So, there is no interference. The only problem I have is when I drop the sail and shorten the topping lift - I need to swing the boom out around the bimini to raise it.

I am having a hard time picturing that: the boom under the bimini, under sail, and the topping not interfering with the bimini before, during, or after you shorten it. But then again, your mast is curved.

really short bimini? I have the same issue of having to move the boom to the side to raise the bimini, but can sail with the bimini in place and all the side and rear windows up, less the two front windows and connector between the bimini and the dodger. The mast should have a 1 inch aft curve in it for proper sail shape.

[DaveC426913]

DaveC426913 wrote:
Under sail, the boom goes under the bimini, but the sail does not come as far astern as the boom does. So, there is no interference. The only problem I have is when I drop the sail and shorten the topping lift - I need to swing the boom out around the bimini to raise it.

I am having a hard time picturing that: the boom under the bimini, under sail, and the topping not interfering with the bimini before, during, or after you shorten it. But then again, your mast is curved.

Why would a topping lift ever interfere with a bimini under sail? Topping lifts are supposed to be slack when under sail. True, when I drop sail and go to raise the boom, the topping lift goes taut and contacts the bimini.

I don't know how other topping lifts are arranged, but mine is adjusted directly at the boom-end, it is not routed along the boom and up the mast tot he masthead like many boats do. So, when I go to raise the boom, I must uncleat the topping lift from the boom, raise the boom bu hand, then reconnect it a foot higher to the topping lift. (Actually, I've got it on a 2:1 pulley now, arranged so that, when I pull down on a short line, the boom goes up).

[DaveC426913]

But then again, your mast is curved.

Seriously though. If you look up the length of your mast when correctly rigged, it should bow backwards a couple of inches i.e. a line strung down the trailing edge of the mast from masthead to step should be one to two inches away from the mast at the midpoint.

It's not a lot, but it's enough to interfere with measuring a rake angle of just a degree or two.

[March]

by DaveC426913 » Thu Feb 13, 2014 2:08 pm

March wrote:
But then again, your mast is curved.


Seriously though. If you look up the length of your mast when correctly rigged, it should bow backwards a couple of inches i.e. a line strung down the trailing edge of the mast from masthead to step should be one to two inches away from the mast at the midpoint.

Seriously. The mast will curve because it is made of aluminum and aluminum is flexible. Anyone can see that easily enough when the mast is in a horizontal position when trailering. There is room for a couple of inches of flex in the middle of the mast, let alone at the end. I can easily insert a support made of PVC in there, where the foot of the mast goes and it will stay put. Or I can remove it by pulling the mast up. Does that mean the mast is curved? Or that it should be?

My commonsesical guess is, the mast is supposed to be straight, yet it allows for a little flexing. Two inches at the top will never result in two degrees of tilt. You can tighten the forestay or the back-stay and you'll get your two inches at the top of the mast, even when the mast is NOT curved.

I am not a metal worker, but my guess is, manufacturing a curved mast that's gonna flex anyway based on the tensions applied, is an unnecessary hassle, especially since the radius of the curve is so huge.

[DaveB]

With the boat in the water with all gear onboard, take a 4 ft. level and put it at the base of mast. Measure the distance from bottom of level to top of level when level is plum in a vertical position. You now have a distance of maybe 1/4 inch more or less. Divide your mast height by 4 ( Length of level) than multiply it by the 1/4 inch or so and that will give you inches of mast rake aft. Or just use the 4ft. measurement and convert to degrees.
There is no mast bend at 4ft.
As I stated before you always want a little weather helm so the boat heads up in a heavy gust. This generally is about a 1-1/2 degree rake aft on the MacX but may varies in how your boat is loaded. Most of the time it could be from 1-2 degrees raked aft.
Dave

But then again, your mast is curved.

Seriously though. If you look up the length of your mast when correctly rigged, it should bow backwards a couple of inches i.e. a line strung down the trailing edge of the mast from masthead to step should be one to two inches away from the mast at the midpoint.

It's not a lot, but it's enough to interfere with measuring a rake angle of just a degree or two.

[seahouse]

Your method will be accurate if some conditions are met, Dave.

After the boat is loaded with the gear on board, the bootstripe must be parallel to the waterline- but it doesn't always work out that way. Otherwise a zero degree reading on the level will not correspond to the mast being perpendicular to the boot stripe. So the payload would need to be redistributed to trim the boat to be level the bootstripe.

Also the mast must be straight - there must be no mast prebend prior to setting the rake this way.

As an extreme example, the lower part of the mast can actually tilt forward with excessive mast bend, even though effectively, the mast is raked toward the stern. Picture a (bow and arrow) bow with the bowstring tilted back towards you (that's the aft rake), and yet the lower part of the bow is actually tilting away from you (that's what the level would erroneously be measuring).

Note that mast rake is measured as a straight line from the top to the bottom points of the bent mast, which makes a halyard pulled taught, as mentioned by a poster above, a good reference line to measure mast rake from. The length of the forestay is what determines and sets mast rake.

These things might seem small, but they can cause considerable error when measuring quantities in the order of a degree or two.

It also looks like some of the posters in this thread have not considered that there are differences between the M and X setups to be aware of.

-Brian.

[mastreb]

The mast for the X is supposed to be about 2% bent forward when the rig is properly tuned, according to the X manual. I think this is inline with Dave's comments. The mast for the M exhibits so little bend that it's not measurable when properly tuned according to its manual, but easily rotates by hand on the mast step. If your M mast does not rotate easily when not under load, your rig is out of tune, your mast is bent, or your bearings need work. Heck, I've had both broken bearings and a bent mast, and it still rotates easily as long as the rig is correctly tuned so the mast is straight on it's waterline and side-to-side. Even a little bit of off-side tuning issue or too much forward pull from slack side-stays will stop rotation cold however.

[seahouse]

The mast for the X is supposed to be about 2% bent forward when the rig is properly tuned, according to the X manual. I think this is inline with Dave's comments. The mast for the M exhibits so little bend that it's not measurable when properly tuned according to its manual, but easily rotates by hand on the mast step. If your M mast does not rotate easily when not under load, your rig is out of tune, your mast is bent, or your bearings need work. Heck, I've had both broken bearings and a bent mast, and it still rotates easily as long as the rig is correctly tuned so the mast is straight on it's waterline and side-to-side. Even a little bit of off-side tuning issue or too much forward pull from slack side-stays will stop rotation cold however.

You meant 2 degrees rake rake aft. (?) Or 2" bend forward in the middle(?)

Yeah, my observations too re: the M rigging. I do tune for some rake, and bend- it can't be much.

[DaveB]

Seahouse,
I tried to make this as simple as I can for members who want to adjust there rake.
I could have suggested laser transits or other means on a perfect level boat on trailer .
But this works for a average sailor.
Please note that my previous post stated in water with gear aboard.
You don't measure the Mast in a vertical line as it bends aft. Why the 4ft. level.
Think you should go back and read a few treads. (you missed some major things)
Dave

Your method will be accurate if some conditions are met, Dave.

After the boat is loaded with the gear on board, the bootstripe must be parallel to the waterline- but it doesn't always work out that way. Otherwise a zero degree reading on the level will not correspond to the mast being perpendicular to the boot stripe. So the payload would need to be redistributed to trim the boat to be level the bootstripe.

Also the mast must be straight - there must be no mast prebend prior to setting the rake this way.

As an extreme example, the lower part of the mast can actually tilt forward with excessive mast bend, even though effectively, the mast is raked toward the stern. Picture a (bow and arrow) bow with the bowstring tilted back towards you (that's the aft rake), and yet the lower part of the bow is actually tilting away from you (that's what the level would erroneously be measuring).

Note that mast rake is measured as a straight line from the top to the bottom points of the bent mast, which makes a halyard pulled taught, as mentioned by a poster above, a good reference line to measure mast rake from. The length of the forestay is what determines and sets mast rake.

These things might seem small, but they can cause considerable error when measuring quantities in the order of a degree or two.

It also looks like some of the posters in this thread have not considered that there are differences between the M and X setups to be aware of.

-Brian.

[seahouse]

Sure- I understand making it simple, and we all are after that result, Dave. Just trying to clarify some things that might not be immediately apparent to the readers of the thread, as simply as possible, and so that they still get the desired result of proper tune on their boat.

Mast rake is the rearward angle that the mast takes, measured as a straight line from end to end in the case of a bent, referred to as “curve” in this thread, mast; as compared a line running perpendicular to the boot stripe. Simple enough.

Also to be clear - no offense was intended of course, and I did not say that your suggested method would not work, or that there was anything "wrong" with it, but rather I stated that the variables that I mention need to be heeded. Just supplementing what you said, not disagreeing. My caveats are valid and clear, I'm not sure if you are disagreeing but I do believe we are “on the same page” here.

- Brian.