raising the boom

[zephyr101]

thanks for your ideas. will let you know what i do when i do it, proably nov. when i go south again. got a different boat up north in ct.1971 35 finsailor ,motor sailor with inboard deisel 70hp.compleatly different handeling boats both not th best sail boats but both good for me only started sailing 10years ago.
Howie

[zephyr101]

Found I had a sliding gooseneck from a 76 hunter and it fits in sail groove on mast and attaches to the boom with a longer 1/4 bolt.raising the sail all the way raises it about 8". real close on rubbing the back stayup top.Have moved the bale on the boom to clear the front of the bimini.I am tweaking the bimini and out haul on main sail.got to check mast rake next an install down haul on boom.Almost there and can see it will all work.
Howie

[Doupirate]

Il you move your mainsail center of thrust up the mast, the heel momentum will increase. The ballast will then become insufficient, the stays and mast not strong enough.

You will not have a MacGregor sailboat any more. The marine surveyor will notice and NOTE it. The insurance and the prospective buyer also.

This is a major modification, far beyond the reach of a non marine specialized engineer. I would not even raise the sails on such a modified boat without putting on a life jacket.

Hope you change your mind.

[mastreb]

Here's what the math says:

Wind load (lbs.) = wind speed (kts)^2 * sail area (sq.ft.) * 0.00431.

20 knot wind on a 150 sq.ft. mainsail: 258.6 lbs.
Torque: Force * lever arm length * sin (angle of heel). I'm using a lever arm height of 10 feet to match the _center_ of effort on the sail. This is an estimate, but it's pretty close.
Vertical: 2586 lbs.
30 degree heel: 2239 lbs.
70 degree heel: 884 lbs.

With a mainsail raised 1 foot:
Vertical: 2844 lbs.
30 degree heel: 2462 lbs.
38 degree heel: 2241 (equal to 30 degree heel in the above example)
70 degree heel: 972 lbs.

Righting torque of the Mac ballast (assuming that the point of ballast is 2 feet below the center of rotation, which is an estimate on my part): 3200 lbs. (at 90 degrees rotation. 0 lbs. at vertical, which is why the boat is tender).

As you can see, the force on the mainsail decreases with the sin of the heel angle. This is obvious when you think about it--a sail at 90 degrees (flat to the ocean surface) has zero torque because the wind is no longer blowing on it.

The ballast, however, becomes increasingly effective as the boat rotates from vertical. By the time you're at 45 degrees, there's 2200 lbs. of righting torque countering 1600 lbs. of pushing force. The boat won't reach this point in this example--heeling stops when the two countering forces are equal.

So, while raising the sail will definitely cause considerable additional heel (figure ten degrees more) it will not cause a blow-down under any circumstances and it does not over power the ballasts ability to keep the boat upright. It just means that you'll be farther over all the time.

So in sum, ballast becomes increasingly effective as the boat heels, while the force on the sails becomes decreasingly effective. This balance of forces is why sailing works.

Consider that a musclehead main has more torque on it than the stock mainsail raised 1 foot. People who own them have not reported having been blown down.

Annoying, but not unsafe.

[Doupirate]

Annoying, but not unsafe.
mastreb
Captain

My Mac is not modified. I keep it on a 20 miles long, 1 mile wide lake, with nice mountains and cliffs. Real nice.

On a nice summer morning, at zero speed, I was enjoying the music, waiting for the noon breeze to kick in, all sheets out, taking advantage of any breath of wind as it would come. Actually, once in a while, I would move a little. I was alone.

At one point, I saw a nice little gust moving toward me on the glassy water surface. I prepared to take advantage of it to tack.

At zero speed (the boat would not round-up) the heel almost instaneously rose to 30 degrees, then exceeded the range well beyond 45 degrees, something like 60.
The speed still at zero.

I stood up on the side of the lower bench cover (starboard) holding to my dear life with my whole left arm on the port side of the ...hull. I succeeded at staying on board.

«Annoying», indeed, but not «unsafe» since I am a fairly good swimmer. Besides, my stays held just fine, since they were not prematurely worn out, being the appropriate gauge for the nominal heel of this boat.


Note: my editing is as frequent as the instances I wish to correct my English writing. Believe it or not, I am actually a pretty good writer.......in French !

[Crikey]

I thought we carried only about 1200lbs of water ballast. You can factor in some of the other weight, but other amounts are above the center of rotation and would have a subtractive effect on your final results.
A blow down to ninety degrees is definitely going to be uncomfortable, but is not going to guarantee a capsize.

[mastreb]

Annoying, but not unsafe.
mastreb
Captain

At zero speed (the boat would not round-up) the heel almost instantaneously rose to 30 degrees, then exceeded the range well beyond 45 degrees, something like 60.
The speed still at zero.

«Annoying», indeed, but not «unsafe» since I am a fairly good swimmer. Besides, my stays held just fine, since they were not prematurely worn out, being the appropriate gauge for the nominal heel of this boat.

Precisely. The boat did not go over.

There's no resistance at all from the ballast to tipping when the boat is upright. It will tip immediately. Resistance increases as the boat goes over, to the point at which it balances against whatever force is causing the tipping, at which point it stopped. In this case, because you weren't moving, the daggerboard's hydrodynamic lift was not assisting in countering heel, and you were relying entirely on the ballast. In motion the boat would not have gone over as quickly or as far due to the oppositional lifting force of the daggerboard.

At 0 degrees heel, the ballast is 0% effective in reducing heel.
At 30 degrees heel, the ballast is only 50% effective.
At 45 degrees heel, the ballast is 70% effective.
At 60 degrees heel, the ballast is 86% effective.

So it sounds like exactly what would have happened if you were hit by a sudden 15 knot gust filling the mainsail.

The point of all of this is that you'd have gone over a further ten degrees if your sail was a foot higher, but you still would not have been blown down. Whether or not you would have been dunked is a completely different matter, and I'm glad you got your footing.

These boats have 1300 lbs. of water ballast and 300 lbs. of permanent ballast. My guess is that the ballast is 2 feet below the center of rotation, which means that at 90 degrees there'd be 3200 lbs. of righting torque.

Consider that without the ballast in, there's so little righting torque that the boat will blow down in any wind whatsoever.

[Doupirate]

The facts are a sailboat is a compromise.

Very competent people work on the design, they meet, consider all possible options, and end-up with a design which will meet the needs of the target market. The MacGregor market is definitely, the first boat buyer.

They know we are not seasoned sailors. They provide for a forgiving boat, that will take care of itself, whatever the nonsense we impose on it. I once tried opposing round-up with full opposite rudder. It heeled quite a lot, but, yes, it rounded up. Good pet! From then on, I would balance the sheets so the rudder would be at neutral, as it should be, then leave the wheel alone, go to the can for a number 2, watch the genoea through the handy bridge window, and get back to the wheel, once the job done...

Now, you believe you will improve on that design, relying on basic trigonometry and rough estimates....?

Well, my answer is LOL

Besides, marine surveyors are there to make sure you own for long your «modified racing beast».

Doupirate is «over and out»

[mastreb]

This isn't a design improvement--increasing heel is a bad thing period. I'm just saying it's not unsafe, and the math proves it irrespective of the estimates I used. It doesn't matter if the center of effort is higher or lower, or the center of rotation. The effect is the same: The farther over the boat heels, the more the ballast resists and they will with certainty reach equilibrium before 90 degrees of heel. No amount of sail that could be hung on this boat is going to be unsafe, just uncomfortable and poorly balanced.

As you say, it's because the boat is so well designed that its very forgiving.

[Crikey]

My mistake! I should've done my ballast math better with the 1300lbs + 300lbs X 2 (distance from rotation point).

Hey Doug! Good thing you finished your number two before it rounded up

Sure would've scared the crap outa me!

It would be an interesting stand-alone post to canvas how many of us had their MacGregor as a first boat.

[Doupirate]

I'm not Doug. Whoever he may be, I believe he is a no-nonsense fellow, humble enough to respect the work of people quite more knowledgeable than him in their field (Mac Gregor engineers), and not afraid to speak out his mind.

[zephyr101]

Took off the old boom conection today and installed down haul Closed old opening for sail slugs and bent new opening lower down mast.schould be all set to test out. from all the talk,I guess i will have to reef five minutes sooner then others but I don't care. Better then having someone getting hit in the head.SAFETY is more inportant then heeling TO ME

[Crikey]

I'm not Doug. Whoever he may be, I believe he is a no-nonsense fellow, humble enough to respect the work of people quite more knowledgeable than him in their field (Mac Gregor engineers), and not afraid to speak out his mind.

Amen, the fault was mine!

[Divecoz]

Looking at some boats today.. I see some have their booms run "up" at an angle of say 8=12 degrees.. Mast to Stern.. It appears this is done to allow standing room at the Helm?
If so, can we 1. Cut our main sails at an angle
2. When we get a new main have it cut to fit etc. etc.
My real question is?? Could I have two different "style" Main sails ( foot ) and just allow the boom to swivel as needed...??

[Judy B]

Looking at some boats today.. I see some have their booms run "up" at an angle of say 8=12 degrees.. Mast to Stern.. It appears this is done to allow standing room at the Helm?
If so, can we 1. Cut our main sails at an angle
2. When we get a new main have it cut to fit etc. etc.
My real question is?? Could I have two different "style" Main sails ( foot ) and just allow the boom to swivel as needed...??

Hi,

I'm a sailmaker. I'll take a stab at answering your questions.

Is the boom on your 26M parallel to the cockpit floor or or does it droop at the aft end? It should be parallel to the floor if it's made right.

There's no reason we (or any competent sailmaker) couldn't build you a mainsail that has the end of the boom up higher than usual. It would sail just fine . We'd have to check and make sure the gooseneck will allow the vertical travel.

A typical 26M mainsail has an angle of 83.25 degrees between the mast and the boom. That ensures that the boom is horizontal and parallel to the cockpit floor. But we can change the design for you so that the end of the boom is higher up than usual, with the foot cut at an angle to give more headroom at the helm,

New vs recut?

Usually, it's more cost effective to sell the old sail for a fair price and get a new one designed from the start to do what you want it to do.

One thing that's important to note is that sailmakers align the panels such that the threads resist the forces put upon it. That's part of the design of a mainsails that will hold its shape. So you shouldn't recut the foot, willy-nilly any which-way if you want it to last a few years.

Recutting the foot at a different angle might be possible, if you're only talking about moving the clew up a very small distance -- an inch or two or three. (I don't recommend that you cut across a horizontal seam -- that's usually a sign that you are way out of alignment with the threads of the cloth). If the sail is in almost-new condition, it might be worth the time and expense.

Another consideration: Reefs are designed to keep the boom in the same position as when un-reefed. If you recut the foot, the end of the boom will "droop" again. If you get a new mainsail cut with a higher clew, the reef points will be installed so the boom is always in the same position.

Hope this helps,

Judy B