Mast increases comfort?

[Login3]

I took my mast off the boat as I had some rigging things I needed to do and test, and a friend's wedding was going on with or without me, so I stripped the mast to save time also at the dock because I had a friend generously launching the boat for me.

I'd be curious to know whether the boat ( ) a 2001 X, might be less prone to uncomfortable sudden shifts in waves and responsiveness with the mast up, as opposed to simply less top-heavy with the mast removed entirely.

Something about the mass of the mast (and boom) buffering the wave action?

I found the boat to be very "responsive" to wave input without it.

[Russ]

That's a good question and there are many here who have gone mastless trawler mode.

Your theory makes sense to me. The mass and even the amount of wind resistance would make the boat more stable.

Good question. I hope someone can provide real world experience.

[Be Free]

The inertia of the raised mast will dampen the boat's response to waves.

I had to go back and look up these formulas. I think I remember enough of my college physics to select the right one. Please correct me if I'm wrong.

The formula for the moment of inertia of a cylinder (the mast) rotating about its base is 1/3mL^2 where m is the mass of the body and L is the length of the cylinder. A quick search on the Dwyer site says that a 3x4 mast (like ours) is 1.55 lbs per linear foot. The X mast is 28'. That means the mast weighs 43.4 pounds (ignoring spreaders, rigging, and anything you might have on it. That seems low but I've not weighed my mast and I don't think I've picked it up recently so what do I know?

The rotation is not going to be at the cabin top (bottom of the mast), it's going to be below the water line but that complicates finding the center of mass so I'm going to ignore that because I have no idea what the top half of the boat weighs much less what anyone might have in it. Besides, all that is still there when the mast is down and we are discussing the difference in comfort between mast and no mast so I think I'll still be in the ballpark if I ignore the rest of the boat. I am sure I would have to dust off some even older calculus skills to get it exactly right and it's way too close to bed time to try to wake up those brain cells.

Plugging all the numbers in we have 1/3 of 43.4 pounds * 28 feet squared. That comes to 11,342 pound feet squared. Please note that this value is only valid on Earth. Anywhere in the known universe (including earth) you may use 477.5 kg.m^2 instead.

[kmclemore]

Well, from a physics perspective, having the mast up definitely increases the mass moment of inertia for the boat. This increase in resistance to rotation - fore & aft as well as port & starboard - would smooth out the boat’s angular transitions and make the boat seem more stable.

On edit: Bill, you beat me to it!

[Be Free]

Ah, but was my math correct? It's going on 50 years since I've messed with them.

[Login3]

It was the explanation of the metric "comfort ratio" on sailboatdata.com that triggered this thinking for me, and I'm glad to hear that I wasn't off-base with it.

If I can figure out how to weigh the mast I will, for science. Since, after all, it's lying on the ground!

Definitely a hard thing to measure, since boat loading, wind, wave state, and other factors are always in flux, but I bet someone who has experienced it enough could say with some authority that having the mast up, even if not sailing might result in a general better sense of comfort.

I might get a chance to try it, but having had the boat on the water once with a mast * two years ago when I trialed it * and two days on Icy Strait, one lumpy, one a bathtub, both without mast, I have little to compare it to.

Part of this is really a question for me: Since I'm likely to get a chance to have only one 1-2 night outing with the boat this season, with my wife, before prepping for winter, should I bother with the mast? Hmmm.

[kmclemore]

Ah, but was my math correct? It's going on 50 years since I've messed with them.

Looks pretty good to me!

[Starscream]

Ah, but was my math correct? It's going on 50 years since I've messed with them.

Well, yes, except the mast isn't rotating about it's base, it's rotating about the approximate waterline, probably about 5' below the mast base.



I can't do anything I learned in engineering school any more, so color me impressed. Reading my university notes is like trying to interpret the heiroglyphs. Yeah it's my handwriting, but how could I have possibly understood what's written there? Whelp, at least I have the software/experience/logic triad to keep me out of court.

[Be Free]

Ah, but was my math correct? It's going on 50 years since I've messed with them.

Well, yes, except the mast isn't rotating about it's base, it's rotating about the approximate waterline, probably about 5' below the mast base.



I can't do anything I learned in engineering school any more, so color me impressed. Reading my university notes is like trying to interpret the heiroglyphs. Yeah it's my handwriting, but how could I have possibly understood what's written there? Whelp, at least I have the software/experience/logic triad to keep me out of court.

I did mention that in my first post. I don't know about 5' below but it will definitely be below the waterline.

The question was whether the mast made a difference and if the difference would increase comfort over that of the boat without the mast. Like you, I'm drawing on some very old and rusty concepts, but I believe that when calculating the moment of inertia for an irregularly shaped object you would sum the moments of inertia of each portion. The moment of inertia of everything below the mast step would not change whether the mast was up or down so my focus was on the increased (and comfort enhancing) effects of the mast.

I'm a little disappointed that no one commented on my assertion that the first value was only valid on earth.