how to determine if boat is balanced fore and aft?

scosch · #1 (**permalink**) 10-03-2008

After reading Guilietta's informative rig tuning article, as well as other tuning info, Im always left wondering how to achieve the very first condition always required before tackling the rigging itself. Typically it is required for the boat to be level. I can easily imagine how to do this side to side but how do I do it fore and aft? Do I rely on the bootstipe which has been repainted by numerous POs (correctly?), or do I just use my boat as is, loaded the way I think is appropriate for typical conditions?
If Im setting mast rake to the manufacturers recommendation, seems like the hull would need to set fore and aft to their specs too.

artbyjody · #2 (**permalink**) 10-03-2008

In a perfect world - and if you are racing, everything is about weight. Usually the boot stripes are painted to the same spot as what was designed to to begin with. Real world, when you add in all the cruising items (food, bevs, linens etc) you need to adjust the weight around according to how it lists and will be evident. My C-27 used to be stern heavy due to all the stuff that just comes onboard. You can try to shift things around as always and should if it is evident but some items are dynamic such as holding tanks etc. IN most cases there is nothing really that proper trimming will not handle...

However, when racing - that is a different story, and more attention is played to balancing. BUt that is to squeeze out that .5 knots...

sailingdog · #3 (**permalink**) 10-03-2008

If there is a compression post inside the boat, with a deck stepped mast, it is usually pretty close to vertical, at least in the design... since that is the kind of load it has to resist.

Often, there are other parts of the boat that can give you an idea of the boat's fore-aft trim—for instance, the cabin or salon table, I'd imagine is supposed to be pretty close to level as well, so putting a level on it would give you a rough idea of how close to level the boat is.

Even if your boat isn't level fore-and-aft, as long as you know how far off it is from level, you can still rake the mast properly. For instance, if the mast is supposed to have 5˚ of rake, and the boat is tipped aft 3˚... you'd set the mast rake at 8˚... but it isn't an exact science... since a boat that is heavily unbalance fore-and-aft will also alter the center of effort and the center of lateral resistance a bit... so YMMV.

scosch · #4 (**permalink**) 10-03-2008

I was wondering what Jody meant by "evident" Seems like by the time it was evident to a novice, it might be pretty bad.
I like the suggestion of using something inside the cabin and checking for plumb to determine level. My compression post is part of a bulkhead and that seems like a place I might try.
As far as balancing fore and aft in the real world, I can see where a heavy bow would tend to dig in but what effect would I first notice with a heavy stern? Just squatty looking? And given that were all constrained by storage locations and fixed things like tankages, how much does one fuss with this fore and aft thing other than just being aware and spreading the heaviest things
around as best as one can?

scosch · #5 (**permalink**) 10-03-2008

whats YMMV?

sailingdog · #6 (**permalink**) 10-03-2008

YMMV-

Your mileage may vary.

newpbs · #7 (**permalink**) 10-03-2008

This is an interesting question. My Ericson 32-200 has more rake than the tuning directions seem to suggest. I have let the backstay out as much as possible. I also seem to have a lot of weather helm in some conditions. I have never considered that the boat is not properly balanced for and aft.

Anyone have experience with this?

Paul

SEMIJim · #8 (**permalink**) 10-03-2008

Quote:

Originally Posted by newpbs

This is an interesting question. My Ericson 32-200 has more rake than the tuning directions seem to suggest. I have let the backstay out as much as possible.

Mast rake is set with the forestay, not the backstay.

Just for grins, as I was setting the mast rake on Abracadabra this spring, I experimented with backstay tension. Made no discernible difference.

Quote:

Originally Posted by newpbs

I also seem to have a lot of weather helm in some conditions.

Too much mast rake will do that.

Our boat is billed as a cruiser/racer. I believe your boat is, too. I set our mast rake to about 1-1/2 degrees. (I think I used Giu's numbers for doing the calculation.) We can literally let go of the tiller on most tacks, under most reasonable conditions, and it'll stay put. Going to weather, under reasonable conditions (i.e.: Not on her ear), she's got just a touch of weather helm, which is just how we like it. By "touch," I mean we can still let go of the tiller, but she'll eventually begin to gradually head up.

See also Giu's new video on using the mainsheet traveller. Even if your boat is in trim: If she's on her ear you'll be hanging on to the tiller or wheel for dear life. De-power things a bit, let her stand up, and she'll be going just as fast, probably faster, a lot more comfortably and with a lot less strain on boat and crew

.

Jim

sailaway21 · #9 (**permalink**) 10-04-2008

You can get the boat on her lines and then install a clinometer and a trim-o-meter in locations of convenience. Note that neither need be either on the centerline of the boat nor amidships. You'll then have the reference point that Dog alludes to. For these purposes you'll want the large scale, zero to five degrees, bubble guages that are widely available at reasonable prices.

Once installed you'll be able to observe the effects of loading as well and better trim your boat. While a half a knot may seem of no issue to the cruiser I would beg to differ in that it represents an inefficient use of the vessel and will result in poor handling when your primary concern may not be speed but efficient sailing in weather.

sailingdog · #10 (**permalink**) 10-04-2008

btw, if your fore-aft trim is off by more than two or three degrees, it should be pretty obvious.