MacGuyver required for moveable ballast...

Howdy folks!

In case you didn’t quite know what the subject meant, it harkens back to those good ol late 80s and early 90s when the show MacGuyver (spelling?) was broadcast into millions of homes. MacGuyver of course, is that mullet headed genius who could build anything out of toothpicks, gum, and a match… which brings me to my puzzle:

With the following items, construct a deck mounted moveable ballast system. Now I’m a college student, and as such $ are short. Thus I’m making due with what I have. What I want is a lead “sled” that will slide side-to-side on aluminum tubes, and can be adjusted to keep a boat relatively level while sailing.

What you get:

1- 18 inch wide “rack” which consists of two “capping” pieces a foot long with two dowels and two aluminum tubes running between them. (It basically looks like a drying rack, if that means anything)

1- arm sail winch

1- lead sled. Actually a wooden sledge that will have grooves that will keep it on the aluminum tubes, allowing for side to side travel.

any number of screw-eyes and hundreds of feet of fishing line.

oh yeah, and a one foot long winch arm (but it could be shorter).

OK guys, go at it!



OK Graham -

but more info is needed!

What kind of boat is this going to be installed on?

What is the freeboard available?
(How high is the deck from the water?)
How much can the boat heel (degrees or angle) befor the outer tips of the “rack” hit the water/waves?

As a college student I assume you have already made use of your math education [:-graduate] and have calculated the diffence in righting moment from a lead keel bulb at XX inches below the water weighing YY lbs. versus your sliding weight at 9 inches? (1/2 the length of your 18 inch “rack”) What weight do you need to equal the righting moment of a standard keel at XX inches below the water?

If you haven’t done that yet, and you want to experiment, run those numbers first.

Once you have the basics for your evaluation, you can determine if:

The 9 inch length of the rack will be long enough
How much weight the rack will have to support
If your winch has enough power to even move that much sliding weight
If a multiple part purchase of the lines used to move the weight is needed
The sled will actually “slide” or will there be too much friction?

…along with a few other questions bound to appear.

[:D] You know the old saying …"(maybe)… You can’t get there from here!"


Some pictures would help… But it sounds like you have a setup awefully close to what Doug Lord uses for his PBS system:

I think (by your description) that you have 4 rods running between the two end caps (2 dowels and two aluminum rods). This should make the installation relatively easy. I am assuming that the sledge will run on two of the rods on your rack (I will assume it is the alluminum tubes) and the other two (the dowels) can be used to slide the rack from side to side on the boat?

Are any of your “screw eyes” big enough for the dowels to pass through? If so, then you are home free. It is even better if your screw eyes have a little bit of slop…

Step 1: mount 2 screw eyes to your deck (I’m assuming the deck of your boat is strong enough to handle this). The fore/aft distance should be equal to the spacing between the dowels in your rack (the two that are for sliding the rack).

Step 2: mount the sledge onto the rack on the tubes.

Step 3: slide the two dowels through the screw eyes and attach the other end cap. At this point you should be able to slide the rack from side to side and also slide the sledge from side to side such that the two do not interfere with each other.

Step 4: Attach a small screw eye to the inner edge of each end cap in the center (lengthwise) of the end cap. This is going to be for two lines that will pull the sledge around on the rack. If you have pulleys these would be better because a simple screw here is going to have quite a bit of friction. but since this is McGuyver, we have to make do with what lays before us.

Step 5: Attach a 36" length of line to the center of the deck in between the two screw eyes and in the middle of the line (18" on each end). You may want to leave it a little longer than 36 inches and cut it to length in the next step.

Step 6: Pass one end of the line through the screw eye on one end cap and then tie it to the sledge. Pass the other end of the line through the screw eye in the other end cap and tie it to the sledge. The lines should be somewhat loose but not excessively so - just enough to prevent binding. At this point, if you pull the rack from side to side, the sledge should move with the rack (at twice the speed) so that when the rack is fully extended to starboard, the sledge is at the far starboard edge of the rack (and likewise on port).

Step 7: Attach two pieces of line between the end caps and the top of the mast to make two “trapeeze” wires. The further forward on the rack you can attach the trapeeze the less they will interfere with the sail. You may need to play with the tensions in these lines to prevent the system from binding at any point in the travel.

Step 8: now we need to figure out how to move the rack with your sail winch. If it is waterproof, I would mount the sail winch right to the sledge along with the battery and maybe even a seperate reciever for just that channel (McGuyver does not know if you have a second reciever laying around). You probably need to waterproof the battery and reciever. I’m not sure if this will fit under your boom or not. If it does not, go to alternate step 8 below. Set your arm so that at the midway point in the travel, it is pointing straight aft. You may not need the full 12" length of the arm. That will depend on how much rotation you get out of your servo. If you get 180 degrees, then you only need 9". If you have less rotation, then you will need a longer arm.

Step 9: attach a 12" long piece of line to each end cap of the rack. then attach both of these lines to the end of the servo arm. This will pull the sledge toward the endcap. When the sledge is at either end cap, the arm will be pointed toward the boat.

That’s it! You’re done!

alternate step 8: If the sail arm servo will not fit under the boom when mounted on the sledge, then you will need to mount it in the boat. I’m assuming that your boat is not 24" or even 12" wide, so you will need to mount the arm above deck. You will have to find a spot on the deck where you can swing that arm and have it clear all your sheets, backstay, etc, Perhaps just behind the aft rack screw eye would work (with the arm pointed straight aft at the midpoint of the travel).

Alternate step 9. use the same pieces of line that you sould have used in step 9 above and again attach them to the arm. but this time when the arm swings to the end of the travel it will be pointed to the same side the rack is out on. The arm will pull the other end of the rack toward the center of the boat thereby pushing the rack out to the other side.

Done again!

Let me know if any of this is confusing and I will try to explain it better…

(chad - we need a chalkboard around here…)

Edited for spelling typos

  • Will

Will Gorgen


T H A T W A S A W E S O M E ! ! !

Thank you for the explanation that was both extremely clear and useful!

With regards to some of the points you had:

I had done some initial computing, and the boat I’m building is designed to heel no more than 30 degrees before the endcaps start kissing the water. This will make heavy air sailing interesting, but that’s what makes it fun right?

My boat only has 2" of freeboard, but I’m mounting the rack an inch off the deck for additional allowable heel.

The hull I’m building this for is only two feet long (I’ll get to this a little bit later) so if I had designed the keel for this boat to be the only ballast carrier, it would probably be 10-12" long. This would mean that at 30 degrees heel, the boat would have ballast approximately 5-6" off centerline. Now, with the rack as I had initially designed it, the rack would be fixed to the boat and only the sledge would be able to travel back and forth, it would still be able to get ballast 9" off centerline (with CG ~ 8.5" off centerline) at zero degrees heel, which would maximize righting moment and forward motion. So, the first evolution of my rack was going to have 2/3 the weight in the rack, whilst retaining just enough lead in the keel to right the boat in case of a capsize. This may turn out to be too much lead on the bottom as compared to the rack, but I’m just playing around.

I really like your (and, I guess, Doug Lord’s) idea of the sliding rack and sledge. I don’t think my winch will be strong enough to handle this though, especially with wooden rods going through the big eyes. Very interesting thought though, I really like it.

I think with my current equipment, I’ll try the sledge only configuration and just see if I can get that to work, and then with my winch upgrade (going to be getting a Hitec drum for my narrow boats) see if I can use that for a possible second experiment.

Thank you so much for the clear explanation!