mac M as a tow boat

[Ixneigh]

Not recommended but if you have to...

some goofball nearly hits me one night last week in a squall, and manages to get tangled up with the dinghy painter. I cast the whole smeal loose and off he goes, with my dinghy, drifting away into the stormy night. Next day the guy is attempting to sail back into the bay here against a pretty good breeze, but all his sails blow out. So now he is drifting out to sea, with my dinghy, next stop Cuba. I cast off, and cruise down wind to him. I have 200 feet of 3/8 dyneema line to toss him. I should have rigged a bridle but instead, secured my end to my stern cleat and commence towing operations. Slowly. I find that with the board half down, I have pefect control even at a crawl. Its a pretty heavy 28ft keelboat im towing and with many powerboats, if you dont have a bridle, or a real, properly positioned towing bit, its a huge pita to keep the boat from crabbing. The M did fine though. It took an hour to tow him two miles. Got my dinghy back.
Ix

[NiceAft]

Good info., and a nice story. I love happy endings

Ray

[seahouse]

Hey Ix - nice job!

Maybe this is exactly what you meant by " bridle", but a quick and giant bowline ( like 10') on the end of the towline looped over both stern cleats would form a triangle and balance the helm easily?

-Brian.

[BOAT]

Hey Ixneigh, I'm glad you got your dinghy back - that guy owes you big time.

[mastreb]

Yeah, without boards a powerboat is going to crab, but the boards do a good job of keeping the mac rail straight.

I took the family out whale watching on Sunday outside of Mission Bay to about five miles off shore, which turned out to mostly be whale watching tour boat watching (we did see a few blows). On the way back we had large period fast rolling following seas (4 foot rollers, about 40 feet between swells, and running about 16 knots). They were difficult to keep up with ballast in at WOT with boards up, with the boat surfing down a face for about a minute, then being overcome as the wave crested and falling down the backside with an attendant loss of about 30% of speed. The boat wallowed around quite a bit, like 60 degrees off track, as the waves passed under. I finally gave up, went down to six knots and put the boards back down. Although we did quite a bit more bobbing, the boards kept the boat MUCH more on track. I thought it was a blast surging from 5 knots down the backside to surfing 10 knots before the waves on the same throttle, but I think my kids got pretty tired of it. The boards can solve just about any tracking problem below hull speed.

One of the great things about a Mac is that with the big motor, they can tow a heck uv a lot more than a typical sailboat their size. I've towed my bro-in-law's Ranger 33 on and off his ball when his electric motor batteries gave up similarly with no issues.

They're probably the best tug boat in the sailboat market

[Tomfoolery]

I would think you'd want the opposite of a fixed vee bridle off the stern, as that puts the 'pivot' for the tow line well behind the prop, making it very difficult to steer. This has been a problem for me towing folks on a wakeboard at slow speed (when they're still in the water) to point away from shore when the wind is blowing me sideways.

Tugs used for towing as well as dedicated tow boats have the tow line guided from some point forward of the rudder. Like this.





But a bridle with a block to allow the tow line to align itself would put the instant center of rotation further forward would allow the prop thrust to actually turn the boat. I'm going to experiment with this arrangement this summer.



The sum of the lengths of both legs for each angle (color) is the same, as it would be with a real bridle.

[NiceAft]

Interesting point. I've noticed that many ski boats have their point of attachment of the towline, forward of the props and rudder.

[Tomfoolery]

Wakeboard boats, too, with the tower up high, but the attachment at some point forward of the prop(s).

Here's a side-by-side of a self-centering bridle, using a sheave on the end of the tow rope (left) and a fixed bridle, like what I have now. On the left, the prop thrust is always outside the line of action of the drag (skier), so the prop can put some turning moment into the system, with the drag inside the thrust vector. On the right, the drag is always outside the thrust, so it's trying to keep the boat straight. Like sticking a long pole out the back, rigidly mounted, and towing a skier from that - the long lever tends to not let you turn. No matter how much you turn the engine, the drag vector is always outside of it, and trying to keep you straight.



I suppose there's such a thing as too much of a good thing (like tying the ski rope to a bow cleat, assuming the mast wasn't in the way, making it totally unstable), so a little experimentation with bridle length would be in order, but there's no reason to think I can't improve the ability to turn at slow speeds by allowing the tow rope to find its own center on a continuous bridle between dock cleats.

Worth a try, at least.

[seahouse]

The first thing my Dad added to a new power boat was a ski bar for attachment of a ski rope. (He was still doing ski tricks and 360's into his 80's).

I'm going to guess the bars were mostly located a foot or two or three ahead of the stern, and effectively stopped the skier from steering the boat. My last power boat had a commercial stainless ski pylon (tripod) that was mounted on two quick-release balls and a plate with a bayonet mount bolted to the floor- on and off out of the way in seconds. It depends on a lot of factors, but the latitude of the mounting position looks to be wide, and is as much a function of locating it in a practical point in the boat as any other position you might calculate. Not that calculating is something to dispense with, of course. For running a slalom course there are other methods (skegs) used in addition to keep a straight line through the course for each competitor.

The bridle arrangement is more of something that is better than nothing when you don't or can't have a proper attachment point for towing.

[Tomfoolery]

The bridle arrangement is more of something that is better than nothing when you don't or can't have a proper attachment point for towing.

Yeah, that's pretty much where I'm going with this, and since I haven't tried it yet, it's still just navel gazing. But without question, on a windy day, my boat will move itself beam-to-wind which usually puts me toward the shore, and I can't turn away and head into the wind with my son in the water (creep speed), since dragging him at a crawl results in just going straight with the wheel dialed full over. Trying to do so without him on the rope also isn't so easy, as the wind almost always blows the boat around quickly, and it's toward the shore we go. At least until he pops up and I can turn away, as long as we haven't drifted too close.

The other side of the coin is that it's very stable at speed right now with the fixed bridle, and I don't know what will happen when I put a sheave on it, but it's free, so I'll give it a shot.

[seahouse]

The giant bowline might tell you whether or not the travelling sheave will help, without buying a bridle (unless you already have one). And (unless something is in the way???) you will get your stern cleats "flossed" at the same time!

Q: If the wet line happened to break, and you got sprayed by it, is that what you would call a "bridal shower"?

[Tomfoolery]

Q: If the wet line happened to break, and you got sprayed by it, is that what you would call a "bridal shower"?

<groan>

[Ixneigh]

My primary reason for a bridle was to share the loading on the stern cleats.
This summer I want to make some cockpit combing pockets for small items. When I do the cut outs, i intend to add fiberglass to the underside of the cleat location.
For someone serious about it, a bit located aft of the helm, on the floor, bolted to some serious backup plate, would probably be ideal. The towline should? clear the motor top, and only bear on the corners on the motor cutout, provided you had your rudders down. (On the M model)
Can anyone else concur? assess hardware mounting options?
Ix

[Tomfoolery]

. . . provided you had your rudders down. (On the M model)

I have an X, and I put the rudders essentially horizontal for towing a skier. Gotta remember not to turn hard when pulling the throttle all the way back, as the stern wave will catch up and grab the rudders, turning that sucker in a very scary way. With no ballast in it, it can get pretty hairy for a few seconds. Not that I'd know anything about that first-hand, of course.