Just wondering if anyone has removed the rigging and keel from a Mac 25 (or similar boat) to use it as a trawler. I have removed the mast and rigging from mine already but a little leary about removing the keel, so figured I`d see if anyone has tried it and if they removed the entire keel or took some weight out of it and how much? How did it work out?
removing keel off Mac 25
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removing the keel might affect steering. The keel is meant to set up lateral resistance in the water even with the keel up. You might do okay in calm waters but if you get hit from the side you might not be able keep a straight line. Any thoughts from somebody else?
Hi freedom 77, I agree with you about the steering part. I have a rather large piece of plastic (like what they make cutting boards out of) about 2 feet X 4 feet X 2 inches thick that I was going to use. Bolt it into the same place where the cast iron keel is and shape it so it would go completely up in the groove in the bottom of the hull so I could beach the boat easily, put could drop it down just a foot or so for when the boat is motoring. But this weights very little and was worried about the lack of weight with the keel gone
I was going to turn a 224 into a trawler for my daughter and her kids. The idea was to put a couple of bolts through the section where the hull is housed when up, then turn the boat over and fill the trunk with cement (the bolts would help hold it in place). Next was to glass over trunk, smooth with the bottom. I was then going to lower the cockpit by cutting out the floor and dropping it into the laz. The propulsion would be an out board - 15 to 25 hp. But the bank took her home and we had noplace to work on the boat. Still sounds like a fun project. Oh yeah; we were also going to go to standing headroom with a forward tilting windshield - controls outside. Don't forget to offer the keel to someone in need. The cement should add suitable stability without too much weight.
Hi aamwiggie!
Untrimmed, the piece of plastic you describe figures out to 2304 cubic inches, or about 1.333 cubic feet of material. (Or a bit less, depending on how much you shave off in shaping.)
It displaces about 83.2 pounds freshwater; 85.3 pounds seawater. If the piece weighs, say, 25 pounds, it has a positive buoyancy of 58.2 pounds, or 60.3 pounds, respectively.
Introducing additional positive buyoancy at the keel will change the relationship of the Vertical Hydrostatic Center of Buoyancy to the Vertical Center of Weight, and alter the boat's hydrostatic CG somewhat.
Not knowing the boats actual Weight and Balance specs, I can't calculate exactly how much the variance might be, or what precise effect it might have on stability.
But considering that we're talking about replacing a 500# (very negatively buoyant) keel with a plastic part (that might be positively buoyant), off the top of my head it seems the resultant change in stability could be pretty significant.
Hope this helps.
VBR,
Pat
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if you have no keel to keep the boat from tipping over, what will you replace that with?
you need some kind of balast, to displace water. cement is not a good choice unless you can add about 30% more volume.
if its just a flat water lake or use is for liveaboard houseboat, fine, but just removing it and adding an engine is not well thought through.
you need some kind of balast, to displace water. cement is not a good choice unless you can add about 30% more volume.
if its just a flat water lake or use is for liveaboard houseboat, fine, but just removing it and adding an engine is not well thought through.
I don't know much-at-all about sailboats; but I've learned a little about other kinds of boats. I'd have to co-sign what Mr. Bill said.
When I said the effect on stability could be "significant", I should have specified "in a bad way."
I don't know if it would work, but it seems to me it has to be less stable than the designer intended for that hull.
In any case, good luck with your project.
VBR,
Pat
Thanks alot guys, really appreciate all the advice. Nemosuit, what you said helped alot, its advice like that, that I was hoping to get. Looks like I`ll have to rethink the plastic part for a keel. Now I`m thinking maybe a flat piece of steel , and shape the plastic so it fits snuggly in the groove flush with the bottom of the boat. Cut a dado the lenght of the plastic and mount it to the top edge of the flat steel so the steel hangs down about 6 - 8 inches below the hull. Mount this where the old keel was , making it weight around 150lbs. This should address the lateral resistance needed for steering and also help with stability. What do most of you think of 150lbs as far as being suitable for keel weight. Remember the mast and all rigging is already off the boat
Like I said, I don't know much about sailboats, but I have had some experience with nautical design in other types of vessels. I can tell you that a 2'X4' piece of 1/2" steel weighs about 160 lbs.; less if you trim it.
That's going to be about 100 lbs negatively buoyant in seawater, but again without the exact W&B specs for the boat, it's impossible to accurately calculate the resultant change in stability.
It's night time, so I'm not going down to measure my keel right now; will try to do that tomorrow. Then I can tell you what it's weight versus potential buoyancy is.
What seems important to me at this point is: The boat comes with a long, heavy keel that hangs down below the boat; so, the moment-arm of that station is a goodly distance down below the boot stripe. Your design sounds like it wants to eliminate that significant stability factor, and replace it with something that's going to be lighter, and at less of a moment-arm from the waterline. It looks like that's going to greatly reduce the boats positive dynamic stability: the tendency to return to a normal attitude when displaced therefrom.
Then again, I've got to remember: the keel was designed to offset the considerable forces induced by the sail and rigging. You're talking about eliminating the sail entirely. That's got to be points in your favor, stability-wise.
Now, it starts to get beyond me. I don't feel capable of calculating what the forces generated by the sails, et al, might be; or how much the lack thereof might contribute to the stability of a boat with the keel modified as you suggest.
It's a lot more complex than it looked at first glance.
If I had to guess (and that's all it is, an uneducated guess) I'd think if you had that 160 pound keel tucked up inside the keel trunk or hanging slightly below (or maybe one that was made out of two layers of 1/2", so let's say 320 lbs, more or less due to trimming) and there isn't a sail trying to tip you over that the keel has to resist, your idea might have a fair chance of working.
But again, this is just how it seems to me off the top of my head, and without any real math (boat stability specs) to work with.
When I get my Mac22 into the water, the first thing I'm going to do (after I check for leaks) is take it for a short drive without the rigging, on the outboard motor alone. I have a motorized keel winch which brings the iron fin up and down pretty quickly; and I might try running on the motor with the keel up, just to see what happens. I can let you know how that works, for what it's worth. But again, it won't be for a while yet.
Wish I could be more certain, but right now that's the best I've got.
VBR,
Pat
IF I were going to try this I would look at squaring off the back end of the hull.
If you look at the boat with its rounded hull you can see there is not much to control the roll axis and if you have been in one without the sails up you know it is very rolley.
Now look at a power boat with its rather flat angled stern that applies a righting moment as soon as the hull starts to roll.
Try just gluing a weight inside a 2 liter plastic bottle and then try gluing wooden blocks on the out side and see the difference.
If you look at the boat with its rounded hull you can see there is not much to control the roll axis and if you have been in one without the sails up you know it is very rolley.
Now look at a power boat with its rather flat angled stern that applies a righting moment as soon as the hull starts to roll.
Try just gluing a weight inside a 2 liter plastic bottle and then try gluing wooden blocks on the out side and see the difference.
For what it's worth (and admittedly, that aint much) I think those are good points. If I had to put a bottom line on it, in past practice I've usually figured the designer built it as he did for a reason. I tend not to drift too far from stock configurations any more.
All food for thought.
VBR,
Pat
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