So I purchased a '77 Mac 25 on Monday (April 9th.) The hull is punked under the icebox and the head. I lifted it off the trailer and when the punking didn't pop out I realized I will need to cut out about 6 sf of hull and replace it. I've a lot of FG experience but wonder if I need to do anything special as this replaced section will bear weight on the trailer bunks.
Replacing part of hull
- Thread starter TangoXray
- Start date
First off, give it a co,upkeep of days in the warm sun. It may pop out on its own you also should look at how to relieve the pressure in the future. Generally the boat should be evenly balanced on the bunks and sitting on the keel. These pressure points can "oil can" in but usually pop out after a few days.
Trying to replace a major section of hull could be trouble without the original mold. It will be very hard to get an exact match to the opposite side.
Good luck
Trying to replace a major section of hull could be trouble without the original mold. It will be very hard to get an exact match to the opposite side.
Good luck
Be sure to lower the keel into its resting place on the trailer to take the 700 pounds off the hull.
Timebandit, we did lower the keel and will at some point remove it to clean it and repaint it. I have a plan with some heavy floor jacks and jigs to support the keel from flopping over.
whosington, the cause was that the bunks rotted at the forward end and the keel beam ended up pushing into the forward roller. We'd bought the boat for parts but realized it was salvageable with a hull repair. The current plan is the cut out the bad sections and insert some 3/8" marine ply. The ply will be notch cut about 3/16" in lines and inch apart to let it flex. We'll insert that into the inner hull with 1-2" overlap for and aft and secure it with countersunk brass screws. It should provide a reasonable facsimile of the original hull shape to lay in the new fiberglass. We plan to use the best cross-woven mat we can find. Thoughts?
This is an interesting issue. The boat was bought for parts so clearly repair tolerances will be much greater. That said i wonder if matching hull shape is possible by first creating a template on the good side?
Measure from the bow back and trace the shape from top to bottom onto cardboatd or foam. Do that every couple inches.
Should be able to use the template on the otherside once the patch is applied.
Just a conceptual problem solving technique for shits and grins if you cant make a laser point cloud and 3d print your template .
Well, both port and starboard are canned, port a bit less than starboard. That said I'm going to leave the hull intact as the canning has hit a strong point of resistance and I don't want to compromise strength. My plan has changed to sanding down to the glass and then creating a rough hull shape on port with rabbit cage wire. It will be screwed into the hull and serve as a structure for expansion foam to build on. The foam will be sanded to shape and then laid over with new glass. Once port is done I'll follow your advise and make cardboard templates for the other side and repeat the process. As long as the glass bonds well, is watertight, has strength to support the cradle and is 95% symmetrical I think it will work. It's sort of an expansion foam as Bondo approach. It's an Okie boat so let's call it filling a hail dent. ; )
Actually, I did a little online research and Grainger sells high-density styrofoam sheets. I'm just going to cut, glue, sand, cut, glue, sand, cut, glue sand that until I get the shape to glass. It will have much better strength than expansion foam.
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Timebandit,
The roller looks added later. It's galvanized on the OE steel MacGregor trailer. We removed it and will lengthen the
bunks for and aft by a few feet to avoid a future canning.
The roller looks added later. It's galvanized on the OE steel MacGregor trailer. We removed it and will lengthen the
bunks for and aft by a few feet to avoid a future canning.
Based on your description I think I would try to pop out the "punked" section and then reinforce it from the inside. Getting it to pop out may require cutting a long slit down the middle of the punked area to relieve the pressure but it's still easier that replacing the whole section.
I have had that thought as well. The next chance I get I am going to build a box out of thick 1 1/2" styrofoam insulation. It will go from the ground about 2' up and be cut to form-fit the bad hull overhead. I plan to put a space heater in it and turn it up to heat the punked hull. When it's good and hot I will try to pull it out using one or two toilet plungers as suction. If it's going to pop out on its own, this will do it. If that doesn't work the next option is the slit cuts, pull and patch.
After the heating I would use a jack from the inside against a piece of plywood. somewhat smaller in shape than the dent and keep it in place for a few days or so. Then you could reinforce it with a partial bulkhead or brace to keep the hull from rebounding. I would never attempt to repair it by cutting the oil-canned part out.