How to Make your bottom Pretty (Hull Repair)


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After my humbling experiences in recent attempts at racing sailboats, I have decided to write about the only subject in which I remain at the front of the fleet. If you carefully follow the directions put forth in this article, you can have the nicest bottom in your fleet.<O:p> <?XML:NAMESPACE PREFIX = O /><O:p></O:p>

First, you must acquire the proper attitude about taking care of your boat. If you still pull your boat up on a dock without first checking for nails, screws and gravel, don’t even bother reading this article. Your Laser only has about enough gelcoat for two bottom rescue jobs. Don’t do the first one until you are ready to do whatever it takes to keep from scratching it again. Save the second for the shine that sells the worn out hull to the next owner. There is nothing wrong with selling your worn out boat when you buy a new one, but at least save the new guy a pretty hull. <O:p> <O:p></O:p>


1. a place to work for about 12 hours that can be washed down with water afterwards<O:p></O:p>

2. gelcoat to match your hull and catalyst<O:p></O:p>

3. acetone<O:p></O:p>

4. buffing compound (Dupont 101, Acme 50, 3M Super Heavy Duty, or a similar grit)<O:p></O:p>

5. a sharp knife<O:p></O:p>

6. cardboard cut in a bout 10” x 10” squares<O:p></O:p>

7. stir sticks (popsicle sticks)<O:p></O:p>

8. a bucket and water<O:p></O:p>

9. 12 chunks of terry cloth (cut up old bath towels into 8 chunks each)<O:p></O:p>

10. wet-sand paper in 320, 400, 500, 600, 800, 1000, and 1500 grits. If your scratches are particularly large or numerous you may also want 180 and 240 grit papers. For whichever grit you use first you will need about 5 sheets. For the other grits you will need about 1 sheet each.<O:p></O:p>

11. Gel Gloss or TR 500 <O:p></O:p>

12. Maguire's Deep Crystal paste wax<O:p></O:p>

13. a squeegee ( I use a Thalco laminators squeegee but a good window squeegee will do the job)<O:p></O:p>

14. a pencil<O:p></O:p>

15. cleansers (Comet or Ajax)<O:p></O:p>

16. sanding blocks (I use a 9” block from an automotive paint supplier)<O:p></O:p> <O:p></O:p>

DIRECTIONS:<O:p> <O:p></O:p>

The boat needs to be supported upside down at a height where you can stand over it for hours and hours and hours. You don’t want to damage the boat or your back. <O:p></O:p>

1) Read all of these directions before you do anything to your boat. If you don’t understand the directions, or if you have any trouble making the various steps come out correctly, take your boat to a professional and get it done right.<O:p> <O:p></O:p>

2) Wash the boat with a good cleanser and then clean it again with acetone.<O:p> <O:p></O:p>

3) Every scratch that you can feel will need to be filled. Use a sharp knife and lightly re-gouge the scratches. Your scraping should create dust, not chunks. You must have a freshly roughened surface so your repairs can adhere to the grooves.<O:p> <O:p></O:p>

4) Blow away the dust and wash the boat again with acetone. Make sure that you have removed every last particle . If your repairs are made over a dirty surface the repairs will stick to the dirt but not to your boat.<O:p> <O:p></O:p>

5) Test the gelcoat to make sure it doesn’t set up too fast or too slowly by mixing a small amount on your cardboard. Dribble a half dollar size disk of gelcoat off a stir stick. Then dribble a pea sized amount of catalyst into the center of the gelcoat and mix it as well as you can. Scrape, wipe, smear and swirl that puddle of material until you are sure that it is mixed. Play with the stuff for 15 minutes to make sure that it isn’t becoming hard too fast--if it sets up too fast you won’t have time to apply it to the boat. Catalyzed gel coat can get really hot. Set the cardboard down somewhere where it can’t start a fire if it ignites. Go away for an hour. When you get back the surface of the puddle should be sticky but the material underneath should have hardened. To see if it is hard, fold the cardboard. The puddle should break. If your test batch matches this description, you have learned how to mix gelcoat. If the gelcoat didn’t cure, start with a new batch and either add more catalyst or find a warmer place to do your work.<O:p></O:p> <O:p></O:p>

6) Once you have learned to mix the gelcoat, mix a fresh batch. Using your stir stick or an artists brush, paint each of the scratches. Just try to fill the gouges level with the boat surface. This may take a couple of passes between which you need to go away for a soda or a beer depending on your age and preference. Do not wait more than a couple of hours, period.<O:p> <O:p></O:p>

7) After you are convinced that all the scratches are filled, put on one more coat. This last coat can be mixed with a little extra catalyst to hurry along the process. Gelcoat does not fully cure when it is exposed to moisture in the air, so this last coat is to help cure the sticky part of the previous layer. This is a good place to stop for the night to allow the gelcoat to harden.<O:p> <O:p></O:p>

8) Fold one of your terry cloth pieces and soak it with acetone. (It’s nice if your terry cloth is a contrasting color to the hull.) Wipe off the part of your gelcoat that will soak easily free. Keep wiping until the towel shows no more color coming off. If you have lots of scratches this may take a couple of towels. You will also need a fresh towel to wash the sticky stuff off your hands. <O:p></O:p>

9) It is time to use sandpaper. Sandpaper can follow the contour or the surface and remove the softest part, or it can ride gently over the surface, trimming off only the high spots. YOU MUST FOLLOW THESE RULES: <O:p> <O:p></O:p>

<BIG><BIG><BIG><BIG>Use Sharp Sandpaper! <O:p></O:p></BIG></BIG></BIG></BIG>
<BIG><BIG><BIG><BIG>Do Not Press Down Hard!<O:p></O:p></BIG></BIG></BIG></BIG>

10) It is time to sand off the extra gelcoat. Use sharp sandpaper. Do not press down hard. Ideally, you will use the finest grit that your patience will allow and a wood block. You will sand away the excess gelcoat without ever touching the adjacent pristine surface of your boat. I usually accomplish this task with as tiny a wood block as I can hold and a lot of brand new sandpaper. The sandpaper should not touch anything other than your repair until the excess is almost totally removed. Be patient. Use sharp paper. Do not press down hard. I recommend 320 or 240 for this step. Stop often and look at how you are doing. Remember that you do not want to sand anything except the stuff sticking out above the scratch. Occasionally you should use your squeegee to dry the work area. Stop. Look and feel how you are doing.<O:p></O:p><O:p></O:p>

Let me digress a moment here. What I just described can be more easily accomplished using dry sandpaper. I use the white or gold type of paper. However, if you choose to sand dry you will be creating a lot of dust and adequate protection is necessary. You will need a protective mask and the work area will be coated by your dust. The advantage of dry sanding is that you can wipe away the dust and see exactly where you have sanded.<O:p></O:p><O:p></O:p>

11) When all the repairs are flat and level with the hull surface it is time to begin working on the whole hull. Do not begin sanding the whole hull until you have finished sanding all the individual scratches. You need the shiny surface of the hull as a reference until the heavy sanding is finished so that you don’t make the surface wavy.<O:p></O:p>

Now it’s time to get all the ripples off the entire hull. As long as you can smell styrene inside your boat the plastic is shrinking, becoming more crystalline and just plain getting uglier. You want to remove all the tiny ripples that your boat has developed as the plastic has continued to cure since it left the production mold. Remember that you are not attempting nor are you allowed to change the shape of your boat. This is a cosmetic repair, not a speed enhancement.<O:p> <O:p></O:p>

I usually start the whole hull job with 320 paper. Using a soft rubber block, I sand at 45 degrees to the centerline until the entire hull is a consistent, dull finish with all of the sanding scratches parallel. The reason to keep all of the scratches parallel is so that when you switch to another grade of sandpaper, you can sand in a different direction and know when you have removed all of the scratches from the previous grade.<O:p></O:p><O:p></O:p>

It’s graffiti time. Use a pencil to make marks all over your hull. When Eric Faust does this part he creates cartoons and other nonsense, but lazy guys like me just scribble. The object is to make enough pencil marks so that it is easy to tell where you have and have not already sanded. Turn your sanding to the other 45 degree angle and shift up to your next finer grade of paper. Sand away all the pencil marks and then inspect your work. All the sanding scratches should run in the new direction. In areas where the old scratches still show, pencil and sand again.<O:p> <O:p></O:p>

Repeat the penciling and sanding with 400, 500, 600, 800, 1000, 1200 and 1500 grit papers. You can skip grits or stop at a heavier grit but your boat will not be as shiny if you don’t use the whole series. To make your bottom heavenly, you have to sand the hell out of it. <O:p></O:p>

12) Now, smear buffing compound all over the hull and with one of your clean pieces of terry cloth, rub it until you are sick of rubbing. Rubbing compounds work a lot like sink cleansers--the more you stroke the surface the better the final appearance.<O:p> <O:p></O:p>

13) Using water and a clean rag, rinse off the remaining compound.<O:p></O:p> <O:p></O:p>

14) Apply Gel Gloss according to the directions on the can. If you are not paranoid about the possible loss of boat speed you may also want to wax your boat. When you go to a really important event in fresh water, you may wish to remove the wax with a strong detergent. I think that a hull coated with Gel Gloss is faster than a good clean hull in brackish water. I don’t like to have crud stick to my hull--I think it probably slows my boat down. When sailing in Lake Pontchatrain a J-24 coated with Gel Gloss will remain clean for a week while boats without Gel Gloss acquire a nasty yellow coating. Make your own decision.<O:p></O:p> <O:p></O:p>

A final note: the gelcoat on your hull is only thick enough to endure this process a couple of times. If you aren’t sure that you will take care of your boat starting immediately, do not waste the repair opportunity now.<O:p></O:p>

Next time you are approaching the starting line you can strike fear into the competition by having your boat glare at the other sailors.

Feedback report follows:

I used the bottom repair guide from the Laser FAQ on my 76 Laser for filling and fairing. The whole process was pretty slow, mainly because it was hot out and I applied a large amount of gelcoat that didn't have enough catalyst.

I had lots of scratches and following the guide the X-acto knife soon didn't have the endurance. I tuned to an engrave made by Dremel and was able to clean up the scratches very quickly. I sent a gelcoat sample to GCP International in Washington for a gelcoat match. The match was very close, the only setback was that it was 94 for a quart. If it really matters this it the way to go, but if not-- use white. I used an orbital air sander with wet sand 320 grit when I grew tired of hand sanding, and that helped speed things along.

For somebody attempting this project in the future:
Make sue to use PLENTY of catalyst as you will be VERY sorry if the gelcoat sets up too soft.
If you have a fairly sizable project ahead invest in a cheap engraver.
Bondo applicators work well for applying the gelcoat.
Don't use a grit less than 240. You will put fairly sizable scratches in your hull otherwise.
Sharp sandpaper makes the job go much easier.
Use a stiff sanding block or drywall sander to take off the high spots.
And last but CERTAINLY not least- don't try to fill the scratches in one huge heaping load of gelcoat. It is very hard to take off. Use thin layers with plenty of hardener. You will be much happier.

Hope this helps you that plan on filling your scratches.

See you on the course. I will be sailing the blue Laser with no scratches on the hull.


Removing old Paint question and a long answer
I bought a used Laser and it looks like someone painted the hull at some
time. It is falling off in flakes, looks like crap and is all rough and nasty. If I
were to use chemical paint stripper would it damage the fiberglass or do I
have to sand the whole thing down before I re-gelcoat the hull? How hard is
it to apply gel coat and get a nice finish?




Most paint strippers will harm the gelcoat finish on your boat. Even the ones like Pintoff from Interlux are brutal to the plastic. The plastic is attacked a bit by the chemicals and either remains permanently soft or dries to permanently too crystalline. I wouldn't use a stripper for those reasons.

But there is more. Toxicity and your one and only birth issued liver is another factor. Sanding dust can be washed off your skin, washed out of your clothing and kept pout of your lungs by a $30 respirator. I always sand instead of ever using chemicals for that reason.
Respirators: Don't waste your life on a cheap respirator. Buy a $30 to $40 mask with filters and make certain that it fits tightly. Hold your palms over the cartridges and suck with all your might. If you can get air the mask is useless. If you can smell stuff while sanding or painting the respirator is useless.
Sniffing paint fumes and eating dist will shorten your life. "What would you pay to be alive for a few extra years," is only part of the question. What would you pay to avoid a miserable and slow death from failing lungs or cancer is the real issue. Wear a really good respirator or be stupid. ( That statement is literal too, because the fumes attack your brain.)

Back to the job at hand>
I like to start out with fine papers and work with the finest grit that my patience will allow. The finer the paper, the longer it will take to remove the old paint. The finer the paper, the less damage you will do when you inadvertently sand through the paint and scratch the gelcoat.

I usually play around for a couple hours with various grits of sandpaper until I find a grit that actually allows me to remove all the paint in a reasonable time period. Here is the order that I would use:
1. Try the high pressure setting on your hose. If all the paint blasts right off polish the boat and go sailing. ( I will not suggest trying the local car wash because that would constitute illegal pollution. I have heard rumors that some people have had success with that sort of thing.)
2. Try sanding the boat with a good old half sheet vibrating sander. For about $100 you can get a sander that will even collect the dust. For about $250 you can get a really good half sheet sander like the Porter Cable tool that we used in our boat shop for the last 20 years. The sanders just seemed to run forever but you are only sanding one boat. If you do buy a cheap sander, make sure you buy a set of $10 hearing muffs. Those cheap sanders vibrate and make your hands itch and they are loud.
Using the half sheet sander, try some 320 paper and see if you can remove the paint in a reasonable period of time. Work on a square foot and do the math to guess your time.
Important trick: If your goal is to restore the original finish, do not attempt to remove 100% of the paint with the roughest grit. If you start with 180 paper, sand until you begin to see through the paint and then go after the rest of the paint with 240 or 320. If your plan is to repaint the boat, grab some 80 grit and prepare the surface on the first try. I am going to continue this note assuming that restoration is the goal.

3. You are going to have to use sandpaper held I your fingers to get all the paint off the inside of the gunwales. pay attention to the edge of the sandpaper that is leaning against the hull. It is very difficult to sand the paint off the inside of the gunwale without accidentally sanding through the gelcoat about one inch up on the side of the hull. Pay attention and don't make this mistake. One helpful method is to cut the sheets of sandpaper to various sizes instead of always using 1/4 or 1/2 sheet. This method helps to vary the place where the edge of the paper digs into the adjacent surface.

4. Read "How to make your bottom pretty" at and it will take you from the removed paint level to the shiny boat.

5. Last thing. You asked about applying gelcoat. Gelcoat is heavy and thick and not particularly suited for refinishing. If you want to have a re-gel coated Laser that is also a good Laser you need to have a number of skills. You need to be able to remove all the old gelcoat without harming the laminate or gouging the boat. you need to understand how to mix and apply the new gelcoat. You need to have a place to spray the messy substance and the equipment for application. You need to apply a sealer to help the gelcoat cure. You need to sand the gelcoat to reestablish a smooth shiny surface. You need to accomplish the sanding and polishing without sanding through the gelcoat or you also need to understand how to gelcoat and blend small areas with out leaving a patched look.
If you are going to repaint a Laser and you are not a really terrific gelcoat technician, I would always suggest painting the boat with a two package urethane paint. ( I usually suggest Interthane Plus sold by Courtaliads )

Good luck

Fred Schroth