How to Cut a Fiberglass Hull

This blog post briefly describes how to cut windows in a previously marked fiberglass hull. Cutting windows in a fiberglass hull, even a thick one like my Nassau hull, is far easier than making a wood hull from scratch. This is the first part of a series of articles I will write while building my German Dreadnaught Nassau.

Disclaimer
It is your responsibility to keep yourself safe. I may not have listed all the precautions you should take. You should do your own research to insure that you are keeping yourself safe. I am only describing what I was comfortable doing.

After you have finished marking your hull you will need to cut the windows out. To do this you will need:

• Dry stable place to work outside - preferably with a slight breeze
• Dremel, Rotozip, or similar tool
• Drill bit
• Pack of reinforced cutting wheels
• High quality, well fitting, respirator (do not rely on paper dust masks)
• Well fitting chemical safety googles - not glasses - you need a air seal around your eyes
• Long sleeve shirt you don't care if you wear again - preferably with tight cuffs
• Long pants or jeans - once again you should not care if you can't wear them again
• If you skin is sensitive you might consider latex gloves

The thing to remember is there will be a ton of extremely fine dust that is basically microscopic glass shards that have been coated with carcinogenic resin. If it gets in your eyes you might loose the use of them. If you breath it into your lungs you might loose the use of them. Don't think you can just hold the ship away from you as you cut. Don't think glasses are good enough.

Warning
At all times you should keep in mind that cutting wheels often chip and break. When they chip they will tend to grab or jump unexpectedly. When they break they will throw pieces with great force. Carefully follow all of the recommendations of the manufacturers of the roto-tool and cutting wheels you are using.
 

Step 1: Nassau's Windows Marked

The first step is to follow William's article on marking your hull. Before you cut you should consult with your club's technical officer to make certain your windows are correctly sized and spaced. Because this can be an itterative process I recommend covering the hull with a layer of masking tape and then drawning out the windows on the tape. This will allow you to easily erase your markings by tearing off the tape if you need to make changes.

Step 2: Corners Drilled

The dust while cutting will make it hard to see your marked lines. It will be very easy to cut past corners. So you should carefully drill a hole in the corner of each window. You want this hole to be within the material being removed.

Step 3: Vertical Edges Cut

You will want to cut your vertical edges first. This will help insure that you don't accidentally cut too far when you cut the horizontal lines. (You really don't want your ribs an weaker than they will be already) Cut a line connecting the two drilled holes on that edge. Remember to keep cut on the side of the line that you are removing - not on the side of the line that will remain as a rib.

Step 4: Top Edges Cut

It probably does not matter if you cut your bottom or top edges first. You basically follow the same technique that you used to cut the vertical edges. Remember to cut below the line.

Step 5: Bottom Edges Cut and Windows Removed

Now you can cut out the bottom edge. Remember that the fiberglass will be moving as you cut. You will almost certainly break several cutting wheels. While cutting this hull we had one cutting wheel shatter with such force that it took a chuck out of a pair of safety goggles.

Nassau After Cutting

Here is the hull after removing all of the windows!