ontinuing on from our previous video about watching your weight, Shayne takes us through the process of how we made waterline markers for our catamaran. The idea behind this trick is simple: to give you a visual tool to monitor how your boat is sitting in the water.
It’s not meant to be a conclusive test, but rather a simple, at-a-glance reference to let you know whether you are sitting higher or lower in the water than usual.
Finding Your Baseline
If you already have an idea of where your boat should sit—for example, if the water sits 50mm above the bottom of the transom and 50mm above the bottom of the bow—then you are already halfway there. That gives you a target weight for your design. Some production boats will even have this information in their specifications.
If you have the opportunity to weigh your boat next time you haul out, by all means, do so. However, be careful: travel lift scales are notoriously inaccurate. Cranes and load cells are a better option, though they aren’t always readily available. Using this method to haul out a catamaran comes with its own set of challenges.
The “Overweight” Scenario
If you are like us and you know you are overweight, the first thing to do is start taking out the junk. Be realistic. Go through all the extra tools and things you don’t really need or want on your boat. You are still going to need spares and tools for cruising, so set the boat up the way you are actually going to sail.
If you want to monitor the weight compared to a totally empty boat, take everything off. If you want to set it up with bare basics, do that. For us, we kept only the things we wanted for normal everyday liveaboard cruising—the items we need for repairs or the comfort of living.
The “Feel” Test
We went on several test sails before we knew exactly where we wanted the boat to be in the water. How did we know? Well, that’s a bit more intuitive.
We had an idea of the speed this design should do. When we could achieve those speeds easily, we knew we were close. The boat also felt a lot easier to sail. The helm felt balanced, top speeds were easy to reach and maintain, and the boat felt relaxed—not loaded up. It’s something that you, as the skipper, should feel naturally is right for you.
Once you think you have your ideal weight, it’s time to put your markers on.
The High-Tech Tools (And a Trick to Avoid Drilling Through Your Boat)
The process is straightforward, and having those marks as a reference is incredibly handy. If you are at all interested in doing the same to your multihull, it is well worth the effort next time you haul out.
Here’s a look at the “high-tech” tools we use for the job:
- A drill (battery drill)
- Drill bits
- Masking tape
I use a 6mm drill bit (though mine is broken, so in the video I used a 5.5mm). When I drill, I don’t drill a whole hole. I only drill from the very tip to the shoulder of the countersink.
Here’s the secret: wrap the end of the drill bit in masking tape.
You want to keep rolling the tape around until you build up a nice shoulder. Believe it or not, this really helps stop the drill bit from biting in and drilling a hole straight through your hull. Still, be very, very careful. The masking tape can peel back if you push too hard, so do it lightly and gently. Just “beep, beep, beep” to take away the countersink depth.
If you have a proper countersink bit, use that. But if you’re using a standard drill bit, the tape acts as a stopper collar.
The Race Boat Version (For a More Permanent Solution)
On race boats, we do things a little differently. We use small machine screws (stainless steel, or titanium to prevent rust bleeding on carbon boats).
Ideally, you plan ahead and put a little insert of solid core where the mark goes. But nine times out of ten, everyone forgets. So, we drill, backfill, and then drill and tap the hole for the screw.
We countersink the hole so the screw sits flush with the hull, but we countersink it just a little too far. This allows the screw to be adjusted in and out. Once we have the waterline exactly where we want it, we set it in resin to hold it in place.
We use a flathead screw for the waterline (so you can line the slot up horizontally) and a Phillips head for areas where we are marking a vertical component, like transoms or stems. The reason we use screws instead of little dots is that they are more permanent. When we paint the boats, we leave these screws shiny silver so they are very identifiable.
Reading the Markers
Looking at our boat now, you can see the dots on the transom and the bow. Even with a little bit of waves and swell, you can get a general idea of where the waterline is sitting. Right now, the water is sitting a little above the dot on the transom, which tells us we are a bit bummed down (heavy in the stern) at the moment. It’s a good indicator to start moving some gear around to balance the trim.
When you are in a marina or a really still bay, it is incredibly easy to see your trim. Without the dots, you might not know if you are 20mm up or 20mm down. With the dot, you have a precise reference point.
It’s a simple trick, and if you’re at all interested in monitoring your boat’s weight and trim, it’s well worth the effort next time you haul out