How to Safely Clean a Boat or RV with a Pressure Washer

The First Time I Trashed a Boat

I remember my first boat. A beat-up 17-foot bowrider that I loved like a child. I also remember the day I pressure washed it. I cranked my machine up to 3200 PSI, walked right up to the gelcoat with a zero-degree nozzle, and pulled the trigger. The result wasn't a clean boat. It was a boat that looked like it had been attacked by a flock of angry seagulls with sandpaper. Etched lines, chipped paint, and a decal that was now confetti.

Don't do that. Pressure washers are amazing for boats and RVs, but they are also the fastest way to cause hundreds (or thousands) of dollars in damage if you're cocky. I've made that mistake so you don't have to. Let me walk you through cleaning your rig without destroying it.

What You Actually Need

Let's start with the gear. Don't just grab your driveway washer and go.

• Pressure Washer: You want a machine that runs between 1200 and 2000 PSI. That's it. Anything above 2400 PSI on a boat or RV is asking for trouble unless you keep a football field of distance. Gas models are fine, but electric units (like a 1600 PSI Sun Joe or a 1800 PSI Ryobi) are actually better here because they have a gentler flow. I use a 1.2 GPM electric unit for my camper.
• Nozzles: Throw away (or hide) the red 0-degree nozzle. That thing is a paint-stripping laser beam. Use the white 40-degree nozzle for everything on the body. For the undercarriage or really caked-on mud on the trailer frame, a green 25-degree is fine. I'm serious. White only on paint and gelcoat.
• Boat/RV Soap: Don't use dish soap (it strips wax). Don't use bleach (it eats rubber seals). Buy a dedicated RV or marine wash. I like the Wash Wax All from Starbrite. Costs about $15 a bottle, but one bottle lasts me a full season. It's a concentrate and leaves a little protection behind.
• Soft-Bristle Brush: One on a pole. A pressure washer gets the loose dirt off, but you still need physical contact to remove the grime and bird bombs without grinding them into the paint.
• Bucket and Microfiber Mitts: For the stubborn spots.

Prep Work: 20 Minutes of Patience

You can't just hose this thing down. Prep is where you save your seals and electronics.

First, seal everything. RV roofs have vents, AC units, and antenna mounts. Boats have hatches, compartments, and the outboard motor. Tape a plastic garbage bag over the engine cowling on a boat. Tape over the fridge vents on an RV. Water forced into those spots at high pressure will leak into your interior. I learned this when I flooded the cabin of my camper because I blasted water into the refrigerator exhaust vent. Use blue painter's tape. It comes off easy.

Second, rinse by hand first. Use a hose with a spray nozzle. Get all the loose dust and sand off. If you start with a pressure washer, you are just grinding that sand across your clear coat.

Third, soak the dirt. Spray your soap mixture (follow the bottle—usually 2-3 ounces per gallon) onto the entire surface. Let it sit for 3 to 5 minutes. This "dwell time" lifts the grime. Don't let it dry out, though. If it's sunny, do one side at a time.

The Actual Cleaning Technique

Here is the rhythm I use. It takes about 1.5 hours for a 25-foot boat and maybe 3 hours for a 30-foot RV.

1. Start low, go slow: Begin at the bottom of the boat or RV. Spray from the bottom up. This prevents streaks of dirty water from running down over your clean work. Keep the nozzle at least 12 to 18 inches away from the surface. For gelcoat or painted RV siding, I keep it closer to 24 inches.
2. Use the fan sweep: Hold the wand so the spray is a horizontal fan. Sweep side to side like you're painting a wall. Keep the wand moving. The worst thing you can do is stop and hold the trigger in one spot. That creates a "pressure ring" that eats a hole in the paint. I see it all the time on RVs where people try to blast off a bug stain.
3. Scrub the tough stuff: For the waterline scum on a boat (that green line) or the road grime on an RV front cap, your pressure washer is just a pre-rinse. Spray it down, wash it with the soft brush dipped in your soap bucket, then rinse again. Do not try to laser the grime off with your wand. You'll lose the clear coat.
4. Rinse from top to bottom: Once you've scrubbed and rinsed a section, do a final overhead rinse with the pressure washer turned down (if you have a variable pressure knob) or using the widest fan setting. Let the water sheet off the roof. Don't let it pool.

Mistakes I've Seen (and Made)

Mistake #1: The Roof Walk. Never walk on an RV roof with dry shoes. You'll crack the membrane. And don't pressure wash an RV roof if it's a rubber membrane (EPDM or TPO). The pressure can separate the seams. Use a hose and a soft brush up there.

Mistake #2: Forgetting the Trailer. If you're cleaning a boat, don't forget the trailer. But never wash your trailer bearings. The high pressure will blow the grease out of the bearing buddies. Keep the wand away from the hubs and leaf springs. I saw a guy at the ramp blow a wheel bearing 20 miles down the road because he "cleaned the trailer really good."

Mistake #3: Bleach. Bleach eats vinyl, decals, and stitching. If you have mildew on your RV awning or boat seats, use a dedicated mildew cleaner (like Simple Green Pro HD or a 50/50 water/vinegar mix). Bleach makes the fabric brittle and yellow.

Mistake #4: Washing in Direct Sunlight. The soap dries on the surface and leaves hard water spots that you have to polish off with a compound. I learned this cleaning my RV in July. I spent the next weekend buffing out water spots. Wash in the shade or early morning.

Finishing Up: Dry and Protect

Don't let the thing air dry. You'll get spots. Use a microfiber drying towel or a silicone squeegee (the big ones for windows work great on flat RV sides). For boats, a chamois is king.

If you want the clean to last, apply a spray wax while the surface is still damp. Grab a bottle of 303 Aerospace Protectant or a spray-on wax like Meguair's Boat/RV Wax. Spray it on, dry it off with a microfiber cloth. It takes 20 extra minutes and makes the next cleaning take 10 minutes because dirt won't stick.

Here's a pro move: Put a drop of your boat soap on your finger. If it doesn't bead up on the gelcoat or paint, you have no wax left. That means your next pressure wash will be a paint disaster. Re-wax before you store it for winter. Trust me.

FAQ

Can I use a 3000 PSI pressure washer if I just stand far back?

Technically yes, but I don't recommend it. The risk of accidentally moving too close or hitting a corner edge is too high. If you have to use a high-pressure machine, buy a pressure washer nozzle extension kit (about $20) that lets you swap to a low-pressure tip. Better yet, just buy a cheap electric 1800 PSI unit for this specific job. They're $100. Cheaper than one repair bill.

What's the best nozzle for removing bird poop?

Don't use a nozzle. Use a microfiber towel soaked in soapy water. Lay it on the poop for 60 seconds. Wipe off. Then rinse. Pressure washing bird poop just smears the acid into the paint, etching the clear coat. I know it's satisfying to blast it off, but it's a trap.

Do I need to remove the boat from the water to wash it?

Yes, absolutely. Pull the boat onto the trailer or the dry dock. Washing it in the water is bad for the lake or ocean (soap kills aquatic life) and you can't see the grime line at the water level. Also, you look like a jerk to the other boaters. I use a self-service wash bay at the ramp. Costs me $4 in quarters for a rinse.

How often should I pressure wash my RV?

Twice a year. Once at the start of the season to get the winter crap off, and once before storage to seal in the wax. If you wash it every month, you rub the paint thin. Let the rain do its job in between. If it's just dusty, use a California Car Duster. Save the pressure washer for the caked-on bugs and road tar.

Can I pressure wash the engine of my boat?

No. That's a separate job called "flushing the engine" and uses a garden hose and a set of muffs that clamp over the water intake. Pressure washing an outboard motor forces water past the seals and into the cylinders. I did this once and thought the engine was seized because water filled the spark plug wells. Use a bucket and a rag on the outside cowling only.