Prepping for bottom paint - what sander

[down_shift]

About to paint my bottom for the first time (C36) later this month. There are years of Interlux CSC build up over the Interlux barrier coat. What is the best sander to prepare the surface with? I have the palm Porter Cable 5" DA (with dust collection port) that would work but I think is too small for the job. Also have the 7" Mikita sander/polisher, but that does not have dust collection. If I need to invest in another sander, what is the best option these days? I just want to knock down/feather a few areas and lightly prep the entire surface. Is 80 grit the paper to use?
Thanks

 

[Ken Cross]

You want it to be orbital. You won't get the surface you want with rotary machine. I personally have used a 5 inch craftsman for the last 2 days. doing Micron CSC. I used 80 grit and connected it to my shop vac. I think a larger heavier sander would be difficult to hold up there for a long time. As it is I take frequent breaks.

You will still need to protect your lungs from fine dust. That stuff is toxic. I use a dust mask when working low and a respirator when working close to or above my face.

Ken

 

[finding41]

Use the 5" random orbital sander with 80 grit. You will need about 20+ sanding disks. Have a wire brush handy to clean them as they get plugged with paint.
Go get a good respirator first. Use it for all sanding. Any dusty dirty job really!
If you want to get fancy hook the sander up to your shop vac and suck the dust away. You still need to wear the respirator.
I used my respirator today while wire wheeling under my truck.
That white stuff I'm laying on isn't sand.

 

[Ron20324]

Some marinas rent out the 7" sander and vac for a reasonable amount. You buy the paper. Half day rent might be $45?

 

[down_shift]

Marty - great picture. LOL.
My marina does rent for ~ $15/hour but it is nice to have an excuse to purchase a new tool (and I don't want to be stuck should the rental be out that day). My little 5" Porter Cable DA has been going strong for 20 plus years. Just finished sanding my teak so guess it is up to the job for the hull. 50 pack of Norton 80 grit shipped from Amazon is only $36. Yes to the breathing apparatus and appropriate PPE. My dad lost his bladder to cancer, most likely to dust from working on pressure treated lumber.

 

[caguy]

I used a 5" orbital and a shop vac attached to the exhaust. I have seen where others have used air orbital sanders with wet n dry 80 grit paper. If I had one I would go that route.

 

[Ron20324]

... (and I don't want to be stuck should the rental be out that day)....

You pre-reserve the sander.

 

[CloudDiver]

When doing my bottom job my 5 inch orbital wasn't cutting it either. I bought a 6 inch Rigid orbital from Home Depot for about $100. It has 2 settings, one for overall speed and the other changes degree of random orbiting from 1/8" to 1/4" so you can tweek the settings for finer or more aggressive sanding. Its a heavier sander and will wear you out faster holding it up on the hull, but it has much bigger handles for a secure grip. Believe it or not the difference between a 5 inch and 6 inch in surface area is significant. It also has a dust collection port.
80 grit is probably perfect, you are just sanding before top coating with new, but same brand/type of bottom paint, not trying to remove it all. You should get excellent results with 80 grit on a 6 inch orbital.
I'd recommend getting or borrowing one of these, pic below. The cyclone drops most of the dust into the bucket before it hits the filter in the shop-vac (works line a Dyson vac). Otherwise you'll loose suction pretty quick as the fine dust clogs the paper vac filter. This thing comes in handy for any shop tool you have that has a vac port and creates saw dust or any other kind of dust.

I got my Dust Deputy from Amazon.com for $40

 

[Warren Milberg]

Herrington North used to rent out some heavy duty sanders connected to a shop vac for about $15/hour -- a good deal for a few hours which is all you need. Best part is they do the clean up of the machine. But wear a respirator.

 

[Regular Guy]

Can confirm what CloudDiver said;
Also I used the Rigid R2611 bought from Home Depot. The DIY marina I was in did not allow open sanding. I could have rented from them a Festool vacuum ($60/day), which they combined with a Harbor Freight 5" sander (cheaper to replace). I wanted rather to have my own tools and bought a 2.5 Gal shop vacuum with paper bags plus hose extension and a Rigid R2611 sander. It's a 6", 4Amp orbit sander, stays easy in your hands and sucks up the dust very well, love that tool.
I did also all my compounding and waxing with the Rigid R2611 by attaching a foam pad and on low speed.

 

[thinwater]

On some paints I have found dri-wall sanding sheets to be the ticket; no clogging and great dust collection.

For a 34-foot cat, usually about 3 hours to do what you describe with a 4x5 DeWalt sander. Been using this sander for everything for over 20 years and it looks like hell... but works like new.

The bucket collector looks neat. Gonna try that.

 

[down_shift]

Sanded the boat on Sunday. The little DA and 80-grit paper worked effortlessly. Cleaning the dust collection was a different story. Ended up hosing everything down to make a slurry what was poured in a few HD trash bags and tossed the one air filter in there too. 3 hours sanding and probably another hour cleaning the tools. The weather was perfect. 55F and >20 kts blowing right down the centerline.