Marking hull line?

[dgadee]

Planning to blast hull prior to coppercoating. How do you mark the line between underwater and topsides? Gouge a thin line?

 

[Hacker]

If you mark the bow and each side of the transom then you can recreate the waterline afterwards. We tend to use a fine saw to make a subtle scratch mark.

 

[Daydream believer]

When my boat was blasted the operator left 50mm of antifoul paint at the waterline to avoid damage to the gel coat above. I was able to mark the hull as I chipped the very thick paint away.

 

[tjbrace]

If you mark the bow and each side of the transom then you can recreate the waterline afterwards. We tend to use a fine saw to make a subtle scratch mark.

Could you please explain how to recreate the waterline from the 3 referenced marks. Genuine interest from me thanks

 

[dankilb]

We just masking taped a line a few inches above - the blasting was surprisingly accurate and left 90% intact. (And this was with ‘wet’ blasting before anyone says it won’t work - decent quality masking tape genuinely held up well)

 

[Charlie Boy]

After blasting I'd be very surprised if the mark wasn't clear. Any blaster worth their salt won't go above the line meaning that it will be very apparent

 

[dankilb]

After blasting I'd be very surprised if the mark wasn't clear. Any blaster worth their salt won't go above the line meaning that it will be very apparent

Aye - it is amazingly/surprisingly accurate! Better to hand sand the last few mm than end up with ‘textured’ topsides.

 

[Hacker]

Could you please explain how to recreate the waterline from the 3 referenced marks. Genuine interest from me thanks

Number of different ways. If you have enough space either side of the boat then set up a laser and join the bow and transom mark (obviously repeat for the other side). Another option is to use a water level set up on one mark and then use masking tape to put marks along the side. The other method is to use string lines running from battens set level across the bow and transom, each time you contact the hull use masking tape to make a mark. Hopefully you should be able to find video/images to explain as it’s tricky in words!

 

[tjbrace]

Number of different ways. If you have enough space either side of the boat then set up a laser and join the bow and transom mark (obviously repeat for the other side). Another option is to use a water level set up on one mark and then use masking tape to put marks along the side. The other method is to use string lines running from battens set level across the bow and transom, each time you contact the hull use masking tape to make a mark. Hopefully you should be able to find video/images to explain as it’s tricky in words!

Thank you for taking the time to explain it. I think I understand the theory.
All the best. T.

 

[davidmh]

The water level system works if the boat is set up level ashore. You need to make a mark at the bow and a mark at the stern and one on the port side and starboard side. Set up the gauge on the bow and move the pipe to the stern mark. and the port and starboard marks If the boat is not level the gauge will show the error, if it is only minor it probably does not matter and you can go ahead with the marking,
David MH

 

[alahol2]

Last time I did it I measured vertically down from the toerail to the waterline at several stations (every couple of feet). It was then relatively easy to put a dab of masking tape at each distance and join them up with another line of tape exactly on the waterline. I was actually doing it when removing and replacing the boot top paint so took two measurements at each station.. Note to "look right" the top edge of the boot top needs to curve slightly upwards towards bow and stern.