Right now Seahorse is purchasing primed steel to be used on the hulls. When they are ready for priming the boat they sandblast the exterior and then prime the boat.

However, they do not sandblast the interior. Bill briefly told me they have a different process they do on the inside though I don't know/remember the details.

Since properly preparing and priming steel is probably the single most important factor to a long lived steel hull (along with preventing galvanic corrosion)I wanted to understand how SeaHorse handles this step.

HERE IS THE QUESTION!

Does anybody who has spoken with Bill, or seen the new process firsthand, know how the inside of the boat is prepared and primed? I believe they started using pre-primed steel sometime after hull 4 or 5.

Even though parts of the Steel are already primed how do they handle the abriaded sections or welded sections. All the Epoxy guys require white metal before Epoxies are put on steel.

I know that the inside will be in general dryer than the exterior but since so much of the metal is not exposed here even small areas that begin corroding could cause significant damage before they become visible.

I'm hoping to put this issue to bed so I can stop thinking about it.



Hugh

I too am very interested in this as we all know the failure mode is most likely rusting from the inside out.

The yard is back to work now after CNY, and hopefully Bill or Fido will comment.

I intend to visit the yard during sandblasting/priming to inspect this process.

See attached URL for surface prep on aluminium and steel.
Interesting

http://www.yachtpaint.com/usa//general/perfection/pdf/leaflet.pdf

Robert,

I read your link and it reminded me of what Bill had mentioned to me.

If my foggy memory serves me correctly Bill did say he used the 2 rag method on the interior and sandblasting to white metal on the exterior. So they would in essence be relying (for the interior only) on the steel factory to apply the epoxy primer in the proper fashion and then Seahorse would degrease and grind(maybe with flapper wheels) in areas that were abraided or welded before applying primer. I would imagine that you would need a lot of care to not miss small areas.

Bill had mentioned in the past that he has been working with the steel supplier to improve the quality of their primed steel and now feels confident that he is getting good pre-primed plate.

I hope that Bill or Fido can chime in on the specific procedure used on the interior. I don't know if Bill is back at the factory yet. But with being gone that long and the new workers he hired I'm sure swamped is an understatement.

Hugh

Is the pre-primed steel a 2 part epoxy, or common red oxide? From the look of it I would think red oxide and need to hear from Fido.

In any case, I do not recall noticing that the longitudionals and interior structure was pre-primered.

I would like to know more about this very important process.

Robert,

I'll post some photos, maybe tomorrow that show the primed metal.

Hugh

Anybody???

I have faith that there are people out there with the answer to this one


Hugh

See Randall's post today about colours. He notes that 381-1 is being sandblasted on the inside prior to priming.

This is great new news, and I would appreciate if Fido or Bill could clarify the interior metal prep process.


Robert Straghan

I just returned from the yard, and understand that they are now using shot blasted, pre-primed steel. Having said that some sections of my hull were not pre-primed.

My understanding is that the interior welded sections are cleaned up by hand, primed and painted. The hull interior is not sandblasted.

I beleive that the use of pre-primed plate began on hull #7. So hull 1 of the 382 as well as the sedan have been built with pre-primed steel. Bill had mentioned when I was there that they were not going to sandblast the interior as it was too much work/mess and took to long to clean up.

However, you still have all the welded, abraided and otherwise scuffed up areas to treat. So I was curious about the specific technique.

I'll find out from the yard some time and post it.


Hugh

Don't know if anyone is still reading this but for what it's worth I am building my own boat right now - a 43 foot Ted Brewer design in steel and I have done COPIOUS amounts of research on paint systems.
I'll summarise what I've learn't and am doing myself.
1) getting the interior of the hull properly blasted and coated is MORE IMPORTANT than getting the exterior. In fact if you want a long lived boat the interior is fundamental. The reasons are simple. The interior will be foam coated for insulation then built over during fitout so you can never easily get at it to check it or repair a rust spot. Rust on the exterior is visible and easy to get at and fix quickly.Steel boat rust from the inside out.
2) I am using pre blasted steel coated with a 2 pack low zinc epoxy primer or shopprimer for the whole hull. This can be left on as the base coat (like Seahorse is doing) on the interior only. However is has to be cleaned up and removed wherever welding or cutting has damaged the coating then stripe coated to restore coverage. Having said this I would never let someone else pre blast my steel and paint it wothout checking that the work being done is of the highest quality.My sandblaster is a local guy who is happy for me to watch what he is doing and cuts no corners. We waited 2 weeks for the right weather conditions efore doing the last lot.I'm using a Jotun pre weld primer called Muki 2001. These are specialised products and very few can be left on as the base coat.So you are very dependent on the quality of work being done by whatever Chinese factory is supplying the steel and doing the blasting and priming.
3) I agree with Seahorse's approach because it means you can get the bits between the frames/stringers and hull plating blasted and coated whereas after construction it is impossible to get at these bits.
4) I noticed a photo on their web site of blasting being done at night - not good practice because of dew point in the air. My guy starts at about 10.00 am and blasts for 3 hours then paints and tries to always be finished by about 3.30 in the afternoon to operate in the best possible conditions.

I'm interested in this site because we are thinking of building a 44 Duck and cruising it to North America across the Nth Pacific then probably selling it.

MP