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Post Options Post Options   Likes (0) Likes(0)   Quote Blucky Quote  Post ReplyReply Direct Link To This Post Topic: Painting 12ft Tinny
    Posted: 17 Sep 2018 at 2:10pm
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I've recently bought a 12ft startcraft aluminium hull and am looking at painting the hull, building a ply floor and carpeting the inside.

It currently has a camo paint job done with spray cans so I was planning on sanding that off.

What is the best type of paint & primer to use on the cheap?

Was looking at a 2 pot epoxy primer with a polyurethane gloss topcoat, although even that is rather expensive.

Any ideas or links to good products?

Cheers
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Post Options Post Options   Likes (1) Likes(1)   Quote MikeAqua Quote  Post ReplyReply Direct Link To This Post Posted: 17 Sep 2018 at 3:01pm
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There aren't any shortcuts with alloy.  You need the right prep and paints. 

For DIY options have a look at Altex.   They do a system with epoxy primers and filler and a one pack enamel top-coat.  I've spoken to them and they said the enamel is OK on the sides (but not the hull) of a trailer boat.

If you are installing a ply floor I suggest making sure it can be removed/opened so the bilge can dry out between trips

BTW I used to have 12ft Starcraft.  Great little dinghy.


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Post Options Post Options   Likes (0) Likes(0)   Quote Blucky Quote  Post ReplyReply Direct Link To This Post Posted: 17 Sep 2018 at 3:36pm
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My plan was to fully sand back to alloy and prep the whole hull with epoxy primer.
Would a polyurethane top coat be ok for the whole hull? Or are there any other options for the hull to keep it well protected?

I was going to either have a few hatches for storage, or use expansion foam and fill underneath the floor for extra buoyancy as I would be doing some diving off it.

Nice mate seems like a solid little boat, just want to get it up to scratch before summer.
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Post Options Post Options   Likes (1) Likes(1)   Quote Steps Quote  Post ReplyReply Direct Link To This Post Posted: 17 Sep 2018 at 3:53pm
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As above...there are shortcuts or 'cheap.. be it a car boat or house.. they will all rnd up bad very quick
 Use the search button above.. lot of good threads on the subject.

May like to look at vinyl , or even a deoxidation (mild acid wash), and polish to get rid of the heavy oxidation...

 keep in mid, alloy is like gav (zinc) it forms a thin oxide 'skin' the molecules are larger than the alloy, and extremely hard/ durable.. and this skin prevents further oxisiation.
 With Steel/ iron .. the oxidation  (rust is nor durable , flakes off and the iron underneath become further exposed  till have a big hole.

Polished alloy will oxidise, since it is smooth the oxide layer tends to stay very thin  giving a grey appearance.
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Post Options Post Options   Likes (0) Likes(0)   Quote MikeAqua Quote  Post ReplyReply Direct Link To This Post Posted: 17 Sep 2018 at 5:01pm
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Originally posted by Blucky Blucky wrote:

My plan was to fully sand back to alloy and prep the whole hull with epoxy primer.
Would a polyurethane top coat be ok for the whole hull? Or are there any other options for the hull to keep it well protected?

I was going to either have a few hatches for storage, or use expansion foam and fill underneath the floor for extra buoyancy as I would be doing some diving off it.



If you want polyurethane The Altex system uses: -

- Epoxy aluminium primer (Important etching coat);
- Epoxy barrier undercoat;
- Top coat (two pack brushable poly);

But it's marketed as a topside paint.  Might be OK on the sides of dinghy.

I wouldn't put foam under a ply floor on your star craft - asking for corrosion.  if you're gin with storage then leave hatches open when not in use (assuming you will store the boat under cover)

Foam won't add buoyancy under normal conditions.  If you swamp the boat, the foam will add buoyancy, but only enough to keep the boat at the surface.  You won't be bailing it out or driving it home.  Been there, done that.

Better to add foam under the bench seats (that's how the starcrafts were built).

If you want more buoyancy than that consider sponsons like these
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Post Options Post Options   Likes (0) Likes(0)   Quote viscount Quote  Post ReplyReply Direct Link To This Post Posted: 18 Sep 2018 at 4:33am
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Cost out the whole paint system then compare to wrapping the top sides.
Calling fishing a hobby is like calling brain surgery a job - Paul Schullery
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Post Options Post Options   Likes (0) Likes(0)   Quote Blucky Quote  Post ReplyReply Direct Link To This Post Posted: 18 Sep 2018 at 9:53am
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Sounds like a good system, don't want to skimp out for a good finish.

Was hoping for something to cover the entire hull including the submerged section to prevent any corrosion.

What would be a better alternative to expansion foam?
Would rather the boat at the surface than the bottom of the ocean if I do swamp it LOL.
Did you manage to recover your dinghy?

I haven't much experience with vinyl, is it easy to install and are there certain types to look for?
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Post Options Post Options   Likes (1) Likes(1)   Quote MikeAqua Quote  Post ReplyReply Direct Link To This Post Posted: 18 Sep 2018 at 10:02am
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Originally posted by Blucky Blucky wrote:

Sounds like a good system, don't want to skimp out for a good finish.

Was hoping for something to cover the entire hull including the submerged section to prevent any corrosion.

What would be a better alternative to expansion foam?
Would rather the boat at the surface than the bottom of the ocean if I do swamp it LOL.
Did you manage to recover your dinghy?

I haven't much experience with vinyl, is it easy to install and are there certain types to look for?


The hull will look after itself if left as bare alloy, via the galvanising process Steps explained.  I wouldn't suggest painting the bottom of an alloy dinghy.  If you drag it up on beaches or whatever it will scratch.

If it was me I would use painted polystyrene blocks under the bench seats as buoyancy.  You don't really want your buoyancy under the floor.  If you get partly swamped you then have water sloshing around above your buoyancy layer which will increase the risk of capsize

I swamped my boat few times doing beach launches and bar crossings (shallow).  Happens.  Managed to recover it every time.

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Post Options Post Options   Likes (0) Likes(0)   Quote Blucky Quote  Post ReplyReply Direct Link To This Post Posted: 19 Sep 2018 at 1:26pm
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Is there much of a downside to leaving the hull bare?
Note taken, I'll chuck in some extra buoyancy under the seats.

Also does anyone know the best way to strip paint from an alloy hull?
Been looking at regular paint strippers which contain methylene chloride, but I've also heard that its bad for aluminium and alloy.

Cheers
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Post Options Post Options   Likes (0) Likes(0)   Quote pjc Quote  Post ReplyReply Direct Link To This Post Posted: 19 Sep 2018 at 1:48pm
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Acetone on a rag should remove spray can paint,it did when I used on a glass dinghy that been sprayed,
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Post Options Post Options   Likes (0) Likes(0)   Quote MikeAqua Quote  Post ReplyReply Direct Link To This Post Posted: 19 Sep 2018 at 3:25pm
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Originally posted by Blucky Blucky wrote:


Also does anyone know the best way to strip paint from an alloy hull?



If it's a cheap spray-can job as you suspect, then a decent water blaster will probably knock it it off.

If it was me I would: -

- Water blast the bulk of the paint off.
- Use acetone as suggested above for any stubborn bits
- Acid wash (off the trailer, on blocks or tyres on the lawn) in accordance with instructions on can. for example https://www.boat.net.nz/product/ultimate-aluminum-cleaner-restorer/

There is no harm in then leaving the bare alloy to oxidise and self protect.

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Post Options Post Options   Likes (0) Likes(0)   Quote Steps Quote  Post ReplyReply Direct Link To This Post Posted: 19 Sep 2018 at 4:23pm
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If it was me I would use painted polystyrene blocks 
 Some old WATER BASED paint
otherwise oil based the polystyrene melts.. disappears into nothing Wink
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Post Options Post Options   Likes (0) Likes(0)   Quote MikeAqua Quote  Post ReplyReply Direct Link To This Post Posted: 20 Sep 2018 at 8:49am
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Originally posted by Steps Steps wrote:

If it was me I would use painted polystyrene blocks 
 Some old WATER BASED paint
otherwise oil based the polystyrene melts.. disappears into nothing Wink


Definitely water based Smile

I've seen about half a dozen Starcraft and all originally had big blocks of yellow foam in a thin alloy casing under the back and middle seats. The casing was for physical protection - wasn't water tight.  These buoyancy compartments had flat bottoms running between the bottom edges of the topsides.

Mine eventually corroded through the alloy casing from the inside and started to fall to bits.

I replaced all three seats with marine ply/epoxy boxes that I sealed and filled with  polystyrene.  I made the seats longer (especially front and back seats) and I was able to follow the angles of the hull more closely that the original buoyancy.

Because of the increased buoyancy compartment volume, I was able to build in a few storage compartments and still end up with significantly more buoyancy (tested this) than the original configuration.
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Post Options Post Options   Likes (1) Likes(1)   Quote Blucky Quote  Post ReplyReply Direct Link To This Post Posted: 23 Sep 2018 at 4:51pm
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So far have stripped paint with regular paint stripper and sanded off excess.
Done etch primer, pre kote and toplac, 2 coats of each. Gonna do the trim with white.

Might scrap the idea for putting a floor in due to the weight but lay some carpet and add some buoyancy under seats.
Going to bitument seal the indside base of the hull and then use contact adhesive to lay carpet straight over that and the sides, and chuck an 8hp on it.

Any downsides or potential corrosion issues with having bitumen sealer or contact adhesive in direct contact with the aluminium?

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Post Options Post Options   Likes (0) Likes(0)   Quote MikeAqua Quote  Post ReplyReply Direct Link To This Post Posted: 24 Sep 2018 at 3:54pm
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Nice shade of red.

I'm not familiar with bitumen sealers.

I used a product called Duram 195 on the inside of the seams on my Starcraft.  Stunk for weeks, but did the job and no corrosion issues after 5 years. Quite goey stuff and needs masking tape to give tidy edge.

In the US they all seem to use a product called "coal-tar epoxy" to coat the outside of alloy underfloor fuel tanks in boats.  I have no idea what that is.


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Post Options Post Options   Likes (0) Likes(0)   Quote MikeAqua Quote  Post ReplyReply Direct Link To This Post Posted: 24 Sep 2018 at 3:58pm
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 I had a 9.9hp and then a 15hp on my 12ft Starcraft.  You may find the 8 hp a little light.
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