Thread: New Iain Oughtred Shearwater dinghy in Newcastle

Nice.

I was intending to use low sheen house paint myself on my new boat, but there's no way I'll be giving it 4-6 weeks before it first gets wet. It'll have to make do with 4-6 days, most likely, but I'll be treating it well and can always touch up the bottom.

Sumbloak,

I hear what you say,but as was oft quoted in the classic movie "The Castle", & not wanting to offend,I feel like saying "tell him he's dreamin' ".

I adhere to what a lot of professional wooden boatbuilders seem to do & that is not to sand the ply planks before applying one or two coats of primer/sealer/undercoat owing to the thin layer of the outside ply, so as not to go through to the glue line.The initial application of the undercoat seems to raise the grain so that after coating,it can be sanded back to a reasonably smooth surface with say 100 to120 grit paper.This is then followed with two coats of low sheen gloss paint,sanding with progressively finer grades of paper between coats 2,3,& 4,then a final two coats.Yep,SIX coats of top coat.There's sanding between some coats don't forget.( Paint manufacturers claim that the undercoat is not needed with modern acrylics,but being old-fashioned,I stick with the sealer coats.)The grades of paper you use depend on the finish you are after.In my case,I describe my finish as a "quality work-boat finish" without being obsessive with detail as the boat is going to get knocked about in normal use.Certainly not a "show boat" finish.I use a top quality brush & the finish is quite acceptable to my eye.

The secret,which is really not a secret any more,is to LET THE PAINT DRY & HARDEN FOR AT LEAST 4-6WEEKS BEFORE USING THE BOAT.

From my research & experience,the reported bad experiences with water based acrylics stem from launching before the paint is sufficiently dry & is too soft to take knocks. This applies of course to any coating,but acrylic paints seem to take quite a while to harden to a state where they can stand up to use on a boat,as opposed to a coating protecting a house.In fact,after a year when the first touch-ups are needed on a well used boat,you will be amazed at how hard the coating has become & how easy it is to fair out dings & scrapes & slap a couple of coats on.

I have also used single pack poly marine enamels successfully in the past & love them but find acrylics so much easier to use & maintain & when fully cured are more than hard enough for normal boating.

Part of the success of any coating is of course in the prep followed by sufficient time for that type of coating to cure to a useable state.


Cheers.

Al.

AINT GONNA HAPPEN. It just wont. It'll be in the water in a week at most. Been building the thing too long. Want to row it. Them's the breaks. The bottom and garboards are glassed and epoxied anyway, so if some paint comes off the bottom it will just get touched up.

Mine is so light it is never going to be dragged up the beach. I can pick it up with one hand.

ETA: Come to think of it, if using house paint is going to take 6 coats and 6 weeks to be durable, I'd be better off forgetting about house paint and using Aquacote. It's more expensive per litre, but with 3 coats it'd be bulletproof in 6 days. So it'd end up being at least as cheap, less work to apply, and more probably durable.

Aquacote I have used successfully....once.Very durable,good finish & hangs on well.Difficult to apply though as it doesn't cover well even in white so you may need more coats than you would like.Took me 3 coats to get enough cover.Don't forget you have to build up a couple of coats of high build epoxy undercoat first to fair the surface.This sands easily but the poly top coat does not so you have to get it right first time.I used the "roll & tip" method for the top coats that gave a pretty good finish.If you haven't used it before,see if you can find someone locally who has a lot of experience with it & get their advice.The finish is also very dependent on the correct weather conditions.Get this wrong & it'll drive you nuts!

Six coats of acrylic over one or two sealer coats can be brushed on in 4 days with two coats/day.A lot is sanded off but a good well cured thick base is a great foundation for future maintenance coats.

Where in NSW are you?

Al.

I'm up on the Tweed, although from Newcastle originally (many years ago). TBH I'm not much of a painter. Can generally make something look decent whenever I pick up a brush sort of thing. I have heard that Aquacote can be tricky, although I gather that they have changed some things to make it easier to use. Might do some more research.

I don't actually want a gloss finish. I'd prefer matte or low sheen, not only to hide imperfections but just for the look. However, there's just no way I'll leave the boat sitting around for 6 weeks while the paint cures. It'll pretty much be throw it on the truck and head down the river as soon as the bugs wont stick to it, so realistically that means using a finish that will cure to a usable level in a week at most.

I rest my case.

Good luck.

Al.

Congratulations, your pictures show an outstanding job.

How does she go recovering from a capsize? You don't appear to have a great volume of bouyancy tanks.

Ross,

The fore & aft compartments are fairly large & I have not calculated where she will sit if swamped,but intend to deliberately swamp her at first launch which will be soon.

I had anticipated fixing floatation foam under most of the seats as these are close to the gunwales & would give lots of buoyancy high up.

Final decision will be after deliberate swamping.

Al.

G'day Al,

I thought I'd add my thoughts on flotation & buoyancy. Buoyancy say via foam is more effective the lower it is, it becomes less effective as a lifting tool the higher it is. So if you put your buoyancy up high it'll lift the boat to the surface and hold it there but what you really need is for it to lift the gunwales up a bit to get some freeboard back so that when you bail it doesn't come back in and the only way to achieve that is to get the buoyancy as low as possible so that it is working hard when you need it.

Just looking at the size of the fore & aft compartments, I reckon you have heaps and won't need any foam.

Cheers
Rod

G'day Rod,

Thanks for the thoughts.

If it was just a swamping,foam floatation down low would help to the extent of of the volume & weight of water the foam displaces,but when capsized the boat is on its side.She only weighs about 200lb, so the floatation compartments should give enough lift to float her reasonably high,so not take too much water when righted.

If you think about it,when on her side,the foam floatation out near the gunwales will be low under the water & will provide extra lift initially added to that from the buoyancy chambers,& this lift will reduce to nil as she comes level,but in doing so will provide a positive buoyancy moment soon after I put downward pressure on the centreboard & will help right her.That's why it needs to be high & wide.The further the boat rotates to level,the greater the moment.Trying to fix foam somewhere low in a hull this shape would put it in towards the centreboard case down level with the keel & if she floats high enough with the floatation chambers alone,this foam would probably not be submerged & so would have no effect on buoyancy with the boat on its side.

I have been through this process with several previous wooden boats (sailing) but this time I have not carefully calculated the amount of buoyancy provided by the chambers as a previous builder of this design has assured me the compartments will do the trick.

The capsize test will reveal all

Al.