Soundness of balsa cored hulls

[Fore and Aft]

I spoke to a boat builder who used to be a huge fan of boat building with those pre-made Duflex Balsa panels. He must have built 15 boats? with those panels. Anyway he was no longer a fan of them. I was not surprised as everyone of his boats I had surveyed had random rot areas. Again a lot of it was caused by people not coring out the Balsa when installing fittings.
Rudders are a totally different issue, I think I have seen every type of material fail for rudders. Even last week a solid metal rudder had badly corroded welds where it attached to the shaft.
Cheers

[clockwork orange]

Originally Posted by Fore and Aft

I spoke to a boat builder who used to be a huge fan of boat building with those pre-made Duflex Balsa panels. He must have built 15 boats? with those panels. Anyway he was no longer a fan of them. I was not surprised as everyone of his boats I had surveyed had random rot areas. Again a lot of it was caused by people not coring out the Balsa when installing fittings.
Rudders are a totally different issue, I think I have seen every type of material fail for rudders. Even last week a solid metal rudder had badly corroded welds where it attached to the shaft.
Cheers

This is very interesting to me, we don't have anything like that here in the US but i have read a lot about boats built from Duflex panel kitset. One guy was commenting on how many pinholes he needed to fill which to me indicated that perhaps they are press molded. In my experience infusing panels on a table you don't get pinholes. Do you happen to know how ATL makes the panels. If they are press molded they would likely be wet preg off an impregnator which does allow for optimal fiber fraction but you would not get any resin between the blocks, or not much. Infused panels will completely surround every block with resin but you will end up heavier, even with an optimal fiber fraction, a worthwhile trade off with balsa. BTW, i have about 300ft2 of Duracore strips that i have no idea what i will use it for. For those who are not familiar, it is 1/2" end grain balsa sandwiched between thin meranti veneers, bonded with resorcinal glue, cut into strips 8 ft long x 1.5" wide with both ends finger jointed. It was a way to build a one off end grain balsa hull by strip planking like with WRC.
Yeah, most rudders are crap on production boats, hollow aluminum ones with an aluminum shaft can be nice, carbon shafts can be nice. I have done a few hollow daggerboard style blades, no core. Much better.

[Fore and Aft]

Clockwork Orange I am not sure how they're made but the pinholes are no joke. I didn't want to mention them in case I got shouted down. But I am a firm believer that when you find a random patch of rot on the topsides with no fittings that it has been caused by high humidity in the cabin. I have worked with those panels and really a layer of 6oz glass seems to be the best way to seal them. Even extra resin rolled over the top doesn't get every pinhole.
Cheers

[smj]

Originally Posted by Fore and Aft

Clockwork Orange I am not sure how they're made but the pinholes are no joke. I didn't want to mention them in case I got shouted down. But I am a firm believer that when you find a random patch of rot on the topsides with no fittings that it has been caused by high humidity in the cabin. I have worked with those panels and really a layer of 6oz glass seems to be the best way to seal them. Even extra resin rolled over the top doesn't get every pinhole.
Cheers

Could the pinholes be caused by the balsa off gassing? Pretty sure that was a problem when coating fresh plywood with resin.

[donradcliffe]

Originally Posted by boatpoker

After over 5,000 surveys Im pretty sure I know the difference between a 35' and a 37'. I've surveyed it 5 times over the last 30 years and it would have a different MIC than the one in the photo below taken from my latest report.

My bad. I didn't realize that Goman Boats pirated the Express name from the US built line of boats which was in production several years before the Canadian one.

[clockwork orange]

Originally Posted by smj

Could the pinholes be caused by the balsa off gassing? Pretty sure that was a problem when coating fresh plywood with resin.

It always a good idea to coat plywood when the temperature is going down, not up. When the wood is inhaling not exhaling. If you coat wood with epoxy and then put it out in the sun it will actually blow bubbles in the epoxy.
You may be right if they press molded the panels with heated platens which is likely for quick turnaround.

[smj]

Originally Posted by clockwork orange

It always a good idea to coat plywood when the temperature is going down, not up. When the wood is inhaling not exhaling. If you coat wood with epoxy and then put it out in the sun it will actually blow bubbles in the epoxy.
You may be right if they press molded the panels with heated platens which is likely for quick turnaround.

We would let the first coat kick, then sand, then put subsequent coats on while still tacky.
The weather in the Fl Keys was hard to work around!

[s/v Jedi]

When I add fiberglass to plywood I vacuum and brush it first, then use a heat gun to warm it up, drape the cloth over it and pour resin on, spread with plastic spreader and use aluminum fin rollers to work air and excess resin out.

When I just coat plywood with resin, I also vacuum and brush, then the heat gun. I switched to TotalBoat penetrating epoxy, pour it on and use a wide brush to spread it. After cure, like others wrote up-thread, I sand and put on a second coat. With the penetrating epoxy, after sanding it looks like bare wood but feels like plastic and is very hard. I have successfully coated with more epoxy, with paint incl. rustoleum and with varnish. Pinholes are rare when preheating with the heat gun but I have encountered some. I think they are caused by a small void in the plywood.

[GordMay]

FWIW:
Excellent basic information, from Composite Envisions’ [a distributer] extensive “Knowledge Hub”:
➥ https://compositeenvisions.com/knowledge-hub/

Including:

Core Materials ➥ https://compositeenvisions.com/document/core-materials/

Composite Fiber Characteristics ➥ https://compositeenvisions.com/docum...aracteristics/

Removing Bubbles in Resin ➥ https://compositeenvisions.com/docum...bles-in-resin/

Spraying Clear Coat & Dealing with Pinholes ➥ https://compositeenvisions.com/docum...with-pinholes/

and much more ...