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Old 16-07-2016, 18:24   #1
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Foam core polyester V's cedar plank/balsa epoxy

Hi,
Have searched on here and google.
The above title is in relation to purchasing a 38' to 43' cat for cruising (2 or more yrs). And longer ownership of boat.
1/ Trying to work out, the for and against for each construction method.
2/ Strength - cruising safety - hitting submerged objects.
3/ The boat may be 20+yrs old - Epoxy v Polyester Gelcoat - Osmosis and other longer term issues.
4/ Ongoing maintenance costs for polyester gelcoat v epoxy with painted top coat.
5/ The cedar plank epoxy will be heavier the foam core, by?%.

Thanks
Boris.
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Old 17-07-2016, 00:08   #2
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Re: Foam core polyester V's cedar plank/balsa epoxy

A well built strip cedar epoxy boat is light years in front of a foam polyester boat. Light years, built properly it won't be that much heavier, and be stronger, stiffer and highly resistant to osmosis.
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Old 20-07-2016, 13:20   #3
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Re: Foam core polyester V's cedar plank/balsa epoxy

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A well built strip cedar epoxy boat is light years in front of a foam polyester boat. Light years, built properly it won't be that much heavier, and be stronger, stiffer and highly resistant to osmosis.
Factor: +1
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Old 20-07-2016, 16:06   #4
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Re: Foam core polyester V's cedar plank/balsa epoxy

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A well built strip cedar epoxy boat is light years in front of a foam polyester boat. Light years, built properly it won't be that much heavier, and be stronger, stiffer and highly resistant to osmosis.
Agree if we are talking about low quality, non bagged hand laid production boats.

But one off building has moved on a lot since cedar was the norm. A cedar boat will be considerably heavier, for similar strength and stiffness than a one shot infused foam/glass boat

The infused boat will be quicker and easier to build with less mess, effort (no fairing!) and boat building ability required Intelligent Infusion Harryproa

eg
20mm cedar core (s.g. .35) with 600 gsm glass each side weighs ~9 kgs per sq m assuming a 'normal' 1:1 hand laminated resin fibre ratio.
20mm foam (s.g. 08) with 900 gsm triax each side will weigh ~5 kgs/sqm (1:2 resin fibre ratio typical of infused laminates)
They will be near enough equally stiff, strong and durable. The infused boat gets lighter again if all the additional laminate, ring frames, stringers, coving, tabbing etc is included in the infusion.

The savings, particularly time, are even higher when it comes to the fitout.

The cedar raw materials wil be a little cheaper, but the time and mess savings will far outweigh this.
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Old 21-07-2016, 00:43   #5
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Re: Foam core polyester V's cedar plank/balsa epoxy

Cedar is too expensive in Oz now, people doing strip are using Kiri (Paulownia) which is lighter again however a 1:1 glass resin ratio for hand layup requires skill and diligence even in a female mould so over end grain balsa it ain't gunna happen ! Infusion is the go if you have the workshop space.
P.S.
Most of what is written about strip planking in forums is hysterical bullshit, gluing on one strip at a time might work for canoes but for bigger craft there are way more time efficient methods. IMHO.
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Old 21-07-2016, 01:04   #6
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Re: Foam core polyester V's cedar plank/balsa epoxy

Redreuben,

What "hysterical bullshit" are you referring to re strip planking? It can actually be a very efficient technique if you are organised. Have you ever done a boat in strip plank yourself?

For example, two of us did a 47' cat in cedar, and a hull and champher panel took us 2 days.
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Old 21-07-2016, 01:38   #7
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Re: Foam core polyester V's cedar plank/balsa epoxy

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Redreuben,

What "hysterical bullshit" are you referring to re strip planking? It can actually be a very efficient technique if you are organised. Have you ever done a boat in strip plank yourself?

For example, two of us did a 47' cat in cedar, and a hull and champher panel took us 2 days.
Exactly, Beakie exactly, I have built 2 Farr 9.2's and helped out on a 40' something or other, the Farr's were built with Kiwi builders who knew all the tricks, the 40 was built by a pedantic idiot who couldn't be told.
Read any forum on strip planking and people go on and on about how time consuming it is, it isn't, it's one of the fastest ways to build complex curves there is, if you know how to go about it, one strip at a time isn't it.
RR
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Old 21-07-2016, 04:13   #8
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Re: Foam core polyester V's cedar plank/balsa epoxy

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if you know how to go about it, one strip at a time isn't it.
Just curious, how exactly do you lay down more than one strip at a time? Multiple strips at a time? I don't get it.
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Old 21-07-2016, 04:19   #9
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Re: Foam core polyester V's cedar plank/balsa epoxy

Strip planking took me about 200 hours for a 35 foot mono hull including table sawing the 20mm strips from 2 by 5 inch planks. Strip planked hull doesn't need any 0 deg glass just + - 45 biax for transversal loads so the skins are much lighter compared to foam cored (or end grain balsa). Less build time frames too..

BR Teddy
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Old 21-07-2016, 05:12   #10
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Re: Foam core polyester V's cedar plank/balsa epoxy

Is 20mm normal for strip? Mine is 6mm cedar strip, glass on both sides and zero defelection. There are four ring frames on each hull, at the crossbeams.

Edumacate me.



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Old 21-07-2016, 05:45   #11
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Re: Foam core polyester V's cedar plank/balsa epoxy

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Is 20mm normal for strip? Mine is 6mm cedar strip, glass on both sides and zero defelection. There are four ring frames on each hull, at the crossbeams.

Edumacate me.
Depends what are the designed loads of the vessel, safety factors, framing and laminate schedules. I used D Gerr's Boat Strength scantlings for the schedules.. 20mm strip planks,1500gsm biax out side and 1200gsm inside biax..

BR Teddy

Ps. Nice cat!
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Old 21-07-2016, 06:59   #12
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Smile Re: Foam core polyester V's cedar plank/balsa epoxy

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Just curious, how exactly do you lay down more than one strip at a time? Multiple strips at a time? I don't get it.
In a nutshell you plank the hull dry using double headed nails. Where the bilges turn the planks have a natural gap, on flatter areas cut the planks with a bevel to leave a gap. You'll find all the planks have no gap on the inside. Use thin ply or pallet strapping and staples to hold planks fair where necessary.
Screed the whole hull in thickened epoxy to fill the gaps, remove the double headed nails, a rough fair with a long plane and a 7'' pad then glass. DB on outside, uni on inside.
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Old 21-07-2016, 07:04   #13
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Re: Foam core polyester V's cedar plank/balsa epoxy

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In a nutshell you plank the hull dry using double headed nails. Where the bilges turn the planks have a natural gap, on flatter areas cut the planks with a bevel to leave a gap. You'll find all the planks have no gap on the inside. Use thin ply or pallet strapping and staples to hold planks fair where necessary.

Screed the whole hull in thickened epoxy to fill the gaps, remove the double headed nails, a rough fair with a long plane and a 7'' pad then glass. DB on outside, uni on inside.

Wouldn't the excessive use of thickened epoxy in place of the cedar ad weight to the boat. I'm thinking in the terms of a multihull.


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Old 21-07-2016, 17:30   #14
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Re: Foam core polyester V's cedar plank/balsa epoxy

Smj; the filler only has to be as strong as the Cedar or Kiri so it's a pretty lightweight mix not a heavy duty adhesive type mix.


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Old 21-07-2016, 18:32   #15
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Re: Foam core polyester V's cedar plank/balsa epoxy

[QUOTE=paxfish;2171158]Is 20mm normal for strip? Mine is 6mm cedar strip, glass on both sides and zero defelection. There are four ring frames on each hull, at the crossbeams.

Edumacate me.[QUOTE]

The first large strip boats were cats like yours, built in NZ. 6mm cedar with 200 uni inside and out. Some of them are still sailing. When cruisers started using it, the scantlings grew. Early 40' cats were 15mm with 400 each side, but by the end of the boom, they were up to 20mm with 600 each side.
I am not sure why, but suspect "erring on the side of caution" by designers who were not engineers was a big part of it.

I built the first strip planked kiri boat in Aus ~12 years ago (Red Reuben, it was in one of the grain sheds on the north side of the Swan river mouth, rats as big as cats). Kiri is much nicer than cedar. The dust is not toxic, it sands easier, is nearly rot proof and the splinters seemed less sharp. Needed to be a bit cautious about heart wood (very soft) in those days, but suspect they now have this sorted.

Kiri is also lighter (s.g.28 vs .35 for cedar). Using it in the examples above, the weight would be 8 kgs per sqm. Still a lot more than the Intelligently Infused boat, which does not need to be faired.

Dry planking and bogging afterwards is quicker than individual wet planking, but if you set up properly, the bog can be applied to 5 strips at a time and these placed on the frames and screwed/nailed/taped to any frames they don't touch, which is usually not many. Any small gaps get filled with resin when the laminate is applied. Scarphing the planks is not required as long as the joins are staggered, so planking goes very quickly, which is one of the reasons it was such a popular build method in the 70'-90's.

The interplank bog only has to be as strong as the edge grain of the cedar, so can be very powder rich. Weighs very little more cedar. You save more weight by rebating the glass joins so they don't need to be faired and a bunch of other minor tricks.
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