Books about composite boatuilding

[giegs]

Are 20mm foam and 20mm cedar that comparable? Seems like you'd end up with two hulls with a lot of differences beyond just weight.

 

[Cheap Beer]

Ply - even lower resale value. I base this on the asking price of larger wood core boats I've seen for sale. Usually I say "wow that's a deal" - and then read it has a wood core and I figure out why.

Here's a 25-year-old wood composite boat that sold last year for $13m.
46m Delta, ex-Affinity, ex-Daedelus.
Balsa-cored, e-glass skins. Like a lot of boats under 50m.

 

[Zonker]

I wasn't talking about balsa core which is quite "normal". I was speaking of strip WRC or other wood epoxy boats.

 

[harryproa]

Are 20mm foam and 20mm cedar that comparable? Seems like you'd end up with two hulls with a lot of differences beyond just weight.

For sure, but the most important variable is skin stiffness and this is hugely dependant on thickness (2 x thickness = 8 x stiffness). The highly curved bow area could possibly be thinner, but it needs to be stiff when hammering upwind and have decent impact resistance, so I doubt anyone goes below 20mm in this area.
I could be wrong, it is a long time since I was involved with a 40' mono and that one had a pointy bow. It would be interesting to know the base laminate of the 40'ters?

Huey,
The writer of that article doesn't have a clue and the builder is not much better.
Baking resin has nothing to do with infusion, everything to do with maximising the resin properties (usually not required) and reducing print through, especially on poly and vinyl ester boats with light laminates.
Infusion dry spots can't happen if the set up is correct, and are easily seen on one offs. Gel coated, not so much, but generally speaking, if one side is wet out, so is the other, due to perforations in the core.
Segmented foam is almost as bad as plywood for boats that will not be conscientiously built and/or maintained.

 

[sam_crocker]

Cold molded boats are still the best if they are one offs. More sustainable and less Eco damage and much likely cheaper. Done right - they are as nearly the same weight as an modern vacuum method with less sophisticated tooling. The boat will also have a more secure feel under way.

I love cold molded boats but you have to fair every layer. Lotsa sanding.

 

[sam_crocker]

Twill has more resin in it as the weave is not flat and because it is a surface layer and pinholing/resin starvation means more finishing work.

This effectively only applies to wood and balsa. And even then is not really correct. Vacuum infused timber is rot proof (and heavy).

Absolutely.

For sure, but the more you do, the more confident and skilled you get and the less important it becomes. We have infused 20mm thick carbon tow (filaments, with nothing holding them together) without doing anything special

We regularly get this (70/30) with infusion and unis, more like 67/33 (2:1) with stitched. The difference is small. The cost, time and hassle difference is huge.

Strip planking is definitely easier than cold moulding, especially with scow bows which would be a lot of work and waste to spile the veneers. Strip is also easier than building a plug and mould, or just a plug for a foam boat. But it will not be lighter. From the 'are they full of shit thread?':

Suitable base laminates for a performance 40'ter:

20mm cedar with 600 glass each side
20mm foam with 900 triax each side

Assuming the cedar is hand laid, the resin will weigh as much as the glass.
Assuming the foam is bagged or infused the resin will be half the weight of the cloth, plus 200g each side to wet the foam.

20mm cedar (sg 0.35) weighs 7 kgs per sq m, plus 2.4 kgs of glass and resin: 9.4 kgs/sqm
Bagged/infused 20mm foam (sg 0.08) weighs 1.6 kgs per sq m, plus 3.1 kgs of glass and resin: 4.7 kgs/ sq m.
Hand laid 20mm foam (sg 0.08) weighs 1.6 kgs per sq m, plus 3.1 kgs of glass and resin: 5.6 kgs per sq m

The moulded boats will probably weigh a little more due to the bedding compound needed for the core, but roughly speaking, the hand laid cedar hull will weigh double the infused foam strip one.

If the foam strips are only glassed on the inside, fairing the outside will be easier than fairing cedar. Both will be a pain in the arse around the bow.

John Fox did a side by side comparison of strip cedar and foam core one offs in Professional Boatbuilder issue 69 a few years ago (https://pbbackissues.advanced-pub.com/). He compared two pretty similar boats, 35' or so and similar displacements (both Mills Designs). Both built in the same yard and both vacuum bagged. The foam core boat came out at 8.835 kg/m^2, the cedar core boat 8.816. Cost wise they were about a wash (wood core $280 less for the hull materials, ~2001 era). Less material thrown away on the wood core.

This was not an infused foam boat, but with 45% resin in the hull I can't see it changing the weight significantly by infusing.

 

[harryproa]

John Fox did a side by side comparison of strip cedar and foam core one offs in Professional Boatbuilder issue 69 a few years ago (https://pbbackissues.advanced-pub.com/). He compared two pretty similar boats, 35' or so and similar displacements (both Mills Designs). Both built in the same yard and both vacuum bagged. The foam core boat came out at 8.835 kg/m^2, the cedar core boat 8.816. Cost wise they were about a wash (wood core $280 less for the hull materials, ~2001 era). Less material thrown away on the wood core.

This was not an infused foam boat, but with 45% resin in the hull I can't see it changing the weight significantly by infusing.

Thanks for the reference. That was in the days when PBB was a wonderful source of info. The article is too blurred/small for me to read. Could anyone copy and paste it or tell me how to open it in a readable format. Ta.

 

[sam_crocker]

Thanks for the reference. That was in the days when PBB was a wonderful source of info. The article is too blurred/small for me to read. Could anyone copy and paste it or tell me how to open it in a readable format. Ta.

On the viewer, the top bar on the right has a bunch of icons - you can download a pdf. You might have to register to get that option. That said, even in pdf format the table with weights is hard to read.

 

[Sail4beer]

I love cold molded boats but you have to fair every layer. Lotsa sanding.

That’s why pneumatic long boards or air files are so useful.

 

[Zonker]

Both built in the same yard and both vacuum bagged. The foam core boat came out at 8.835 kg/m^2, the cedar core boat 8.816. Cost wise they were about a wash (wood core $280 less for the hull materials, ~2001 era). Less material thrown away on the wood core.

So nearly the same weight and cost. Cedar core boat will have much lower resale unfortunately.

 

[harryproa]

On the viewer, the top bar on the right has a bunch of icons - you can download a pdf. You might have to register to get that option. That said, even in pdf format the table with weights is hard to read.

Tried that, got
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Took a screen shot and think I can read Table 3, the laminate for the foam boat. No surprise it is the same weight as the cedar one. Their resin ratios are not far off unbagged hand laminates and they allow a kg to wet the glass, which only requires 0.4kgs. Maybe they applied the foam seperately and this includes the bog layer, a step not required with strip foam or flat panel infusion.

They have 2,500 gsm on the outside of the core, which is way more than the monos I used to be involved with. If someone can provide a readable copy, I will do further analysis. Otherwise, I stick with the weight differences I mentioned earlier. Regardless, anyone building a boat should build, weigh, test and destroy a few sample panels before they start.

 

[Somebody Else]

Only if you use a suitable core material.
Even with bent foam, the butt joints between core panels will always have gaps. Those will fill with solid resin under vacuum infusion.

Why can't you just slather on microballoons or whatever same as hand layup before the next layer and the subsequent sucking?

 

[longy]

Because this will prevent the even/complete flow/infusion of the resin

 

[sam_crocker]

Tried that, got
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Took a screen shot and think I can read Table 3, the laminate for the foam boat. No surprise it is the same weight as the cedar one. Their resin ratios are not far off unbagged hand laminates and they allow a kg to wet the glass, which only requires 0.4kgs. Maybe they applied the foam seperately and this includes the bog layer, a step not required with strip foam or flat panel infusion.

They have 2,500 gsm on the outside of the core, which is way more than the monos I used to be involved with. If someone can provide a readable copy, I will do further analysis. Otherwise, I stick with the weight differences I mentioned earlier. Regardless, anyone building a boat should build, weigh, test and destroy a few sample panels before they start.

It looks to me like there is quite a bit less glass on the wood core boat (which makes sense if you read the article - Fox took the Cedar Core and basically assumed it was a unidirectional reinforcement running fore and aft). The wood boat has a total of ~56kg of glass and the foam ~128kg. Exterior glass topsides are 690 gsm and exterior bottom is 940. I don't know exactly how he broke up the layers in the foam boat but on the exterior it looks to be about 1240 gsm (plus some local uni reinforcement). On the interior about 1120 plus what I'm guessing is reinforcements around the keel area.

 

[Cheap Beer]

I wasn't talking about balsa core which is quite "normal". I was speaking of strip WRC or other wood epoxy boats.

And I was simply pointing out the contradiction in the perception of WRC or Doug Fir "wood" cored boats vs. balsa wood-cored boats. Both are wood, both are encapsulated with resin. Balsa-cored laminates are very dependent on lamination quality and any penetration of the skin for hardware, etc.
I believe the resale value discrepancy has more to do more with home-built quality issues than the actual material. There are plenty of cedar-strip composite boats out there still going strong.