Foam sandwich plans

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jacquesmm
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Foam sandwich plans

Post by jacquesmm »

Many ask for a foam sandwich version of my plans. It is correct that many of my designs can be built in foam sandwich and I know the material well: I designed for foam sandwich well before plywood-epoxy.

A good foam sandwich version of my designs will have the same hull shape and be close in weight but many parts must be recalculated.
The foam sandwich boat will use more layers of glass, use a different type of resin (SilverTip), specific types of foam. The hulls will be thicker, the framing spaced more widely and the gull assembly different.
I want to redesign the boats for foam sandwich and supply good building instructions.

Except for a few boats (PH15, LB26 and maybe some others that I forgot), there are no official plans for foam sandwich boats. For some designs, I have given specs to a few builders but I prefer to offer complete plans for foam sandwich versions with a nice shop manual. You can't simply switch the core type, there is much more to it if you want it done right.
I am almost ready with a very detailed foam sandwich shop manual for small boats but I have to work more on the layout, change some pictures then proofreading. It is already between 35 and 100 pages depending on the size of the drawings.
There will be more than one manual.
The first one will cover small boats built without a jig.
The second one will be for small to medium size boats built on a jig. Later, the third one will be for large units.
I started writing them as one manual 2 years ago and it was confusing, I had to separate them in 3 books with many common parts.
The plans will follow. There are differences: the framing is different, there are many high-density inserts and because of the thickness of the core many dimensions change.
In the mean time, this the traditional method to build in foam sandwich:
http://bateau2.com/howto/foam1.php

The manuals that I am working on will show a faster, easier method close to our plywood-epoxy boats.
Jacques Mertens - Designer
http://boatbuildercentral.com

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WildThing
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Re: Foam sandwich plans

Post by WildThing »

Hi Jacques, I just came across a post of yours from 2018 re: foam sandwich plans & manuals. I have a set of your PH16 plans in wood, but would very much like to explore a PH18 in a "no wood", foam core structure. Did you ever get these finished and published and I just haven't come across them yet? Thanks for the great designs and plans you've put out - you've inspired a whole cadre of builders to take the plunge! Jeff Wirs, Margate, FL

fallguy1000
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Re: Foam sandwich plans

Post by fallguy1000 »

The plans were never done in foam. They would require a n/a and composites engineer to draw.
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viewtopic.php?f=12&t=62495

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cape man
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Re: Foam sandwich plans

Post by cape man »

Unfortunately Jacques is no longer with us so the plans we have are it until someone else picks up where he left. Jacques ' brilliance for me was taking classic and popular types of boats and producing simple, light weight, and affordable plans for plywood, epoxy, and fiberglass construction that allows for folks like me to make a boat. The PH18 as presented is an awesome boat, and the "no wood" crowd doesn't understand that it's all about sealed and unsealed wood, and the type of wood (i.e. BS1088 ply)
The world always seems brighter when you've just made something that wasn't there before - Neil Gaiman

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Re: Foam sandwich plans

Post by fallguy1000 »

After Capeman replied, i realized my reply was poor.

I will tell you and everyone here that I am a foam boat builder and most of the time I was building in foam; I dreamt about how much better it would have been to build in plywood. Hulls are formed and shaped in weeks versus months or years. Plywood is so much faster. Most of the builders here may have learned that watching my build of 12,000 hours for a dual hull 32' cat.

For the PH series of boats; they cannot be made in foam without paying attention and modifying the hullsides to bottom and hullsides to gunwhale interfaces. This is because foam core will crush at high G forces which occur with boats hitting waves at high speeds. Foam cores typically used on sides and bottom do not have enough crush strength and the hullsides will crush the top or bottom of the boat unless that interface is made special with solid glass and tapers to foam. This requires some sort of jig or mold.

The PH18 would easily take around 12 months to get the hull laid up in foam; something you can do in plywood in at least half the time.

Foam has some advantages over ply on frame. In ply on frame; the inside of the ply is usually not sealed and water ingress will rot frame and ply from the inside. But the boat designs here are not ply on frame afaik, but monocoque.

For monocoque construction, plywood is a miracle material. It is stiff enough to mostly hold its shape and presents as an alternative to solid frp which must be build over a mold that can take years to build before starting the boat. The hull is completely encapsulated. As the owner/builder, you can take extra measures on thru hulls and encapsulated them in epoxy putty to maintain the encapsulation of the entire hull. Same with screw holes. Or you can use other cores and make mounting pads for things you want to screw on, like a transducer. This keeps the hull free from almost all penetrations.

When you are done, you don't have a wood boat. You have a composite hull, made with fiberglass and epoxy with a plywood skeleton.

These boats are very hard to beat. After two hip replacements, I may not build again, but if I get the notion; it'll be a +10% PH22 in plywood. Or a small foam ultralight dinghy to push weights down, but only maybe a 10 footer from Mertens td3 plans that can be used as a lifeboat on my cat.
My boat build is here -------->

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WildThing
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Re: Foam sandwich plans

Post by WildThing »

Thanks guys. I came across another post later on re: Jaq passing away - he'll be a sorely missed source of info and expertise to all who decide to delve into the boat-building hobby.

I've had a set of plans for the PH16 sitting on the shelf for way too long and am finally getting close to beginning it, so thanks for expanding on the ply vs foam conundrum. I am curious though if anyone's "calculated" the feasibility of using one of the "plywood equivalents" ie., Coosa or Kay-Cell or such? I have no qualms about using good plywood, just considering the resale value for when the next project comes along. SO many buyers just don't have a good understanding of a properly built and maintained wood/epoxy boat.

Thanks!

fallguy1000
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Re: Foam sandwich plans

Post by fallguy1000 »

You would need to do a side by side engineering analysis.

I can help if you post the tds for okume as specified for the boat and coosa here.

One thing is flexural rigidity; will coosa stay in dev shape on the jig..?
My boat build is here -------->

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TomW1
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Re: Foam sandwich plans

Post by TomW1 »

There are two sets of plans for the PH15 one in ply and one in foam. Tom
Restored Mirror Dinghy, Bought OD18 built by CL, Westlawn School of Yacht Design courses. LT US Navy 1970-1978

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