FS18 - new build - foam&carbon fiber

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JoRoesler
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Re: FS18 - new build - foam&carbon fiber

Post by JoRoesler »

Thanks.
After all, it seems to me that the standard FS18 transom shape should work fine with a jack plate and a 20" motor. What got my attention in the first place is that in the picture section of the FS18 plan website there are many different versions of transom heights represented. Some of the more hard core looking builds (La Flaca anyone?) seem to have gone to great lengths to raise and modify the transom shape.

I'm very well aware of the fact that for boats this small there are no real weight savings to be achieved by using foam cores & carbon fiber laminates compared to using high quality marine plywood with thin protective glass fiber skins. Reason is that with a foam sandwich laminate the outside skin still needs to be thick enough to possess sufficient puncture strength for everyday usability. That leads to a laminate thickness (and weight) much greater than what's needed for panel strength alone. So what I expect to end up with is a boat of similar weight but incredible stiffness and durability. And a good portion of the needed positive buoyancy will already be built in via the 5/8" foam sandwich cores. But the building process will be much more complex, yes. Luckily New England winters are long.

Some of my other projects:
Phantom18:
https://photos.google.com/share/AF1QipO ... lGTG9FaU9n

Surf n' Turf:
https://photos.google.com/share/AF1QipO ... A5Nm9EY0xR
Video:
https://vimeo.com/200625657

R2AK/Angus RowCruiser:
www.KairosAdventures.com

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VT_Jeff
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Re: FS18 - new build - foam&carbon fiber

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JoRoesler wrote: Fri Dec 02, 2022 3:34 pm Some of my other projects....
Ok, I am officially a SLACKER!

Incredible work!

Just saw you're in Millerton, you ever hit Grey Fox out your way?
There are only two seasons in Vermont: boating season, and boat-building season.

Completed Paul Butler 14' Clark Fork Drifter
Completed Jacques Mertens FS14LS + 10%, Build Thread
Started Iain Oughtred Tammie Norrie

JoRoesler
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Re: FS18 - new build - foam&carbon fiber

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“Just saw you're in Millerton, you ever hit Grey Fox out your way?”

Not familiar with it. Do you mean the bluegrass place in the Catskills?

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VT_Jeff
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Re: FS18 - new build - foam&carbon fiber

Post by VT_Jeff »

JoRoesler wrote: Sat Dec 03, 2022 7:51 am “Just saw you're in Millerton, you ever hit Grey Fox out your way?”

Not familiar with it. Do you mean the bluegrass place in the Catskills?
Yes, Ancramdale originally, its since moved around a bit. Great fest!
There are only two seasons in Vermont: boating season, and boat-building season.

Completed Paul Butler 14' Clark Fork Drifter
Completed Jacques Mertens FS14LS + 10%, Build Thread
Started Iain Oughtred Tammie Norrie

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Evan_Gatehouse
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Re: FS18 - new build - foam&carbon fiber

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Carbon and foam are a general mismatch as elongation of foam is about 8% and carbon 1-2%. That is not to say it cannot be done, but even determining the schedule is harder.
This is not correct. Neither are elongating that much. You keep elongation lots below the carbon's breaking point. The foam is experiencing shear but not tensile/compressive loads except for direct local pressure. There are LOTS of high end racing boats that are carbon/foam. It is very common.

But you wouldn't use PET foam because it's material properties are a lot lower than PVC foams. Sorry about that. Thankfully the 5/8" foam is maybe OK for a small hull with relatively low speeds with a 25 HP outboard.
Carbon floats
No it doesn't. You may be thinking of Kevlar which has a density lower than typical resins.

But yes I agree it's usually very wise to vacuum bag it to ensure good adhesion to a foam core. For small parts I've done hand layup but a cored hull really should be bagged on the outside too. It should be easy to add a flange around the hull to get a good seal with the hull outside laminations too.

But how are you going to do the lamination schedule? Jacques has offered in the past if you purchased the materials from BBC but it sounds like you've done well on your own to source the CF.
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fallguy1000
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Re: FS18 - new build - foam&carbon fiber

Post by fallguy1000 »

Evan_Gatehouse wrote: Mon Dec 12, 2022 5:07 pm
Carbon and foam are a general mismatch as elongation of foam is about 8% and carbon 1-2%. That is not to say it cannot be done, but even determining the schedule is harder.
This is not correct. Neither are elongating that much. You keep elongation lots below the carbon's breaking point. The foam is experiencing shear but not tensile/compressive loads except for direct local pressure. There are LOTS of high end racing boats that are carbon/foam. It is very common.

But you wouldn't use PET foam because it's material properties are a lot lower than PVC foams. Sorry about that. Thankfully the 5/8" foam is maybe OK for a small hull with relatively low speeds with a 25 HP outboard.
Carbon floats
No it doesn't. You may be thinking of Kevlar which has a density lower than typical resins.

But yes I agree it's usually very wise to vacuum bag it to ensure good adhesion to a foam core. For small parts I've done hand layup but a cored hull really should be bagged on the outside too. It should be easy to add a flange around the hull to get a good seal with the hull outside laminations too.

But how are you going to do the lamination schedule? Jacques has offered in the past if you purchased the materials from BBC but it sounds like you've done well on your own to source the CF.
Well, kevlar floats, but carbon is hard to lay and determine fully wet and so carbon is hard to hand laminate well without vacuum, so I took a

The issue with carbon is it cannot take the same elongation as the epoxy or the foam and I stand by my comments. Anyone can read the datasheets for epoxies, foams, and carbon and compare these to verify my comment.

The reason carbon and foam are used together is the builders generally don't care about impact. But a dock impact with a foam and carbon hull leads to easier delamination than fiberglass and foam and for most builders here; it would be relevant.
My boat build is here -------->

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JoRoesler
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Re: FS18 - new build - foam&carbon fiber

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After some experimentation and measurements I have settled on a laminate schedule for the main hull panels.
The inside of the panels will receive 600-800 grams/sqmt (about 2 x 9-12 oz) of stitched carbon fiber fabric, kiwi-pregged & vacuum bagged. The 5/8" medium density PET foam first gets a surface preparation with 407 thickened resin. All wet-in-wet, of course. Silvertip resin all the way. The such prepared panels will be assembled stitch-and-glue style. The outside then receives the same amount of carbon and surface preparation, plus an 10oz woven glass fiber layer, but hand layup only. This works out to a panel weight of 1.18 lbs/ft2, about the same as when coating 1/4" marine plywood with 10oz of glass on either side.
Oh, and I have put together a set of carbon fiber trim tabs. At a fraction of the weight of their stainless steel alternatives.
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IMG_3843.jpeg

JoRoesler
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Re: FS18 - new build - foam&carbon fiber

Post by JoRoesler »

Engine choices:
20 HP four stroke, @110 lbs, or
30 HP four stroke, @160 lbs.
What top speeds would you expect in either case?

fallguy1000
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Re: FS18 - new build - foam&carbon fiber

Post by fallguy1000 »

What are you doing at the hull bottom/hull side interface and the hull side/hull deck interface(s)?
My boat build is here -------->

viewtopic.php?f=12&t=62495

JoRoesler
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Re: FS18 - new build - foam&carbon fiber

Post by JoRoesler »

fallguy1000 wrote: Thu Jul 13, 2023 5:17 pm What are you doing at the hull bottom/hull side interface and the hull side/hull deck interface(s)?
Gaps in the foam will be filled, and inside joints will be tabbed with 45/45 diagonal carbon tape.

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