Boat Builder Central - Builder Forums

Hello,
I'm going to build a new FS18, starting some time next year. I happen to have come across lots of free dry carbon fiber fabric (recycled/production waste), and am planning to use it. I purchased a load of 5/8" recycled PET foam, and will be glueing it all together with the System Three Silvertip resin. The inside skins will be vacuum bagged onto the individual foam sheets (1st step), the outside skin will be hand layup. I will take my sweet time, as I have a well functioning PH18 at hand. Power will be a 25HP four stroke.
Questions for other builders:
What is the point of using a 15" vs. a 20" shafted outboard? Do you need the one or the other if you also plan to use a jack plate? Do you need to increase the height of the transom if you are planning to use a jack plate? Thank You.

Short shaft or 15" motors are not readily available. The problem with them on a larger boat is backing and launching,

Backing into oncoming seas on a short shaft transom results in water coming over the back and into the boat. It happens on 20" shafts transoms as well, but lots less.

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.

If you build it, we'd love to see it blogged here.

I believe the fs18 calls for 20" engine. Keep it as designed. If you have a 15" shaft on hand, that's a different story. I had to run a motor well since the deck sits at around 15". May be different with a jp.

Carbon fiber is over rated. There's much more to carbon fiber. These carbon/ kevlar boats are more of a sales pitch vs reality. I am a big fan of just 10oz cloth. Much of jaqs designs call for 12oz biaxial.

I am also a big fan of basalt cloth. It has similarities to carbon/ kevlar strength and puncture resistance. It lays up better and much less cost.

If you use carbon fiber on the outside, you need to vacuum bag it also to get the correct adhesion to the foam. Carbon fiber tends to float. What thickness is the carbon fiber, you may need more than one layer or a layer of fiberglass for strength. Tom

If possible, measure your motor before cutting your transom to final height. May not matter so much with a jackplate but my 20" transom was surprisingly short for my 20" motor.

Thank you. So the question becomes: If I know that I’m going to use both a jack plate and a 20” shaft motor, do I need to modify the standard FS18 transom design?

Fair question but outside my paygrade, ill defer to those that use them.

I’m not familiar with the FS18 design enough to say for sure, but my suggestion is to leave the center section of the transom “long” and then trim once you flip it over and can mock it up or set things in place on the mostly finished hull.

With a jackplate you can bring the cav plate slightly above the bottom of the hull so you want to make sure you have it set up where you have a little up/down play in the plate.

I made some miscalculations when I went from a short shaft with PT-35 tilt and trim bracket to a long shaft with jackplate and my jackplate is maxxed out to have the motor where it needs to be.

JoRoesler wrote: ↑Thu Dec 01, 2022 11:55 pm Thank you. So the question becomes: If I know that I’m going to use both a jack plate and a 20” shaft motor, do I need to modify the standard FS18 transom design?

No need to modify the transom. I am installing a jack plate on my FS18 with a 20" shaft 25 HP Suzuki. The jack plate will mount right below the level of the aft deck. I went with a Bobs Versa Jack Plate, manual but has an option to add the hydraulics. (no need for hydraulics IMO since the FS18 doesn't have a tunnel) It has a 6" set back. I also plan to run a tiller extension.
I also agree with some of the others when it comes to carbon fiber. It sounds fancy but I don't believe it will add much benefit to the FS18. As you already know, from your previous build, these boats are already lightweight by nature and build method. Carbon fiber and/or foam core will not give any significant weight savings over the coarse of this relatively small boat. It will definitely add to the complexity of the build. That being said, if you already have the materials and are doing the build this way in order to try something new then go for it! I will definitely be eager to watch this build. I would, however, have Jacques help you out with the lamination schedule. Using Foam Core will definitely change things.
Best of Luck!!!
-Reid

Good info Reid!

You will also need to layup those panels flat with some 4oz/ 6oz. If you don't lay these up prior to installing them on the frames, you will get a lot of sagging.

I would also recommend getting a lam schedule from jaq. Builds in foam core I've done, I use 4 layers of 10oz outside and 3 layers inside. But take jaqs advice over mine.

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

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?

“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?

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!

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.

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.

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.

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

What are you doing at the hull bottom/hull side interface and the hull side/hull deck interface(s)?

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.

JoRoesler wrote: ↑Thu Jul 13, 2023 2:37 pm Engine choices:
20 HP four stroke, @110 lbs, or
30 HP four stroke, @160 lbs.
What top speeds would you expect in either case?

I could give you those numbers. if I knew what the boat would weigh as it left the dock, people gear etc. Which brand of motor will you be using.

Tom

TomW1 wrote: ↑Fri Jul 14, 2023 11:28 am

JoRoesler wrote: ↑Thu Jul 13, 2023 2:37 pm Engine choices:
20 HP four stroke, @110 lbs, or
30 HP four stroke, @160 lbs.
What top speeds would you expect in either case?

I could give you those numbers. if I knew what the boat would weigh as it left the dock, people gear etc. Which brand of motor will you be using.

Tom

Let's assume 350 lbs for the boat, plus engine, plus 400 for people and equipment. The boat is 18 ft long but only 54" wide.

JoRoesler wrote: ↑Thu Jul 13, 2023 6:06 pm

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.

That is not the proper hull bottom to hullsides interface.

The foam can crush. Now, at the engines you've chosen less an issue. But. The way to avoid it is well published.

JoRoesler wrote: ↑Fri Jul 14, 2023 11:46 am

TomW1 wrote: ↑Fri Jul 14, 2023 11:28 am

JoRoesler wrote: ↑Thu Jul 13, 2023 2:37 pm Engine choices:
20 HP four stroke, @110 lbs, or
30 HP four stroke, @160 lbs.
What top speeds would you expect in either case?

I could give you those numbers. if I knew what the boat would weigh as it left the dock, people gear etc. Which brand of motor will you be using.

Tom

Let's assume 350 lbs for the boat, plus engine, plus 400 for people and equipment. The boat is 18 ft long but only 54" wide.

Jo about 30mph for the 20HP using Yamaha specs, you gain only 4mph to 34mph with the 30HP Yamaha. Jacques does not recommend more than 25HP which would put you at around 32mph. The 20 comes with a prop the 30 will need you to add a prop.

Tom

Some progress has been made:
/Users/joeroesler/Pictures/Photos Library.photoslibrary/resources/derivatives/D/DD1680E4-B438-47AE-B364-954B505FEB24_1_105_c.jpeg

More pics:

[img]https://photos.app.goo.gl/1ojkSs8R2m2KPo4F9/img]

[img]/Users/joeroesler/Pictures/Photos Library.photoslibrary/resources/derivatives/5/58C0A2C1-C307-4BBB-A925-FACCAE641BB7_1_105_c.jpeg/img] Preparations for the jack plate.

/Users/joeroesler/Pictures/Photos Library.photoslibrary/resources/derivatives/7/7EAE8A78-4583-4C1D-8B92-AD4B5EB53B54_1_102_o.jpeg

And then there appeared a boat...

Users/joeroesler/Pictures/Photos Library.photoslibrary/resources/derivatives/1/1B9AF697-E043-4553-896E-7EC9A31198B6_1_105_c.jpeg

That's looking good!!

I have also convinced myself that a Yamaha 25HP is the right engine for this. I'm going with tiller steering, and a grab bar in the center of the open cockpit.