Hull Extension

[tomherrick]

Some of you may be aware a repair project that got out of hand... A rotten transom repair turned in to a four-foot extension project. An earlier thread on this subject can be found at Holy Nip-N-Tuck Boatman (http://www.c-brats.com/viewtopic.php?t=11925&postdays=0&postorder=asc&start=0).

A quick background on the project: I developed plans using FreeShip and the exported files were reviewed by a Naval Architect who gave them a thumbs up. He also referred me to a Marine Surveyor in Louisville who has provided good advice and will inspect the project at various stages to ensure that all is being done properly. The surveyor suggested using C-Flex (http://seemanncomposites.com/index.php?option=com_content&view=article&id=22&Itemid=22) rather than building traditional forms; it's in the shop awaiting its turn. C-Flex will be stapled to the plywood forms you see in the pics and epoxied; the rest of the fiberglass will be applied directly over the C-Flex which becomes part of the boat.

To fiberglass and gelcoat the hull exterior, I flipped the boat - which was a project in itself. A coupla pics to show the technique are below. The main thing I learned is that it'll go better next time with three come-alongs simultaneously turning each wheel; the reverse flip will go much more smoothly.









Now that the boat's upside down in the shop I've run into a couple of problems. I was planning on using the existing boat as the template for the extension. The port running strake isn't parallel with the center or starboard strakes. Further, the chine on the port side is 6 5/8" from the port running strake; it's 6" on the starboard side. The simplified drawing below shows an exaggeration of my description; the view is from below.



I'm not too concerned about the non-parallel running strakes on the existing boat because they'll be out of the water when planing and I don't think will have all that much effect at displacement speeds. The strakes will be parallel in aft 7-feet that I build (I cut off an additional three feet due to old hull problems). I wonder about the chine, though. If the two sides of the boat aren't parallel are they likely to steer the boat? The difference would be 5/8". Is this a mountain out of a molehill, or something I should be concerned about?

[thataway]

Neat and interesting project. C-Flex is still alive and well. It was one of the first glass building techniques. (See
http://www.ericgreeneassociates.com/images/Bill_Seemann.pdf )

Are you using the 39 or 65 C-flex? The only "problem" with C-flex, is that you may have to fair it a bit more than some other techniques and might be slightly heavier --it is very strong, and a good technique.

A couple of years ago I looked at a Caracal which was owned by an engineer who works at the current SCI yard in Gulfport, MS. They do most DOD and commercial projects. There were a number of C-flex boats built in Calif. yards which I frequented from the 50's thru the 80's.

It is not at all unusual to find that production hulls are not symetrical. Some boats even have a list because of this. This is usually due to an error in lofting. The 5/8" difference should make absolutely no difference.

Good luck--I thought that one of our problems was going to be headroom in the garage! We all will be interested in seeing your photos as the boat evolves.
Anyone reading this thread needs to look at his previous posts!

[tomherrick]

Thanks, doctor for the favorable prognosis regarding the unsymmetrical hull. I've got one leg longer than the other and don't walk in circles; may be there's a correlation here...

I'm using the thinner C-39 (0.80") so that the primary thickness is from the 1708 stitched biaxial/mat. The forms are 12" o.c.; closer than Seemmann's recommended 14" spacing. I'll let the epoxy cure on this first, then fair and continue with the biaxial laminations. I'd be concerned that the weight of the additional laminations prior to cure might cause the "C" to flex more than I want. I like this epoxy: U.S. Composite's 635. I've used West System for over 15 years on old house restoration and like it, but the cost...

[BrentB]

amazing
You are making progress

[tomherrick]

Thanks, Brent. Progress measured in geological time, no doubt, but progress just the same. Taking the day off the boat project to do some cooking and reflect on how I'll proceed after Bob's reassuring comment; several options available.

I'm really looking forward to this boat. More than eight feet of cockpit from cabin door to lazarette...! Elbow room for six back there with sundowner elbows extended. A big back porch or living room depending on the weather. And, lots of storage...

[tomherrick]

Moving forward with the woodworking; rounding over plywood core edges and reshaping the C-Flex forms. I thought I'd done a pretty good job when the boat was upright, but with it upside down I could tell right away that the profile wasn't very accurate. It would look like a C-Dory from a quarter-mile, but... I have the starboard side re-done and now it's what I had in mind with that concave profile on the top 'plank' and all the 'planks' tapering to the transom. I took some pics.

[tomherrick]

A quick update for those following this project.

Forms for the C-Flex are finished on both sides of the hull. I've also rechecked and made slight adjustments to the old/new sole to ensure they are in the best possible alignment. That was tough since the old hull is pretty wavy; even the running strakes vary in height from 13/16" to 1-1/8".

To keep the C-Flex and subsequent fiberglass layers from being epoxied to the forms, they're covered with wax paper.



Then I started with the C-Flex. There's a bit of an art to applying this stuff to a form and get it to come out looking right. Bill Seemmann had recommended not overlapping it onto the scarph joint and I found out why; it causes the section between the first two forms to deform. I cut off the overlap and all is well.



First 'plank' is on. I didn't like the way the C-Flex formed around the 'plank' offsets on the forms. I ended up using a marker to identify one of the rods at the old/new joint and re-stapled the C-Flex keeping that rod aligned to the outside of the plank corner. Much, much better...

[BrentB]

How exciting

[tomherrick]

Done for the day. Tomorrow, the port side gets the same treatment - then it's epoxy time. You're right, Brent - I'm definitely excited. It almost looks like a boat...

I can see what Dr. Bob meant about C-Flex needing more fairing than other approaches; it will. I'm surprised, though, at how well this material conforms to the forms; once one gets the hang of how to apply it...

[thataway]

Looking good! It sounds as if you are going to epoxy the C Flex, and then do any partial fairing before the 1708. Since you are using epoxy--are you going to paint the boat--or attempt to bond gel coat? I also assume that you will have a long scarf inside of the hull, after turning the boat over again--to finish the 1708 on the inside of the boat.

[tomherrick]

Ahhh, to paint or gelcoat? It seems to be a Ford vs. Chevy, Mac vs. Windows question on all the forums and from the vendors; either it's not chemically possible and certain to fail or it's done all the time by reputable folks with good results going back many years.

I've not made a final decision as yet. I don't have a need or interest in a bottom paint, but my understanding is that linear polyurethanes are topsides paints and will deteriorate in water after some time. I've not found any definitive information on how long continuous submersion may be acceptable with an LP paint; a week, a month, longer? I do plan on several coats of epoxy below the waterline on the entire hull to reduce the potential for blisters in the event that this boat is ever afforded a slip. But, it seems to me that gelcoat would be the way to go. If one were to believe those who use gelcoat over epoxy, there are important steps that must be followed to ensure positive results; the most important being two weeks of curing after final fairing and prep. From my conversations with those who say gelcoat can't be used over epoxy, they tend to back off that position a bit when I say that it'll be de-blushed, sanded, and cured for two weeks. It seems that the main reason they're against it is that too many customers spray gelcoat directly over epoxy that still sports the amine blush and they don't want to have their product badmouthed due to poor workmanship. Further, LP is much more expensive than gelcoat and I'm on a budget, although I want the results done right. My gut instinct is to follow the proper steps, spray on gelcoat to 30-microns and sand, and sand, oh, and sand...

At the suggestion of my marine surveyor, I will be installing two (per side) hollow hull stiffeners that will also serve as channels for wiring, propane lines, engine control cables, etc. Details to be determined later. Those hull stiffeners and the entire interior of the hull from the cabin to the transom will have two laminations - perhaps more - of the 1708. I don't plan on scarph joints on the interior; just overlaps that will terminate at the transom and tapered at the Alaska bulkhead. The interior cockpit sole will get four layers of the 1708 tapering up the hull eight inches; two layers all the way to the gunwale.

At the suggestion of a local naval architect who reviewed my drawings, I may also install supports that run from the gunwale to the sole out of fiberglassed plywood to ensure that the gunwale doesn't flex. These would go in front and behind the saddle tanks; they'd be useful for mounting tank covers as well...

It's been a long week today; sorry if this is confusing...

[digger]

Love the project, and really want to see the outcome...having a hard time waiting! I hobby on boats all the time but your project is about at the same level as boat building (which I'd love to do, but don't have the patience to complete so long a project}. Keep up the updates, and the progress. Really want to see your boat in the water. Ron

[tomherrick]

Thanks, Ron. You and me both want to see it in the water. I don't know if it's so much about patience; more because I didn't have any experience with this kind of work and I wanted to see it stay on top of the water... I've learned lots and have lots more to learn before it's done, but I think when it's done it'll be worth it.

I'd love to do some boating in your neck of the country. My grandfather homesteaded near Quincy, WA (WSW of Ephrata). I've always liked the area between the Cascades and Idaho Rockies. Looks like some great lakes to explore up there...

Oh, if the wait is just killing you, I could use a hand down here...

[thataway]

From West Systems:
"In repairs above the waterline, gelcoat applied over properly prepared WEST SYSTEM epoxy has a great track record. Many boats have been repaired this way and are performing well in a variety of climates. Boats that are dry sailed or trailered have also had good success with gelcoats on underwater epoxy repairs. Concern about adhesion occurs in situations where boats are in the water constantly and need to have a high level of finish on their bottoms that requires gelcoat. Such a situation might occur with a boat kept in a pristine lake where antifouling paint is often not used. Since the polyester gelcoat is not very good at preventing moisture from permeating through to the laminate, there has been a concern that, over time, the gelcoat will detach from the more moisture resistant epoxy layer.

Understanding the materials
Polyester resin laminates achieve their highest strength when the bonds between layers of fiberglass are chemical or primary bonds as opposed to mechanical or secondary bonds. The manufacturing process for polyester boats has been developed so that a chemical bond exists between the gelcoat and the laminate. When a polyester boat is built, polyester gelcoat is first sprayed onto the mold surface. The first layer of the laminate is then applied to gelcoat, which has not completely cured. The two layers eventually cure together with a chemical bond between them.

Applying gelcoat to a cured laminate relies on a mechanical bond. Because of the difference in curing chemistry, it is not possible to achieve a chemical bond between epoxy and polyester gelcoat."

System III also makes a specific tie coat for putting gel coat over epoxy resin.

The LP will not do well with long time in the water. I personally would paint the bottom.

Also LP is much easier to maintain than gel coat in dark colors--ie use LP for the dark stripe and accent--that will give you at least 10 years before it needs to be redone.

I was taught in boat building with fiberglass if there is a hard place, you want to layer out the interface. I suspect that the C FLex and epoxy will be less likely to flex than the original laminate. I personally would taper out the overlap on the interior of the hull. My impression is that your "addition" will be considerably stronger than the original hull. It will be interesting to see what the weight per sq foot is in comparison--my guess is that your new construction will be heavier.

[tomherrick]

Thanks, Bob. I've got that West System article; it's what makes me think that the nay-sayers are more interested in CYA than making something work. Those Gougeon brothers, et al, are no slouches when it comes to the technical aspects of epoxy and boats.

I hadn't considered LP for the stripes... ...hmmm... My wife will be happy to hear that idea. You shoulda heard her ideas for the color scheme... ...but, then, she's an artist. I think she'll live with the off-white as long as she can get an interesting color(s) for the stripe(s). Good idea - thanks.

T