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How would you....
http://www.hobie.com/au/en/forums/viewtopic.php?f=13&t=16850		 Page 1 of 2
Author:  ncmbm [ Wed Nov 11, 2009 10:29 am ]
Post subject:  How would you....
attempt to get inside a 18 hull to rebuild it without a foam core?

I have cut several of these boats apart and am aware of how they are joined but do not understand how the top cap and hull layer together, at least that is how it appears. I realize that this is not reccommended but am interested in seeing if it can be done. My initial thoughts were to cut the top cap off. After further thought it would seem that removing the top cap would allow the hull to move out of shape, especially once the inner glass and foam have been removed. My current thought is to cut along the edge of the top at a 45 degree angle, angled in. That would give a solid surface to glass back to.

I have a boat that was left nose down for years. The original gelcoat has never been worn off the keels and the sails were as crisp as new. The hulls are garbage, soft from the crossbar all the way out on both sides but the top cap is solid. I already tried to repair as described but the hull continues to zipper apart, outer skin is solid.

Just for the fun of it lets hear your ideas on how to do this! I know it most likely will not work so don't go there :lol:
Author:  Tom Machette [ Wed Nov 11, 2009 4:25 pm ]
Post subject:  Re: How would you....
First I would build a jig to cut the top like you said.
Image
You would have to do the cross bar connections by hand and I would add rear port holes first so you can access the rear ones.
I would also first remove the Dagger board well with a dremel and a cut-off wheel.
If you are thinking about converting this into a F18 or lighter 18 you could change the dagger wells at this time as well. I would dremel along the top of the boat as apposed to a 45degree and also cut out the bottom also.

Good luck and take pics I wanna see it.
Author:  srm [ Wed Nov 11, 2009 6:21 pm ]
Post subject:  Re: How would you....
Quote:
do not understand how the top cap and hull layer together


The deck and hulls are built separately and then glued together in a jig (this can be seen very clearly on "red glue" boats since the red glue is visible at the hull/deck seam).

Quote:
After further thought it would seem that removing the top cap would allow the hull to move out of shape, especially once the inner glass and foam have been removed.


I think this would be a MAJOR issue. You'd more than likely have to build a jig that you can lock the hull into to hold it's shape before you start tearing things apart. The foam sandwich gives the sides of the hulls all of their rigidity, once you remove the inner layer of glass, you'll be left with only a flimsy, thin, outer layer.

So the question is, why do you want to go away from the foam core/sandwich construction? A solid fiberglass hull will probably have to be close to the same thickness as the current sandwich in order to be stiff enough. This would equate to a serious weight increase. I think you'd be better off replacing the foam core using sheets of divinycell and then laminating a new inner layer of glass. Probably first cut the core to the correct size, apply resin, then pull the core against the outer skin using screws through the hull skin, distribute the load using long strips of wood. You might also consider installing bulkheads for increased stiffness.

sm
Author:  ncmbm [ Wed Nov 11, 2009 7:54 pm ]
Post subject:  Re: How would you....
Thanks for both of the replies. I always thought the hulls were glassed together at the lip, glue makes more sense. Would it be possible to separate the two at the seam? I would also assume the dagger well is glued. Chances are the glue is stronger than the glass.

I had considered the weight issue of solid glass and strength. Really think some carbon and then e-glass or roven would be strong enough but I haven't consulted my glass guy on this yet. Carbon core should have similar strength if not superior to a foam core. I'm purely speculating on this, I'm no master glass guy or engineer. I just like tinkering with the boat and have some ruined hulls to play with. That and being layed off every other week!
Author:  RushMan [ Thu Nov 12, 2009 1:59 am ]
Post subject:  Re: How would you....
Have the side walls of the hulls delaminated ? If so it sounds just like the boat I recently purchased.

Photo of the hull before repairs
Author:  srm [ Thu Nov 12, 2009 7:06 am ]
Post subject:  Re: How would you....
Separating the deck/hull seam would probably be nearly impossible. The problem is that the glue is spread around the entire joint at least 90 degrees if not more. You could probably separate the vertical portion of the seam (the flange) but I don't see how you'd get to the glue at the horizontal area of the seam- you'd have to cut around a 90 degree curve.

Quote:
Really think some carbon and then e-glass or roven would be strong enough but I haven't consulted my glass guy on this yet. Carbon core should have similar strength if not superior to a foam core.


Would still be heavy and a poor use of materials. You wouldn't want a carbon fiber core. The whole idea of a sandwich construction is to have the high strength material on the outside and the light weight material on the inside (think I-beam). You'd be doing the exact opposite by putting the highstrength, heavy (compared to foam) material on the inside of the sandwich.

The only way I could see you sucessfully using a single skin would be if you installed a series of bulkheads. These would lock the deck, and both sides of the hull together.

sm
Author:  ncmbm [ Thu Nov 12, 2009 8:25 am ]
Post subject:  Re: How would you....
Rushman, this boat has way more damage than yours shows. The boat has delamination on both sides of both hulls from the front crossbar to the bow. If I messed with it much by flexing the skin I probably could zipper the delam all the way to the back.

SRM - you have a really good point. I like the bulkhead idea. I have another damaged hull that I could use as a template for the bulkheads. Would you think a horizontal bulkhead should also be incorporated? The europe boats have both vertical and horizontal bulkheads inside. The outer skin is quite substantial on the H18, do you feel it has enough integrity on its own with bulkhead supports or would you think it still needs some reinforcing? And, thanks for your input :D
Author:  srm [ Thu Nov 12, 2009 10:15 am ]
Post subject:  Re: How would you....
Hard to say, I'm certainly no expert when it comes to designing boats. I would think tieing the sides of the hull and the deck together would go along way towards resisting buckling of the hull sides.

The outboard side of the hull sees a strong tensile load and likewise the inside sees a similar compressive load. So basically, you need enough material on the skin that it can hold up to those loads. And the skin needs to be rigid enough that it doesn't buckle under the load.

So at a minimum, I would think that even if you eliminate the core, you still want to maintain the same overall amount of fiberglass. I have no idea what the current layup is, but for example, if it's 5 layers of glass outside, then 1/4" core, then 5 layers inside, then if you were to go to a non-cored construction, you'd still want to maintain 10 overall layers of glass. This would give you the same tensile/compressive stength as existing (but reduced buckling resistance since no core). Then tie the hole structure together with vertical bulkheads so that the sides can't flex (buckle).

I also think that, given how flexible the hulls are currently, you would want to lock the shape in as best as possible before cutting into anything. I would make a fixture that allows you to screw supports directly into the hull sides and lock them where you want them (you can use your good boat as a template for the fixture). Currently, the deck is providing the majority of the structure for your hulls. Once you cut it off, the hulls will be a floppy mess (I'm guessing).


sm
Author:  Tom Machette [ Thu Nov 12, 2009 11:25 am ]
Post subject:  Re: How would you....
I agree with SRM, also I think that a 1 horizontal and many vertical bulkheads would be best.

You could also use the hull as a mold and lay carbon on the out side with a wax or somthing to get it to release from the actual hull, then you can lay foam and more carbon on the inside of the carbon shell and make a whole new hull.
Author:  jerin513 [ Thu Nov 12, 2009 11:51 am ]
Post subject:  Re: How would you....
I have also thought about doing this and put a little thought into it as well. I would just build a wooden frame with stations every foot or so to screw the top of the hull into and a cradle for the keel (also wood). Every foot I would have horizontal 2x4 and two vertical 2x4 posts coming up to the sheer line, spaced the width of the beam. Then i would run a 2x4 on a 45 on each post to keep it from flexing. Set the cut hull in the form and cut out the foam in the areas for screws to go into the stations and screw them in so they are flush with exterior skin. Then I would rip out all the interior glass and foam, sand it down, cut new foam, and glue it in with epoxy. Then you can glass over that with e-glass, s-glass, or carbon. I would not build a boat with just skin on bulkheads. You could lay wooden frames in the inside and do a skin on frame method but the foam core sandwich is superior. Not only do you have an infinite number of I-beams but you have two separate layers of glass (in case you get T-boned and the first one gets punctured). Bulkheads are a good addition to either of the methods, they add overall strength and rigidity, but cannot take the place of a frame. If you tried to make the boat strong by using a bunch of glass it would not only weigh a lot more but it would cost a lot more too. If you built it with a thin skin and bulkheads, the bulkheads would actually cause it to crack. Say you are sliding it on a trailer for instance, as the rollers roll down the hull, the skin will flex a little bit and as it approaches a bulkhead, the bulkhead will be stiff which will cause high shear force on the skin. That's where it will crack, right before the bulkhead.
My opinions:
Big project? Yes
Worth it? Probably
Skin on Bulkhead? No
Author:  jerin513 [ Thu Nov 12, 2009 11:57 am ]
Post subject:  Re: How would you....
I think we are talking about two different things now, a bulkhead is a plane that runs horizontally and vertically. Like a wall. Maybe you are talking about stringers or frame members?
Author:  srm [ Thu Nov 12, 2009 11:58 am ]
Post subject:  Re: How would you....
Making a whole new hull is another option (hey it's your time and money we're playing with). You could use your good hulls as a plug for the mold. You would want to prep the "plug" hulls really well by filling in and fairing any scratches etc. And then be sure to use plenty of release agent. I would definitely NOT use carbon fiber for the mold though. Major waste of very expensive material. Glass fiber would be totally fine and is what's commonly used and easier to work with. Carbon would be cool for the actual hull though. Would be very stiff if done correctly (most likely would want to vacuum bag).

Actually, if the top decks are still good on your bad hulls, you could probably cut them off the hulls, grind away the flange down to the glue seam. Then you could re-use the decks with your new hulls.

Of course any of these "repair" options is going to take a serious amount of time and money. I suspect that if/when you complete the project you'll have a good understanding as to why Hobie wants $7000 for a new pair of 18 hulls.

sm
Author:  Tom Machette [ Thu Nov 12, 2009 12:18 pm ]
Post subject:  Re: How would you....
jerin513 wrote:
I think we are talking about two different things now, a bulkhead is a plane that runs horizontally and vertically. Like a wall. Maybe you are talking about stringers or frame members?


nope I ment bulk heads

Quote:
the term bulkhead applies to every vertical panel aboard a ship, except for the hull itself.
from wikipedia
Author:  ncmbm [ Thu Nov 12, 2009 12:26 pm ]
Post subject:  Re: How would you....
I really appreciate all of the input. Let me give some additional details so you will understand that I am not crazy. I have a good buddy that ran a boat repair shop, he went out of business and still has rolls of fiberglass cloth and carbon. So the cost will not be as crazy as it could and I am layed off every other week until the end of the year at least. I just finished rebuilding a '75 bass boat and am currently rebuilding an '82 S-10 Blazer. So this project is another diversion for me.

Again thanks for all the input.
Author:  RushMan [ Thu Nov 12, 2009 10:58 pm ]
Post subject:  Re: How would you....
ncmbm ..... Can you post a photo of the damaged hull. It might make it easier.

By the way... The hull I posted the photo of had 10' x 1' of foam replaced on the inside and then it was put back together. It is not perfect but it will do for what I plan on using it for. The other hull was worse !
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