Can you build a boat this way?

[Dreed]

Hi everyone, i´ve been thinking about building myself a boat in a few years in foam and epoxy, yet the ways of accomplishing this seems to pretty much be limited to either a female mold or a setup of frames to build around using strips of foam and getting them to form the hull, after that you have to flip the boat around and start ripping out the support frames and installing the bulkheads.
so my question is this, would it be possible to use the bulkheads instead of supportframes and build around them instead, i was thinking something like this: (and any input would be great)

[Raggi_Thor]

I think you will need some longitudinal stringers to get the curvature smooth.
If you use epoxy, you can have some wooden stringers.

[Dreed]

thanks for the reply raggi_thor
yeah i was thinking about that also, might be a good idea with stringers, some extra work though.
i´m not really sure how far apart bulkheads (not really sure if bulkhead is the proper term for what i´m thinking of either) are supposed to be mounted, but i was thinking that a lot of "bulkheads" constructed light (weaker) spaced aprox 25-30cm (10-12") apart should get the curvature about right? wouldn´t this create quite a strong hull also? if made correctly that is

I have another question also, regarding how foam core bulkheads are designed!?
I´ve seen quite a few on various pages, but i haven´t really got a good look at how they are laminated, i guess for the sandwich to work properly you´d have to laminate the whole thing but the strongest laminate in the same way as the hull?

[nero]

Your bulkheads can be spaced at 50 cm ... except at places where the curve tightens up. Of course that will leave the inside of the hull unusable. The hull would be too heavy also. Using temperary frames is the normal way of strip-planking on male frames.

Keep in mind that all your frames and bulkheads have to be positioned and secured in place before any strips or sheets are planked. This could be a challenge with foam.

I do not think it would be possible to wrap a solid, flat pannel over these forms and have a fair surface. The surface is curving in two directions. Scored foam pannels would work, but then you have to fill all the scores to have an effective core. Was reading somewhere about water wicking along score lines. Resulting in added weight and eventual core degradiation.

If you want to see how much tension is being induced into each pannel you are trying to stress, make your design in TouchCad. It will show each pannel with the amount of tension over the surface.

[nero]

Looking again at your post.

It seems that you are building a male mold. Then adding an inside laminate over a release film, to which you want to then bond a core foam pannel, and an outside laminate.

How do you plan to have your bulkheads touching the inside laminate when there is a mold layer inbetween them?

Also, How and when do plan to fair the surface(s)?

[Dreed]

hi nero, thanks for the reply
first of all, i´m not sure if bulkhead is the appropriate term for what i´m thinking of, therefore i´ll write "bulkhead" from now on oh and pictures i refer to as 1,2,3 and 4 are the first four pictures i posted

sorry if my pictures are a bit har to understand, there is no release film involved unless used in a bagging operation and in that case a top layer of tear off material for a nice surface to bond additional layers of glass to.
the procedure i´m thinking of is as follows:

first, cut and position "bulkheads", where "bulkheads" are formed to allow for the airex sheet (thin one) to be epoxied between two bulkheads creating a flat outside surface. (pictures 1 and 2)

second, if possible vacuum infuse material onto flat(curved) surface created by "bulkheads" and thin foam and add epoxy and glass until required thickness for inner skin of primary hull is aquired. (already done on pict 3)

third, epoxy thick sheets of foam to the outside of the boat, "outer" skin now becomes inner skin for the foam added. (pictures 3 and 4, 4 is what it should look like before adding the last layers of resin and glass)

fourth, epoxying outer skin of the boat to required thickness.

fifth, turn the boat over and epoxy the inside of the hull so you don´t have bare foam in the boat

it should look something like this:

[Raggi_Thor]

Take a look here, http://www.mboats.no/B18/B18_building_pictures.htm
If your frames and some longitudinal stiffeners ar cut with a cnc laser they can fit perfectly into each other's "slots", like an "egg crate" (I think it's called that). We did this with plywood, you can do the same with divinycell or simmilar (for three times the cost :-).

[Raggi_Thor]

Three times the cost and three times as much work :-)

[Dreed]

three times the cost, i already figured it would be ALOT more expensive than plywood for example, but three times the work?? really? instead of frames you´d just cut the "bulkheads" instead, wouldn´t that save some time? sure you´d have to laminate them on the sides, that would indeed take som time!

[nero]

One thing that doesn't seem possible is attaching the frames to the inside skin. That extra layer of foam will not transfer the fillet and biaxel covering over the fillet down to the inside skin.

Secondly, each inbetween 10mm pannel of flexible foam would not have straight edges. So it would have to be designed to flex and fit in.

It seems that you are going thru the problem of building a male mold and then loosing that mold by enclosing it into the boat. I decided on female frames to hold the core (wood) in place while I added the inside laminate and bulkheads etc. The hull then lifts from the frame so I can use it again. (catamarans have the pleasure of building two hulls. smile)

Still do not see how you will avoid a faceted stern to bow shape. But hey I'm only guessing. smile

[Dreed]

"One thing that doesn't seem possible is attaching the frames to the inside skin. That extra layer of foam will not transfer the fillet and biaxel covering over the fillet down to the inside skin."
i´m sorry, but i don´t understand what you mean? the inside skin would be whats covering the "bulkheads" and the thin sheets of airex would only be for getting a surface to work on, thinking about it, 10mm would be to thick for this perhaps?

"Secondly, each inbetween 10mm pannel of flexible foam would not have straight edges. So it would have to be designed to flex and fit in."
i´ve been thinking of this also, using some kind of plaster so create a good surface perhaps? (some kind of material that would work well with the properties of the foam!)

"It seems that you are going thru the problem of building a male mold and then loosing that mold by enclosing it into the boat."
yeah you´re probably right about that

"Still do not see how you will avoid a faceted stern to bow shape. But hey I'm only guessing."
perhaps stringers could be utilised to get a nice curve, only where neccesary though

[nero]

Will the 10 mm pannels be removed from the final boat? Maybe I am catching on that you are trying to seperate your form into blocks that could be removed and reused? This might be possible in that you could simply sandwhich roughed out preglassed bulkhead foam inbetween these hull shaped blocks. Give a go with a sander and then glass over everything.

If you radius the form blocks you could add the tabbing (or at least the fillet) just before you start laying in the glass.

Perhaps one disadvantage is that you will have a secondary bond between the inside laminate and the core. Also you could be entrapping air and the resin will not be able to degass. (holed core foam might eliminate this) And this is a blind layup. Are you willing to waiste some material on trials?