Mould or jig

[Banshee Ambulance]

Is there any significant advantage to vac bagging an all glass shell over just using a jig?

EDIT- Sorry, badly worded. I know it is technically possible to make a glass boat off a jig but is vac bagging onto a male mould really the best way of doing it these days? Is it really worth the extra work? I know it would be for a carbon boat but what about a glass one?

[rich_taylor]

Do you mean a Male mould, also called a "Buck" or "plug" (such as the current E5 tool).  A female mould, such as the Daemon project / subtle knife or forming foam over a series of pattern frames and stringers (like Velocipede?).

[Phil Alderson]

Vac bagging should give you better consolidation and better glass to resin ratio's so should give you a stronger lighter hull. As you are likely to be heavier using all glass than using carbon it is probably worth while

There is an extra cost for the consumables and for building the mould, weather this extra money would be better spent on more carbon or go fast bits would be hard to say. getting a loan of a pump and using alternative consumables will help.

[phil_kirk]

I'm pretty sure you can't vac bag onto a Jig of frames and battens but you can vac bag using a male mould (plug) or a female mould.

A Jig would as phil A says take less time to put together and cost less to produce but is still a significant peice of work.

I haven't attempted either but would expect that hand laying large areas of cloth onto foam attached to a jig will require more skill to get good contact than vac baging onto a mould. With hand laying you can take a bit more time over it as you butter the foam, lay and wet out cloths and apply peal ply along the length.  You will use more resin to achieve wet out and will remove less with the peal ply.

The balance of cost, time and value between the diferent methods would be interesting to calculate.  if you can produce a boat to weight with sufficient stiffness to provide the performance of  a modern boat you haven't really lost much.

[Banshee Ambulance]

Mould it is then:

[dwlee]

If you are making 2 or 3 hulls then make a full male mould so you can vacuum the foam down to the inner skin, thus saving time of having to attach the foam the the jig. If you are making a one off hull just use a stringer jig (preferable female). If you're making more than 3 hulls make the first hull on a stringer jig and when also most finished take a female mould off the hull.

In terms of weight I have found that for a skiff the order from lightest to fattest is stringer, female, male mould if you are careful and know what you are doing. The reason I say that a stringer mould will produce the lightest hull is that you don't need to use as much bog glueing the foam to either the outside or inside skin. This gives a weight saving in the order of 200grams per square metre. On such small hulls vacuuming the inner and outer skin is a little overrated (but still beneficial) as the laminates are so thin you can get very good resin ratios by hand if you can take the time and know what you're doing.

[Will_Lee]

I've never seen a female stringer jig. Can you post a picture please?

[dwlee]

This is the best photo I could find, strip plank Paulownia in a female mould. The biggest beneift is that you can fit the internal frames and floor before taking it off the mould making it much easier to deal with as it isn't flopping all over the place.

[Phil Alderson]

That makes a lot of sense, it would probably be easier to fix the core in place to.

If you made the sides a bit taller than normal, could you vac the outer skin in place?

[dwlee]

Fixing the core in place is still a pain . It might be possible to vacuum the outside skin, but it would be difficult to get a good seal for the edge of the bag and the inside skin is highly likely to have some porosity under a vacuum given how thin the skin is and the gaps in the foam that aren't filled completely. If you were going to try this you would want to try a dry vacuum run to make sure it seals well, holds a vacuum and the bag tension does not distort the topsides.

[roland_trim]

Confused. I'm still can't see how a female mould or stringer jig could result in a lighter boat? Whilst I would conceed that the argument is almost pointless and at most a few hundred grams, I'd love to hear more of the explanation.

The mental stumbling block for me is the corners. For EJ the majority of our resin went into wetting out the cloth and very little into butter or foam joints. The key to the foam being to do it in several hits and place the laps in such a way that the foam that is stuck down provides a butt or can be sanded to ensure you have fly-by surface. This also makes placing the foam a doddle, as where they overlap you dump it on and sand off the excess bog/foam when it is set. However the real drag on this method is to ensure you actually get the shape you intended at the chines. I still can't think of a way to do this on a female mold and would love an explanation of how the corners do not just become a mass of bog? Is this because you are working in Nomex?

[dwlee]

The weight difference between a full female and male moulded hull is not much and is dependent on how well the foam is pre-fitted. The process for a fully moulded hull we generally use is;
1: Final prep of mould, lay up skin and allow to start to gell, apply butter (approx 400 grams per metre) to pre-fitted foam and vacuum.
2: Remove bag, fair foam/bog, prime foam (approx 200 grams per metre), lay up skin and vacuum.
3: Female - remove bag and release hull, fit frames  etcwhile still in the mould
3: Male - remove bag and apply fairing bog and then fair hull
4: Male - remove from mould and fit frames etc.
Weigh difference is in the fairing bog (not much if you're careful).

With a stringer mould;
1: Attach foam and prime foam with bog (approx 200 grams per metre)
2: Lightly sand foam and lay up skin
3: Female - fit frames etc
3: Male - build retaining cradle
4: Remove from mould, fair foam and prime foam with bog (approx 200 grams per metre)
5: Lightly sand foam and lay up skin
6: Male - fit frames etc and apply faring bog to the outside of the hull and fair
6: Female - Apply fairing bog and fair the hull

Weight difference between the stringer and full mould is aprox 200 grams per metre that is required to glue the foam to the skin during vacuuming resulting in the weight difference of approximately 1.2kg. You can apply less butter to glue the foam, but you start to run the risk of not getting a good bond which can reduce the hull life span due to delamination.

With a full female mould the only way to avoid the chines becoming a mass of bog is careful prefitting and shaping of the foam or as is often done with vacuum infusion don't have any foam at the chines at all but add extra reinforcements.

The main point's of my original post was that you don't need a full mould to build a strong, light weight hull and that the true benefits of a full mould is time when you're building multiply hulls.

[roland_trim]

Ta muchly.
That response greatly improved my mood after a 2 hour delay in the airport and a heap of FE models to manually extract results from - thanks for taking the time.

[phil_kirk]

All clear now.

I'm sure the step by step process will help RS405 greatly with his build.  Many thanks

[Banshee Ambulance]

Change of plan. After reading these informative posts I will be using a male jig rather than a mould. Added an extra station at the bow yesterday giving 200mm intervals in that area as I have placed stations at 400mm intervals everywhere else, rather than the recomended 300mm. Then I took the flair out of the topsides forward so I could remove the snout. I will be going for the 12 style tube and bob stay arrangement, the reasons for this being; the jig fits in the garage and the placement of foam will be a much easier job.

My next question is which foam? I have found a place in Soton that sells corecell but it seems to come in a variety of confusing letters.

Then the question is what layup? I was thinking of: Outside skin from outside to inside - light glass weave, 300g biax glass, kevlar over the bottom. Then inside skin - 300g biax. Any advice?