Mold and Flange Construction

[sneakyb]

I am in the process of building a foam sandwhich, one-off skiff. After the skiff is complete, I plan on pulling a mold off boat the hull and deck. Although I am not vacuum bagging the initial one-off skiff, I plan on bagging all the boats build out of the mold.

I have seen that when building a mold for vacuum bagging, the flange has to be extended a few additional inches to allow for bag attachment to the mold. However, I would very much like to build the hull so that the flange portion turns 90-degrees downward. The deck would have a matching down-turned edge which would fit over and outside the hull flange. I have attached a quick sketch showing the resulting hull to deck joint that I am wanting to achieve.

My question is, given that I need to have a wider mold flange but also want to incorporate a down-turn, which way do I extend the mold flange to allow for bag attachment? ALso, what is this kind of hull to deck joint called? I've sketched two options on the attached drawing and labeled them as Option 1 and 2. Any help would be greatly appreciated.

[anthony goodson]

Which ever way you do it ,it would be prudent to "relieve " the corners.

[sneakyb]

Roger that. This is a hard-chined hull so care will have to be taken to not create voids at any of the sharp edges int he mold. I am leaning towards option 2 with the flange. This way, the mastic can all be in a the same plane rather than it being "Wrapped" around the mold. Also, it seems like it would be easier to part the molded hull from the mold using Option 2. Any input would be grealty appreciated.

[jim lee]

I'd do option 1. We have a few Option 2 versions here and they are a pain.

-jim lee

[sneakyb]

Jim:
Thank you for your input and it means a lot given that you've tried both. If you don't mind me asking, why is option 2 a pain? Is it mainly the layup around the abrupt transitions? Also, are you vacuum bagging using a flange similar to option 1 or doing conventional layup?

[jim lee]

Option 2 gives us trouble because it gives a part that's hard to trim. It gives an edge that's rounded so its not really defined. Its hard to pack 'cause glass doesn't like corners.

Option 1 the glass lays flat and you can just scratch a cutoff line in the mold where you -really- want the part to be trimmed to. Easy peasy!

I learned this from the tooling guys in the shop here. We'd start something that, in theory, was a good idea and they'd politely say things like. "You know, maybe it would be better to do it this way? Donno' just wondering, that's all."

P.S. Actually looking at your part again, option three, beyond the cutoff line; Maybe rounding it out in a large radius, 1"+ would work nicly too?

-jim lee

[sneakyb]

Thanks Jim, I really appreciate it.

[Herman]

-1. I would like to see all corners rounded off, in both options, but I guess you have got that. With the rubrail you will then end up llike this: deck - rounded transition to vertical part (say r=1/4"), rubrail. This will mean your rubrail sits 1/4" lower.

-2. I have had molds build like option 2. Although the horizontal part is nice to easily apply sealant tape and the bag, next time I would do option 1. It is not even needed to scribe a cut line, but I come to that later. It is very much easier to apply some force with a wedge to start the demoulding process. You could opt for option 4: A slightly angled outwards flange, say 15 degrees, starting below your cut line. This makes applying tape a bit easier, and still allows wedges to be used. Option 3 is also something to think about, a large radius, then a horizontal part. If you ever want to start infusion, the horizontal parts makes it easier. (for taping some peelply, a runner and the sealant tape)

-3. Cutting the part: After glueing the deck and hull together, make an attachment on your grinder, which slides over the deck, and which makes your diamond blade cut right on the right height. (which is the width of your rubrail, plus the 1/4" that I mentioned.)

-4. When making moulds, do not forget to include an air vent somewhere in the middle, to be able to blow air between mould and part when demoulding. When a mould is broken in, this makes demoulding a 1 minute process, and saves your part and mould. I like the ones made by Composite Integration in the UK.
Also do not forget to mark your waterline in a different colour gelcoat, in the mould. In case you want to gelcoat waterlines in a different colour.

[thoannguyen]

Hi everybody !

If I made a plug what type of Q-cell would I use ?

[Herman]

-1. It is considered not done to hijaack someone elses thread, unless the question is related very, very closely to what is being discussed, and comes forth out of that discussion. (for instance if we were dicussing Q-Cell already, and you would like to know which type)

-2. In general, you will get as much info back, as you give. Which, in this case, is hardly anything. Based on the info you gave us, I would say: the white, grey or brown one.

So to be nice, a question for you:

-what will you be making.
-what will be the construction method.
-where and how are you planning on using the Q-Cell.

[tunnels]

What ever flange you pick on make sure its 75 mm or more wide all round from stem to stern !!
This will help the mould retain its shape better over a long period of time . Moulds change shape usually for the worse as they age ,so the wide flange can slow this down !! .

[thoannguyen]

Thanks Herman!

I begin make mold composite boat first time, so I don't know much about composite boat. In Viet Nam, Composite boat is new.
I very happy if you tell me it.

[Herman]

@Tunnels: Let's pull this guy through the basics first. Flange is important, but there are many things higher on the priority list.

@thoannguyen:

OK, you would like to build composite boats. Can you tell us what you have available already, and what can be bought over there?

-workshop: temperatures, inside or outside
-mould:, do you have a mould already, or do you have a basic model (plug), or do you need to make one?
-which materials can be bought: polyester in different types, gelcoat, glassmat, anything else? PU paint would be nice to have, can you obtain that

Also, what kind of boat are you planning to make? Length, width, purpose of the boat? (tourists, fishing, export?)

[Vulkyn]

Herman good post! good luck in ur build sneakyb

[Herman]

I do everything for a couple of spring rolls / dumplings....