Will this shape release from mold?

[nautique210]

Hi People,

I really want to incorporate this shape into the gunwale of a design (See attachment of section). It would run from the windscreen through to the transom and taper off at both ends on a 21' runabout.

Anybody had success with such shapes? The design will have the transom molded as part of the deck so I though that maybe it could be released by pulling it back. BUT, there will also be some curvature fore-aft. I haven't noticed any production builders with a step like this so naturally thought that it is impossible, maybe it's doable but too much effort? (hoping!)

Any help would be appreciated.

Thanks, Shaun

[Herman]

Although theoretically it might be possible, by pulling the product rearwards from the mold, you will experience you need enormous amounts of slip from your mold release.

I fear that your moulds will not survive for a long time.

However, have you considered a split mould, which you can remove in 2 pieces? Try and locate the seam so that a bit of rework is easy to do, so no splits in concave areas, not through anti skid areas, but on corners, on places where fittings or strips will be mount, etc.

While you are at it, consider release valves somewhere in the middle of the mould. Preferably in areas that will be cut out anyhow (hatch openings, etc). These can save a lot of time and effort demoulding parts.

[tinhorn]

No way, man, not with fore-and-aft curvature in the mold. You have the perfect spot for a parting line on that black sticking-out bulge below your fancy-schmancy design work.

Split molds aren't that much extra work, and your design will certainly make the boat stand out from all the slick-sided production boats designed mainly for quick mold turnaround. If you do split the mold on that bulge, before gelcoating it, make a paste of gelcoat and Cabosil, and carefully squeegee it into the parting line. Spray the gelcoat before the paste kicks. This will provide some flash for easy sanding, AND it'll eliminate bubbles under the first layer of 'glass.

[DGreenwood]

It is not impossible. Just difficult. A good tool builder can fashion a removable mold insert that comes out with the part and is reinstalled into the mold each time. It would necessitate Gel buffing at the top edge (the top point where it turns horizontal). The bottom of the insert could be under the rub strake so that would save a little labor. It would be tricky and a very fussy insert but probably doable.

Edit: A split mold make more sense still.

[tunnels]

Originally Posted by nautique210

Hi People,

I really want to incorporate this shape into the gunwale of a design (See attachment of section). It would run from the windscreen through to the transom and taper off at both ends on a 21' runabout.

Anybody had success with such shapes? The design will have the transom molded as part of the deck so I though that maybe it could be released by pulling it back. BUT, there will also be some curvature fore-aft. I haven't noticed any production builders with a step like this so naturally thought that it is impossible, maybe it's doable but too much effort? (hoping!)

Any help would be appreciated.

Thanks, Shaun

You could make the very corner the edge of your deck and hull join !!

[nautique210]

Hey Guys, thanks for the responses. I probably didn't clarify the sketch enough. The green line would be the deck, the orange the hull and the black bit the rub-rail that would traditionally cover the hull-deck joint.

That may or may not have any implication on the responses, but looks like it is doable, although more difficult and time consuming. The thought of a split mold had crossed my mind, although i'll have to research that method. I plan to cap the hull & deck at the transom and part way up the gunwale so i'd like to avoid too much work!

I do have a plan B but think I need to model some 3D surfaces to get my head around exactly what it's going to look like.

Cheers,
Shaun

[tunnels]

Originally Posted by nautique210

Hey Guys, thanks for the responses. I probably didn't clarify the sketch enough. The green line would be the deck, the orange the hull and the black bit the rub-rail that would traditionally cover the hull-deck joint.

That may or may not have any implication on the responses, but looks like it is doable, although more difficult and time consuming. The thought of a split mold had crossed my mind, although i'll have to research that method. I plan to cap the hull & deck at the transom and part way up the gunwale so i'd like to avoid too much work!

I do have a plan B but think I need to model some 3D surfaces to get my head around exactly what it's going to look like.

Cheers,
Shaun

You still wont get the artical out !! theres a 30mm pull to get what ever past be it deck or hull doesnt matter !! Make the furtherest point out the join line or simply reduce the size to 5 mm or less on each side . It would be better to rethink the line and the hull deck join and make a wooden pattern full size and make it work for your self . The absolute minimum amount of draw needs to be 1.5 degress of draw even that is a little on the straight side as moulds change shape over time and could get harder and harder to get out as time goes by .
You could always make a flexable mould that will twist !!! Now thatll make a few people think !!! Stiff artical and twist the mould off it !!Bit like taking a tyre off a rim !!