How are fiberglass plug made with complex curves?

Hi, I am knew to the forum, but have been poking around for awhile because of my own interest in boat building. I am interested in fiberglass boat design and am curious how the plugs work for boats with complex curves. For example, the Chris Craft Carina has a curved back making it hard to lift straight out.
This Chris Craft no seam

where this Frauscher has a seam to achieve the curved rear.

This aquariva seamingly (sorry ha) has no seam and yet is concave and not totally vertical.

Do they pull it forward, or is this a two piece mold. If anyone has any pictures of two peice molds or of the process it would be helpful. In addition, if there are two piece molds made how is there not a imperfection in the hull? Thank you!

 

There is an imperfection from where the halves join called a molding line. Use extra gelcoat in that area so that when you grind the ridge away you can just polish it afterwards.

 

Molds can have many parts. If they are well matched with the seam waxed and polished, it should not show a line. You can find books of mold making for casting and ceramics. The techniques are the same regardless of material.

 

As mentioned a complex mould usually has joins with the matching flanges having male/female locators to align the sections.
I would suggest however that the boats pictured may have been released by lifting the bow first and drawing the part forwards.

 

I'd have thought it wouldn't have released from a one piece mould, not for me anyway.

 

The hull is at its thickest in the midsections, so, release the hull and draw it forwards as you lift the bow up.
But you have to raise one eyebrow and poke your tongue into your left cheek as you do it

 

Hi,

The moulds can be splitted in several parts.


There seems to be at least a third part at the stern according to the alignment holes.

The pictures are linked from http://www.distantshores.ca/boatblog_files/category-southerly-boats.php
I hope they don't mind.

 

There are a lot of fibreglass/composite kit and fully manufactured cars around. Plenty of split lines with those!.

 

this is my hull mould i recently built.

to get the boat out you have to pull the transom of first , then the sides of the mould and then the tunnel section of the mould pulls downwards.

the mould is in 5 pieces with the tunnel in 2 pieces but that stays bolted together.

i made the tunnel in 2 pieces so its easier to man handle.

if you look at the flanges you will see the male and female locators.

 

Wow, thanks for the help. All great info and pictorials.

Redrueben, I found a ChrisCraft factory tour video, and you were right. They pull the boat up and forward to pop it out. I supposed that when engineering a mold they calculate the tolerances needed to lift it out easily.

Garrybull, thanks for you the step by step. That is a fantastic illustration of your mold. What kind of plug did you use to achieve a mold like that? CNC or wooden plug? If you built it yourself it certainly is impressive to get the fittings and female/male locking mechanisms.

 

thanks mselle, that resource is very useful to see the multiple mold process.

 

yes i made it all myself.

i used a hull mould which i already had which is a 3 piece mould.

i built a melamine tunnel and bolted it in between the outer hull sections and then added a melamine transom panel.

then it was all waxed and polished and a coat of pva put on.

then gelled up and layed up a fibreglass hull.

i then raised up the sides of the new hull etc.

turned it over and did any repairs and painted it with duratec surface primer and wet flat it down and polished it up.

after that i put on the flanges for the new mould and built the mould up a section at a time.

the locators are made out of 30mm nylon turned down on a lathe to have a chamfer on them.

they are then screwed to the flange and gelled over when making the mould.

its taken me a few months to get to where i am now but im loving every minute of it.

i have just made the wheelhouse plug which im hoping to paint later thisd week.

 

Why don't share the source. It's probably interesting for a lot of people.

M.

 

http://www.youtube.com/watch?v=PM4WGsLpxws

Removal of boat at 2:40-ish

 

Yup, thats the video. Kind of hard to tell, but you can see they lift it up and forward.