Hull Question

ScottD · Post by **ScottD** » Dec 27th, '06, 15:51

Were the 31 hulls laid up in two pieces, then glassed together, or were the molds two piece with the hull laid up as one then the mold split? I have heard both at different places and am not sure which is correct. While it would seem more like the two piece mold would be the eaiser choice, I always thought the halves were laid seperate.

Scott

In Memory of Vicroy · Post by **In Memory of Vicroy** » Dec 27th, '06, 16:55

Two pc. mold. I have some pix of them splitting the molds at the factory.

UV

Rawleigh · Post by **Rawleigh** » Dec 27th, '06, 19:11

Why then do I have thicker gel coat and glass down the middle of the boat from stem to stern? The thickness in the middle of the transom seems like they put two pieces together.

CaptPatrick · Post by **CaptPatrick** » Dec 27th, '06, 20:00

When hand laying up a hull, the mold is tipped over on one side. This allows the workers to layup on a more horizontal surface, making their job faster and more consistent. It also keeps the un-gelled resin from draining down and puddling at the bottom of the mold.

Each side is laid overlapping onto the other side at the keel. Once that side starts to gel, the mold is rolled to the other side and that surface is worked, again overlapping onto the other side. Only a single layer of glass & resin are applied per side before turning the mold.

This process is repeated through the total number of courses in the lay up schedule. This method naturally dictates that the overlapped centerline will be as much as twice as thick as the adjacent area outside of the overlap.

It also makes the centerline much stronger and able to withstand more shock in case of hitting a hard object.

Because a split mold will transmit a line at the joint of the two parts, a heavier layer of gel coat is usually applied so that the line can be sanded out. There is sometimes a faint print which can lead to the confusion of the hull being produced in two parts...

In reality, it would be impossible, especially with the materials, design, and techniques used by Bertram in the period of the B31, to join two half hulls and have them not split apart.

There is absolutely NO way that any of the two part hull mold models were ever produced as two separate halves and then joined together...

Br,

Patrick

Tommy · Post by **Tommy** » Dec 27th, '06, 20:31

Ditto Uncle Vic and Patrick's comments. The B-31 one-piece hull was laid up in a split mold because of the tumblehome towards the stern (the top of the hullsides has less beam than at the midpoint of the hullsides). Without the ability to seperate (split) the mold, the hull could not be removed (consider the shape of an icetray that allows the cube to freely pop out). The tumblehome is one of the hull design features that makes the B-31 unique. It cost more to build a boat with this design, and I believe all the subsequent Bertrams were designed without the tumblehome so they could use one-piece molds.

Tommy

JP Miller · Post by **JP Miller** » Dec 28th, '06, 08:23

Hey UV,
Sure would love a copy of those factory pics. I am putting together a photo album of my 62 Sedan project and they would be a great way to start them off. Maybe you could post them online??
jp

Rawleigh · Post by **Rawleigh** » Dec 28th, '06, 09:56

Well, there there you have it from the mouths of the experts! Thanks for the lesson guys! At least I know the source of my crazed gel coat now!! It makes much more sense that way - should have figured that out on my own!

In Memory of Vicroy · Post by **In Memory of Vicroy** » Dec 28th, '06, 10:52

JP, I'll dig them out and have them scanned.

UV

ScottD · Post by **ScottD** » Dec 28th, '06, 16:12

A two piece mold does make more sense, thanks for the explaination on the lay-up, like Rawleigh I was stuck on the very thick centerline.

ScottD

bertram31.com

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