Male or Female frames for strip build?

[Nojjan]

Which is faster, more accurate, simpler, stronger, cheaper, etc. ?

Share your experience.

Thanks / Jon

[nero]

I decided on female forms for strip planking my 14.5 meter cat hulls. It is very accurate, and works well. The advantage is that the sheathing can be added before and bulkheads. Also the bulkheads are added before the hull quits the mold.

Have not done a male mold so can not contrast or compare the two from experience.

[alan white]

Smaller boats could benefit from female molds. Canoes in particular built of cedar strips sheathed both inside and out with epoxy, often end up with unfair hulls due to in-flexing during sanding the exterior.
The hull is being sanded without the stiffening benefit of the cloth/epoxy on the opposite side. If the inner surfaces were sanded first, possible only using female frames, and then clothed and epoxied, it would seem that the boat would fair better on the outside once the boat is freed from the molds.
In the case of larger hulls, the bulkheads, stringers, and the whole structural interior would be installed before the boat leaves the mold. A friend built a Chris White skyhook tri using 1/2" cedar between cloth/epoxy (to 5/8" generally), and the outer hull surface ended up needing re-fairing later with microlight (male mold).
I think you're right on target using female molds. I would guess it's more time-consuming to set up the molds accurately due to obvious things like eyeing fairing battens, etc., but given the clear advantages of having an inner surface already stiffened by the glass layup, it makes a whole lot of sense. And it sure sounds easier to deal with the inside sanding/cloth/epoxy before fitting and glassing in the permanent bulkheads if they are not needed to create the molds in the first place. The idea of a continuous inner skin is attractive for reasons of ultimate strength as well.

A.

[Eric Sponberg]

Personally, I would prefer to build a one-off wood strip or composite hull upside down over male stations. And the reason is simple. The human eye is the final judge of fit, fairness, and proportion. This is most easily seen over a male form; they are nearly impossible to detect with 100% fulfillment inside a female form. Our computer design programs have an amazing capability allowing us to create 3-D shapes which we can transfer to either male or female stations, but we are still restricted to judging it on a flat screen in 2-D space. To have the proper shape in male form before our very eyes and there to touch and feel, upside down for the hull, and right side up for a deck, is by far the best check of trueness to shape. This is why some people still prefer to work with half models which is still a very valid method of design.

As far as time and complications of male vs. female construction, there are trade-offs. Where you may spend more time on one task in one method, you will trade it off for more time doing something else in the other method. In the end, all tasks have to be done, and the overall time and money spent for construction will average out pretty close to the same foir both methods. This is assuming, of course, of an equal degree of talent and skill for proponents of both methods.

With the current state of technology that we have today, a male form of construction will get you the truest and fairest hull and deck.

Eric

[nero]

I am using female forms for my 14 meter catamaran. The form shapes were made in TouchCad. Layed out the cut line by XY coordinates. Cut the partical board with a jig saw. The forms are set up on 50 cm intervals and the planking is 18 mm cypress.

Respect the control edge when setting the unbeveled forms.

Seems to have worked amazingly well. The outsides of the hull have not been glassed yet.

Making a 1/10 scale hull model is an excellent way to see your design and proof the plans before doing it for real. Using metric system makes scaling a simple task.

[Nojjan]

Thanks for your input guys. I am a beginner so I will take the advice of Nero and build a scale model just to see how it works. My hull is only 22ft long so I will try with 1:5.

Best regards / Jon