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Old 06-06-2020, 09:48   #1
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Boat: 50’ performance cruising cat, 50’ Gulfstar (under contract)
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What Would Be Easier to Install? Bow Tube or Longeron?

So I see a couple different ways to take the force of a forestay, screecher and jib on catamarans.

Since I have absolutely nothing installed at all yet, I can go with the best solution. I notice a lot of the latest performance cats are using the longeron.

I’m also weighing heavily which will be easiest to install.

The standard bow tube has 2 attachment points and about a million little points of attachment for the tramps. It also has a seagull striker and associated attachment points to convert the tension from the forestay to shear at the hull attachment points.

Then there is the longeron. One single spar (including acting as a bowsprit) attached at one side only. One attachment point at the base, then a set of guy wires to the hulls to keep it in place and translate the forestay tension to both sheer and tension at the hulls. Free bowsprit is a cool bonus.

Which is easier to install? Which is better?

Here are examples of each. First pic is traditional bow tube and seagull striker. Second pic is longeron.
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Old 06-06-2020, 10:31   #2
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Boat: Amel 53, Super Maramu
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Re: What Would Be Easier to Install? Bow Tube or Longeron?

It is NOT a question of easier to install, it is which one can your hull design support. Both of these designs are taking the vertical pull of the rigging, and converting it to horizontal loads.

The bow tube is under significant compression, and because of this it takes the rigging loads that are trying to pull the bows together. Rigging loads on the hulls at the bow are relatively small.

The "longeron" accepts none of the load that is trying to pull the hulls together, the hulls have to resist that themselves, and these loads are VERY large. It does present the hulls with some backwards loading at its attachment point midships, but this isn't very big. With no rigging supporting the forward end of this spar, it needs to be extremely strong and stiff to support a sail out at the end.

One is not "better" than the other. It depends on the hull design and what loads the hull can accept. Certainly which one is easier to install should not be the primary criteria.

This is not a decision that is best made at the end of the design process. Either the hulls can accept the inward loading, or they can't. If you don't know, the bow tube is probably the safer choice.
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