Hello all. I’m new here. I’m on a 45 I just acquired. I’ll have 1000 questions as I get her going, but I’ll start with this: has anyone ever heard of a gun mount spinnaker for a 45? I used one a lot on a friend’s 32 back in the day, but this is a bit of a mystery. Thanks!
Maxwycisk,
I’ve never heard of a F45 with a gun-mount spinnaker. However I have seen F45 running cruising spinnakers (no prod asyms designed to run and broad reach). With no shrouds or spreaders to foul the sail, these big sails are pretty easy to handle. .
Well, the question is whether there are definitive arguments against the idea: kind of like we know by now you will most likely break your mast eventually if you try racing your Freedom with a spinnaker flown from top of the mast that has a big head: that’s where most pressure will be and with no backstay you are asking for it. However, and im just speculating here, the gun mount spinnakers are cut kind of upside down with the “head” below centre and most of the pull is on the gun mounted spar. Logically, that should make it a viable idea but i think a naval architect should chime in here - any idea where to find one, from the T/P ranks? A gun mount would be easy to manufacture and my 45 has a very robust pulpit. (It could even be a carbon fiber spar, thus saving a fair bit of weight at the bow). What do y’all think?
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I am not a naval architect but I did study aerodynamics at University. The force exerted on a sail is proportional to its area and the wind speed squared. Actually it is a bit more complicated than that but for a flat surface, the force is 1/2air densitywind speed^2areasin of angle the air hits the surface. Anyway, there is no intrinsic reason the gun mount spinnakers, like on my baby F21, should not be scaled up to a 45. I think the full head on a regular spinnakers is to limit interference from the mainsail, which can be a problem on a dead-downwind run with the gunmount spinnaker. You are right though the gunpoint spinnaker on the 21 and larger models is fuller down low and also is a fractional sail rather than being flown from the masthead. I will always sail 10 degrees or so off the wind with mine even though it may entail gybing to get to where I need to go. I am sure you could do some stress calculations using just the cross sectional area of the sail you want to fly and divide the resultant force by the three attachment points to get an idea of the forces on on the structure supporting the gunmount and mast. Note that the forces on the attachment points needs to be resolved along the line of the tack/halliard. Just because a spinnaker id fuller at the top does not mean there is more force there. However the fullness will give you a stronger resultant force perpendicular to the mast because of the angle that fullness makes on the halliard.
Hope this helps.
Hello newt2u, thank you for the response! I just saw it as i am still unfamiliar with the ins and outs of this forum. While i am not sure i can follow the formulas without some help from a sailmaker it is clear from your opinion that there is no reason NOT to attempt to design a system and have a sail made for the 45. Very encouraging and i appreciate the input from someone who studied aerodynamics. The 32’ i sailed extensively in the 80’s with this system behaved extremely well when it was deployed, while the jib was basically decorative it seemed…lol.