Bowsprit design - How strong is strong enough?

Somewhere I have some photos of Northshores bowsprit for their Southerlies. They are fitted to the stemhead and whilst I don't know the spec re wall thickness I doubt it is anything more than run of the mill 11/2" 316 I am going to Northshore this weekend so will try to find out a bit more and post some pics.
 
IAN13 said:
We have one on our Beneteau 323 . Its a Selden one extending out the bows by about 600mm . We can open the chain locker with the pole on deck .

DSCF0239.jpg


The pad eye by the right hand stantion is the position the pole goes in when its extended . The tip of the pole is then directly inline with the bows :D You can also use the anchor . I fitted a Selden fitting and made a mounting bracket for the side of the bowroller
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Interesting photo, but unfortunately mounting one to starboard on my boat is not possible as it would obstruct launching and retrieving the anchor, which has to sit in the starboard part of the double bow fitting, in order to line up with the windlass. The space between the locker hinges and the toe rail on the port side is too narrow for the Selden pole, which would prevent the locker being opened. I think I might be able to fit a Selden pole, (if obtainable in Turkey) but only if I can get a bracket that would allow me to hinge it upwards from the bow fitting to open the chain locker, Before considering that I would need to do some careful measuring to ensure that it would clear everything when raised. Before going down that route I want to investigate getting a short stainless one that can either retract into the chain locker, or be detached entirely when not in use.
 
Bowsprit

I am also considering making a small bowsprit just to clear the furling gear on our boat. the whole length would be about 600-700mm with about 300-350mm extending clear of the boat.

I cannot grasp how the bowsprit will come under a compressive force (unless I ram the boat next door). I was looking to brace for sheer stress, torsional stress and tensile i.e. bending,twisting and pulling apart.

I wanted to fit a simple brace under the bowsprit and side plates. I appreciate that there is a need to brace under the bowsprit as it will act as a lever etc...

Am i missing something

Thanks
 
I think the compressive loads were referring to conventional bowsprites, with the bobstay and wisker shrouds converting the side loads to compression.
 
DownWest said:
I think the compressive loads were referring to conventional bowsprites, with the bobstay and wisker shrouds converting the side loads to compression.
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Yep. With a strut only secured at its ends, by pivoting joints, I don't think it's possible to induce any force other than compression or tension. I'm not an engineer though.

In the case of my bowsprit, the outer end is all pivoted (shackles) and the inner end pivots up and down on a pin. It doesn't "formally" pivot sideways but I'm sure the fittings would flex given enough force. Thus it behaves like the strut model, and sees only compression.

It does pass through a gammon iron at the stemhead, but that's not a tight fit. There was room for me to fit a layer of leather for anti-chafe (it slides against here when being stowed) and to get a finger in from time to time to apply tallow to the leather. When rigged and sailing, the sprit is meant to "fly" in the middle of the gammon iron.

Pete
 
Ok chaps......

So how do you suggest I rig one on my boat.....



The distance from the forestay attachment point to the deck in front of the anchor locker is too short for me to be comfortable about it being able to take the loading ( see required protrusion distance below ), and
The deck/hull joint is capped with teak and sits well above deck level, and
The pole needs to protrude about 800mm beyond the bow, and
Its quite a big chute ( the I measurement is 15.15m ).


The only thought I have come up with so far is a v long pole ( about 3m long and Selden are advising it to be the c100mm dia version ) that would have its inner end sitting on the raised coachroof. But, I still cant see where i would fix the ring through which it would have to pass to hold it down! Such an arrangement would in any event prevent the anchor locker lid from being opened while the pole was deployed.

All suggestions gratefully received!
 
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OK.. Since it is unlikely you will anchor with any force on the pole, how about a second attachment on the side deck for the heal, so it swings in it's bow loop. The position of the front is not important at this stage. Only prob is if you need to access the hatch with the sail full.
 
Weverbird

I don't know if this helps.
As an experiment I wanted to see how much benefit a sprit would add. I have a 42' boat with a ~1000 sq ft cruising chute and made a bowsprit of iroko. The sprit is ~ 1m long and has a diameter of 65mm and when extended just clears the anchor (40cm extension). This diameter allowed the sprit to run in the spare anchor roller (which was substantial). My plan is to keep using until it breaks and determine whether it added sufficient benefit to warrant a more robust solution. No problems so far but have only used up to about F4 - it has however made an enormous difference to the set and control of the sail
 
That hole would be 100mm in the vertical dimension, but a very looooong hole fore and aft. What you need is a soft lined strong loop welded to the stem head fitting.
 
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