Rigging a bobstay without cutting any holes

[Greenheart]

First things first...it's a dinghy, not a yacht, so the strength and security of the finished item won't be subject to extended offshore use and abuse.

Secondly, credit to Thinwater of this forum, whose recent advice eventually led me to stop worrying about what my bowsprit's made of, and to just 'stay' it instead.

His advice was that most of the movement of the six-foot protrusion of the sprit from the foredeck will be upward, from the asymmetric spinnaker which the Osprey isn't designed to carry...so a bobstay is the answer.

I don't want to drill into the forefoot, but it occurs to me that I could drill a little ring into the tiny space behind the keel-band at the lowest point of the bow...then I could secure a wire inside the centreboard case, and lead it along the centreline adjacent to the keelband...and where it emerges at the upward angle of the bow, it would be led through the tiny ring, so that in use, the bobstay leading up to the end of the sprit would never weave sideways but maintain a central downward force.

Anybody see any big holes in that plan? Thanks.

I'm still thinking through the process of keeping the bobstay from dragging free while keeping the bowsprit retractable...some sort of shockcord contrivance.

 

[lw395]

I'm not sure a bobstay is needed.
But why not just attach it to the keelband?
If it's held on by half a dozen screws and some epoxy, it should be fine?
I'd probably use spectra or some other hi tech string for the stay, a bit of spring in it won't hurt.

 

[Daydream believer]

Anybody see any big holes in that plan? Thanks.
.

Well there is one in the hull for a start !!!!!!:nonchalance:

 

[Greenheart]

Thanks for your replies, but I'm not sure I've been understood.

A bobstay needs securing low on the stem...as low as possible in fact.

That's going to be below the water a lot of the time, and the inside of the Osprey's bow is not an accessible place to waterproof or reinforce...

...so avoiding drilling through the hull at all, seems preferable to any alternative. Especially if I can secure the bobstay's inboard end inside the centreboard case.

My keelband was a real pain to secure, so it doesn't itself represent a strong point for anchoring a stressed line like a bobstay. Drilling between it and the hull, won't risk any water ingress, but would allow the positioning of a small ring which would only act as a fairlead, the bobstay wire itself running back and up the centreboard case.

The point of resorting to a bobstay is because the sprit itself is only a slender carbon windsurfer mast, which may not be equal to the forces applied by 150 sq ft of asymmetric to its unsupported outside end, 6ft beyond the bow.

Regarding stretch in the line, I had supposed that 'staying' requires as little movement as possible. Not so?

 

[Wansworth]

You could rig a strut halfway and rig a stay set up with bottle screw so the spar is prtensioned

 

[Ingwe]

The only dinghy that I can think of that uses a bobstay is the 18 foot skiff if you Google a few pictures of them you will get a fair idea how they do what you are after, but bear in mind that due to the fairly poor angle of a bobstay on a 6 foot pole (even with a strut) you are going to need to pretension it to a pretty high load.

 

[Plum]

First things first...it's a dinghy, not a yacht, so the strength and security of the finished item won't be subject to extended offshore use and abuse.

Secondly, credit to Thinwater of this forum, whose recent advice eventually led me to stop worrying about what my bowsprit's made of, and to just 'stay' it instead.

His advice was that most of the movement of the six-foot protrusion of the sprit from the foredeck will be upward, from the asymmetric spinnaker which the Osprey isn't designed to carry...so a bobstay is the answer.

I don't want to drill into the forefoot, but it occurs to me that I could drill a little ring into the tiny space behind the keel-band at the lowest point of the bow...then I could secure a wire inside the centreboard case, and lead it along the centreline adjacent to the keelband...and where it emerges at the upward angle of the bow, it would be led through the tiny ring, so that in use, the bobstay leading up to the end of the sprit would never weave sideways but maintain a central downward force.

Anybody see any big holes in that plan? Thanks.

I'm still thinking through the process of keeping the bobstay from dragging free while keeping the bowsprit retractable...some sort of shockcord contrivance.

Why not just try it out without a stay. You are obviously not going to use this upwind and therefore need to maintain good luff tension.

Www.solocoastalsailing.co.uk

 

[Greenheart]

Well, you're probably right that I ought to try it out before making changes...if I'd started with that approach, I might well have mastered the symmetrical spinnaker by now, and the necessity for a bowsprit would be an idle daydream.

But wisely or otherwisely, I'm now some distance down asymmetric avenue. A week ago, I'd reached such a state of doubt regarding the windsurfer-mast's suitability as the bowsprit, I started looking afresh at my old, untried symmetric spinnaker. After reading Thinwater's reckoning that the slender carbon bowsprit would whip around unless stayed, it took me a few more days...

...until the simplicity of rigging a bobstay a là Sydney Harbour 18, struck me. I had lately even wondered whether I shouldn't just pay for a new RS400 bowsprit to go with the kite...but on balance, considering the whole punt at converting a proven 2-man symmetric dinghy to an asymmetric singlehander is a long shot, it's probably smarter to pay a tenner for some dyneema, then wire up a bobstay for the sprit I've so far contrived.

The only question being, how? The 'strut' seems smart - effectively, a dolphin-striker I suppose, which can dip deeper than the bottom of the bow, without needing any underwater holes being drilled in the hull.

I'll take some string down to the boat in the morning and see how it looks. If I didn't have to spend all afternoon in a safety boat helping the racers, I might achieve something useful.

 

[DownWest]

Fitted a B/Sprit to a little dinghy and just made up an SS strip to a V that I screwed to the lower (GRP) stem, from each side, with a couple of screws and some Araldite. Left a bit of room in the apex of the V for a shackle. Used it for years and the jib improved the balance nicely.
In your case, a small block down there and run the line from the front of the sprit, down over the block and back up to the sprit, then aft to tie off.

 

[Daydream believer]

You do not need loads of tension on the bobstay. The bowsprit is off a sailboard & is designed to bend a lot anyway. So take the line from the bow to the end of the bowsprit
Do not have pullies below the water line as they may catch weed & any slack line will want to tangle more if doubled up. In fact do not have any tension system.
Any tensioning system will load up the retract system on the bowsprit & make it harder to extend. A fixed line on the bowsprit for the bobstay is one less line to adjust every time you extend the sprit. Then all you need to do is pull in a bit of slack as it comes in. ( Bungee) You can forget it when extending the sprit as it will just go out on its own & not being too tight will not stop you getting full extension.

If you really want to complicat things then do not actually attach the line to the end of the sprit at all.
this needs some concentration & study
take a line from the tack of the sail through a double pulley on the end of the sprit down to the stem of the dinghy , round a pulley & back up to the other sheave on the pulley on the sprit then back to the cockpit.
Now when you pull out the sail you do not put any upward load on the sprit at all. ( well a lot less) as it all transmits down the line which is now the bobstay as well as your tack line.
As the sprit comes in it releases the tack line length because the distance that it travels is less so the tack can come aft along with the sprit all in one action
You have a length of tack line trailing so you have to get that in but a ring round the bobstay part with a bungee gathers that in for you.
You can always just let the sail off on its own & the sprit will still be Ok as there will be mo load as the sail will not be set.

You actually do not need to take the line right back to the stem =. you could put the stem pulley on a length of line so that the pulley was ,say 6 inches below the extended sprit. However, it may want to twist in which case the double pulley will need to be 2 single pullies & be set apart with one pulley a few inches back along the sprit to stop this

 

[lw395]

I have a dinghy with a bowsprit.
The sprit is about 8 ft long and about 18 inches max stay in the boat.
It's carbon.
It weighs very little, probably less than 8ft of sailboard mast.
It carries nearly 300 sqft of sail in up to 25 knots of breeze, although I chicken out before then, I'm too old!

I'd say just try it and ease the sheet (and/or bear off!) when the bend in the pole gets silly.

What DownWest said is very workable too.

 

[Greenheart]

Thank you for many good pointers and contributions, gentlemen.

After a fairly horrendous freezing three hours in the safety RIB today, it's unlikely I'll want to put the bowsprit to the test afloat until a gentle day in spring or possibly later. So I needn't hurry to get it right.

I'm willing, in fact keen to believe that the bowsprit won't need staying at all...but I don't want to risk getting shoved back to the drawing board by an avoidable breakage in the early tests. I know numerous asymmetric classes manage without a bobstay, but they are thoroughly engineered. My set-up wasn't only designed on a cigarette packet, it's practically made from them.

I'll try fitting the bowsprit and seeing how rigid or floppy the set-up is. If as I rather expect, it looks like needing support, I'll refer back here for options.

 

[DownWest]

Cup of tea has revived the brain
How about making up the stay in wire or synthetic and securing it to a point on the stem, then running it round a sheave at the end of the sprit. Whatever the terminal is, make up a positive stop ( if a swage, then run it through a hole, so the swage comes up against a plate or plastic block) Run your bungee inside the sprite, so when you retract it, the stay is pulled down inside it.

 

[Greenheart]

Thanks DownWest, and apologies for waiting two weeks to reply. Frightful technical troubles...new computer, etc.

Surprisingly, time not discussing it has brought me closer to a solution. Certainly the shock-cord slack-uptake-line makes sense...

...but the inside of the sprit is so crowded with stuff (some hollow stiffening, some fairly solid) that there's no space for a shockcord.

My plan is now substantially loonier than what I started with...more lines, so hopefully a stiffer bowsprit with incorporated retractor...

...and critically, no holes at all in the hull. DownWest, thanks again…

…just made up an SS strip to a V that I screwed to the lower (GRP) stem, from each side...

…that’ll work fine, with some alternative thinking to obviate the need for screws.

But I've said more than was probably smart, I do my best stuff when I'm not talking about it. Thanks also to all you gents for helpful thinking. You may claim your input when I finally assemble and take photos. Of course it may be 18°C and light at 7pm, by then.