Bowsprit end hardware - cranse iron

[mauro.iachelli]

Hi All,

I'm in the process of building a bowsprit for my 1975 Amel Euros 41 ketch, I want her to have a double headsail to improve windward capabilities. My project is to have a 3' long (from stem) bowsprit tubular shape made in carbon fiber/epoxy (wall thickness 1/2") with a "defensive" fbg/epoxy outer layer of 3/16" . I'd like to keep a light 130% furling genoa on the main forestay attached to the cranse iron (1/4" SS316) and just aft to that (max 12" from eye to eye) another fitting to attach a movable stay where to set a Yankee sail. This second "band ring" will be welded to the cranse iron with two lateral bands of the same material to keep it in place and add stiffness. The piece will become one only. Now my questions are:
1) Do I need another bobstay for that? I 'd like to avoid it, if possible and I think the very close proximity between the two stays chainplates should allow that, but I'd like to hear the experts opinion.
2) Do I need to reinforce the linkage between the cranse iron and the second fitting with a lower band? I wanted to avoid it to let water seep through freely, but I understand that this is the place in which the bowsprit head will substain the most stress from the Yankee sail (in case I'm not installing a 2nd bobstay).

Thanks to all who can help.
BTW, I have a little sketch I can email for easier understanding.

All the best
Mauro

[SV Papillon]

There are others much more versed than me, but 3' sounds really short for a bowsprit. I would also wonder on the benifit of having the inner forestay 2' fwd of the stem vs. directly on the stem which is the most secure location. The bow sprit is all compression load so there needs to be considerable thought into the fitting that recieves it on the boat. Just a suggestion but for something like this your best money would be to sit down with a NA for a couple hours and look at the most efficiant placement of sail area to get the windward performance you are after. If dual headsails is the answer then there may be a simplier fabrication solution on your stem fitting that will get you there without nessesitating a full on bowsprit with associated rigging, bobstay wisker stays tangs on the boat that all have to be re-enforced etc.

Jake

heres a pic of what I think is a sistership for a visual

[mauro.iachelli]

Hi Jake,

thanks for your thoughts. I've been working with a NA and there are some alternatives we are looking into, but this is the one I'd like to pursue.

Having a bowsprit longer than 3 feet (remember I'm talking about outside measure, not total) will not be feasible for my boat and also the staysail chainplate is further aft the stem of about a foot. This means that between my yankee and the staysail I'll have a good 3' of area, which I think it is plenty.

The sail plan of my ketch is pretty conservative and the mast height from deck is only 33' with a J of only 10'.

Best Rgds
Mauro

[Stumble]

This is a lot of effort to recreate what is already on the market.

Take a look at the retrofit bowsprits available from Selden, forespar, or sparcraft. They are bolt on additions that work really well. One of the local racers is using one, and I am in the process of adding one to my new boat.

Then buy a Code zero on a furling drum. Total cost for the system, $2700 give or take, plus the cost of the new sail. And you can always add a downwind a-kite to the mix just by buying a new sail.

[CAM]

Originally Posted by mauro.iachelli

Hi All,

I'm in the process of building a bowsprit for my 1975 Amel Euros 41 ketch, I want her to have a double headsail to improve windward capabilities. My project is to have a 3' long (from stem) bowsprit tubular shape made in carbon fiber/epoxy (wall thickness 1/2") with a "defensive" fbg/epoxy outer layer of 3/16" . I'd like to keep a light 130% furling genoa on the main forestay attached to the cranse iron (1/4" SS316) and just aft to that (max 12" from eye to eye) another fitting to attach a movable stay where to set a Yankee sail. This second "band ring" will be welded to the cranse iron with two lateral bands of the same material to keep it in place and add stiffness. The piece will become one only. Now my questions are:
1) Do I need another bobstay for that? I 'd like to avoid it, if possible and I think the very close proximity between the two stays chainplates should allow that, but I'd like to hear the experts opinion.
2) Do I need to reinforce the linkage between the cranse iron and the second fitting with a lower band? I wanted to avoid it to let water seep through freely, but I understand that this is the place in which the bowsprit head will substain the most stress from the Yankee sail (in case I'm not installing a 2nd bobstay).

Thanks to all who can help.
BTW, I have a little sketch I can email for easier understanding.

All the best
Mauro

I'll add my doubts to this project increasing windward capabilities. Ask for a money back guarantee from this NA?

If your "tubular" shape is more than a couple inches in diameter, then your carbon sprit will be fine (and quite heavy) at that thickness. Consider making the aft end a lot wider than the tip to avoid needing side stays (if attaching directly to the bow). Also consider an internal end fitting (machined aluminum, or fabricated G10) to receive the bobstay and possibly tack lines if you ever fly an asymmetric kite. Can be as simple as a tight-fitting glued-in "slug" with a vertical-cut slot to ring hitch the bobstay and strops through. Your second "chainplate" can be a webbing strop that spiral wraps to the tip, sort of like a vang attaches to a carbon boom. "Cranse iron" and "carbon bowsprit" don't seem compatible to me, and all the places where the hard, sharp edged metal isn't a perfect fit will point load the spar and possibly crush it.

I built a 1 meter bolt-on sprit for a 40' race boat, and its wall thickness was in the 1/4" range. A slightly bigger "glue-on" sprit for a 52' boat had a wall thickness in the 3/8" range. Both were set up to run zero's, so high luff loads were needed. If you are using wet, hand layup methods and cloth instead of uni's, increase the wall thickness by about 75% or so -about what you quoted.

Good luck

[allene]

I want to point out that most bow sprits that are added to boats these days and as I understand it the pre-made ones quoted, are for downwind sailing. Some will not even allow a Code-0 sail. A downwind sail puts much less load on the bowsprit than what you would have if you have a forestay on the bowsprit and an upwind sail.

I would be very surprised if you could take the loads of a forestay and an upwind sail without a bobstay and perhaps even side stays. Find an expert before deciding it is good enough based on what someone did for a downwind sail.

Allen
L-36.com

[mauro.iachelli]

Hi All,

Stumble....I understand your point, but I have to admit I tend to agree with Allen. The bowsprits you are talking about are built to set light sails for downwing sailing and are not considered to be used in strong winds and close hauled. I wouldn't consider it safe to add that kind of bowsprit and and no rigging to it.

Allene.... I'll certainly go for a more traditional rig.

CAM... while I keep my opinion on the better windward capabilities of this type of rig (owners of Whitby 42 that made the same modifications are agreeing with me) I certainly find your avices very solid and worth noting. My bowsprit will have a diameter of 120mmm (a little less than 5") and a wall thickness of 12mm (1/2") which I think it will be enough to make extra solid. Do you think it will be too heavy? I wouldn't like to have a carbon bowsprit that would be as heavy as a wooden one....
Other thought could be given to the SS hardware, I agree on the problem and that's why I was thinking of an outer layer of about 3mm (3/16") of fbg/epoxy to defend it from possible hit and metal cuts. Don't you think it would be enough?

I don't know anything about alternative options for fittings of a carbon, can you give me any advices where to study some? Website?
Thanks a lot to all.

Mauro

[CAM]

https://picasaweb.google.com/m/viewe...75016574624786

Pics of the 40'ers sprit the day we bolted it on. That's not the finished bobstay, just some line to hold it firmly in place. I think if you scroll through the pics you can see how it was made. They successfully raced the boat to Hawaii that summer, so it's gone that far at least.

Here's the drawing:

http://4.bp.blogspot.com/_5HeG270aMb...00/40Sprit.JPG

Note I'm not a pro, this was done for some friends I race with. I crunched numbers to the best of my ability, and had access to another NA-drawn plan to refer to and validate my figures. I present it just for your information, not to solicit work, nor would I guarantee this design would work for you.

Your fg covering will add abrasion resistance for sure, probably something more important for a cruising boat that deals with anchor chain regularly. If you could cast the metal part into the sprit, maybe you could get 100% contact. The problem as I see it is the steel will still be assymmetrically loaded, with the bobstay trying hard to pull the bottom aft. Since carbon doesn't give much before failure, the sprit doesn't dent and distribute the point load away from the point of contact. Maybe the glass will address this, I don't know. I do know soft attachments are easier to keep from slicing the carbon though.

[Stumble]

Again, take a look at the sparcraft pole (the one I am adding), it has a factory option to add a bobstay that allows for the use of a code zero. This is a $100 part but of course you also have to add a toggle to the bow of the boat. Which is a pretty easy addon.

These things are not a panacea since they have a limited projection, but within their design limitations they are pretty simple additions, and work quite well.

[Olinelooo]

Consider making the aft end a lot wider than the tip to avoid needing side stays (if attaching directly to the bow). Also consider an internal end fitting (machined aluminum, or fabricated G10) to receive the bobstay and possibly tack lines if you ever fly an asymmetric kite. Can be as simple as a tight-fitting glued-in "slug" with a vertical-cut slot to ring hitch the bobstay and strops through.????