Bowsprit for Code 0 Dear friends,
I believe that this question is primarily for LARS.
I wonder how to calculate the right dimension for a bowsprit to be used with a code 0 sail. I assume that a bowsprit for a Code 0 is different from that for a gennaker. The code 0 in question has a straight luff and 115 m2. Some details:
1/ What would be the RM at 30' for a S&S 47?
2/ What maximum service load one should calculate with and what would be the reasonable distance between the different supports of the spar on the deck .
3/ What is the reasonable length of the unsupported part of the spar.
Many thanks in advance for any help in this issue.
Dear Philippe
Guess you consider components from Selden when you ask for the righting moment at 30 degrees. For Swan 47 this moment is 90 kNm, and you can well look at their gennaker bowsprits, but pls note that the loads for a Code 0 are twice as big.
Therefore the recommendation is:
1/ use only half the unsupported bowsprit length given for a gennaker
2/ consider that 1/ increases the load in the stemhead fitting to 1.67 times over the gennaker load, and modifications to the fitting are required.
Kind regards
Lars
Dear Lars.
Yes, I am looking at Selden as a first step.
1/RM 90 seems to correspond to a displacement of 13,1 T and the unsupported length is ca 600mm. I understand that this can be reduced to 300mm and it is alright.
2/If one considers a higher displacement, say 15,6T, which corresponds to the actual weight of a 47, then the RM is 105 (is this a problem) and the unsupported length is 528mm. This can also be divided by two, say to 260mm, but how to manage the load on the steam head of the spar? A small stay connecting it to the bow? Probably doable but ugly! Any other possibility?
Dear Philippe
Allow me to provide some additional information referring to your item 2/:
The 47 is slightly narrower than newer boats, and this reduces stability in relation to displacement. It is not necessary to consider the actual displacement here, you can look at the stability column only.
By the stemhead fitting I mean the forward deck fitting holding the sprit, and this fitting including its deck attachment needs to be beefed up for the increased load if you go for Selden with a halved unsupported length.
Kind regards
Lars
Many many thanks for your clarifications. I now understand the issue of RM vs displacement. I also realise that Selden does not carry proper bowsprit for te code 0 or similar that are meant to be fitted on a AT and a drum. There Gennaker spar does not assume any drum. So, I might look elsewhere. See their site on this:
http://www.seldenmast.com/products/gennaker_bowsprits.html
Dear Lars,
I am sorry, but I am not able to trace among the pictures of the GMT pdf anything similar to an original fore deck of a Swan 47. I understand and I agree that the area of the ancor roll looks much more solid and afore for fixing the bowsprit than the usual left side. And a good reason to stow somewhere else the anchor, which is not bad for performance. Thank you, Matteo, Grampus 47/16
I am considering, too,the installation of a removable bowsprit.
It would be much appreciated to know the soluton adopted from other 47 owners.
Taking into consideration the installation on the port side, which has no anchor roller, I have observed that there is a vertical cross plate, bow to aft, reinforcing the stay chainplate. Left and right there are two sheaves. These sheaves, around 4 cm diameter, have probably been projected to downhaul or to tension the luff of the sail in some conditions. I have never used them.
This plate is in that area around 25 mm thick.There must be a bush inside it of, I guess, 25mm or more. (I hope that the professor can check this construction detail).
My questions are the following: 1)Has someone adopted this solution, by aid of a large rod welded to the bowsprit ring or to a steel block containing the ring? 2) Would not the leverage on this rod be too high without any other welding or bolting on the area of horizontal steel plate deck?
Thank you all and regards,
Matteo, Grampus 47/016
Dear Lars and all of you,
I am enclosing the pictures of the chainplate area, I believe that they are still theoriginal production. Abaft the chainplate, which is about 80x8 mm, there is a thick element, about 22 mm, which supports the two sheaves. I believe it can support a bolt or a rod of about 25mm diameter. In case this bolt would be welded to a plate with a collar containing the bowsprit, would only this be sufficient?
Otherwise I might be compelled to add another fixing of the plate with the collar to the steel area of the foredeck. I am not thinking for the moment to furlers and code0, but only to fly gennakers.
Thank you and regards,br>
Matteo45 grampus 47/016
Dear Matteo
Thank you for the photos.
A 25 mm pin of rod rigging would be strong enough to hold a short gennaker bowsprit, but the 22 mm vertical plate is too weak here for attachment in the sheave bolt hole.
It is suggested that you enlarge the hole at the forward lower end of the vertical plate so the 25 mm pin just fits through.
A simple locking arrangement on the starboard end is needed, but there appears to be little space because of the anchor roller. Removal of the sheaves may help.
The pin could simply be straight with loups for holding the bowsprit on the upper side. A big washer screwed to the end would prevent the loups from sliding off.
Avoid welding rod rigging, this reduces its strength very much.
Depending on the required free length of the bowsprit forward end a thicker pin may be needed, pls advise.
The deck plate is not as thick as suggested by the edges each side, it is about half this thickness.
Kind regards
Lars
Dear Lars,
thank you for your advise, as always very useful.
I appreciate particularly your suggestion to avoid welding, because, too, I am planning to make these operations with the boat on the water.
I have seen that the clevis pins (only checked on the Blue Wave catalogue) might be too short for the purpose. I think that I might utilize a 25mm bolt secured by a washer and a nut on the opposite side.
I believe that one reason for keeping my Swan is the unique assistance that you are giving us.
I feel grateful to you.
Best regards,
Matteo grampus 47/016
Dear Matteo
Pls note that for this you need a piece of 25 mm thick rod rigging, suggest you contact a rigging shop, and ask for a short scrap piece, about 250 mm depending on sprit diameter.
If you are unable to find rod, a piece of Aquamet propeller shafting would also do, the strength is about equal. Ordinary stainless is not strong enough.
If you intend to use a long bowsprit, or less strong pin material it would be necessary to support the pin with a vertical strap from the stemhead plate up to the pin.
Kind regards
Lars
Here is a picture of our approach to adding a bowsprit to Sarabande. I removed the stem head fitting and had a starboard wing and roller welded on to match the original port side arrangement. This allows me to moor to a strop on port without having to move the anchor on starboard. We made a up a sprit out of SS tube to fit into the new port side roller cheeks. On Lars advice, we then strengthened the tube by simply welding a piece of vertical strap along the top side of the tube. We have used it many times now with a Code 0 sail, which brings very powerful forces to the whole rig.
I am sure there may be other ways of achieving the same result, ( ours is a bit heavy) but it is strong and provides a useful second bow roller.
Rob. Sarabande 47/029
Dear Rob,
thank you for your pictures, every piece looks so tidy and well polished. Your solution is really beautiful. I am thinking too, to a stainless steel tube. What is the length and the diameter of your bowsprit? Your situation is different from mine: 1) you have a different pulpit without the upper front arch, and this reduces the minimum length out of the bowsprit.
2)the fulcrum in this way is positioned in the most afore part of the stemhead.
With my actual hardware I would need around 70cm bowsprit out, compared to your probably necessity of only 50-60cm.
I am not thinking to make a new stemhead plate with two rollers for the anchor and ropes, nor to change the pulpit.
But I might adopt 100% of your solution on the starboard side, with the little but productive effort of storing the anchor somewhere else close to the mast. And the weight of the anchor with its tail of chain is surely greater than that of the bowsprit!
Only one observation: thinking at the use of the code0, should not the diameter of the pin of the bowsprit be equal or greater than that of the forestay chainplate? I guess that the cross tubes of your bowsprit are only for lateral control.
Thank you very much, you have a very brilliant foredeck!
Best regards,
Matteo45 Grampus 47/016
My dear President,
thank you very much for your interest,I have heard that one of the 47's in italy or france might have the solution of the pin of the bowsprit installed in the area of the two sheaves abaft the forestay chainplate. I know that Walidada and Black Tie, too, have bowsprits.
It would be good to hear from Mr. Roby Aymone, he will surely have installed something interesting.
I am looking more for a simple solution with stainless steel and assembled locally, rather than an already assembled kit.
For reasons of economy and style, although I understand quite well that a sandard product assembled by a rigger might give a more reliable result.
Thank you for your continuous care!
Best regards,
Matteo45 Grampus 47/016
I reply to your last post with pictures and answers to your questions.
Firstly - I am not convinced that the job we have done to Sarabande is perfect. It looks OK, has so far served its purpose, but intuitively I feel it could be better ( lighter and stronger - maybe carbon).
1. I took advice from the rig designer ( Eric Duchemin at Axxon- Carbon) on the the optimum Spinnaker Pole Length. This data informed my choice of length of bowsprit - ie. they are the same length for IRC purposes.
2. I have an excellent Stainless Steel fabricator who works on many Superyachts in Pendennis and is a good tradesman.
3. I am unscientific, but work on intuitive instincts on my boat which I know very well.
The Sprit measurements are:
Overall length: 1.25m
Overhang ( extension from roller) 360mm
Diameter of Sprit: 60 mm
Regret I do not have the gauge, but it was the heaviest available ( 4mm?)
The athwartship cheeks are there for support only.
I do not know the answer to your query about the pin - it seems ok so far!
I had the Pulpit re designed and removed the top rail as in the pictures and also reduce the mid rail. I want to be able to fly Cruising Chutes ( Tack leading aft) and big A2 downwind ( Tack leading forward) without any chafe on the pulpit. We also need good access to clip on tack blocks, furling drums etc. The openings fit the Cat 3 Offshore regulations.
Lars advised me on the loads and I adjusted the sprit spec by adding a vertical welded strap ( see pictures) which has worked - but transferred the load further aft and there is still a bend! This is because of the Code 0 which has brought forces, so far unknown to the rig- Beware of this!
Good luck with your alterations, and I wish you well.
