Do you want to be informed on new Posts on this Thread? (members only)

Sail & Rigging - Rig weight
08 June 2014 - 13:47
#1
Join Date: 01 March 2007
Posts: 147

Rig weight
I sense Lars may be able to help me with the following, but I am interested to hear from all.
As discussed on other threads, I have put a carbon rig on Sarabande, 47/029 which has had the effect of raising the waterline in the bow. I would like to find out the weight of the old nautor rig which it replaced, incl standing rigging, so I can better understand the changes and how best to approach trimming the hull.

Rob.

Sarabande 47/029

09 June 2014 - 09:21
#2
Join Date: 02 January 2008
Posts: 1547

Dear Rob
The average recorded original rig weight is 445 kg, and this is likely to include a headsail furler. Has the new rig been weighed?
I can assist with longitudinal trim calculations provided you inform how much change is needed.
Was there changes to anchor chain length?
Kind regards
Lars

12 June 2014 - 10:52
#3
Join Date: 01 March 2007
Posts: 147

Dear Lars,

Many thanks for your reply.
The new mast weighs 201Kg and the boom weighs 80.4 Kg.
The standing rigging has been changed from Rod and Wire to Navtec TFC carbon fibres with the exception of the V1's up to the first spreader and the forestay which are both Rod. We have retained our Harken Aluminium foil and furler on the forestay.
We have replaced the 2 Nautor Spinnaker poles with 1 Carbon pole for which I do not have the weight to hand, but I suspect the carbon pole is 50% of the weight of a single Nautor pole.
Other issues affecting the hull trim are a Generator installed in the aft cabin which weighs 75Kg approx.
We carry a 60 pound CQR anchor with 60m of chain.
There are trim screws in the stem and stern. The screw in the stem is located in the antifouled section whereas the trim screw in the stern is in the Boot top. I am not confident these were the original positions and I am unsure whether to use these as a datum - can these positions be checked somehow?
The keel has 2 voids which I assume are original?
When stationary,the top of the rudder is submerged.
I would be very pleased to hear your comments, and any recommendations you may have on the positioning and quantity of ballast required to get the boat into the correct position on the waterline.
Kind regards
Rob
Sarabande 47/029

13 June 2014 - 08:36
#4
Join Date: 02 January 2008
Posts: 1547

Dear Rob
Thank you for the interesting information. It is perhaps not so well known that replacing the standing rigging with carbon fiber usually saves more weight than replacing the aluminium spars with carbon ones. Here you did both, plus the spinnaker poles.
Calculation suggests that all this together with the genset aft caused the trim to change nearly 2", i.e. 30 mm up forward, and 16 mm down aft.
If you would like to check the influence of added weight in the forward end you can do this empirically, just by standing enough crew there. Would also be a good opportunity to add anchor chain, perhaps not in the same chain locker which may be full already.
The keel voids are original.
The original boot top lower edge was about 35 mm higher up in the bow than in the stern with the yacht floating level, would the trim screws reflect this?
If another 47-owner having trim screws would be kind enough to measure their positions in reference to the boot top, as well as along the stem from the stemhead, and along the hull from the transom lower tip, this would confirm their position.
For finding level trim one possibility is to measure the actual freeboards at bow and stern, and compare with recorded level trim numbers.
Such numbers are: FF 4.65' taken 3.754' from the bow, and FA 3.18' taken 44.037 from the bow, i.e. at transom corners.
Stern trim is not detrimental to performance, but may look a bit odd.
Kind regards
Lars

13 June 2014 - 11:38
#5
Join Date: 01 March 2007
Posts: 147

Dear Lars,

Thank you very much for your comments and advice.As for the measurements, they are difficult to cross check when afloat but I will look at this later today.
I have attached a couple of photos of the Trim Screws.
The aft one is clearly in the middle of the Boot top whereas the forward one is deep into the antifouling. The measurements from the 2 Trim Screws to the waterline are currently, (more or less), even at 7 inches, depending on sail stowage/crew position etc.
This is where my doubt lies, because with the reduced rig weight forward and increased weight (genset) aft, they should not be equal. The boat looks aft heavy. with much more antifouled area exposed at the bow than the stern.

If I were to add more chain as per your suggestion, I would think more toward the centre of the boat (centre of effort) would be preferable to less further forward? -but perhaps I am wrong in that. I feel the gains in performance are to be made by reducing pitching.

Kind regards

Rob

13 June 2014 - 14:05
#6
Join Date: 02 January 2008
Posts: 1547

Dear Rob
Thank you for the information and photos.
Suggest that you check if the blue and white stripes in the boot top are original, if so their edges should be perfectly flush and smooth when tested with the finger tips.
In case raised edges can be felt the stripes have been painted on afterwards, and probably moved.
If the stripes are original there are three of them - blue upper, white, blue lower - and their total width should be twice the width of the upper blue stripe.
The lower edge of the lower stripe is now hidden under antifouling, and my suggestion to check the height above the water is better done to the upper edge of the upper stripe, forward the height should be about 90 mm more at level trim.

It looks like the aft screw could be original, measure it's vertical height below the upper edge, then the forward screw should be located this distance plus 90 mm below the upper edge of the upper stripe.

You are right that weight up forward affects pitching more, and it would be preferable to keep it further aft, but then you need more. Some compromise needs to be found.
If heavy equipment is kept in the lazarette it would be advisable to move it forward.
Kind regards
Lars

17 June 2014 - 08:44
#7
Join Date: 01 March 2007
Posts: 147

Dear Lars,

This detail is extremely helpful, I now have a much clearer picture. Thank you very much.

As you say, the lower blue stripe on Sarabande has been lost, the upper one is not paint but the original blue gelcoat and therefore I will now use your measurements from the upper edge of the Boot top. Approximate measurements in the water confirm your calculation with the bow being approx 2.5 inches high. Now I can experiment moving weight around.

Best regards

Rob.
Sarabande 47/029

  • Threads : 1701
  • Posts : 10214
  • Members: 820
  • Online Members: 3