In the excellent video of the conference posted by Matteo ( Lars conference ) Lars mentions that our hulls were made with" Trim Screws" left in the ends of the hull which were used as reference points to establish the correct position of the waterline. Apparently they are 12 " (inches) above the waterline, so should be somewhere above the boot top on the bow and stern. Lars explains that these have often been removed because owners did not understand what they were. He has suggested that if any owners still have these on their hulls, it would be a fantastic opportunity to convey to the forum, and develop an accurate record, so that those that have had them removed over the years, can re-check the measurements. If you can help with this, eg. with a distance off the original boot top, please reply to this thread.
Thanks.
Rob. Sarabande. 47/029
Dream Of Swan (44/063) still have it's original trim screws.
If it helps, we will be at Elba for the 2013 rendez-vous, feel free to ask for a closer view...
Well lo and behold, I have found my Trim Screws. Perhaps Lars could confirm how we use these datums. Is the idea that they are equidistant from the waterline? Is there a record of the correct measurements? Note the bow has the screw approx 150mm below the antifoul line, and the stern screw is in the boot top. I would be fascinated to hear from other 47 owners on this.
Rob
You are right, when both screws are at the same height from the water surface the yacht floats parallel to her Design Water Line.
Most yachts do not float like that because of various equipment, and it appears trim by the stern is preferable over bow trim.
If the height of both screws is known the displacement of the yacht can be calculated.
Kind regards
Lars
Thank you, I find this so interesting. Sarabande goes back in the water soon, and I cant wait to measure the waterline. Will you then be able to calculate the displacement if I provide the dimensions?
When you say " it appears trim by the stern is preferable over bow trim." are you saying that if there is an imbalance, then it is better for stern to be closer to the waterline than the bow?. If so, that would agree with comments I have heard experienced sailors talk about S&S designs in general. The successful models had that "high bow" look about them.
Dear Rob
Yes, the displacement can be calculated from the trim screw heights. The density of the water also needs to be considered, is there for example ocean water, or a river mouth? Measurers usually know the local value.
If there is a swell or wash from passing traffic it is difficult to get accurate numbers, can suggest some tricks.
Trim by the stern increases stability somewhat, and is not considered detrimental if it is a reasonable amount. This also depends on the hull shape, and the optimum is not easily defined.
Classic S&S yachts have comparatively high freeboard at the bow compared to the stern, and this makes them drier in waves.
Kind regards
Lars
I have carried out a measure of the Trim Screws above the water line - not an easy process, but accurate enough to establish the difference between fore and aft.
The mean measurement from the trim screws to the waterline for Sarabande is 180mm aft, and 185mm forward. I would say that during measuring the water was pitching approx 25mm. I would also say that she is "high on her lines" with tanks less than half full and little domestics. The anchor is also inboard along with 80m of chain!
From your earlier comments on this thread, these measurements suggests she is pretty well balanced. I would be fascinated to hear of your views and what other information is required to carry out a calculations of her displacement.
