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Securing the open stern

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Merinalle View Drop Down
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    Posted: 18 January 2021 at 18:59

We never get used to the open stern during the first years with our yacht. Not only standing behind the wheel, but especially changing the helmsman while the weather is hard and yacht is heeling, was somewhat unpleasant. We solved the problem with this kind of rail, and have been more than satisfied with it during the last ten years:

 

Now I thought that it may be useful to share this in our forum. It is quite long story, and maybe not too easy to follow, sorry for it. Furthermore, although the bended metal tube itself was not expensive, there are some other things that may limit interest to have one. First of all, if you are used to moor stern against the dock, this may not suit for you. It is also complicated to measure the right bending, and connecting the tube to existing stern rails is a little difficult, too. Anyway, here is my description how I done it. Naturally, I donít take any kind of responsibility if you try to follow this and are not satisfied!

Letís start from the tube profile and the connections. Because the opening between the stationary rails is quite wide, I thought the tube should be sturdier than the typical 25 mm. So, I selected an available standard tube profile: 33.7 mm x 2 mm. The connections are shown here:

 

 

 

 

The starboard end is shorter because of the stern light. I removed these pieces from the tube so that there is about 26 mm wide opening in both ends. (The upper guardrail can still be opened without removing the tube):


To mark the right place for the cutting, I used masking tape and set the bended tube straight ends parallel against the existing aft rails. (See the blue line in my first drawing.)

 At the pictures can be seen that the tube ends are not smoothly against the rail, and there is a reason for it. The tube is isolated from the standing aft rail with approximately 300 mm long halved piece of a plastic tube (not visible), and the clamps are isolated with approximately 5 mm x 25 mm x 30 mm rubber pieces. The isolation is to protect the stationary rail against scratches and corrosion, although both the tube and the clamps are A4. Installing or removing the tube takes only a couple of minutes.


Now we come to the most confusing part of the project, calculating the measures for the tube. In reality, it is not as difficult as it looks like. I try to explain the procedure, but remember that English is not my best language.

At least with our Hanse 320, The starboard and port stationary rails are symmetrical. Their upper horizontal parts open upwards and backward. I mean that the middle point of the new tube will be higher and more backward than its ends.

 The new tube should be bended so that the tube ends (that will be connected to the standing aft rail) are straight, and the rest of it is bended to arch with a constant radius. An essential thing is that the tube will be 2D, not 3D. Confusing? I tried to explain that when the tube is ready bended and set on for example against the floor, it touches the surface all the way.

Because the existing stern rail corners are not straight 90 degrees (contrary my drawing) but curved, it is a little difficult to mark the place where the bending of the new arch starts. However, because the radius of the new tube is quite big, it is not so important to reach the exact point. It is more important that you use same markings when making all measurements. Thus, use masking tape and make the markings to the end of the straight parts of the stern rails.

 Now come the best news: you need to make only three measurements! To do it, all you need is a tape measure and other common tools, some screws and straight (wooden) batten. The batten and screws are for making a big try-square. While making it, try to do it as precisely as possible. Take a look to my drawing 1:

 

At first, measure the distance C between the points P1 and P2. Next, use your try-square to measure distances A and B. Just rotate the longer part of your new handmade precise instrument around the stern rail so that they are exactly linear. The important surface contact you have to control is marked with blue in my drawing 1. First find the maximum for distance A. Then measure the distance B, too. Fast control: make sure that A2 + B2 = C2.

 


Now we can start calculations. At first, we need the angle α, it is arctan A/B. As you can see from my drawing 2, the angle between points P1 and P2 measured from imaginary point P3 is 2α. (Point P3 is somewhere under the keel, donít try to make any markings there.) The radius R1 is thus possible to calculate: C = 2 x R1 x sinα, so R1 = C / (2 x sinα).

 Now we can calculate the length of the curved part of the tube. It is 2α/360į degrees of the length of a circle, whose centre is P3 and which goes through points P1 and P2. Thus, measure D1 = 2 x π x R1 x (2α/360į).

 Now I must admit that I made a small mistake when ordering the tube ten years ago. Those measures R1 and D1 are from points P1 and P2, which are on the upper surface of the standing aft rail. To calculate correct inner radius R for the tube, it should be about R1 - 30 mm. Thus, the correct measure D should be approximately R/R1 x D1. Because R1 is more than four meters, this is not fatal. The error was less than one percent.

 I know that there are slight differences with measures of even same year models of Hanses, so I recommend to do your own measurements. Just for comparison, here are my numbers:

  • A: 570 mm
  • B: 2183 mm
  • C: 2256 mm
  • α: 14.6į
  • R1: 4470 mm
  • D1: 2280 mm

I ordered the tube so that its full length is 2760 mm, the straight ends are 240 mm, and the middle part (2280 mm) is bend with 4470 mm inner radius. It has fitted perfectly. The only thing I would have done differently concerns finishing the new A4 tube. Polishing it was more difficult than I expected. Probably the tube supplier would have made polishing with moderate expense.

 If you are still interested, and there is something I couldnít explain clearly, donít hesitate to ask.



Edited by Merinalle - 23 January 2021 at 15:19
320#166
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Martin&Rene View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Martin&Rene Quote  Post ReplyReply Direct Link To This Post Posted: 21 January 2021 at 11:52
Merinelle

That looks a super job and it certainly must make helming feel a bit more secure and comfortable.  When we bought our yacht (second hand) one of the options was a new 320 and as we very rarely moor stern-to, the open transom did not seem to give any positive points for us. 

Having bought the 341, I did not like the fact that the stern guard rails hung down loose like yours appear to do.  I changed the guard rails so that they were fitted with these threaded pelican hooks.


These mean we can set the guard rails very tight, but then they can be easily released so we can access the dinghy over the stern when at anchor.   

The name may be confusing as "Pelicans" are birds with big bills.
Martin&Rene Hanse 341 Dipper Wheel steering, 3 cabin layout & shallow keel, normally based in Scotland
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S&J View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote S&J Quote  Post ReplyReply Direct Link To This Post Posted: 21 January 2021 at 13:36
I have often felt vulnerable leaning against the stern guard rails, especially when alone on deck or at night.  I know that Mark & Catherine made a similar solid connection between either side of the pushpit rails.  I really should have a go at something similar, but I'd need it to be easily removable for stern to mooring or using the swim platform.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote cptgood Quote  Post ReplyReply Direct Link To This Post Posted: 21 January 2021 at 17:37
I think a good solution would be using unbraid Dyneema 5mm (easy to splice) instead of the 2 inox wires. 
With a long line, one could make a better safety net, as he likes, using the pushpit all the way down.
Hanse320 - Hull#127/08 - Wheel - ST headsail - Yanmar 3YM30 - SD20
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Ratbasher Quote  Post ReplyReply Direct Link To This Post Posted: 22 January 2021 at 09:00
Although its best practice to clip on (and certainly always at night) this is unlikely to happen in 'real world' practice during the day.  I too changed to pelican clips but these cannot be guaranteed, especially if subjected to the sort of sudden impact caused by someone falling on them.  As part of my 'preps for sea' I back those lines up with two tightly-tied lengths of dyneema which have withstood my not-inconsiderable weight on several occasions. Come harbour time they're easily removed, not just for ease of access but also to prevent UV damage.

As we all rig our boats for the way we use them as individuals, ours spends a lot of time at anchor/moored so the back end is by far the easiest way to board; I'd be loathe to block entry with a rigid bar but I do appreciate why others have done so.
H400 (2008) 'Wight Leopard', Gosport, UK.



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Merinalle View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Merinalle Quote  Post ReplyReply Direct Link To This Post Posted: 23 January 2021 at 15:22

Nice to see feedback, here are some comments from me.

 As mentioned before, the rail is really an obstruction if you want to go to dock through stern. However, it doesnít prevent swimming or using a dinghy. Just open the guardrails, and there is some 102 cm free room below it in the middle. If you can get back from the water, the tube will not obstruct you.

 It would be possible to innovate some kind of mechanism that makes it easier and faster to install and remove the tube. There would still be the problem where to store it when it is removed. Because we have never moored stern against the dock since year 2008, I havenít thought about it. We install the tube at spring and remove it at autumn.

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samuel View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote samuel Quote  Post ReplyReply Direct Link To This Post Posted: 24 January 2021 at 07:55
If one wanted an easily removable horizontal bar I would try 2 vertical tubes, or even pairs of stainless steel loops attached to a metal strip which could clamp to the upright- at each end- fitted to the uprights. It would be easy enough to fabricate clamps to hold them to the existing stanchion.

Then the horizontal bar would have a vertical leg pointing downwards each end, that just dropped into the sockets. It could be removed in a few seconds & still look neat.It could be curved or straight , whichever one desired. If one wanted it higher, one could let the sockets project to whatever height one needed.
One could fit 2 sockets lower down & provided there was enough gap to lift the bottom rail out then a second rail could possibly be fitted


Edited by samuel - 24 January 2021 at 08:00
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Post Options Post Options   Thanks (0) Thanks(0)   Quote S&J Quote  Post ReplyReply Direct Link To This Post Posted: 24 January 2021 at 08:09
If you look t the third picture in this thread you can see a solid rail attached to the regular mounting points.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Black Diamond Quote  Post ReplyReply Direct Link To This Post Posted: 24 January 2021 at 21:45
My wife felt the same way about the open stern,  and we have two dogs that we didn't want going into the water by accident, so we ended up just using Phifertex and closing it off that way.  Works fine.

I like the stainless work, but this was a lot cheaper..   Its very strong.  No one is going to slide thru it, not just the dogs.




Rick
S/V Black Diamond
Hanse 575 Build #192, Hull# 161
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