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Post by pagoda54 on Apr 25, 2019 19:38:18 GMT
Our 42i (P) has a gas strut Rodkicker that appears to be rated at 1200N force. There is no sign of damage or rust.
It holds up the boom quite happily with no sail or sailbag present, but does not manage well with the main and the sailbag fitted.
Looking at the Selden site - there are several force levels available for the Kicker, Standard/Hard etc.
SGS engineering also make struts in stainless with adjustable force. (https://www.sgs-engineering.com/gssv14-250)
Have people replaced like with like ? or gone for a strut force that will definitely hold up the boom+sail+bag ?
I really don't want to spend £££ on a replacement at 1200N which does the same as the original!
thanks, Graeme
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Post by rene460 on Apr 26, 2019 2:03:33 GMT
Hi Pagoda54,
We have a much smaller boat but the principles are the same, just smaller strut and lower spring force.
My rod kicker never seemed to quite do the job I thought it should, but I was recently prompted to revisit the whole setup when the two halves separated. It was originally fitted by the agent who did not put the instructions with our documents. They are now clearly on the Seldonmast website for each size model.
I found that when I checked my installation against those instructions, that something was not quite right. Pretty obvious when it came apart. Lucky we did not loose any bits overboard. I decided that the boom fitting was too far from the mast so I shifted it back to the position I got when I followed the instructions. Not a trivial job with the spring force even on our little boat.
This made a huge difference, so the original spring was easily able to lift the furled sail on the boom. In fact it was too much, and I could hardly apply enough pull on the line to apply adequate vang tension. I would have needed a winch which should not really be necessary on a small boat. However it proved the point that the spring was fine, but the setup needed adjustment.
I had marked the original position on the boom, and now marked the new position from following the installation guide. I have now moved the boom fitting a couple of inches back towards the original position. I did this by going as far as I could while still able to insert one of the fixing screws in the holes already drilled rather than drill more holes. In truth, I had little choice as I had left the drill at home with the correct size drill bit.
I think I will move the fitting a bit more away from the boom the next time I have the drill on board, but I am very pleased with the setup now it is much closer to the optimum setup.
I am still not totally sure if the original set up was actually wrong (it seems unlikely really) or whether it was ok for the original sails when new, but gradually became wrong as the sails stretched, and definitely wrong for my new sails due to a combination of the extra weight of those full length battens and possible differences in sail dimensions and clew height compared with the original sails.
So back to your question, I suggest that before you replace the gas strut, you carefully check the setup. There are such a limited number of alternative struts that yours is most likely the right selection for the boat. However, the precise position of the boom fitting makes a huge difference and enables the one strut to work well on a range of sail and boom weights.
It is not a trivial job, 1200N is a force equal to about 120 kg, so it needs to be kept under control with your adjustment line. If necessary rig up an extra pulley or two to increase your mechanical advantage, as you have to take that force on the line to adjust the boom accurately to get the pins out of the clevis. I recommend enlisting a mate or crew member with some muscle to help and use the topping light to support and adjust the height of the boom.
The guides in the website are slightly different for each of the three strut sizes. I read all three before I was sure I could see what was going on. The differences are subtle rather than reaching a different point and I am not sure why they are different, but I ended up using the one that made most sense to me, sitting on the cabin top and looking at the components.
I hope that helps. Moving the boom attachment fitting towards the mast will increase the spring force by shortening its length so your current spring will easily lift boom, sail and bag.
rene460
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Post by johannes on Apr 26, 2019 8:07:05 GMT
I think 1200N might be too weak for the 42i. 1200N is usually recommended for 35-40 ft boats. The next step up is 2500N. I would ask a rigger for advice, or e-mail Selden directly.
The idea with the Rodkicker is that the strut should be strong enough to lift the boom even with the heaviest load. Then there should be a vang tackle with enough purchase so that you can always compress the strut. The Rodkicker has one cascade pulley built in that doubles the purchase, and then you should add a 4:1, 6:1 or whatever is needed. With 6:1 you get 12:1 in total, so you only need a force if 2500N/12 = about 20 kg to compress the strut.
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Post by johannes on Apr 26, 2019 8:18:02 GMT
By the way, moving the attachment point on the boom could work but it is not recommended by Selden. The attachment point should be so that the boom is at the lowest desired point (shortest possible mainsheet) with a small bit of margin before the Rodkicker bottoms out. You do not want the Rodkicker at the end of the telescopic travel with still some way to go on the mainsheet, that could break the boom.
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Post by rene460 on Apr 26, 2019 12:09:04 GMT
Hi johannes,
You are quite right. And that point is covered clearly in the instructions.
The need for moving the attachment point comes from checking the installation and finding it is not correctly set, in my case quite possibly due to a change of sail shape.
If the spring is the correct one, it should carry the boom, bag and furled sail when properly set. If the installation is correct but will not lift the boom as required, then the next spring is most likely required. First thing is to check the installation. Correct setting means the strut is not bottomed out when the main sheet is fully sheeted down with the sail hoisted. We hoisted the sail in the early morning calm and measured the height of the underside of the boom above the dodger bar so we could lower the sail before the wind came up.
rene460
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Post by pagoda54 on Apr 27, 2019 16:23:23 GMT
Hi johannes, You are quite right. And that point is covered clearly in the instructions. The need for moving the attachment point comes from checking the installation and finding it is not correctly set, in my case quite possibly due to a change of sail shape. If the spring is the correct one, it should carry the boom, bag and furled sail when properly set. If the installation is correct but will not lift the boom as required, then the next spring is most likely required. First thing is to check the installation. Correct setting means the strut is not bottomed out when the main sheet is fully sheeted down with the sail hoisted. We hoisted the sail in the early morning calm and measured the height of the underside of the boom above the dodger bar so we could lower the sail before the wind came up. rene460 Thanks for your collective replies. I'll try to check the attachment position before doing anything else. I am fairly sure nothing has been altered from the original configuration. The spring could simply be weak, but having already removed it and looked at it closely, it appeared pretty strong (without any measurement!), stroking out to full size promptly. I'll be at the boat next week. |
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Post by Madicken on Apr 28, 2019 16:16:27 GMT
I have replaced my gas damper. From original, 1,2 to 2,5 and I'm very pleased with it.
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Post by pagoda54 on May 18, 2019 20:16:41 GMT
I ordered the 2500N (Adjustable) SGS stainless gas strut. (and one of the Selden plastic end pieces- one was seized to the old strut). Replacing the parts was all of a 10 minute job. Identical fitment and size. Easy.
While the increase in available force looks excessive, in practice it works well. The 2:1 kicker set up copes perfectly well with the coach roof winch in use.
It's possible to reduce the strength of the strut in +-30N /second bursts through a bleed valve but that is a one way process as an end user. I think I'll leave it alone and see how it performs over the season.
Graeme
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