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Old 16-04-2008, 17:55   #31
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I have the details for a Hartley Figian 43. This boat requires a mast with these moments Ixx(x10 to6 mm4) 15.6100 and a Iyy(x10 to 6mm4) 38.4900 and a shell weight 11 kg per mtr
The boat has a RM of around 10000 kg m
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Old 16-04-2008, 23:34   #32
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The Fijian is a totaly different boat design. Very high Topsides and they are all cement up high. The boat is much heavier above water line. You really can not compare the two. In fact you would be closer comparing the Elan, even though it is also a completely different boat. And of course it will be strong enough. It is only 10Kg/m asked for in the plans. This mast is at least this if not more.
I have not guessed at this. I have passed all this by a very experienced mast rigger. The Mast is currently in his loft. The only difference in thinking between him and me is that he suggested we remove the two metres of extra mast. But he has not considered the issues of the fittings and the issues of the spreaders. Where as me being an engineer and also putting much more thinking time into the issue, have been thinking the issues.
The current mast I have on there now is a third of the weight needed. Yet it hasn't fallen over yet and I assure you we have put it through some situations where I expected it to have. The issue is the compression bend when we tension the rig correctly. The issue is getting the heavy wire gauge to the correct working load ends up putting to much stress for the extrusion and kicks it out of column.
As for selling this one and looking again, Nup, not possible. If we were to go new, we would be looking at money we simply can not ever dream of ever having. So that is out of the question. Interestingly there has never been another mast of the size we need ever advertised again. It was a one of special situation that and I wont get that chance again I think.
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Old 17-04-2008, 03:42   #33
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Quote:
Originally Posted by Alan Wheeler View Post
The Fijian is a totaly different boat design. Very high Topsides and they are all cement up high. The boat is much heavier above water line. You really can not compare the two. In fact you would be closer comparing the Elan, even though it is also a completely different boat. And of course it will be strong enough. It is only 10Kg/m asked for in the plans. This mast is at least this if not more.
I have not guessed at this. I have passed all this by a very experienced mast rigger. The Mast is currently in his loft. The only difference in thinking between him and me is that he suggested we remove the two metres of extra mast. But he has not considered the issues of the fittings and the issues of the spreaders. Where as me being an engineer and also putting much more thinking time into the issue, have been thinking the issues.
The current mast I have on there now is a third of the weight needed. Yet it hasn't fallen over yet and I assure you we have put it through some situations where I expected it to have. The issue is the compression bend when we tension the rig correctly. The issue is getting the heavy wire gauge to the correct working load ends up putting to much stress for the extrusion and kicks it out of column.
As for selling this one and looking again, Nup, not possible. If we were to go new, we would be looking at money we simply can not ever dream of ever having. So that is out of the question. Interestingly there has never been another mast of the size we need ever advertised again. It was a one of special situation that and I wont get that chance again I think.
I wasn't trying to compare the two boats.
In what you have said the Fijian would have less a RM that yours at any rate. The RM given of the Fijian was only based on a displacement of 17500kg
And as you have stated your boat weighs 26 ton.
Without engineering it out I would guess the mast size that had at least a 1.5 safety margin in the panels would be around 305mm F/A and around 195mm Athwart ships and have a shell weight of 13kg per mtr
If you do go ahead with the Elan mast cut it down.
You will need everything going for you.
As far as the plan giving a shell weight of 11kg per mtr what was the intended displacement of the of the boat?
I have built an Elan 43 mast that and the shell weight of that mast was around 8.7 kg per mtr
In the industry we see plans drawn in the 60's, 70's and 80's that have specified masts that are way undersized compared to industry standards today.
Just because the boats are similar in length does not mean that the moments required in the mast are similar as well.
You may also find that on your sail plan the rigging will be undersized.
I see that you are in NZ. Ask your rigger to get Chris Mitchell to have a look at the numbers before you go ahead.
As I have seen a lot of good money spent that has gone to waste over the years due to inexperience or people taking the wrong advise.
However it is your yacht and you are responsible for its sea worthiness and safety of those on board. Your Call.
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