New Mizzen mast build and price F35 cat ketch

New Mizzen mast build and price F35 cat ketch

Postby Saorsa » Sat Mar 07, 2015 5:42 am

Hi Guys
First post on here so bear with me.
The boat next to me blew over in its cradle on 9th Jan 2015 and his forstay took my mizzen mast off at deck level.
So I am in the process of finding a replacement mast. All the information on the forum has been great and I am going to get Rob to build me one
http://harryproa.com/index.php/rob-denney

before he finalises the quote he is asking for the righting moment of the boat/mast.
in order to make sure he builds it to a similar spec.

That's a bit beyond my pay grade he has given me a basic quote based on a figure he has pulled out (based on similar boats he says)
Heres his quote
Assuming a righting moment of 5100 kg.m (based on other similar boats), 250mm diameter at base, 12000mm long.
- tapering
- freestanding,
- round X-section,
- filament wound carbon fibre
- with internal sail track (tube with slot style)
- no fittings
- around 35kg weight
- to suit Freedom 35 Cat Ketch

AUD $8,500 unfinished, or
$10,200 finished, plus shipping.

Could anyone help me as I live in France in the winter and I don't have any of my boat paperwork till I get home to the boat in Scotland in the spring.
Im not even sure if it would be in the manual/Handbook?

Does anyone have knowledge of this number or know how to work it out?

Does robs number sound right? 5100 kg.m

Engineers out there im happy to have a lesson how this number is derived , I have no clue, and to be honest maybe I don't need to, just need what the number is!

Any help greatly appreciated.
I promise ill post updates of the project as we go. I feel people are put off our boats because of the difficulty/cost in getting a replacement mast. As insurance is paying the costs im able to have a crack at it. But so far not as ridiculous price as I had at first thought. Standby!

All the best

Andy
Saorsa
 
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Re: New Mizzen mast build and price F35 cat ketch

Postby Castaway » Sat Mar 07, 2015 6:11 am

Andy,

Have no idea about righting moment, but 12000mm sounds a bit short (I think mine are about 13m), and 35kg a long way off the mark. The main and mizzen masts ought to be almost identical, so you could get the weight & measurements from that, as well as wall thickness, taper dimensions, etc, from which your supplier could calculate the expected strength & flexibility.

There used to be a firm based in Inverness who made C/F masts; have you tried them? They would presumably be able to go and check out your boat for themselves, thus avoiding shipping costs. That might be significant if adjustments were needed. I don't think the Inverness firm is cheap, but it is (if still in business) much closer than Australia.

Another boat here had its mizzen repaired after a similar incident (vessel name "Mo Saorsa"!), but I don't know, offhand, where it was done. I can make enquires, if you are interested.

Gerald
Gerald Freshwater,
s/y 'Castaway', (UK F35 cat ketch)
Lerwick Boating Club
Shetland Isles, Scotland
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Re: New Mizzen mast build and price F35 cat ketch

Postby unfetteredalexandria » Sat Mar 07, 2015 11:03 am

Basing the righting moment on similar boats may be the best you can do, short of either (1) having access to the lines of the hull and a naval architect who knows how derive the righting moment from these, or (2) performing an in-water heeling test that pulls the boat over far enough to find the maximum heeling force (maybe past 90 deg!).

There is a simpler measurement than anyone can do, which is related, and might be possibly be of some use. For small angles of heel, there is a number called the metacentric height that is related to how stiffly the boat resists roll. All you have to do is measure how far your boat heels when tipped over by a known weight at a known distance from the centerline. For example, have a few hefty friends sit on the rail while the boat is in its slip. You can measure the heel angle with an app on your smartphone. Then if W = is the weight, D is the (mass) displacement, theta is the heel angle in degrees, and r is the distance of the weight from the centerline, the metacentric height is W*r/D*57.3/theta. The measurement should be more accurate if you can get about 10 deg of heel.

Since your boat is not in the water, maybe someone else with an F35 cat ketch could make this measurement for you.

More generally, it might be nice if Freedom owners could undertake measurements of this sort, with the data hosted somewhere on this website, since we have very little information of this nature after Freedom Yachts went out of business.
1984 round-mast Freedom 25
Western Shore of the Chesapeake
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Re: New Mizzen mast build and price F35 cat ketch

Postby Saorsa » Sat Mar 07, 2015 1:48 pm

Hi guys
Thanks so far! Gerald yes been in touch with the Inverness
Based firm they did me a quote to repair the original which I was less keen on!
Fourtunatly a new one shipped at the moment is the route insurance is happy to go.
Shipping came to £700 plus £200 insurance to Glasgow. Hence why I'm going this route.
New ones they can only make a wing profile not a round one. And there masts are 100k each!

Yes when i got the measurements exactly the mizzen is 12500mm I used 12m for the base of
The quote. Rob says that whilst these old masts were fantastically heavy made. Modern technology
Means we can build them with thinner walls and they end up lighter than the masts but for the same
Sort of strength. He's the expert so I am inclined to believe this.yes the old mast from 30 years ago might weight
100kgs but does the new one need to?
You both may be right the best I am likely to get might be an educated guess at how strong this thing
Needs to be.Its just a lot of effort if it's not right.

I just want to give the builder best known facts about the original then let him make a decision based
On that.thanks for the comments so far

Keep them coming!

Andy Freshwater
Saorsa
 
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Re: New Mizzen mast build and price F35 cat ketch

Postby Saorsa » Sat Mar 07, 2015 1:51 pm

Yes guys agree that with each incident comes knowledge and that's really the purpose
Of my post. To share the knowledge in case someone else needs to go tthrough the same
Carry on!

I'll keep you posted on how it goes

Andy
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Re: New Mizzen mast build and price F35 cat ketch

Postby Saorsa » Thu Apr 30, 2015 5:56 am

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Mizzen mast break
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Re: New Mizzen mast build and price F35 cat ketch

Postby Saorsa » Mon Apr 18, 2016 10:48 am

So its been a long slow winter whilst I wait on an update on the mast and for various reasons we are behind schedule . However now that the mandrels have finally been made the guys are in the position to start laying up the mast at last!
The guys have made all the sections that the carbon will be wrapped onto so for anyone else out there any further masts might be now cheaper and quicker to assemble.
here are a few pictures of the process so far

enjoy,

Andy
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Saorsa
 
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Re: New Mizzen mast build and price F35 cat ketch

Postby Saorsa » Sat Feb 24, 2018 10:54 am

New pictures of mast finished, finally!
Delivery April. Hope to be sailing soon.
Cant say i could recomend this route.
Honestly wish i had repaired the old one....

Still here we are and looking forward to having a shiney new mast.

Andy
Saorsa
 
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Re: New Mizzen mast build and price F35 cat ketch

Postby Saorsa » Wed May 30, 2018 4:08 am

Mast is on site.
Just have to bond top section and top cap in place and im back in the game!

Hope the engine starts....
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Saorsa
 
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Re: New Mizzen mast build and price F35 cat ketch

Postby Saorsa » Wed May 30, 2018 4:14 am

More pics
Original mast back in
New mast next!

Andy
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